A novel method for prediction of stone composition: the average and difference of Hounsfield units and their cut-off values.

Purpose: The purpose of the study was to investigate the predictive value of stone measurements by including a novel method on non-contrast computed tomography (NCCT) images for stone composition.
Methods: We retrospectively evaluated patients who had stone analysis, NCCT images, and underwent percutaneous nephrolithotomy between 2013 and 2016. Patient characteristics, stone measurements on NCCT images, and stone analysis results were evaluated. Hounsfield unit (HU) values (maximum (HU _max ), minimum (HU _min ), and average (HU _ave ) of HU values) were investigated on NCCT images. HU _diff was calculated as the difference between the HU _max and the HU _min values. Patients were divided into seven stone groups and data were compared. Then patients were separately divided into two groups according to mineral complexity (mono-mineral and multi-mineral groups) and calcium-based (calcium and other stone groups) evaluation.
Results: In the study, 115 patients were evaluated. Age, gender, HU _min , HU _max , and HU _ave were significantly different between the stone groups. HU _diff and HU _ave were found to be 341.5 HU (AUC = 0.719, p = 0.017) and 1051.5 HU (AUC = 0.701, p = 0.029) as cut-off, respectively. Seventy of 72 > 341.5 HU _diff patients and 64 of 67 > 1051.5 HU _ave patients had multi-mineral stones (p = 0.001, OR 9.26, and p = 0.028, OR 4.27), respectively. In multivariate analysis, > 341.5 HU _diff rate was significantly higher in multi-mineral and calcium stone groups; HU _ave was also significantly higher in the calcium stone group.
Conclusions: HU _diff and HU _ave were significant predictors of mineral complexity. HU _diff of < 341.5 HU showed 81.8% sensitivity and 67.2% specificity for identification of mono-mineral stones.