[Dual-wavelength photoacoustic microscopy for evaluation of microcirculatory dysfunction and spatial heterogeneity in...

To investigate microcirculatory dysfunction and spatial heterogeneity in mice with liver fibrosis using dual-wavelength high-resolution photoacoustic microscopy (PAM).

In a male C57BL/6 mouse model of CCl₄-induced liver fibrosis, multiparametric imaging of intrahepatic microcirculation was performed using dual-wavelength PAM. The acquired images were used for reconstruction of blood oxygen saturation (sO₂) distribution maps based on PAM signals and using a spectral unmixing algorithm. The portal area and central vein region within the hepatic lobule were defined as the main regions of interest, and Evans Blue dynamic extravasation analysis was used to assess vascular permeability and spatial heterogeneity of fibrosis progression. Intrahepatic microvascular blood flow velocity was measured using the Doppler bandwidth broadening method, and the local metabolic rate of oxygen (MRO₂) was calculated based on sO₂ parameters.

Compared with normal mice, the mice with liver fibrosis exhibited disorganized intrahepatic microvascular network architecture, focal rarefaction, and impaired branching structures with significantly decreased intrahepatic microvascular sO₂ [(93.62±2.44)% vs (85.53±3.37)%, P<0.05). Evans Blue dynamic tracing showed increased extravasation in the liver fibrosis group, and tracer diffusion kinetics differed significantly between the portal area and central vein region within the hepatic lobule, indicating marked spatial heterogeneity. Microvascular blood flow velocity was significantly lower in liver fibrosis group than in the normal control group (3.43±0.32 vs 4.16±0.25 mm/s; P<0.05). The local MRO₂ showed a decreasing trend in the liver fibrosis group compared with the normal control group (0.40±0.026 mL·100 g^-1·min^-1vs 0.35±0.048 mL·100 g^-1·min^-1).

Multiparametric imaging based on PAM enables systematic and multidimensional assessment of microcirculatory structural and functional alterations in mice during liver fibrosis progression, highlighting significant reductions of intrahepatic microvascular sO₂ and blood flow velocity. This approach combined with spatial heterogeneity analysis provides important imaging evidence for staging assessment, mechanistic study, and therapeutic efficacy evaluation for liver fibrosis.