Prediction of the Chemical Composition of Urinary Calculi Using CT

Abstract

Purpose: Our objective for this study was to determine the precision of spiral CT in identifying the chemical composition of different types of urinary calculi with measurement of absolute HU values of region of interest (ROI)using unenhanced spiral CT.

Materials and methods :A total of ( 50 ) urinary stones, obtained from patients who underwent open surgery ,were scanned with a multidetector row scanner using ( 2 ) mm collimation at energy level of ( 120 ) kV at (200 ) mA .Two post-scanning protocols were used for the HU value assignment ,tissue and bone windows. In both protocols ,three transverse planes were defined in each stone , one near the top, one in the middle ,and one near the bottom. Three regions of interest (ROI ) were obtained in each plane .The absolute HU value was determined by three methods :the mean of nine ROI ,the mean of the central three ROI ,and the central ROI in the middle plane .Determination of the stones composition was performed using the absolute HU value measured at ( 120 ) kV .All stones were analyzed by infrared spectroscopy to determine their chemical composition.

Results : the calculi classified into groups according to their chemical composition .A total of 50 calculi ,include ( 34 ) pure stones[ (14 )uric acid (UA), ( 15 ) calcium oxalate monohydrate (COM), (5) Struvite] ,and (16) mixed stones [(7) COM +hydroxyl apatite (HA), (4) COM +uric acid, (5) mixed Struvite + COM + hydroxyapatite] were included in the statistical analysis. Using the absolute HU values at ( 120 ) k V , we could distinguish ,with statistical significance ,all pure types from each other ,from the least to the most dense , the pure stone types were UA , struvite ,COM . Mixed UA + COM calculi were more dense and significantly different from pure UA but insignificantly different from Struvite , Struvite and COM can differentiated from each other but there were insignificant differences between them and mixed stones (COM+UA and struvite+COM+HA ) . Mixed COM + HA stones were the most dense stones and can differentiated from other types.

Conclusion :This study suggest that the measurement of absolute HU values at a single energy level utilizing CT scanning with small collimation size can uncover significant differences among all pure stones and insignificant for mixed stones.