EDELMAN INDEX / VOCAB Flashcards
ABSORPTION
~ occurs when U/S energy is converted into heat or reflected/refracted out of field
~ lower tissues return less U/S
~ directly related/proportional to frequency
~ causes high frequency waves to attenuate more than lower frequency waves
~ bone has highest absorption
~ high in muscle and skin, low in fluid-filled
~ calorimeter measures total power in a sound beam undergoing absorption
REGISTRATION ACCURACY
~ the ability of the system to place reflections in proper positions while imaging from different orientations
RANGE ACCURACY = VERTICAL DEPTH CALIBRATION
~ the system’s accuracy in placing reflectors at correct depths located parallel to the sound beam
~ differences and errors between scan and pin locations caused by system malfunction OR speed of sound not being 1540 m/s
ACOUSTIC IMPEDANCE /
CHARACTERISTIC IMPEDANCE
~ impedance is the acoustic resistance to sound traveling in a medium
~ multiply the density of a medium by the speed at which sound travels through it
~ calculated in Rayls, represented by Z
~ typical values = 1.25 to 1.75 Mrayls
ACOUSTIC VARIABLES
~ pressure = concentration of force in an area, density = concentration of mass in a volume, distance = measure of particle motion
~ pressure (Pa / pascals), density (kg / cm3), distance (cm / mm / feet / mile)
~ used to distinguish between sound waves and other types of waves
ACOUSTIC PARAMETERS
~ used to describe characteristics of a sound wave
~ 7 parameters = period, frequency, amplitude, power, intensity, wavelength, propagation speed
ACOUSTO - OPTICS
~ based on interaction of sound and light
~ Schlieren shadowing system allows view of the shape of a sound beam in a medium
~ an example is jet shock waves from the interaction of sound and light
AIUM CONCLUSIONS
~ no confirmed harmful bioeffects from exposure to diagnostic U/S have been reported
~ possible that bioeffects may be identified in the future
~ the benefits outweighs the risks
~ appropriate to use diagnostic
~ use to benefit patient, not entertain
IN VITRO BIOEFFECTS (AIUM)
~ in vitro bioeffects research is important
~ in vitro bioeffects are real even though they may not apply to the clinical setting
~ in vitro bioeffects research that claims direct clinical significance be viewed with caution
ALARA
~ As Low As Reasonably Achievable
~ when modifications to either output power/receiver gain can improve the quality, the first choice is one that will minimize the patient’s U/S exposure
~ image too dark, first increase receiver gain (does not increase patient exposure)
~ image too bright, first decrease output power
ALIASING
~ most common error with pulsed Doppler
~ occurs when sampling rate is too low in comparison to the measured blood velocities
~ false identity where very high velocities in one direction are incorrectly displayed as going opposite
~ flow above baseline indicates flow towards transducer
~ top of display is Nyquist limit, bottom is aliasing
~ display can happen in opposite direction too
ALIASING CONDITIONS
~ occurs ONLY with pulsed (PW) Doppler
~ occurs when Doppler sampling rate is too low compared to measured blood velocities
ALIASING LIMITS
~ Nyquist limit is the highest Doppler frequency or velocity that can be measured w/out the appearance of aliasing
~ aliasing appears when Doppler shift exceeds the Nyquist limit
~ Nyquist limit is 1/2 of the PRF
ALIASING SAMPLE VOLUME DEPTH
~ velocities are sampled many times/sec
~ sampling rate is the system’s PRF
~ sample volume too deep, PRF/Nyquist is low and velocity is sampled less (no measuring accuracy which creates aliasing)
~ sample volume shallow, PRF/Nyquist is high and velocity is sampled many times/sec (measures high velocities w/out aliasing)
ALIASING TRANSDUCERS
~ higher frequency transducers create more aliasing
~ smaller Doppler shifts from lower frequency transducers are less likely to exceed the Nyquist limit
~ higher frequency transducers create higher Doppler shifts, lower frequency transducers create lower Doppler shifts
ALIASING TECHNIQUES
~ ridding aliasing improves ability to measure the maximum velocity with Doppler
~ adjust scale to maximum
~ select new ultrasonic view with shallower sample volume
~ select a lower frequency transducer
~ use baseline shift
~ use continuous wave Doppler
ALIASING ADJUSTING SCALE TO MAX
~ sometimes PRF is not maximized (so Nyquist isn’t as well)
~ maximizing PRF raises Nyquist, less aliasing
~ higher PRF reduces sensitivity to low velocities
~ with very high velocities, aliasing artifact can occur even when scale is maximized!!!!!
ALIASING USE SHALLOWER SAMPLE VOLUME
~ shallower sample volume increases the PRF
~ can also adjust the PRF to raise it
~ use a new view with shallower depth
~ no disadvantages to this method!!!!
ALIASING USE LOWER FREQ TRANSDUCER
~ Doppler shift is directly related to freq of transducer (lower Doppler w/lower freq trans)
~ lower frequency sound reduces the height of Doppler spectrum
~ no significant disadvantage except lower freq sound produces lower quality image
ALIASING USE BASELINE SHIFT
~ bidirectional Doppler, flow towards trans above, flow away below
~ slides the display baseline down so that the entire velocity scale is devoted to 1 direction
~ visually appealing but aliasing can remain
~ baseline shift ineffective when Doppler shift so high signal completely wraps around itself
ALIASING USE CONTINUOUS WAVE DOPPLER
~ never appears with CW Doppler
~ range ambiguity limitation where exact location of moving blood cells cannot be determined (results from overlap blending of transmit and receive beams to form spectrum)
ALIASING FLOW REVERSAL
~ colors touching each other correspond with map (flow reversal indicated thru middle of map, aliasing indicated thru outside colors on map)
A MODE DISPLAY
~ appears as a series of upward spikes
~ x - axis represents reflector depth
~ y - axis represents strength/amplitude
AMPLIFICATION / RECEIVER GAIN
~ first function of the receiver
~ measured in db (typically 60 to 100)
~ required as electrical signals are too low to be displayed
~ each electronic signal returning made larger
~ ALL signals undergo an equal amount of amplification
~ patient exposure are not altered with amplification changes (unlike output power)
~ amplification alone cannot make an image uniform in brightness top to bottom
~ does not improve signal-to-noise ratio since they are amplified equally