Physics 1 Module 3 & 4 Flashcards
When electric pulses or voltage are applied to certain crystals they will produce sound waves
Reverse piezoelectric
What 4 variables affect sound as it travels through a medium?
- Pressure
- Density
- Particle motion
- Temperature
What can pressure be expressed as?
A sine wave
Regions of low density
Rarefactions
Regions of high density
Compressions
Back and forth particle motion parallel to direction of wave travel
Longitudinal waves
Perpendicular motion to wave travel
Transverse waves
What type of wave is a sound wave?
Longitudinal
Only solids can support which type of waves?
Transverse
When one type of wave is converted to another type of wave
Mode conversion
What’s an example of mode conversion?
Tissue-bone interface
A measurement of how often something happens; the number of complete variations an acoustic variable goes through in one second
Frequency
What is the unit for frequency?
Hertz
The time it takes for one cycle to occur
Period (in microseconds)
The length of space one cycle takes up commonly expressed in millimeters
Wavelength
How does an increase in frequency affect period and wavelength?
Decreased period and wavelength
F=1/T
F=c/wavelength
What is the equation for frequency in relation to period and wavelength?
F=1/T
F=c/wavelength
What is the speed of sound in soft tissue?
1.54 mm/microsecond
1540 m/second
What are the 3 ways to describe the strength of a wave?
Amplitude, intensity, power
Maximum variation of an acoustic variable
Amplitude
Power of wave divided by the area
Intensity
Total energy over the entire cross-sectional area
Power
A small change in amplitude results in what to intensity?
A large change in intensity
How is intensity related to power (p) and area (a)
I=P/a
Where is the beam most intense?
At the center
What is the beam uniformity ratio?
BUR = SP/SA
Where is the spatial average of the beam?
At the face of the transducer
What is the equation for duty factor?
DF = TA/TP(PA)
What does duty factor tell us?
The amount (percent) of time the transducer is “on”
Which intensities combination is used for biological considerations in ultrasound?
SPTA
M-mode, real time, doppler, continuous wave
Lowest to highest values of SPTA
What are the SPTA values dependent on?
Depth
What is the speed of sound in fat and in bone?
Fat: 1460 m/s
Bone: 4080 m/s
What is the range equation?
D = c x t
What does the D, C and t mean in the range equation?
D= distance to the reflector AND BACK C= average speed of sound in soft tissue T= time for the ROUND TRIP
How would you get the distance to the reflector in the range equation?
Divide by 2
What is the 1 cm rule?
The time it takes sound to travel out and back to a depth of 1cm
13 microseconds
The time it takes for one pulse to occur
pulse duration
What is the pulse duration (PD) equation? What are the typical units?
PD = T x Cycles in a pulse (RD)
Microseconds
The length of the pulse
Spatial pulse length
What is the SPL equation? Units?
SPL = wavelength x RD
In mm
How does RD relate to SPL?
Decreased ring down (# of cycles in a pulse) will decrease the SPL
Increased frequency = decreased wavelength = decreased SPL
Decreased SPL does what for resolution?
Improves it
Number of pulses emitted in one second
Pulse repetition frequency (PRF)
The time from the beginning of one pulse to the beginning of the next
Pulse repetition period (PRP)
What is another way of expressing the go-return time calculated by the range equation?
PRP= d/C
PRP is the equivalent of t
What is the relationship between PRF and PRP?
Reciprocal
PRF = 1/PRP
How is DF related to PD and PRP?
DF = PD/PRP x 100
A medium with low compressibility will do what to sound velocity?
Increase
As bulk modulus increases, what happens to velocity?
Increases
Another way to describe bulk modulus
Stiffness
If ONLY density increases, what happens to velocity?
Decreases
Firing a second pulse before the first one returns
Range ambiguity/high PRF mode
What is the limiting factor for PRF?
Depth
Increased wavelength does what to:
A) frequency
B) SPL
C) Resolution
A) decreases
B) increases
C) decreases (lower SPL is better)
Quantities including pressure, density, particle motion and temperature
Acoustic variables
The effects that the tissue has on sound as it travels
Acoustic propagation
The effects of sound on tissue as it travels
Bioeffects
If the PRF of a system were to increase then what will happen to the duty factor?
It increases
As the PRF increases what will happen to the transducer frequency?
There is no change
If the region of interest doubles the depth then what will happen to the PRF?
It will half
As the frequency of the prob is increased what is true of the PRF?
No change as they are unrelated
