Multi-Velocity Encoding Four-Dimensional Flow Magnetic Resonance Imaging in the Assessment of Chronic Aortic Dissection

Abstract

Background: Chronic descending thoracic aortic dissection (CDTAD) following surgical repair of ascending aortic dissection requires long-term imaging surveillance. We investigated four-dimensional (4D)-flow magnetic resonance imaging (MRI) with a novel multi-velocity encoding (multi-VENC) technique as an emerging clinical method enabling the dynamic quantification of blood volume and velocity throughout the cardiac cycle. Methods: Patients with CDTAD (n = 10; mean age, 55.1 years; standard deviation (SD) 10.8) and healthy volunteers (n = 9; mean age, 37.1 years; SD 11.4; p < 0.01) underwent 3T MRI, and standard views and 4D-flow data were obtained. Flow measurements were made in selected regions of interest within the ascending and descending thoracic aorta. Results: The overall flow profile at peak systole was reduced in the false lumen (FL) compared with the true lumen (TL) and normal aortas (p < 0.05 for velocity < 0.4 m/s). Peak systolic flow rate per aortic lumen area (mL/s/cm2) was lower in the FL than in the TL (p < 0.05), and both rates were lower than that of control aortas (p < 0.05). Blood flow reversal was higher in the FL than in the TL throughout the descending aorta in CDTAD patients (p < 0.05). A derived pulsatility index was elevated in the TL compared with that in the FL in CDTAD patients. Generated pathline images demonstrated flow patterns in detail, including sites of communication between the true and FL. Conclusions: 4D-flow MRI revealed FL blood flow and reduced blood flow velocity and flow rate in the TL of CDTAD patients compared with normal aortas of healthy participants. Thus, multi-VENC 4D-flow MRI could serve as an adjunct in the long-term assessment of CDTAD following surgical repair of ascending aortic dissection.

Parametric Hemodynamic 4D Flow MRI Maps for the Characterization of Chronic Thoracic Descending Aortic Dissection

“…Similar to our study, a recent 4D flow MRI study of 10 chronic DAD patients after AAo repair found high levels of slow flow in the FL compared to the TL and normal aorta. However, they found lower overall flow profiles and no differences in flow reversal in the TL of patients, compared to controls.…”

“…4D flow magnetic resonance imaging (MRI) (ie, 3D time‐resolved phase contrast MRI with 3‐directional velocity encoding) is uniquely poised to evaluate complex flow patterns in DAD because of the ability to measure 1) blood flow in all three main directional components, and 2) volumetric coverage to allow for quantitative analysis of the entire aorta. This technique has detected flow alterations in aortic dissection related to aortic dilatation (visualization of helical flow and distal dominant entry tears, quantification of flow velocity in the FL), found substantially higher flow in the TL with FL thrombus, and has been used to identify small dissection flap fenestrations . Previous studies are promising, but were limited by either the utilization of qualitative assessment of flow patterns or localized quantification of hemodynamic metrics, and thus the systematic parameter mapping of flow in the TL and FL is needed .…”

Impact of sequence type and field strength (1.5, 3, and 7T) on 4D flow MRI hemodynamic aortic parameters in healthy volunteers

“…32 So far, 4D flow MRI been applied using various sequence types and at different field strengths. In clinical studies, it has been used at 1.5T 11,15,18,33,34 and 3T 9,[12][13][14]35,36 or at both clinical field strengths. 16,19,20,[37][38][39] Furthermore, 4D flow MRI has been evaluated at 7T.…”

“…5,6 WSS has shown to have great potential in this field as several studies have shown the additional benefit of determining the WSS in different patients with aortic valve pathologies or pathologies of the thoracic aorta. [7][8][9][10][11][12][13][14][15] It was shown that hemodynamics were altered in the ascending aorta in the presence of an aortic valve stenosis. Such alterations included a local increase in WSS and were related to stenosis severity.…”

Computational modeling of the fluid flow and the flexible intimal flap in type B aortic dissection via a monolithic arbitrary Lagrangian/Eulerian fluid‐structure interaction model

“…For this reason, numerical simulations and ex vivo experiments can play an important role in studying the chronic AD progression in order to prevent lethal outcomes. Considerable amount of work has been dedicated to understanding the hemodynamics in the AD in ex vivo models, experimental phantoms, using numerical simulations of phantom models, using numerical simulations of real AD patients, and most recently using 4D phase‐contrast MRI AD data …”