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Advancements in magnetic resonance imaging of the prostate.

P rostate cancer is a major medical and socioeconomic problem. Prostate cancer is the most common noncutaneous cancer and the second most common cause of cancer death in American men. The 2008 report from the American Cancer Society estimated 186,320 new cases of prostate cancer and 28,660 deaths due to the disease in the United States. It is anticipated that the aging population will lead to increases in prostate cancer incidence. Limitations of traditional screening methods for detecting, localizing, and staging prostate cancer, such as digital rectal examination, assessment of the prostate-specific antigen level in serum, and transrectal ultrasonography (TRUS) with biopsy, have led to extensive research in the field of magnetic resonance (MR) imaging focused on prostate tissue characterization at both gross anatomical and cellular/molecular levels. With its high soft tissue resolution necessary for morphological imaging and diverse capabilities for functional tissue imaging, MR imaging (MRI) is poised to offer the most significant gains in noninvasive prostate cancer detection and characterization. The standard imaging of the prostate with T2-weighted sequences is now routinely augmented with functional and molecular techniques such as diffusion-weighted imaging, MR spectroscopy, and dynamic contrast-enhanced MRI. In this issue of the Topics in MRI, Jacobs et al discuss 2 functional prostate MRI techniques, diffusion-weighted imaging and MR spectroscopy, pointing out the challenges in the optimization of imaging protocols needed to achieve diagnostic results in clinical setting. Bonekamp and Macura review the application of dynamic contrast-enhanced MRI in the diagnosis and staging of prostate cancer to include an outline of principles in kinetic analysis of microcirculation data and a discussion of false-positive and false-negative results. The role of MRI in prostate cancer staging has been reviewed by Fütterer et al. Magnetic resonance imaging is being used in many institutions in detecting the presence and location of extracapsular tumor extension and seminal vesicle invasions. Despite welldefined MRI criteria for organ-confined versus extraglandular tumor extension, MRI has been reported to have a wide range of sensitivities (13%Y95%) and specificities (49%Y97%) for extracapsular tumor extension detection with a similarly wide range of sensitivities (23%Y80%) and specificities (81%Y99%) for seminal vesicle invasion detection. Threetesla MR scanners are becoming widely available and offer the promise of the increased signal-to-noise ratio compared with that from 1.5 T, with the potential of shortening the imaging time and increasing the spatial, spectral, or temporal resolution for multiparametric prostate imaging. Fütterer et al address both the advantages and the limitations in local staging of prostate cancer with MRI at 3 T. Although the systematic sextant biopsy approach with TRUS guidance has improved the detection of prostate cancer, the sensitivity and specificity of TRUS in diagnosing impalpable prostate cancer still remain low: the number of false negatives in a single-sextant biopsy session reported ranges between 30% and 45%. In addition, the intraglandular anatomical localization of prostate cancer is often incorrect on sextant biopsy, when compared with final prostatectomy results, owing to a combination of sampling error and technical problems in localizing the exact site of origin of the specimen during biopsy. Accurate tumor detection, localization, and staging is critical in guiding the selection of treatment modality as either radical (prostatectomy, hormone ablation, and radiotherapy) or local minimally invasive (cryoablation, radiofrequency ablation, and focused ultrasound). EDITORIAL