A new application of magnetic resonance (MR) imaging to map the spatial and temporal distribution of the effects of Nd:YAG lasers on tissues was studied. The temperature dependence of MR relaxation mechanisms and the high sensitivity of MR to changes in the mobility and distribution of tissue water make it particularly suitable for the demonstration and control of thermal energy deposition in tissues. In heterogeneous tissues, MR imaging does not follow changing temperatures directly because even in the case of reversible thermal interactions, there is a hysteresis in the dynamic relationship between MR signal intensity and temperature. Appropriate matching of the laser and MR pulse sequences can, however, optimize the detection of relatively small laser energy deposition, and reversible and irreversible tissue changes can be distinguished. There is a potential for the integration of MR imaging and lasers for three-dimensional control and monitoring of laser-tissue interactions.
The sequence of histological change induced by CO2 laser irradiation was discussed in terms of two factors: the physiomechanical factor and the physiochemical factor. At sufficiently high heat energy levels, the immediate findings are characterized by crater formation resulting from rapid vaporization of the water and ejection of the solid component. In the immediate vicinity of the crater edge, the maximum tissue temperature rise is 65 degrees C above the 32 degrees C ambient tissue temperature and it decreases to the primary tissue temperature within a distance of 2 mm. The healing process of CO2 laser induced lesions proceeds with minimal delay. The lymphatic and vascular channels are occluded in the marginal area of coagulation resulting in a marked hemostatic effect. This sealing effect increases the margin of safety in preventing possible dissemination of tumor cells. By selecting the appropriate power, time, and focus cone angle, precise destruction of preselected areas of tissue can be achieved with an extraordinary hemostatic effect without damaging the underlying tissue. These advantages are especially helpful in function-preserving surgery.
Since 1972 we have been cautiously exploring the use of CO2 laser in the management of carefully selected cases of localized carcinoma of the oral cavity. At the present time our experience is based on the treatment of 57 patients with cancer of the oral cavity. The CO2 laser has been found to be an indispensable tool in the transoral management of T1 carcinomas, multiple superficial carcinoma, extensive leukoplakia and verrucous carcinoma. The laser allows precise excision of the lesion and involved mucosa and provides and excellent specimen for histologic verification of the margins. The morbidity of laser excision is minimal, so that a tracheotomy is not needed and patients can almost always be discharged on the following day. (Follow-up data on those patients at risk for 30 months indicate excellent control rates).
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