Sato Shunichi, Shi Yi-Wei, Matsuura Yuji, Miyagi Mitsunobu, Ashida Hiroshi
Division of Biomedical Information Sciences, National Defense Medical College Research Institute, 3-2 Namiki, Tokorozawa 359-8513, Saitama, Japan.
Lasers Surg Med. 2005 Aug;37(2):149-54. doi: 10.1002/lsm.20210.
Short-pulse solid-state lasers have recently received much attention as new coherent light sources for medical applications, but steady transmission of their high-energy output pulses through a solid quartz fiber is difficult because of the onset of laser-induced breakdown. We previously demonstrated that hollow waveguides could be used to deliver nanosecond laser pulses for tissue ablation. The aim of this study was to determine the optimum laser pulse energy and range of defocused distance for obtaining a deep and sharp ablation channel in myocardial tissue with laser pulses transmitted through a hollow waveguide.
STUDY DESIGN/MATERIALS AND METHODS: Cyclic-olefin-polymer-coated silver hollow waveguides of 1 mm in inner diameter and 1 m in length were used. A vacuum-cored scheme was applied to the waveguides to suppress laser-induced air breakdown. Porcine myocardial tissue was irradiated with 300 laser pulses that were delivered through the waveguide in vitro at various laser energy levels and defocused distances, and depths and diameters of channels were measured. Histological analysis of the ablated tissues was also performed.
At an ablation energy of approximately 60 mJ/pulse, deep (>4.5 mm) and sharp (depth-to-diameter ratio of > 6) channels were created in tissue in the range of defocused distances of -4 approximately + 0.5 mm. Under these conditions, waveguide bending did not cause a remarkable change in ablation characteristics. Histological analysis of ablated tissue showed limited thermal damage but suggested a certain extent of mechanical effects in the tissue.
With near-infrared, nanosecond laser pulses delivered through a cyclic-olefin-polymer-coated silver hollow waveguide, efficient and sharp ablation of myocardial tissue can be achieved, suggesting the usefulness of the hollow waveguide as a new flexible delivery system for high-intensity laser pulses.
短脉冲固态激光器作为医学应用中的新型相干光源，近来备受关注，但由于激光诱导击穿的发生，其高能量输出脉冲难以稳定地通过固体石英光纤传输。我们之前证明了中空波导可用于传输纳秒激光脉冲以进行组织消融。本研究的目的是确定通过中空波导传输激光脉冲时，在心肌组织中获得深且锐利的消融通道的最佳激光脉冲能量和散焦距离范围。
研究设计/材料与方法：使用内径为1 mm、长度为1 m的环烯烃聚合物涂层银质中空波导。对波导采用真空芯方案以抑制激光诱导的空气击穿。在体外，以不同的激光能量水平和散焦距离，通过波导对猪心肌组织发射300个激光脉冲，并测量通道的深度和直径。还对消融组织进行了组织学分析。
在约60 mJ/脉冲的消融能量下，在 -4至 + 0.5 mm的散焦距离范围内，组织中形成了深度大于4.5 mm且锐利（深度与直径比大于6）的通道。在这些条件下，波导弯曲并未导致消融特性发生显著变化。对消融组织的组织学分析显示热损伤有限，但表明组织中存在一定程度的机械效应。
通过环烯烃聚合物涂层银质中空波导传输近红外纳秒激光脉冲，可实现对心肌组织的高效且锐利的消融，这表明中空波导作为一种新型的高强度激光脉冲灵活传输系统具有实用性。
