背景资料:PSMA is a cancer antigen that is widely expressed as a noncovalent homodimer on the surface of prostate cancer cells, rather than on normal cells, therefore it is an interesting target to image prostate tissues when being used with radioactive antibodies. PSMA is expressed on the surface of novel blood vessels that nourish a broad range of other solid tumors. PSMA is a type II membrane protein with folate hydrolase activity produced by prostatic epithelium. PSMA expression is found in extraprostatic tissues, including small bowel and brain.