Is there such a thing? I remember when I was a rads resident we did CTA for GI bleed and now that I work in the ED with a large geri population, I wonder if I can just order my CT abd/pelvi as a CTA abd/pelv to r/o x, y, z, mesenteric ischemia... Is there a difference in contrast load? Does it affect sensitivity in detecting other pathology?
mesenteric phase CT abd/pelv?
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CT for GI bleed should be noncon, arterial, PVP
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You don't want to skip the noncon because hyperdense fecal material can look like extravasated contrast. You need the noncon to compare.
You don't want to do a split bolus because the portal venous or systemic venous delayed phase is meant to look for the contrast to spread out. A hypervascular polyp would light up on the arterial but remain unchanged on the delay.
You don't want to do a split bolus because the portal venous or systemic venous delayed phase is meant to look for the contrast to spread out. A hypervascular polyp would light up on the arterial but remain unchanged on the delay.
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To answer your question, the CTA would be several times the radiation dose compared to the routine portal venous phase CT, because of the additional phases and, secondarily, also higher tube current settings designed to reduce noise / improve resolution to evaluate smaller vessels. The IV contrast volume is about the same. Since the CTA mesenteric is essentially a portal venous phase CT plus two other phases, the sensitivity of detection for other pathology is similar. The possible exception is that the CTA is done without oral contrast (so you can detect contrast extravasation into the lumen). Oral contrast can be helpful for detecting bowel pathology (eg, masses, perforation, inflammation, obstruction) particularly in patients who are not overweight or have had bowel altering surgery.
Cool, thanks a bunch for that helpful info. My main goal is to get adequate imaging of the mesenteric vessels, celiac axis in a single pass CT to look for any lesions that can be treated in case the patient's cause of abdominal pain, rectal bleeding turns out to be mesenteric ischemia so I don't have to get a dedicated CTA. I'm not so much concerned about imaging for hypervascular polyp or obtaining imaging to locate source of bleeding, although, it would be great to see contrast extrav into the lumen to locate source, that to me is more extra information, not the primary goal, and I don't usually give oral contrast anyway. Most of these patients will get an EGD, colonoscopy, capsule to look for source; we don't rely on the CT as much but can't determine a proximal SMA, celiac axis stenosis or large embolic clot cutting circulation on endoscopy.
If there is no added radiation or contrast dose and I can get CTA quality imaging with a split dose bolus timed for mesenteric arterial phase and portal venous phase in a single pass CT, I would prefer that as long as the diagnostic yield is not affected by less contrast during the PVP.
Thanks again
If there is no added radiation or contrast dose and I can get CTA quality imaging with a split dose bolus timed for mesenteric arterial phase and portal venous phase in a single pass CT, I would prefer that as long as the diagnostic yield is not affected by less contrast during the PVP.
Thanks again
Never understand why people are obsessed with radiation savings when the risk of typical diagnostic radiology radiation remains theoretical.
How many lives do you think you’re saving by cutting the radiation in half on your GI bleeding population of 70+ year old patients?
How many lives do you think you’re saving by cutting the radiation in half on your GI bleeding population of 70+ year old patients?
CT abd on GI bleeding pts is not routine. I'm actually adding more radiation, not cutting. I just adding the CT abd to broaden differential as most of them are 70+ and can have weird stuff and not just your daily variceal, ulcer, diverticular bbleed. I'm just trying to optimize my initial screening study as to avoid another study or, ideally, get as much info I can get in least time wasted.
Lol
Lol
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But that's why we are confused at what you are trying to do. It's already a somewhat atypical imaging indication, and if this is actually to identify/exclude another cause for the symptoms, why not do the proper study from the beginning?
If you did an I-, Arterial, and Portal venous, you'd have all the phases in a single trip to the donut of truth. It's not like the patient has to go back to CT for anything. Is this a systems issue at your hospital where a CTA is a pain in the butt to get from technologist inertia or something? The arterial could even be done as a CTA. Everything would be with a single contrast load.
By doing this weirdo-split-bolus mishmash of timings, you degrade lesion detection of everything else while getting a so-so picture of the mesenteric vasculature.
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Split bolus works for Hematuria / CT urogram studies because you want contrast simultaneously in the ureters and portal venous phase at the same time. Because it takes a few minutes to get good ureteric opacification, the contrast washes out of the organs so you can give the rest of the bolus and still see things well. The same technique doesn't work when arterial and portal venous timings are so close together.
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I understand the question now. It's actually a good idea we should consider, as they tried out at BIDMC: Split-bolus single scan CTA for evaluation of mesenteric ischemia. - PubMed - NCBI
The split bolus technique does require a higher total contrast dose to achieve the same level of opacification of relevant structures (really they should call it re-bolus rather than split bolus). But you save on radiation and number of images.
The split bolus technique does require a higher total contrast dose to achieve the same level of opacification of relevant structures (really they should call it re-bolus rather than split bolus). But you save on radiation and number of images.
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The way to do it would be to inject for a PV timing, then maybe 40 seconds later, inject again for arterial. It’s a similar concept as double and triple rule out studies. You *can* do them, but at the cost of either
1. Using way more contrast
2. Suboptimal images for one of the two phases due to timing complexity
The question really is why would you go through the hassle of doing this when you can just scan again?
If it’s a radiation dose reason, then work on dropping overall acquisition dose will be better than trying to get it all at once.
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Yea at some point we'll just be arguing about an incremental change in one theoretical and difficult-to-quantify risk (radiation-induced cancer at diagnostic doses) versus another (contrast-induced nephropathy and physiologic contrast reactions). The consideration of diagnostic image quality should come first in that case.
Can you explain to me why some places don't do double rule out studies?
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