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Image science principles > ultrasound > Flashcards

ultrasound Flashcards

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1
Q

4 ways ultrasound can be attenuated

A

reflection
refraction
scatter
absorption

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2
Q

equation for velocity

A

velocity = frequency x wavelength

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3
Q

range of sound frequencies in medical ultrasound

A

2 MHz - 20 MHz

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4
Q

human hearing range

A

50 Hz - 20 kHz

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5
Q

low frequency sound waves in relation to penetration

A

they can penetrate deeper into the human body compared to high frequency

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6
Q

low frequency waves in relation to resolution

A

has lower anatomical resolution

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7
Q

abdomen ultrasound frequency

A

3-5 MHz - good penetration, but poor resolution

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8
Q

small and superficial parts

A

5-10 MHz

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9
Q

skin, eyes ultrasound frequency

A

10-20 MHz

- poor penetration, but good resolution

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10
Q

x-ray vs ultrasound oscillation

A

x-rays - transverse waves and oscillation in their amplitude is at right angles to the direction of travel.

ultrasound - longitudinal wave and oscillation in its amplitude is in the same direction of travel

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11
Q

sound waves need to pass through a…..

A

Medium such as air, water or solids

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12
Q

acoustic impedance

A

is the resistance that the sound waves experience when passing through matter/tissue

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13
Q

practical significance of acoustic impedance

A
  • impedance is high in bone, but less in soft tissue
  • allows us to see a range of structures
  • sound reflection is stronger at boundaries with different impedance values.
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14
Q

How can a sonographer improve the visualisation of deep structures in the body

A
  • use a lower frequency to increase penetration - however, this decreases the resolution
  • perhaps the use of different probes - adjusts beam focus
  • time gain compensation
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15
Q

time gain compensation

A
  • reduces the impact of wave attenuation by tissues through the increased intensity of the received signal in proportion to the depth
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16
Q

acoustic shadowing

A

occurs at boundaries between significantly different tissue impedances - which leads to signal loss and a dark appearance.

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17
Q

an example of acoustic shadowing

A
  • decreased signal behind calcifications. e.g. a gull stone in the gall bladder, as the gull bladder is fluid-filled and a gull stone is dense -high difference in acoustic impedances
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18
Q

useful artefacts

A
  • stones/ calcifications

- fluid structures like cysts can have acoustic enhancement behind them - brighter image response

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19
Q

how are ultrasound waves produced in a transducer

A
  • piezoelectric effect - when an electrical current is passed through the crystals, they vibrate to a set frequency and emit sound
    crystals in the probe acts as a transducer and emits and receives sound waves.
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20
Q

how are ultrasound waves received in a transducer

A
  • when sound waves return back from the body, the crystals start to vibrate too - giving us an electrical return signal
  • the changes in sound waves sent and received gives us the differences on our image.
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21
Q

Why do sound waves travel faster through denser materials

A

because the vibrations of sound pass faster through molecules that are packed close together

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22
Q

acoustic impedance and sound reflection

A
  • if the acoustic impedance is between tissues is large, then a lot of sound is reflected and not much sound penetrates deeper
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23
Q

when does reflection work best?

A

when the tissue boundary is at right angles to the probe

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24
Q

what happens when the tissue boundary is not at right angles to the probe

A

the refelcted sound is not received by a simple probe

some sound is refracted

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25
Q

what is refraction

A
  • where the angleof incident sound is not at 90 degrees to the boundary
  • sound velocity changes between the tissues and therefore the direction of travel changes
26
Q

ultrasound scatter

A

reflectors such as Blood cells and non-smooth tissue interfaces vase sound to fan out in all directions

  • this causes speckle or irregularity in the image
27
Q

a bleed will show up with

A

multiple small echoes that come from the blood cells and platelets - may look grainy

28
Q

what happens as ultrasound passes through the body

A

The ultrasound is attenuated (reduction in beam intensity) with increasing depth in the body

29
Q

what do decibels measure

A

the relative difference between 2 sound intensities

e.g. intensity between a produced sound beam and a returning echo

30
Q

types of image resolution

A

lateral resolution and axial resolution

31
Q

lateral resolution (at right angles to the beam)

A

depends on the diameter of the ultrasound beam - best with narrow beam

32
Q

axial resolution (in direction of the beam)

A

depends on the sound frequency - high frequency = good resolution

33
Q

types of ultrasound scan

A
  • A Mode
  • B Mode
  • M Mode
  • 3D and 4D
  • Doppler
33
Q

types of ultrasound scan

A
  • A Mode
  • B Mode
  • M Mode
  • 3D and 4D
  • Doppler
33
Q

types of ultrasound scan

A
  • A Mode
  • B Mode
  • M Mode
  • 3D and 4D
  • Doppler
34
Q

types of ultrasound scan

A
  • A Mode
  • B Mode
  • M Mode
  • 3D and 4D
  • Doppler
35
Q

The piezoelectric effect

A
  • when an electrical current is applied across the crystal, it resonates sending out a sound wave
  • when a force is applied perpendicular to the crystal, an electrical charge is produced
  • the frequency of the sound is determined by the thickness of the crystal
36
Q

A mode scan - Amplitude modulated

A
  • produces a graph whose height shows the strength of reflection over time time
37
Q

B Mode scan - brightness modulated

A

this produces a 2D greyscale image based on the strength of reflected sound echos, according to depth - most common scan

38
Q

M Mode

A

Shows motion (e.g. heart valves), over time

39
Q

3D and 4D scan

A
  • volume and video images
40
Q

Doppler scan

A
  • ## change in sound frequency shows the speed and direction of blood flow
41
Q

Duplex ultrasound

A
  • Combines Doppler colour-coded blood flow direction
  • red towards the probe and blue away from the probe
  • flow speed with a 2D B-mode anatomical scan
42
Q

rotating transducer

A
  • produces an arc or fan shaped image section
43
Q

linear array transducer

A
  • consists of row elements and produces a straight sided image section
44
Q

Array transducers

A

can be focused to either examine either shallow or deep tissues

45
Q

Anechoic

A

no echoes

46
Q

Exhogenic

A
  • Brighter than (compared to something next to it)

- E.g. Bone is echogenic

47
Q

hypoechoic

A

less echoes than surroung structures

48
Q

Hyperechoic

A

higher level of echoes then surrounding structures

49
Q

cystic

A

no echoes with echo enhancement behind

50
Q

complex mass

A

components of solid/cystic tissue

51
Q

solid mass

A

internal echoes, no enhancement behind

52
Q

homogenous

A

same appearances/texture, smooth throughout .I.e liver/uterus

53
Q

heterogeneous

A

different irregular pattern, different echo characteristics

54
Q

biological effects of ultrasound

A

Thermal effects

mechanical effects

55
Q

factors affecting temperature increases

A

frequency of the ultrasound beam - heating increases with F

power in watts

Attenuuation (acoustic impedance) of tissue - heating is greatest at bone

scan time

56
Q

factors affecting mechanical indices

A

peak ultrasound beam pressure - related to power

frequency of the ultrasound beam - mechanical effects decrease with F

Beam focus depth - mechanical effects decrease with focus depth

57
Q

Ultrasound ALARA

A
  • use minimum power output

keep scanning time to a minimum

do not rest the transducer on the skin surface when not scanning

58
Q

Artefacts – misleading or incorrect information

A
  • caused by:
  • the nature if the tissue
  • the operator

Equipment malfunction

59
Q

Artefacts: Assumptions made by the machine

A
  • the beam being infinitely thin

propagation being in a straight line

the speed of sound being exactly 1540 m/s

the brightness of the echo being directly related to the reflectivity of the target

60
Q

propagation

A
  • the speed at which a sound wave travels through a medium

Image science principles (12 decks)

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