2213 SEMI-AUTOMATED VOLUMETRIC MEASUREMENT OF RENAL STONES: A SIMPLE AND MORE COMPLETE DESCRIPTION OF STONE BURDEN

Abstract

INTRODUCTION AND OBJECTIVES: In nephrolithiasis, the decisions for treatment and the modality chosen are largely determined by the size and configuration of renal stones. While the greatest stone length and two-dimensional area in a single plane are commonly reported measures of stone burden, stone volume provides the most complete description of stone size. We sought to characterize the performance of standard stone measurement methods including greatest diameter and area on computed tomography (CT) imaging of stone phantoms and actual stones in a clinical cohort of patients versus a new semi-automated computerized volume calculation software. METHODS: Both actual and CT-derived in vitro measurements of four irregularly shaped and differently sized stone phantoms were performed. Actual length, area and volume were determined by straight line ruler, Image-J analysis of stone perimeter and water-displacement techniques, respectively. CT length and area in a single coronal view were derived using standard Centricity PACS system tools (GE Healthcare). CT volume was determined with a novel threshold-based, semiautomatic segmentation algorithm that additionally allowed for image rendering. All measurements were repeated x5. CT values were retrospectively obtained for a cohort of 17 patients with complete staghorn calculi that underwent PCNL between March 2006 and March 2010 for comparison. RESULTS: As noted in the Table, CT volume calculations of phantom stones had the lowest mean difference (13%) with actual measurements as compared to diameter (18%) or area (25%). Additionally, relative standard deviation between measurements was lowest with CT volume (0–0.46%) as compared to diameter (1.48–3.16%) and area (1.58–5.37%). In the clinical analysis of 17 patients (mean age 53, 53% male), large variations in stone size were noted: diameter (23.8–70.3mm), area (431– 2585mm), volume (3737–37714mm). CONCLUSIONS: In the evaluation of renal stones, stone volume provides the most descriptive measurement of overall stone burden. Our early studies using a novel semi-automated computer program may provide a more accurate and precise tool to determine stone size than is currently being utilized. Further clinical application will determine its utility in treatment planning, patient counseling and clinical outcomes. Source of Funding: None