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Intercalation > Ultrasound > Flashcards

Ultrasound Flashcards

1
Q

Describe how a sound wave is formed

A

A piston moves and the air is momentarily squashed into areas of high and low pressure.
The direction of particle displacement is along the direction of propagation

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2
Q

What are areas of high pressure in wave formation called?

A

Compression

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3
Q

What are areas of low pressure in wave formation called?

A

Rarefaction

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4
Q

What is frequency?

A

f
The number of complete cycles per s
Hz

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5
Q

What is wavelength?

A

The distance travelled over 1 cycle

It is the distance between adjacent areas of high pressure

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6
Q

What is a period?

A

T

The time for one complete cycle

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7
Q

What is the relationship between time and frequency?

A

T = 1 / f

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8
Q

What is the fundamental equation that applies to any wave?

A

C = f x wavelength

Speed of sound = frequency x wavelength

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9
Q

What is the average speed of sound in soft tissue?

A

1540 ms-1

It is much slower than electromagnetic radiation

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10
Q

Define ultrasound

A

Sound of frequency above that which the human ear can hear

Any frequency above 20kHz

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11
Q

What is the average range of sound a person can hear?

A

20Hz - 17kHz
Some can achieve 20kHz
The upper end of the hearing range decreases with age or damage

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12
Q

What is the ultrasound range used in medical imaging?

A

2-15MHz
Most sound frequencies are not used clinically
These frequencies do not occur in nature

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13
Q

What are the consequences of increasing the frequency used for imaging?

A 
Increased resolution
Decreased penetration 
Increased absorption
Increased heat
Increased intensity attenuation coefficient (mu)
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14
Q

What do you need to consider when choosing a frequency to use for imaging?

A

Depth of penetration - shallow penetration = high frequency
10-15cm needs 3MHz
Each scanner comes with a range of transducers for different uses and depths

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15
Q

What effect does ultrasound exploit?

A

Piezoelectric effect

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16
Q

What is the natural occurring substance that displayed the piezoelectric effect?

A

Quartz

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17
Q

What is the piezoelectric effect?

A

Applying a STRESS to a piece of quartz creates a VOLTAGE on it that is PROPORTIONAL to the STRESS

Stress creates charge/electricity
It turns mechanical energy into electrical energy

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18
Q

Describe the piezoelectric effect

A

Applying a voltage causes a change in shape
Varying voltage causes vibrations
Ultrasound echoes from the body cause an electrical signal
It is useful for generation and detection of ultrasound

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19
Q

Describe the production and detection of ultrasound

A

Production - excitation voltage is applied and the material deforms
Detection - echoes return exerting pressure which creates an electrical signal

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20
Q

What material is currently used for generation of ultrasound?

A

PZT
Lead zirconate titanate
New synthetic piezoelectric material
Ceramic

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21
Q

What is the advantage of using PZT?

A

Can make any shape
Ceramic material
Synthetic

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22
Q

How is PZT created?

A

Poured into a mould and heated above the Curie temperature
High voltage is applied
Leave voltage applied and cool

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23
Q

What can degrade PZT?

A

Mechanical damage - it is very vulnerable to dropping/breaking
Heating
Exceeding electrical limits

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24
Q

What is the pulse echo principle?

Use a diagram to explain

A

Assume speed
Measure time
Can then calculate distance
Distance = speed x time

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25
Q

What are the problems with the pulse echo principle?

A

It assumes sound travels in a cone
This is not the case in reality
You do not know where the echo generating material lies

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26
Q

How are the problems with the pulse echo principle improved?

A

Using a narrower beam can give a better idea of where the echo came from
You can get a better judge of distance
Multiple small narrow beams provide more information

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27
Q

What are the assumptions of the pulse echo principle?

A

Propagation is in a straight line
There is a thin beam
Want a non diverging beam

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28
Q

What causes ultrasound artefacts?

A

Caused by the failing of assumptions

Machines are designed as if assumptions are true

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29
Q

Why is scanning bone and air problematic?

A

When there is a change in the speed of sound
Bone is much slower (4080ms-1)
Air is much quicker (330ms-1)
Works well in soft tissue where the speed of sound is similar in many tissues (1540-1580)

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30
Q

How is the speed of sound in a material calculated?

A

Speed = square root of: stiffness/density
Sqrt k/p
K can also be referred to as elasticity

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31
Q

What is the most important component in determining the speed of sound in a tissue?

A

Stiffness
It is more important than density
Stiffness has a 3x greater magnitude than density
Ultrasound is stiffness mapping

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32
Q

Describe what happens to ultrasound in the body

Use a diagram to explain

A

Body is complicated and has multiple reflectors
A certain fraction of energy is reflected at each reflector
Some carries on and it reflected later
There are many echoes per pulse
Each echo can be separated as they do not arrive simultaneously

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33
Q

What happens if you have a high reflector anterior?

A

It will cast a shadow

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34
Q

What is an A scan?

A

It is the raw data seen by the machine not the operator
It is not a 2D image
It is the measured signal
This can then be converted to a spot with a brightness proportional to the signal amplitude

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35
Q

How is a 2D image generated?

A

Machine detects the signals
Creates a spot with a brightness that is proportional to the signal amplitude
Need multiple rows
Need multiple transducers
These are all in a line
They are fired one at a time, to not confuse the signals

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36
Q

What is M mode?

A

Use one direction to represent time rather than space
Displays depth vs. time
Can measure velocities, minimum and maximum dimensions
It displays motion
Exclusive to echocardiography

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37
Q

What is time gain compensation (TGC)?

A

The largest signal (generally) will be from the first reflector
Energy is lost as it passes through the tissue and because of reflection
It would result in deep structures having a low signal without TGC
It is controlled by the operator
It can amplify echoes from specific depths

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38
Q

What is sound?

A

It is the transfer of mechanical energy from a vibrating source through a medium
It is a mechanical wave and cannot travel through a vacuum
It is a longitudinal wave

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39
Q

What would happen without TGC?

A

Deep structures would have low signal

Incorrect representation of the anatomy

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40
Q

What does TGC do?

A

Corrects for the loss of signal as the echo progresses
It can create an artefact if done incorrectly
Operator dependent

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41
Q

What can happen if TGC is applied incorrectly?

A

Creates an artefact

Noise is always present and it can create an echo where there isn’t one by amplifying noise

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42
Q

What are the 5 tissue interactions?

A
  1. Beam Spreading (diffraction)
  2. Reflection
  3. Scattering
  4. Refraction
  5. Absorption
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43
Q

Describe beam spreading

Use a diagram to do so

A

Beam maintains width of source to a point and then it starts to diverge
Divergence point can be calculated NF = r^2/wavelength
This creates a near field and a far field
Ideally want a long near field

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44
Q

How do you calculate the length of the near field?

A 
NF = r^2 / wavelength
NF = near field
2r = width of transducer
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45
Q

How do you increase the length of the near field?

A

Increase the size of the transducer

Decrease the wavelength

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46
Q

What is focusing?

Draw a diagram

A

Using a lens in front of the transducer to focus the beam
It will focus at the focal depth
Lens is electronic

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47
Q

What is the consequence of focusing?

A

This creates a narrower beam but creates a larger divergence after the focal point
Degrades the quality of the image
Sharpens the image at the focal depth

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48
Q

When focusing what is the calculation to determine beam width?

A

BW = F x wavelength / A

BW = beam width
F = focal depth
A = aperature of transucer
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49
Q

What are the problems with focusing?

A

It degrades the quality of the image outside of the focusing depth
Can focus at the wrong depth or use the wrong lens (poor operator)
Operator dependent

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50
Q

How would you reduce beam width?

A

Increase the aperature (size of transducer)

Decrease the wavelength used

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51
Q

What is reflection?

A

It is essential for ultrasound
It is not frequency dependent
Reflection at a boundary depends on the change of acoustic impedance at the boundary
Ultrasound signal is generated from boundaries
It works well if 2 adjacent materials have similar Z values

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52
Q

What happens if gas in the beam?

A

Air has a very low characteristic acoustic impedance (Z)

Any gas will create a perfect mirror as all ultrasound is reflected back

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53
Q

How do you calculate acoustic impedance?

A 
Z = pc
Z = acoustic impedance
c = speed of sound
p = density
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54
Q

How do you calculate reflection correlation coefficient? R

A 
R = reflected intensity / incident intensity
R = (Z1-Z2/Z1+Z2)^2
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55
Q

What is the R value between soft tissue and soft tissue?

A

R

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56
Q

What is the R value between soft tissue and bone?

A

R = 0.5

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57
Q

What is the R value between soft tissue and air?

A

R = 0.999

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58
Q

What is shadowing?

A

It occurs when a high proportion of the ultrasound beam energy is either reflected or attenuated by the target

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59
Q

When does shadowing occur?

A

Air/soft tissue interface
Bone
Calcification

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60
Q

What happens when the wave does not approach the boundary at 90 degrees? Use a diagram

A

The wave is reflected at an angle equal to the incident angle
As the probe rotates it changes the image considerably

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61
Q

What is scatter?

A

It is critical in the blood
Erythrocytes are perfect scatters - redirecting energy in all directions but weak
The proportion of energy scattered is proportional to frequency^4
Causes an exponential decrease in intensity

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62
Q

When does scatter occur?

A

It occurs when the object is small compared to the wavelength
It is highly frequency dependent

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63
Q

What is refraction?

A

When there is a change of speed of propagation and the beam is bent from its original path
There is no significant change of speed between soft tissue
Not a big problem in ultrasound

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64
Q

When can refraction occur and why does it cause problems?

A

It can occur when passing through muscle

Causes problems as the machine assumes the beam travels in a straight line

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65
Q

What is absorption?

A

BAD!
Transfer of mechanical energy to heat
Direct conversion of energy to heat
All ultrasound creates heat
Heat increases linearly with frequency
In soft tissue, absorption accounts for >80% of total intensity reduction
Causes an exponential decrease in intensity

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66
Q

What causes absorption to occur?

A

Frictional (visco-elastic) losses

Relaxation processes

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67
Q

What is the consequence of increasing frequency? Absorption

A

Increased absorption

Increased heat

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68
Q

Draw the graph the depicts the relationship between beam intensity and depth of penetration with varying frequency

A

Image

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69
Q

What is attenuation?

A

Occurs due to all interactions with matter

It is the loss of energy from the beam

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70
Q

What interactions with matter causes an exponential decrease in intensity?

A

Scatter

Absorption

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71
Q

What is the intensity attenuation coefficient? mu

A

The fraction of energy removed from a plane wave by the combined processes of absorption and scattering in unit path length

it is tissue specific
it is frequency dependent

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72
Q

What is the normal mu (intensity attenuation coefficient) in soft tissue?

A

1dBcm-1MHz-1

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73
Q

What are the reasons for a gynaecological ultrasound?

A
  • Irregularities of the menstrual cycle
  • Congenital/structural abnormalities
  • Presence of a mass
  • Carcinoma (organ or origin or involvement of adjacent structures)
  • Presence of metastatic disease
  • Assisted contraception programmes
  • Intrauterine contraceptive device (IUCD localisation)
  • Screening program
  • Acute pelvic pain
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74
Q

What are the 2 methods for gynaecological exams?

A

Transabdominally

Transvaginally

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75
Q

How is the patient prepared for a gynae exam?

A

Bladder filling
Drink 1 pint of water before hand
It allows you to look through the bladder to the uterus

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76
Q

Describe the transabdominal technique for a gynae exam

A

Full bladder
Longitudinal, transverse and oblique sections
Contralateral technique
Identify anatomical structures

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77
Q

What are the advantages of transvaginal technique for a gynae exam?

A

Transducer is closer to the area of interest
Can use high frequency
Increase the definition of the structure
Increased quality of image

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78
Q

What observations should be made in a gynae exam?

A

The scan should demonstrate:

  • Normal anatomy/ varients
  • Assess size, outline, echotexture and echogenicity
  • Pathological findings
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79
Q

What are the normal variants that can be seen in a gynae exam?

A

Age and menstrual status related appearances of the ovary and uterus

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80
Q

Describe the different appearances of the ovaries depending on menstrual status

A

Image

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81
Q

Uterus examination

  • What should be examined
  • What is the normal appearance?
A
  • Position
  • Size
  • Shape
  • Ultrasound characteristics of endo and myometrium
  • Centre of the uterus generates a linear echo
  • Uterus changes with cycle
  • Thickens from ovulation to menstruation
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82
Q

How can uterine perfusion be determined?

A

Using Doppler
Blood flow to endometrium changes
Can be useful in IVF

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83
Q

Ovary examination - what should be examined?

A 
Position
Size
Shape
Ultrasound characteristics
Number and size of follicles
Internal echo pattern of follicles
They are small and hard to find - appearance changes with menstrual cycle
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84
Q

How does the size of the ovaries and uterus change with age?

A

Largest during reproductive years

Shrinks in menopause

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85
Q

How do you assess infertility by ultrasound?

A

Initial ultrasound is on day 10-12 of cycle
Can use grey-scale US to assess
Can use Doppler to assess blood flow of endometrium and ovaries
Can use sonohysterography
- Injection of contrast medium to assess uterine cavity and tube patency

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86
Q

What are the sonographic characteristic features of pelvic masses that should be considered?

A

Location and size
Internal consistency
Borders
Ascites and other metastatic lesions

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87
Q

When looking at the location and size of a pelvic mass what features should be noted?

A

Unilateral - adnexal or intrauterine

Bilateral - pelvoabdominal or not defined

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88
Q

When looking at the internal consistency of a pelvic mass what features should be noted?

A

Cystic - homogenous, sepataed, solid foci, multiple cysts, multicystic
Complex - predominantly cystic or solid
Solid - mildly, moderately or markedly echogenic

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89
Q

When looking at the borders of a pelvic mass what features should be noted?

A

Well defined
Moderately defined
Poorly defined

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90
Q

Describe the appearance of polycystic ovarian disease

A

Over 12 follicles
Follicles are small and never fully develop
Due to abnormal hormone levels

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91
Q

Why use ultrasound?

A 
Relatively inexpensive
Patient friendly
Safe in experienced hands
No radiation
1st line examination for some presentations
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92
Q

What is the national screening program for obstetric US?

A

Scan in 1st trimester and at 20 weeks

Common practice - done in all pregnancies

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93
Q

What are the indications for obstetric ultrasound?

A 
Placental site and abnormalities
Uterine abnormalities
Detection of a pelvic mass
Foetal position
Control for invasive procedures
Detection of foetal compromise - monitoring of foetal wellbeing
Foetal growth monitoring
Estimation of foetal weight
Amniotic fluid volume
Medico-legal issues
Client-consumer expectations
Viability
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94
Q

What are the NICE guidelines around obstetric US?

A

Pregnant women should be offered an early ultrasound scan between 10 weeks and 14 weeks to determine gestational age and detect multiple pregnancies

Ensures consistency of gestational age assessment and reduce the incidence of induction of labour for prolonged pregnancy

Crown-rump length should be used to determine gestational age - once this is over 84mm, should use head circumference

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95
Q

What should the first obstetric screening scan establish?

A

Gestational age
Viability (foetal heart beat)
Foetal number
Detection of abnormalities

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96
Q

In obstetric examination what features should be measured and when?

A 
Mean gestation sac diameter
Gestation sac volume
Crown rump length 6-13 weeks
Head circumference 13-25 weeks
Femur length 13-25 weeks
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97
Q

What is foetal biometry?

A

Measurement of an anatomical parameter of a foetus

Estimate the age from the measurement

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98
Q

In foetal biometry what determines which areas are measured?

A

Reproducibility of the measurement

Correlation of the size to the age of the foetus

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99
Q

When and why is foetal biometry done?

A

Can be used to look for intrauterine growth restriction
Can use Doppler to assess the umbilical artery
Done in high risk pregnancies

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100
Q

What are the objectives of the foetal national screening program?

A
  • Foetal anomaly screening (18-20wks)
  • Benefits outweigh risks
  • Reduce perinatal mortality by detecting malformations (requires a high level of expertise)
  • Reduce indications for induction of labour for post term pregnancy
  • Earlier detection of multiple pregnancies (improved management)
  • Earlier gestational age assessment
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101
Q

What features of the foetus need to be scanned at 20 week and what abnormality can it reveal?

A
  • Head and Neck (brain and nuchal fold - Down’s)
  • Face (lip - cleft palate)
  • Chest (4 chamber heart, outflow tracts, lungs)
  • Abdomen (stomach, abdo wall (omphalocele), bowel, renal pelvis, bladder)
  • Spine (vertebrae - spina bifida)
  • Limbs
  • Uterine cavity (amniotic fluid, placental site)
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102
Q

What percentages of abnormalities are picked up on foetal scanning?

A

Depends on the condition
Anencephaly = 99%
Cardiac abnormalities = 50%

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103
Q

What are the advantages of US in obstetric management?

A
  • Detection of pregnancy at a very early age (4-5 weeks)
  • TV approach has increased sensitivity for detection of ectopic pregnancies
  • TV allows for detection of foetal movement from 5-6 weeks
  • Aids management of multiple pregnancies
  • Application of foetal biometry to reliable data
  • Aids management of complicated pregnancy
  • Diagnosis of congenital abnormalities
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104
Q

What are the 3 transducer array types?

A

Linear
Curvilinear
Phased

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105
Q

What does a linear array look like and what is it useful for?

A

Long flat front face

Carotid artery
Thyroid
Breast

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106
Q

What does a curvilinear array look like and what is it useful for?

A

Curved face
Fan Beam

Obstetrics
General abdominal

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107
Q

What does a phased array look like and what is it useful for?

A

Flat face
Small area

Cardiac

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108
Q

Why do you use a phased array for cardiac imaging?

A

It is difficult
There is a small area for ultrasound due to the lungs and the ribs
Small window requires a small transducer

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109
Q

How do you decide which transducer to use?

A

Choose the field of view that matches the area of interest
THEN choose the frequency.
If it is superficial use a higher frequency

Operator determined

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110
Q

What are the specialist transducer types?

A

Transrectal
Transvaginal
Intraoesophageal

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111
Q

How do you calculate the minimum time required for one line?

A

2 x depth / speed
2D/C
seconds

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112
Q

How do you calculate the time required for one frame?

A

2 x N x D / c
N = number of lines per frame
D = depth
c = speed of sound

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113
Q

How do you calculate frame rate?

A

C / 2xNxD
c= speed of sound
D = depth
N = number of lines per frame

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114
Q

What can you do to increase the frame rate?

A

Decrease the number of lines in the scan

Decrease the depth

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115
Q

How many frames per second is required to get a real time image?

A

20-25fps

If it is lower you get a jerky image

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116
Q 
How many lines will be in the image using:
Frames per second = 25
c = 1540ms-1
depth = 10cm
Describe the resultant image quality
A 
N = C / FR x 2 x D
N = 1540 / 25 x 2 x 0.1
N = 308 lines

This will give a poor image - there is not enough time to get an adequate number of lines

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117
Q

What can you do if there is not enough time to get an adequate number of lines?

A

Can use false frames

Only if the image is not moving quickly

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118
Q

In what situations can you not use false frames?

A

Liver, cardiac, kidney

when the object is moving quickly

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119
Q

How are false frames created?

A

Uses linear interpolation

  • Can miss very small features
  • Must not detect a depth that is too much as you are throwing away information
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120
Q

Describe the interconnecting components of a B scanner using a flow diagram

A

Image

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121
Q

What is the clock in a B scanner?

A

It sends sychronising pulses around the system
It instructs the pulses of the ultrasound
Each pulse corresponds to a command to send a new pulse from transducer
It determines the pulse repetition frequency
It communicates with the transmitter,TGC generator and Beam controller
Need to wait for echo to return before sending out the next pulse

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122
Q

What is the pulse repetition frequency?

A

PRF
The rate of ultrasound pulse generate (kHz)
NOT US FREQUENCY (MHz)

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123
Q

How do you calculate PRF?

A

PRF = 1 / time per line

PRF = speed / 2 x depth

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124
Q

What is the transmitter in a B scanner?

A

Responds to clock commands by generating high voltage pulses to excite the transducer
It is housed very closer to the transducer (likely to be within it)
It causes the transducer to vibrate/oscillate to create the sound

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125
Q

Where is the transmitter, why?

A

Housed very close to the transducer (likely to be within in)

This reduces time and ensures there is no loss of voltage

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126
Q

How is an ultrasound created? (different components involved)

A

Clock instructs the transmitter
Transmitter creates a voltage
Voltage creates an oscillation in the crystal

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127
Q

What is the ADC?

A

Converts analogue signal into digital signals for further processing
Once digitised, everything else is software
Receives analogue signals from the transducer
Transmits digital signals to the signal processor

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128
Q

What are the required properties of the digitisation rate?

A
  • Be fast enough to cope with the highest frequencies
  • Have sufficient levels to create an adequate grey scale e.g. 1024
  • Be higher than frequency so as not to lose information
  • Can be fast or have lots of levels
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129
Q

What is the signal processor?

A

It is different for each manufacturer. The digital signal from the ADC is passed to the signal processor.

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130
Q

What are the 4 functions of the signal processor?

A

TGC Application
Overall gain
Signal compression
Demodulation

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131
Q

What is TGC?

A

Time gain control

Applying different gains at different depths set by the operator

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132
Q

What is overall gain?

A

Treats all echoes equally as all echoes are small and need extra amplification

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133
Q

What is signal compression?

A

Returning echoes have a wide range of amplitudes and these should be represented by different grey values
Signals converted to a grey levels

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134
Q

How do you calculate dynamic range?

A

Largest signal level below saturation / smallest signal level above noise.

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135
Q

What is the dynamic range?

A

It is the ratio of the largest to the smallest signal
Usually expressed in decibels
Range 10uV to 1V

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136
Q

What limits the largest signal in US?

A

Saturation - it a signal goes above the saturation point it is viewed as the same colour as the maximum

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137
Q

What limits the smallest signal in US?

A

Noise - signal will not be displayed if it is below noise

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138
Q

What is a decibel?

A

It is a relative unit
1 dB = 10log10 (p1/p2)
x compared to y

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139
Q

Describe the relationship between power and voltage

A

Power is proportional to voltage squared
1dB = 10log10 (v1/v2)^2
1dB = 20log10 (v1/v2)

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140
Q

What is the normal dynamic range?

What is the dynamic range of a display?

A

Generally around 100dB
There is a massive ability to distinguish different sounds
Typical monitors have DR = 25dB

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141
Q

What is the problem when displaying signals?

A

They are converted to a grey scale
Lose a lot of information
Displays are not good enough to display all sound levels
Brains cannot distinguish all of the subtle differences

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142
Q

What are the 2 methods for assigning grey levels to echo amplitudes?

A

Linear

Transfer curves

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143
Q

Describe linear assignment of grey levels to echo amplitudes

A

Divide range into equal segments in a linear fashion

Problem: all small signals are assigned a grey scale level one and you lose all contrast resolution for small echoes

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144
Q

What is the use of transfer curves?

A

Assigning grey levels to echo amplitudes

Optimise the curve to the clinical requirement

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145
Q

Describe transfer curves - draw their typical appearance

A

Image
Curve 1 - using most grey scales for lower echoes
Curve 3 - lost information for small echoes and use more grey scales for higher echoes

Machines have presets
Loads curve that is best for a particular application
Different curves for different manufacturers

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146
Q

What are the X, Y and Z values for imaging?

A

X and Y are positional information and this comes from the beam controller
Z value is the grey scale level

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147
Q

What is the function of the image store?

A

Takes Z (brightness) signal from the processor
Positions it in the image memory using the X and Y information from the beam controller
Assembles an image for each frame
Presents assembled image to display

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148
Q

How many images can be stored?

A

100-200 images/frames on a cineloop

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149
Q

How are the X and Y co-ordinates determined by the beam controller?

A

X value - depth determined by timing and speed of sound assumption
Y value - distance from the edge of the array at which the pulse was launched

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150
Q

What is pre-processing and what does it include?

A

Anything which is done to the signal prior to storage in the image memory
It is DESTRUCTIVE (cannot be undone)
Includes TGC, depth scale, compression

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151
Q

What is post-processing and what does it include?

A

Anything which is done to the image/signal AFTER storage in the image memory
It is non-destructive
Includes: alpha numerics, calipers, black and white inversion, read zoom
Can be scaling or transfer function

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152
Q

What is frame averaging?

A

In any frame, some of the information displayed will be noise
It removes unwanted signal and decreases the noise errors
It will pick up any noise in the environments
Taking the maximum or minimum value (rather than averaging) will emphasise noise.

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153
Q

Where are the sources of noise?

A

electronics, acousitc, environmental

Noise is expected in every frame because of the random nature

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154
Q

What happens as you increase the number of frames averaged?

A

Decreased noise errors

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155
Q

What happens as you increase the number of frames in frame averaging?

A

Increase time
Slower to respond to genuine changes
Lose some information relating to movement

Trade off between frame rate and noise reduction (incorporated into machine presets)

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156
Q

Describe the function of the transducer

A

Sends out short ultrasound pulses when excited electrically

Detects returning echoes and presents them as small electrical signals

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157
Q

What is the effect of decreasing transducer size?

A

Decrease near field

Increase lines

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158
Q

What are overlapping groups?

A

Partial solution
Fire several elements together
Electrically connect a block of transducers
1 pulse = several transducers fire
Move down by one element e.g. 1-7 then 2-8 etc.
Repeat but block size is maintained
Mimics the effect of a large source but produces multiple lines
SYNTHETIC APERTURE

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159
Q

What is the advantage of using overlapping groups?

A

synthesises an artificially larger transducer
Increase near filed as N^2
Usual element size is 1mm and this creates a short NF
Extends this

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160
Q

What is array focusing?

Use a diagram

A

It introduces delays to compensate for the extra path length of the outer elements
Increases the delay at central transducers
At an arbitrary point, signals will arrive at the same time
You choose that point
This is done on transmission and reception
Same effect as a lens
Increases the quality at a specific depth

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161
Q

Why is array focusing necessary?

A

Waves from outer elements have greater path lengths - therefore signals do not arrive simulateously at the target

  • Reflections from the target do not arrive at all elements at the same time
  • Blurring on way in and way out
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162
Q

What are phased arrays?

A 
Can direct beam off all axis
Can use all the elements each time
Can fire beam at any angle by changing delays
No stepping along the array
Small sources
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163
Q

What is multizone focusing?

A

Focusing makes the image worse at other depths
Instead of moving the array down - send out beams at different time delays
Start collecting echoes after the cross over point
Multiple beams
Creates multiple images with various foci which are then combined

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164
Q

What is the consequence of multizone focusing?

A

Increases the quality of the image

Increases time

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165
Q

How many focal zones should be used?

A

Operator needs to put in as many zones as possible but keep the frame rate high enough to detect movement
Many in breast, few in cardiac

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166
Q

When is multizone focusing used?

A

Linear

Curvilinear

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167
Q

Draw a diagram to explain multizone focusing the the composite focus that can be achieved

A

Image

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168
Q

What is the effect of increasing the size of the lens aperture?

A

Smaller beamwidth
Depth of focus is reduced
Determined by the manufacturer

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169
Q

What are the 3 resolution orientations?

A

Axial
Lateral
Slice thickness

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170
Q

Describe axial resolution

A

It is the resolution in the direction parallel to the direction of the beam
The resolution along any point of the beam is the same
Depends on pulse length

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171
Q

What is the effect of increasing the frequency on axial resolution?

A

Increasing frequency = decreased wavelength

This gives increased axial resolution as there are shorter pulses

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172
Q

What pulse type gives the best axial resolution? Use a diagram

A

Short pulse

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173
Q

What causes an increase in axial resolution?

A

Increase frequency
Decrease wavelength
Decrease the number of cycles in a pulse

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174
Q

Describe lateral resolution

A

lateral resolution is defined as the ability of the system to distinguish two points in the direction perpendicular to the direction of the ultrasound beam

It depends on beam width
The object is viewed as wide as the beam width

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175
Q

Draw a diagram to show the effect of beam width on lateral resolution

A

Image
Object is viewed as wide as the beam width
Increasing beam width = decreased lateral resolution

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176
Q

What is the effect of increasing beam width on lateral resolution?

A

Decreased

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177
Q

What determines beam width

A 
Shape and size of transducer
Depends upon the focusing
BW = F x wavelength / A
F = focal length. A = aperture
As frequency goes up, the wavelength goes down = beam width goes down = lateral resolution increases
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178
Q

How do you increase lateral resolution?

A

Decrease beam width by:
Increasing frequency
Increasing the size of the aperture

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179
Q

Describe slice thickness

A

It depends on the thickness or height of the beam
Normally poor as there is no electronic focusing
Decreases as frequency increases
Usually the worst resolution

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180
Q

How can improve resolution in the slice thickness direction

A

1.5/2D arrays improve focusing and resolution
Can focus the beam in 2 planes
Can send a beam out in any direction

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181
Q

What is Doppler?

A

The technique of using ultrasound to measure flow.

Have increase in frequency when direction is towards observer and decrease when it is away.

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182
Q

When does the Doppler effect occur?

A

When either the receptor or the generator is moving relative to the other
If there is no movement the frequency emitted it equal to the frequency received

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183
Q

What happens in Doppler if an object is moving towards the observer?

A

Moving source - stationary observer
Increase pitch
Increase frequency
Waves are squashed in the direction of travel.

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184
Q

What happens in Doppler if an object is moving away from the observer?

A

Decrease frequency

Waves are stretched

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185
Q

What is the result of having a moving observer with a stationary source?

A

Also get a Doppler shift.

If the person is moving towards the source then it picks up waves more rapidly causing an increase in frequency

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186
Q

What causes an increase and decrease in frequency in Doppler?

A

Motion towards = Increase frequency

Motion away = decrease frequency

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187
Q

Describe the Doppler effect in the body

A
  • Sound is transmitted to the blood and will irriadiate the RBCs
  • They are moving
  • The frequency the RBCs receive different to sent out
  • They scatter the signal in all directions
  • The backscattered shifted signal is sent out in all directions

First there is a stationary source (transducer) and moving receiver (RBC)

Then the RBC acts as a moving source and the transducer becomes the stationary receiver

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188
Q

What is the result of the 2 doppler effects in the body?

A

They do not cancel each other out - it is doubly shifted.

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189
Q

What is the doppler shift frequency?

A

Doppler shift (delta f)
It is the difference between the received frequency (fr) and the transmitted frequency (ft)
Change in frequency of the echo due to the motion of the target

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190
Q

How do you calculate Doppler shift frequency? (delta f)

A 
cos(angle) x 2 x ft x v  /  c
ft = transmitted frequency
c = speed of sound
v = target speed
2x due to the double Doppler shift 
angle = angle between the beam and flow
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191
Q

Why is Doppler done at an angle?

A

No Doppler shift occurs if it hits at 90 degrees
Ultrasound is generally done at 90 degrees to not get a signal from blood
Maximal Doppler shift is at 0 or 180 degrees
Need to know the angle used

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192
Q

What is colour Doppler?

A
  • Superimpose the Doppler information on top of the underlying grey scale image.
  • Use colours to represent the Doppler shifts
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193
Q

What is are the principles of colour Doppler?

A
  • Repeated firing along one scan line
  • Compare lines in consecutive pairs
  • Divide each line into segments
  • Compare segment by segment
  • Use frequency content of each segment
  • 6 or 8 samples down each line
  • Look at the similarities and differences between the pairs
  • If the segments are identical = no Doppler shift
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194
Q

What is displayed in colour Doppler?

A

Superimposed colours on greyscale image
Doppler shift frequency is not displayed
Displays PHASE
Measure phase difference

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195
Q

Describe the rate of change of phase in colour Doppler

A

Frequency = rate of change of phase = Speed

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196
Q

How is colour mapping done in colour Doppler?

A

Colour indicated direction: Blue Away Red Towards
Blue - movement away from transducer

Shade = velocity

Variance - how wide spread are the velocities?

Colour options: hue, brightness, saturation

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197
Q

What colour is given to turbulent blood flow?

A

Green/yellow

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198
Q

What is Doppler priority?

A
  • Determines whether to display colour or grey scale
  • If the grey level is large enough, a colour is not put there
  • If the grey level is less than the threshold value then display colour
  • The decision is arbitrary
  • If there is a large signal e.g. from a boundary then you want it to be displayed
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199
Q

What decides whether to use the B signal or Doppler signal?

A

Blood/tissue discriminator

The discrimination point is determined by the operator - Doppler priority

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200
Q

Where is the change of phase calculated?

A

Autocorrelator

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201
Q

How is the area determined for colour doppler imaging?

A

Operator places a box over the region of interest
This instructs the machine to look in that area to determine Doppler effect
Keep the box as small as possible

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202
Q

What happens if you increase the size of the box for viewing colour Doppler?

A

Increase size of box
= decreased frame rate
due to increased lines

203
Q

What is power Doppler?

A

More sensitive than normal colour but does not give the velocity information

204
Q

What are the differences between colour Doppler and power Doppler?

A

In Colour - the values collected are sorted into velocity bins. Anything below noise will not be detected - any components are not represented strongly will not be detected

Power Doppler - all values placed into one bin. The one value bin is way above the noise level

205
Q

What are the advantages of power Doppler?

A
  • Better signal to noise ratio
  • Better at picking up low volume flow
  • Better for peripheral areas and areas of low flow e.g. stenosis
  • Powerful sensitivity
  • Insensitive to Doppler angle
206
Q

What are the disadvantages of power Doppler?

A
  • Gives no velocity estimate
  • may not have directional discrimination (no idea if negative or positive flow)
  • has no measure of turbulence
  • no quantification
207
Q

What does tissue Doppler do?

A

Suppresses blood flow, looks at the movement of vessels. It is colour Doppler set up slightly differently.

Turn down Doppler gain
Use low pass filter - to supress blodd
Removes the wall thump filter
Displays colour on vessel walls
Detects tissue motion
208
Q

When is tissue Doppler used?

A

Used for low velocities

Used to view the vessel walls

209
Q

What is a wall thump filter?

A

Vessels move slower than blood
If the velocity is less than X then remove
Applied by this high pass filter
Suppresses detail from blood flow.

210
Q

What is continuous wave Doppler?

A

It is the purest form of Doppler
Permanently emitting and receiving - separate send and receive transducers are used
It provides a snap shot of what is happening in the vessel

211
Q

What are the advantages of continuous wave Doppler?

A

Simple
Cheap
High quality spectral information available

212
Q

In continuous wave where are the reflections from?

A

Stationary targets e.g. organ boundaries

Slow moving large targets e.g. vessels walls

213
Q

What is the purpose of continuous wave Doppler?

A

Need to filter out clutter signal

214
Q

Describe the velocity distribution within the blood

A

Blood moves with a range of velocities
The velocity distribution changes with time
Flow is pulsatile
You get different appearances at different points in the cardiac cycle

215
Q

Draw a diagram depicting continuous wave Doppler

A

image

216
Q

What does the continuous wave Doppler spectrum display?

A

It displays the range of velocities along the x axis
It displays the delta f (Doppler shift frequency) along the y axis
At each time point there is a range of velocities present and their relative intensities
The orange/brown colour is used to display intensity
It details systole and diastole
Shows peak velocity

217
Q

What are the advantages of continuous wave doppler?

A

Shows lots of detailed information
Each artery has a different Doppler spectrum
Very sensitive to pathology but requires an expert

218
Q

What is the key error that can be made in continuous wave doppler?

A

Ignoring the angle

Changing angles changes the spectrum

219
Q

What are the the problems with continuous wave doppler?

A 
Do not know vessel angle
May have overlying vessels
Do not have an image
No depth discrimination
Requires an expert 
Need to be certain of anatomy
220
Q

What are the uses of continuous wave Doppler?

A

Need to be certain of anatomy

  1. Check for vessel patency in vascular surgery
  2. Foetal heart detection
  3. DVT detection
221
Q

How does pulse doppler work?

A 
Uses long pulses NOT continuous waves
Approximately 6-7 cycles
Have gating to select depth
Can have an associated image 
Pulses give depth information
222
Q

What are the features of pulse doppler?

A 
Everything is compromised
Poorer axial resolution
Can distinguish overlying vessels
Too short for frequency information but also lose spatial information
Can get a pressure
223
Q

What is the main disadvantage of pulse doppler?

A

Aliasing

224
Q

What is aliasing?

A

Undersampling can lead to a misleading image

Limit for aliasing = Nyquist theorem

225
Q

What is the maximum doppler shift you can detect without ambiguity?

A

Less than PRF/2

If PRF = 1kHz, can’t detect doppler shift greater than 500Hz

226
Q

What is the Bernouilli equation?

A

p1-p2 is approximately equal to 4V^2
p1-p2 = pressure gradient
v = peak velocity at narrowing

If you can measure the peak velocity, can non-non-invasively calculate pressure change over a pathology.

227
Q

What are the advantages of pulse doppler?

A

Depth information
Can combine with an image
Good spectral infromation

228
Q

What are the disadvantages of pulse doppler?

A

Aliasing
Need to know where to look
Can only look at one place at once

229
Q

How is stenosis viewed using ultrasound?

A

Is it characterised by high pressure gradients across the narrowing
Use colour doppler first then guided pulse doppler to get spectral information

Using pulse doppler can get pressure and the pressure difference is related to the density and velocity of fluid movement in the vessel.

230
Q

Describe a transducer

A

They are a resonant device
They have a natural frequency
The thickness of each element in the housing depends on the wavelength

Range from 3-10MHz

231
Q

How is the transducer thickness determined?

A

Thickness = wavelength / 2

232
Q

What happens to the frequency as you decrease transducer width?

A

Increase frequency

233
Q

Draw a diagram of the transducer including its layers.

A

Image

234
Q

What are the different layers of the transducer?

A 
Backing material
Electrodes - the transducer has electrodes evaporated onto the transducer. 
Transducer
Electrodes
Matching material
235
Q

What is the purpose of the transducer backing material?

A

Dampens the resonance

Allows you to control the pulse (very short) to get better axial resolution

236
Q

What happens to axial resolution as you decrease pulse length?

A

Increase axial resolution

237
Q

What does the transducer backing material do?

A

Absorbs some of the sound to dampen oscillation

Needs to allow sound in readily but stop it leaving

238
Q

What are the important features of the transducer backing material>

A

Needs to be a good absorber
Needs a high absorption coefficient
Needs to have a similar Z value to that of the transducer
ZT= ZB

239
Q

What is the consequence of increasing the high absorption coefficient of the backing material?

A

It makes the transducer less efficient

Heats during use

240
Q

What is the purpose of the matching material in the transducer?

A

Gets the energy out of the transducer and into the patient

241
Q

What is the Z value (acoustic impedance value) of the matching material?

A

Halfway between the Z of the patient and the transducer
Zm = SQR (ZT x Zpt)
ZM = acoustic impedance of matching material
ZT = acoustic impedance of transducer
Zpt = acoustic impedance of patient

242
Q

What materials are the backing and matching materials made out of?

A

Unknown

Different in different manufacturers

243
Q

A backing material NEEDS:

A

to have a high value of attenuation
to be well matched to Z of PZT

but it reduces sensitivity and efficiency

244
Q

A matching material NEEDS:

A

to have a Z value matched to transducer and patient

this will always be a compromise

245
Q

What is the optimal thickness of the matching material?

A

approximately 1/4 of the wavelength

246
Q

What are the features of PZT composites?

A

Have other materials included to reduce Z value and increase efficiency
Allows for use of multi-frequency transducers
Capable of being used away from optimum frequency

247
Q

What is the main feature of a continuous wave transducer?

A

Transducers for CW only do not need a backing material - does not use pulses

This makes them very efficient and sensitive.

248
Q

What does a Fourier analysis do?

A

Involves breaking down a signal into its component parts.

249
Q

Draw a continuous wave and its fourier analysis

A

image
One fixed frequency
Fixed amplitude
No width in Fourier analysis - single line

250
Q

What are the features of a pulsed wave?

A

Varies in amplitude
Contains a range of frequences
Complicated in shape
Fourier analysis shows a spread of frequencies

251
Q

Draw a long pulsed wave and its fourier analysis

A

image
similar to continuous wave but there is a spread of frequency
Narrower range of frequencies than short pulse

252
Q

Draw a short pulsed wave and its fourier analysis

A

large range of frequencies

wider bandwidth

253
Q

What happens to bandwidth as you increase pulse length?

A

Increase pulse length = decrease bandwidth

254
Q

What is the impact of attenuation on bandwidth?

Diagram

A

High frequency components are attenuated MORE than low frequency components
- Tissue attenuation is frequency related
- As it travels through the tissue it changes
- Change in frequency content and change in shape of pulse
Image

255
Q

What are the consequences of attenuation on the shape of the beam?

A

Reduction in bandwidth
Decrease in central frequency

Same process as beam hardening

256
Q

Draw the pulse and fourier analysis for a typical B mode image.
What are the features?

A

Wideband
Good spatial resolution
Increased axial resolution due to wide bandwidth

257
Q

Draw the pulse and fourier analysis for a typical colour Doppler image.
What are the features?

A

narrowband
Medium spatial resolution
Better control of frequency (therefore better for Doppler)

258
Q

Draw the pulse and fourier analysis for a typical spectral power Doppler image.
What are the features?

A

Narrowband
Poor spatial resolution
Pulse wave 7-8 cycles
Decreasing bandwidth from B mode and colour.

259
Q

Draw the pulse and fourier analysis for a typical continuous wave image.
What are the features?

A

No pulse
No axial spatial resolution
Image 250

260
Q

Describe the beam as it passes through tissue in areas of high and low pressure

A
  • As the beam is travelling through tissue it is changing shape
  • Momentarily there are changes in pressure and alters the tissue and the speed of sound
  • Slope rotates clockwise
  • Tissues causes non-linear distortion of the beam
  • High pressure = tissue compressed, higher velocity
  • Low pressure = tissue expanded, lower velocity
261
Q

What causes the non linear distortion of the beam in tissue

A

High energy/ amplitude of the beam

Distortion increases on the return journey back to the transducer

262
Q

Draw a normal wave and a distored wave and their fourier analysese

A

Image

Peaks in distorted are multiples of the original frequency e.g. f, 2f, 3f

263
Q

What are harmonics>

A

Peaks that are multiples of the frequency f, 2f, 3f etc. of the original frequency

Part of the wave is coming back at higher than the frequency sent out

264
Q

What is harmonic imaging?

A

Send out a wave at frequency f
Measure frequency returned at 2f

Harmonics are generated in the tissue - creates better resolution

265
Q

What are the advantages of harmonic imaging?

A
  • Reduces clutter due to artefacts (a lot of clutter is low amplitude and doesn’t contain much 2f)
  • Improved spatial resolution
  • Increased contrast
266
Q

What are the disadvantages of harmonic imaging?

A

Reduced dynamic range

Reduced penetration

267
Q

What are the 2 methods for applying harmonic imaging?

A

2 main methods

  • filtering
  • pulse inversion

Each manufacturer does it slightly different

268
Q

Describe filtering as a method for applying harmonic imaging?
Diagram

A
  • Divide the bandwidth into 2 and use the low end for transmission and the upper end for reception
  • Makes smarter use of bandwidth available
  • Excite at below the resonant frequency
  • Put in a filter and filter out anything but 2f
269
Q

What are the consequences of using the filtering method apply harmonic imaging?

A

Bandwidth is reduced therefore pulses are longer

Degrades axial resolution

Improved lateral resolution at the expense of axial. (Axial is better so can lose a bit more)

270
Q

Describe pulse inversion as a method for applying harmonic imaging

A
  • Send out 2 pulses, one of which is the inverse of each other
  • Add them together
  • Expect A+-A = 0 if they are symmetric
  • However distortions are not symmetric and harmonic is left behind
  • Assume symmetry - not true to do non-linear propagation.
  • The inverted pulse is distorted differently to the original
  • Pulses cancel out but the echoes do not
  • Summing up of echoes gives 2f
271
Q

What are the advantages and disadvantages of using pulse inversion for harmonic imaging?

A
  • Uses short broadband pulses
  • No degradation to axial resolution
  • Frame penalty - have to send out 2 pulses
272
Q

Which is the better method for harmonic imaging?

A

Both work well and achieve objectives with different costs

  • If frame rate is a problem do not use pulse inversion
  • Cardiac uses filtering
  • Most others will use pulse inversion and accept a slower rate
273
Q

What is the purpose of contrast agents?

A

It makes an area visible that was not previous visible

They attempt to map function in a way that raw imaging does not

274
Q

What contrast agent is used in ultrasound?

A

Small encapsulated gas bubbles.

  • Injected into the blood stream
  • Administer small amounts in a controlled environment
  • Give a large echo
275
Q

How is signal enhanced using gas bubbles?

A
  1. They have a strong acoustic impedance mismatch
    (Z in air is low, low density and speed of sound. Relative to soft tissue there is a large difference)
  2. At some point frequencies are RESONANT and this provides further enhancement (x1000)
    (If the bubble is hit with the right frequency you will get a large increase in the quality of the signal
  3. Have more non-linearity than soft tissue and can therefore be detected using harmonic imaging
276
Q

What are the features of the contrast agent used?

A
  • Agents travel through a peripheral vein through the blood by encapsulating
  • It is stabilised by an outer shell
  • Use heavy inert gases to increase life time
277
Q

What is the purpose of the shell around the gas in a contrast agent?

A

It is stabilising

Creates a longer half life

278
Q

Why do you use a heavy inert gas in bubbled?

A

Creates an extended bubble life

Less diffusion out of the shell

279
Q

What is the mean size of a bubble?

A

1-6 micrometerres

280
Q

What gases are used in bubbles?

A

Air
Octofluoropropane
Nitrogen

281
Q

What chemicals are used for the bubble shell?

A

Albumin
Lipid/surfactant
Polymer

282
Q

Give an example of a microbubble contrast agent

A

Albunex
Definity
Sonovue

283
Q

What determines what happens to the bubbles?

A

Pressure in the pulse

284
Q

What are the 3 options that can happen with bubbles?

A

Linear oscillations
Non-linear oscillations
Transient scattering/ bubble destruction

285
Q

Describe linear oscillations with bubbles

A

Occurs at pressures

286
Q

Describe non-linear oscillations with bubbles

A
  • Occurs at pressures above 50kPa
  • Arise primarily from contrast agent in blood as the bubbles exhibit stronger non-linearity
  • Harmonic generation is minimal in tissue
  • Work in this area when working with contrast agents
287
Q

Describe transient scattering/ bubble destruction when working with bubbles

A

Occurs at pressure over 1MPa

As intensity increases, the shell becomes leaky and will eventually burst releasing free microbubbles

288
Q

What is MI?

A

Mechanical index

Related to the pressure of the singal

289
Q

What MI does linear oscillation occur?

A

0.006-0.06 MI (3MHz)

10-100kPa

290
Q

What MI does non-linear oscillation/harmonic generation occur?

A

0.06-0.6 MI (3MHz)

100kPa-1MPa

291
Q

What MI does bubble collapse occur at?

A

0.6-6 MI (3MHz)

1-10MPa

292
Q

When using contrast agents what considerations need to be made?

A
  • Bubble size
  • Gas content
  • Encapsulation
  • Administration
  • Detection
293
Q

How do you calculate the resonant frequency of an UNencapsulated bubble?

A 
f = 3.3/r
r = bubble radius (micrometres)
f = resonant frequency (MHz)

Encapsulated bubbles are more complex

294
Q

What frequency will a bubble with a 2um diameter resonante?

A 
f = 3.3/1
f = 3.3MHz
295
Q

What happens to resonant frequency as bubble diameter decreases?
Draw relationship

A

Higher resonant frequency

296
Q

What is the maximum size of bubble? Why?

A

Nothing over 10 micrometres

Large bubbles will be trapped in the lungs and cause emboli

297
Q

What determines the choice of gas?

A

Normally: air or heavy gases like perflurocarbon or nitrogen.

  • Heavy gases are less water soluble so they are less likely to leak out from the microbubble to impair echogenicity
  • Heavy gases last longer in circulation
  • Choice does not matter acoustically
  • Needs to be non-toxic
298
Q

What determines the material of encapsulation?

A
  • currently: albumin, galactose, lipid or polymers
  • The more elastic the material the more acoustic energy it can withstand before bursting
  • BUT stiffer shells generate more harmonic signals
  • Behaviour on compression is different from behaviour on expansion
  • If the pressure is too great the surface tension can’t support the bubble and BUCKLING occurs (depends on shell material)
299
Q

How are the bubbles administered?

A

Normally venous either bolus or slow transfuction

  • Have multiphasic response
  • Can use a destruction pulse to temporarily clear a region and monitor re-population (useful for diagnosing metastases)
300
Q

What is the advantage of bolus administration of contrast agent?

A

Can watch tissue or organ dynamics

Plot wash in and wash out curves

301
Q

What is the advantage of slow transfusion administration of contrast agent?

A

Look at steady state response

Image over several frames to identify regions of high/low uptake

302
Q

How is contrast agent detected?

A

Use harmonic content of back-scattered bubble

Use enhanced Doppler signal since the bubble is moving and backscatter from the bubble is larger than from RBC

303
Q

What are the specific clinical applications of contrast agents?

A
  • Study of transcranial and neck vessels
  • Contrast echocardiography
  • Liver imaging to detect portal hypertension and thrombosis
  • Oncology
304
Q

Describe targeted ultrasound

A
  • Microbubbles are targeted with ligands that bind to certain molecular markers that are expressed by the area of imaging interest or by direct binding to the cell of interest
  • Microbubbles travel through the circulatory system, finding respective targets and binding
  • If a sufficient number bind they become visible
  • Place part of a binding pair on the surface of the bubble
305
Q

What are the potential uses of targeted ultrasound?

A
  • Tumour marker
  • Attach a chemotherapeutic agent in/on the bubble and use high energy ultrasound to burst the bubble
  • Agent is released and enters tumour via sonoporation
306
Q

What are the challenges faced using contrast agents?

A
  • Life time in blood stream
  • Adhesion/specificity
  • Unwanted immune response
  • Toxicity
  • No toxic biproducts
307
Q

What are the advantages of ultrasound?

A
  • Safe
  • Well tolerated
  • Relatively low cost
  • No ionising radiation
  • Few technical limitations
  • Patient friendly (no claustrophobia)
  • Metallic implants not a problem
  • Better for real time dynamic studies
308
Q

What are the limitations of ultrasound?

A
  • Highly operator dependent
  • Requires in depth anatomy knowledge
  • Limited in joint assessment
    (intra-articular not viewable)
  • Bad for knee and hip
309
Q

What transducers are used in MSK US?

A

7-17MHz linear transducers
High frequecy
Can use curvilinear if you need to see a mass or deeper structure

310
Q

What are the different ways of viewing MSK in US?

A
  • Panoramic - wide field of view. Builds up as you go across
  • Dual screen (allows you to compare one normal image with pathological sample)
  • Power/colour Doppler (is sensitive and is good in rheumatology. A lot of masses will have vascularity. Can tell if pt has synovitis.)
311
Q

What structures can you view using MSK US?

A 
Joints
Tendons
Muscles
Bones (cortical surface)
Ligaments
Bursae
Nerves
312
Q

What are tendons?

A

Attach muscle to bone
Fascicles type 1 collagen, orientated mainly parallel to the long axis
Covered in paratenon and epitendineum
If they need more movement they are in the synovial sheet

313
Q

How do tendons appear on US?

A

echogenic fibrillar structures
multiple parallel lines in longitudinal section
multiple dots on transverse section

314
Q

How does the synovial sheet of tendons appear on us?

A

thin echogenic fluid containing structure that surrounds the echogenic tendon

315
Q

How do nerves appear on US?

A

Looks very similar to ligaments and tendons
Facicles are more spread out
Hypoechoic group of fascicles
Have perineurium and epineurium (echogenic)

316
Q

Describe the strucutre of muscles

A

Muscle fibres are grouped into fascicles separated by septa of fibroadipose tissue (perimysium)
Whole muscle enclosed in a fascial sheath (epimysium)

317
Q

What do muscles look like on US?

A

Transverse perimysium is seen as dot echoes or short lines scattered throughout hypoechoic background
Large intramuscular septa are echogenic
Produce a reticular pattern
Intermuscular septa are brightly echogenic

318
Q

Describe the appearance of a contracted muscle

A

Muscle alters shape and becomes hypoechoic and increased angulation of echogenic septa

319
Q

How are muscles/tendons/ligaments imaged?

A

Imaged at stress and in extension.
It can look pathological if not
State alters echogenicity

320
Q

What can be viewed in joints?

A

Cartilage
Synovial fluid
Joint Capsule
Fat pad

321
Q

What is the main artefact seen on MSK US?

A

Anisotropy
It can make tendons look pathological
This is the effect that makes a tendon appear bright when it runs at 90 degrees to the ultrasound beam, but dark when the angle is changed.
Need to scan at appropriate angle

322
Q

What is the role of MSK ultrasound?

A
  • Rheumatoid arthritis and joint disease– management of the disease, small joint assessment
  • Soft tissue masses, lumps and bumps, hernias
  • Sports medicine – muscle tears, sprains, athlete rehabilitation
  • Trauma – muscle tear, tendon rupture
  • Age related degenerative changes – rotator cuff disease, osteoathritis
323
Q

What are the pathologies seen most commonly in MSK US?

A
  • Tendon tears
  • Tendinosis
  • Tenosynovitis
  • Joint effusions/bone erosions from RA
  • Bursitis, ganglion cysts, lipoma, muscle tears, nerve masses, ligament sprains

History taking can aid diagnosis

324
Q

What interventional procedures can be guided by US? (MSK)

A
  • Joint aspirations
  • Therapeutic steroid injections
  • Biopsy of masses
  • Nerve block
325
Q

What are the 3 mechanisms in which ultrasound can cause damage?

A

Cavitation
Microstreaming
Heating

326
Q

When is cavitation most significant?

A
  • Concerned with activity of small bubbles when exposed to ultrasound
  • Most significant when using large pressures and low frequencies
  • Important close to gas collections (lung)
327
Q

Describe cavitation

A
  • Dissolved gases in the surrounding area diffuse into bubbles under positive pressure (positive half cycle)
  • Negative half cycle = expands and some gas diffuses out
  • Negative half cycle is more efficient at moving gas
  • In a complete cycle the bubble will grow and have less gas within it

At the end of the pulse everything goes back to normal (not a problem with a short pulse)

In a long pulse, pressures become so great that the bubble cannot be supported by surface tension and will collapse inwards - dangerous

328
Q

Why is cavitation not important?

A

It does not take place in vivo with diagnostic US levels.

Oscillations at lower levels can cause change in micro-circulation and alter cell permeability

329
Q

When is ultrasonic heating most important?

A

All procedures causes heating due to the deposition of energy.

Normally most significant in pulsed or colour Doppler.

330
Q

Why is heating greatest in Doppler?

A

Exposure is either continuous or with long pulses

There is also repeated firing down one line

331
Q

At which interface does the greatest ultrasonic heating occur?

A

Soft tissue - bone interfaces

Strong reflection and as a result lose a lot of energy here.

332
Q

What determines the rate amount of ultrasonic heating?

A

Depends on the time averaged intensity and/or power.

333
Q

What are the safety indices?

A

MI - mechanical index

TI - thermal index

334
Q

What is the MI?

A

Mechanical index
Risk of cavitation damage
Advised to keep below 0.3 (no adverse data below 0.3)

335
Q

What is the TI?

A

Thermal index

Risk of thermal damage

336
Q

How do you calculate the mechanical index?

A

MI = p/ sqrt (f)

p = peak negative pressure (MPa)
f = frequency (MHz)
337
Q

How do you calculate the thermal index?

A

TI = power emitted/W deg

Wdeg = power required to raise temperature by 1oC
Ratio of total power to Wdeg
Keep below 0.5
Any increase in temperature of a body part by 1.5 degrees is fine

338
Q

Is ultrasound safe?

A

No one has ever shown to have been damaged by a diagnostic ultrasound examination

339
Q

Where can safety advice for US be found?

A

BMUS website

340
Q

What is the BMUS advice regarding an MI >0.3?

A

There is a possibility of minor damage to the neonatal lung or intestine. Try to reduce exposure time as much as possible

341
Q

What is the BMUS advice regarding an MI >0.7?

A

There is a risk of cavitation if an ultrasound contrast agent is being used containing micro-spheres.
Risk increases with MI values above this threshold

342
Q

What is the BMUS advice regarding an TI >3.0?

A

Scanning of an embryo or foetus is not recommended however briefly

343
Q

What is the BMUS advice regarding maximum exposure time and TI?

A 
TI = 0.7 max time = 60min
TI = 1.0 max time = 30min
TI = 1.5 max time = 15min
TI = 2 max time = 4min
TI = 2.5 max time = 1min
344
Q

What is good practice for US safety?

A
  • Use maximum receiver gain and minimum output power to achieve diagnostic image (gain does not affect MI or TI)
  • Avoid pulsed Doppler in early pregnancy in early pregnancy unless critical
  • Minimise dwell time
  • Do not perform scans with no clinical justification
  • Ensure that operators at adequately trained
345
Q

What is the basic principle of elastography?

A

Apply stress (cause) and measure strain (effect)

346
Q

What is elastography?

A

Imaging technique for soft tissue stiffness assessment

An imaging technique whereby local axial tissue strains are estimated from differential ultrasonic speckle displacements

347
Q

Why is elasticity imaged?

A

Changes in elasticity are generally correlated with pathological phenomena
Equivalent to palpation

348
Q

How to you calculate stress?

A 
Stress = F/A
F = force
A = area
Stress = pressure
349
Q

How do you calculate strain?

A

Change in length/original length

Fractional change in length of the material

350
Q

How do you calculate Young’s modulus?

A

E = Stress/Strain

Units = same as those of pressure

Young’s modulus = stiffness

351
Q

Why is Young’s modulus useful?

A

Abnormalities have different Young’s modulus values

Increase in tumours

352
Q

What are the 3 steps in elastography?

A
  1. Generation of a low frequency vibration
  2. Imaging
  3. Elasticity estimation
353
Q

How is elastography done?

A

Image of tissue - store
Push transducer harder - store image
Comparing the 2 images will show resultant strain due to tissue deformation

354
Q

How is stress measured?

A

A fully compliant stand-off later (of known EM) is introduced
It allows free passage of ultrasound waves
Simultaneous measurement of strain in this layer enables calculation of axial stress distribution

355
Q

How is strain measured??

A
  1. A scan performed without compression
  2. Slight compression with the probe
  3. Cross correlation - compare the 2 A scans. Produce a map along the A scan and repeat for different lines
356
Q

What are the different methods of applying force for elastography?

A
  • Manual static pressure
  • Internal pressure (cardiac, respiratory - useful for liver can use breathold)
  • External dynamic pressure (mechanical movement of the transducer)
  • External dynamic pressure (push pulses - can use ultrasound internally to cause stress)
357
Q

What is required for strain quantification?

A

Autocorrelation of before/after A lines
Autocorrelation of before/after frames
Measurement of shear wave propagation

358
Q

What are the reported drawbacks for static elastography?

A
  1. User dependent - some people will push more than others.
  2. Stress applied not reproducible
  3. Indirect stiffness measurement
  4. Difficult interpretation
  5. Need direct access e.g. breast, prostate
359
Q

What is transient elastography?

A

Electrodynamic transducer rhythmically pulses the ultrasound transducer on the surface of the skin - very heavily used in heptaology

360
Q

Does transient elastography work?

A
  • Can confirm cirrhosis
  • Hard to pick up different types of cirrhosis
  • Can’t differentiate mild and significant fibrosis
  • There is a stretch in the axial direction
361
Q

What is shear wave elastography? Diagram

A
  • Deformation of tissue
  • Greater differentiation between normal and abnormal
  • Send out high MI pulse
  • Fire in succession at different depths
  • Causes rapid expansion of the tissue in all directions
  • Creates a lateral pressure
  • Shear waves travel slowly 3-4ms-1
362
Q

Shear waves have a fast attenuation rate, what do they do to compensate?

A
  • Multiple points in depth are emitted with a focused US beam
  • A shear wave front is created which corrects the fast attenuation
  • Emitted pulses are triggered at a speed greater than the speed of the shear wave propagation
  • Shear wave front creates a Mach cone
363
Q

What are the 2 types of elastic wave?

A

Compressive

Shear

364
Q

What is a compressive wave?

A

Compressive wave velocity is nearly uniform in soft tissue and is observed and sonic and ultrasonic frequencies

c^2 = K/p

C = speed
K = bulk modulus
p = density
365
Q

What is a shear wave?

A 
Velocity varies strongly in the soft tissue - only observed at sonic frequencies (less than 1 kHz) 
C^2 = G/p
C = speed
G = shear modulus
p = density
366
Q

What is the advantage of supersonic shear imaging?

A

Much quicker
Higher frame rate
Combines shear and high frame rate and could cause a bit change
Acquired data from large zones rather than multiple lines

367
Q

What are the issues with shear elastography?

A
  • Don’t know frequency content of the propagating shear wave

- Do not know optimum frequency at which to probe the mechanical properties of the tissue

368
Q

What 3 factors causes artefacts?

A
  • artefacts that arise within the patient
  • Artefacts that arise within the equipment
  • Artefacts that are operator induced
369
Q

What are the assumptions the imaging system makes about propagation of ultrasound?

A
  • Beam axis is straight
  • Pulse only travels to targets that are on the beam axis and back to the transducer
  • The beam is thin (has negligible lateral width and slice thickness)
  • the speed to sound is constant
  • the attenuation in tissue is constant
370
Q

What is the result of the assumptions not being necessarily true about US propagation?

A
  • Echoes appear when structures are not really there
  • No echoes appearing where there is a structure
  • Size, shape and location of structures is inaccurate
371
Q

Artefacts in US occur as structures that are:

A
  • Not real
  • Missing
  • Improperly located
  • of incorrect brightness
  • Incorrect size
  • Incorrect shape
372
Q

What are the in patient propagation artefacts?

A
  • Acoustic shadowing
  • Acoustic enhancement
  • reverberation (comet tail)
  • Refraction
  • Edge shadow (refraction)
  • Mirror image
  • Speed of sound artefacts
373
Q

When does acoustic shadowing occur?

A

When there is a high impedance mismatch between structures aligned along the axis of the beam, almost total reflection can occur.
e.g. soft tissue and ribs - no echo is retrieved from the areas distal to ribs

It will also occur when the beam passes through a structure that is highly attenuating e.g. lesions, cirrhosis.
Most of the sound energy is lost through absorption and little detail can be seen distal

374
Q

Draw a digram showing acoustic shadowing

A

Image

375
Q

What methods are used to visualise tissue posterior to acoustic shadowing?

A
  • By adapting the scan angle (best)
  • Compound imaging
  • In most instances, it is possible to interrogate areas posterior to the shadowing structure
376
Q

When does acoustic enhancement occur?

A

When the sound beam passes through a structure that is of low attenuation.
The echoes posteriorly appear brighter than surrounding tissue with the loss of information
- Saturation of the image (turn down gain, change TGC)

377
Q

Draw a diagram showing acoustic enhancement

A

Image

378
Q

What is reverberation?

A

This occurs where the sound pulse bounces back and forth between 2 highly reflective surfaces

So much energy is reflected from the boundary and it is reflected back off the transducer and back into the material.

Machine assumes travel in straight line

Get equally spaced false series reflectors.

379
Q

Draw a diagram to show reverberation

A

Image

380
Q

What is a comet tail artefact?

A

This is produced by a short pathway reverberation of the pulse between structures of high impedance mismatch.
Pulse travels back and forth between the closely spaced reflectors producing a short time delay between each echo.

381
Q

Draw an image depicting comet tail artefact

A

Image

382
Q

What is the difference between comet tail artefact and reverberation?

A

Comet tail is a type of reverberation

Comet tail occurs between 2 reflectors rather than between reflector and transducer

383
Q

When does refraction occur?

A

Occurs at the boundary between 2 media where the speed of sound is different

  • When the beam hits the boundary at an angle, it is bent away from original course
  • Can lead to misleading appearances

Doesn’t happen very often

384
Q

When can refraction occur?

A

Can look like twins due to refraction at abdominal muscles

385
Q

Draw an image to show refraction

A

Image

386
Q

Describe edge shadowing

A
  • Curved interface at an oblique angle such as the edge of a cyst or soft mass within a solid tissue
  • Beam transmission is diverted (refracted) to a new direction
  • Shadow is caused by few echoes returning to the transducer from the original line of site
387
Q

Draw a diagram showing edge shadowing (refraction)

A

Image

388
Q

When does a mirror image artefact occur???

A
  • Occurs due to specular reflection at a large smooth interface
  • High acoustic impedance mismatch
  • Reflected beam encounters a scattering target
  • Echoes from the target return via the same path to transducer
  • Mirror image seen behind the smooth reflector

Strong reflector is meeting the beam at an angle - sound no longer travels in straight line (right angles) and the target is placed on straight line

389
Q

Draw a diagram showing mirror image artefact

A

Image390

390
Q

Where does mirror image artefact most commonly occur?

A

Diaphragm

391
Q

What are speed of sound artefacts

A

Where the speed of sound in tissue between the target and transducer is higher than 1540ms-1 the target will appear closer to the probe than it really is.

If it is slower it will appear further away

392
Q

What are the consequences of speed of sound artefacts?

A

Measurement/size errors
For most purposes displayed size changes +/- 5% not noticeable
May need correction

393
Q

Why do equipment related artefacts occur?

A

As a result of a number of false assumptions:

  • It assumes that any returning echo will have originated from the central axis of the beam
  • It assumes it has negligible lateral and slice thickness
394
Q

What is beam width?

A

Width along scan plane
Varies with distance from the probe
Narrowest in the focal region
Dependant on the type of focusing used

395
Q

How can an equipment artefact arise from beam width?

A

2 reflectors placed side by side within the beam will be resolved only if the spacing between them is greater than the affective beam width

396
Q

What is slice thickness?

A

Width of the beam at right angles to the scan plane

397
Q

How can slice thickness cause an artefact?

A

Causes overlap of echo information from structures that lie outside the scan plane.

Most noticeable in small liquid filled areas. They can have echoes from surrounding areas instead of being echo poor.

398
Q

What is clutter?

A

Spurious signals that arise from echoes induced by ultrasound transmission outside the main beam

Degrades the image
Inhibits detection of weak echoes.

399
Q

What is grating lobe artefact?

A

These are side lobes which can occur on any probe having regular spaced elements

Weak replicas of the main beam at up to 90 degrees on each side of the beam

Contribute spurious echoes to the image and effectively widen the beam in the scan plane.

Reduces lateral and contrast resolution
Reduced by use of harmonic imaging

400
Q

How can you reduce grating lobe artefact?

A

Use harmonic imaging

401
Q

Draw a diagram showing grating lobe artefact?

A

Image 402

402
Q

Draw a diagram showing beam width artefact?

A

Image 403

403
Q

What are the artefacts that are operator induced?

A
  • Misuse of controls such as overall gain and TGC
  • Movement (FR not fast enough to show movement smoothly
  • Caliper inaccuracy (relies on correct calibration of pixel number to actual distance)
  • Transducer damage (loss of transmission by any of the crystals will lead to loss of image formation in that area. )
404
Q

Describe a TGC artefact

A
  • Occurs when applied compensation does not match the actual attenuation
  • May be due to operator error or due to large difference between actual and assumed constant values
  • Results in bright or echo poor banding across the image
  • 2 useful TGC artefacts are post cystic enhancement and acoustic shadowing
405
Q

What is the result of having incorrect gain?

A

Overall gain too low (areas mimic fluid created where echo information is lost)
If too high cystic areas will appear solid.

406
Q

Vascular US: What can be determined in B Mode imaging?

A

Anatomical position of vessel
Detail of vessel wall
Lumen

407
Q

What is B mode?

A

Brightness Mode
Real time 2D imaging
Single frames are acquired and played sequentially

408
Q

Vascular US: What can be determined using colour encoded Doppler?

A

Map the course of the vessel
Demonstrates vessel patency
Identify stentotic segments
Identify areas of flow turbulence

409
Q

In colour Doppler, what do the colours represent?

A

Hue or colour saturation are used to indicate mean Doppler frequency or variance

Colour is used to indicate flow

410
Q

Vascular US: Main areas of application?

A
  • Extracranial carotid arteries
  • AAA screening and surveillance
  • Lower limb arterial or venous disease
  • Graft surveillance and perioperative vein mapping
  • Haemodialysis fistulas
  • Upper limb disease
411
Q

What are the common reasons for referral to examine carotid arteries?

A

Transient ischaemic attack (symptoms less than 24 hours)
Loss of power or sensation of arms/legs/face
Stroke (symptoms over 24 hours)

US identifies the presence and extent of disease
Ideal screening tool
Treat: endarterctomy

412
Q

Vascular US: Which transducer? Carotid arteries

A

High frequency - good resolution

4-17MHz linear

413
Q

What are the common reasons for referral to examine aorta?

A
  • Palpable pulsatile abdominal mass
  • Surveillance of AAA
  • Screening for AAA
  • Suspicion of AAA (seen on radiograph)

AAA= dilation over 3cm

414
Q

Which transducer would you use to examine the aorta?

A

3-6MHz Curvilinear

Need penetration

415
Q

How do you measure aorta?

A

Just inferior to renal arteries or if suspect AAA, at the widest point.

Measure inner wall to inner wall.

AP - must be at 90 degrees to long axis (no salami slice)

416
Q

What are the common reasons for referral to examine lower limb arteries?

A

Intermittent claudication
Absent pulse

Screening of symptomatic patients
Diagnosis, location and grading of disease

417
Q

Which transducer to examine lower limb arteries?

A

4-17MHz linear

Use spectral Doppler

418
Q

What are the common lower limb venous diseases?

A

DVT

Varicose veins

419
Q

What is DVT? Reasons for referral?

A

Common
Can result in fatal PE

Painful swollen leg
Chest pain

420
Q

Which modality is best for DVT?

A

US now investigation of choice (not x-ray contrast venography)

MRI useful for iliac veins where access is difficult (expensive)

Need to assess the patency of deep veins, exclude the presence of a thrombus

421
Q

Which transucer to examine DVT?

A

4-17MHz linear

422
Q

What are the different types of venous grafts?

A

Synthetic

Native vein

423
Q

What is the advantages of native vein grafts?

A

Best long term patency
Mapping prior to surgery
Avoids removal of unsuitable veins
Reduces wound necrosis

424
Q

Why is graft surveillance important?

A

30% of native will develop significant stenosis
Reduces the risk of graft failure
Intermittent claudication

425
Q

Which transducer would you use to check vein grafting?

A

4-17MHz linear

426
Q

What is a haemodialysis fistula? Which transducer to image?

A

AV connection that allows for high flow rates and can stand repeating needling for dialysis patients

4-17MHz linear

427
Q

What are the common problems with haemodialysis fistulas?

A

Stenosis
False aneurysms from repeated needling
Clot formation

428
Q

What are the objectives of 3D US?

A
  • Acquire a set of 2D mages with positional information
  • Assemble the data into a 3D computer memory
  • Retrieve sleeted subset for display
  • Process and display selected data
429
Q

What are the 3 scanning option for 3D US?

A
  1. Conventional 2D transducer motor driven in predetermined format
  2. Conventional transducer hand held with positional sensors allowing maximum operator freedom
  3. 2D matric array
430
Q

What are the different motor driven systems in 3D US?

A

Linear
Sector format
Anatomically constrained systems

431
Q

Describe the linear motor driven systems for 3D

A

Linear movement
Creates multiple slices in a 3D box
Useless for patient scanning

Simple
Bulky (too large and inflexible)
Impractical

432
Q

Describe the sector format driven system for 3D

A

Motorised rocking sector
Get a truncated pyramid with different slices
Can rock with motor instead

Reduces footprint
Gives fan out
Slice thickness is depth dependent

433
Q

Describe anatomically constrained systems for 3d imaging

A

E.g. Intra vascular probe
At each location it produces a slice at right angles to the probe
Build an image from the inside out

Successful in blood vessel

As the region bend the machine is not aware and creates straight line

434
Q

What are the features of a manually scanned system for 3d image acquisition?

A

Have position sensors attached to probe
Operator has considerable freedom
May not acquire optimum sections for reconstruction
Machine determines images using operator movement
There may be some gaps and some double scanned

435
Q

What are the important features of position sensors in 3d imaging.

A 
Operate using electromagnetic coupling 
Room conditions important
Room needs to be fitted with detectors to work out where probe is
Can't move machine out of the room 
Precision may be a problem
436
Q

What are the disadvantages of using manually scanned systems for 3d image acquisition?

A

Can’t move machine out of room
Won’t work if the couch is made of a conductive metal
Location and precision can be problematic (need to know within 0.5mm in 3 axes and 2 angles)
Operator may acquire suboptimal information

437
Q

Describe matrix arrays for 3d image acquisition?

A 
Allows for scanning in any plane
Expensive and relatively uncommon 
Price will drop as increase manufacturers 
Can focus in 2 planes
Can fire several at one time
438
Q

What are the typical storage requirements for 3d imaging?

A

250k/slice
To cover 10cm need approx 100 slices (if slice thickness 1mm)
100x250 = 25Mb

439
Q

What are the 3 methods for reconstruction in 3d imaging?

A

Select an arbitrary section for display (most common)
Use segmentation
Use surface or volume rendering

440
Q

What is multiplanar imaging analysis?

A

Have 2 screens
1 clinical image and one showing where you are located
Can see scans in different planes

441
Q

What is image segmentation?

A

Subdividing the image into component parts

Can be done manually or automatically

442
Q

What is surface rendering?

A

Using pseudo lighting to highlight a surface

May need perspective transformation

443
Q

What is volume rendering?

A 
Not a true plane
Visualisation of 3d structures as a 3d image
Visualise surfaces (foetus) and internal structures (bones and vessels)
444
Q

What does 4d imaging need?

A

High speed acquisition involving multiple simultaneous line processing

445
Q

What are the advantages of ultrasound.

A 
Readily available
Cost effective
Reliable, repeatable, reproducible
Noninvasive
Safe
Rapid
Tends to be first line investigation
446
Q

What areas of the abdomen are commonly scanned?

A

Liver
Biliary system
Urinary system
Spleen

447
Q

Where is ultrasound imaging done in the patient pathway?

A

Prior to a and e - improve likelihood of poly traumatised patients
POCUS - point of care us
2y e.g. Radiology department

448
Q

Who is responsible for providing us?

A 
Sonographer
Radiologist
Paramedics
Emergency physician 
Trauma radiographer
449
Q

What transducer is used in abdominal us?

A

3.5-6MHz curvilinear

Use 6+ in paediatrics or slim patients

450
Q

What are the equipment settings that need to be considered?

A 
TGC 
Overall gain
Focus on ROI
Consider MI and TI
Compound imaging / harmonic imaging
451
Q

What happens if you increase the number of focal zones?

A

More fine detail
Increased lateral resolution
More confident about diagnosis
Time is a problem

452
Q

What should be done in us of abdomen?

A

Survey all upper abdomens and surrounding areas
Use 3 planes
Additional views with sub costal and intercostal views
Measure where relevant
Outline: liver, ligaments, gall bladder, kidneys, vessels, porta hepatic, cbd, pancreas, spleen
Include colour and pulse Doppler to evaluate vessels

453
Q

What needs to be assessed in abdo us?

A 
Size of organs and vessels
Shape of organs and vessels
Anatomical relationships
Positions of organs and boundaries
Texture
454
Q

What are the reasons for referral for a liver and biliary system examination?

A 
Ruq pain
Epigastric pain
Jaundice 
Abnormal LFTs
Reflux
455
Q

What is the normal appearance of the liver?

A 
Homogeneous
Midgrey echo texture 
Echogenic thin capsule surrounding
Similar or slightly increase compared to kidney 
Ligaments are echogenic and linear
456
Q

What are the common liver pathologies?

A

Diffuse disease e.g. Cirrhosis
Masses
Biliary dilation
Portal hypertension

457
Q

What are the advantages of us contrast?

A 
Confined to intra vascular space (mr and ct is extra cellular) 
Easy to administer
Immediate effect
Well tolerated
Good patient safety record
Provides additional information
Cost effective
458
Q

What is the function of us contrast?

A

Characterises focal lesions
Detects metastases
Confirms normality
Demonstrates vessel patency

459
Q

What is the normal appearance of gall bladder?

A

Distended pear shaped sac
Anechoic
Echogenic thin wall
Variable positions, size and shape

460
Q

What are the common gall bladder pathologies?

A

Gall stones
Polyps
Wall thickening

461
Q

Describe the appearance of gallstones

A

Echogenic
Posterior acoustic shadowing
Mobile
Us very accurate at detecting

462
Q

What are the features of a gall bladder polyp?

A 
Common
Not significant  without gallstones
Small intra luminal echogenic structure
Fixed to wall
No acoustic shadow
Can be inflammatory, cholesterol or adenomyoma
463
Q

What is the normal gall bladder wall thickness?

A

Less than 3mm when fasting

464
Q

What are the common pancreatic pathologies.

A 
Pancreatitis 
Dilation of pancreatic duct
Pseudo cysts 
Masses
Stones in pancreatic duct
465
Q

How does pancreatitis appear?

A 
Hypos choir
Enlarged
Pseudo cyst
Pancreatic duct dilation 
Ascites
466
Q

What do pancreatic pseudo cysts look like?

A 
Echo free mass in lesser sac
New has thin wall
Old has thick
Irregular borders
Complex internal contents
467
Q

What are the reasons for referral for a urinary system scan.

A

Loin pain
Recurrent UTI
Haematuria
Abnormal urine rest

468
Q

What are the common pathologies of the urinary system

A 
Renal or bladder calculi
Renal or bladder cancer
Hydronephrosis
Renal cysts
Congential abnormalities
469
Q

What are the reasons for referral for spleen scan

A

Luq pain
Lymphoma
Leukaemia
Trauma

470
Q

What are the common spleen pathologies.

A

Cysts
Metastasis
Lacerations
Splenomegaly

471
Q

What are the uses of Doppler in the abdomen.

A

Identify CBD from portal vein and hepatic artery
Observing hyperaemia e.g. Cholecystitis
Differentiating benign and malignant
Portal vein assessment - patency, direction, thrombus, occlusion
Splenic varies

472
Q

What is a FAST ultrasound ?

A

Focused assessment with sonography for trauma

Rules in free fluid
Yes or no
Primary assessment of blunt abdo trauma
Very quick can be performed during resuscitation

473
Q

WHat are the strengths of us?

A 
Good for soft tissue
Real time
Blood flow information
Well tolerated
Inexpensive
Portable
Non ionising
Control of invasive procedure
474
Q

What are the weaknesses of us?

A

Difficult in patients with high bmi due to poor penetration
Unable to penetrate bone
Can’t image lungs
Limited views if gas overlying
Operator dependent
Need to label as no way to orientate after

475
Q

What are the different types of echocardiography?

A 
Transthoracic
4d
Trans oesophageal 
Stress echo
Contrast studies
Dyssynchrony studies
CRT optimisation
Bubble studies
476
Q

Outline transthoracic echocardiography

A

Assess cardiac structure and function
Various views: parasternal (long axis and short axis), apical (2,4,5 chamber and long axis), sub costal, suprasternal and right sternal edge

477
Q

What is the optimal position for echocardiography

A

Left lateral decubitus
Raise left arm to open rib spaces
Moves heart to front of chest

Supine for sub costal and suprasternal views

478
Q

Where is the probe placed for parasternal long axis

A

Left sternal edge 4th ic space

479
Q

Describe parasternal long axis assessment

A

Use m mode for left ventricle to get internal dimensions e.g. Ejection fraction
Colour flow
M mode for aorta and left atrium

480
Q

What should be assessed at parasternal short axis?

A

Left sternal edge rotate 90 degrees from long axis
Colour flow
Doppler for peak velocity over valves
Assess left ventricle, mitral valves and papillary muscles

481
Q

What should be assessed in apical 4 chamber view?

A 
Image from apex of heart
Identify wall segments
Colour flow through mitral valve
Mitral pulsed Doppler
Mitral cw Doppler
Tricuspid colour flow Doppler
Tricuspid cw Doppler
482
Q

What is sub costal echocardiography good for?

A

Identifying pericardial effusion

View IVC to see size and respiratory response

483
Q

What should be viewed from suprasternal echocardiography

A

Aortic arch
Good for aortic dissection
Aortic Doppler
Aortic cw Doppler

484
Q

What probe is used for echocardiography

A

Phased array - need small footprint

2-4MHz

485
Q

What is the triple assessment of breast assessment.

A

Clinical examination
Imaging
Tissue sampling

486
Q

What is the role of breast imaging

A

Screening program - a symptomatic 3yr mammogram

Symptomatic breast clinics - symptoms or post surgical surveillance

487
Q

What breast pathology is most common in younger people?

A

Fibroadenoma (benign)
Localised benign mass
Abscesses in pregnancy

488
Q

What are the common breast pathologies in the older woman

A

Cancer
Increases with age
Cysts

489
Q

What are the guidelines for breast imaging

A 
Mammography for over 40
Us for under 40
Standardised care
Breast tissue over 40 is less glandular and less radio sensitive 
Mammogram is more sensitive than us
490
Q

What is the role of us in breast imaging

A

Lesion characterisation.
Assessment of axila prior to sentinel node biopsy
Intervention
Evaluation of areas of asymmetry on mammo
Exclusion of masses
Implants
Male patients
Follow up measurements during chemo
When mammo contraindicated (pregnancy)
Evaluation of microcalcifications picked up on mammo

491
Q

Why is breast mammography not a screening tool?

A 
Highly operator dependent
Time consuming
Small subtle changes can be missed
Needs skilled use of equipment
Microcalcifications hard to see
492
Q

What probe is used in breast us.

A

7-15MHz linear array
Dynamic range 60dB

Can do compound imaging, harmonic imaging, extended Fov, Doppler or elastography

493
Q

What are the malignant appearances breast Doppler

A

Chaotic irregular branching pattern
Hypervascular
Large vessels for lesion size

494
Q

What are the benign appearances breast doppler

A

Organised vasculature
Peripheral
Aligned with septa
Low number of vessels

495
Q

What is the patient position for breast imaging

A

Supine with ipsilateral arm above head
Better visualisation of lower quadrants
Flatten breast to chest wall
Minimise movement of breast

496
Q

What are the different breast scan orientations

A

Longitudinal
Radial
Transverse
Anti radial

497
Q

What is gynaecomastia

A

Ductal proliferation
Hyperplasia of glandular epithelium
Increase stromal tissue

498
Q

Define margins/borders and what comments can be made on them

A 
Transition of echogenicity from mass and surrounding tissue 
Signifies change in acoustic appearance 
Well circumscribed
Lobular end
I'll defined
Irregular
Hyperechoic
499
Q

Define echo texture, what are the options?

A

Comparison of echogenicity of surrounding tissues
Hypo/hyper/an. - echoic
Homo/Herero. - geneous

500
Q

What are the features of a benign breast mass

A 
Round
Well defined
An or Hyperechoic
Homogeneous
Posterior acoustic enhancement
Compressible 
Mobile
Wider than deep
Surroundings unaltered
501
Q

What are the malignant features of a breast mass

A 
Irregular
Ill defined 
Hypoechoic
Heterogeneous
Posterior acoustic shadowing
Rigid
Fixed or mobile
Deeper than wide
Altered surroundings
502
Q

How are breast masses classified using us

A 
1 normal
2 benign
3 indeterminate - probably benign
4 suspicious of malignancy
5 highly suspicious of malignancy

Follow up 345

503
Q

What procedures breast can be guided using us

A

Cyst aspiration

Hook wire placement

Intercalation (4 decks)

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