In phase B, 20 high risk prostate cancer patients determined to undergo radical prostatectomy are screened with 68Ga-PSMA-11 PET/MRI, and then given GNRH antagonist therapy. 68Ga-PSMA-11 PET/MRI is repeated at the time of maximum PSMA expression based on phase A results. The patients then undergo radical prostatectomy and lymphadenectomy and imaging findings are matched with histological data.