CT能谱成像对肾结石成分分析的初步研究

Spectral CT imaging in the evaluation of composition of kidney stones

目的 探讨能谱CT在体外区分肾结石成分的价值.方法 168枚经外科手术取出的肾结石,分别置于猪肾中.行能谱扫描（ GSI）及常规120 kVp扫描.测量计算GSI图像上结石的有效原子序数（Zeff）、钙水比值（CWR）、能谱衰减曲线斜率、50 keV单能量CT值及120 kVp混合能量CT值,并采用方差分析或秩和检验比较各组结石上述指标的差异.分别采用红外光谱分析仪测定其成分,成分单一的结石108枚,其中尿酸类结石组13枚、鸟粪石结石组24枚、胱氨酸结石组14枚、磷酸钙结石组18枚、草酸钙结石组39枚.结果 5组结石的Zeff、CWR、50 keV单能量CT值、120 kVp混合能量CT值及能谱衰减曲线斜率分别为：尿酸类结石组为7.4±0.4、0.0085±0.0021、（503±168） HU、（495±106） HU、-0.77、鸟粪石结石组为11.8±0.9、0.1743±0.0677、（1056±290） HU、（799±165） HU、18.72,胱氨酸结石组为11.2±0.6、0.1253±0.0297、（740±172）HU、（565±129） HU、12.79,磷酸钙结石组为16.0±0.4、0.6781±0.0952、（2567±178） HU、（1602±200） HU、37.14,草酸钙结石组为15.4 ±0.4、0.5683±0.0759、（ 2267±385） HU、（ 1489±284） HU、36.36,组间差异均有统计学意义（P值均＜0.01）.组内两两比较,有效原子序数、钙水比值及50 keV单能量CT值差异均有统计学意义（P值均＜0.05）.结论 能谱CT成像为区分肾结石成分提供了新的方法,有效原子序数、钙水比值及50 keV单能量CT值,3个指标均可以明显区分尿酸类、鸟粪石类、胱氨酸、磷酸钙类及草酸钙类结石.

Objective To evaluate the feasibility of determining the chemical composition of kidney stones using gemstone spectral imaging （ GSI ）.Methods One hundred and sixty eight extracted human kidney stones immersed in a 10 cm deep water tank underwent CT （Discovery CT750 HD） scans with GSI mode and conventional polychromatic imaging （ CPI,120 kVp） mode.All GSI data were transferred to Workstation AW 4.4 to acquire monochromatic images of 50 keY,effective atomic number （Zeff） mapping images,water （calcium）-based images and calcium （Water）-based images with GSI Viewer.CT numbers of stones were measured and compared at 50 keV monochromatic images and 120 kVp polychromatic images,the mean Zeff,calcium density and water density were measured at Zeff mapping images,Calcium （Water） -based images and Water （Calcium）-based images,respectively.The mean Zeff,spectral HU curve slope and calcium water ratio （CWR） were compared with ANOVA and Wilcoxon test.The composition of kidney stones was determined by infrared spectrometer after CT examination.According to the result of stone composition determined by infrared spectroscopy,108 pure kidney stones were divided into five groups：Uric acid stones （ UA,n = 13 ）,struvite stones （ STR,n = 24）,cystine stones （ CYS,n = 14）,calcium phosphate stones （ CaP,n = 18）,and calcium oxalate stones （ COX,n = 39）.Results The mean Zeff,CWR,the mean CT numbers at 50 keV images,120 kVp images and spectral HU curve slope of each group were listed as the following：UA [ 7.4 ± 0.4,0.0085 ± 0.0021,（ 503 ± 168 ） HU,（495 ± 106 ） HU and - 0.77 ] ; STR [ 11.8 ± 0.9,0.1743 ± 0.0677,（ 1056 ± 290 ） HU,（ 799 ± 165 ） HU and 18.72 ] ; CYS [ 11.2 ± 0.6,0.1253 ± 0.0297,（ 740 ± 172 ） HU,（ 565 ± 129 ） HU and 12.79 ] ; CaP [ 16.0 ± 0.4,0.6781 ± 0.0952,（ 2567 ±178 ） HU,（ 1602 ± 200 ） HU and 37.14 ] ; COX [ 15.4 ± 0.4,0.5683 ± 0.0759,（ 2267 ± 385 ） HU,（ 1489 ±284） HU and 36.36 ],there were significant differences among groups （ P 〈 0.01 ）.The differences in the mean Zeff,CRW,spectral HU curve slope were statistically significant among the five groups （ P 〈 0.05 ）.Conclusion Spectral CT imaging provides a new method to characterize the kidney stones with the information orovided by mean Zeff,CRW and the CT numbers at 50 keV.