Treatment of urinary stone diseases requires radiographic imaging to optimize treatment selection. Non contrast helical computerized tomography (CT) has become the radiographic modality of choice in acute flank pains due to rapid and accurate determination of stone parameters. It was used by some groups to correlate treatment success, however, no specific recommendations have yet resulted from this series. Objective: To determine how non-contrast helical computerized tomography hounsfield unit (HU) measurement of surgically collected calculi correlates with in vitro stone breaking strength. Methodology: The specimens were obtained from patients who underwent open stone surgery at our institution from January 1, 2006 to September 30, 2006. Stones with sizes between 1-2 cm in their greatest dimension wer^ included in the study. In vitro measurement of the individual stone hounsfield unit values was done using the center's Neusoft CT C 3000 Spiral CT Scanner. Breaking strength of each stone was determined using Tinius Olsen low capacity Universal Testing Machine (UTM). Results were recorded and statistical analysis was performed using the Pearson correlation coefficient and linear regression from the commercially available SPSS statistical software. Results: A total of 38 stones were obtained from open stone surgery during the period covered in the study were included. Specimen sizes ranged between 1 to 2 centimers (cm) with an average size of 1.37 cm. The mean hounsfield unit of the stone specimen was at 588.34 HU and an average breaking strength of 57.54 Ib load. The Pearson correlation coefficient between the Hounsfield reading and that of breaking load is r = 0.406. This is indicative of a moderate yet significant (p-0.008) association between the two scores. A linear regression model may be fitted for these two scores with breaking load as dependent variable and hounsfield unit as predictor. A caveat on the model is its low adjusted R-square (16%). The resulting equation was: Estimated Breaking Load = 30.422 + 0.0461 (Hounsfield Unit). Conclusion: The breaking load of a urinary stone has a tendency to have a higher value as the Hounsfield score increases. Hounsfield unit is a predictor for stone's breaking strength but not a sufficient one.

Urinary Calculi ; Urolithiasis