How to find and recognize the SMA by Ultrasound for sonography students

Superior Mesenteric Artery;  Go from SMApprehensive to SMAwesome

The Mesenteric Arteries are often requested by physicians to be interrogated with Doppler to rule out abnormalities in flow that could contribute to bowel conditions such as ischemia. I also include it in any Doppler request, even if its only the hepatic vessels being requested–just because I love it. You should try to love it too. It makes you more valuable to Radiologists and to techs who loathe the little blood bearing beasts. So lets start with the SMA.

The SMA is one of the easiest arteries to find by ultrasound really, especially once you become familiar with the waveform which is VERY high resistance (in an NPO state). Place your probe up by the xyphoid process, where you would place it to get the left lobe of the liver.

You’ll notice the aorta rising up towards your probe (aka anteriorly). Turn your color on–the SMA has very prominent flow and turbulent appearance at its origin–and its easy to distinguish from the celiac–which will come into play as the first branch off of the abdominal aorta–because remember that the SMA runs sagittal–along WITH the aorta–if you can find the aorta, you’ll also have the SMA in view. Its only about 1 cm from the celiac axis, and its velocity is much greater than the aorta–SMA is around 200-300 cm/s with a more narrow lumen-the aorta will be under 100 cm/s and more visibly pulsatile.

The waveform for the SMA is VERY distinct. This is what normal looks like.

Abnormal:notice how very sharp and peaky the waveform is in systole, diastolic velocity is elevated and there’s no dip below baseline as you see in the normal waveform, the peak systolic velocities are in excess of 300 cm/s with ischemic disease/stenosis.

 

So, there you go, you’re an official SMA waveform interpreter…. bet you cant wait ’til your next NPO patient comes in for a simple gb ultrasound…I know you’re gonna slide on over and check out the mesenteric arteries…mmm hmm, just make sure you turn down the volume on your PW dial so you don’t freak the patient out (or find yourself at the end of a patient’s insatiable appetite for answers!). Good luck, SMA sleuth!