Volumetric quantification of absolute local normalized helicity in patients with bicuspid aortic valve and aortic dilatation

Purpose: Absolute local normalized helicity (LNH) can differentiate flow alterations in the aorta between healthy controls and bicuspid aortic valve (BAV) patients. Methods: A total of 65 controls and 50 subjects with BAV underwent in vivo four-dimensional (4D) flow MRI. Data analysis included the three-dimensional (3D) segmentation of the thoracic aorta (ascending aorta, aortic arch, and descending aorta) and calculation of absolute LNH. The mean velocity in the entire aorta was used to identify peak systole, systolic deceleration, and middiastole. A sensitivity analysis was performed to identify the optimal absolute LNH threshold, comparing control and BAV groups. A reproducibility test was performed for 3D segmentation and absolute LNH. Results: Absolute LNH above 0.6 was significantly higher (P < 0.001) in BAV in comparison to controls for all aortic segments and cardiac time frames. Absolute LNH in the ascending aorta correlated with maximal aortic diameter (R = 0.83, P < 0.001, at peak systole; r = 0.84, P < 0.001, at systolic deceleration; R = 0.88, P < 0.001, at middiastole) and significantly increased (P < 0.001) with aortic stenosis severity. Intra- and interobserver errors were 5 ± 2% and 12 ± 6% for 3D segmentation and 7 ± 6% and 12 ± 7% for absolute LNH. Conclusion: Absolute LNH can differentiate between controls and subjects with aortic dilatation, and was associated with maximal aortic diameter and aortic stenosis severity. Magn Reson Med 78:689–701, 2017.