Detection and Hemodynamic Evaluation of Flap Fenestrations in Type B Aortic Dissection with 4D Flow MRI: Comparison with Conventional MRI and CT Angiography

Purpose: To compare dissection flap fenestration visualization between three-dimensional time-resolved phase contrast MRI with three-directional flow encoding (hereafter, 4D flow MRI), clinical combined MRI and MR angiography (hereafter, MRI/MR angiography), and clinical CT angiography and to describe the presence of hemodynamically active fenestration flow using 4D flow MRI. Materials and Methods: Nineteen patients with type B dissection (mean age, 57 years +/- 5 [standard deviation]) who had undergone standard-of-care chest MRI/MR angiography, including 4D flow MRI, were retrospectively identified. Fourteen of the 19 patients also had CT angiography performed within 2 years of MRI/MR angiography, with no interval surgery. Image review was performed independently by two radiologists. The number of fenestrations (including entry and exit tears), location, and flow directionality were recorded. Differences in the rate of detection between techniques were assessed by using a Wilcoxon signed-rank test. Results: More fenestrations were detected with 4D flow MRI than with MRI/MR angiography (reviewer 1, +3 [10%]; reviewer 2, +5 [20%]). A similar number of fenestrations was detected with 4D flow MRI and CT angiography (reviewer 1, +1 [4%]; reviewer 2, -3 [-12%]). MRI/MR angiography depicted fewer fenestrations than did CT angiography in this cohort (reviewer 1, -6 [-24%; reviewer 2, -5 [-19%]). No differences were significant. Combining 4D flow MRI and MRI/MR angiography resulted in detection of additional fenestrations. Most fenestrations showed biphasic flow over the cardiac cycle (flow entering the false lumen during systole and exiting during diastole; reviewer 1, 18 and 33, respectively; reviewer 2, 16 and 30, respectively). Conclusion: The 4D flow MRI technique can be used to detect small flap fenestration in patients with type B dissection while yielding additional information about flow through fenestrations throughout the cardiac cycle relative to CT angiography and conventional MRI.