Flashcards in Ultrasound Scanner Output Measurements Deck (15)

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1

## What is the equation for the pressure in an ultrasound wave at location x and time t?

###
p(x,t) = p_A*sin(wt-kx)

w is the radial frequency

k is the wave-number

2

## How is the particle velocity related to the pressure?

### u(x,t)=p(x,t)/Z

3

## What is the equation for the intensity of the sound wave in terms of the energy density epsilon?

### I = epsilon*c

4

## What is the equation for the instantaneous intensity of the ultrasound wave in terms of the pressure?

### I(x,t) = {p(x,t)^2}/Z

5

## What is the equation for the time-averaged intensity of the ultrasound wave in terms of the pressure?

### I(x,t) = {p_A(x,t)^2}/(2*Z)

6

## What is the equation for the power of the ultrasound beam through a surface S?

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E = I.S = [{p_A(x,t)^2}/(2*Z)]*S

=F.c

F is the force

c is the speed of sound in the medium.

7

## What are the fundamental parameters we want t measure from an ultrasound beam?

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- Pressure and its time and spatial derivatives (Spatial Peak Time-Averaged, Spatial Peak Pulse-Averaged, Spatial Peak, Spatial Averaged).

- Intensity and its time and spatial derivatives.

- Power and its time and spatial derivatives.

8

## What are the two measurement devices we have to measure an ultrasound beam?

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- Hydrophone

- Force Balance

9

## What are hydrophones best used for?

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- They are special piezoelectric device used for picking up the local pressure in real time.

- They are best used as a point element and for measurements of the interruption-fre ultrasonic field in water.

10

## What do hydrophones measure?

### - They directly measure the acoustic pressure.

11

## What are the advantages and disadvantages of using a hydrophone?

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+ Accuracy

+ Detailed field measurements

- Complex devices requiring a high level of competence to use.

12

## What are force-balances best used for?

### - General measurements of probe/tansducer output.

13

## What are the tree types of radiation force balance?

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- Reflection

- Absorption

- Combined

14

## What is the equation for calculating the power from a force balance reading?

###
F=(E_0)/c=I_0*cos(theta)*(S/c)

E_0 is the acoustic power

c is the speed of sound in the medium

I_0 is the acoustic intensity

theta is the angle of the reflector (45) or absorber (0) to the horizontal.

S is the surface area of the reflector/absorber.

15