Abstract
Background and Objective
Previous investigations have reported evidence of wavelength dependence on cortical bone ablation. This study used mid‐infrared laser wavelengths generated by a free electron laser (FEL) and mass removal measurements to further examine the ablation efficiency of a wavelength (2.79 µm) not previously reported and three wavelengths (2.9, 6.1, and 6.45 µm) previously demonstrated by crater morphology alone to be efficient for cortical bone removal.
Study Design/Materials and Methods
The wavelengths examined were provided by an FEL emitting 4 microseconds macropulses consisting of 1–2 picoseconds duration micropulses delivered at 350 picoseconds intervals. The mass removal measurements were conducted by a microbalance, and the collateral thermal injury and crater morphology of cortical bone were examined by light microscopy following standard histologic processing.
Results
The study demonstrated that the highest mass removal was achieved at λ = 6.1 µm followed by, in order, λ = 2.9, 6.45, and 2.79 µm. The zones of thermal injury and crater morphology created in cortical bone at the selected wavelengths were examined at the radiant exposure of 28.3 J/cm^2^. Ablation using λ = 6.1 µm provided the largest crater size and the least collateral thermal injury. The greatest amount of collateral thermal injury was produced by λ = 2.79 µm at both the sides and base of the ablation crater.
Conclusions
The mass removal of cortical bone produced by FEL ablation at selected mid‐IR wavelengths was measured as a function of incident radiant exposure. The ablation efficiency was found to be dependent upon wavelength. The λ = 2.79 µm did not offer any improvement over the other wavelengths evaluated, suggesting that a potential shift in the dynamic optical properties of water during tissue irradiance with the FEL does not present an advantage to the cutting of cortical bone. The λ = 6.1 µm provided the highest ablation efficiency with deepest crater and the least amount of collateral thermal injury. Lasers Surg. Med. 39: 332–340, 2007. © 2007 Wiley‐Liss, Inc.