4-D flow magnetic resonance imaging: blood flow quantification compared to 2-D phase-contrast magnetic resonance imaging and Doppler echocardiography

Abstract

Background Doppler echocardiography (echo) is the reference standard for blood flow velocity analysis, and two-dimensional (2-D) phase-contrast magnetic resonance imaging (MRI) is considered the reference standard for quantitative blood flow assessment. However, both clinical standard-of-care techniques are limited by 2-D acquisitions and single-direction velocity encoding and may make them inadequate to assess the complex three-dimensional hemodynamics seen in congenital heart disease. Four-dimensional flow MRI (4-D flow) enables qualitative and quantitative analysis of complex blood flow in the heart and great arteries. Objectives The objectives of this study are to compare 4-D flow with 2-D phase-contrast MRI for quantification of aortic and pulmonary flow and to evaluate the advantage of 4-D flow-based volumetric flow analysis compared to 2-D phase-contrast MRI and echo for peak velocity assessment in children and young adults. Materials and methods Two-dimensional phase-contrast MRI of the aortic root, main pulmonary artery (MPA), and right and left pulmonary arteries (RPA, LPA) and 4-D flow with volumetric coverage of the aorta and pulmonary arteries were performed in 50 patients (mean age: 13.1±6.4 years). Four-dimensional flow analyses included calculation of net flow and regurgitant fraction with 4-D flow analysis planes similarly positioned to 2-D planes. In addition, 4-D flow volumetric assessment of aortic root/ascending aorta and MPA peak velocities was performed and compared to 2-D phase-contrast MRI and echo. Results Excellent correlation and agreement were found between 2-D phase-contrast MRI and 4-D flow for net flow (r=0.97, P<0.001) and excellent correlation with good agreement was found for regurgitant fraction (r= 0.88, P<0.001) in all vessels. Two-dimensional phase-contrast MRI significantly underestimated aortic (P= 0.032) and MPA (P<0.001) peak velocities compared to echo, while volumetric 4-D flow analysis resulted in higher (aortic: P=0.001) or similar (MPA: P=0.98) peak velocities relative to echo. Conclusion Excellent flow parameter agreement between 2-D phase-contrast MRI and 4-D flow and the improved volumetric 4-D flow velocity analysis relative to echo suggests that 4-D flow has the potential to become a clinical alternative to 2-D phase-contrast MRI.

Clinical assessment of aortic valve stenosis: Comparison between 4D flow MRI and transthoracic echocardiography

“…Nevertheless, it affords a uniquely detailed assessment of flow patterns in the heart and aorta. Validation studies have compared 4D PC‐MR with echocardiography in healthy volunteers and in patients without valvular disease (ie, subjects with laminar flow patterns), and found good agreement between both modalities . However, as previously reported by others, we found that systolic flow jets in AS patients are often eccentric .…”

“…Furthermore, the entire acquired volume can be analyzed in a search for the highest flow jet velocity. In healthy volunteers and patients with normally functioning valves, 4D PC‐MR has shown improved flow quantification relative to echo . We hypothesized that in AS patients, who often exhibit eccentric and dynamic flow jets, the technical features of 4D PC‐MR could be even more advantageous .…”

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

“…Positioning and orienting analysis planes in 3-D space at one or more specific anatomical locations as an additional post-processing step can be time consuming and also result in poor reproducibility across subjects and between operators due to its operator dependence. Volumetric ROI analysis, as used in our study as well as others, 11, 25 can reduce operator dependence and the risk of missing the true systolic peak velocity. Systolic flow patterns, which can give a qualitative sense of hemodynamics, as has been shown in other work investigating the relationship between flow patterns and energy loss, 26 are readily apparent in 4D flow MIPs.…”

Advanced flow MRI: emerging techniques and applications

“…Previous studies have shown that the technique can reliably identify altered 3D flow characteristics related to the post-interventional status in patients with CHD 149-152 . In addition, 4D flow MRI based flow quantification has been shown to be equivalent or even improved when compared to 2D techniques, while needing less imaging time than the positioning of multiple planes 58,61,64,67,68 . More recent developments combining parallel imaging or compressed sensing with 4D flow MRI have high potential to reduce scan times to <5 minutes.…”