Multi-angle fluoroscopic lung perfusion imaging using x-ray pulsatility index: A pilot study in healthy subjects.

BACKGROUND: X-ray pulsatility index (XPI) quantifies cardiac-synchronous attenuation changes as a surrogate for regional lung perfusion, but current implementations are limited by projectional overlap and the lack of reference values in healthy individuals. PURPOSE: To characterize regional XPI patterns and establish preliminary reference values in healthy participants using a novel multi-angle fluoroscopic imaging system. METHODS: Nineteen healthy participants underwent an 8 s breath-hold during fluoroscopic imaging using 15 fps at four simultaneous projections (LPO, AP caudal, RPO, AP cranial) using a novel scanner. Frames were cropped to exclude initial x-ray tube stabilization and bulk motion. Spectral analysis exploited the periodic signal attenuation in the lungs to create XPI maps, as previously described. To focus on the clinically important regions of lung perfusion, the peripheral 3 cm of lung was manually segmented and divided into upper, middle, and lower lung zones. XPI values from these regions were compared to evaluate laterality and cranial-caudal differences using paired t-tests corrected with the Benjamini-Hochberg procedure to control the False Discovery Rate (FDR). Peripheral XPI contrast-to-noise (pCNR) was calculated in the AP caudal projection to quantify signal-to-background separation. Data were retrospectively resampled to assess the effect of reduced frame rate (7.5, 5 fps) and shorter acquisition time using multiple regression analysis. Radiation dose was estimated using phantom measurements and simulation. RESULTS: All participants performed the breath-hold without difficulty. XPI maps demonstrated bilateral lung perfusion across all four views, enabling multi-projection assessment of regional perfusion. No focal defects were observed; however, one participant demonstrated globally reduced XPI. Significant cranial-caudal gradients in XPI were observed across projection angles, consistent with known gravity-dependent physiology. Following FDR adjustment (Q = 0.05), the lower zones continued to demonstrate significantly higher values than the upper zones in 3 of 4 projections (all q < 0.05). There were no significant laterality differences (q > 0.05). XPI values remained stable across acquisition lengths and frame rates, indicating robustness of the metric. CNR increased with longer acquisitions and higher frame rates, reflecting reduced noise and improved signal reliability. CONCLUSION: Multi-angle XPI fluoroscopy enables non-invasive regional lung perfusion assessment with low radiation exposure and provides preliminary reference values for future clinical investigation.