# Aortic Hemodynamics with Accelerated Dual-Venc 4D Flow MRI in Type B Aortic Dissection
## 4 Discussion
_Comparison to previously published dual-venc studies_  
[PERSON] et al. use the k-t GRAPPA-accelerated DV 4D flow MRI sequence in sixteen volunteers to evaluate its utility to assess intracranial hemodynamics including net flow and PV. The regional flow quantification in their study demonstrates a similar PV at all arterial locations, as seen in both TL and FL analyses in our study. Net flow analysis demonstratessignificantly higher values in both arterial and venous systems in the DV data compared with the HV data. Our results indicate similar FF results between SV and DV acquisitions in both TL and FL, and RF is relatively lower in DV acquisition compared with the SV. The phantom experiments in their study demonstrate 51.4% noise reduction in DV acquisitions compared with HV and the volunteer data shows decreased noise in DV compared with HV [22]. In another study, [PERSON] et al. acquire k-t GRAPPA-accelerated DV 4D flow MRI with ascending and descending aorta coverage in four Marfan syndrome patients and one bicuspid aortic valve patient and demonstrate an improved VNR in the DV 4D flow MRI data compared with the HV scan and significantly correlated PV results between DV and HV in ascending aorta and arch, as seen in our TL analysis results [20]. The TL VNR results in our patient group maintain the high VNR values in DV acquisition without any significant change compared with SV acquisition. However, as expected, HV data results demonstrate a VNR reduction compared with both DV and SV acquisitions reaching to the significance level only in comparison with DV acquisition. Our results confirm that DV acquisition preserves the favorable VNR of the low-venc (LV) data and the reduction in the VNR in HV data might be related to the CS acceleration which is neutralized by using both LV and HV reconstruction in the DV acquisition. Additionally, descending aorta dissection is the unique pathology in our study, distinctly from the above studies, and CS-acceleration and DV reconstruction methods are investigated in both high- and low-flow environments. The scan-time reduction by DV 4D flow MRI acquisition is 46.4% compared with the conventional 4D flow MRI in our study, supporting the potential of the CS-accelerated DV 4D flow MRI for clinical translation with significantly shorter scan times, entire velocity dynamic range coverage in the TL and FL avoiding the velocity aliasing and improved VNR relative to the HV acquisition alone. Shorter scan times increase the imaging efficiency and improve patient comfort, which is desirable in critically ill TBAD cases along with the importance of faster imaging for clinicians to take accurate steps in treatment management. The rigidly set velocity encoding value has been a common issue in 4D flow MRI in various pathologies including aortic dissection. In TBAD, this problem specifically lies in the substantial differences in the blood velocity of TL and FL. However, the measurement of high and low flows in the vessel can be effectively achieved by the advanced Bayesian multipoint velocity encoding method [24; 25; 26]. The DV 4D flow MRI technique has been used in various studies representing the dynamic velocity range more accurately in brain and cardiac vessels [22; 26; 36; 37; 38]. However, the effects resulting from the combination of the CS acceleration and DV technique on 4D flow MRI based hemodynamic flow quantifications in TBAD have not been reported in TL and FL separately. Additionally, these 4D flow MRI-derived hemodynamic parameters have not been implemented in diagnostic and/or prognostic criteria in TBAD and neither any gold standard hemodynamic flow quantification method nor any 4D flow MRI based hemodynamic parameter value has been validated as a reference for TBAD patients.