Chapter 21 - Vascular lab - arterial duplex Flashcards
Two parts of duplex
1) blood flow acquisition = pulsed doppler spectral analysis 2) anatomic = B-mode and color doppler imaging
Duplex frequency for artery
5-12 MHz
Duplex frequency for visceral or abdominal and transcranial doppler
2.5-3.5 MHz lower frequency = higher tissue attenuation
Duplex image orientation
left towards head
Two types of doppler ultrasound display
1) color flow doppler - flow velocity distribution over wide area 2) spectral doppler - time-varying flow velocity distribution at selected sample volume
Optimal scan line angles for doppler
60 degrees or less relative to transducer insonation beam and arterial wall
Doppler angle + or - 5 degrees away from recommended 60 results in this much measurement error
+5 = 15% -5 = 8%
Pulse doppler sample volume criteria
1) size to < 1/3 of flow lumen 2) center stream of flow
Color gain setting on duplex
1) increase gain until noise speckle appears within flow region 2) reduce slightly after that
Excessive color gain problem
1) color-coded flow pixels bleed into or beyond artery wall 2) makes flow lumen appear larger than reality
Blood flow velocity exceed mean peak velocity threshold of color bar
1) color aliasing
Nyquist limit
When sampling rate defined by pulse reptition frequency no longer sufficient
What does color aliasing look like
Wraparound color show in color bar showing flow in opposite direction
How to fix color aliasing artifact
1) increase pulse reptetition frequency 2) increase doppler angle
Color doppler appearance of stenotic lesion
Post-stenotic turbulence with flow jet mosaic color flow
Tissue bruit
vibration of arterial wall appear as low velocity flow signal outside of artery lumen
Power doppler
Display blood flow based on amplitude of backscattered signal increase sensitivity 3-5x “color angio”
B flow imaging
1) shows blood flow in gray scale 2) demonstrate complex flow patterns at bypass graft anastomoses and AVF
What does broadening or increased width of velocity spectra mean spectral broadening
1) sample volume of pulse doppler too large 2) too close to arterial wall
Velocity spectra waveform parameters used to interpret duplex
TABLE 21.1
Resistive index calculation
(PSV - EDV) / PSV
Normal resistive index
< 0.7 Abnormal >0.85
Pulsatility index calculation
peak-to-peak velocity spectral shift DIVIDED BY mean velocity
Normal pulsatility index
> 4 (femoral > 6; popliteal > 8)
Damping factor calculation
Division of distal artery pulsatility index by proximal artery pulsatility index
Normal damping factor
> 0.9
Systolic acceleration time during systole - normal value
< 133 ms
Tardus-parvus
Slow systolic acceleration usually > 200 ms rounded upslope configuration on duplex
Mirror image artifact what is it and cause
Tissue structure reproduced at an incorrect location When strongly reflecting surface is further reflected by other strongly reflecting surfaces
Refraction what is it and cause
misregistration of image and doppler sample volume when ultrasound beam passes through mediums with different propagation speeds
Crosstalk what is it and cause
mirror image when identical spectra appear above and below baseline when excessive receiver gain setting or incident angle near 90
Ghosting what is it and cause
when low velocity motion from pulsating vessel walls produce small doppler shift that cause color flashing into surrounding anatomy fix with wall filters
PSV ratio across stenosis correlation with diameter reduction
> 2 is > 50% stenosis > 4 is > 70% stenosis
Signs of pressure-reducing arterial stenosis
1) PSV ratio > 3.5 2) PSV > 250 3) EDV > 40
PSV measurement variation that’s normal
+/- 15%
Artery diameter and PSV in healthy subjects in various segments
TABLE 21.2
Duplex classification of PAD in terms of degree of stenosis
TABLE 21.3
Using PSV ratio > 2.5 to define significant stenosis on duplex sen, spe and accuracy
Sen, spe, accuracy = 76, 93, 89%
Duplex criteria for 50-75% stenosis
> 50% PSV > 200 PSV ratio > 2.5 > 75% PSV > 400 PSV ratio > 5 EDV > 40
Velocity of CFA that signify proximal iliac lesion
< 45 cm/s with monophasic waveform
Risk stratification for vein graft occlusion based on duplex
TABLE 21.4
Time to repair based on risk stratification on duplex for vein grafts for each category
Category 1 = prompt repair Category 2 = elective repair 1-2 weeks Category 3 = serial scan 4-6 week interval Category 4 = 6 months rescan
PSV predictive of prosthetic graft failure
> 300 cm/s < 60 cm/s
duplex finding correlated with treatment failure after peripheral intervention
PSV > 300 PSV ratio > 2 ABI decrease > 0.15 abnormal CFA waveform analysis
