False lumen regurgitation fraction and energy loss in the aorta measured using four-dimensional flow MRI to predict expansion of acute uncomplicated type B aortic dissection: a prospective study.

Aim: To assess the relationship between four-dimensional (4D)-flow-derived false lumen regurgitation fraction (FLRF) and energy loss (EL) percentage in the descending thoracic aorta (DTA) with the aortic growth rate in uncomplicated type B aortic dissection (uTBAD).

Methods And Materials: In this prospective study performed on 15 patients with uTBAD, computed tomography (CT) angiography and 4D-flow magnetic resonance imaging (MRI) were performed at the initial presentation with follow-up CT at 2 years. 4D-flow parameters, including maximum peak systolic velocity (PSV), FLRF, and percentage of EL were measured using Circle CV42. The significance of these parameters for expansion (>3 mm/year) of aortic dissection was analysed.

Results: Five patients had an enlarging aorta, while 10 had a stable aortic size. The Mann-Whitney U-test showed entry tear >10 mm (p=0.026), FLRF (7.6 ± 8.9 versus 64.8 ± 16.7%; p=0.002), EL in the DTA in (1.61 ± 1.99 versus 2.21 ± 0.32 μW/cm; p=0.014) and percentage of EL in the DTA to overall energy loss from the ascending aorta to the DTA (37 ± 15% versus 66 ± 17%; p=0.005), having a statistically significant different expanding stable dissection. A positive significant Spearman correlation was noted with the aortic growth rate (in millimetres over 2 years) with FLRF (r=0.71, p=0.003), EL in the DTA (r=0.56, p=0.007), and percentage of EL in the DTA (r=0.62, p=0.003).

Conclusion: 4D flow parameters, including FLRF and the percentage amount of EL in the DTA may help predict aortic growth at an early stage in uTBAD.