胆系结石金属成分与MRI信号的相关性研究

Correlation between MRI features and metal compositions of gallstones

目的：探讨胆系结石金属成分与MRI信号的相关性以及结石MRI信号表现的成因。方法回顾性分析术前行上腹部轴面三维脂肪抑制快速扰相梯度回波（3D-FSPGR-FS）T1WI、脂肪抑制快速扰相梯度回波（FSPGR-FS）T1WI、稳态采集快速成像（FIESTA）和脂肪抑制快速自旋回波（FSE-FS ）T2WI序列扫描，且手术取出最大径〉8 mm的胆囊或胆管结石的30例患者。30个结石中，胆色素石16个，胆固醇石14个。对患者和离体结石标本进行上述序列的MRI检查。观察在体、离体不同成分结石（新鲜结石、干燥结石和浸水结石）的信号特点，计算信号强度率，并采用t检验、Mann-Whiteney U或Wilcoxon检验进行比较。测定干燥结石标本中的金属物含量，并采用线性回归Linear Regression分析结石金属含量与3D-FSPGR-FS T1WI中结石信号强度率的相关性。结果胆色素石在3D-FSPGR-FS T1WI上表现为高信号。3D-FSPGR-FS T1WI上，胆色素石的信号强度率高于胆固醇石，分别为2.02±0.53和0.51±0.24，差异有统计学意义（t=10.26，P〈0.01）。胆色素石在3D-FSPGR-FS T1WI上，干燥结石、新鲜结石和浸水结石的信号强度率分别为0.21±0.06、1.42±0.35和1.68±0.86，干燥结石和新鲜结石、浸水结石的差异均有统计学意义（t值分别为13.49和－6.63，P均〈0.01）。胆色素石和胆固醇石中钙含量的中位数分别为28.186和2.347 mg/g，差异有统计学意义（Z=－4.66，P〈0.01）。结石中钙与结石在3D-FSPGR-FS T1WI中信号强度率间呈正相关，回归方程为SI=65.40 logCa－166.67。结论胆色素石内部含有较多水分和金属离子，钙可能是胆色素石在3D-FSPGR-FS T1WI序列中呈现高信号的主要原因。

Objective To analyze the correlation between the metal components and MRI signal intensities of gallstones, to investigate the causes of gallstone signal features on MRI. Methods The MRI data and the metal components of the gallstones in vivo and in vitro of 30 patients were retrospectively analyzed. The MR sequences, namely 3D fast spoiled gradient-echo with fat saturation T1-weighted imaging （3D-FSPGR-FS T1WI）, fast spoiled gradient-echo with fat saturation T1-weighted imaging（FSPGR-FS T1WI）, fast imaging employing steady-state acquisition（FIESTA）and fast spin-echo T2-weighted imaging with fat saturation（FSE-FS T2WI）, were performed on the gallstones in vivo and in vitro. According to the characteristics of the surface and cross section, gallstones were divided into pigment gallstones（ n=16） and cholesterol gallstones（n=14）. The MR signal characteristics of the gallstones were observed and the signal intensity rates of the gallstones were calculated. Preoperatively, the signal intensity rates of cholesterol and pigment stones of each MR sequence were compared by using t test and Mann-Whiteney U test. Postoperatively,the signal intensity rates of the fresh,dried and re-soaked gallstones were compared by using paired t test and Wilcoxon test. The correlation between the signal intensity rates of gallstones on the 3D-FSPGR-FS sequence and their metal components was analyzed by using Linear Regression analysis. Results The pigment gallstones showed high signal intensity on the 3D-FSPGR-FS T1WI. The signal intensity rates of the pigment gallstones were higher than the rates of the cholesterol gallstones on the 3D-FSPGR-FS T1WI, which were 2.02 ± 0.53 and 0.51 ± 0.24 （t=10.26,P〈 0.01）, respectively. On the 3D-FSPGR-FS T1WI, the signal intensity rates of the drying pigment stones were significantly lower than the＆nbsp;rates of the fresh ones, the rates of the two states of the pigment gallstones were 0.21±0.06 and 1.42±0.35（t=13.49,P〈0.01）,respectively. The signal intensity rates of pigment gallstones showed significant rebound after re-soaking, the rates of the two states of the pigment gallstones were 0.21±0.06 and 1.68±0.86（t=-6.63,P〈0.01）,respectively. The metal components of pigment gallstones were significantly higher than the cholesterol stones. In the pigment gallstones and cholesterol gallstones, the medians of the Calcium were 28.186 and 2.347 mg/g（Z =-4.66,P〈 0.01）,respectively.For pigment gallstones, there was a significant correlation between the calcium and the signal intensity rate on 3D-FSPGR-FS T1WI. The regression equation of linear regression analysis was SI=65.40 logCa-166.67. Conclusions The pigment gallstones containing much more water and metal showed high signal intensity on 3D-FSPGR-FS T1WI. The Calcium in the pigment gallstones may be the main cause for this MR appearance.