Optical fiber-based handheld polarized photoacoustic computed tomography for detecting anisotropy of tissues

Abstract

Background: Photoacoustic computed tomography (PACT) is a fast-developing biomedical imaging modality and has immense potential for clinical translation. It utilizes laser excitation and acoustic detection to achieve high spatial resolution and considerable imaging depth in biological tissues. Current PACT primarily treats the absorption coefficient of tissues as a scalar variable while reconstructing the image, which limits its use for anisotropic evaluation of the tissues. Thus, by incorporating polarized imaging methods to evaluate anisotropy, applications of PACT can be further enhanced. So far, dichroism-sensitive PACT has been suggested for polarization detection of biological tissues. However, this approach is unsuitable for intraoperative imaging, since high-power spatial light is needed for excitation, which is dangerous and inconvenient to operate. Thus, there is a need to develop a polarized PACT system suitable for clinical use.Methods: Herein, we have proposed a specially designed handheld polarized PACT (HP-PACT) system, which was designed to promote intraoperative anisotropy detection of biological tissues. Excitation light was delivered by an optical fiber and reshaped by a compact set of lenses at the output end of the optical fiber. A polarizer was applied to generate linearly polarized light, and the polarization direction was adjusted by simply rotating the half-wave plate. Photoacoustic imaging (PAI) using excitation with several different polarization directions was carried out. Optical axes and the structure of the anisotropic objects were obtained using the principle of polarization detection with the PAI.Results: We experimentally demonstrated the performance of HP-PACT by imaging both the polarized and unpolarized plastic films. The results showed that HP-PACT can successfully detect the direction of the optical axes of polarized plastic films and has the ability to image at different depths. When linearly polarized light with different polarization directions was used as excitation, PAI studies on a highly anisotropic bovine tendon and relatively low anisotropic mouse leg showed the structural differences between the 2 tissues. The quantified degrees of anisotropy of the bovine tendon and mouse legs were 0.6 and 0.3, respectively. Conclusions:The proposed HP-PACT is able to determine the anisotropic substances' optical axes and distinguish anisotropic substances from isotropic ones. Thus, HP-PACT has the potential for intraoperative diagnosis and treatment of anisotropic tissues, including nerves and tendons.

Photoacoustic imaging plus X: a review

“…The handheld probe in Ref. 62 enables detecting optical anisotropy for assessing tissues such as nerves and tendons during surgical procedures. Non-contact imaging developed in Refs.…”

Research and development of polarized photoacoustic imaging technology

“…] . (10) 3 偏振光声成像技术的发展与分类 偏振光声成像技术2012年首次被提出后沉寂 了一段时间 [45] , 直到2018年Lihong V. Wang团 队和华南师范大学邢达/杨思华团队 [43,44] 针对偏 振光声的采集方式和提取参数进行了开拓式的研 究, 分别提出了偏振光声计算层析成像和定量式偏 振光声显微成像技术, 之后的几年该技术得到了光 声成像领域的重视, 相继有香港城市大学王立代团 队和香港理工大学赖溥祥团队 [46] 合作, 于2019年 提出了一种光纤延时的偏振光声成像系统, 实现了 单次扫描即可重建偏振光声图像; 2021年, 中国科 学院深圳先进技术研究院刘成波团队 [47,48] 发展了 一种手持偏振光声探测成像方法, 演示了大视野量 化各向异性生物组织结构; 2021年, 华盛顿大学 的Song Hu团队 [49] 发表了利用刚果红染色实现 了偏振光声技术可视化脑中淀粉样蛋白的研究;…”

“…Fig.8. Polarized photoacoustic technology for fiber delay single scan[46] : (a) Schematic of the dual-fiber single-shot dichroism OR-PAM system; WT, water tank; (b) PA images of three linear polarizers excited with polarized light at 0°, 45°, and 90°; (c), (d) calculated dichroism image and polarization angle of the three linear polarizers.…”

Multispectral Optoacoustic Tomography Enables In Vivo Anatomical and Functional Assessment of Human Tendons

“…[ 20 , 21 ] Furthermore, tendon tissue anisotropy has been characterized ex vivo using fiber‐based polarized techniques. [ 22 ] Nevertheless, to date, in vivo MSOT characterization of human tendons has yet to be explored. In this work, we investigate the feasibility of clinical MSOT assessment for tendon morphology and physiological function in response to exercise.…”