Flashcards in US: Basic Ultrasound Physics Deck (22)

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1

## What is the speed of sound in tissue assumed by most commercial ultrasound scanners?

### 1540m/s

2

## How is the speed of sound in a medium related to the bulk modulus (K) and the density (ρ)?

### c = (K/ρ)^0.5

3

## How is the acoustic impedance related to the speed of sound and the density?

### Z = pc

4

## What is the equation for the depth of the far field?

###
D = (a^2)/λ

a is the aperture (1/2 diameter of the transducer array)

λ is the wavelength

5

## What is the equation for the angle of divergence in the far-field?

###
Θ = arcsin(0.61λ/a)

a is the aperture (1/2 diameter of the transducer array)

λ is the wavelength

6

## What is another name for the near-field?

### Fresnel zone

7

## What is another name for the far-field?

### Fraunhofer zone

8

## For a focused lens (with speed of sound c1) with a curvature of R, what is the equation for the length of the near field (F)?

###
F = R /[(c2/c1)-1]

c2 = speed of sound in tissue.

9

## What is the equation for the beamwidth at the focus?

###
w = λF/a

λ = wavelength

F = focal depth

a = aperture radius

10

## What is the equation for the amplitude reflection coefficient?

###
R = (Z2-Z1)/(Z2+Z1)

Z2 and Z1 are the acoustic impedances of the two media.

11

## What is the equation for the intensity reflection coefficient?

###
I = [(Z2-Z1)/(Z2+Z1)]^2

Z2 and Z1 are the acoustic impedances of the two media.

12

## Under what conditions is specular reflection observed?

### When the diameter of the object is much larger than the wavelength.

13

## Under what conditions is Rayleigh scattering observed?

### When the diameter of the object is much smaller than the wavelength.

14

## What is the scattered power proportional to?

### (d^6) x (f^4)

15

## What causes ultrasonic scattering in tissue?

### Microscopic variations in acoustic properties within tissue parenchyma.

16

## How does scatter appear on ultrasound images, and what is the reason for this appearances?

### Scatter is low-power and non-directional, leading to a dark uniform speckled appearance.

17

## What is the equation for attenuation of an ultrasound beam through tissue?

###
I=I(0)*Exp(-α*z)

α is the frequency-dependent ultrasound coefficient (dB/cm).

z is the depth in tissue.

18

## What is the equation for the frequency dependent ultrasound coefficient?

###
alpha = af^b

a is the frequency independent ultrasound coefficient (dB/cm/MHz)

b~1.1.

19

## What is the value of b for liver and muscle?

### 1.1

20

## What is the value of b for blood and bone?

### 1.2

21

## What is the value of b for breast tissue?

### 1.5

22