Intracranial Carotid Artery Calcification Scoring

All included patients had available non-contrast cranial CT axial scan (Philips Brilliance 64 CT Scanner; Philips Healthcare, Andover, MA, USA) with slice thickness of 5 mm at admission (routine practice in China).
We detected ICAC scores according to the modified version of the Woodcock visual scoring (15 (link), 16 (link)). In brief, the ICAC score of carotid siphon on each axial CT slice was defined as follows, 0 for no ICAC; 1 for thin, discontinuous ICAC; 2 for thin, continuous ICAC or thick, discontinuous ICAC; 3 for thick, continuous ICAC (Figure 2). The score assigned for each axial slice was finally added up to create a total score for each ICA. Carotid siphon was defined as the portion between the petrous apex and anterior clinoid (13 (link)). Two independently neurologists blinded to the clinical data of the patients evaluated the bilateral calcification score of each slice in the Picture Archiving and Communication System (PACS) workstation, using a fixed bone window setting (window level of 500 HU and window width of 2000HU). They had received standardized training before CT images evaluation. The intraclass correlation coefficient (ICC) values of right and left side scores from the two observers were 0.851 (P < 0.001) and 0.956 (P < 0.001).