Chapter 3 Ultrasound Physics

Question 1

What is rarefaction in ultrasound imaging?

Answer 1

Low pressure

Rarefaction refers to the phase of a wave where the pressure is lower than the ambient pressure.

Question 2

What is compression in ultrasound imaging?

Answer 2

High pressure

Compression is the phase of a wave where the pressure is higher than the ambient pressure.

Question 3

Define frequency in the context of ultrasound.

Answer 3

Number of times a wave is repeated per second.

Question 4

What is wavelength in ultrasound?

Answer 4

Distance travelled by a sound wave in one cycle.

Question 5

What determines the velocity of sound in an acoustic medium?

Answer 5

Physical density and stiffness.

Question 6

What is the average velocity of sound within soft tissue?

Answer 6

1.54 mm/us.

Question 7

Define acoustic impedance.

Answer 7

The product of the tissue’s physical density and sound velocity within the tissue.

Question 8

What does amplitude represent in ultrasound imaging?

Answer 8

Proportional to the difference in acoustic impedance in two adjacent tissues.

Question 9

What is the angle of incidence?

Answer 9

The angle at which a sound wave encounters a medium.

Question 10

What happens if the angle of incidence is not perpendicular?

Answer 10

The angle of reflectance equals the angle of incidence.

Question 11

Fill in the blank: The amount of attenuation is determined by the _______ and the frequency of the sound wave.

Answer 11

Distance travelled

Question 12

List the three components that determine attenuation.

Answer 12

• Absorption
• Reflection
• Scattering

Question 13

What do transducers contain to convert electric current into sound waves?

Answer 13

Piezoelectric crystals.

Question 14

What is pulse repetition frequency (PRF)?

Answer 14

The number of times sending and receiving is repeated within 1 second.

Question 15

Define spatial pulse length (SPL).

Answer 15

The length of space in one pulse of ultrasound.

Question 16

What is axial resolution?

Answer 16

The ability to distinguish two separate reflectors along the direction of the sound wave.

Question 17

How is axial resolution related to spatial pulse length?

Answer 17

It is equal to half of the SPL.

Question 18

Define lateral resolution.

Answer 18

The ability to distinguish two separate reflectors perpendicular to the direction of the sound wave.

Question 19

List the types of array transducers.

Answer 19

• Linear
• Convex
• Annular

Question 20

What is broad bandwidth technology in ultrasound?

Answer 20

Allows transducers to emit a wide range of frequencies.

Question 21

What is harmonic imaging?

Answer 21

Integer multiple of the frequency of the transmitted ultrasound pulse.

Question 22

What does spatial compounding do?

Answer 22

Generates a composite image by combining multiple frames from ultrasound beams at different angles.

Question 23

Name the two modes of echo display.

Answer 23

• Brightness mode (B-mode)
• Motion mode (M-mode)

Question 24

List the basic scanner controls in ultrasound.

Answer 24

• General gain
• Time gain compensation (TGC)
• Frequency
• Focal point or region
• Depth of field

Question 25

What is doppler shift?

Answer 25

The frequency difference between the incident sound waves and the reflected sound waves.

Question 26

What is the condition for measuring doppler shift accurately?

Answer 26

The doppler angle should be less than 60 degrees.

Question 27

What is continuous-wave doppler?

Answer 27

Uses two separate crystals in one transducer, one emitting sound continuously and one receiving echoes continuously.

Question 28

What is pulsed-wave doppler?

Answer 28

Uses the same crystal for both sending and receiving sounds.

Question 29

What does colour doppler indicate?

Answer 29

Red indicates net blood flow toward the transducer; blue indicates net blood flow away.

Question 30

What is power doppler?

Answer 30

Analyzes the total strength of the doppler signal determined by the concentration of moving red blood cells.

Question 31

What does microvascular imaging help to show?

Answer 31

Low-velocity and small-diameter blood vessel flow.

Question 32

What are microbubbles used for in contrast-enhanced ultrasound?

Answer 32

Enhance the ultrasound signal.

Question 33

What is ultrasound elastography used for?

Answer 33

Evaluates tissue elasticity/stiffness.

Question 34

Define acoustic shadowing.

Answer 34

Regions of decreased echogenicity distal to structures of high reflectivity.

Question 35

What is acoustic enhancement?

Answer 35

Regions of increased echogenicity distal to structures of low attenuation.

Question 36

What is the comet tail artifact?

Answer 36

Reverberation caused by two closely spaced, discrete highly reflective surfaces.

Question 37

Define mirror-image artifact.

Answer 37

Duplication of normal structure on the opposite side of a strong reflector.

Question 38

What are side lobes and grating lobes?

Answer 38

Secondary sound beams that result in an error in the positioning of the returning echo.

Question 39

What is range ambiguity?

Answer 39

Occurs when PRF is high enough that not all returning echoes are received before the next pulse.

Question 40

What happens during aliasing in pulsed wave doppler?

Answer 40

A portion of the tracing wraps around on the spectral tracing to the opposite direction.