Measurement of Prostate Volume with MRI (A Guide for the Perplexed): Biproximate Method with Analysis of Precision and Accuracy

Purpose To review the anatomic basis of prostate boundary selection on T2-weighted magnetic resonance imaging (MRI). To introduce an alternative 3D ellipsoid measuring technique that maximizes precision, report the intra- and inter-observer reliability, and to advocate it’s use for research involving multiple observers. Methods A demonstration of prostate boundary anatomy using gross pathology and MRI examples provides background for selection of key boundary marks when measuring prostate volume. An alternative ellipsoid volume method is illustrated. An IRB approved retrospective study of 140 patients with elevated serum prostate specific antigen levels and/or abnormal digital rectal examinations was done with T2-weighted MRI applying the new (Biproximate) technique. Measurements were made by 2 examiners, correlated with each other for interobserver precision and with an expert observer for accuracy. Correlation statistics, linear regression analysis, and tests of means were applied using p≤0.05 as the threshold for significance. Results Inter-observer correlation (precision) was 0.95 between observers. Correlation between these observers and the expert (accuracy) was 0.94 and 0.97 respectively. Intra-observer correlation for the expert was 0.98. Means for inter-rater reliability and accuracy were all the same (p=0.001). Conclusions Anatomic foundations for the boundaries of the prostate are reviewed. Precision and accuracy of total prostate volume using an alternative method is reported and found to be reproducible.