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In vitro Assessment of Aortic Regurgitation Using Four-Dimensional Flow Magnetic Resonance Imaging
Published on: February 25, 2022
Baseline 4D Flow-Derived in vivo Hemodynamic Parameters Stratify Descending Aortic Dissection Patients With Enlarging
Stanley Chu1, Ozden Kilinc1, Maurice Pradella1
1Department of Radiology, Northwestern University, Chicago, IL, United States.
Insights
Four-dimensional flow MRI can predict adverse outcomes in type B aortic dissection (TBAD) by assessing true lumen and false lumen hemodynamics. This hemodynamic assessment aids in early identification of at-risk patients for timely intervention.
Area of Science:
- Cardiovascular Imaging
- Medical Physics
- Biomedical Engineering
Background:
- Type B aortic dissection (TBAD) poses significant risks, necessitating improved methods for predicting adverse outcomes and aortic growth.
- Traditional imaging modalities like MRA and CTA provide morphological data but may not fully capture the dynamic hemodynamic changes within the aorta.
Purpose of the Study:
- To evaluate the predictive value of true lumen (TL) and false lumen (FL) hemodynamics, compared to aortic morphology, for adverse-aorta related outcomes (AARO) and aortic growth in TBAD patients.
- To explore the utility of 4D flow MRI in assessing hemodynamic parameters relevant to TBAD progression.
Main Methods:
- Retrospective analysis of 51 patients with TBAD or residual TBAD (rTAAD) using 4D flow MRI.
- Manual segmentation of TL and FL from 4D flow MRI data to generate 3D hemodynamic maps.
- Comparison of hemodynamic parameters (kinetic energy, stasis, peak velocity, flow patterns) and aortic diameter between groups with and without AARO, and with different growth rates (≥3 mm/year vs. <3 mm/year).
Main Results:
- Patients with AARO exhibited larger baseline aortic diameters and altered FL and TL hemodynamics, including lower FL reverse flow and TL kinetic energy.
- In the de novo TBAD subgroup, AARO was associated with larger diameters, lower FL stasis, and lower TL peak velocity.
- A higher FL to TL kinetic energy ratio was observed in patients with aortic growth ≥ 3 mm/year in both the overall cohort and the de novo TBAD subgroup.
Conclusions:
- Four-dimensional flow MRI offers valuable hemodynamic insights into TBAD, potentially surpassing traditional imaging techniques.
- Hemodynamic assessment via 4D flow MRI can aid in the earlier identification of patients at higher risk for AARO and aortic growth.
- This advanced imaging technique holds promise for integrating into routine TBAD management, guiding timely interventions.
Purpose:
The purpose of our study was to assess the value of true lumen and false lumen hemodynamics compared to aortic morphological measurements for predicting adverse-aorta related outcomes (AARO) and aortic growth in patients with type B aortic dissection (TBAD).
Materials And Methods:
Using an IRB approved protocol, we retrospectively identified patients with descending aorta (DAo) dissection at a large tertiary center. Inclusion criteria includes known TBAD with ≥ 6 months of clinical follow-up after initial presentation for TBAD or after ascending aorta intervention for patients with repaired type A dissection with residual type B aortic dissection (rTAAD). Patients with prior descending aorta intervention were excluded. The FL and TL of each patient were manually segmented from 4D flow MRI data, and 3D parametric maps of aortic hemodynamics were generated. Groups were divided based on (1) presence vs. absence of AARO and (2) growth rate ≥ vs. < 3 mm/year. True and false lumen kinetic energy (KE), stasis, peak velocity (PV), reverse/forward flow (RF/FF), FL to TL KE ratio, as well as index aortic diameter were compared between groups using the Mann-Whitney U or independent t-test.
Results:
A total of n = 51 patients (age: 58.4 ± 15.0 years, M/F: 31/20) were included for analysis of AARO. This group contained n = 26 patients with TBAD and n = 25 patients with rTAAD. In the overall cohort, AARO patients had larger baseline diameters, lower FL-RF, FL stasis, TL-KE, TL-FF and TL-PV. Among patients with de novo TBAD, those with AAROs had larger baseline diameter, lower FL stasis and TL-PV. In both the overall cohort and in the subgroup of de novo TBAD, subjects with aortic growth ≥ 3mm/year, patients had a higher KE ratio.
Conclusion:
Our study suggests that 4D flow MRI is a promising tool for TBAD evaluation that can provide information beyond traditional MRA or CTA. 4D flow has the potential to become an integral aspect of TBAD work-up, as hemodynamic assessment may allow earlier identification of at-risk patients who could benefit from earlier intervention.
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