Medical Ultrasound

Question 1

What is ultrasound?

Answer 1

Soundwaves with frequencies higher than human audible range > 20kHz.

Question 2

What is a sound wave?

Answer 2

• Mechanical wave created by changes in pressure from vibrations in a medium.
• Wave will displace particles in the same direction as the wave (longitudinal wave).
• The speed of sound depends on the properties of the medium in which it is travelling in.

Question 3

Wavelength =

Answer 3

wave speed/frequency.

Question 4

What is the piezoelectric effect?

Answer 4

• Ability of the material to generate an electric current when pressure is applied, material is
  synthetic.

Question 5

How do we produce an image?

Answer 5

• Probe emits sound waves and receives the echoes from the original wave.
• Measure time for wave to get back to probe, calculate distance, (distance = speed x time/2).
• Acoustic impedance (Z = density x speed of sound in tissue),

Question 6

What is an acoustic interface?

Answer 6

• Soundwave can interact with an acoustic interface (two different tissue types meet).
• Soundwave can be reflected/transmitted/attenuated.
• Difference in Z values means more reflections and less transmission of sound wave.

Question 7

• How will the ultrasound be displayed?

Answer 7

• Brightness of pixels depends on amplitude of the returned wave.
• Bone/gas (high amplitude), Fluid (low amplitude).

Question 8

What are the different types of transducers? (1) C———

Answer 8

• Curvilinear = very common, abdominal, obstetric, deeper structures, low frequencies.

Question 9

What are the different types of transducers? (2) L—–

Answer 9

• Linear = vascular, musculoskeletal, poor depth, mid frequencies.

Question 10

What are the different types of transducers? (3) P—– A—-

Answer 10

Phased Array = between ribs, area of heart, low frequencies.

Question 11

What are the different types of transducers? (4) E—

Answer 11

Endo = transvaginal, transoesophageal, intraluminal, poor for depth, high frequencies.

Question 12

What are the 3 modes of ultrasound? (1) B _ —-

Answer 12

B-Mode =

• common, brightness
• 2D/greyscale/cross sectional image
• real time imaging
• make measurements

Question 13

What are the 3 modes of ultrasound? (2) A _ —-

Answer 13

A-Mode =

• less common,
• x (depth)/y (amplitude)
• axis,
• optic nerve scan.

Question 14

What are the 3 modes of ultrasound? (3) M_ —-

Answer 14

M-Mode =

• motion,
• heart valve scan,
• single scan line.

Question 15

What is doppler?

Answer 15

• Visual display of direction/velocity of blood
• Change in wavelength = change in frequency = change in pitch.
• Frequency of a soundwave depends on position of the observer/velocity of the point of origin of the sound.
• Power (low velocity flow), spectral (flow rate), colour (presence, direction of flow).

Question 16

What are the safety instructions for ultrasounds?

THERMAL

Answer 16

• Thermal effects = reduce scan times, high training levels, equipment maintenance, access to PACS system.

Question 17

What are the safety instructions for ultrasounds?

NON- THERMAL

Answer 17

• Non-thermal effects = increased pressure/intensity can cause micro bubbles in tissue/cavitation/cell damage.

Question 18

Why would you need an ultrasound for the heart? (7)

Answer 18

• Congenital heart disease
• trauma
• cardiac masses
• arrhythmias
• effusion
• valve stenosis
• cardiomyopathy

Question 19

Why would you need an ultrasound for the lungs?

Answer 19

• Pneumothorax (greater accuracy than X-ray).