Comparison of Lung Perfusion Using X-Ray Pulsatility Index With Pulmonary Angiography in Chronic Thromboembolic Pulmonary Hypertension

PURPOSE: We compared lung perfusion abnormalities using non-contrast X-ray pulsatility index (XPI) to pulmonary angiography in patients with suspected CTEPH. MATERIALS AND METHODS: Volunteers suspected of CTEPH between April 2023 and May 2024 were enrolled and provided consent for the IRB-approved prospective study, resulting in 13 patients (6 male; 7 female) and 18 independent lungs. Fluoroscopic acquisition (70 kV, 30 frames/s) was acquired over an 8-second breath-hold. The temporal signal from each pixel was decomposed into individual frequency components using spectral analysis. Signal oscillating at the heart rate was isolated using a band-pass filter and the amplitude (XPI) mapped to form an image. Immediately after each fluoroscopic acquisition for XPI, digital subtraction pulmonary angiography was performed using catheter-injected contrast in the same projection for comparison. Both XPI and DSA perfusion maps were segmented using a semi-automated technique. Segmentation maps were compared using the Dice similarity score, a statistical measurement of overlap. RESULTS: Non-contrast fluoroscopy and contrast DSA images were obtained in 18 lungs. All patients were able to perform satisfactory breath-hold, despite several with moderate to severe CTEPH. Direct comparison of segmentation maps revealed an average Dice score of 0.70, suggesting excellent agreement between XPI and pulmonary angiography in depicting regions of blood flow and perfusion defects. CONCLUSIONS: XPI is a non-contrast method to evaluate and monitor pulmonary perfusion, producing maps with excellent agreement to pulmonary angiography, which is confirmatory for CTEPH. This technique could improve clinical efficiency as a screening or diagnostic test to augment clinical pulmonary function assessment.