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Diagnostic Imaging > Ultrasound > Flashcards

Ultrasound Flashcards

1
Q

Ultrasound

A

Describes sound waves with frequencies that are higher than the range of human hearing which beyond 20k Hz
Sound is emitted from a transducer into the body at one or multiple frequencies
Sound encounters various organs/tissues within the body
Images are created when the echoes are reflected back to the transducer

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2
Q

Echolocation

A

Similar phenomenon that occurs within out patients bodies when an ultrasound exam is preformed.
Emitted wave hits object and a reflected wave goes back

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3
Q

Frequency

A

the number of times a cycle or wave is repeated per second

Hz

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4
Q

Wavelength

A

Distance traveled by the sound waves and is expressed in mm

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5
Q

Velocity

A

speed at which sound travels through a medium

sound travels fastest in solid objects (closeness of molecules) and slowest in gases (molecules further apart)

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6
Q

Ultrasound equation

A

V=f times wavelength

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7
Q

Resolution

A

Being able to detect 2 structures separately located in a parallel beam

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8
Q

Penetration

A

how far the sound waves are allowed to travel

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9
Q

Resolution increased

A

short wavelength

inc frequency

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10
Q

penetration inc

A

dec frequency

longer wavelength

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11
Q

Attenuation

A

sound waves lose strength as they travel through a medium

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12
Q

Absorption

A

conversion of sound energy to heat. very low in ultrasound machines

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13
Q

Reflection

A

sound waves encountering tissues of different acoustic impedance. Only sound waves that get back to the transducer contribute to the image

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14
Q

Scattering

A

Sound waves encounter small and uneven surfaces and would regenerate weak echos
Parenchymal appearance of organs

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15
Q

Refraction

A

Bending of the beam when encountering a change in medium when the beam strikes the interface at an oblique angle
As a result the bending of the beam leaves a shadow at the edges of curved structures such as the gall bladder and cysts

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16
Q

Attenuation increased with

A

increased distance from the transducer
More heterogenous medium with increased acoustic impedance mismatch
higher frequency transducers

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17
Q

Acoustic impedance

A

Product of the tissue density and the velocity of the sound within that tissue
Changes in impedance from one tissue to the next determines how much sound is reflected back to the transducer and also how much is transmitted to the next tissue
if large difference- much sound reflected
if small difference- little sound reflected
if no difference- no sound reflected

Air and bone have the strongest interface

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18
Q

Image display

A

Based on the pulse echo principle:
-sound is emitted 1% of the time and transducer listens 99% of the time
electric signals from returning echoes enhanced to display image
Transit time directly related to depth
Amount of reflected sound depends on the tissue impedance
Ultrasound machine assumes a constant speed in tissue at 1540 m/s

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19
Q

Artifacts

A

Certain assumptions are made by the ultrasound machine when generating an image
sound waves travel in a straight line
all echoes originate from objects in the beam axis
echoes return to transducer after single reflection
Speed of sound in tissues is constant
The strength of the echoes is directly related to the reflecting/scattering properties of the objects
The depth to the reflecting or scattering object is proportional to the round trip time of the sound wave
The strength of the sound wave is attenuated evenly

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20
Q

Artifacts

A 
In ultrasound they can be helpful or confusing
May be present in ultrasound study
acoustic shadowing
acoustic enhancement
edge shadowing
slice thickness artifact
mirror image artifact`
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21
Q

Acoustic shadowing

A

structures of high reflectivity appear white and distal to them a shadow is created
Interface absorbs or reflect all the sound

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22
Q

Clean acoustic shadowing

A

clean shadow is the result of all the sound being absorbed or reflected
No reverberation artifact
Anechoic or black

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23
Q

Dirty acoustic shadowing

A

tends to happen at the tissue-gas interface (bowel)
most of the sound is reflected
shadow is more gray as a result of inhomogeneous/reverberation artifact

24
Q

Acoustic enhancement

A

sound waves are less attenuated when transmitting through the fluid
Machine processing compensates and overcompensate resulting in a hyperchoic area distal to the fluid filled structure

25
Edge shadowing
small shadows on the edge of rounded structures
26
slice thickness artifact
the sound beam hits the gall bladder wall and also the bile within. the computer combines the two and makes a false sludge image which is curved Real sludge usually creates a straight edge
27
Mirror image artifact
Some of the sound is reflected from the liver back to the diaphragm-lung interface before going to the transducer increased time travel, computer places the artificial image distal to the original
28
Transducers
Coverts electrical current into sound waves and vice versa Piezo electrical crystals Emits sound waves less than 1% of the time and receives sound waves about 99% of the time Dont drop the transducer Different shapes and sizes- selection depends on properties of the transducer and anatomical region being imaged Multifrequency
29
Linear transducer
Produced a rectangular image | emits highest frequency and used for small parts
30
Convex transducer
produces fanned out image with a piece taken out | General purpose
31
Sector transducer
produces pie shaped image | Echocardiology
32
Transducers
``` General- choose the highest frequency that will penetrate the area of the patient during your exam small dogs/cats: 7.5-10 MHz medium dogs: 5-7.5 large breed dogs: 5 large animals: 2-5 tendons and small parts (eyes): >10 ```
33
Ultrasound machine controls
``` power-intensity of the sound output absolute gain-amplification of the returning echoes time gain/depth compensation focus mode measurements freeze ```
34
Power/gain controls
increased gain/power causes increased brightness of the image
35
time-gain compensation
Can selectively amplify weakened echoes from deeper structures and from the different image fields Increased far field gain
36
Focus
Sound waves can be focused Focus can be adjusted on the image manually this is the area of sharpest sound, therefore one wants to place the focus at the level of the organ you are scanning
37
Modes of echo display- B mode
brightness mode | Echoes are displayed as dots in proportion to the amplitude of the returning echo
38
Modes of echo display- M mode
motion mode Used in echocardiography Records images in respect to time
39
Doppler mode
measures blood flow velocity within a blood vessel Colour flow doppler also measure the direction of the blood flow Computer assigns color for direction
40
Blue
Flow away from transducer
41
Red
Flow towards the transducer ( BART)
42
Scanning
``` Patient should be fasted Stress should be avoided fur shaved dorsal recumbency ultrasound machine and examiner on right side of pt pt's head in direction of machine Acoustic gel ```
43
Acoustic gel
sound does not travel through air well | gel provides a medium for the sound waves to travel
44
Scan planes
Sagittal or dorsal plane Transverse plane can be referred to the organ or patient each organ should be scanned in two planes
45
Sagittal plane
transducer pointed cranially
46
Transverse plane
Transducer is turned towards the examiner or the pt's right | cross-section
47
Evaluation of structures
``` size shape number location margination echogenicity=opacity in addition: homogeneity; texture, compressibility, surrounding tissue, vascularity, through transmission ```
48
echogenicity
``` anechoic hyperchoic isoechoic hypoechoic normoechoic ```
49
Anechoic
homogeneously black pure fluids without cellular content very low intensity of echoes returning to the transducer
50
Hypoechoic
Relative to other tissues Dark grey tones low intensity of returning signals
51
Isoechoic
Relative | Same echogenicity as another structure
52
Hyperechoic
relative white structures high intensity signals going back to the transducer Diaphragm is hyperechoic compared to the liver
53
Normoechoic
The expected echogenicity for a certain structure | the expected returning signal
54
Scanning
``` Pick a starting point and go in a clockwise fashion hace to be consistent Liver Spleen left kidney left adrenal left ovary in intact females urinary bladder prostate uterus in intact females area of the internal/external iliacs right kidney right adrenal pancreas stomach and GIT ```
55
My cat loves sunny places
``` Medulla of kidney Cortex of kidney liver spleen prostate ```

Diagnostic Imaging (11 decks)

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