OBGYN physics registry review Flashcards
More superficial the imaging
Choose the higher within the frequency range
More penetration is needed
Lower frequency
ALARA
As low as reasonably achievable
-Reducing acoustic exposure by limiting use of controls that increase output and considering overall scan
-Monitor output display indices (max thermal index TI 0.7 and mechanical index MI)
M-mode
-For fetal heart rate, especially first trimester
-Unable? use cine loop to show cardiac activity
ALARA guidelines
-Exam time should not be extended for non-medical reasons
-Doppler should only be used when clinically indicated and necessary
Color doppler
Important for determining presence and direction of flow
Color flow direction
Top of the scale is positive and bottom is negative (usually red =positive and blue=negative)
Correctly using color doppler
-Size of box should just cover area of interest
-Adjust scale to fit type of flow being evaluated
-Adjust gain so color fills vessel but doesn’t bleed out
PW doppler
Important for quantifying flow velocity and identifying normal perfusion
-ex: RI, PI, S/D ratio
Power doppler
Only when interested in presence of flow
-Benefit: very sensitive to slow flow
-Limitation: no directional information
PRF (velocity scale)
Needs to match type of flow you are evaluating
-Decrease the scale = slower flow or when not sensitive enough
-Increasing the scale = when it’s aliasing
Aliasing
-Mosaic pattern with color
-PW always correlated since the peak cannot be measured accurately
Wall filters and high pass filters
Low frequency/high amplitude
Decrease WF = when not sensitive enough
Gain
Fine tuning only! Adjust scale and wall filter appropriately
-Increase gain to enhance strength of doppler signal
-Decrease if bleeding out of vessel
-High velocity flow
High scale
-Uterine artery
-Umbilical artery
-Aorta/MPA/MCA
