The purpose of this study was to assess the feasibility of color K-edge imaging enabled by spectral photon-counting CT (SPCCT) for simultaneous ventilation-perfusion evaluation using xenon and a gadolinium–based agent within healthy rabbit lungs.

In this animal study, a clinical SPCCT prototype was used to perform lung imaging in five New Zealand white rabbits. A phantom study was performed to assess gadolinium quantification accuracy and cross-contamination. Animals underwent controlled mechanical ventilation with xenon gas wash-in and received an intravenous injection of a gadolinium-based ultrasmall rigid platform (USRP) (dose, 2.3 mL·kg ⁻¹ ; injection rate, 3 mL·s ⁻¹ ; concentration, 0.29 mmol Gd.mL ^-1 ). Material decomposition yielded specific xenon and gadolinium K-edge images. Xenon maps were validated against dynamic specific ventilation maps using Pearson correlation test and linear regression analysis. Regional lung distribution was analyzed using Kruskal-Wallis test.

Five rabbits (mean weight, 2.9 ± 0.06 [standard deviation] kg) were evaluated. In phantoms, measured gadolinium concentrations showed a perfect linear correlation with prepared concentrations ( R ² = 1). In vivo, normalized steady-state xenon maps demonstrated a strong correlation with specific ventilation maps, with a pooled Pearson correlation coefficient of 0.88 and a pooled R ² of 0.78. Simultaneous imaging revealed a homogeneous xenon distribution with a median value across rabbits of 60.2% (first quartile [Q1], 59.3%; third quartile [Q3], 67.9%), with no significant regional differences. The median gadolinium perfusion across rabbits was 6.1% (Q1, 3.0%; Q3, 7.1%), with a significant dorsal-ventral gradient ( P < 0.05) where the median value increased from 0.2% (Q1, -0.2%; Q3, 1.3%) in ventral regions to 6.9% (Q1, 3.8%; Q3, 10.6%) in dorsal regions.

Color K-edge xenon/gadolinium-enhanced lung imaging using SPCCT is feasible in healthy animals, enabling the simultaneous specific and quantitative imaging of lung gas and blood volume.