## 2 Materials and Methods
### Assessment of The Subcutaneous and Visceral Adipose Tissue  
The volume of the SAT and VAT was determined for each patient. The process used in the measurements is described below. The scanned angio-CT images were visualized in the Angio Run Off 5.0 application of the syngo.via Frontier and viewed as read only. For adipose tissue measurements we used the MM Research Platform, the Cardiovascular Risk Assessment and the Abdominal Fat Segmentation applications of the cited image postprocessing software. This program opens the scanned angio CT images of the lower limbs in multiple ways at the same time: transversal, lateral and vertical views. In this application, we especially used the transversal view, because it allowed better identification of the origin of the common iliac arteries, which is the level we selected for all adipose tissue measurements. After finding the origin of the common iliac arteries in vertical, lateral and transversal incidences, we focused on the origin of the common iliac artery. Selection of the left or right iliac artery was done in accordance with the target level selected for measuring the subcutaneous and visceral adipose tissue. At this level manual separation of the visceral and subcutaneous adipose tissues was performed by drawing a line on the muscles of the anterior and posterior abdominal wall. The predetermined attenuation threshold of \(-150\) and \(-50\) HU of the adipose tissue, was than recognized by the software, as this is the established range for the CT density of the adipose tissue. The manually traced line that separates the adipose tissue located exteriorly and interiorly from the abdominal muscles, respectively, separated the two types of fatty tissue: the subcutaneous from the visceral.  
The second measurement was performed at the distal part of the chosen common iliac artery, before its bifurcation into the external and internal iliac arteries. The distal part of the common iliac artery was analyzed in every incidence, using the transversal, vertical and lateral views, focusing on the immediate level of the bifurcation of the common iliac artery. In this transversal view, we again traced a line at the level of the anterior and posterior abdominal muscles, separating the subcutaneous adipose tissue from the visceral one. Whenever the traced line did not follow the contour of the abdominal muscles with precision, we manually edited the line to adjust the contour and obtain a perfect alignment with the contour of the fat.  
To determine the volume of the subcutaneous and visceral adipose tissue at the whole length of the chosen common iliac artery, we used the function of automated interpolation of contours to create the separation line on the anterior and posterior abdominal muscles at the whole length of the vessel, as presented in Figure 3. The volume of the subcutaneous and visceral adipose tissue was then determined automatically and displayed together with the ratio between them. Figure 4 illustrates a diagram of the image postprocessing steps.  
For the purpose of this study, we investigated the association between the amount of PIAT and:  
* complexity of the peripheral artery disease, expressed by TASC (Trans-Atlantic Inter-Society Consensus) class, in which TASC A represents the less complex and TASC D the most complex disease, according to the CT angiographic aspect of the iliac atherosclerotic lesions [12];
* traditional cardiovascular risk factors and co-morbidities;
* the amount of other computer-aided imaging biomarkers characterizing adipose tissue distribution, including the visceral and subcutaneous fat measured at the level of the common iliac arteries.