CT-Based Quantitative Ventilation–Perfusion Imaging for Pulmonary Embolism Assessment
Abstract
Purpose
This study develops a CT perfusion (CTP) method for simultaneous lung ventilation and perfusion imaging, overcoming limitations of conventional V/Q scans such as temporal mismatch, low resolution, procedural inefficiency, and qualitative-only evaluation.
Methods
Eight anesthetized, ventilated pigs underwent supine CT Perfusion (CTP) at 100 kVp and 50 mA, acquiring 6 images per 3-second breath cycle for 45s. Lung tissue time‑density curves (TDCs) captured perfusion (contrast-enhanced blood flow), ventilation (alveolar air volume changes), and motion. Following motion-minimizing deformable registration, voxel-wise perfusion response functions (PRFs) were derived through deconvolution of pulmonary artery and lung tissue TDCs. The perfusion TDC was reconstructed by convolving each PRF with the pulmonary artery TDC, and perfusion was quantified as the PRF peak height. Ventilation curves were isolated by subtracting perfusion from lung tissue TDCs. From these curves, ventilation was quantified as the average fractional air-volume change per breath cycle, scaled by tissue density. Full 3D ventilation‑perfusion maps were reconstructed. For validation, lungs were divided into 12 vertical ROIs; regional perfusion/ventilation and ventilation frequencies were compared.
Results
Fourier analysis of ventilation curves revealed a dominant frequency at 0.34 Hz, matching the ventilation rate used. Both ventilation and perfusion exhibited clear gravity-dependent gradients, with higher values in posterior lung regions. Linear regression yielded slopes of – 0.0025 ± 0.00012 (R² = 0.97) for ventilation and –3.1 ± 0.33 (R² = 0.89) for perfusion, consistent with physiological gravitational effects in the supine position.
Conclusion
This study demonstrates the feasibility of extending CTP to simultaneously assess lung ventilation and perfusion and generate whole lung ventilation-perfusion maps at 2-3 mm resolution. Future work will focus on validation against stable xenon CT for ventilation and 68Ga-MAA PET for perfusion.