An endo rectal MRIS is an excellent idea for anyone considering surgery. It should not affect anything as it is not invasive; just a probe up your butt for an hour.
It will give you valuable information regarding the probability of surgical success as it can identify extra capsular extension, nerve involvement and APEX tumors or tumors close to the margin which are all problamatic for a succefful surgical outcome. If the MRI identifies any of these you should postphone your surgery and get more opinions.
66 years old, rising psa for 10 years from 4 to 40; 12 biopsies and MRIS all negative. Oct 2009 DXed with G6 <5%. Color Doppler biopsy found 2.5 cm G4+3. Combidex clear. Seeds and IMRT, 4 weeks of urinary frequency and urgency; no side affects since then. 2 years of psa's all at 0.1.