Dynamic optical absorption characteristics of blood after slow and fast heating

Abstract

Laser treatment is the most effective therapy in dermatology for vascular skin disorders, such as port-wine stains (PWS). Changes in heat-induced absorbance in blood must be determined for accurate numerical simulation and implementation of multi-pulse laser therapy for treatment of PWS. Thermally induced absorbance changes in hemoglobin in blood were compared in vitro between slow water bath heating and fast heating irradiated by using sub-millisecond Nd:YAG laser. Blood composition at different temperatures was calculated by comparing blood absorption spectra with those of pure HbO, Hb, and metHb at room temperature. Blood absorbance to heat energy were categorized into three stages distinguished by metHb and coagulation points, which are the validity and security thresholds of the optimized therapy, respectively. Rapid laser heating can distinctively enhance blood absorbance by photochemically induced strong instability compared with slow heating at a constant temperature. Slow heating facilitates metHb point at 70 °C and coagulation point at 75 °C as the temperature of the water bath increases. However, the temperature at which metHb or coagulation point shifts to higher than 10 °C when pulses and fluence in laser irradiation change. Laser fluence less than 20 J/cm and more than 50 J/cm is unsuitable for laser treatment because of its low probability to coagulate vascular hyperplasia and high probability to damage normal tissues adjacent to target lesions, respectively. Few bubbles formed after mediate fluence is beneficial to minimize adverse side-effects. Considering blood absorbance, temperature evolution, and bubble formation, we recommend 30-40 J/cm and 2-4 Hz frequency as the optimal laser parameters in sub-millisecond Nd:YAG laser.

Temperature induced changes in the optical properties of skin in vivo

“…They reported an increased contribution from deoxyhemoglobin to absorbance measurements when heated to 60-80 °C. Findings from both Helfmann et al 42 , and Jia et al 43 , confirm the deoxygenation of blood with increasing temperature found in the present study. Nilsson et al 44 , determined the optical properties of whole blood, heated to 25-55 °C, at 633 nm.…”

“…These spectral differences between oxygenated and deoxygenated blood match differences found between 25 and 60 °C absorption spectra found in the present study. Jia et al 43 , measured the absorbance of blood in the spectral range of 500-650 nm while samples were heated to 60-80 °C. They reported an increased contribution from deoxyhemoglobin to absorbance measurements when heated to 60-80 °C.…”

“…Methemoglobin was not detected in the present study at 60 °C. This discrepancy may be explained by the discovery of Jia et al 43 , that measurable amounts of methemoglobin start to form as blood temperatures reach 70 °C.…”

Experimental and numerical investigation on the transient vascular thermal response to multi‐pulse Nd:YAG laser

“…When blood is heated to the temperature that protein denaturation occurs, absorption is greatly enhanced because of the reversible or irreversible biochemical reactions, such as biochemical changes in heated oxygenated hemoglobin and denaturation of heated proteins . Based on this, and when heating process is recalculated and computation result in Figure (red line) was plotted, the average rise of temperature exceeded 100°C immediately after the 10th pulse.…”

Extraction of the Structural Properties of Skin Tissue via Diffuse Reflectance Spectroscopy: An Inverse Methodology

“…There are related non-invasive diagnostic technologies, including video microscopes and other imaging technologies based on charge coupled device (CCD) [ 6 ] and perfusion imaging technologies, such as laser Doppler imaging (LDI) [ 7 ], laser speckle imaging (LSI) [ 8 ], optical coherence tomography (OCT) [ 9 ], optical Doppler tomography (ODT) [ 10 ], photothermal radiometry (PTR) [ 11 ], photoacoustic (PA) [ 12 ], etc. Although we have investigated the influence of laser parameters (wavelength, pulse width, laser energy) [ 13 ] on the treatment effect, the monitoring and extraction of the structural features of the lesion still needs to be solved urgently.…”