Magnetic Resonance Imaging and Spectroscopic Imaging of Prostate Cancer

Abstract

Purpose: We describe the practical technical aspects of magnetic resonance spectroscopic imaging (MRSI), and summarize the current and potential future status of magnetic resonance imaging (MRI) and MRSI in the diagnosis, localization, staging, treatment planning and posttreatment followup of prostate cancer. Materials and Methods: Contemporary series of patients with prostate cancer evaluated by MRI and MRSI were reviewed, with particular respect to imaging accuracy as evaluated by histopathological correlation, and the relationship between MRI and MRSI and outcome. Results: MRI and MRSI have a limited role in prostate cancer diagnosis but may be helpful for patients with a high index of suspicion and negative initial biopsy. High specificity can be achieved for sextant localization of cancer when sextant biopsy, MRI and MRSI are all positive. Volumetric localization is of limited accuracy for tumors less than 0.5 cc. Staging by MRI, which is improved by the addition of MRSI, is of incremental prognostic significance for patients with moderate and high risk tumors. MRI and MRSI may assist in surgical and radiation treatment planning, and posttreatment followup. In particular, the use of MRI to assist radiation treatment planning has been shown to improve outcome. Interventional MRI guided biopsy and therapy remain under investigation. Conclusions: Only MRI and MRSI allow combined structural and metabolic evaluation of prostate cancer location, aggressiveness and stage. MRI provides clinically and therapeutically relevant anatomical information. The technology remains in evolution, and continued advances in accuracy and use are likely. The management of early stage prostate cancer is controversial because we cannot reliably distinguish patients whose disease is indolent and incidental from those whose disease is progressive and life threatening. Current methods of prostate cancer evaluation by digital rectal examination, transrectal ultrasound (TRUS), Gleason score, sextant biopsy and serum prostatic specific antigen (PSA) assay can generally only predict behavior for indolent or aggressive cancers. Most cases fall between these extremes when these techniques are of limited accuracy.1–3 The limitations of traditional methods have driven the development of magnetic resonance imaging (MRI) and magnetic resonance spectroscopic imaging (MRSI) as additional modalities for the local evaluation of prostate cancer. We describe the practical technical aspects of MRSI, and summarize the current and potential future status of MRI and MRSI in the diagnosis, localization, staging, treatment planning and posttreatment followup of prostate cancer. A number of general introductory points are worth noting. MRI allows a “1-stop shop” detailed evaluation of prostatic, periprostatic and pelvic anatomy. Neither TRUS nor computerized tomography (CT) can offer this simultaneous coverage. MRSI is a method that demonstrates normal and altered tissue metabolism and, therefore, is fundamentally different from other imaging modalities such as MRI or TRUS that only assess abnormalities of structure. MRI, and especially MRSI, are relatively new technologies and both are in continued evolution. It is too early to judge the true role of these modalities, which may not be established for many years.