Experimental MRI Study On Differentiation Of Necrosis And Apoptosis After Hepatic Blood Supply Intervention

Objective: After establishing animal models of hepatic necrosis and apoptosis by interfering the blood supply, i.e., ligation of both hepatic artery and portal vein to right hepatic lobe or only right portal vein, a series of advanced MRI imaging sequences including conventional T1WI, T2WI, DWI, MRS and dynamic enhancement MRI were conducted to manifest the morphological appearances and signal characteristics of hepatic necrosis and apoptosis and to demonstrate the diagnostic ability and the differential features of MRI, DWI, MRS, and dynamic enhancement and their consistency with pathological changes of the advanced MRI technology.Materials and Methods: Seventy-eight rats were randomly divided into 13 groups, 6 rats in each group. Rats in group A1, B1, C1, D1, E1, F1 were enrolled for the model of hepatic necrosis after both right hepatic and portal vein were ligated and rats in group A2, B2, C2, D2, E2, F2 for animal model of hepatic apoptosis after only right portal vein was ligated. Six rats were sham-operated for control study. After the surgical operation of ligation, rats in group A(incuding Al and A2), B, C, D, E, F were exmanined in a Marconi 1.5 T Edge Eclipse^?MRI system at different time points of 3h, 12h, 24 h, 3d, 7d, 14d after the procedure. All rats were examined by conventional MRI, DWI, MRS and dynamic CE-MRI. The rats were sacrificed immediately after MRI examination and the hepatic tissue was harvested. The hepatic samples were further examined by HE stain, TUNEL stain, Envision PCNA stain, and electronic microscopy. For each rat, conventional axial T1WI, T2WI, coronal T2WI sequences were conducted initially, followed by DWI imaging with b values of 100, 300, 500, and a PRESS single voxel (size: 3.0×3.0×3.0mm³) MRS with TR/TE = 1500/35.0ms and 1500/135.0ms. The signal intensity on conventional MRI, dynamic CE-MRI and DWI of right lobe was compared with that of left lobe. For MRS curves, the peak values and the area under a specific wave were calculated bythe computer and statistically compared between groups. A version of SPSS 10.0 was used and a T test comparison was introduced for averages between groups. A p value less than 0.05 would be considered statistical significance.Results: The operation for vessel ligation of right hepatic lobe was smoothly conducted. The success rate of anesthesia and surgery is 93.8%. The results of MRI examinations including conventional MRI and functional MRI were satisfactory. HE stain showed hepatic coagulative necrosis or corruption of cell structure, with less apoptosis at early stage, after the ligation of both right hepatic artery and portal vein. When only right portal vein was ligated, apoptosis process can be seen at 3 hrs after the surgery, with a peak at 24th hour. Later on, less necrostic cells can been seen and apoptosis cells would decrease gradually. The right lobe would be atrophied and the left lobe would be hypertrophied. PCNA-LI demonstrated an increase of left lobe at 14d with parallel with the hypertrophy. In the group where rats received a ligation of both right hepatic artery and portal vein, DWI showed a significant high signal intensity on right lobe at early stage. On conventional images of T1WI, T2WI, the right lobe was long T1 and long T2 manifestations. The right lobes of the rats in group A2, B2, C2, distinguishing high signal intensities were observed on T1WI. No signal changes were seen on T2WI in group A2, B2, C2. Blotch or patchy high signal was revealed on T2WI in group D2 and E2. On DWI, right lobes on group A2, B2, C2, were low signal intensity. Iso-density or spot high signal intensity of the lobe were observed on group D2, E2, and F2. When the hepatic lobe was necrosed, Lac peak was increased significantly and the Cho peak was decreased gradually. For the rats in group A2, B2, C2, D2, E2, and F2, The peaks and areas of Lac, Glx, Lip wave were all slightly increased, compared with the control group. Cho was slightly decreased. There was a significant decrease of Cho/Lip ratio. The right lobe of the rats received a single right portal vein ligation was significantly enhanced after administration ofcontrast in arterial phase, but there was a reduction of enhancement on the portal phase compared with the left normal lobe.Conclusions: The animal models of hepatic necrosis or apoptosis can be made by the ligations of both right hepatic artery and portal vein or only right portal vein. The TUNEL stain is a specific approach to clarify the apoptosis. There were significant different signal changes on conventional T1WI and T2WI on the groups of necrosis and apoptosis. Combined with the findings on functional MRI examinations, including DWI, MRS and dynamic CE-MRI, it is possible and practical to detect and differentiate the two pathological processes: hepatic necrosis and apoptosis.