Multi-Parametric Photoacoustic Elastomicroscopy: Quantitative Elasticity Mapping and Microstructural Analysis for Early-Stage Hepatic Fibrosis Detection

Early detection of hepatic fibrosis remains a critical unmet need due to the limited sensitivity of conventional elastography in capturing microstructural and biomechanical changes. In this study, we developed photoacoustic elastomicroscopy (PAEM), a multi-parametric imaging platform that synergizes high-resolution photoacoustic microscopy with time-of-flight (ToF)-based elastography to quantitatively map tissue stiffness and visualize fibrotic microarchitecture. Validated using PDMS phantoms and a drug-induced murine fibrosis model, PAEM can detect early-stage fibrosis through microstructural biomarkers—pseudo-lobule formation and crevice-area expansion, with a relatively high area under the curve (AUC) > 0.91. However, architectural ambiguity in advanced fibrotic stages gradually reduces PAEM's diagnostic accuracy, necessitating complementary reliance on ToF-based measurements for auxiliary staging. In our results, ToF-based elasticity biomarkers revealed progressive stiffness increases with a significant velocity increase of 3.7% in 1-week fibrosis. Furthermore, experimental PAEM outperformed shear wave elastography (SWE) in early-stage sensitivity by identifying significant stiffness changes, quantitatively 7-fold greater velocity differential sensitivity than SWE (5.39% vs. 0.77% change), between healthy and 3-week fibrotic liver tissue. All-stage fibrosis exhibited considerable stiffness rise (AUC > 0.95), correlating strongly with histopathological severity and serum examination. By integrating structural and mechanical biomarkers, PAEM offers a translational tool for early diagnosis, longitudinal monitoring, and staging of hepatic fibrosis, which can potentially be extended for wider applications in tumor margin delineation and other fibrotic pathologies in soft tissue.