Determination of chemical composition of upper urinary calculi by reformatted unenhanced spiral CT in vivo

Abstract

Objectives To investigate the value of reformatted unenhanced spiral CT in predicting the chemical composition of upper urinary stones in vivo. Methods The clinical data of 156 cases with calculi specimen of upper urinary tract were analyzed retrospectively. All of the patients were visualized on reformatted unenhanced spiral CT before stone removal. Unenhanced spiral CT was per-formed by General Electric(GE), high-speed CT/i CT scanner.The average CT-attenuation value was evaluated by soft-tissue window. All chemical qualitative analysis of stones was analyzed by analysis system of infrared spectrum. After statistics analysis, the corresponding CT value range of various composition stone minerals was found. Results 156 cases of reformatted unenhanced spiral CT value were 128~1663 HU. The 57 pure stones were divided into three groups and included 28 cases of calcium oxalate monohydrate, 19 cases of uric acid, 10 cases of pure hydroxyapatite. 99 cases of mixed stones were found. In the analysis of pure stones, the mean CT value of stones composed of calcium oxalate monohydrate, uric acid and pure hydroxyapatite was (915.4±142.9), (469.7±55.1), (868.4±168.8) HU, respectively. There was statistically significant difference in CT value among the uric acid and calcium oxalate monohydrate stones and hydroxyapatite(P<0.05). The analyses showed that the 19 cases of uric acid calculi could be distinguished from calcium oxalate monohydrate and hydroxyapatite stones. A statistically significant difference was found between uric acid stones and other stones by the average CT-attenuation in soft-tissue window(P<0.05). Conclusions Reformatted unenhanced spiral CT would be examined urinary calculi, and the result is satisfactory. The initial clinical study demonstrated that we would be able to difference between pure uric acid and other stones in vivo according the average CT-attenuation value in soft-tissue window of urinary calculi from reformatted unenhanced spiral CT. An average CT-attenuation value in soft-tissue window of urinary calculi lower than 550 HU that can be used as diagnostic criteria of pure uric acid calculi. Key words: Urinary Calculi; Tomography, X-ray Computed