Prostate cancer tumor volume: measurement with endorectal MR and MR spectroscopic imaging. 
To determine accuracy of magnetic resonance (MR) and three-dimensional (3D) MR spectroscopic imaging in prostate cancer tumor volume measurement.  Endorectal MR and 3D MR spectroscopic imaging were performed in 37 patients before radical prostatectomy.  Two independent readers recorded peripheral zone tumor nodule location and volume.  Results were analyzed with step-section histopathologic tumor localization and volume measurement as the standard.  Accuracy of tumor volume measurement was assessed with the Pearson correlation coefficient.  P values were calculated with a random effects model.  Bland-Altman regression analysis was used to evaluate systematic bias between tumor volumes measured with MR imaging and true tumor volumes.  Analyses were performed for all nodules and nodules greater than 0.50 cm(3).  Mean volume of peripheral zone tumor nodules (n = 51) was 0.79 cm(3) (range, 0.02-3.70 cm(3)).  Two readers detected 20 (65%) and 23 (74%) of 31 peripheral zone tumor nodules greater than 0.50 cm(3).  For these nodules, measurements of tumor volume with MR imaging, 3D MR spectroscopic imaging, and a combination of both were all positively correlated with histopathologic volume (Pearson correlation coefficients of 0.49, 0.59, and 0.55, respectively); only measurements with 3D MR spectroscopic imaging and a combination of MR and 3D MR spectroscopic imaging demonstrated statistical significance (P <.05).  Tumor volume estimation with all three methods was more accurate for higher tumor volumes.  Addition of 3D MR spectroscopic imaging to MR imaging increases overall accuracy of prostate cancer tumor volume measurement, although measurement variability limits consistent quantitative tumor volume estimation, particularly for small tumors.