Laser-tissue interactions

The extent of thermal destruction of tissue by visible and near-infrared lasers is governed by heat deposition in the tissue, heat transfer, and temperature-dependent rate reactions. Often the thermal response has been analyzed by linear models with constant coefficients that presume exponential absorption of the laser irradiation with depth. However, for weakly absorbing tissues, light scattering dominates the optical properties. These properties may be altered by thermal damage of the tissue. Also, thermal properties for tissue vary with temperature and water content. Typical therapeutic laser irradiations vaporize water in the tissue causing sharp increases in temperature beyond 100°C, and continued irradiation causes ablation of the tissue. Models for all these events are discussed.

The thermal response of laser irradiated tissue

https://iopscience.iop.org/article/10.1088/0031-9155/35/9/001/pdf

Physics of thermal processes in laser-tissue interaction

https://www.gastrojournal.org/article/0016-5085(87)90918-8/pdf

Biological effects of intrahepatic neodymium:yttrium-aluminum-garnet laser photocoagulation in rats.

The clinical applications of thermal sensory and pain thresholds have been very limited due to large intra-individual variations. In the present paper CO2 and argon lasers were used as thermal stimulators, and the different factors (stimulus parameters and skin conditions) affecting the thresholds are described. The intra-individual variations obtained in sensory (9.3%) and pain (4.3%) thresholds were very low, which suggests that the method can be applied for clinical purposes.

https://jnnp.bmj.com/content/jnnp/51/1/35.full.pdf

Sensory and pain threshold characteristics to laser stimuli.

A mathematical model is presented for the calculation of the 3-D time-dependent temperature distribution in a biological tissue (slab) irradiated by a laser beam of rectangular or Gaussian profile, which takes into account the different thermooptical properties of the tissue. Detailed consideration is given to the phenomenon of redistributive internal scattering, which is of noticeable magnitude in the irradiation by the argon-ion and Nd:YAG lasers commonly used for tissue coagulation in medicine. Satisfactory agreement is found with temperature measurements performed with a thermocamera, and the CO(2) and Nd:YAG lasers are compared qualitatively and quantitatively.

Thermodynamic analysis of laser irradiation of biological tissue

We present the results of experimental and theoretical investigations on the interaction of Nd: YAG laser light with biological tissue in general, and with the bladder in particular. A comparison is made between the thermal effects achieved with this laser and those of the argon and CO2 types. A therapeutically safe yet effective dosage for the endoscopic treatment of bladder tumours with the Nd: YAG laser is given. The operating techniques are described along with the first clinical results.

Endoscopic applications of the Nd: YAG laser in urology; theory, results, dosimetry

Einfluß der optischen Streuung bei thermischer Umsetzung von Laserstrahlung im biologischen Gewebe

Seit 1976 behandeln wir nichtmetastasierte lokalisierte Blasentumoren bei strenger Indikationsstellung durch endoskopische Applikation von Neodym-YAG-Laserstrahlen, meist nach vorausgegangener Resektion. Die gefahrlose, aber wirkungsvolle Dosis in Leistung und Bestrahlungsdauer erfolgt nach experimentellen Untersuchungen und nach klinischen Erfahrungen, uber die an anderer Stelle bereits berichtet wurde [1,2]. Wir haben nun in einer weiteren Versuchsreihe an der Leichenblase Temperaturmessungen mit der Thermokamera System AG 680 in Luft und zur Optimierung der Dosis unter Wasser durchgefuhrt [3,4].

J. Langerholc

Papers

Thermodynamic analysis of laser irradiation of biological tissue

Endoscopic applications of the Nd: YAG laser in urology; theory, results, dosimetry

Einfluß der optischen Streuung bei thermischer Umsetzung von Laserstrahlung im biologischen Gewebe

Probleme der Dosierung bei der endoskopischen Applikation von Neodym-YAG-Laserstrahlen