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CT and MRI scans do they use the same contrast?

hi all. I am asking a question on behalf of my 76-year-old mother. In an office visit recently her endocrinologist told her he would like her to go get a CT of her abdomen, with and without contrast. primarily this is to look at her adrenal glands which she has an ongoing issue with. We reported to him that she has had an allergic reaction to contrast die in the past. He then said she could instead have an MRI with and without IV contrast. We are a little uncertain if that is different, and obviously we don't want her to get severe hives again.
we are a little shaky on her history of contrast and whether her reaction was to oral contrast or IV.
so our questions right now are:
are oral and IV contrast different where she may be allergic to oral and not IV?
are CT and MRI contrast different where she may be allergic to CT and not MRI?
are there different types of contrast and what types can cause allergic reactions?

thank you!
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Avatar universal
Regarding intravenous contrast, the type of contrast is different between CT which uses iodinated contrast versus MRI which uses gadolinium contrast. According to the American College of Radiology (ACR) Manual on Contrast Media, there is no cross-reactivity between different classes of contrast medium. For example, a prior reaction to iodinated contrast medium does not predict a future reaction to gadolinium contrast medium, or vice versa.

Regarding oral contrast, the most common agent used is barium sulfate, which is inert; hence, there is no appreciable risk of an allergic reaction (something like 1 in 750,000). However, some institutions use iodinated contrast made for intravenous injection but dilute it and administer it orally; since approximately 1-2% of this is absorbed through the gut, there is a theoretic risk of an allergic reaction. While oral contrast is administered for most CT abdomen/pelvis, it is typically not administered for most MRI abdomen, with some exceptions such as MRI enterography which evaluates the bowel.

Source: https://www.acr.org/-/media/ACR/Files/Clinical-Resources/Contrast_Media.pdf
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Avatar universal
Regarding your mother's case, it is statistically most probable her prior allergic reaction (hives) was to intravenous contrast rather than oral contrast. Adrenal pathology can be evaluated with different modalities, including CT, MRI, and PET/CT. For CT, the typical protocol is adrenal protocol CT abdomen with and without contrast, which consists of precontrast, postcontrast at 1 min, and postcontrast at 15 min. For MRI, you can get by with just doing MRI abdomen without contrast, because the key sequence is precontrast in- and out-of-phase which will tell if you if the adrenal nodule is an adrenal adenoma versus not an adrenal adenoma. The addition of contrast on MRI is not essential and will add little additional information. While some pathology such as pheochromocytoma may demonstrate intense enhancement, there are other clues such as "light bulb" bright appearance on MRI T2-weighted sequence as well as clinical and/or laboratory presentation that would raise the possibility of this diagnosis. To sum up, it is probably adequate for your mother to get MRI abdomen without contrast. Alternatively, if there is clinical concern for ruling out metastasis, consider PET/CT; this injects nuclear material for the PET portion but does not inject iodinated contrast for the CT portion (at most institutions).
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wow thank you CHIN_C for all the great details! I am a little less concerned now that the MRI seems unlikely to use iodine. We will be sure to ask if the IV is iodinated. I think maybe a little more history might also be helpful,
my mother's reaction to contrast was during a stress test it probably was a stress test before hip replacement surgery or a heart stent/angioplasty

Fast fwd 10 years she also gets a knee replacement surgery and in the hospital has heparin treatment to avoid clots. But then she suffers from "Bilateral adrenal damage (BAD) due to heparin-induced thrombocytopenia (HIT) and is taking hydrocortisone. We are told this is rare. To be even rarer the test for HITS at first comes back as negative. A subsequent and different test confirms HITS.

she is taking hydocortizone permanently now 1 attempt to lower the hydroconrtizone show her adreanals do not function

endocronologist stated the CT or MRI was to see if nodules he saw in previous scans in the adrenals have dissipated. we take that to mean the blood clots that formed from the heparin
There are different types of cardiac imaging tests, including stress echo, nuclear medicine, and CTA cardiac, so not sure which one your mother had. If the reaction was during coronary angiography/angioplasty, that uses iodinated contrast.
Avatar universal
Thank you providing the reason for evaluating your mother's adrenal glands. The more common indications for performing adrenal protocol are to evaluate an adrenal nodule to determine if it is an adrenal adenoma versus something else such as a metastasis. In these cases, performing the CT with and without contrast and obtaining images at precontrast, postcontrast at 1 min, and postcontrast at 15 min are necessary to calculate the washout. In your mother's case, it sounds like the reason for the study is not to characterize a nodule and/or rule out cancer but rather just to evaluate the evolving morphology of the adrenal glands. Hence, I am not really sure if contrast is that critical, but you can discuss further with the ordering doctor (endocrinologist) and/or interpreting doctor (radiologist) who are more familiar with the details of your mother's case. Your mother's case is very unique, so rare I had never encountered it before and had to search the medical literature on PubMed. Here is one case report that sounds similar to what you are describing:


It basically results in a form of adrenal insufficiency. Adrenal insufficiency presents differently at different stages and is best imaged with CT. In the acute phase, the adrenal glands appear enlarged, heterogeneous, and hyperdense (hemorrhagic). In the subacute phase, the adrenal glands appear enlarged with decreased density (caseation or necrosis). In the chronic phase, the adrenal glands appear chronic, small, and atrophic, with or without calcifications. To sum up, it is probably sufficient to get CT or MRI abdomen without contrast, slightly preferring the former since it can better see calcifications and is less susceptible to patient motion artifact.
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thank you again CHIN_C for the detailed answers and followup. my mom is going to have another conversation with her doctor and see if the contrast is definitely needed.  if you practice in NJ I would tell her to come to you for a second opinion!
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