Topic 22: US application + safety

Question 1

Give the 3 ways to display US signals

Answer 1

1) A-mode
2) B-mode
3) M/T-M mode

Question 2

Describe A-mode

Answer 2

• Amplitude of reflected = shown by height of vertical deflection on oscilloscope
• E.g. reflected beam = line with 3 peaks = skull + brain + opposite end of skull
• Accurate in determining depth of reflectors
• Used in ophthalmology

Question 3

Describe B-mode

Answer 3

• Brightness mode = real-time + greyscale display
• Variation in intensity/brightness = different amplitudes
• Brighter = larger reflection = greater intensity = white
• Absence of echo = black
• Intermediate = grey
• Transducer coupled to arm = signals displayed as bright spots = tomographic image of tissue

Question 4

Describe M-mode

Answer 4

• 1D view of moving objects over time
• Use in modality in echocardiography
• Displays echo amplitude from beating heart + motion of valves
• Transducer positioned over heart + kept stationary = record returning echoes over same line of sight
• Limitation = difficult to get consistent/accurate beam placement

Question 5

Describe doppler principle

Answer 5

• Used to portray more rapid movements = blood flow
• Shift in frequency of sound waves as source moves relative to observer
• Change in frequency = related to velocity of movement = allows velocity of flow to be measured

Question 6

How can doppler flow be represented?

Answer 6

1) Trace = shows change in flow velocity with time
2) Sounds emitted = frequency equal to difference between transmitted + returning = audible to human ear
3) Spatial distribution of flow = superimposing flow info in color onto greyscale B-mode image

Question 7

Describe color flow images

Answer 7

• Flow velocities are indicated by colors
• Bright red = large approaching flow
• Dim red = weak approaching flow
• Blue = receding
• Yellow/green = turbulent flows
• Able to know magnitude + direction based off that

Question 8

Describe elastography

Answer 8

• AKA elastic imaging = reveals tissue elasticity parameters directly
  1) Image organ before compression
  2) Again while under known amount of stress
  3) Fine resultant strain
• Soft object = compress
• Stiff = displaced forward

Question 9

Describe thermal effects

Answer 9

• Temp rise due to = absorption energy
• Absorption = organ/tissue composition dependent + US frequency
• Higher frequency = faster energy absorbed
• Not hazardous for patient

Question 10

Describe mechanical effects

Answer 10

• Generation of possible collapse of microbubbles within tissue
• Cavitation = interaction between bubbles + US
• If -ve pressure large = bubbles produce/existing enlarge = violent implosion

Question 11

Give the factors cavitation depends on

Answer 11

1) US frequency
2) US intensity
3) Ultrasonic field focusing

Question 12

Describe the QA

Answer 12

• Important to maintain image quality + ensure patient safety
• New equipment characteristics tested + routinely
• QA confirm parameters don’t exceed characteristic

Question 13

Give the parameters measured in QA

Answer 13

• low-contrast object detectability
• axial and lateral spatial resolution
• sensitivity
• depth of beam penetration
• image uniformity
• Signal to Noise Ratio
• dynamic range
• vertical and horizontal measurement