Introduction: CT volumetry has been widely used in the preoperative volumetric assessment of the liver for liver transplantation. CT volumetry has been traditionally performed by manual tracing of the hepatic contours and summation of the liver area on each axial section with a slice thickness of  10 mm. Despite the fact that the long calculation time in manual methods, automated and semiautomated methods have been carried out. The aim of this study was to  evaluate the  efficiency of manual CT volumetry with a slice thickness of 20 mm through the comparison of total liver volume results with a slice thickness of 10 mm and  comparison of both techniques with real graft weight.
Materials and Methods: From 2013-2017, 75 adult liver donors (41 men and 34 women) with a mean age of 33.6 years (range, 19-65 years) underwent CT with a 16-section multidetector row CT scanner  after  intravenous  injection of a contrast material. Two image sets axial section with slice thickness 10 mm and 20 mm were used. An abdominal radiologist reviewed all images on a workstation. The graft volumetric data were examined in 3 groups: right liver lobe, left liver lobe and left lateral liver lobe . There were 16,13 and 43 patients in groups, respectively. 75 total liver volume data from both data sets were compared with Wilcoxon test and graft volumetric data were compared with Friedman test.
Results: The mean whole liver volumes estimated with CT were 1373 cm³ from 10 mm images, 1364 cm³ from 20 mm images. The difference for total liver volumes calculated from 10 mm and 20 mm were not statistically significant (P >.05). The partial liver volumes of right lobes, left lobes, and lateral segments were evaluated in a similar manner. There were  no statistically significant difference in comparison of both technique. In Friedman analysis when both technique compared with the real weight in the results for left lateral lobes, the  real weight of the grafts are significantly larger  than the volume calculated from 10 mm and 20 mm images (p<.01). Preoperative calculations of total liver and graft volume  according to CT volumetry from 20 mm images did not yield statistically significant over- or under-estimations when compared to the CT volumetry from 10 mm images.  
Conclusion: In conclusion, slice thickness of 20 mm in manual CT volumetry can be used as an alternative, time consuming method instead of the thinner slice thickness volumetric data.