A standard MRI you would have for most other conditions is a bi-parametric MRI, which very crudely put, gives images of water distribution, and images of fat distribution. Clever imaging software can combine these to give images showing different tissue types based on the water and fat densities and ratios. These were not very good for identifying prostate cancer, which is notoriously difficult to indentify from normal prostate tissue.
Then came multi-parametric MRI scans, which add a third set of images. These use a contrast dye which shows up well on MRI scans, containing gadolinium. Towards the end of your MRI scan, the contrast is injected quickly, and forms a slug of die in your blood stream. This hits the prostate, and shows up well the blood flow in it. Tumours grow their own blood supply, which is not the same structure as the original blood supply in the prostate, and they have a different flushing rate - rate the blood passes through. This can be seen by the MRI scanner, and is an extra way to identify tissue which is different in the prostate, i.e lesions, although not necessarily tumours. Sometime around 2016 maybe (not sure exactly when), hospitals diagnosing prostate cancer were supposed to switch to mpMRI scans. I think this technique was first used for brain tumour scans, some of which are similarly difficult to identify. By 2018 when I was diagnosed, about 3/4trs of hospitals in England were doing mpMRI scans for prostates.
However, in the US, concerns were growing over long term side effects of gadolinium dyes. While they only impacted a very small proportion of patients, they were very serious when they did. This caused a move away from their use in the litigious US, and instead advances in image processing software improved what could be derived from bi-parametric MRI scans, particularly when done on high resolution 3T scanners (which were not the norm when mpMRI scans were originally introduced). Apparently, the UK never used the gadolinium brands which were most implicated long term side effects, but there was still concern about the possibility, and there are some patients who get short term allergic reactions, or who can't have the dye because their kidney function isn't good enough to filter it out of the body quickly.
This has caused a move back to bi-parametric MRI scans in some centres in the UK with more advanced imaging, although many places still use mpMRI.
Many scans done for prostate cancer diagnosis are not good enough for planning focal therapy, which obviously does require very accurate identification of all the cancer in the prostate. Sometimes focal therapy centres can use your diagnostic imaging, but other times they'll want you to get better quality scans.
Edited by member 15 Sep 2023 at 12:23
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