Cardiovascular diseases are the number one cause of death worldwide, among which, atherosclerosis is the fundamental pathology. Intravascular photoacoustic imaging (IVPAI), a newly developed non-destructive imaging technology, is of great importance for atherosclerotic plaque study by providing both structure and lipid component information. Comparative study with histology is pivotal to verify the accuracy of IVPAI.
When a biological tissue is excited by the pulse laser, it generates ultrasonic signals that will be detected and recorded. The structure and the optical-absorption distribution of the tissue can be visualized by reconstructing the ultrasonic signals with a back projection algorithm. Therefore, the anatomical images obtained by photoacoustic imaging possess innate advantages of high contrast, high resolution and satisfactory penetration depth. These merits shed light on the application of IVPAI on atherosclerotic plaque identification.
To date, most of IVPAI studies involve samples stored in formaldehyde or under ultra-low temperature, both of which might alter the photoacoustic characteristics of the artery, cause bias on the results explanation and affect the pre-clinically translational research on photoacoustic imaging. Therefore, estimation of effects posed by these two treatments on photoacoustic characteristics of artery is extremely important.
Researchers from a joint research team of Qilu Hospital of Shandong University and South China Normal University made an improvement of the previously reported IVPAI imaging system to enable simultaneous photoacoustic and ultrasound imaging of blood vessels. Then they compared the IVPAI results before and after ultra-low temperature or formaldehyde treatments with histology the golden standard, to validate the effects they made on plaque photoacoustic features. The researchers found that both treatments have little effect on photoacoustic characteristics of the artery samples. Lipid ratios pre- and post-ultra-low temperature treatment were 0.334±0.130 vs. 0.329±0.122 (p=0.299). The ratios pre- and post- formaldehyde treatment were 0.317±0.045 vs. 0.316±0.040 (p=0.854). All these IVPAI derived lipid ratios correlated highly with histological results. This work has been published in Chinese Optics Letters, Volume 16, No. 3, 2018 (Mingjun Xu, et al., Photoacoustic characteristics of lipid-rich plaques under ultra-low temperature and formaldehyde treatment)
Associate Professor Pengfei Zhang and Professor Sihua Yang, directors of the joint research group, believed that these results verified the accuracy of intravascular photoacoustic imaging technology. Moreover, the diameter of this improved IVPAI imaging catheter is only 1.00 mm. Their work laid a solid foundation for in vivo experiments and pre-clinical photoacoustic experiments in the future.
Based on these findings, further work will be focused on translational research from ex vivo to in vivo, and application of IVPAI in monitoring the development or regression of atherosclerotic plaques.
山东大学齐鲁医院和华南师范大学的联合研究团队改进了已报道的光声血管内窥成像系统，实现血管内同时光声和超声成像。利用改进后的系统，通过比较两种处理方式前后光声成像结果，并与组织学这一金标准进行比对，探究两种处理方式对血管光声特性的影响。研究人员发现不同的处理方式对血管光声特性无显著影响 (超低温及福尔马林处理前后脂质占比分别是0.334±0.130 vs. 0.329±0.122, p=0.299和0.317±0.045 vs. 0.316±0.040, p=0.854)，并与组织学结果高度相关。该成果发表在Chinese Optics Letters 2018年第3期上 (Mingjun Xu, et al., Photoacoustic characteristics of lipid-rich plaques under ultra-low temperature and formaldehyde treatment)。