First and foremost - Patient Prep! Your patient prep is one of the most important factors when performing Mesenteric Duplex Ultrasound. Your patient needs to be NPO for at least 6-8 hours before scanning. A test done without the right prep, might as well have not been done at all. This is for a number of reasons:
1. You can't see squat with air and gas in the way!
2. The mesenteric arterial system should be scanned both pre and post prandial for evaluation of stenosis and arterial ischemic response.
•Branching of Common Hepatic Artery and Splenic Artery from the Celiac Artery
•SMA origin, proximal, mid, distal
•IMA origin, proximal and as distal as possible
1. Patient position is an important factor to remember. You should position your patient in a slightly elevated/supine position. This allows for a better view with less pressure on the diaphragm. Another trick is to have your patient lay supine and bend their knees. This also reduces pressure and tension on the diaphragm and allows for better visualization of the structures near the xyphoid process (ie. proximal aorta, celiac trunk, SMA). Having the patient sit erect can also help with evaluation of median arcuate ligament compression and if images are limited otherwise.
2. Using patient respirations to control the movement of structures and improve image quality (especially for Doppler waveforms). Respirations also help to evaluate for median arcuate ligament compression is sometimes a major factor in diagnosing this condition. Patient's with median arcuate ligament compression will have mildly elevated flow in the Celiac Artery with inspiration (this is normal). However, with expiration, the artery will be compressed by the median arcuate ligament and will cause an extrinsic obstruction due to compression and a marked increase in flow velocity. Using patient respirations to assess for this is a major factor of the Mesenteric Duplex exam.
3. Use Power Doppler - on those difficult patients, power Doppler can be your savior! This can also be used to visualize the Celiac Branches, the IMA and other smaller vessels.
Remember that the Celiac Artery supplies the liver, spleen and stomach, which are low resistance vascular beds. Normal Doppler waveforms will show increased diastolic flow because of the organs supplied. Flow may also increase with inspiration.
Don't forget to evaluate the branches! This is best done in a transverse plane.
≥70% Celiac Artery Stenosis will show a peak systolic velocity of ≥200 cm/s.
Remember that the SMA supplies the jejunum, ileum, and both the right and transverse colon. Because of this, waveform characteristics will vary based on state (ie. NPO, post-prandial). Diastolic flow will increase as needed for digestion, post-prandially.
In the normal vessel, post-prandial evaluation should show increased peak systolic flow velocities. If PSV flow does not increase, this is suggestive of a hemodynamically significant stenosis. Also keep in mind that inspiration will show an increase in peak systolic velocities.
≥70% SMA stenosis will show a peak systolic velocity of ≥275cm/s or absence of color flow in the SMA. End diastolic flow velocities of ≥45cm/s are also an indication of ≥70% SMA stenosis.
Also keep in mind that you can find pathology based on the angle of the SMA takeoff from the aorta. If the angle is markedly increased, it may indicate the presence of adenopathy. The SMA should course parallel to the aorta.
The IMA supplies the distal 1/3 of the transverse colon, splenic flexure, descending colon, sigmoid colon and rectum. It's waveform characteristics are similar to the SMA and will vary based on state (ie. NPO, post-prandial). Diastolic flow will increase as needed for digestion, post-prandially.
≥70% IMA stenosis will show a peak systolic velocity of ≥275cm/s or absence of color flow in the IMA.
You may need to get your magic wand out for this one!
Lara Miller, RDMS, RVT, RDCS, RCCS
Diagnostic Criteria Reference: Moneta, et al