Bringing laser-induced thermal therapy to gastroenterology and accepting it as a traditional method continues to be an essential topic of discussion. This discussion highlights coagulation parameters such as laser power, surface scanning speed, beam diameter, and irradiation duration. In addition, the parameters form a large matrix that must be optimized for successful treatment, including minimal damage to surrounding tissues. In this study, we aimed to propose a guide map representing the results of a simulation algorithm developed to provide information about the coagulation parameters of laser-induced thermal therapy of esophageal mucosal tissue. The simulation algorithm is based on the Monte-Carlo method for light transport in tissue, the time-dependent finite difference method for heat transfer, and the Arrhenius damage integral. This study includes validation experiments performed in ex vivo sheep esophagus, including histological analysis, light microscopy imaging, and block-face scanning electron microscopy investigations. The laser wavelength used in the studies is 1.5 µm, providing an optical penetration depth of around 0.5 mm in soft tissue, while the diameter of the laser beam on the tissue surface is 0.9 mm. The simulation algorithm evaluated the photothermal coagulation area in a tissue model with a volume of 4 x 4 x 4 mm3 for laser power up to 0.5 W and a surface scanning speed range of 0.5 mm/sec to 8 mm/sec. Direct comparison of simulation results with ex vivo studies showed significant overlap in laser energy per unit area for successful mucosal coagulation. The findings suggest that the proposed simulation approach can serve as a complementary guide tool for laser-induced photothermal therapy for superficial treatments and as a ground algorithm for future preclinical and clinical trials.
The potential of laser-induced thermal therapy can be reassessed in treating abnormal mucosal tissues with advances in fiber optics, diode laser technology, and optical imaging modalities. In this context, studies optimizing a large parameter matrix (e.g., laser power, surface scanning speed, beam diameter, and irradiation duration) may be of interest. This study presents an artificial intelligence algorithm utilizing a generative adversarial network that predicts dark-field microscopy images from bright-field images of H&E-stained esophageal specimens. The calculated structural similarity index measurement between ground truth and the predicted dark-field image reaches an average of 74%. Also, the mean squared error is 0.7%.
Uncontrolled therapy depth is the significant challenge for achieving an adequate removal of superficial lesions especially for mucosal tissue in the gastrointestinal (GI) tract. Although various treatment methods are available providing some successful applications, an effective approach that limit thermal damage to the epithelium layer is of great interest to therapeutic endoscopy technology studies. In this study, we aimed to propose an endoscopic approach to limit the depth of laser-induced thermal injury by trapping mucosal tissue in the recessed area by using negative pressure. This study includes a Monte-Carlo-based computer modeling for numerical analysis and a protype design for ex vivo animal model which followed by a histological study to assess thermal tissue damage to investigate proposed approach. The laser wavelength used in the studies is 1.5 µm, while the diameter of the laser beam is 0.4 mm and laser power of 0.4 W. The findings suggest that with further refinement in design and preclinical trials, this approach may hold promise for laser-induced thermal therapy in gastrointestinal (GI) tract interventions.
As the innermost layer of the gastrointestinal (GI) tract, the mucosa layer has critical importance in carcinogenesis. Barrett’s esophagus is a pre-cancerous lesion characterized by intestinal metaplasia within the stratified squamous epithelium of esophageal mucosa. Mucosal lesions that are not adequately treated tend to enlarge and become cancerous tissue over the surface and deeper layers. Although various treatment strategies are available, uncontrolled depth of treatment to eliminate lesions is still challenging. Exceeding the treatment depth may cause adverse effects on the underlying healthy tissue layers, while insufficient treatment depth may cause the lesion to recur. Besides, the inhomogeneity of the distribution of the lesions on the esophageal surface makes it difficult to apply ablation therapy in a single session, requiring more sessions. However, a feasible approach is still needed to perform the desired results in photothermal ablation at a single therapy session. This study demonstrates an endoscopy capsule that provides well confined and angle-controlled photothermal mucosal ablation. The capsule consists of three parts: a base that holds a stepper motor and a GRIN lens; a cap that includes gold-coated right-angle prism mirrors; an optically transparent and perforated body for negative pressure unites the base and cap. The mucosa layer is confined to the recessed area of the capsule by negative pressure delivered through holes. The laser beam at 1505 nm is rotated with a constant speed and defined rotation angles for circumferential photothermal ablation.
Uncontrolled therapy depth of treatment strategies for mucosal lesions may lead to adverse side effects. Laser ablation therapy using near-infrared laser irradiation provides confined therapy depth limited with a thickness of mucosa.
Electrical nerve stimulation (ENS) technique has been tested on nerve mapping devices, which are intraoperative diagnostic tools. However, these technologies suffer from general limitations. Optical Nerve Stimulation (ONS) has been a developing technique as a potential alternative to ENS. This new technique using infrared laser radiation can offer many advantages, including a non-contact stimulation mode, improved spatial selectivity, and elimination of stimulation artifacts. However, the stimulation parameters, including laser power, beam diameter, and surface scanning speed, provide a large variable matrix that must be optimized for consistent and reliable nerve mapping using ONS. This preliminary study explores a computational tool to provide a guiding map for determining optimal stimulation parameters for laser-scanning subsurface ONS. It consisted of three parts: (1) Monte Carlo simulations for generating laser energy distribution in the tissue sample, (2) laser-scanning model by moving the heat source at the surface, and (3) thermal transfer simulations to calculate the tissue temperature. The tool was tested on laser wavelengths of 1455 nm, 1490 nm, and 1550 nm. According to the results of calculations, nerve temperature maps were generated for those wavelengths. Each map demonstrated specific optimal parameter values to reach the nerve activation temperature. Additionally, the results of laser power densities at the lowest scanning speeds of 0.4 mm/s in x-axis and 0.5 mm/s in yaxis showed proximate results with our previous study about ONS on rat model. With further development, this tool may hold promise in the development of an intraoperative optical stimulus device for surgical applications.
Optical nerve stimulation (ONS) using infrared laser radiation is a technique developing as a potential alternative to electrical stimulation of nerve tissue. This preliminary study proposes and explores a computer simulation tool for numerically optimizing laser and surface scanning parameters including laser power and surface scanning speed to be used in laser scanning subsurface ONS. This tool consisted of three parts, including the Monte Carlo simulations for generating laser energy distribution in the tissue sample, the laser-scanning model by moving the heat source at the surface, and the thermal transfer simulations to calculate the tissue temperature. In the simulations, the laser wavelength of 1490 nm was used and the surface scan was performed on both x and y axes. In addition, the tissue model was constructed in such a way that the nerve tissue extends over the y-axis. As a result of calculations, the nerve tissue temperature map was produced as a function of laser power and surface scanning speed. According to the temperature map, the optimal laser power to reach the nerve temperature at 43 °C was estimated to be 15 mW at the scanning speeds of 1.2 mm/s in the x-axis and 1.0 mm/s in the y-axis. With further development this simulation tool may hold promise in the development of an optical stimulus device.
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