I don't know the answer to your question, but I can tell
you a tiny bit about other imaging techniques I've seen.

These are _not_ expert answers - just personal experience.

The urologist who biopsied my prostate used a black and
white ultrasound device that showed an image of the prostate
on a TV monitor.  I couldn't tell anything from it.  I don't
think that the doctor could see the cancer on the monitor,
it was just useful in positioning the needles to be sure he
was getting good samples from the right places in the prostate.

I also had MRI's done with a rectal antenna, i.e., an antenna
shoved into the rectum (by a 240 pound technician who
must have warmed up for this by twisting the heads off
screws :)).  The antenna was on the end of a device with
a balloon at the tip that was inflated to press it against the
prostate.

The doctor (a radiation oncologist at NCI) showed me the
computer generated images from the MRI.  A big ugly
tumor showed up very clearly in the images.  She also
showed me the seminal vesicles and other structures
around the prostate - which had no visible (on the MRI)
evidence of tumor growth.

If what you are trying to find out is whether the tumor
has penetrated the prostate capsule or is in the structures
around the prostate, you might ask about MRIs.  I don't
know if their use is standard or even that helpful.  You'd
have to ask an expert.  But my doctors used it.

   Alan