MRI scan of the prostate does cover the other contents of the pelvis as well, so there is some information about other tissues nearby. In my case, the MRI found an aneurysm of the right iliac artery for example, which was subsequently imaged in more detail with a CT Angiogram.
The biopsy only samples tissue from the prostate, so it cannot tell what's going on elsewhere.
Usually if you have a biopsy result which shows cancer, you will get other scans (I had a PET CT scan) to look for spread outside the prostate
Hope this helps
All the best