Physics Principles of Diagnostic Ultrasound

Question 1

The speed at which a wave travels through a medium is determined by:

Answer 1

the density and compressibility of the medium

Question 2

Absorption of the ultrasound beam is highest in …..

Answer 2

bone

Question 3

A longitudinal wave requires a

Answer 3

medium to propogate

Question 4

The propagation speed of ultrasound waves is slowest in

Answer 4

air (330 ms-1)

Question 5

One cycle of a wave is known as

Answer 5

the period

Question 6

Which medium can a sound wave not travel through?

Answer 6

A vacuum

Question 7

What determines the speed of sound?

Answer 7

The medium

Question 8

If the frequency of the wave is 1MHz the period is:

Answer 8

0.000001s

Question 9

In a sound wave regions where pressure is lower than normal are called regions of

Answer 9

rarefaction.

Question 10

What is sound?

Answer 10

A vibration that propagates as an acoustic wave through a transmission medium

Question 11

What type of wave is a sound wave

Answer 11

A longitudinal wave, the vibrations are in a parallel direction to wave travel. They require a medium to propogate

Question 12

What is the audible sound range?

Answer 12

20Hz - 20KHz

Question 13

Diagnostic ultrasound range?

Answer 13

2MHz - 20MHz

Question 14

What is the propagation speed in normal soft tissue?

Answer 14

1540 ms-1

Question 15

What happens to the wavelength as Frequency increases?

Answer 15

Wavelength gets smaller. Higher resolution

Question 16

What happens to wavelength as frequency decreases

Answer 16

Wavelength gets larger, deeper penetration.

Question 17

What happens as US passes through an interface with identical impedences z1 = z2

Answer 17

Total transmission, no energy is reflected, no echo produced. Interface will not been seen on US

Question 18

When does partial reflection occur?

Answer 18

When two tissues have difference impedances (eg. liver vs fat). A fraction of the energy is reflected and the rest is transmitted.

Question 19

When does total reflection occur?

Answer 19

When there is a large difference in acoustic impedance of tissues. (Soft tissue vs air) All energy is reflected and none is transmitted into the second tissue. The interface is seen as a strong linear structure on US.

Question 20

What is the equation for acoustic impedance?

Answer 20

Z = p x c (Ryals)
p = density of the tissue
c = US propogation speed

Question 21

Define attenuation

Answer 21

As an US wave travels through tissue it becomes progressively weaker.