| [Objectives] The aim of this study was to determine whether the analysis ofupper urinary stones seen on noncontrast helical computed tomography could predict their composition in vivo.[Methods] Between December 2005 and April 2007,one hundred and thirty-foururinary calculi were visualized on noncontrast helical computed tomography before stone removal. A Genaral Electric,high-speed CT/i CT scanner evaluated these patients at 120kV, 240mA, and 1．5:1 pitch,with collimation varying between 1mm and 3mm (scan collimation width≤1/2 greatest transverse diameter in millimeters). Each scan was analyzed by two radiologists,who determined the largest diameter and the maximal area in soft-tissue window, the average CT-attenuation value using soft-tissue window or bone window.For each calculus,a region of interest was created overlying the whole calculus on the slice in which it was seen at its largest diameter. These calculi were obtained by URSL/PNL extraction or surgical removal. All stones were analyzed using x-ray diffraction and electron probe microanalysis. Statistical analyses were performed to find the ranges of attenuation values for different stone minerals.[Results] When 134 urinary calculi were imaged using noncontrast helical CT insoft-tissue window,the average CT value ranges from 369 to 1225HU. The pure stones were defined as those with one chemical component comprising more than 70% of the whole. The 88 pure stones were separated into five groups and included 61 calcium oxalate monohydrate, 12 uric acid, 12 hydroxyapatite, 2 calcium oxalate dehydrate, and 1 struvite stones. The 46 mixed stones included several components,each representing less than 70% of the whole. In the analysis of pure stones,the mean HU of the stones composed of calcium oxalate monohydrate, uric acid and hydroxyapatite were 875．08±170．36, 450．00±47．53 and 808．42±103．79 , respectively. The analyses showed that the uric acid calculi could be distinguished from calcium oxalate monohydrate and hydroxyapatite stones (P<0．001 for both). A statistically significant difference (P<0．001) was found between pure uric acid stones (450．83±47．05HU)and other stones (842．65±162．610HU)by the average CT-attenuation value in soft-tissue window.Using the HU value cutoff of 500 or lower ,the sensitivity was 91．67%,specificity 96．72%,positive predictive value 73．33%,and negative predictive value 99% that a stone would be primarily pure uric acid.No statistically significant difference (P=0．879) was noted between calcium oxalate monohydrate(1323．16±101．40HU) and hydroxyapatite(1318．25±105．23HU) calculi by measuring the average CT-attenuation value derived from the region of interest in bone window. Finally, Plotting the average CT-attenuation value in soft-tissue window against the greatest transverse diameter in millimeters ,no stistically significant linear correlation was found between the mean HU and stone largest diameter (P=0．819>0．05) . Plotting the average CT-attenuation value in soft-tissue window against the maximal area ,a statistically positive correlation (P= 0．039<0．05) was observed.But the correlation between radiodensity and stone maximal area was unconspicuous (r=0．179) .[Conclusions] All urinary calculi examined were clearly visible on NCHCTregardless of chemical type. The initial clinical study demonstrated that we were able to differentiatiate between pure uric acid and and other stones in vivo using the average CT-attenuation value in soft-tissue window of urinary calculi from noncontrast helical computed tomography. An average CT-attenuation value in soft-tissue window of urinary calculi lower than 500 HU was highly suggestive of a pure uric acid stone,and the positive predictive value was 73．33%.Stone groups of calcium oxalate monohydrate and hydroxyapatite could not be differentiated using noncontrast helical CT. |
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