Assessing structural order of biological tissues using polarized microwave-induced thermoacoustic imaging

Abstract

The functional integrity of biological tissues is fundamentally linked to the spatial alignment of their microstructures. While structural order may serve as a key indicator of tissue health and function, current clinical imaging modalities lack the capability to assess it directly. Here, we propose polarized microwave-induced thermoacoustic imaging (P-MTAI), a technique that characterizes structural orientation and alignment using multi-angle polarized microwave excitation. P-MTAI irradiates biological tissues with pulsed microwaves at four distinct polarization angles, namely, 0°, 45°, 90°, and 135°, and measures thermoacoustic signals. From these signals, we derive an orientation angle parameter. Its standard deviation quantifies the angular dispersion of microstructure alignment to characterize structural order and further assess tissue functional integrity. Phantom experiments validate that P-MTAI can reliably acquire orientation angles. In assessments of rat Achilles tendons and rabbit hearts, tissue functional integrity shows a strong positive correlation with structural order. Furthermore, P-MTAI demonstrates the ability to assess reversible functional changes under physiological conditions. This work establishes P-MTAI as a powerful tool for the quantitative assessment of the functional integrity and pathological state of ordered biological tissues based on structural order, providing a strategy for functional monitoring and early disease diagnosis.