In vitro comparison of renal stone laser treatment using fragmentation and popcorn technique.

OBJECTIVE: To study the effectiveness of two laser techniques clinically used to fragment renal stones: fragmenting technique (FT) and popcorn technique (PT). METHODS: Phantom stones were placed in a test tube filled with water, mimicking a renal calyx model. A Holmium:YAG laser was used for fragmentation using both techniques. Four series of experiments were performed with two parameters: the technique (FT or PT) and the number of stones in the test tube (one or four). The mass decrease of the phantom stones was measured before, during, and after the experiment to quantify the effect of both techniques. RESULTS: Visualization of PT showed that the main effect of PT takes place, when the stone moves in front of the laser fiber and is subject to direct radiant exposure. Both FT and PT resulted in a decrease in stone weight; the mass decrease of the stones subjected to FT exceeded that of the stones subjected to PT, even with less laser energy applied. This difference in mass decrease was evident in both the experiments with one and four stones. CONCLUSIONS: PT was less effective in decreasing stone weight compared with FT. The FT is more effective regarding the applied energy than PT, even in a shorter time period and regardless of the number of stones. This study suggests that FT is to be preferred over PT, when stones are accessible by the laser fiber. Lasers Surg. Med. 49:698-704, 2017. © 2017 Wiley Periodicals, Inc.

Imaging techniques for research and education of thermal and mechanical interactions of lasers with biological and model tissues.

A setup based on color Schlieren techniques has been developed to study the interaction of energy sources, such as lasers, with biological tissues. This imaging technique enables real-time visualization of dynamic temperature gradients with high spatial and temporal resolution within a transparent tissue model. High-speed imaging techniques were combined in the setup to capture mechanical phenomena such as explosive vapor, cavitation bubbles, and shock waves. The imaging technique is especially used for qualitative studies because it is complex to obtain quantitative data by relating the colors in the images to temperatures. By positioning thermocouples in the field of view, temperature figures can be added in the image for correlation to colored areas induced by the temperature gradients. The color Schlieren setup was successfully used for various studies to obtain a better understanding of interaction of various laser, rf, and ultrasound devices used in medicine. The results contributed to the safety and the optimal settings of various medical treatments. Although the interaction of energy sources is simulated in model tissue, the video clips have proven to be of great value for educating researchers, surgeons, nurses, and students to obtain a better understanding of the mechanism of action during patient treatment.

Transscleral thermotherapy with laser-induced and conductive heating in hamster Greene melanoma.

The purpose of this study was to investigate the cytotoxic effect of heat as induced by transscleral thermotherapy (TSTT), which may be of interest in the treatment of patients with choroidal melanoma. The aim of TSTT is to heat both the sclera and the tumor up to a cytotoxic temperature of about 60 degrees C. TSTT was performed in hamsters with subcutaneously implanted Greene melanoma covered by a specimen of human donor sclera of thickness 0.5, 0.7 or 0.9 mm. A newly developed applicator, which combines conductive episcleral heating at 60 degrees C with laser-induced heating, was used at laser powers ranging from 500 to 1500 mW delivered by an 810 nm diode laser, beam diameter 3 mm, and exposure time 1 min. Temperatures were measured at the scleral surface and at the sclera-tumor interface. The extent of tumor necrosis was examined by light microscopy and the sclera was examined by polarized light microscopy. Maximal depth of tumor necrosis without scleral damage was 4.4 (SD 1.5) mm. The temperature at the scleral surface after TSTT was 58.8 (SD 2.4) degrees C. The temperature at the sclera-tumor interface ranged from 56.4 (SD 3.7) degrees C at 500 mW to 65.3 (SD 4.4) degrees C at 1250 mW laser power. Structural changes to the scleral collagen started to develop at 1250 mW. TSTT with combined laser-induced and conductive heating caused cytotoxic temperatures in the tumor and the sclera, which were well tolerated by the scleral collagen.

Transscleral thermotherapy: short- and long-term effects of transscleral conductive heating in rabbit eyes.

OBJECTIVE: To determine the highest safe treatment temperature, at 30- and 60-second exposure durations, for transscleral thermotherapy (TSTT) of choroidal melanoma. METHODS AND DESIGN: Transscleral conductive heating was performed in 15 rabbits at 50 degrees C to 70 degrees C for 30 or 60 seconds. The thermal lesions in the ocular fundus were monitored for 4 months with ophthalmoscopic, photographic, and fluorescein angiographic examination. Histologic examination included polarized light microscopy. RESULTS: The effect of TSTT was similar for both exposure durations. Vascular occlusion in the retina and choroid developed at temperatures of 55 degrees C and higher. After heating at 60 degrees C, scleral collagen fibers developed a minimal undulation; at 65 degrees C, they became clearly undulated. The undulation resolved in the 3 to 4 months after heating. Heating at 70 degrees C caused persistent severe damage to the sclera. Retinal tears developed after heating at 65 degrees C and 70 degrees C. CONCLUSIONS: A temperature of 65 degrees C was found to be the highest temperature that did not cause permanent damage to the sclera at both exposure durations. A temperature of 60 degrees C may be the optimal temperature for TSTT of choroidal melanoma because retinal tears may develop at 65 degrees C. CLINICAL RELEVANCE: In TSTT, the temperature levels reached are cytotoxic for choroidal melanoma as well as intrascleral tumor cells. Occlusion of choroidal vessels induced by TSTT may contribute to tumor necrosis because these vessels serve as feeder vessels for the tumor.