Values of the unenhanced stage of CT perfusion studies of liver: a multi-centre experience

Purpose: Measurements of the unenhanced values (baseline) in CT perfusion (CTp) studies is of fundamental importance for an accurate computation of CTp parameters. This study aims at assessing whether baseline values of normal liver are reproducible among different Centres. Methods and Materials: 40 patients belonging to a wider multicentre CTp study (PIXEL), with colorectal cancer and no liver disease, who did not develop metastases in the follow up, underwent liver axial CTp in four different Centres (10 patient each), with same acquisition protocol. The time concentration curves (TCCs) were computed over a wide region of interest (ROI) outlined on one central slice of the liver. The baseline segment of each TCC was determined by employing an adaptive 3D filtering and the definite baseline value was computed as the average of the segment TCC values. Mean baseline values of each patient were computed and ANOVA (p-value≤0.05) was applied to check for differences of mean baseline values among Centres. Results: CT number (HU) of baseline values of the four Centres were 57.4±13.3, 60.5±16.3, 57.7±11.1, 62.3±3.8, respectively, with ranges 34.4÷75.8, 28.0÷79.0, 42.0÷78.6, 57.6÷68.2. Statistical tests assessed that there are no differences between Centres as regards the mean baseline values. Conclusion: Baseline values of normal liver of patients with colorectal cancer are compliant with values of normal liver in healthy subjects reported in the literature. The preliminary results of this multicentre study points out a higher homogeneity of values in Centre 4, although there is no evidence that Centres introduce variability on baseline values