Laser surgery under sonographic control: preliminary experimental investigations

The laser has gained increasing importance during recent years as a useful addition to the physician's therapeutic armoury. Reports on successful prostatectomy by ultrasound-guided laser coagulation in an animal model encouraged us to evaluate the possibility of using this technique for gynecological indications (for example, ectopic pregnancy, endometriosis, ovarian cysts, and other areas of medicine). We used two different laser systems. The devices consisted of a real-time abdominal scanner (4-5 MHz) or a transvaginal sector scanner (5-7.5 MHz) coupled to a neodymium : YAG laser with a 1064 nm wavelength or a holmium : YAG laser with 2120 nm wavelength. An experimental set-up using a water bath revealed clear visibility of the fiber tip and the laser irradiation in real-time ultrasound at 7.5 MHz. Subsequently, a needle (routinely used in transvaginal puncture of ectopic pregnancy) was placed in animal and human tissue specimens and the laser fiber was inserted. The tissue was exposed to both laser systems at different energy densities, pulse rates and pulse widths. The sonographic appearance was recorded and correlated with the macroscopic findings. Results indicate that the holmium : YAG laser at a pulse rate of 5 Hz and a power of 2 watts is effective in removing substantial amounts of tissue. Moreover, it offers immediate visualization and control of the damaged area by producing a strongly echogenic focus. The neodymium : YAG laser showed comparatively poorer sonographic visibility and a precarious thermal mode of action, which are important considerations influencing its applicability. The holmium : YAG laser system with its non-thermal mode of action seems promising for the further clinical application of ultrasound-guided laser surgery.