Objective:To investigate the changes of T1 and T2 values in residual liver after major liver resection in rats and the relationship with pathologic indices related to liver regeneration.Methods:Seventy healthy male Sprague Dawley rats, SPF grade, aged 7-8 weeks, weighting 250-280 g, were divided into MR scan group ( n=14) and pathologic analysis group ( n=56). The MR scan group was further divided into partial hepatectomy group ( n=7) and the sham operation group ( n=7). MRI T 1 mapping and T 2 mapping were performed before surgery and on day 1, 2, 3, 5, 7, 14, 21 after surgery. T1 and T2 values of liver parenchyma were measured. In the pathologic analysis group, 7 rats were randomly included at each time point before and after surgery for pathologic examination, the diameter and proliferative activity (Ki-67 indices) of hepatocytes were assessed. The changes of imaging and pathologic indices were observed, and the correlations between MR parameters and liver volume and pathologic indices were analyzed. Results:Both T1 and T2 values in liver parenchyma were increased on day 1 after surgery and reached their maximum values on day 2 ( P=0.005 and P<0.001, compared with baseline), then were gradually decreased, and recovered to the preoperative level on day 14 and 21 ( P>0.05), respectively. T2 value was correlated with hepatocyte diameter, liver volume and Ki-67 indices better ( r=0.640, -0.764, 0.765, respectively, all P<0.001). T1 value was correlated with hepatocyte diameter, liver volume and Ki-67 indices ( r=0.472, -0.481 and 0.444, all P<0.001). Conclusion:The T1 and T2 values of rats liver remnant parenchyma showed regular changes, and were correlated with liver regeneration indices, which reflect the microscopic changes of rat liver remnant parenchyma, and are expected to be used for quantitative monitoring of liver remnant regeneration.