Four-dimensional flow assessment of pulmonary artery flow and wall shear stress in adult pulmonary arterial hypertension: results from two institutions

Abstract

Purpose: To compare pulmonary artery flow using Cartesian and radially sampled four-dimensional flow-sensitive (4D flow) MRI at two institutions.

Methods: Nineteen healthy subjects and 17 pulmonary arterial hypertension (PAH) subjects underwent a Cartesian 4D flow acquisition (institution 1) or a three-dimensional radial acquisition (institution 2). The diameter, peak systolic velocity (Vmax), peak flow (Qmax), stroke volume (SV), and wall shear stress (WSS) were computed in two-dimensional analysis planes at the main, right, and left pulmonary artery. Interobserver variability, interinstitutional differences, flow continuity, and the hemodynamic measurements in healthy and PAH subjects were assessed.

Results: Vmax, Qmax, SV, and WSS at all locations were significantly lower (P < 0.05) in PAH compared with healthy subjects. The limits of agreement were 0.16 m/s, 2.4 L/min, 10 mL, and 0.31 N/m(2) for Vmax, Qmax, SV, and WSS, respectively. Differences between Qmax and SV using Cartesian and radial sequences were not significant. Plane placement and acquisition exhibited isolated, site-based differences between Vmax and WSS.

Conclusions: 4D flow MRI was used to detect differences in pulmonary artery hemodynamics for PAH subjects. Flow and WSS in healthy and PAH subject cohorts were similar between Cartesian- and radial-based 4D flow MRI acquisitions with minimal interobserver variability.

Keywords: 4D flow MRI; pulmonary hypertension; wall shear stress.

Figure 1

a) Time resolved pathline visualization in a volunteer subject from Institution 1 (Cartesian acquisition). 2D CINE images at the pulmonary valve and pulmonary branches are included to show vessel morphology. 2D measurement planes (dotted lines) located at the main, left and right pulmonary artery (PA) were used for b) flow quantification. c) Time resolved pathline visualization in a volunteer subject from Institution 2 (PC-VIPR acquisition) and, d) flow quantification for the PC-VIPR exam.

Figure 2

Conservation of mass (sum of flow through LPA and RPA vs flow through MPA) for the two 4D flow MRI techniques used to assess pulmonary blood flow.

Figure 3

Comparisons of regional WSS derived from Cartesian 4D flow MRI (A) and PC VIPR (B) data (observer 2). The individual plots show the WSS distribution in normal controls compared to patients with PAH. Note that both Cartesian 4D flow MRI and PC VIPR were able to detect similar changes in segmental systolic WSS in PAH patients compared to controls. *All measured locations were significantly different between controls and PAH patients, for both sequences with p< 0.01.

Figure 4

Bland-Altman analysis of inter-observer variability for four different measures of pulmonary artery hemodynamics (peak flow, total flow, peak velocity and WSS). Points represent data from N=19 healthy controls and N=17 PAH patients. For each subject, flow and WSS parameters were evaluated by two independent observers in the three analysis planes (main pulmonary artery, right pulmonary artery, and left pulmonary artery) resulting in N = 3 * (19 + 17) = 108 data points for each Bland-Altman plot. If mean difference exhibited a non-zero slope, 95% confidence intervals are presented in brackets.

Figure 5

Inter-observer agreement of the segmental analyses of peak systolic WSS in the main (MPA), left (LPA), and right (RPA) pulmonary arteries. Each graphs shows the comparison of segmental WSS for all N=36 4D flow data sets (19 healthy controls and 17 PAH patients) which were analyzed by two independent observers blinded to each other’s results.

Figure 6

Systolic WSS (averaged across the circumference of the vessel lumen) as a function of disease state, vessel diameter (D), peak flow rate (Qmax), and measurement location (LPA-left pulmonary artery; MPA-main pulmonary artery; RPA-right pulmonary artery).