Tissue damage by laser radiation: an in vitro comparison between Tm:YAG and Ho:YAG laser on a porcine kidney model

Abstract

The understanding of tissue damage by laser radiation is very important for the safety in the application of surgical lasers. The objective of this study is to evaluate cutting, vaporization and coagulation properties of the 2 µm Tm:YAG laser (LISA Laser Products OHG, GER) in comparison to the 2.1 µm Ho:YAG laser (Coherent Medical Group, USA) at different laser power settings in an in vitro model of freshly harvested porcine kidneys. Laser radiation of both laser generators was delivered by using a laser fiber with an optical core diameter of 550 µm (RigiFib, LISA Laser GER). Freshly harvested porcine kidneys were used as tissue model. Experiments were either performed in ambient air or in aqueous saline. The Tm:YAG laser was adjusted to 5 W for low and 120 W for the high power setting. The Ho:YAG laser was adjusted to 0.5 J and 10 Hz (5 W average power) for low power setting and to 2.0 J and 40 Hz (80 W average power) for high power setting, accordingly. The specimens of the cutting experiments were fixed in 4 % formalin, embedded in paraffin and stained with Toluidin blue. The laser damage zone was measured under microscope as the main evaluation criteria. Laser damage zone consists of an outer coagulation zone plus a further necrotic zone. In the ambient air experiments the laser damage zone for the low power setting was 745 ± 119 µm for the Tm:YAG and 614 ± 187 µm for the Ho:YAG laser. On the high power setting, the damage zone was 760 ± 167 µm for Tm:YAG and 715 ± 142 µm for Ho:YAG. The incision depth in ambient air on the low power setting was 346 ± 199 µm for Tm:YAG, 118 ± 119 µm for Ho:YAG. On the high power setting incision depth was 5083 ± 144 µm (Tm:YAG) and 1126 ± 383 µm (Ho:YAG) respectively. In the saline solution experiments, the laser damage zone was 550 ± 137 µm (Tm:YAG) versus 447 ± 65 µm (Ho:YAG), on the low power setting and 653 ± 137 µm (Tm:YAG) versus 677 ± 134 µm (Ho:YAG) on the high power setting. Incision depth was 1214 ± 888 µm for Ho:YAG whereas Tm:YAG did not cut tissue at 5 W in saline solution. On the high power setting, the incision depth was 4050 ± 1058 µm for Tm:YAG and 4083 ± 520 µm for Ho:YAG. Both lasers create similar laser damage zones of <1 mm in ambient air and in saline solution. These in vitro experiments correspond well with in vivo experiments. Thereby, Tm:YAG offers a cutting performance, coagulation and safety profile similar to the standard Ho:YAG lasers in urological surgery.

Utility and safety of a novel surgical microscope laser light source

“…Similar methods to minimize laser beam coherence have been previously reported [ 12 , 13 ]. The aim of light coherence reduction is to avoid illumination of the harmful coherent laser light on the surgeon’s or the assistant’s eyes and the patient’s brain tissue [ 14 ]. The safety of laser illumination was assured by terminating the light source emission automatically when the connection cable was not attached to the laser light source.…”

Analysis of Hemostasis Procedures through Machine Learning of Endoscopic Images towards Automatic Surgery

“…The surgeons finished the hemostasis procedures because the remaining small amount of bleeding was expected to stop naturally over time. The continuation of the hemostasis procedures increased coagulation, which caused inflammation and damaged normal tissues; (13,28) this was undesirable from an invasive point of view. In other words, even if S c is sufficiently small, caution is still required when the bleeding region is still large; the size of the bleeding region is considered to be part of the termination conditions of the hemostasis procedures.…”

“…In addition, hemostasis induces the thermal degeneration of organs using energy devices. (12,13) Robots capable of highly accurate maneuvers can be expected to more effectively suppress invasion than humans, because the energy device can be guided to the correct place, and coagulation errors can be reduced. The method developed by us in our previous study (9) contributes to the automation of hemostatic procedures by detecting changes associated with the protein degeneration of organ surfaces induced by using energy devices from the color features of endoscopic images through machine learning.…”

Development of detection method for automatic hemostasis using machine learning with abdominal cavity irrigation

“…There are multiple studies on reducing the invasiveness of tissue coagulation by energy devices because tissue coagulation by energy devices often causes loss of normal tissue. [4][5][6] Many studies have attempted to minimize the invasiveness of tissue coagulation by controlling the output of the device. We considered that it is possible to provide feedback to the coagulation device and reduce invasiveness by monitoring the bleeding region and quantitatively judging that hemostasis is complete.…”