10 Ultrasound

Question 1

Sound waves

Answer 1

Pressure disturbance that propagates through a material

Question 2

The amplitude of a wave

Answer 2

The size of pressure difference from the equilibrium value.

Question 3

Wavelength (λ)

Answer 3

The distance between successive wave crests.

Question 4

Frequency (f)

Answer 4

• The number of oscillations in each second.

* The number of wavelengths that pass a given point each second.

Question 5

Longitudinal waves in ultrasound

Answer 5

Have vibrations along their travel direction.

Question 6

Transverse waves in ultrasound

Answer 6

Have vibrations perpendicular to the travel direction.

Question 7

The period

Answer 7

The time between successive oscillations.

Question 8

Diagnostic ultrasound uses transducers with frequencies ranging

Answer 8

1 to 20 MHz.

Question 9

velocity (v).

Answer 9

v = f ×λ (m/s).

Question 10

The ultrasound intensity

Answer 10

Measuring the energy flowing through a given cross-sectional area each second.

Question 11

Relative sound intensity

Answer 11

Measured on a logarithmic scale and may be expressed in decibel (dB).

Question 12

Negative decibel values

Answer 12

Correspond to signal attenuation.

Question 13

Positive decibel values

Answer 13

Correspond to signal amplification.

Question 14

The acoustic impedance

Answer 14

• Describes how much resistance an ultrasound beam encounters as it passes through a tissue.
• The acoustic impedance (Z) of a material is the product of the density (ρ) and the sound velocity (v) in the material.
• Z = ρ × v
• The acoustic impedance unit is called the Rayl.

Question 15

Reflections in ultrasound

Answer 15

A portion of the ultrasound beam is reflected at tissue interfaces.
[(Z2 − Z1)/(Z2 + Z1)]^2.

Question 16

Nonspecular reflections in ultrasound

Answer 16

Diffuse scatter from rough surfaces where the irregular contours are bigger than the ultrasound wavelength.

Question 17

Specular reflections in ultrasound

Answer 17

Occur from large smooth surfaces. Specular reflection intensity is independent of frequency.

Question 18

echo

Answer 18

The sound reflected back toward the transducer

Question 19

Gel is applied between the transducer and skin

Answer 19

To displace the air and minimize large reflections that would interfere with ultrasound transmission into the patient.

Question 20

shadowing.

Answer 20

Lack of transmissions beyond these interfaces results in areas void of echoes

Question 21

Scattering in ultrasound

Answer 21

Occurs when ultrasound encounters objects that are smaller than the ultrasound wavelength.

Question 22

Hyperechoic

Answer 22

A higher scatter amplitude relative to the background signal.

Question 23

Hypoechoic

Answer 23

There is a lower acoustic scatter intensity relative to the average background signal.

Question 24

Organs showing black in ultrasound

Answer 24

Organs that contain fluids, such as the bladder, and cysts have no internal structure and almost no echoes

Question 25

Refraction in ultrasound

Answer 25

The change in direction of an ultrasound beam when passing from one tissue to another having a different speed of sound.

Question 26

Refraction is described by

Answer 26

Snell’s law: sinθi/sinθt = v1/v2, where θi is the angle of incidence, θt is the transmitted angle, v1 is the velocity in tissue 1, and v2 is the velocity in tissue 2.

Question 27

Attenuation in ultrasound

Answer 27

The composite effect of loss by scatter and absorption.

Question 28

Attenuation in ultrasound is normally expressed in terms of

Answer 28

dB and depends on the distance the ultrasound beam has traveled in tissue.

Question 29

A transducer

Answer 29

Device that can convert one form of energy into another.

Question 30

The Doppler effect

Answer 30

Refers to changes in frequency resulting from a moving sound source. –Objects moving toward the detector reflect sound that has a higher frequency. –The increase in frequency is associated with a reduction in wavelength. –Objects moving away from the detector reflect sound that has a lower frequency. –The reduction in frequency is associated with an increase in wavelength.

Question 31

Doppler ultrasound

Answer 31

Used to identify and evaluate blood flow in vessels based on the backscatter of blood cells.

Question 32

Attenuation of −10 dB −20 dB −30 dB

Answer 32

* 10%. * 1%. * 0.1%.

Question 33

Depth gain compensation accounts for tissue attenuation

Answer 33

By increasing echo amplification for later echoes.

Question 34

The average velocity of sound in soft tissue

Answer 34

1,540 m/s.

Question 35

Velocity is inversely proportional to the square root of

Answer 35

The material compressibility.

Question 36

Intensity transmitted in ultrasound

Answer 36

(4Z1× Z2)/(Z1 + Z2)^2.

Question 37

Attenuation of ultrasound in soft tissue at 1 MHz is most likely

Answer 37

0.5 dB/cm.

Question 38

Increasing the transducer thickness is most likely to increase the sound

Answer 38

Wavelength, since the crystal thickness is one half of the ultrasound wavelength.

Question 39

The damping material behind the crystal transducer reduces the

Answer 39

The pulse length.

Question 40

The pulse repetition period in ultrasound (listening time) is given by

Answer 40

1/PRF (i.e., 1/4,000seconds).

Question 41

Ultrasound signals are converted to a video monitor display using:

Answer 41

Scan converts.

Question 42

It takes 13 μs to get an echo from an interface from a depth of

Answer 42

1 cm.

Question 43

The thermal index (TI) value indicates the possible increase in tissue

Answer 43

Temperature.