Efficient method for volumetric assessment of peak blood flow velocity using 4D flow MRI

Abstract

Purpose To test the feasibility and effectiveness of using maximum intensity plots (MIPs) based on 4D flow MRI velocity data to assess systolic peak velocities in a cohort of bicuspid aortic valve (BAV) patients. Materials and Methods 4D flow MRI at 1.5 T was performed on 51 BAV patients. MIPs were generated from the 4D flow MRI velocity data and used by 2 users to determine peak velocities in 3 regions of interest (ROI): ascending aorta (AAo), aortic arch and descending aorta. 4D flow MRI peak velocities in the AAo were compared to peak velocities recorded by 2D phase contrast MRI (2D PCMRI) in a subcohort of 36 patients and by Doppler echocardiography in a subcohort of 34 patients. 4D flow MRI peak velocities recorded by each observer were compared for all ROIs to test for inter-observer variability. Results 4D flow MRI recorded significantly higher velocities compared to 2D PCMRI (2.04 ± 0.71 m/s vs 1.69 ± 0.79 m/s, 17.2% difference, p < 0.001) and similar velocities compared to Doppler echocardiography. There was excellent agreement between the observers with a mean difference of 0.005 m/s and an intraclass correlation coefficient of 0.98. Conclusion 4D flow MRI velocity MIPs allow for efficient measurement of peak velocities in BAV patients with higher accuracy than 2D PCMRI and similar accuracy to Doppler echocardiography.

Aortic Valve Stenosis Alters Expression of Regional Aortic Wall Shear Stress: New Insights From a 4‐Dimensional Flow Magnetic Resonance Imaging Study of 571 Subjects

“…3D phase contrast MR angiograms were computed based on the 4D flow data and used to obtain a 3D segmentation of the aorta using a commercial software package (Mimics; Materialise, Leuven, Belgium) 21. To quantify degree of AS in patients, peak velocity during systole was quantified at the aortic root using an oblique sagittal maximum intensity projection of the absolute velocity 22. Degree of AS was classified according to current guidelines with respect to the peak transvalvular vena contracta velocity, that is, no AS: <2.0 m/s; mild AS: 2.0 to 2.9 m/s; moderate AS: 3.0 to 3.9 m/s; and severe AS: ≥4.0 m/s 23.…”

4D flow MRI, cardiac function, and T1‐mapping: Association of valve‐mediated changes in aortic hemodynamics with left ventricular remodeling

“…The aorta segmentation was used to mask the 4D flow velocity data and to calculate a maximum intensity projection (MIP) of the peak systolic absolute velocities in sagittal orientation as shown in figure 1e. This method has recently been introduced and has been proven valuable for fast and improved detection of regional peak systolic velocities frequently found in BAV patients (23). Regions of interest in the peak velocity MIP covering the AAo, arch and DAo were used to automatically extract maximum velocities in all three aortic segments (23).…”

Transcatheter aortic valve replacement alters ascending aortic blood flow and wall shear stress patterns: A 4D flow MRI comparison with age-matched, elderly controls

“…In TAVR patients and controls, the ascending aorta was defined as the segment between the first circumferential area of the ascending aorta not susceptible to metal-induced artefacts and the origin of the brachiocephalic trunk. The ascending aorta was segmented and corrected for eddy currents, Maxwell terms and velocity aliasing using inhouse software programmed in MatLab (MathWorks, Natick, MA, USA) [14,15]. Mean and maximum blood flow velocity and WSS were calculated at the peak systolic time frame using previously published algorithms [16].…”