Eli5:Why would you get an MRI with AND without contrast?

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From my understanding, an MRI with contrast provides a much better image and you can get a lot of info from it. I also understand that there are risks with contrast/possible allergies and certain contraindications. And I understand that mri without contrast can be sufficient in many cases. So why would a doc order an MRI with AND without contrast? Why not just with?

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If you are getting an MRI with different parts of a body, the doctor might order only part of the test with contrast to minimize the amount of contrast they inject into you.

Gadolinium (the MRI Contrast) is injected at a specific rate per 15 seconds during the stage of the MRI that needs it. If you are getting multiple areas and only 1 needs contrast, they can just inject the contrast during that part, minimizing the amount of gadolinium you have injected.

This may reduce the amount of adverse reactions. Studies vary on this. Its also very expensive, so reducing the amount used would have a cost benefit.

I’ve been a MRI Technologist for 7 years and injected at least a third to half of my patients with gadolinium based contrasts. Not all exams need contrast. But I have scanned patients and seen nothing, injected the contrast ordered and like a lighthouse in the middle of the night there’s the tumor, it’s not until I locate it after contrast that you can barely make out the tumor in noncontrast images, the difference in some cases is just a very slight difference like comparing kelly green with Forrest green sometimes the gray scale is just slightly different.

Contrast is a tissue differential, it will highlight tumors that are feeding off your blood supply, identifying tumors. The amount usually given is 1cc per ten pounds of weight of the patient, no faster than 1cc per 2 seconds, most gadolinium based contrast have a low allergic reaction. I can count all reactions during my career on both hands and its nausea most of the time, but if given faster than recommended, over 2 seconds per 1cc you will have a reaction.

If your exam is to rule out tumors, i.e. sudden issues with brain function or organ failure in the abdomen or pelvis, or prior history of cancer, positive PET or CT scan, rule out a mass seen on ultrasound, contrast would be highly recommended by your doctor but…
Injuries sustained from repetitive use or accident, do not need contrast all of the time, you would have to come back for contrast if a mass is seen on the exam. Some doctors will order an arthrogram which is contrast injected into a joint space to better see small tears in ligaments and tendons but for the most part these can be seen in most MRIs.

If you’re concerned about an allergic reaction have it done at a hospital with a staff that can better treat you if it happens. Each hospitals protocol is different, so ask first, you are in control of what goes into your body.

Hope this helps

The one reason I am positive about why a person would chose not to use contrast is based on kidney function. When my mother had one working kidney and was a transplant patient every time we took her to the hospital we were told by her nephrologist to never allow contrast unless it’s life threatening. Apparently the contrast can damage the kidney or let’s just say it’s hard on the kidney. It wouldn’t damage it if you had a properly functioning kidney but once it’s struggling it could make it struggle more. And if you only have one kidney that was donated from another human being (most likely as a result of them dying), you protect that kidney with your life. So even when it’s working properly you baby it and don’t take anything that could harm it or make it weaker. The gift of life is hard to come by.