Background

The clinical efficiency of laser treatments is limited by the low penetration of visible light used in certain procedures like photodynamic therapy (PDT). Second Harmonic Generation (SHG) PDT is an innovative technique to overcome this limitation that enables the use of Near Infrared (NIR) light instead of visible light. NIR frequency bands present an optical window for deeper penetration into biological tissue. In this research, we compare the penetration depths of 405 and 808 nm continuous wave (CW) lasers and 808 nm pulsed wave (PW) laser in two different modes (high and low frequency).

Methods

Increasing thicknesses of beef and chicken tissue samples were irradiated under CW and PW lasers to determine penetration depths.

Results

The 808 nm CW laser penetrates 2.3 and 2.4 times deeper than the 405 nm CW laser in beef and chicken samples, respectively. 808 nm PW (pulse frequency—500 Hz) penetrates deeper than CW laser at the same wavelength. Further, increasing the pulse frequency achieves higher penetration depths. High frequency 808 nm PW (pulse frequency—71.4 MHz) penetrates 7.4- and 6.0-times deeper than 405 nm CW laser in chicken and beef, respectively.

Conclusions

The results demonstrate the higher penetration depths of high frequency PW laser compared to low frequency PW laser, CW laser of the same wavelength and CW laser with half the wavelength. The results indicate that integrating SHG in the PDT process along with pulsed NIR light may allow the treatment of 6–7 times bigger tumours than conventional PDT using blue light.

中文翻译：

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近红外激光照射的更高脉冲频率可增加新型生物医学应用的穿透深度

 背景

激光治疗的临床效率受到光动力疗法 (PDT) 等某些手术中使用的可见光穿透力低的限制。二次谐波产生 (SHG) PDT 是一种克服这一限制的创新技术，可以使用近红外 (NIR) 光代替可见光。近红外频段提供了一个光学窗口，可以更深入地渗透到生物组织中。在本研究中，我们比较了 405 和 808 nm 连续波 (CW) 激光以及 808 nm 脉冲波 (PW) 激光在两种不同模式（高频和低频）下的穿透深度。

 方法

在连续波和脉冲波激光下照射厚度不断增加的牛肉和鸡肉组织样本，以确定穿透深度。

 结果

808 nm 连续激光在牛肉和鸡肉样品中的穿透深度分别是 405 nm 连续激光的 2.3 倍和 2.4 倍。 808 nm PW（脉冲频率 — 500 Hz）比相同波长的 CW 激光穿透更深。此外，增加脉冲频率可实现更高的穿透深度。高频 808 nm PW（脉冲频率 — 71.4 MHz）对鸡肉和牛肉的穿透深度分别是 405 nm CW 激光的 7.4 倍和 6.0 倍。

 结论

结果表明，与低频PW激光、相同波长的连续激光和半波长的连续激光相比，高频PW激光具有更高的穿透深度。结果表明，将 SHG 与脉冲近红外光结合到 PDT 过程中，可以治疗比使用蓝光的传统 PDT 大 6-7 倍的肿瘤。