SPI Flashcards
What is a wave?
A cyclical transfer of energy
What kind of wave is a sound wave?
A mechanical longitudinal wave
What are the types of interference?
Constructive, destructive, partial
What is the classification for diagnostic ultrasound?
2 mhz to 15 mhz
What is the propagation speed in tissue?
1540 mhz, 1.54 m/sec (154,000 cm/sec)
A longitudinal wave propagates by a series of ______ and ________ back and forth in the same direction as the wave propagates.
Compression, rarefaction
What are the acoustic variables of wave propagation?
Pressure, density, temperature, partical motion
What is the equation for the frequency of the wave?
f = 1/p
Frequency and period are determined by what?
The source
What is the propagation velocity equation?
Square root of: Bulk modulus / Density
If the density increases, what happens to the Bulk modulus and propagation velocity?
The Bulk modulus increases and the propagation increases.
If the density of the medium decreases, what happens to the Bulk modulus and propagation velocity?
The Bulk modulus decreases and the propagation decreases.
Stiffness is the same as what?
Bulk modulus
Stiffness and compressability are ______ related.
Inversely
What is the equation for the wavelength?
Wavelength = c / f
What is the amplitude?
Maximum variation of a variable from its mean.
What are the equations for the amplitude?
Max - min, Mean - min, Max - min / 2
Power is proportional to the amplitude _______
Amplitude squared
What is the definition of intensity?
I = Power / Area
The top Diagnostics frequencies are limited by what?
Penetration
Low frequencies are limited by what?
Resolution
3 dB factor of ?
2
10 dB factor of ?
10
What is attenuation?
The conversion of sound into heat.
What are the factors of attenuation?
Absorption, reflection, refraction
What are the key factors of absorption?
It is the dominant form of attenuation and it increases exponentially with increasing frequency.
What are the two types of reflection?
Acoustic and geometric
What are the kinds of geometric reflectors?
Specular reflectors, scatterers, Rayleigh scattering
What causes refraction?
Different propagation speeds, oblique angles of incidence
What causes lateral displacement?
Refraction, the machine is not aware that refraction occurs.
What is total internal reflection caused by?
Critical angle
What is the attenuation rate in soft tissue?
0.5
What is the attenuation coefficient of soft tissue?
1 / 2 fo
What is the equation for conservation of energy?
Reflection % + Transmission % = 100 %
Describe anechoic
No echogenicity
Describe hypoechoic
Low echogenicity
Describe hyperechoic
High echogenicity
Describe calcified
Strongly echogenic, usually w/acoustic shadowing
Type of reflection that occurs at an interface depends on what?
The size of the wavelength compared to the size of the surface geometry.
Acoustic impedance is measured in what?
Rayls
How is pulsed wave created?
The pulser is turned on and off.
What is the range resolution equation?
SPL / 2
Explain the wave parameter period
The time it takes for one cycle to occur ( p = 1 /f ) measured in seconds and is determined by the source.
Explain the wave parameter pulse duration
The time for one pulse to occur, PD = P # Cycles, measured in seconds and is determined by the source.
Explain the wave parameter pulse repetition period
The time it takes between repeating pulses, 13 msec x depth, is measured in seconds, determined by the source.
Explain the wave parameter pulse repetition frequency
1 / PRP, reciprocal of PRP (measured in Hz)
Explain the wave parameter wavelength
The physical distance on the cycle takes up, measured in meters, wavelength = c / f , determined by both the medium and the source.
Explain the wave parameter spatial pulse length
The physical dimension the pulse occupies in space, SPL = wavelength # of cycles, (measured in meters) determined by the source and the medium.
What is frame time?
The time it takes to create one frame, it is measured in seconds and is determined by the source.
What is frame rate?
Inverse frame time, fr = 1 / ft (measured in Hz) the amount of time it takes to make one line
What is bandwidth?
The range of frequencies at which a single transducer can operate.
What is fractional bandwidth?
Bandwidth / operation frequency
What is a factor in regards to the bandwidth?
1 / Fbw
What are the other names for range resolution?
LARRD - Longitudinal, Axial, Range, Radial, Depth
For better resolution a ________ number means better resolution.
Smaller number
What is duty factor?
The percent of time the machine is doing work, PD / PRP
What does the backing layer do?
It is used to shorten the SPL improving the range resolution.
What is the difference between non scanned and scanned is what?
Scanned transmits the beams in different directions.
What does color doppler do to resolution?
It worsens the resolution because of the color packet.
What is the amplitude?
It is the “loudness” Max - min, Mean - min, Max - min / 2
Relationship between power and amplitude
Power = amp (power of 2)
What is the intensity equation?
I = power / area
What unit is intensity measured in?
Watts
What is a transducer?
Any device which converts energy from one form to another.
What adds in changing focus?
Curved elements, lens and electric focusing
What is sequencing?
Turning on groups of elements over time.
What is phasing?
Time delay to echo element used for steering.
Explain mechanical steering
Wobbling done with a motor to move the transducer head to steer the beam.
What is the zone from the transducer to the focal zone, what happens to the beam between those two points?
The near zone (Fresnel zone), convergence
What is the zone from the focal zone and beyond? What happens to the beam after the focal point?
The far zone (Fraunafer zone), divergence
What is the area called when the diameter is halved?
The natural focus / focal point
What does increasing the diameter crystal do to the beam?
Makes the focal zone bigger and deeper.
What does the thickness of the beam affect?
The operating frequency
What is the equation for operation frequency?
Propagation speed / 2 thickness of crystal
What does the lens do?
Helps focus the beam in the elevation plane.
What does the matching layer do?
It decreases the acoustic impedance between the transducer and skin
What does the PZT crystal do?
Converts voltage into an acoustic wave and back to voltage.
What does the backing layer do?
It shortens the SPL improving range resolution.
What does the pulser do? Is it pre-processing or post-processing?
Sends energy out of the system to the transducer, pre-processing.
What does the A/D converter do? Is it pre or post processing?
It converts the analog signal to digital (A mode) pre-processing.
What does the receiver do and is it pre or post processing?
It receives the digital information and the image can be adjusted, pre-processing.
What is the scan converter and is it pre or post processing?
Converts A mode imaging into a picture B mode using gray scale compression mapping. Gain and compression are done post-processing.
The storage and monitor receive the same image unless you do what?
Change the monitor settings
What is read zoom and what is another name for it?
Blows up the picture, has poor resolution and is also called non acoustic zoom.
What is write zoom and what is another name for it?
Pre-processing area zoomed, better resolution and is also called acoustic zoom.
What is the doppler effect?
An apparent change in frequency due to a change in wavelength that is caused by motion.
If motion is moving towards the transducer, what happens to frequency, wavelength and pitch?
Frequency increases, wavelength decreases and pitch increases.
If motion is moving away from the transducer, what happens to frequency, wavelength and pitch?
Frequency decreases, wavelength increases and pitch decreases.
The faster the motion the ______ the doppler shift.
Greater
How are the doppler effect and the propagation speed related?
Inversely related
What does mixing to baseband do?
It is a mathematical process that takes the received frequency and subtracts out the frequency sent in to get the shift.
How do wall filters work?
They only let high frequencies go through giving them the name high pass filters, reducing noise.
What is FFT?
Fast fournier transform, mathematical process necessary to separate the collection of shifts into frequency bits.
When does aliasing occur?
When the Nyquist criteria is broken, PRF / 2
What is variance?
Anything that is outside the mean velocity (bar next to color bar)
What is a normal color packet size range?
3 - 12 pulses per line
What is autocorrelation?
Detects mean velocities, direction of shifts and variance
What kind of doppler shift has arrows kissing?
Positive shift
What kind of doppler shift has arrows in the same direction?
Negative shift
How do you get rid of aliasing?
Increase PRF, change baseline, HPRF, lower the op frequency, increase the doppler angle (not gain!)
What is refraction? What assumption is broken?
Lateral displacement of a structure within an image caused by a high acoustic impedance mismatch / AB is “transmitted wave travels along a straight line path from the transducer to the objection and back.”
What is reverberation? What assumption is broken?
Unwanted structures repeated the same distance apart caused by sound bouncing between multiple structures / AB is that each reflector contributes to a single echo which integrates along a single scan line.
What are the two types of reverberation?
Ring down (cause by air filled structures), comet tail (cause by metallic structures).
What is multipath? What assumption is broken?
Structures appear deeper than reality because of elongated path length / AB is that each reflector contributes to a single echo which integrates along a single scan line.
What are grating lobes and what assumption is broken?
Lateral displacement caused by energy outside of the main beam / the assumption broken is that all detected echoes originate from the axis of the main beam.
What is speed error and what assumption is broken?
Structures drawn at an incorrect depth / the assumption broken is that the U/S wave travels at a rate of 1540 m/sec in tissue.
What is range ambiguity and what assumption is broken?
Result of reflected data from the previous acoustic transmit adding to the
What is range ambiguity and what assumption is broken?
Result of reflected data from the previous acoustic transmit adding to the reflection of the current acoustic line / AB all received echoes are derived from the most recent pulse.
What is mirroring and what assumption is broken?
Artificial structures symmetrical to the actual structure on the other side of a specular reflector / AB the transmitted wave travels along a straight line, all detected echoes originate from the axis of the main beam.
What is shadowing and what assumption is broken?
The dark portion under an object caused by excessive reflection, absorption or refraction / AB are that the attenuation of sound is uniformed along a path and that the amplitude of the echo is derived from the object scanned alone.
What is speckle and what assumption is broken?
The result of varying degrees of constructive and destructive interference of sound waves caused by a low operating frequency / AB is that attenuation of sound is uniform over a scan line.
What are the kinds of doppler artifact?
Aliasing, range ambiguity, spectral mirroring, spectral broadening, blossoming, color bleeding and wall filter saturation.
What is bioeffect?
An undesired change in tissue as a result of interaction with the insonating beam.
What are the two types of bioeffects?
Thermal and mechanical
What is thermal bioeffect?
Temperature, time related (related to temporal averaging, duty factor, scan time, non scanned)
What are 3 thermal indices?
TIS (Thermal index in soft tissue), TIB (Thermal index of bone), TIC (Thermal index of cranial bone)
What is a mechanical bioeffect?
Related to cavitation, scanned
What are the two types of mechanical bioeffects?
Stable and transient / inertial cavitation
What kind of cavitation causes the microbubbles to not burst?
Stable cavitation
What kind of cavitation causes the microbubble to implode causing damage to the tissue around it?
Inertial / transient
What is mechanical index?
Risk of cavitation
What is the mechanical index equation?
Peak rarefaction / op frequency
What is the eqation for intenity?
Power / Area
Which common intensity has the most intensity?
SPTP, Spatial Peak Temporal Peak
Which of the common intensities is a common mechanical intensity?
SPPA, Spatial Peak Pulse Average
Which of the common intensities is a common thermal intensity?
SPTA, Spatial Peak Temporal Average
Which of the common intensities is the smallest intensity?
SATA, Spatial Average Temporal Average
What is the max unfocused intensity?
100 mw/cm squared
What is the max focused intensity?
1 w/cm squared
Duty factor in relation to bioeffect.
PD/PRP = TA / PA
What is B.U.F.?
Beam uniformity factor, a measure of how the beam intensity uniformity over space.
What is the B.U.F. equation?
SP / SA
What is a hydrophone?
Routinely used to make power measurement in a water bath.
What does contrast do?
Increases the acoustic impedance mismatch within the blood as a result of the high compressability and low density of the gas.
What is harmonics?
The transducer sends at one frequency and receives at one twice the frequency.
What kind of transducer is needed to use harmonics?
Broadband transducer
What are the two types of harmonics?
Tissue and contrast
What part of the beam has the strongest harmonic response?
The mid field
What does harmonics do to grating lobes?
Reduces them
What is the object used to test equipment?
Phantoms
What are the components of a doppler flow phantom?
Imaging face, a medium, flow conduit, pump, reservoir, blood mimicking fluid
What are doppler flow phantoms used for?
For directional discrimination, flow velocity, sensitivity, maximum penetration or location of flow.
What are doppler string phantoms?
String around a pully with the transducer over the moving string helps test.
What are the string phantoms to test?
Peak velocity, spectral broadening, gate depth accuracy
What is a vibrating plate doppler phantom? What does it test?
Plate vibrates and test sensitivity
Imaging phantom tests what?
Detail resolution (axial, lateral an elevation) sensitivity, contrast resolution, the dead zone and dimensional measurement accuracy.
What is Q & A testing?
The statistical measurement used to determine the quality of a test compared to the gold standard.
How do you calculate accuracy?
TP + TN / ALL
Define power.
The rate at which energy is transferred.
