Axial bone window images at the level of the cavernous sinuses for different grades of arterial calcium. LOW CALCIUM SUBGROUP. A: Grade 1: Bilateral grade 1 cavernous carotids. Tangible arterial calcifications. B: Grade 2: Bilateral grade 2 cavernous carotids due to thin scattered calcifications. HIGH CALCIUM SUBGROUP. C: Grade 3: Bilateral grade 3 calcifications. Thick, interrupted on the right and thin confluent on the left. D: Grade 4: Bilateral grade 4 ICAC seen as thick, contiguous calcifications.