What is an MRI?
An MRI is a special kind of x-ray. It uses a large magnet to look at the water and fat content of the body and so build up a picture of the internal structures of the body. It does not use radiation like a normal x-ray. It is slow, noisy and expensive but a very useful tool for looking at the anatomy of the prostate. Its use is still somewhat controversial but becoming more accepted by the day. It is becoming more common for patients to have an MRI before a biopsy.
Why have an MRI of the prostate?
When we think about it there is no other organ or cancer that we would take a biopsy based on a blood test without an x-ray or image of the organ. For a long time this has been the norm, that is we take a biopsy without imaging the prostate properly. This is because in the past the images were quite fuzzy. For prostate MRI we can also look at how the water molecules move through tissues, this is called a DWI image. Sometimes a 'contrast' agent is used as well to show blood flow within the prostate, this is called a multi-parametric MRI.
MRI prostate can be used therefore before the first prostate biopsy, or before a second biopsy if one is needed. Sometimes it will be used when cancer has been found, especially if only a little amount was found and active surveillance is being contemplated. If we are planning to follow a low-grade cancer then we need to be sure we have correctly sampled the prostate and found the most important cancer in the prostate. If an MRI was not done before the biopsy then it is very useful afterwards.
If the MRI is normal do I need a biopsy?
Probably. By using MRI of the prostate before a biopsy we can potentially identify or spot abnormal areas in the prostate which need to be biopsied. This makes the prostate biopsy much more accurate. Sometimes this will indicate a need for a transperineal biopsy rather than a transrectal biopsy.
If the MRI is normal there is about a 10% chance of a cancer being present but not seen. Opinion is divided as to whether these are important cancers or not, and whether a biopsy is needed. The decision on whether you have a biopsy with a normal MRI will depend on your other risk factors (rectal exam, PSA, prostate volume, PSA ratio test, and family history).
Can I have an MRI if I have had a hip replacement?
An MRI is a giant magnet, so metal distorts the images. Hip replacements cause a lot of abnormal magnetic fields and this degrades or reduces the quality of the MRI. This artefact makes MRI of the prostate less helpful in patients with a hip replacement and especially so if both hips have been replaced.
What if I am claustrophobic?
MRI machines have a narrow tube which you must pass through and so if you have claustrophobia then you may require sedative pills before the scan. You should discuss this with the MRI staff. It may be possible to have a friend sit in the room with you. It is very important to try and be still when the machine makes a clunky noise as that is when the pictures are being taken.
A powerpoint presentation of prostate MRI from Nijmegen can be found here
Normal MRI of the Prostate