Temporal and Spatial Temperature Profile of the Bladder Serosa in Intravesical Neodymium-YAG-Laser Irradiation

Abstract

Up to now irradiation of bladder tumors has only been possible in places where the wall is not in contact with the intestinal loops. To expand the therapeutic range, in the present investigation the parameters of this form of laser irradiation were adjusted to the biological conditions. The most important parameter which defines the tissue reaction during the irradiation is the temporal temperature profile. For the purpose of determining this parameter for bladder tissue, rabbit bladders with various wall thicknesses were irradiated intravesically and the spatial and temporal temperature profiles of the serosa were recorded simultaneously with a thermocamera. The tissue thickness was established with a specially designed endo-ultrasound transducer which can be used transurethrally. To test the applicability of the results in the clinical sphere, the temporal temperature profiles of a human bladder were obtained. The results can be used to determine a sufficient and safe therapy when dealing with bladder tumors. The transurethral application of the neodymium-Y AG laser for the destruction of bladder tumors has been used with clinical success since 1976. Using the neodymium-YAG laser we get a deep, often transmural necrosis by contactless thermal coagulation. The mechanical stability of the denaturated tissue is not damaged. In contrast to electrocoagulation, photocoagulation with the neodymium-YAG laser induces calculable lesions. During irradiation the photo energy of the neodymium-YAG laser is converted upon interaction with the tissue into phonon energy on the molecular plane. This energy considerably disturbs the cell metabolism; induction of a tumor regression, for example, already being possible. However, the decisive feature of laser therapy is thermal coagulation by the heat generated in the tissue during irradiation. Radical destruction of a tumor can only be achieved by total necrosis extending as far as the base of the tumor. Because of its wavelength (λ = 1,060 nm) and the associated strong forward and multiple scattering within the tissue, the radition of the neodymium-YAG laser has a depth of penetration that is remarkable in comparison with other types of lasers.