Optical low-coherence reflectometry and confocal microscopy images were taken of the rat dorsal skin flap window model. Blood vessel depths and diameters measured with the two techniques, and preparation thickness determined from reflectometry images, are in reasonable agreement with measurements from histologic sections. Blood vessels appear as areas of low signal when constant-depth reflectometry images are taken at a depth near the center of a vessel, whereas they appear bright when taken close to the blood-dermis boundary. Doppler shift plus increased light absorption in blood, and the blood-dermis index of refraction mismatch, are discussed as possible causes of the dark- and bright-appearing vessels, respectively. One reflectometry image was used to generate an input grid for a novel Monte Carlo analysis program that is capable of determining the light distribution and heat generation [J/m3] within complex blood vessel geometries. The feasibility of imaging skin blood vessel accurately with optical low-coherence tomography, and using the acquired knowledge of blood vessels structure to create more realistic Monte Carlo analyses is demonstrated by the results of the study. © 1997 Society of Photo-Optical Instrumentation Engineers.

Background and objective

Several published reports describe the benefits of using the carbon dioxide laser for cutaneous resurfacing. The mechanisms on which skin resurfacing work are still not completely understood. This study was performed to obtain quantitative and qualitative information describing the thermal response of skin during high-energy, short-pulsed CO2 laser irradiation.

Study design/materials and methods

A Tissue Technologies TruPulse CO2 laser was used to irradiate an in vivo rat model. The laser parameters that were used were a 100-micros pulse width, a 1-Hz repetition rate, a 3 mm x 3 mm square spot size, and 2.4 J/cm2 and 3.9 J/cm2 radiant exposures. A 3-5 microm thermal camera was used to obtain temperature information during irradiation. Single spots were irradiated with one pulse, and the temperature-time history was obtained. In a different experiment, 15 pulses were applied to single spots, and both thermal and video images were obtained.

Results

Irradiation with one pulse at 2.4 J/cm2 and 3.9 J/cm2 led to peak temperatures >100 degrees C. The temperature relaxation time was approximately 25-150 ms. Multiple-pulse irradiation at 2.4 J/cm2 led to a slight rise in the peak temperature with each pulse. At 3.9 J/cm2, the peak temperature increased with successive pulses until pulse 10, after which the peak temperature oscillated between 300 and 400 degrees C. Video images showed concurrent burning events that occurred during pulses 10-15.

Conclusion

Temperatures >100 degrees C were measured during CO2 laser irradiation of skin. Pulse stacking can lead to peak temperatures approaching 400 degrees C and to tissue charring with as few as three stacked pulses. It is crucial for the physician to manipulate the laser handpiece at parameters with which he or she can avoid pulse overlap.

The application of pulsed carbon-dioxide lasers for skin resurfacing has been described by several authors. The procedure uses 30 microseconds to 1 ms laser pulses with pulse energies from 100 - 600 mJ to ablate skin for the purpose of smoothing skin irregularities: that is, wrinkle removal. The carbon-dioxide laser has been selected because it ablates a limited layer of tissue (approximately 10 micrometer at a radiant exposure of 5 J/cm 2)4 and produce minimal thermal damage. The purpose of this study is to measure the surface temperature created during a resurfacing procedure and discuss the thermal implications of the measurements. ©2005 Copyright SPIE - The International Society for Optical Engineering.

The effects of cooling, laser irradiation, and laser irradiation with cooling on blood vessels were investigated with Color Doppler Optical Coherence Tomography (CDOCT). CDOCT may contribute to an understanding of the dynamics of laser-blood vessel interactions and aid in better optimization of laser parameters to be used. In this study, hamster dorsal skin flap window vessels were irradiated with a KTP laser operating at 532 nm. Irradiation sites were imaged with CDOCT prior to, during, immediately after, and several days after irradiation. KTP laser parameters were: radiant exposures in the range of 7-14 J/cm2, 3 mm spot size, and 10 ms pulse duration. Magnitude and color Doppler images provided information such as vessel size, depth, and changes in blood flow velocity. Vessel constriction, temporary occlusion, and changes in flow were frequent results of laser irradiation visualized with CDOCT. In addition, the effects of cooling alone were imaged with CDOCT and its effects on blood vessel flow and morphology were investigated before and after laser irradiation.