Interaction of mid-infrared laser radiation with soft ureter tissue H. Jelínková a , O. Kőhler b , M. Němec a , P. Koranda a , J. Šulc a , P. Drlík b M. Miyagi c , Y.-W. Shi c , Y. Matsuura c , M. R. Kokta d , P. Hrabal e a Czech Technical University, Faculty of Nuclear Sciences and Physical Engineering, Břehová 7, 115 19 Prague 1, Czech Republic e-mail:hjelin@troja.fjfi.cvut.cz b Central Military Hospital, Clinic of Urology, 169 02 Prague 6, Czech Republic c Tohoku University, Graduate School of Engineering, Department of Electrical Communications, Sendai 980-8579, Japan d Bicron, Saint-Gobain, Washougal, WA, USA e Central Military Hospital, Clinic of Pathology-Anatomical, 169 02 Prague 6, Czech Republic ABSTRACT Aim of the work was an investigation of ureter wall perforation possibility by various types of mid-infrared radiations (from 2.01 μm (Tm:YAG) up to 2.94 μm (Er:YAG)) and exploration of the interaction basic characteristic for ureter surface (epithelium) and its deep structures (mesenchym). From results follow that CTH:YAG, Er:YAG, and CTE:YAG laser radiations accomplish a good wall ureter perforation. A distinguished difference appeared in modifications of the ureter tissue - epithelium and mesenchym. Keywords: urology, ureter, solid state lasers, Er:YAG, CTE:YAG, CTH:YAG, Tm:YAG, hollow waveguide. 1. INTRODUCTION Over the past twenty years a variety of laser systems have been tested for an urology surgery, such as: a treatment of urethral and ureteral strictures, treatment of BPH (benign prostatic hyperplasy), or a stone desintegration (lithotripsy). So far, the long term results from the strictures treatment are not fully sufficient – high rate of recurrence still existing. Therefore, new methods of treatment in which the ureter tissue vicinity will not be affected, are highly appreciated. In the case of using laser radiation for this treatment, the ureter tissue must be ablated. The depth of the vaporized channel mainly depends on the spectral absorption of the radiation in a tissue and, as water is a prominent component of biological tissues, this depth is mainly given by the absorption of laser radiation in water. In mid-infrared region, a family of solid state lasers (based on Er, Tm or Ho ions) is available which radiation has sufficient absorption in OH-containing media [1]. From a literature, a promising results with Er:YAG laser radiation, applied during animal experiment [2], are known. The objective of this study was to investigate and compare the ablation effect of selected mid-infrared laser radiations (Tm:YAG, CTH:YAG, CTE:YAG, and Er:YAG) on a human ureter tissue; an attestation of perforation possibility of the ureter wall by these types of lasers and investigation of basic interaction characteristic with its surface and deep structure. 2. EXPERIMENTAL METHODS 2.1. Laser systems For the experiment four laser systems Tm:YAG, CTH:YAG, CTE:YAG, and Er:YAG generating in a mid-infrared region were used. All systems were designed and constructed at the FNSPE * laboratories. Guiding of all systems was performed by an independent He-Ne lasers (λ = 0.63 μm). A radiation delivery from the laser to the interacting tissue was realized by the special sealed hollow waveguides. The laser and delivery system specification are as follow. 2.1.1. Er:YAG laser system In Er:YAG laser oscillator (λ = 2.94 μm), an active crystal 5 mm in diameter and 100 mm long was used along with xenon flashlamp. These elements were placed inside a diffused ceramic pumping cavity. The resonator consists of a plane total reflecting copper mirror and an output coupler with the optimal reflectivity R out = 80 %. The wavelength generated was 2.94 μm and the pulse duration was measured to be 190 μsec (FWHM). The radiation was delivered to the ureter tissue by the special hollow waveguide (see section 2.2) so, the fluence on tissue reached 26 J/cm 2 . 2.1.2. CTE:YAG laser system The laser head of CTE:YAG laser (λ = 2.7 μm) consists of a Cr:Tm:Er:YAG crystal with a diameter of 5 mm and a length of 100 mm pumped with a linear xenon flashlamp in an elliptical silver coated pumping cavity. The resonator had plan- parallel configuration and was formed by two mirrors with the reflectivity R = 100 % and R out = 47 %. The same delivery * FNSPE -Faculty of Nuclear Sciences and Physical Engineering, Dept. of Electronics, Laboratory of Solid State Lasers.