doppler instrumentation & hemodynamics Flashcards
what would be the most likely result form lowering color threshold?
increased visibility of small vessel flow in a parenchymal organ
increased color writing on the vessel or wall
decreased flash artifact
increased frame rate
improved color peneatration
increased color writing on vessel or cardiac wall
threshold controls brightness of shade of gray that color is allowed to overwrite
if you inc doppler transmit freq what will happen? velocity will increase penetration will increase frame rate will increase doppler freq shift will increase nyquist limit will increase
doppler freq shift will increase
what would be the result from increasing the transmit freq of color doppler?
improved penetration for imaging flow in deep tissues
reduced flash artifact obscuring sm vessel flow
reduced color doppler aliasing
improved visibility of complex flow hemodynamics
improved sensitivity to flow
improved sensitivity to flow
you have inc the packet size while using color doppler to evaluate flow. what negative result will occur? decreased frame rate decreased penetration decreased flow sensitivity increased variance increased spectral broadening
decreased frame rate
inc packet size inc the number of pulses per scan line
you measured an area reduction of 90% in this artery. this is equal to a diameter reduction of?
75%
area percent stenosis and diameter percent stenosis are not equal; 50% diameter stenosis = 75% area; 75% diameter = 90% area stenosis
when color doppler is activated; in order to maintain frame rate; what may be reduced in the b-mode image? the number of focal zones scan line density frame averaging a&b b& c
a& b
decreased pressure occurs in areas of high flow speeds known as: continuity rule bernoulli effect reynolds number poiseuille's law nyquist limit
bernouilli effect
describes decreased pressure that occurs at a stenotic site as a result of the inc blood velocity w/in the stenosis
what two controls affect the spatial res of the color image? line density and ensemble length ensemble length and priority freq and ensemble length priority and freq freq and line density
freq and line density
after a short walking exercise the venous pressure at the ankle of a standing normal subject:
is lower than the standing ankle pressure at rest
is greater than the standing ankle pressure at rest
is the same as standing ankle pressure at rest
is not affected by chronic venous insufficiency
is not affected by DVT
is lower than the standing ankle pressure at rest
what is the advantage of using high PRF doppler? improved range res higher frame rate ability to measure high velocities greater sensitivity to slow flow improved spatial res
ability to measure high velocities
what limitation is present when you use high PRF doppler? frame rate spatial res sensitivity to slow flow range res both c & d
both c & d
high pro mode increased the # of pulses per sec that any single transmit pulse have been sent out along the dopppler beam line before echoes arrive from the sample volume
while evaluating liver vasculature with color, you are unable to obtain signals from deeper vessels. what should you do to enhance deep flow? decrease packet size inc scan line density inc wall filter decrease u/s freq inc prf
decrease u/s freq
lower freq have inc penetration compared to higher freq
which control optimization should you make to improve color doppler sensitivity to slow flow? lower the packet size lower the wall filter lower the transmitted u/s freq raise the PRF lower threshold
lower the wall filter
what aspect of the doppler spectrum is color encoded with color doppler? ampllitude power velocity bandwidth freq shift
freq shift
what describes the axial length of the sampling vol for a color pixel? packet size prf prp color gate line density
color gate
a commonly used process for determining direction in a doppler instrument is? zero crossing detecting phase quadrature detection autocorrelation range gating spectral analysis
phase quadrature detection
what is likely to result from inc transmit freq of color doppler?
improved penetration for imaging flow in deep tissues
reduced flash artifact obscuring sm vessel flow
reduce color doppler aliasing
improved sensitivity to slow flow
improved visibility of complex flow hemodynamics
improved sensitivity to slow flow
inc color dopp transmit freq will result in lg freq shifts from slow flow & improved visibility. it will decrease penetration to flow in vessels deep in tissues
according to the doppler eq, for any given velocity, the req shift will inc by inc the: doppler angle transmit freq pulse length prf all of the above
transmit freq
at low velocities, RBCs adhere to one another forming multicellular clumps: rayleigh scattering huygens principle newtonian fluid rouleaux formation parabolic flow
rouleaux formation
what does the doppler signal spectral display depict?
depth to ea vessel
vol flow rate
transmit freq
acoustic power
relative signal power at ea freq in doppler signal
relative signal power at ea freq in doppler signal
your patient has edema involving right lower extremity caused by: dec venous htn dec venous hypervolemia inc venous hypovolemia inc intravenous pressure inc extravascular pressure
inc intravenous pressure
you inc packet size while using color dope to evaluate flow. what negative result occurs? dec penetration dec frame rate dec flow sensitivity inc variance inc spectral broadening
dec frame rate
color flash artifact is obscuring anatomy of interest in and aorta. what can reduces the impact? inc color gain dec PRF inc packet size inc doppler transmit freq inc wall filter
inc wall filter
flash artifact is high amp low freq shift signal
reynolds number inc with inc: flow speed vessel diameter blood density blood flow viscosity all of the above
all of the above
