1352408 - 4D flow MRI derived hemodynamic parameters are associated with false lumen thrombus status in descending aortic dissection

Uncomplicated type B aortic dissection (TBAD) can be managed by anti-impulse therapy, however rapid growth in descending aorta in TBAD has critical treatment implications and significant proportion of medically managed TBAD patients still require surgical intervention during their follow-up. False lumen (FL) thrombus status is closely associated with progression in TBAD as patent FL increases the risk of adverse outcomes and quantitative hemodynamic flow parameters associated with FL thrombus status may aid clinicians in risk-stratification of TBAD cases. We hypothesize that 4D flow MRI derived quantitative flow parameters may be associated with FL thrombus status and aid clinicians in monitoring and treatment plan for TBAD cases.

Methods: Using an IRB-approved protocol, 37 de novo TBAD patients (57.78 ± 12.42 year-old, 16 female) were retrospectively and prospectively recruited. All patients underwent 4D flow MRA scan with conventional GRAPPA accelerated acquisition. Preprocessing of the 4D flow MR images (MatLab, MathWorks, USA) was followed by manual segmentation of true lumen (TL) and FL on a designated software (Mimics, Materialise NV, Belgium). In the next step, voxelwise total kinetic energy (KE), mean 5th percentile peak velocity (PV), mean stasis (percentage of cardiac cycle that velocity is < 0.1 m/s averaged over the entire FL volume), mean forward flow (FF) and mean reverse flow (RF) in FL were quantified. FL thrombus status was graded by an experienced radiologist through the conventional clinical images obtained on the same day of 4D flow MRI and thrombus level was divided into 2 groups as low level (≤ 25% thrombus, level 1, n = 26) and high level (25-100%, level 2, n = 11). Independent T test was used for normally distributed data, Mann Whitney U test was used for non-normally distributed parameters.

Results: In the overall cohort; KE, PV, FF and RF were significantly higher (p = 0.031, 0.002, < 0.001 and 0.005 respectively) and stasis was lower (p < 0.001) in the patient group with low level of thrombus compared to the high thrombus group. Similarly, in acute + subacute cases subgroup (level 1, n = 11 and level 2, n = 6) KE, PV, FF and RF were significantly higher (p = 0.015, 0.012, 0.002 and 0.019 respectively) and stasis was lower (p = 0.011) in low thrombus group compared to the patients with high level of thrombus. In chronic cases (level 1, n=15 and level 2, n=5), FF was higher (p = 0.033) and mean stasis was lower (p = 0.042) in low thrombus group.

Conclusion: Certain quantitative flow parameters showed significant differences between two groups of de novo TBAD patients with low and high level of FL thrombus in overall cohort and in subgroups based on the acuity of the dissection. These results demonstrate the potential role of hemodynamic assessment for improved monitoring and risk-stratification during the clinical course of TBAD cases and these quantitative 4D flow MRI derived flow parameters may assist clinicians in treatment plans of the TBAD cases.