Correlation between MRI features and metal compositions of gallstones

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 Marara-Whiteraey U test. Postoperatively, the signal intensity rates of the fresh, dried and re-soaked gallstones were compared by using paired t test and Wilcoxora test. The correlation between the signal intensity rates of gallstones on the 3D-FSPGR-FS sequence and their metal components was analyzed by using Liraear Regressiora 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 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. (authors)