Duplex / color Flow imaging (LE) Flashcards
Calcific shadowing
Limitations
Df= 2 Fo V Cos 0
c
The Doppler equation
Df
Doppler shift
Fo
Carrier Frequency
Transducer frequency directly related to doppler frequency
V
Velocity of moving reflectors
Cos 0
Angle
c
Speed of ultrasound through soft tissue
Speed of ultrasound through soft tissue is
1540 m/sec
The number is 2 represents
two Doppler shifts (in and out)
Ideal Doppler angle for vascular exams is
60 degrees
Not reliable Doppler angle is
> 60 degrees
For native arteries you scan with what type of probe
7 - 5 MHz frequency linear array
If a > 50% diameter reduction is suspected obtain
Pre- stenotic PSV
PSV (highest) in stenosis
GSV - taken out
Small end is now Proximal
Large end is distal
Vein valves stay open due to arterial flow pressure
Branches are ligated (tributraies are cut off)
Reversed saphenous vein graft (RSVG)
GSV stays in place
Small end is distal ‘
Large end is proximal
Prior to surgery, valves broken up with special instrument; branches ligated
In - situ Vein graft
Inflow artery
Proximal anastomosis
Entire length of the vein bypass graft
Distal anastomosis
Outflow artery
Also check for branches (that could form AV fistulas), valves, and or other abnormalities
Vein bypass graft evaluation
Inflow artery
Proximal anastomosis
mid graft
Distal anastomosis
Outflow artery
Synthetic bypass graft evaluation
Doppler signals are triphasic
Some patients may have biphasic flow without any disease
Normal
2:1 ratio =
> 50% diameter reduction
4:1 ratio =
> 75% diameter reduction
> 400 cm/sec PSV =
75 percent diameter reduction
Pre - stenotic Doppler spectra
(monophasic) and dampened
Doppler spectra obtained AT the stenosis
Highest PSVs documented
Post stenotic turbulence and decreased PSVs
> 50% stenosis
Lower resistance flow patterns may normally be expected.
Some retrograde flow in the native artery may be evident at the distal anastomosis of RSVG, which proves and additional source of collateral flow. (retrograde flow results from a pressure gradient)
Normal
Decrease in ABI of > 0.15
Observes for post-complications such as: AV fistula (can siphon off graft flow); valve cusp
Insitu only- if tributary is not ligated
Abnormal findings
Anastomosis sites should be evaluated well for aneurysm and/or stenosis
Can loosely apply the previous data to determine whether a > 50% diameter reduction exists
Observe for graft occlusions
Synthetic grafts
In general velocities stented arteries may have elevated peak systolic velocities
Greatly elevvated peak systolic velocities are abnormal and suggests hemodynamically significant diameter reduction
Post endovascular intervention
Gray scale is most important
Used for checking patency of the anastomotic sites
Evaluate any suspicious stenotic or turbulent areas that can occur in vein bypass grafts
Use highest frequency imaging transducer available
Intraoperative monitoring
