Quantification of periaortic adipose tissue in contrast-enhanced CT angiography: technical feasibility and methodological considerations

Abstract

To examine the feasibility of the quantifcation of abdominal periaortic fat tissue (PaFT) (tissue within − 45 to − 195 HU) in enhanced CT-angiographies compared to unenhanced CT-scans and identify methodological issues afecting its clinical implementation. Using OsirixMD, PaFT volume and mean HU value were retrospectively measured within a 5 mm periaortic ring in paired unenhanced and enhanced abdominal aortic CT-scans. The correlation between PaFT values was examined in a derivation cohort (n=101) and linear regression analysis produced correction factors to convert values from enhanced into values from unenhanced CTs. The conversion factors were then applied to enhanced CTs in a diferent validation cohort (n=47) and agreement of corrected enhanced values with values from unenhanced scans was evaluated. Correlation between PaFT Volume und Mean HU from enhanced and unenhanced scans was very high (r >0.99 and r=0.95, respectively, p<0.0001 for both). The correction factors for PaFT Volume and Mean HU were 1.1057 and 1.0011. Potential confounding factors (CT-kilovoltage, slice thickness, mean intraluminal contrast density, aortic wall calcifcation, longitudinal variation of intraluminal contrast density, aortic diameter) showed no signifcant efect in a multivariate regression analysis (p>0.05). Bland-Altman analysis of corrected enhanced and unenhanced values showed excellent agreement and Passing–Bablok regression confrmed minimal/no residual bias. PaFT can be quantifed in enhanced CT-angiographies very reliably. PaFT Volume scores are very consistently slightly underestimated in enhanced scans by about 10%, while the PaFT Mean HU value remains practically constant and ofers distinct methodological advantages. However, a number of methodological issues remain to be addressed.