Quantitative Assessment of Regional Pulmonary Transit Times in Pulmonary Hypertension

Background Pulmonary hypertension (PH) contributes to restricted flow through the pulmonary circulation characterized by elevated mean pulmonary artery pressure acquired from invasive right heart catheterization (RHC). MRI may provide a noninvasive alternative for diagnosis and characterization of PH. Purpose To characterize PH via quantification of regional pulmonary transit times (rPTT). Study Type Retrospective. Population A total of 43 patients (58% female); 24 controls (33% female). RHC-confirmed patients classified as World Health Organization (WHO) subgroups 1-4. Field Strength/Sequence A 1.5 T/time-resolved contrast-enhanced MR Angiography (CE-MRA). Assessment CE-MRA data volumes were combined into a 4D matrix (3D resolution + time). Contrast agent arrival time was defined as the peak in the signal-intensity curve generated for each voxel. Average arrival times within a vessel region of interest (ROI) were normalized to the main pulmonary artery ROI (t(0)) for eight regions to define rPTT for all subjects. Subgroup analysis included grouping the four arterial and four venous regions. Intraclass correlation analysis completed for reproducibility. Statistical Tests Analysis of covariance with age as covariate. A priori Student's t-tests or Wilcoxon rank-sum test; alpha = 0.05. Results compared to controls unless noted. Significant without listing P value. ICC ran as two-way absolute agreement model with two observers. Results PH patients demonstrated elevated rPTT in all vascular regions; average rPTT increase in arterial and venous branches was 0.85 +/- 0.15 seconds (47.7%) and 1.0 +/- 0.18 seconds (16.9%), respectively. Arterial rPTT was increased for all WHO subgroups; venous regions were elevated for subgroups 2 and 4 (group 1, P = 0.86; group 3, P = 0.32). No significant rPTT differences were found between subgroups (P = 0.094-0.94). Individual vessel ICC values ranged from 0.58 to 0.97. Data Conclusion Noninvasive assessment of PH using standard-of-care time-resolved CE-MRA can detect increased rPTT in PH patients of varying phenotypes compared to controls. Level of Evidence 1 Technical Efficacy Stage 3.