Imaging

Abstract

Radiology. 2007; 245: 499-506 Purpose: To characterize benign and malignant prostate peripheral zone (PZ) tissue retrospectively by using a commercial magnetic resonance (MR) spectroscopic imaging package and incorporating the choline plus creatineto-citrate ratio ([Cho + Cr]/Cit) and polyamine (PA) information into a statistically based voxel classification procedure. Materials and Methods: The institutional review board approved this HIPAA-compliant study and waived the requirement for informed consent. Fifty men (median age, 60 years; range, 44-69 years) with untreated biopsyproved prostate cancer underwent combined endorectal MR imaging and MR spectroscopic imaging. Commercial software was used to acquire and process MR spectroscopic imaging data. The (Cho + Cr)/Cit and the PA level were tabulated for each voxel. The PA level was scored on a scale of 0 (PA undetectable) to 2 (PA peak as high as or higher than Cho peak). Whole-mount step-section histopathologic analysis constituted the reference standard. Classification and regression tree analysis in a training set generated a decision-making tree (rule) for classifying voxels as malignant or benign, which was validated in a test set. Receiver operating characteristic and generalized estimating equation regression analyses were used to assess accuracy and sensitivity, respectively. Results: The median (Cho + Cr)/Cit was 0.55 (mean +/-standard deviation, 0.59 +/-0.03) in benign and 0.77 (mean, 1.08 +/-0.20) in malignant PZ voxels (P = .027). A significantly higher percentage of benign (compared with malignant) voxels had higher PA than choline peaks (P < .001). In the 24-patient training set (584 voxels), the rule yielded 54% sensitivity and 91% specificity for cancer detection; in the 26-patient test set (667 voxels), it yielded 42% sensitivity and 85% specificity. The percentage of cancer in the voxel at histopathologic analysis correlated positively (P < .001) with the sensitivity of the classification and regression tree rule, which was 75% in voxels with more than 90% malignancy. Conclusion: The statistically based classification rule developed indicated that PAs have an important role in the detection of PZ prostate cancer. With commercial software, this method can be applied in clinical settings. Editorial CommentThe ratio of choline and creatine to citrate (Cho+Cr/Cit), is the parameter for the detection of prostate cancer on MR spectroscopic imaging (MRSI). As we know this ratio is increased in prostate cancer due to the elevation of choline (high turnover of phospho-lipid in cell membranes of the proliferating tissue) and reduction in the level of citrate (converted to a citrate-oxidating metabolism).Although there is no consensus, voxels are considered very suggestive of cancer if the ratio of choline and creatine to citrate is more than 3 standard deviations above the average ratio (1). However, using these criteria false positive results occurs due to prostatitis and prostatic atrophy. The authors of this meticulous and well-performed prospec...