Accurate Prostate Volumes from Manual Calculations-A Comparison of PI-RADS v2 and v2.1 Measurement Techniques

There is a theoretical risk of volume overestimation if prostate AP dimension is taken on axial imaging given the anatomic obliquity of the gland on axial plane. This is analogous to slicing a salami sausage diagonally rather than perpendicularly to obtain larger slices. The most recent PI-RADS update (v2.1) now recommends obtaining the anterior-posterior measurement on sagittal imaging to mitigate the theoretical risk of the so called "salami effect" when using the ellipsoid formula for volume calculations. The authors of the recent article Comparison of PI-RADS Versions 2.0 and 2.1 for MRI-based Calculation of the Prostate Volume found the theoretical "salami effect" may not be as significant as originally thought, and perhaps slight overestimation of the AP diameter on axial measurements may yield more accurate volume estimates. Future validation studies are needed for to validate their findings. In this contemporary study, there is excellent interreader agreement among radiologist' three dimensional measurements-confirming manual calculation can be reliably replicated in practice settings where of software-based segmentation tools are not available.