We have devised an original predictive residual index (PRI) using 99mTc diethylenetriaminepentaacetic acid galactosyl human serum albumin (99mTc-GSA) liver dynamic SPET for the pre-operative assessment of hepatectomy, including the prediction of residual liver function before hepatectomy. The aim of this study was to evaluate the usefulness of the PRI by using 99mTc-GSA liver dynamic SPET before and after percutaneous transhepatic portal embolization (PTPE) to induce compensatory hypertrophy of the remnant lobe, and to compare the results with the prognosis after hepatectomy. The subjects included eight patients with cholangiocellular carcinoma, five with gallbladder cancer, four with hepatocellular carcinoma and three with metastatic liver cancer. 99mTc-GSA liver dynamic SPET was performed immediately before and 2 weeks after PTPE. Dynamic SPET with 35 continuous rotations was performed to obtain the k-value according to the accumulation curve in each voxel (0.54 cm × 0.54 cm × 1.08 cm) of the liver immediately after a bolus injection of 185 MBq 99mTc-GSA. Each rotation consisted of 180° turn in 64 steps in a 64 × 64 matrix. The acquisition time of each rotation was 35 s. We devised an original PRI by combining the k-value with functional liver volume which were measured by liver dynamic SPET. Hepatectomy was performed following the second SPET. The correlation between the PRI and post-operative patient prognosis was investigated retrospectively. The functional liver volume of the remnant lobe and the PRI significantly increased after PTPE compared with respective values before PTPE (P<0.005 and P<0.0001, respectively). Regarding the relationship between the PRI and the clinical course following surgery, postoperative complications were observed in only two patients. The PRI values of these two patients were 0.323 and 0.394. When the PRI was above 0.400, no patient had symptoms of hepatic failure. The results of this study suggest that, when the PRI value is above 0.400, there is a low probability of hepatic failure after hepatectomy. We conclude that the PRI devised in this study is useful in the pre-operative assessment of hepatectomy after PTPE.