To reiterate what others have said, my doc indicated there was such a low probability with low PSA of anything showing up on a scan, that the scan isn't considered a needed diagnostic. Since I had lots of anxiety over the diagnosis, he said he would order scans to put me at ease. Honestly, I appreciated the "look" since it covered lots of other stuff too.
As far as the tumor in the prostate itself, the scans don't tell anything. The biopsy is the most definitive information docs can get pre-surgery/treatment. Since surgeons and radiologists don't do "lumpectomies" on prostates or just target affected areas of the prostate, but rather remove or target the entire prostate, it really doesn't matter where in the prostate the tumor is. Only a post surgery pathology can tell with certainty if there are extracapsular extensions (meaning the tumor has spread outside the prostate). The earlier you are with diagnosis, the better your chances that your post surgery pathology will show negative margins (no penetration of the prostate capsule), though there are no guarantees for this. It's really all just statistics at this point, but the good news is the stats are in your favor. If you chose something like radiation, then the patient really never knows but the whole prostate and surrounding areas are treated to ensure braod coverage for the possibility of extracapsular extensions.
At least that what I understood from my research...hope that helps some.