The change of tissue elasticity has been recognized as a biomarker of many disease conditions. Elastography has been investigated by observing the strain and stress correlation or shear wave propagation in tissue. The strain measurement can be achieved via speckle tracking in ultrasound (US) and optical modalities whereas the stress in deep tissue cannot be directly measured. Assuming that the collapsing of the vasculature could reflect the stress exerted on a tissue volume, the photoacoustic (PA) signals of the hemoglobin content within the vasculature could be an alternative measurement of the stress. This study investigates the strain-PA correlation with phantoms and a rat model in vivo. Parallel PA-US imaging was achieved by combining a compact linear US array and fiber optics delivering 720nm illumination. The phantom study simulated the vasculature with a piece of sponge soaked in ink, and the surrounding tissue with porcine gel with varied elasticity. The strain was generated by pushing the PA-US probe against the phantom surface. A correlation of 0.9 was found between the strain within the sponge and the PA signal changes. The rat model possesses inflammatory and fibrotic intestinal strictures comparable to those in the Crohn’s disease patients. The strain within the strictures was achieved by pushing the PA-US probe against the rats’ abdominal walls. Approximately twice more significant PA signal changes were observed in the fibrotic strictures than those in inflammatory ones under the same strain (p<0.001). All the results support that strain-PA imaging is capable of estimating the tissue elasticity.
Guan Xu, Yunhao Zhu, Laura Johnson, Jie Yuan, Xueding Wang, Jonathan Rubin, and Peter Higgins, "Strain-photoacoustic imaging: an alternative approach for elasticity measurement (Conference Presentation)," Proc. SPIE 10496, Optical Elastography and Tissue Biomechanics V, 1049613 (Presented at SPIE BiOS: January 28, 2018; Published: 15 March 2018); https://doi.org/10.1117/12.2292362.5752213066001.
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