Performance Characteristics of MR Imaging in the Evaluation of Clinically Low-Risk Prostate Cancer: A Prospective Study

Purpose: To prospectively evaluate diagnostic performance of T2-weighted magnetic resonance (MR) imaging and MR spectroscopic imaging in detecting lesions stratified by pathologic volume and Gleason score in men with clinically determined low-risk prostate cancer. Materials and Methods: The institutional review board approved this prospective, HIPAA-compliant study. Written informed consent was obtained from 183 men with clinically low-risk prostate cancer (cT1-cT2a, Gleason score <= 6 at biopsy, prostate-specific antigen [PSA] level < 10 ng/mL [10 mu g/L]) undergoing MR imaging before prostatectomy. By using a scale of 1-5 (score 1, definitely no tumor; score 5, definitely tumor), two radiologists independently scored likelihood of tumor per sextant on T2-weighted images. Two spectroscopists jointly recorded locations of lesions with metabolic features consistent with tumor on MR spectroscopic images. Whole-mount step-section histopathologic analysis constituted the reference standard. Diagnostic performance at sextant level (T2-weighted imaging) and detection sensitivities (T2-weighted imaging and MR spectroscopic imaging) for lesions of 0.5 cm(3) or larger were calculated. Results: For T2-weighted imaging, areas under the receiver operating characteristic curves for sextant-level detection were 0.77 (reader 1) and 0.82 (reader 2). For lesions of >= 0.5 cm(3) and <1 cm(3), sensitivities were significantly lower when the lesion Gleason score was <= 6 (0.44 [reader 1] and 0.61 [reader 2]) rather than when the Gleason score was >= 7 (0.73, P = .02 [reader 1]; and 0.84, P = .05 [reader 2]). For lesions of >= 1 cm(3), lesion Gleason score did not significantly affect sensitivity (0.83 [reader 1] and 1.00 [reader 2] for Gleason score <= 6 vs 0.82 and 0.92 for Gleason score >= 7; P >= .07). MR spectroscopic imaging sensitivity was low and was not significantly affected by pathologic lesion volume or Gleason score. Conclusion: In men with clinically low-risk prostate cancer, detection of lesions of <1 cm(3) with T2-weighted imaging is significantly dependent on lesion Gleason score; detection of lesions of >= 1 cm(3) is significantly better than detection of smaller lesions and is not affected by lesion Gleason score. The role of MR spectroscopic imaging alone in this population is limited.