Color mapping of 4D-CTA for the detection of cranial arteriovenous shunts

Four-dimensional CT angiography (4D-CTA) is increasingly used in clinical practice for the assessment of different neurovascular disorders. Optimized processing of 4D-CTA is crucial for diagnostic interpretation because of the large amount of data that is generated. A color-mapping method of 4D-CTA is presented for improved and enhanced visualization of the cerebral vasculature hemodynamics. This method was applied to detect cranial AVFs. All patients who underwent both 4D-CTA and DSA in our hospital in the period 2011-2018 for the clinical suspicion of a cranial AVF or caroticocavernous fistula (CCF) were retrospectively collected. Temporal information in the cerebral vasculature was visualized using a patient-specific color-scale. All color-maps were evaluated by three observers for the presence or absence of an AVF or CCF. The presence or absence of cortical venous reflux was evaluated as a secondary outcome measure. In total 31 patients were included, 21 patients with and 10 without an AVF. Arterialization of venous structures in AVFs was accurately visualized using color-mapping. There was high sensitivity (86-100%) and moderate-to-high specificity (70-100%) for the detection of AVFs on color-mapping 4D-CTA, even without the availability of dynamic subtraction rendering. The diagnostic performance of the three observers in the detection of cortical venous reflux was variable (sensitivity 43-88%, specificity 60-80%). Arterialization of venous structures can be visualized using color mapping of 4D-CTA and proves to be accurate for the detection of cranial AVFs. This makes color-mapping a promising visualization technique for assessing temporal hemodynamics in 4D-CTA.