Department of Biomedical Engineering & Physics, Academic Medical Centre, University of Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands.
Lasers Med Sci. 2010 May;25(3):439-47. doi: 10.1007/s10103-009-0749-1. Epub 2010 Feb 10.
Endovenous laser ablation (EVLA) is commonly used to treat saphenous varicosities. Very high temperatures at the laser fibre tip have been reported during EVLA. We hypothesized that the laser irradiation deposits a layer of strongly absorbing carbonized blood of very high temperature on the fibre tip. We sought to prove the existence of these layers and study their properties by optical transmission, optical coherence tomography (OCT) and microscopy. We analysed 23 EVLA fibres, 8 used at 810 nm, 7 at 940 nm and 8 at 1,470 nm. We measured the transmission of these fibres in two wavelength bands (450-950 nm; 950-1,650 nm). We used 1,310 nm OCT to assess the thickness of the layers and the attenuation as a function of depth to determine the absorption coefficient. Microscopy was used to view the tip surface. All fibres showed a slightly increasing transmission with wavelength in the 450-950 nm band, and a virtually wavelength-independent transmission in the 950-1,650 nm band. OCT scans showed a thin layer deposited on all 13 fibres investigated, 6 used at 810 nm, 4 at 940 nm and 3 at 1,470 nm, some with inhomogeneities over the tip area. The average absorption coefficient of the 13 layers was 72 +/- 16 mm(-1). The average layer thickness estimated from the transmission and absorption measurements was 8.0 +/- 2.7 microm. From the OCT data, the average maximal thickness was 26 +/- 6 microm. Microscopy of three fibre tips, one for each EVLA wavelength, showed rough, cracked and sometimes seriously damaged tip surfaces. There was no clear correlation between the properties of the layers and the EVLA parameters such as wavelength, except for a positive correlation between layer thickness and total delivered energy. In conclusion, we found strong evidence that all EVLA procedures in blood filled veins deposit a heavily absorbing hot layer of carbonized blood on the fibre tip, with concomitant tip damage. This major EVLA mechanism is unlikely to have much wavelength dependence at similar delivered energies per centimetre of vein. Optical-thermal interaction between the vein wall and the transmitted laser light depends on wavelength.
静脉内激光消融术（EVLA）常用于治疗大隐静脉曲张。据报道，在 EVLA 过程中，激光光纤尖端的温度非常高。我们假设激光照射在光纤尖端沉积一层温度极高的碳化血液强烈吸收层。我们试图通过光传输、光学相干断层扫描（OCT）和显微镜来证明这些层的存在，并研究它们的性质。我们分析了 23 根 EVLA 光纤，其中 8 根在 810nm 下使用，7 根在 940nm 下使用，8 根在 1470nm 下使用。我们测量了这些光纤在两个波长带（450-950nm；950-1650nm）的传输。我们使用 1310nm 的 OCT 来评估层的厚度和衰减随深度的变化，以确定吸收系数。显微镜用于观察尖端表面。所有光纤在 450-950nm 波段的波长略有增加，而在 950-1650nm 波段的波长几乎独立。OCT 扫描显示在所有 13 根研究过的光纤上沉积了一层很薄的层，其中 6 根在 810nm 下使用，4 根在 940nm 下使用，3 根在 1470nm 下使用，有些在尖端区域存在不均匀性。13 层的平均吸收系数为 72±16mm-1。根据透射和吸收测量值估计的平均层厚度为 8.0±2.7μm。从 OCT 数据来看，平均最大厚度为 26±6μm。对 3 根光纤尖端（每根 EVLA 波长 1 根）进行显微镜检查，发现尖端表面粗糙、开裂，有时严重损坏。除了层厚度与总输送能量之间存在正相关外，层的性质与 EVLA 参数（如波长）之间没有明显的相关性。总之，我们有强有力的证据表明，所有充满血液的静脉内激光消融术（EVLA）程序都会在光纤尖端沉积一层碳化血液的强烈吸收的高温层，同时伴随着尖端损伤。在类似的每厘米静脉输送能量下，这种主要的 EVLA 机制不太可能有太多的波长依赖性。静脉壁与传输激光之间的光热相互作用取决于波长。
