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首页> 外文会议>Photons Plus Ultrasound: Imaging and Sensing 2006; Progress in Biomedical Optics and Imaging; vol.7, no.9 >Subsurface photodisruption in pig skin as monitored by high-frequency ultrasound
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Subsurface photodisruption in pig skin as monitored by high-frequency ultrasound

机译：高频超声监测猪皮肤表面的光破坏

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For diagnostic or therapeutic technologies using femtosecond laser-induced optical breakdown (LIOB) in turbid biological tissues, pulses of sufficient fluence must be delivered to the site of interest. As light attenuates and diffuses rapidly due to wavelength-dependent absorption and scattering, it is important to develop penetration optimization schemes. In this study, we use a high frequency (50MHz) ultrasonic technique to investigate the precision and penetration depth limitations of infrared femtosecond laser-induced photodisruption in excised pig skin. Optical parameters varied include laser fluence (energy density in J/cm~2) and focusing numerical aperture. Our ultrasonic method uses sensitive detection of laser-induced bubbles to measure breakdown extent. Using a geometrically focused Nd:Glass laser (1053 nm, 800 fs) source, we show that acoustically detectable bubbles can be produced as deep as 900 urn into excised porcine skin. As penetration exceeds several hundred microns, however, multiple bubbles stacked at different depths can be produced with a single laser excitation. Secondary bubble creation is more likely at supra-threshold fluences or with low NA (≤ 0.4) focusing, where optical self-focusing may occur near threshold fluences. However, as the numerical aperture is increased (> 0.4) for deeper focusing, aberrations can severely distort the beam, increasing the perceived LIOB-threshold with maximal penetrations of less than 500um. Using an index matching fluid (i.e. aqueous glycerol solutions) to help reduce scattering, we are able to improve penetration. However, multiple breakdown sites and the corresponding reduction in precision is still likely in skin even with glycerol treatment.
机译：对于在浑浊的生物组织中使用飞秒激光诱导的光学击穿（LIOB）的诊断或治疗技术，必须将足够通量的脉冲传递到感兴趣的部位。由于光依赖于波长的吸收和散射而迅速衰减和扩散，因此开发穿透优化方案非常重要。在这项研究中，我们使用高频（50MHz）超声技术来研究红外线飞秒激光在切除的猪皮中引起的光破坏的精度和穿透深度限制。改变的光学参数包括激光能量密度（能量密度在J / cm〜2中）和聚焦数值孔径。我们的超声方法使用激光感应气泡的灵敏检测来测量击穿程度。使用几何聚焦的Nd：玻璃激光（1053 nm，800 fs）光源，我们显示，在可切除的猪皮中，可探测到900 n深的气泡是可听觉检测到的。但是，当穿透力超过几百微米时，一次激光激发就可以产生堆叠在不同深度的多个气泡。在超阈值通量或低NA（≤0.4）聚焦下，次级气泡的产生更有可能，在该范围附近，光学自聚焦可能会在阈值通量附近发生。但是，随着数值孔径的增加（> 0.4）以实现更深的聚焦，像差会严重扭曲光束，从而增加可感知的LIOB阈值，且最大穿透深度小于500um。使用折射率匹配的流体（即甘油水溶液）有助于减少散射，我们能够提高渗透率。但是，即使采用甘油处理，皮肤上仍然可能出现多个击穿部位并相应降低精度。

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