- Patients have an endorectal coil MRI scan. For this test, a tube is placed in the rectum, just behind the prostate, to increase the amount of signal received by the magnetic resonance (MR) unit. Other coils may be wrapped around the pelvis to further improve the quality of the scan. The patient lies on the scanning table for about 75 to 90 minutes while images are obtained. During the scan, a contrast agent called gadolinium is injected through an intravenous (IV) line to brighten the images.