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?
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?
- 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?
- Hydrophone
- Force Balance
9
What are hydrophones best used for?
- 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?
+ 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?
- 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
