Vascular Ultrasound Q&A with Leading Experts in Vascular Sonography

You asked, and our experts answered!  Our most recent Vascular CME Webinar was a success and Mindray is pleased to present the following questions and answers from that session to share you and with our Mindray Insiders!

Volumetric Flow Rate Q&A

with Vascular Sonography Expert Tony Smet, BS, RDMS, RVT

Educator and Vascular Sonographer
San Leandro, California

After serving eight years of service at home and abroad in the Air Force, Tony Smet decided to make a new career in Vascular Technology. He specializes in noninvasive vascular procedures including: cerebrovascular, arterial peripheral imaging and physiological testing, upper and lower peripheral venous imaging, dialysis access imaging, renal hemodynamic testing and abdominal arterial and venous imaging.

2.  Is obtaining three cycles absolutely necessary for flow volume?

Best practice is to obtain at least three, but you can obtain more. The white paper methods described three-to-five waveforms as being acceptable. This is because are obtaining an average velocity, so we want to average at least three waveforms for accuracy.

3.  What is the criteria of AVF stenosis?

There are several published peer reviewed criteria. Your lab leadership needs to determine what criteria they would like to use.

4. Why is there no cursor in the dialysis access Doppler images? Are we not supposed to use a cursor indicating a 60-degree angle?

The Volumetric Flow Rate auto measurement feature on the system I use removes the angle correction line (after you angle correct) from the center of the lumen and places it at the walls to ensure you are true to the wall.

5. Why is color Doppler not used for the VFR evaluations? Are there diameter parameters for an accurate VFR?

Color is not used so the walls can be clearly identified/acquired and measured precisely.

6. What happens if my sample volume/ gate is outer to the outer wall when measuring VFR?

Having the sample gate outside the wall, or even into the tissue will not significantly alter your Volumetric Flow Rate, however, could create instability in your Doppler spectra due to wall noise the machine will pick up when the vessel pulses.

7. If intimal thickening is present, do you measure the residual lumen?

Yes, the lumen diameter is to be measured. Optimally, a different location, without wall abnormalities is chosen to capture the measurements.

8. What does it mean if the Volumetric Flow Rate (VFR) flow rate is really high or really low?

There are many reasons for high or low VFR. Reasons for high VFR could be a large diameter, an overactive access, or tech error (sample volume not open and only capturing highest velocities in calculation). Low VFR could be attributed to a severe stenosis limiting flow, a small access that has not yet matured, or underestimating the diameter of the access.

9. What should you do if there is not a straight segment, or the entire segment is aneurysmal?

Some dialysis accesses do not have an ideal segment to measure. You can create a lab policy with your leadership to decide if they want you to take a VFR and note it is over/underestimated or decide to not take the measurement. This should be noted in the report, so it is understood as well.

Peripheral Arterial Duplex Ultrasound Q&A

with Vascular Sonography Expert Laurie Lozanski, RVT, RVS, CCI

Educator and Vascular Sonographer
Chicago, IL

Laurie Lozanski is an adjunct faculty member for the College of Health Science at Rush University in Chicago where she serves on the Vascular Ultrasound Board of Advisors and has been teaching vascular ultrasound to undergraduates for 20 years. She also holds the position of Technical Director of the Non-invasive Vascular Laboratory at the University of Chicago and has co-authored two textbooks on vascular ultrasound and presented at national meetings.

2.  Should you not do a color invert, when you see blue color in deep femoral artery?

You shouldn’t automatically invert your color just because you know the flow should be “red” or towards the feet, away from the heart for example. Before you do, orient yourself and try to understand what is happening with the flow. Maybe there is an occlusion above the segment and the artery is acting as a collateral as the example illustrated in the talk. It is vital that each vascular sonographer be able to determine flow direction in any vessel. If the flow is reversed in direction, it should be shown as reversed (blue) in both color and waveform on the spectral tracing so that anyone who looks at the image can see that there is reversal of flow.

3. Should we invert the color and waveform when we see reversed flow throughout a vessel?

It is vital that each vascular sonographer be able to determine flow direction in any vessel. If the flow is reversed in direction, it should be shown as reversed (blue) in both color and waveform so that anyone who looks at the image can see that there is reversal of flow. Then it can be determined as to why.

4. What is the major concern in peripheral aneurysms?

Blood clots and distal emboli.

5. Which flow condition is the most common site for arterial disease development?

Flow at branch points.

6. What could be the cause of the spectral window filling on the PW doppler trace?

 There could be several causes:

- Doppler gain is too high

- Sample gate is placed at an area of flow separation

- Reynold’s number is greater than 4000.

7. Why is the sample waveform shown considered biphasic?

We would describe this waveform as "biphasic" because of the upstroke. It still has a sharp upstroke ("straight up") and forward flow in diastole that does not reverse (or dip below the baseline). The upstroke or systolic phase of a monophasic waveform is more rounded in comparison

8. Should we always keep the gate wide in an artery?

Not always. Wide gates are best to detect flow when you suspect venous or arterial occlusion. Wide gates are also important when you are measuring volume flow, for example in a dialysis access. Two examples of when small gates are appropriate would be when you want to pick up a tight stenosis or high flow (like in the setting of an AV fistula). Larger sample gates often result in too much spectral broadening and that might affect the accuracy of your spectral Doppler measurement or characterization of the waveform. Also, sometimes if your gate is too wide, you might pick up flow that you don't really want to, like from the adjacent vein or a collateral coming off.  Thirty years ago, before duplex systems had color flow, we would always use a wide gate so we could sample flow across the whole artery. But now, you can use appropriately adjusted color flow scales as an additional tool to find segments suspicious for significant disease.

9. Where is the correct area to place the sample in the CCA bulb?

Whenever you are in a bulbous segment, there is probably going to be some flow separation happening. Normally, using color flow can help guide you where to place the sample gate so you can document representative antegrade flow. It might be along the far wall or maybe along the near wall, it just depends.  If there is luminal reduction or a significant stenosis in the distal CCA, at the ostia/proximal segment of the ICA, then you should place your sample gate wherever the highest velocity seems to be.    

The Role of Color Duplex After EVAR Q&A

with Vascular Sonography Expert George Berdejo, BA, RVT, FSVU

Educator and Vascular Sonographer
White Planes, New York

George Berdejo has been in the vascular ultrasound field for almost 40 years and is currently the Director of Vascular Ultrasound Services at White Plains Hospital in White Plains, NY. He is a past President of SVU, Inaugural President of the SVU Foundation and Inaugural Chair of its DE&I Council. He serves as Co-Chair of the Annual Conference Committee and Chair of the AVID symposiums.

2.  A significant advantage to DU over CTA is obviating the need for an IV infusion of a potentially nephrotoxic contrast agent and giving the patient a full abdominal dose of radiation.

3.  Any work on off label use of contrast imaging for technically difficult patients? Especially renal compromised patients?

There may be a role for contrast enhanced ultrasound (CEUS), however I do not think this is true for routine surveillance especially in the context of stable/shrinking residual aneurysm sac size as studies have shown that non-contrast US is performing equal to or better than computed tomography for the detection and classification of endoleaks…in good hands.
One exception may be the patient with increasing aneurysm sac size with compromised renal function in whom the standard duplex scan does not detect endoleak. The CEUS may add information that was not seen. If there is a relatively recent prior CTA available, one might proceed directly to angiography for therapeutic purposes.

Vector Flow has the potential to predict cardiovascular disease rather than simply diagnose and monitor progression. With advanced analysis tools such as Oscillatory Shear Index (a method of measuring turbulence of flow) and Wall Shear Stress (considered as a key factor for atherosclerosis development), this technology is on the forefront of predicting and quantifying vascular and neurovascular conditions.

4.  Are some endoleaks more dangerous than others?

•    Types 1 and 3 (direct pressure leaks) are the most dangerous because they have the highest risk of rupture.

•    Type 2 endoleaks are the most common type of endoleak, accounting for approximately 50% of all endoleaks. However, they are usually benign and have a very low risk of rupture. Up to 90% of type 2 endoleaks resolve spontaneously or are not associated with sac enlargement. However, there is literature that suggests that a low-resistance, high-flow or to-fro flow type 2 endoleak has higher chances of sac enlargement, rupture, and requiring reintervention.

•    Type V endoleaks are characterized by enlargement of the aneurysm after EVAR without visible blood flow in the aneurysmal sac by any of the imaging modalities. There is currently no consensus on how to manage type V endoleaks.

5.  Do you change surveillance intervals according to the type of endoleak?

We have in our practice. Types 1 and 3 (direct pressure leaks) generally go on to CTA scan and intervention.

Type 2 with stable size/small increase who exhibit low-resistance, high-flow or to-fro flow type who have relative contraindications often are seen at shorter intervals to assess for aneurysm sac enlargement.

6.  Does the presence of endoleak mean that the patient requires intervention?

Type 1 and type 3 endoleaks are repaired in all instances because they represent direct communication of the aneurysm with the systemic circulation.

Type 2 endoleak management is more varied, with roles for observation and embolization depending on changes in the residual aneurysm sac size.

7. What percent of people with AAA and pop aneurysm  have  been found with cerebral aneurysm?

Studies suggest that the co-existence of AAA and cerebral aneurysms, also known as intracranial aneurysms (IA), is higher than their individual prevalences in the general population. Estimates of this co-prevalence vary, ranging from 5% to 22% of patients with AAA also being found to have an IA. Other sources cite a prevalence of 7.2% for IA in patients with AAA.

There's a well-documented association between popliteal artery aneurysms (PAA) and AAA. Approximately 30% of patients with PAA also have an AAA, according to the American Heart Association Journals. Given this, while a direct percentage for PAA and IA isn't readily available, the association between PAA and AAA suggests that patients with PAA could have a higher likelihood of also having IA than the general population. A systematic review found that approximately one in four patients with a popliteal artery aneurysm harbors an additional aneurysm at a different location.

8.  What are your thoughts on using contrast to assess endoleak on a challenging patient?

I have not used contrast since my very early experience when we were investigating its efficacy. Where there has been sac shrinkage, the likelihood is that there will be endoleak is small. If there is sac expansion that warrants intervention, even when the duplex is endoleak negative, a CTA scan is in order. We do not feel that the additional time and effort is warranted. If the sac size is stable, we simply continue with the prescribed surveillance schedule.

9.  I work in a vascular lab, but I don’t evaluate enough EVARS, where could I get more training in this?

I think that going to the SVU Annual Conference is a good start. They often have both lectures and hands-on workshops around EVAR assessment. You might also try contacting the SVU office, 651-288-3431 or the website SVU.org for information regarding working with a mentor who can help.