The purpose of this study was to investigate the short-term biological effects of Excimer Laser. The surface of the skin in the rat was irradiated with KrF Excimer Laser at wave length of 248nm for 30 seconds at pulse repetition rate of 10Hz and pulse width of 15nsec.
Energy density was 3.1mJ/cm², 47.6mJ/cm², 160.0mJ/cm², 576.9mJ/cm² or 1714.2mJ/cm².The irradiated skin tissue was removed of various times between 1 hour and seven days after rradiation and with H-E stain for pathological examination. Necrosis was observed in epidermis irradiated at 47.6mJ/cm² and in dermis irradiated at 576.9mJ/cm², and defect of the muscular tunic was observed in tissue irradiated at 1714. 2mJ/cm². These results indicate that depth of skin defect is related to energy density and that necrosis occurs at energy density ranging from 3.1mJ/cm² to 47.6mJ/cm². Satisfactory wound was observed after irradiation at each energy density.

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The research for the endoscopic coronary laser angioplasty system using excimer laser and a very thin diameter endoscope has been performed since 1987 by us. To date, the laser endoscopic system, which is able to approach into the coronary artery percutaneously, could be developed. However in-vivo study showed that there remained the following problems; 1) it was impossible to make the laser aiming under the moving visual field caused by the beating of the heart, 2) it was impossible to perform the operation successfully within a few minutes of manipulation inside coronary because of the ischemie of the heart.
In order to improve these problems, we tried to examine the possibility of the procedure in the arrested heart by using the circulatory assistance.
The PCPS system was used for the circulatory assistance. The endoscopic coronary laser angioplasty system consist of the long-pulse excimer laser (308nm wave length, 8Ons pulse duration) and the ultra-thin laser endoscope (1.5mm diameter) for the coronary artery was used for the experiment. The endoscope had the 4-directional bending function at the tip.
Four goats with about 50kg weight were used. When the heart was beating, it was impossible to aim the target with the laser. However, when the heart was arrested under the circulatory assistance, the target could be aimed successfully with laser. The arrested heart was begun to beat again with the DC shock after the examination. In the experiment of the endoscopic coronary laser angioplasty, the heart was arrested immediately after the insertion of the skin tissue into the coronary artery by the acute myocardial infarction. Under the circulatory assistance, the excimer laser did not failed to be aimed to destroy the obstruction. However, the length of the obstruction was too long to remove the obstruction completely. The safety and reliable endoscopic coronary laser angioplasty would be possible, if the safety cardiac arrest condition was obtained in future.

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The KrF excimer laser is a high power pulsed laser oscillating in the ultraviolet field and able to destroy or amputate molecules of tissue without thermal damage.
In order to evaluate the effects of KrF excimer laser irradiation on human mandibular bone, we examined by visual, pathological and SEM observation.
The laser irradiation on human mandibular bone resected by oral and maxillofacial surgery had a pulse energy: 65mJ, spot size: 0.80×0.50mm₂, energy density: 16J/cm², water volume: 6.5ml, assist gas (N₂): 301/min, frequency: 80Hz, incision speed: 5, 10, 15mm/min.
Visual observation: the incisions were sharp without thermal damage, and the depth of the inicions ranged from 0.68 to 2.53mm according to the incision speed.
Pathological observation: the inicisions were almost sharp and there was almost no thermal damage layer.
SEM observation: the incision section was slightly wavy, but the incision surface was almost clear at 20 magnification. Crystals formed at the incision surface at all incision speeds, and there was no melting of bone tissue at 5000 magnification.

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Experimental results of fiberoptical delivery and a reaction on atherosclerotic tissue using a long pulse excimer laser are described. In order to improve the maximum energy delivered through optical fiber, a long pulse excimer laser which had the pulse duration of 100nsec was examined. The quartz fibers with both 300 and 400μm core diameter were used for the laser energy delivery. As a result, the maximum energies transmitted through optical fiber were 30mJ/pulse with 400μm core fiber and 16mJ/pulse with 300μm core fiber. And the average energies transmitted constantly were 20mJ/pulse and 10mJ/pulse with 400μm core fiber and 300μm core fiber, respectively. The energies were about 3 times lager than these using a conventional short pulse excimer laser. The laser energy delivered through the fiber was irradiated on the sample of atherosclerotic aorta of a rabbit in saline to investigate the tissue reaction on atheroma. The result shows that the fiberoptically delivered energy of long pulse excimer laser was enough for the destruction of atherosclerotic tissue.

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Recently, lasers operating at shorter and shorter wavelengths have becomeavailable. The excimer laser emits pulses of ultraviolet wavelengths.The KrF excimer laserhas high incision efficiency, and can cut hard tissue without thermal damage. An incisionwas made on the mandibular bone of a pig by laser under the following conditions. Frequency: 60Hz, pulse energy: 32mJ, pulse width: 15ns, beam spot size: 1.5×0.4mm2, energy density: 5.3J/cm2, irradiation time: 5min, volume of distilled water: 5l/min, andvolume of assist gas: 30l/min. After irradiation, visual, pathological and SEM observations was carried out. There were almost no thermal damage layers. The surface of boneincision was comparatively sharp. But, SEM finding showed the melting of tissue at the surface of bone.

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A pulsed ultraviolet excimer laser has been investigated as a cutting-ablating tool for bone surgery. The special feature of the KrF excimer laser is that it cuts bone tissue without thermal damage. In our earlier report, we determined the best frequency for healing of femur wound. In the present study, femurs were examined over a long period. The laser was used at pulse energy: 50mJ, beam spot: 0.015cm², pulse width: 15ns, peak power: 3.3MW, energy density: 33.3J/cm², incision speed: 4mm/min, irradiation time: 30s, and frequency: 20Hz. The femurs were examined histopathologically just after the operation, and at 1, 2, 4, 8, 12, and 48 weeks after the operation.
In the case of femurs examined at the postoperative 48th week, there was remaining the rmal damage around the cortical bone, and the new bone did not connect with the cortical bone.

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一は, 熱作用を伴うことなく, 鋭く組織を切断できると考えられる。我々は, 本レーザーの脳神経タト科領域への応用の可能性を検討するため, ラット脊髄後索を用いて切断実験を試みた。Kr-F (波長248nm) のを. 2×O.2mmのビームとして, ラット脊髄後索に照射し切断後, 切断創を光学顕微鏡, 透過型および走査型電子顕微鏡により観察した。30mJ以下の条件では, 切開創, およびその周囲組織には明らかな熱作用による変化は認められなかっだ。この条件では, 軸索. 髄鞘, グリア細胞など異なる組成の組織が, 電顕的にもほぼ均-に切断され, 極めて鋭い創面を得ることができた。
上より, は条件を適切に設定すれば, 中枢神経における組織の部分切除, 除去などに, 応用可能であると考えられる。

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