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If you’re having an MRI scan soon, you may have discussed with your radiologist whether you’ll have an MRI with contrast or not. But what’s the difference? Which is better, and why might you need one but not the other?

Read on to find out more about the differences between the two, and why one or the other might be best for you.

MRI with contrast vs without

Image courtesy of Storyblocks.

MRI with contrast vs without: how does each work?

Both methods of taking MRI scans are actually the same. The only difference is that in an MRI with contrast, you either need an injection, or to take orally a solution that will enter your bloodstream. Both kinds of MRI are procedures that are supposed to spot changes in your soft tissue.

MRIs are completely painless. Unlike X-ray scans, MRIs do not use radiation to take images inside the body. Instead, they use a powerful magnetic field and radio waves to create detailed images of your soft tissue.

You will almost certainly have seen an MRI scanner at some point, but you might not have known what it was. MRI scanners are long and large, big enough to lie down in. The way that an MRI scanner works is that it temporarily realigns the hydrogen atoms inside your body; radio waves then interact with these newly configured atoms to produce a very faint signal. This signal is what is produces the actual MRI scan.

Both MRIs with contrast and without use this same method of scanning. The only difference is that the medium you are injected with during an MRI with contrast is magnetic. This makes detail in the soft tissue stand out, since the medium is absorbed by organs and tissue from the bloodstream.

MRI with contrast vs without: image clarity

The main difference between an MRI with contrast and a basic MRI is that one is clearer than the other. An MRI with contrast is designed to highlight certain parts of the soft tissue. As we’ll cover later in the article, this can help your radiologist to diagnose your conditions. In particular, serious developments like the growth of a tumor are easier for your radiologist to spot in an MRI with contrast.

Because a regular MRI scan cannot identify moving fluid, like blood in an artery, the contrast dye makes the bloodstream stand out. Without the dye, the veins and arteries appear as ‘flow voids’, which are plain black in your MRI scan. That being said, an MRI without contrast is still useful. In fact, the majority of MRI scans are performed without the ‘dye’ used in the contrast medium.

MRI with contrast vs without: cancer diagnosis

If a radiologist uses dye during your MRI to make parts of the soft tissue appear more detailed, they are better able to spot tumors as they begin to grow. The image to the left is an excellent example. The second image, of the tumor at an advanced stage, could be made using either kind of MRI scan. It’s so large that you can’t miss it! But in the image to the left, the tumor is only just beginning to form, and isn’t anywhere near as obvious. If a tumor is only just starting to grow, it can be difficult for even a radiologist to spot.

MRI with contrast vs without: assessing MS

MRIs with contrast are an excellent way of tracking the progress of multiple sclerosis. MRI scanning has revolutionized the way that radiologists diagnose MS. In fact, MRI scans are now the primary method of diagnosing MS, to the exclusion of other methods like CT scans. This is because the lesions appear quite distinctly in MRI scans.

MRIs with contrast aren’t actually necessary in diagnosing MS. The lesions are typically fairly easy to spot already. But even so, MRIs with contrast are useful for spotting the formation of new lesions as they form. This can be a good way of finding out how quickly the condition is progressing. This in turn can help your radiologist assess which kind of MS you have. You can have either relapsing/remitting MS, secondary progressive MS, or primary progressive MS.

MRI with contrast vs without: safety concerns

The only drawback to an MRI with contrast are safety concerns. Regulatory bodies do test MRI contrast agents to make sure they are as safe as possible. But it is still possible for you to have an allergic reaction to them. The main ingredient of the most common MRI contrast agent- gadolinium- is toxic if administered on its own. But in the context of an MRI with contrast, the gadolinium injection contains another fluid. This makes it non toxic. Even so, it is still possible for you to experience an allergic reaction.

The reaction is basically the same as allergic reactions in other contexts, ranging from hay fever to anaphylactic shock. If you have a mild allergy, the area around the injection site may itch, and in some cases turn red. A severe allergic reaction will cause the same symptoms as anaphylactic shock. But this is very rare, and only affects 1 in 10,000 patients. The good news is that any center like ours which offers MRI with contrast has to stock medication that can reverse the condition (like an EpiPen).