Quantification of vortex flow in pulmonary arteries of patients with chronic thromboembolic pulmonary hypertension

Purpose: This study proposes an objective method of quantifying the vortex flow in pulmonary arteries to compare the duration of its presence before and after balloon pulmonary angioplasty (BPA) in patients with chronic thromboembolic pulmonary hypertension (CTEPH). Methods: Thoracic 4D-flow magnetic resonance imaging was performed in 28 CTEPH patients before and after BPA. Planes were set in pulmonary arteries to evaluate volume flow rate (VFR), the duration, and area of backward flow in the pulmonary trunk, which is a component of the vortex flow. The full width at half maximum (FWHM) of the peak of the time course of VFR of backward flow was assessed to quantify the duration of the vortical flow. Results: Although overall flow patterns after BPA appeared to be the same as the one before BPA, significant decreases in the FWHM, area, and VFR of the backward flow after BPA were found (FWHM: before, 1.88 × 10⁻¹ ± 1.51 × 10⁻² [cardiac cycle] vs. after, 1.65 × 10⁻¹ ± 1.86 × 10⁻² [cardiac cycle]; area ratio: before, 2.67 × 10⁻¹ ± 1.30 × 10⁻² vs. after, 2.38 × 10⁻¹ ± 1.31 × 10⁻²; VFR: before, 13.6 ± 2.21 [mL/s] vs. after, 11.3 ± 2.36 [mL/s]). Conclusion: BPA promoted significant decreases in the FWHM, area, and VFR of backward flow in the pulmonary trunk, thereby facilitating efficient blood transport. The tendencies for these changes were to be larger for cases where BPA more greatly decreased the pressure. The results suggest that the FWHM, area, and VFR are useful indicators for the noninvasive evaluation of the therapeutic effects of BPA.