Advancement of MR and PET/MR in Prostate Cancer

Multiparametric magnetic resonance (mpMRI) imaging has assumed a larger role in the diagnosis and management of prostate cancer. The current method of detecting prostate cancer relies on blind systematic biopsy, guided only by transrectal ultrasound that generally directs the needle biopsy to sextants of the prostate rather than specific lesions. MpMRI is playing an increasing role in the detection of primary cancer as it can visualize cancers and direct biopsies. However, even mpMRI is inherently nonspecific and numerous biopsies performed under MR guidance prove to be negative. Positron emission tomography (PET) has the potential to improve the sensitivity and specificity for prostate cancer in combination with mpMRI. Prostate-specific membrane antigen is a widely expressed tumor antigen in prostate cancer for which multiple PET ligands, labeled with ⁶⁸Ga and ¹⁸F, are being developed. However, the low spatial resolution of PET mandates that it be combined with a higher resolution imaging modality, which typically has been computed tomography (CT). However, MRI is not only better at localizing lesions in the prostate and prostatic bed, but it is also more sensitive than CT for early bone marrow changes in bone metastases caused by prostate cancer. Prostate-specific membrane antigen-based PET agents show promise in the early detection of recurrent and metastatic disease. Recent developments in hybrid imaging now allow PET/MRI to be performed simultaneously on a single scanner allowing one-to-one correspondence between the PET activity and MRI findings. This offers the opportunity for both high sensitivity and specificity with excellent anatomic location and could allow for more targeted biopsies and treatments. Here, we review the current status of PET/MRI for prostate cancer.