OBJECTIVE: Photon-counting CT (PCCT) combines improved dose efficiency with spectral imaging, enabling dynamic functional imaging at chest CT dose levels. Dual energy CT typically uses perfused blood volume (PBV) as a static perfusion surrogate. This study compared low-dose dynamic PCCT compared with reference-dose PCCT and static PBV imaging. MATERIALS AND METHODS: Six minipigs with left lung transplants underwent dynamic perfusion imaging using PCCT at reference and low-dose settings, along with a static PBV scan. Perfusion metrics-Blood Flow Deconvolution (BFD), Mean Transit Time Deconvolution (MTTD), Flow Extraction Product (FEP), and Time to Start Deconvolution (TTSD)-were normalized and analyzed across six lung regions using Kruskal-Wallis tests and Bland-Altman analysis. RESULTS: Low-dose and reference-dose dynamic PCCT showed strong agreement across perfusion parameters (BVP bias: 0.03; BVD bias: 0.04), with no significant differences in BVP (p = 0.995) or BVD (p = 0.374). Kinetic metrics were stable across dose levels (all p > 0.2). While low-dose imaging showed slightly greater perfusion heterogeneity, BVP remained robust. Static PBV differed significantly from dynamic BVP (reference dose: p < 0.001; low-dose: p = 0.04). Left-right perfusion differences were detected in two animals by all methods. Estimated doses were 2.37 mSv (reference-dose) and 1.36 mSv (low-dose), comparable to chest CT (1.49 mSv) and below conventional CT perfusion (3-10 mSv). CONCLUSION: Dynamic PCCT enables quantitative lung perfusion imaging at radiation doses comparable to standard chest CT. Low-dose dynamic PCCT shows strong agreement with reference-dose acquisitions, while dynamic parameters reveal functional differences not captured by static PBV imaging. RELEVANCE STATEMENT: Dynamic low-dose photon-counting computed tomography enables lung perfusion quantification at radiation doses comparable to standard chest CT, facilitating dose-efficient functional imaging in pulmonary disease. KEY POINTS: Low-dose PCCT (~ 1.36 mSv) is feasible, comparable to single chest CT (1.49 mSv). Strong agreement was seen between low- and reference-dose PCCT (BVP bias 0.03; BVD bias 0.04). Kinetic perfusion metrics remained stable across dose levels (all p > 0.2).
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