The safety of the donor is the most important principle in donor assessment. Additionally, the amount of hepatic issue should meet the metabolic needs of the recipient. The preoperative assessment should contain routine tests, including history collection, physical examination, assessment of the key organ function, imaging examination, mental condition assessment, determination of anesthetization risk, and an ethics review. Ages from approximately 18–55 years are most suitable, and the blood type should be compatible. Diabetic patients who are being treating with insulin and patients with unmanageable hypertension, physical diseases, or a history of malignancies and serious abdominal surgery should be excluded. Moreover, obese patients should be avoided due to the increased risk of cardiovascular disease, especially in patients with body mass indexes (BMIs) above 25, which significantly increases the operative risk during the perioperative period.

A three-dimensional reconstruction using computer tomography angiography (CTA) of the liver can be used to measure the volume of the liver grafts. Experts from the University of Ulsan in Korea recommend that the residual liver without hepatic steatosis in donors who are 20–30 years of age should be more than 30 % of the whole liver volume. For those who are 30–50 years of age or exhibit mild or mid-stage hepatic steatosis, the residual liver volume should be more than 35 % [12]. In healthy adults, the right lobe of liver occupies an average of 67 % of the whole liver volume (Table 30.1). However, this figure is greater than 70 % in approximately one quarter of the donors [13]. In this situation, hepatectomy of the right lobe increases the risk to donors, whereas the left lobe is too small to transplant. RPS resection could be an approach for liver transplantation. The resection of the RPS requires that its volume be more than the sum volume of the left lobe and the caudate lobe, and the excess portion should be more than 3 % of the whole liver volume. At the same time, the estimated liver volume should be 40 % of a standard liver volume (SLT), or the graft-to-recipient weight ratio (GRWR) should be more than 0.8 %.

The assessment of hepatic vessels includes the three-dimensional reconstruction of the artery, portal vein, and hepatic vein using hepatic CTA. The hepatic duct should be visualized using magnetic resonance cholangiopancreatography (MRCP). Most studies have reported that the choice of RPS should consider the anatomy of the vessels. As mentioned above, the most suitable variant types are type III for the portal vein and type IV for the hepatic duct and extrahepatic RPS artery branches. Due to the lack of an independent branch, type I is not suitable for RPS grafts. However, research from Korean experts in 2011 recommended that if the RPS volume is suitable for transplantation, the vessels should not be considered. These authors performed 13 cases of RPS graft resection in 65 LDLTs, showing excellent results [6]. Nevertheless, based on the experience of many transplantation centers, the anatomy of the portal vein is still an important factor in RPS resection [5, 7, 14].