Ultrasound

Question 1

What is ultrasound?

Answer 1

• Ultrasound is sound above 20,000 Hz which is at a higher frequency than humans can hear.
• It travels as a pressure wave containing compressions and rarefactions.

Question 2

What are compressions and rarefactions?

Answer 2

Compressions are regions of higher pressure and rarefaction are regions of lower pressure.

Question 3

The features of longitudinal sound waves are:

Answer 3

• They can’t travel through a vacuum. The denser the medium, the faster a sound wave travels.
• The higher the frequency or pitch, the smaller the wavelength.
• The louder the sound, or the more powerful the ultrasound, the more energy is carried by the wave and the larger its amplitude.

Question 4

Wave vibrations

Answer 4

• In a longitudinal wave the vibrations of the particles are parallel to the direction of the wave.
• In a transverse wave the vibrations of the particles are at right angles to the direction of the wave.

Question 5

When ultrasound is used to break down kidney stones:

Answer 5

• A high-powered ultrasound beam is directed at the kidney stones.
• The ultrasound energy breaks the stones down into small pieces.
• The tiny pieces are excreted from the body in the normal way.

Question 6

What happens when ultrasound is used in body scans?

Answer 6

• When ultrasound is used in body scans, a pulse of ultrasound is sent into the body.
  
  • At each boundary between different tissues some ultrasound is reflected and the rest is transmitted.
  • The returning echoes are recorded and used to build up an image of the internal structure.

Question 7

Ultrasound can be used for body scans because:

Answer 7

• When ultrasound is reflected from different interfaces in the body, the depth of each structure is calculated by using the formula distance = speed x time, knowing the speed of ultrasound for different tissue types and the time for the echo to returns.
• The proportion of ultrasound reflected at each interface depends on the densities of each of the adjoining tissues and the speed of sound in the adjoining tissues.
• If the tissues are very different (e.g. blood and bones) most of the ultrasound is reflected, leaving very little to penetrate further into the body.
• The information gained is used to produce an image of the body scanned.

Question 8

Ultrasound is preferred to x-rays because:

Answer 8

• It is able to produce images of soft tissues.
• It doesn’t damage living cells.