The purpose of this project is to collect initial data regarding biodistribution, reproducibility, and dosimetry for the radiotracer Ga-68 PSMA-HBED-CC, an agent which may be useful for the early detection of metastatic prostate cancer. Investigators will use a test and re-test design in all patients to determine reproducibility of lesion detection and signal intensity, and will include dynamic imaging in some patients for the purposes of dosimetry. Patients with known metastatic prostate cancer will be recruited and imaged on two occasions within the course of 15 days.