The purpose of the MRI scan is two-fold. Firstly to see if anything that looks like cancer shows up in the prostate (tumours have a different appearance to healthy tissue) and secondly, if something that looks like cancer is seen, to guide the subsequent biopsy so samples are taken from the suspicious areas. With a PSA of 19, I suspect that he will have a biopsy. It’s worth noting, though, that blood in the urine can have causes other than prostate cancer, so don’t make assumptions.
Best wishes,
Chris