Photoacoustic imaging is a promising technique to provide guidance during multiple surgeries and procedures. One challenge with this technique is that major blood vessels in the liver are difficult to differentiate from surrounding tissue within current safety limits, which only exist for human skin and eyes. In this paper, we investigate the safety of raising this limit for liver tissue excited with a 750 nm laser wavelength and approximately 30 mJ laser energy (corresponding to approximately 150 mJ/cm² fluence). Laparotomies were performed on six swine to empirically investigate potential laser-related liver damage. Laser energy was applied for temporal durations of 1 minute, 10 minutes, and 20 minutes. Lasered liver lobes were excised either immediately after laser application (3 swine) or six weeks after surgery (3 swine). Cell damage was assessed using liver damage blood biomarkers and histopathology analyses of 41 tissue samples total. The biomarkers were generally normal over a 6 week post-surgical in vivo study period. Histopathology revealed no cell death, although additional pathology was present (i.e., hemorrhage, inflammation, fibrosis) due to handling, sample resection, and fibrous adhesions as a result of the laparotomy. These results support a new protocol for studying laser-related liver damage, indicating the potential to raise the safety limit for liver photoacoustic imaging to approximately 150 mJ/cm² with a laser wavelength of 750 nm and for imaging durations up to 10 minutes without causing cell death. This investigation and protocol may be applied to other tissues and extended to additional wavelengths and energies, which is overall promising for introducing new tissue-specific laser safety limits for photoacoustic-guided surgery.

中文翻译：

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光声引导肝脏手术激光安全性的实证评估

光声成像是一种很有前途的技术，可以在多次手术和程序中提供指导。这项技术面临的一个挑战是，在目前的安全限制内，肝脏中的主要血管很难与周围组织区分开来，而后者仅存在于人类皮肤和眼睛中。在本文中，我们研究了为用 750 nm 激光波长和大约 30 mJ 激光能量（对应于大约 150 mJ/cm ²影响）。对六头猪进行剖腹手术，以凭经验研究潜在的激光相关肝损伤。激光能量的施加时间为 1 分钟、10 分钟和 20 分钟。激光肝叶在激光应用后立即切除（3 头猪）或手术后六周（3 头猪）。使用肝损伤血液生物标志物和总共 41 个组织样本的组织病理学分析来评估细胞损伤。在体内手术后 6 周内，生物标志物通常是正常的学习时段。组织病理学显示没有细胞死亡，尽管由于操作、样本切除和剖腹手术导致的纤维粘连而存在额外的病理学（即，出血、炎症、纤维化）。这些结果支持研究激光相关肝损伤的新协议，表明有可能将肝脏光声成像的安全极限提高到大约 150 mJ/cm ²，激光波长为 750 nm，成像持续时间长达 10 分钟，而不会导致细胞死亡。这项调查和协议可能适用于其他组织，并扩展到额外的波长和能量，这总体上有望为光声引导手术引入新的组织特异性激光安全限制。