Laser-Tissue Interactions: Fundamentals and Applications
Abstract
Laser-Tissue Interactions by Prof. Dr. Markolf H. Niemz (Heidelberg University) has become the standard reference book in this fast growing field. It addresses basic concepts such as optical and thermal tissue properties, hard and soft tissue ablation, and photobiomodulation. Clinical applications are reviewed according to the latest references. The last chapter covers today's standards of laser safety with a careful selection of essential guidelines published by the Laser Institute of America.
This fourth edition has been completely revised and updated. Color illustrations, summaries, and questionnaires with solutions transform this book into a useful guide for graduate students, scientists, and medical practitioners.
OPHTHALMOLOGY
DENTISTRY
GYNECOLOGY
UROLOGY
NEUROSURGERY
ANGIOPLASTY AND CARDIOLOGY
ORTHOPEDICS
DERMATOLOGY AND COSMETICS
GASTROENTEROLOGY
OTORHINOLARYNGOLOGY
“An extremely useful reference companion.”
LASERS IN SURGERY AND MEDICINE
... The laser applicator usually consists of an optical fiber (with radius r f ) incorporated within a catheter. The diameter of the optical fiber for medical applications varies between 200 µm and 600 µm [30], while the laser beam diameter is 2 mm [1]. Thus, we may assume r f = 0.25 mm [28]. ...
... Photon transport. The photon transport is governed by the diffusion approximation of the radiative transfer equation (see, for instance, [30,42,35] ...
... The reduced scattering coefficient obeys µ ′ s = (1 − g)µ s , with g being the scattering anisotropy coefficient and µ s being the scattering coefficient. The biological tissue is a strongly scattering media and then g ranges from 0.7 to 0.99 for most biological tissues [30]. The optical parameters of the tissue are known (cf. ...
The present paper deals with the study of the fluence rate over both healthy and tumor tissues in the presence of focal laser ablation (FLA). We propose new analytical solutions for the coupled partial differential equations (PDE) system, which includes the transport equation modeling the light penetration into biological tissue, the bioheat equation modeling the heat transfer and its respective damage. The present building could be the first step to the knowledge of the mathematical framework for biothermophysical problems, as well as the main key to simplify the numerical calculation due to its no cost. We derive exact solutions and simulate results from them. We discuss the potential physical contributions and present respective conclusions about (1) the validness of the diffusion approximation of the radiative transfer equation; (2) the local behavior of the source of scattered photons; (3) the unsteady-state of the fluence rate; and (4) the boundedness of the critical time of the thermal damage to the cancerous tissue. We also discuss some controversial and diverging hypotheses.
... Thermal laser-tissue interactions are generally considered hard to model because they involve multiple complex physical processes, including light propagation and heat transfer [18]. These interactions are influenced by numerous factors, including the laser's specific wavelength, power, and exposure time as well as the specific properties of the targeted tissue. ...
... From [18], the thermal dynamics of laser-irradiated tissue are governed by a partial differential equation of the form ...
... Readers familiar with heat transfer theory will recognize Eq. (1) as the well-known heat equation used to describe heat conduction in solids, with the addition of an input term S, which denotes the heating produced by the laser. In first approximation, this term can be calculated as [18] ...
This paper presents a computational model, based on the Finite Element Method (FEM), that simulates the thermal response of laser-irradiated tissue. This model addresses a gap in the current ecosystem of surgical robot simulators, which generally lack support for lasers and other energy-based end effectors. In the proposed model, the thermal dynamics of the tissue are calculated as the solution to a heat conduction problem with appropriate boundary conditions. The FEM formulation allows the model to capture complex phenomena, such as convection, which is crucial for creating realistic simulations. The accuracy of the model was verified via benchtop laser-tissue interaction experiments using agar tissue phantoms and ex-vivo chicken muscle. The results revealed an average root-mean-square error (RMSE) of less than 2 degrees Celsius across most experimental conditions.
... The temperature distribution in the skin was calculated using the non-stationary heat conductivity equation [18]: ...
... where ρ is density, c is specific heat capacity, κ is thermal conductivity, t is time. and Q E r is the volume density of heat sources in the environment, calculated as follows [18]: ...
... The collimated component of illumination decays exponentially due to absorption and scattering [18]: where E E r; O s 0 is the intensity at point E r in the absence of an environment (tissue), O s 0 is the direction of propagation of the primary beam; μt = μa + μs is the total attenuation coefficient and l is the depth of propagation of "unaltered" photons in tissue between the entry point into the biological tissue and point E r of the volume element under consideration. ...
The main requirements for the technical characteristics of laser medical devices for non-ablative treatment of vascular, pigmented, and uncolored skin defects in the periorbital area are formulated and approaches to solving them are proposed. Numerical modeling results were used to select parameters for copper vapor laser radiation at a green wavelength (511 nm) and a yellow wavelength (578 nm), minimizing the risk of damage to the organs of vision. The Yakhroma-Med copper vapor laser medical device, which meets these requirements, has been developed and registered by the Ministry of Health of the Russian Federation. Clinical trials have shown that this device has high efficacy in the treatment of neoplasms in the periorbital area.
... Absorption of light ( ) by specific molecules is wavelength-dependent. According to the equation of heat deposition, the relatively weak absorption in the near infrared region results in low heat deposition, [12]; ...
... The use of ns pulse width is accepted within the limit of the selective photothermolysis rule. At the same time, microvessels have diameter range of 10-30 μm with a thermal relaxation time of approximately 0.5-12 ms [12]. Pulse durations much shorter this thermal relaxation time lead to mechanical rupturing in these micro-vessels [7]. ...
In laser tattoo removal, selective photothermolysis permits the selective destruction of tattoo pigment molecules with very limited damage to surrounding tissue. To maximize the breakup of tattoo ink, the energy density (fluence), wavelength , and pulse duration of the laser need to be optimized. White domesticated Albino rabbits were used in our trials. Each received simultaneous injections of a color pigment tattoo while under general anesthesia, followed by sessions of Q-switched Nd: YAG (1064 and 532 nm), (100-800) mJ, and 5 and10 ns laser pulses for tattoo removal. The spectroscopic properties of black, brown, green, blue and red tattoo inks were studied in our trial. Laser fluence damage threshold of tattooed tissue was also investigated in order to select the optimized conditions for obtaining scar-free skin following tattoo removal. A histological observation of laser treated tissue, before and after laser treatment, was then performed using optical microscopy. Histological images of the biopsies taken after thirty days of laser treatment of both black and brown tattoos showed a marked reduction in pigment granules' size, with no appearance of hyperplasia, inflammatory cells, or vacuolations. Our results suggest that the coexistence of macrophages is responsible for actively phagocytosing the laser-dispersed tattoo pigment. Skin biopsies have demonstrated local redistribution of ink granules. In addition to shuttering tattoo particles, the laser created some vacuolations, adding extra mechanical damage to the pigment.
... Depending on the exposure time scale, there are four regions: continuous wave or exposure times longer than one second for photochemical interactions; exposure times from one minute to one microsecond for thermal interactions; exposure times from one microsecond to one nanosecond for photoablation; and exposure times shorter than one nanosecond for plasma-induced ablation and photodisruption. The difference between the latter two is attributed to different energy densities [3]. ...
... Depending on the exposure time scale, there are four regions: continuous wave or exposure times longer than one second for photochemical interactions; exposure times from one minute to one microsecond for thermal interactions; exposure times from one microsecond to one nanosecond for photoablation; and exposure times shorter than one nanosecond for plasma-induced ablation and photodisruption. The difference between the latter two is attributed to different energy densities [3]. Under highly concentrated peak irradiances and shorter exposure times, in the picosecond and the femtosecond (fs) range, one can not only break molecules-as during photoablation-but even strip electrons from their atoms and accelerate them. ...
(1) Background: Ultrashort high-energy laser pulses may cause interaction mechanisms, including photodisruption and plasma-induced ablation in the medium. It is not always easy to distinguish between these two processes, as both interaction mechanisms rely on plasma generation and overlap. The purpose of this paper is to discuss prominent cavitation bubble models describing photodisruption and plasma-induced ablation and to explore their nature for different threshold energies. This exploration will help to better distinguish the two interaction mechanisms. As a second aim, we present an alternative model for the low-energy regime close to the laser-induced optical breakdown (LIOB) threshold, representing the phenomenological effect of the plasma-induced ablation regime. (2) Methods: The cavitation bubble models for photodisruption and plasma-induced ablation were used to calculate the bubble radius for a series of threshold energies (ETh = 30, 50, 70, and 300 nJ) that loosely represent commercial systems currently used in ultrashort-pulse tissue ablation. Taking a photodisruption model coefficient commonly used in the literature, the root mean square error between the two interaction models was minimized using the generalized reduced gradient fitting method to calculate the optimum scaling factors for the plasma model. The refined models with optimized coefficients were compared for a range of pulse and threshold energies. (3) Results: For low ETh (30, 50, and 70 nJ), the plasma-induced ablation model dominates for low energies that are close to the threshold energy. The photodisruption model dominates for high energies that are well above the threshold energy. At very high pulse energies, for all the simulated cases, the photodisruption model transitions and crosses over to the plasma-induced ablation model. The cross-over points from which the photodisruption model dominates tend to be reduced for larger ETh. A new universally applicable model for plasma-induced ablation has been hypothesized that considers the cavitation bubble volume and potentially better explains the bubble dynamics during intrastromal processes. (4) Conclusions: This theoretical exploration and the comparison of the outcomes to empirical data substantiate that inadvertently using the photodisruption model to explain the cavitation bubble dynamics for the entire spectrum of pulse energies and laser systems might provide erroneous estimates of cavitation bubble sizes. A reliable estimate of the true size (the maximum radius) of the cavitation bubble can be reasonably retrieved as the maximum predicted size from the fit of the photodisruption model and the newly proposed plasma-induced ablation model at any given pulse energy.
... The light wavelength and optical properties of the biological tissue determine how deep laser radiation penetrates, and its high energy density and intensity allow high radiation doses to be delivered at high dose ratios. 1 Also, laser devices work as radiation sources, in continuous or pulsed emission mode, depend on the laser active medium or whether the emission is modulated by an electric current. 1 For low-level lasers, low energy densities or doses are applied to body tissues according to the therapeutic applications proposed by device guidebooks or laser practitioners. These lasers cause nonthermal and nondestructive effects but alter biological processes increasing the metabolism and cellular division rate, an effect known as biostimulation or biomodulation. ...
... The light wavelength and optical properties of the biological tissue determine how deep laser radiation penetrates, and its high energy density and intensity allow high radiation doses to be delivered at high dose ratios. 1 Also, laser devices work as radiation sources, in continuous or pulsed emission mode, depend on the laser active medium or whether the emission is modulated by an electric current. 1 For low-level lasers, low energy densities or doses are applied to body tissues according to the therapeutic applications proposed by device guidebooks or laser practitioners. These lasers cause nonthermal and nondestructive effects but alter biological processes increasing the metabolism and cellular division rate, an effect known as biostimulation or biomodulation. ...
Introduction: Low-level lasers are successfully used to prevent and treat diseases in soft oral and bone tissues, particularly diseases in oral cavity caused by chemotherapy and radiotherapy in oncology. However, controversy exists as to whether these lasers induce molecular side effects, mainly on DNA. The aim of this work was to assess the effects of low-power lasers on mutant Escherichia coli cells in DNA repair.
Methods: Escherichia coli wild type cultures as well as those lacking recombination DNA repair (recA-) and la SOS responses (lexA-) irradiated with lasers at different energy densities, powers, and emission modes for cell viability and morphology assessment were used in this study.
Results: Laser irradiation: (i) did not affect cell viability of non-mutant and lexA- cells but decreased viability in recA- cultures; (ii) altered morphology of wild type and lexA, depending on the energy density, power, emission mode, and wavelength.
Conclusion: Results show that low-level lasers have lethal effects on both recombination DNA repair and SOS response bacterial cells but do not induce morphological modifications in these cells.
... The focused laser delivers a pulse peak power density near 7.42 × 10 12 · cm −2 . With a pulse duration of 130 fs, the system has the prerequisite to perform plasma-induced ablation [15,25]. A typical experiment is illustrated in Fig. 2c-e. ...
... At low NIR power, the emitted fluorescence of the marker is non-homogeneous (arrows in Fig. 3f). Ablation, which relies on a multi-photon ionization process [25], is very sensitive to the laser focus being localized at the adherens plane. We observe only partial cuts (arrows in Fig. 3g,h) when scanning a high-power laser along the 2D circular trajectory as ablation is effective in only a fraction of the trajectory (arrows in Fig. 3h). ...
The mechanical actuation of cells by active forces from the cytoskeleton drives tissue morphogenesis. To understand these forces, multicellular laser dissection has become an essential tool for severing tissue locally and inferring tension from the recoil of surrounding structures. However, conventional laser dissection is limited by 2D steering, which is inadequate for embryos and developing tissues that are intrinsically 3D structures. In this study, we introduce a flexible near-infrared (NIR) fs-pulsed laser-dissection system that allows for dissection trajectories to proceed in 3D and adapt to the curved surfaces of cell sheets, which are prominent structures in embryos. Trajectories are computed through an unsupervised search for the surface of interest. Using this technique, we demonstrate sectioning of multicellular domains on curved tissue, which was not possible with regular NIR laser scanning. We apply the developed strategy to map mechanical stresses in the imaginal disc of the developing Drosophila wing. Our targeted, adaptive scans can be used in other nonlinear processes, such as two-photon fluorescence imaging or optogenetics. Overall, this new laser-dissection system offers an innovative solution for studying complex 3D structures and their mechanical properties.
... However, it varies in the depth direction and can be considered based on decrease in the laser intensity according to the Beer equation [87]. Beer's law for laser intensity decay in the penetration depth direction, along with the assumption of a Gaussian laser beam distribution in the radial direction, allows us to assert that the laser intensity in a given depth and radius can be given as [88]. ...
Laser therapy is extensively utilized in dermatology and medicine due to its ability to precisely target tissues, particularly for skin rejuvenation and collagen stimulation. However, the complex interactions between laser irradiation and multilayered skin structures remain insufficiently understood. This study presents a two-dimensional dual-phase-lag heat conduction model to simulate the temperature distribution in multilayered skin subjected to pulsating laser irradiation. The model incorporates the distinct optical and thermal properties of different skin layers, enhancing the accuracy of heat transfer analysis. To regulate laser intensity and maintain surface temperature within a predefined range, a proportional-integral-derivative (PID) control system is implemented. Experimental validation using an agar-based phantom shows strong agreement with simulation results, confirming the model's reliability. The results further indicate that the PID control system effectively maintains the target temperature with minimal overshoot. However, while surface temperature remains regulated, deeper skin layers may experience higher peak temperatures, emphasizing the need for improved subsurface thermal monitoring , particularly in high-absorption treatments. Additionally, the study systematically analyzes the influence of PID gain parameters on temperature regulation, highlighting their impact on system stability and response time. These findings underscore the critical role of integrated control systems in laser-based thermal therapies, enhancing precision, safety, and clinical efficacy. The proposed framework provides a robust foundation for real-time temperature management, contributing to more reliable and effective medical applications of laser technology.
... Two practical aspects of clinical PBM dosing require attention and are discussed in more detail in other articles that have been briefly summarized in a review article. 5,[251][252][253][254][255][256][257][258][259][260][261][262][263][264][265][266][267][268][269] First, the PBM device parameters such as choice of wavelength or combinations (with multiple wavelength units; Figure 4C), PBM light sources (laser vs light-emitting diodes [LEDs]), source-specific beam attributes (spectral range, half-width at full maximum, polarization), mode of operation (continuous wave vs pulsing), irradiance (power density mW/cm 2 ), fluence (energy density J/cm 2 ), and treatment time (session and repetitions). A dose concept has suggested accounting for the individual wavelength photonic energy (eV) that focuses on multiple modes of energy transfer, including absorption and inelastic scattering. ...
... A pulsed laser will be used to heat and shrink the conjunctiva. The laser beam will be focused into a line on the tissue and the situation can be modeled as a one-dimensional heat diffusion problem for the calculation of tissue thermal relaxation time 19 : ...
Conjunctivochalasis is a common cause of tear dysfunction due to the conjunctiva becoming loose and wrinkly with age. The current solutions to this disease include either surgical excision in the operating room, or thermoreduction of the loose tissue with hot wire in the clinic. We developed a near-infrared (NIR) laser thermal conjunctivoplasty (LTC) system, which gently shrinks the redundant tissue. The NIR light is mainly absorbed by water, so the heating is even and there is no bleeding. The system utilizes a 1460-nm programmable laser diode system as a light source. A miniaturized handheld probe delivers the laser light and focuses the laser into a 10x1 mm2 line. A foot pedal is used to deliver a preset number of calibrated laser pulses. A fold of loose conjunctiva is grasped by a pair of forceps. The infrared laser light is delivered through an optical fiber and a laser line is focused exactly on the conjunctival fold by a cylindrical lens. Ex vivo experiments using porcine eye were performed with the optimal laser parameters. It was found that up to 50% of conjunctiva shrinkage could be achieved.
... A laser pulse is applied to the stroma, a particular layer of the cornea, breaking the polypedite bond that binds the amino acids in the collagen fibers. 5,6 There is a slight temperature rise after this action. Ablation and heat transmission should preferably not be combined because heat is the enemy of soft tissues. ...
Laser corneal reshaping is a safe and effective technique utilized to treat common vision disorders. An advanced laser delivery system equipped with a pulsed UV laser with specific parameters is used to ablate parts of the cornea surface to correct the existing refractive error. The argon fluoride (ArF) excimer pulsed gas laser at 193 nm is the most employed type in the commercial devices for such treatments. This laser is generated using a mixture of Argon, Fluorine, and a significant amount of Neon gases. However, due to the ongoing Russian‐Ukraine war, the availability of Neon gas is currently very limited, as this region is considered the primary supplier of pure Neon gas. Consequently we suggest replacing the common ArF laser source in the commercial devices with a solid‐state (forth harmonic neodymium‐doped yttrium aluminum garnet laser at 266 nm). This replacement uses the same operation parameters, optics, and scanning algorithm. Parameters from five commercial devices (Zeiss MEL 90, Technolas TENEO 317, Alcon Wave Light EX 500, Schwind Amaris 750 s, OptoSystems MICROSCAN VISUM) were compared with those of the i‐ablation device, a research device that uses a 266 nm laser source. Our goal is to reduce production costs through a simple modification that has a significant impact. Consequently, the present study aims to find an alternative laser source for the current ArF laser without exchanging the complete system's design. This recommendation is based on a numerical simulation study. The thermal effect on a human cornea model was numerically evaluated using finite‐element solutions of Pennes' bioheat equation on the COMSOL platform by applying two laser wavelengths. The results demonstrated that changing the laser source significantly impacts the thermal effect, even with the same laser settings. All studied devices showed a reduction in the thermal effect to below 40°C, compared with nearly 100°C under ordinary conditions.
... The mechanism that triggers liquid breakdown depends on various factors, including laser pulse duration, pulse intensity, wavelength, and polarization, among others. The use of CW lasers or longer-pulsed lasers (τ > 1 µs) generates a process called laser-induced thermal breakdown [81]. ...
Since Nobel Laureate Arthur Ashkin first introduced the trapping and manipulation of microparticles using light, numerous studies have explored this technique not only for dielectric/metallic particles but also for organic matter. This advancement has significantly expanded the landscape of non-contact and non-invasive micromanipulation at the nanometric scale. However, micromanipulation of particles with a refractive index smaller than the host medium, n p < n m, proves challenging with Gaussian beams. To overcome this obstacle, a force known as thermocapillary, or the Marangoni force, has emerged as a straightforward trapping mechanism for bubbles in liquids. The Marangoni force results from the surface tension of bubbles, induced either thermally or chemically—by creating a temperature gradient or adding surfactants, respectively. The surface tension gradient on the liquid host induces tangential stress on the bubble wall, causing the bubble to move toward the region of lower surface tension, where it faces less opposing force. When the Marangoni force is generated by a laser beam’s temperature gradient, it becomes an exceptionally effective mechanism for the steady-state trapping and three-dimensional manipulation of bubbles, even with low optical power lasers. This force produces both longitudinal and transversal forces, resembling optical forces, creating a three-dimensional potential well capable of handling bubbles with radii of tens to hundreds of microns. This work provides guidance and demonstrates, both experimentally and theoretically, the step-by-step process of quasi-steady-state trapping and three-dimensional manipulation of bubbles through optothermal effects. The bubbles in question are tens of microns in size, significantly larger than those that optical tweezers can trap/manipulate. Furthermore, the study emphasizes the crucial role of the Marangoni force in this process, outlining its various advantages.
... With an average power of 154 mW at the back aperture of the objective, the focused laser delivers a pulse peak power density near 7.42 × 10 12 W�cm −2 . With a pulse duration of 130 fs, the system has the prerequisite to perform plasma-induced ablation [66,67]. To sever the tissue along lines the laser beam was moved 2 to 3 times along the targeted region in the sample with the help of a galvo-based scanner (Cambridge Technologies) at a constant speed of about 500 ums -1. ...
The polygonal shape of cells in proliferating epithelia is a result of the tensile forces of the cytoskeletal cortex and packing geometry set by the cell cycle. In the larval Drosophila epidermis, two cell populations, histoblasts and larval epithelial cells, compete for space as they grow on a limited body surface. They do so in the absence of cell divisions. We report a striking morphological transition of histoblasts during larval development, where they change from a tensed network configuration with straight cell outlines at the level of adherens junctions to a highly folded morphology. The apical surface of histoblasts shrinks while their growing adherens junctions fold, forming deep lobules. Volume increase of growing histoblasts is accommodated basally, compensating for the shrinking apical area. The folded geometry of apical junctions resembles elastic buckling, and we show that the imbalance between the shrinkage of the apical domain of histoblasts and the continuous growth of junctions triggers buckling. Our model is supported by laser dissections and optical tweezer experiments together with computer simulations. Our analysis pinpoints the ability of histoblasts to store mechanical energy to a much greater extent than most other epithelial cell types investigated so far, while retaining the ability to dissipate stress on the hours time scale. Finally, we propose a possible mechanism for size regulation of histoblast apical size through the lateral pressure of the epidermis, driven by the growth of cells on a limited surface. Buckling effectively compacts histoblasts at their apical plane and may serve to avoid physical harm to these adult epidermis precursors during larval life. Our work indicates that in growing nondividing cells, compressive forces, instead of tension, may drive cell morphology.
... Another issue considered is the time required to produce the incision and its effect on the lateral thermal damage. A longer irradiation time is often related to deeper thermal depths (24). Lastly, the sort-term character of this study does not allow conclusions regarding the long-term outcomes of the incisions. ...
Objective: To compare two different wavelengths of the surgical Contact Diode Laser (CDL) for producing a posterior laryngofissure in live pigs.
Methods: Anesthetized pigs underwent a tracheostomy and an anterior laryngofissure through a cervicotomy. They were randomly selected for the CDL wavelength and power (980nm wavelength: Ppeak power of 10W, 15W, and 20W, or 1470nm wavelength: Ppeak 3W, 5W, 7W, 10W). At the end of the experiment, the laryngotracheal specimen was extracted and sent for histology and morphometry measurements (incision size, depth, area, and lateral thermal damage). Hemodynamic data and arterial blood gases were recorded during the incisions. Statistical analysis of the comparisons between the parameters and groups had a level of significance of p <0.05.
Results: Twenty-six pigs were divided into CDL 980nm (n=11) and 1470nm (n=15). There was a larger incision area at the thyroid level in the 980nm CDL and a larger distance between borders in the tracheal level. There were no significant differences in the lateral thermal damage between the two groups and among the power levels tested.
Conclusion: Both wavelengths tested showed similar results in the various combinations of power levels without significant differences in the lateral thermal damage. The posterior laryngofissure incision can be performed safely by combining both wavelengths at low and medium power levels.
... This laser "drill" offers unparalleled precision over traditional drills. SEM and other assays confirm the attainment of crack-free results with resolutions below 10 µm [40]. Additional potential benefits encompass enhanced osseointegration, reduced bacterial adhesion, and increased resistance to biofilm formation [41]. ...
This study evaluated the effects of various mechanical debridement methods on the surface roughness (Ra) of dental implants, comparing femtosecond laser-treated surfaces with conventionally machined and sandblasted with large-grit sand and acid-etched (SLA) implant surfaces. The fabrication of grade 4 titanium (Ti) disks (10 mm in diameter and 1 mm thick) and the SLA process were carried out by a dental implant manufacturer (DENTIS; Daegu, Republic of Korea). Subsequently, disk surfaces were treated with various methods: machined, SLA, and femtosecond laser. Disks of each surface-treated group were post-treated with mechanical debridement methods: Ti curettes, ultrasonic scaler, and Ti brushes. Scanning electron microscopy, Ra, and wettability were evaluated. Statistical analysis was performed using the Kruskal–Wallis H test, with post-hoc analyses conducted using the Bonferroni correction (α = 0.05). In the control group, no significant difference in Ra was observed between the machined and SLA groups. However, femtosecond laser-treated surfaces exhibited higher Ra than SLA surfaces (p < 0.05). The application of Ti curette or brushing further accentuated the roughness of the femtosecond laser-treated surfaces, whereas scaling reduced the Ra in SLA surfaces. Femtosecond laser-treated implant surfaces, with their unique roughness and compositional attributes, are promising alternatives in dental implant surface treatments.
... From the theory of heat diffusion, 23 in a time t heat travels over a distance L obtained by the formula: ...
Optical radiation sources, and in particular lasers, find an ever-increasing number of applications in the medical field. It is essential that personnel who are in the presence of an optical radiation source, whether operator, patient or researcher, know precisely the risks inherent in the exposure of the human body to radiation. In order to reduce the risk of biological damage, beyond the provisions of the law on safety regulations, the precise information and accurate preparation of personnel are the main guarantee for the correct use of these sources. In all the application fields, the possibility of a biological damage cannot be completely eliminated, assuming the connotation of occupational risks. In order to understand the risks and operate their effective mitigation, the basic knowledge of the fundamental concepts at the basis of laser-matter interaction will be presented and discussed, with a focus on the physical parameters needed to efficiently estimate and mitigate the related occupational risks, in both a laboratory and clinical context.
... [1][2][3] Dental lasers depending on their wavelength provide ablation properties and generate defined cutting lines and hemostasis via various interactions with the oral soft tissues such as photochemical, thermal, or ablative phenomena. 4 More specifically, semiconductor laser devices (diode lasers) with wavelengths from 445 to 980 nm are commonly used for coagulation or cutting of oral soft tissues. 1,5,6 Laser radiation, is monochromatic, unidirectional, coherent with adaptable energy and power densities allowing acceleration of wound healing, pain alleviation, and removal of oral soft tissues without bleeding and simultaneous coagulation and thermal disinfection of the wound. ...
Objectives: To investigate quantitatively the cutting efficiency and the thermal effects in the surrounding soft tissues of incisions that are induced by a 940 nm‐ diode laser with different power settings.
Materials and Methods: Fifty‐four gingival samples were prepared from the lower jaws of freshly slaughtered German‐land race pigs and were randomly divided into 9 groups (n = 6) according to the adjusted output power (1, 1.5, 2, 2.5, 3, 3.5, 4, 5 and 6 W). Five incisions were implemented for each sample using a diode laser (940 nm) in continuous wave with an initiated tip resulting in 30 incisions for each experimental group utilizing a three‐dimensional computer‐controlled micropositioner. The samples were prepared for histometric evaluation using a transmitted light microscope. The cutting depth and width and the thermal damage were recorded for each sample and the efficiency factor γ was calculated. Results: The highest cutting efficiency (γz = 0.81 ± 0.03) exhibited the group with 5 W output power (p < 0.05), while the lowest (γz = 0.45 ± 0.11) showed the 1‐W group (p < 0.05). Over 3.5 W there was a rapid increase in the size of thermal damage of the incisions, especially for 6 W, which presented the largest. Conclusions: The most effective power parameters of diode laser (940 nm) for soft tissue surgery were from 3 to 5 W. The outcomes of the current study may help to establish clinical protocols for the use of diode lasers (940nm) in soft tissue surgery in contact mode assisting dental professionals to achieve optimal clinical results and avoid complications.
This study presents a numerical model investigating the thermal effects of laser exposure on the cornea and retina of the human eye, with a focus on the role of blood flow in thermoregulation. Both the anterior and posterior segments of the eye are analysed to provide guidance on whether to account for blood flow in simulations of laser-based eye surgeries. Argon Fluoride (ArF), Holmium:Yttrium–Aluminum-Garnet (Ho:YAG), Neodymium-Doped:Yttrium–Aluminum-Garnet (Nd:YAG), and Ruby lasers are applied to a three-dimensional eye model. The Pennes’ bio-heat transfer equation is solved using the Finite Element Method (FEM) to assess temperature distributions and penetration depths, ensuring that target tissues remain within safe temperature limits. The simulation results show maximum temperatures of 259°C, 89.2°C, 136°C, and 67.4°C for ArF, Ho:YAG, Nd:YAG, and Ruby lasers, respectively. Additionally, the explicit method is employed to model the pupil axis and further investigate blood flow’s impact on thermoregulation. The inclusion of blood flow results in lower temperatures across all laser conditions, demonstrating its crucial role in regulating excess heat, particularly in the retina, which has a denser blood vessel network compared to the avascular cornea. These findings emphasise the importance of incorporating blood flow in thermal simulations to improve the accuracy of predictions and ensure safer outcomes in laser-based eye surgeries. This study employs a comprehensive approach combining precise modelling, simulations, and numerical analysis to investigate the effects of lasers on both the cornea and retina. This offers a wide understanding of laser-tissue interactions and helps in optimizing treatment parameters for both types of ocular tissues. Finally, a comparison table is presented alongside existing studies to highlight the achieved temperatures and penetration depths in laser-tissue interactions.
The optical dispersion broadens laser pulse width of ultrafast lasers and reduces peak power. This study develops liquid lens compressor to compensate dispersion to restore laser pulse width and improve temporal focusing microscopy performance.
Compact sapphire capillary needles for laser-assisted therapy connected to optical fibers by the means of internal channel closed from one side transmit laser radiation to the tissues with minimal loss of energy and simultaneously protect the fibers. The geometry of the internal capillary channel with the curved bottom is a key factor in the formation of the output beam's shape. Various curvatures of the bottom in combination with the different angle of conical needle's tip are studied in detail. When the tissue is covered in a liquid, we have observed forming the ring radiation pattern with a sharp axial peak without additional diaphragms or spatial light modulators. Coagulation of ex vivo liver tissue samples using continuous laser source with 1.06 μm wavelength, offered opportunity to obtain small coagulated spots without carbonization with the diameter of at least 0.8 mm and to enlarge them evenly by tuning the source output power.
Photothermal therapy (PTT) has emerged as a promising alternative to conventional cancer treatments such as radiation therapy, chemotherapy, and surgery. PTT uses light‐absorbing nanomaterials to induce localized hyperthermia and selectively eliminate cancer cells, thus offering advantages over traditional interventions. This literature review focuses on nanoparticles for PTT, their heating properties, and their functions in theragnostic applications for photothermal cancer treatment. It highlights the fundamental principles, recent spectroscopic developments for diagnosis and treatment monitoring, clinical advancements in near‐infrared (NIR) nanoparticle‐mediated PTT, and emerging numerical methods for preclinical planning of PTT.
This paper reports on a study whose goal is to control the tissue temperature at a specific spot during laser surgery, for the purpose of, inducing coagulation or sealing blood vessels. We propose a solution that relies on the automatic adjustment of the laser focus (and thus how concentrated the laser beam is), combined with the use of an infrared thermal camera for non-contact temperature monitoring. One of the main challenges in the control of thermal laser-tissue interactions is that these interactions can be hard to predict due to the inherent variability in the molecular composition of biological tissue. To tackle this challenge, we explore two different control approaches: (1) a model-less controller using a Proportional-Integral (PI) formulation, whose gains are set via a tuning procedure performed on laboratory-made tissue phantoms; and (2) a model-based controller using an adaptive formulation that makes it robust to tissue variability. We report on experiments, performed on four types of tissue specimens, showing that both controllers can consistently achieve temperature tracking with a Root-Mean-Square Error (RMSE)
1 °C.
Objective: The purpose of this study was to demonstrate heat transfer within oral soft tissues using different lasers under the effect of local anesthetics (LA). Methods: Bovine tongue slices were placed in between two glass slides and at a distance from a thermographic camera. In total, 2-cm-long 240 incisions were made along the surface of the tissue parallel to glass slides and the camera capture field. Incisions were performed using 445-nm and infrared (IR) lasers (970 nm and 980 nm on a continuous wave at 2 W) with 320 µm-initiated (concentrated energy at the tip provided by a blue articulated paper and laser irradiation) and noninitiated (defused energy) fiber (30-sec irradiation period). LA was injected into the specimens before irradiation. The temperature changes in °C (ΔT) and vertical and lateral heat transfer (in mm) were recorded at 10-sec intervals for 30 sec, using thermographic images. The amount of lateral and vertical heat transfer was measured. A repeated analysis of variance statistical comparison test was used to analyze differences between the lateral (width) and the vertical (height) heat transfer for initiated and noninitiated lasers and different lasers. Results: The maximum ΔT in °C utilizing initiated tips of 970, 980, or 445 nm were 11.82 ± 3.46, 7.66 ± 3.24, and 18.94 ± 7.01 and using noninitiated tips were 8.27 ± 1.69, 8.87 ± 2.40, and 12.31 ± 8.65, respectively. Heat transfers (height/width) for initiated were 40.65 ± 10.40/90.65 ± 10.77 mm, 41.50 ± 11.83/83.95 ± 11.20 mm, and 33.70 ± 9.10/95.10 ± 11.17 mm and for noninitiated lasers were 52.95 ± 6.89/96.10 ± 11.17 mm, 47.75 ± 7.41/93.75 ± 14.96 mm, and 31.35 ± 11.40/75.20 ± 19.68 mm, respectively. A statistically significant difference was found between all lasers (p < 0.05) for initiated and noninitiated lasers (except for 970/980 nm for noninitiated lasers). Lower penetration depth (p < 0.05) at 445-nm diode and greater lateral heat spreading (p < 0.05) were identified under LA especially utilizing noninitiated tips without significant difference in IR lasers. Conclusions: LA might negatively influence soft tissues creating scattering when noninitiated tips are used and IR diode laser technology.
Plasmonic nanostructures continue to be the most promising alternative to hyperthermia treatment of cancer or tumors by focusing the light locally. Absorption and scattering cross-sections of 48 nanorods encompassing silver and palladium as core and gold and platinum as coating with four different aspect ratios and three different coating thicknesses were examined in an aqueous solution with finite-element method (FEM). According to the highest value of photothermal conversion efficiency (PCE) in each bimetallic compound, three Au@Ag, Pt@Ag, and Au@Pd nanorods, with aspect ratios of 4, 4, and 5, respectively; and all with a coating thickness of 1 nm; were chosen as the best ones named “A,” “B,” and “C”. Each nanorod irradiated by continuous wave (CW) laser radiation with 1 mW·μm⁻² intensity at the LSPR wavelength for 200 ns, the temperature of the nanorods increased from 37 to 82.6, 46.34, and 44.33 °C, respectively. To robustly control the temperature in time and locally, the irradiation intensity of the “A” was decreased to 0.5 mW·μm⁻², that its ambient temperature increased by 45 °C at a distance of 20 nm, which can selectively cause irreparable damage to the cancer cells. In addition, the nanorods were irradiated by pulsed laser for 200 ns periods. The results show that the bimetallic nanoparticles can convert light into heat locally.
Graphical Abstract
Biomedical applications relying on optical radiation, particularly with the advent of lasers, have experienced exponential growth in the last 20 years. Powerful optical sources are now found not only in universities, hospitals, and industries but also in beauty centers, used for tasks such as tattoo removal, and even in our homes. Despite their widespread use, managing the risks associated with lasers, particularly in non-research contexts, has not kept pace with their proliferation. While the risks associated with direct exposure to radiation to the eye and skin are relatively well understood, the hazards posed by reflected and diffuse radiation remain less characterized and monitored. Therefore, there is a critical need to assess potential eye and skin hazards in spaces where lasers and non-coherent light sources are used. This necessitates a detailed analysis of reflective surfaces, with particular emphasis on evaluating their reflectance characteristics at relevant wavelength ranges. This study investigates the reflectance and transmittance (where relevant) properties of commonly used materials in biomedical settings, including fabrics, plastics, and metals, across a broad spectrum from 250 nm (UVA) to visible light and into the infrared (IR) region up to 25 μm. Both specular (at 45° incidence) and diffuse reflectance spectra were measured using spectrophotometric techniques and used to provide a straightforward parameter to classify the specular/diffusive behavior of the different surfaces. Besides, small-angle reflectance measurements in the IR range were performed by Fourier transform infrared spectrometry. The knowledge of the material optical properties used in environments where optical radiation is employed allows for accurate assessment of associated risks. This facilitates the determination of appropriate preventive measures and the establishment of safer protocols, for both operators and, where applicable, patients and the general public. For this scope, the creation of a database of material reflective properties has been initiated.
Three methods are used for a numerical solution, the Monte Carlo method, diffusion approximation equation model, and beam broaden model based on Beer–Lambert’s law equation. The comparison between the first two methods is reported theoretically, and the latter is a better choice in the high-density tissue. However, the comparison between the third method and the first or the second method is rarely reported. Two classical theoretical models describing the interaction between the laser and the bio-tissue are analyzed and compared to determine which is more suitable for analyzing the interaction, the beam broaden model or diffusion approximation equation model. Intensity distribution is simulated and compared for the two models. Temperature distribution and thermal damage are investigated theoretically and experimentally for both models. The differences and the reasons are analyzed. The diffusion approximation equation model is more suitable for analyzing the mechanism between the laser and the bio-tissue based on the degree of fitting between the simulated and experimental data. Theoretical analyses for the two models are carried out in detail. The comparison between the two models is rarely reported, and it is reported in this article for the first time, theoretically and experimentally. This report provides a better choice for quickly analyzing the interaction mechanism between the laser and the bio-tissue.
Using a minipig model, we evaluated the efficacy of the 100 ps Nd:YAG laser in the removal of tattoo pigments, specifically blue, green, red, and yellow. We observed distinct pigment responses to 532/1064 nm wavelengths at various energy settings. Through a combination of clinical, spectroscopic, and histological methods, we found the 532 nm wavelength to be most effective in disrupting all colors, with notable results for green and yellow at 0.4 J/cm ² and red at 0.72 J/cm ² . The 1064 nm wavelength reduced pigment in yellow (1.51 J/cm ² ), green (1.35 J/cm ² ), and blue (1.11 J/cm ² ) tattoos, but was surpassed by the 532 nm in efficiency. Our data underscores the crucial interplay between pigment traits and laser settings in tattoo removal. We advocate for tailored treatment strategies, integrating pigment hue and laser wavelength, to enhance removal outcomes.
As the demand for CO laser surgeries continues to grow, the quality of their main instrument, the laser micromanipulator, becomes increasingly important. However, in many surgery systems, a large ratio of the laser power is wasted due to the reflection from the mirror of a telescopic system, like a Cassegrain telescope, back to the laser side, which not only decreases the system’s efficiency but can also damage the system itself. In this article, we introduce a new design of the micromanipulator telescope for CO laser surgery, which employs a Bessel beam to improve the system efficiency. As in the propagation of a Bessel beam, the power of the light beam can be transferred from the center to a ring shape, the whole power reflected from the first mirror can reach the second mirror and no power goes back to the second mirror hole. The micromanipulator telescope design and optimization are carried out using Zemax Optics Studio, and the integration of the Bessel beam into the system is implemented using MATLAB. Our simulation results show that by applying the appropriate Bessel beam, the system efficiency can reach more than 96%, and the normalized peak irradiance can increase by 40 to 73% for various working distances. In addition to increasing the system efficiency and normalized peak irradiance, resulting in a sharper surgical blade, the use of the Bessel beam enhances the depth of focus, making the system less sensitive to depth misalignment.
The rapid advancement of diagnostic and therapeutic optical techniques for oncology demands a good understanding of the optical properties of biological tissues. This study explores the capabilities of hyperspectral (HS) cameras as a non-invasive and non-contact optical imaging system to distinguish and highlight spectral differences in biological soft tissues of three structures (kidney, heart, and liver) for use in endoscopic intervention or open surgery. The study presents an optical system consisting of two individual setups, the transmission setup, and the reflection setup, both incorporating an HS camera with a polychromatic light source within the range of 380 to 1050 nm to measure tissue's light transmission (Tr) and diffuse light reflectance (Rd), respectively. The optical system was calibrated with a customized liquid optical phantom, then 30 samples from various organs were investigated for tissue characterization by measuring both Tr and Rd at the visible and near infrared (VIS-NIR) band. We exploited the ANOVA test, subsequently by a Tukey's test on the created three independent clusters (kidney vs. heart: group I / kidney vs. liver: group II / heart vs. liver: group III) to identify the optimum wavelength for each tissue regarding their spectroscopic optical properties in the VIS-NIR spectrum. The optimum spectral span for the determined light Tr of the three groups was 640~680 nm, and the ideal range was 720~760 nm for the measured light Rd for mutual group I and group II. However, the group III range was different at a range of 520~560 nm. Therefore, the investigation provides vital information concerning the optimum spectral scale for the computed light Tr and Rd of the investigated biological tissues (kidney, liver, and heart) to be employed in diagnostic and therapeutic medical applications.
This study aimed to investigate the efficacy of a Nd:YAG laser with a pulse duration of 150 ps at different laser parameters. The effects on multiple-colored tattoos with such ultrashort pulses has not been previously described in the literature. In vivo experiments were conducted on porcine skin to analyze the fragmentation efficiency of five different tattoo colors using different wavelengths, pulse energies, and spot sizes. The results showed that the optimal tattoo clearance to safety ratio for blue, green, red, and yellow tattoos with a 532 nm wavelength was 0.96–2.39 J/cm². The laser with a wavelength of 1064 nm demonstrated the highest efficacy in eliminating black tattoos, with positive results observed for green and blue pigments at a fluence of 3.02 J/cm². The study provides valuable insights into the efficacy of laser treatment with 150 ps for removing tattoos of different colors using different laser parameters. This information can help dermatologists and practitioners perform more efficient and effective tattoo removal with fewer side effects.
Background: Despite intensive research, the ideal protocol applied to maximize the overall benefits of antimicrobial photodynamic therapy (aPDT) remains unexplored. Evidence exists that following aPDT, the diffused light beyond the photosensitizer can exert a secondary therapeutic effect known as photobiomodulation (PBM), which stimulates the healing of the surrounding tissues. Therefore, the aim of this study was to examine the attenuation properties of five different photosensitizers activated by their corresponding laser wavelengths. Methods: The illumination of various concentrations of chosen photosensitizers, curcumin, methylene blue, toluidine blue, indocyanine green and a methylene blue derivative, irradiated by their respective laser wavelengths (445 nm, 635 nm, 660 nm and 808 nm) was explored via a spectrophotometric analysis. The onward transmitted light intensities for each combination of a photosensitizer and laser wavelength were assessed. The attenuation percentages observed were statistically evaluated using an analysis-of-variance (ANOVA) model. A Tukey’s post hoc test was performed to determine the significance of differences between individual group mean values. Results: With the exception of toluidine blue illuminated by an 808 nm laser, which showed the lowest intensity loss, all the other photosensitizers presented an attenuation range of 63% to 99%. Conclusions: At appropriate concentrations, all the examined photosensitizers may allow the passage of sufficient wavelength-dependent light transmission. Calculated fluences are proposed to achieve secondary, beneficial PBM effects.
The aim of the study was to determine the temperature parameters when exposed to the area of the attached keratinized gum by laser irradiation and to compile clinical recommendations based on the data obtained. The study was conducted on laboratory animals (mature male rats of the Wistar breed) in accordance with Russian and international rules for conducting preclinical studies. The temperature of the keratinized gum was determined by contact method using low level laser therapy (LLLT) at a laser irradiation wavelength of 445±40 nm, a power of 0.5 W with a distance from the tip of the light guide to the gum surface of 2.5—3 mm (group I) and 4.5—5 mm (group II). As a result of the study, it was found that when exposed to low level laser irradiation (LLLI) with a wavelength of 445±40 nm and a distance of 4.5—5 mm from the tip of the light guide to the gum surface, the temperature increase of the gum tissues on average is 8.37±0.296°C, which does not exceed the threshold temperature index. Low level laser therapy with these parameters can be recommended for use in dental practice after conducting appropriate clinical studies.
Background: Wrist pain is common and debilitating among gymnasts, presenting a tricky diagnostic and therapeutic challenge resulting in falling down in training sessions and during performance. Objective: To find out the effect of high-power laser treatment, either alone or in combination with exercise, on wrist pain, function and joint position sense in female gymnasts with non-specific chronic wrist pain. Methods: Thirty-six female gymnasts (aged 10 to 16 years) who were diagnosed with non-specific wrist pain were recruited as the participants for the study, and were randomly allocated into three groups. The participants of the laser therapy group received only high power laser therapy, the exercise program group participants received exercises only, and the participants of the combined therapy group received both laser and exercises. Pain, function, and joint position sense were the outcomes measures in the study. Results: In all treatment groups, all measured results improved after therapy. The laser therapy group had the least significant impact, whereas the combined therapy group had the most significant impact. Conclusion: It might be early to say whether solely high-power laser therapy is an effective non-invasive modality for treating female gymnasts with non-specific chronic wrist pain. The addition of associated co-interventions to high power laser treatment can improve the beneficial effects of laser therapy.
Purpose
Laser corneal reshaping is a common eye surgery utilized to overcome many vision disorders. Different UV laser wavelengths can be effective in the treatment. However, the ArF excimer laser (193 nm) is the most commonly used due to its high absorption in the cornea. In the current study, we investigate the efficacy of applying a solid-state laser (Nd:YAG fourth harmonic at 266 nm) for the corneal reshaping procedure.
Methods
The utilized laser is generated using an optical setup based on a BBO nonlinear crystal which converts the Q-switched laser (532 nm) to its fourth harmonic (266 nm). Different pulse energies were applied with the same number of the shoots on ex vivo rabbit corneas, and the histological effect is studied. Moreover, the possible thermal damage on the treated corneal tissues was inspected via electron microscope. Additionally, the DNA damage on the corneal cells due to the application of the proposed laser was examined and compared with the existing technology (ArF Excimer laser at 193 nm) using the comet assay.
Results
The histological examination revealed an appropriate ablation result with the minimum thermal effect at 1.5 mJ and 2.0 mJ. The overall results show that applying 50-shoots of the 1.5-mJ pulse energy using the proposed 266-nm solid-state laser produces the optimum ablation effect with the minimum thermal damage, and almost the same DNA damage occurred using the commercial 193-nm ArF excimer laser.
Conclusion
Solid-state laser at 266 nm could be a good alternative to the common 193-nm excimer laser for corneal reshaping procedures.
Lasers emit highly directional light with consistent wavelengths, and recent studies have demonstrated their successful applications in gastrointestinal endoscopic therapy. Although argon plasma coagulators (APC) became the preferred treatment option due to improved safety profile and lower costs, advancements in laser and optic fiber manufacturing have reignited interest in laser treatment. Different laser wavelengths have distinct features and applications based on their tissue absorption coefficient. Lasers with shorter wavelengths are effectively absorbed by hemoglobin, resulting in a good coagulation effect. Near-infrared lasers have ability to ablate solid tumors, while far-infrared lasers can make precise mucosal incisions without causing peripheral thermal damage. Lasers have proven to be highly applicable to endoscopy devices such as endoscopes, endoscopic ultrasound (EUS), double-balloon enteroscopes (DBE), and endoscopic retrograde cholangiopancreatography (ERCP), making them a potent tool to enhance the effectiveness of endoscopic treatments with minimal adverse events. This review aims to help readers understand the applications and effectiveness of lasers in gastrointestinal endoscopy, with the potential to promote the development and application of laser technology in the medical field.
Objectives:
During holmium:yttrium-aluminum-garnet (holmium:YAG) laser lithotripsy to break urinary stones, urologists frequently see flashes of light. As infrared laser pulses are invisible, what is the source of light? Here we studied the origin, characteristics, and some effects of flashes of light in laser lithotripsy.
Methods:
Ultrahigh-speed video-microscopy was used to record single laser pulses at 0.2-1.0 J energy lasered with 242 µm glass-core-diameter fibers in contact with whole surgically retrieved urinary stones and hydroxyapatite (HA)-coated glass slides in air and water. Acoustic transients were measured with a hydrophone. Visible-light and infrared photodetectors resolved temporal profiles of visible-light emission and infrared-laser pulses.
Results:
Temporal profiles of laser pulses showed intensity spikes of various duration and amplitude. The pulses were seen to produce dim light and bright sparks with submicrosecond risetime. The spark produced by the intensity spike at the beginning of laser pulse generated a shock wave in the surrounding liquid. The subsequent sparks were in a vapor bubble and generated no shock waves. Sparks enhanced absorption of laser radiation, indicative of plasma formation and optical breakdown. The occurrence and number of sparks varied even with the same urinary stone. Sparks were consistently observed at laser energy >0.5 J with HA-coated glass slides. The slides broke or cracked by cavitation with sparks in 63 ± 15% of pulses (1.0 J, N = 60). No glass-slide breakage occurred without sparks (1.0 J, N = 500).
Conclusion:
Unappreciated in previous studies, plasma formation with free-running long-pulse holmium:YAG lasers can be an additional physical mechanism of action in laser procedures.
The liver is an essential source of various vital proteins that specify the normal function of the blood coagulation cascade. Coagulation and abnormality in blood clotting levels are considered crucial indicators for many liver diseases such as cirrhosis and assess the liver injury and toxicity. However, detecting the coagulation degree of liver tissue at its initial state is still not completely investigated due to its low-level tissue factor (TF). Recently, optical spectroscopic methods have gained significant interest in different biological investigations. These methods are safe, sensitive, functional, and highly related to critical physiological changes in biological tissue. Spatially resolved steady-state diffuse reflectance and laser-induced fluorescence (LIF) are employed in the present study to monitor laser-induced coagulation in chicken liver samples. Results show that the diffuse reflectance is noticeably increased with the coagulation degree in addition to a decrease in the overall LIF intensity during the coagulation process.
Ultrafast lasers concentrate the energy in a short pulse with a duration of several tens to hundreds of femtoseconds. The resulting high peak power induces various nonlinear optical phenomena that find use in many different fields. However, in practical applications, the optical dispersion broadens the laser pulse width and spreads the energy in time, thereby reducing the peak power. Accordingly, the present study develops a piezo bender-based pulse compressor to compensate for this dispersion effect and restore the laser pulse width. The piezo bender has a rapid response time and a large deformation capacity and thus provides a highly effective means of performing dispersion compensation. However, due to hysteresis and creep effects, the piezo bender is unable to maintain a stable shape over time and hence the compensation effect is gradually degraded. To address this problem, this study further proposes a single-shot modified laterally sampled laser interferometer to estimate the parabolic shape of the piezo bender. The curvature variation of the bender is then sent as a feedback signal to a closed-loop controller to restore the bender to the desired shape. It is shown that the steady-state error of the converged group delay dispersion is around 530 fs ² . Moreover, the ultrashort laser pulse is compressed from 1620 fs in the original condition to 140 fs in the compressed condition, corresponding to a 12-fold improvement.
Background
Laser technology has been widely used in the treatment of hypertrophic scar (HPS). Due to the lack of effective quantitative relationship between laser doses and thermal effect of lesion tissue, the selection of laser doses in clinical laser treatment of HPS is blind, which cannot guarantee the best treatment effect.
Materials and methods
The photothermal model of HPS was established by using finite element method. The effects of laser dose parameters such as laser energy density, pulse width, and spot diameter on the thermal effects of laser treatment were analyzed. According to tissue temperature threshold and thermal damage degree of the simulation results, the optimal laser doses of HPS were selected for the laser treatment experiments of rabbit ear HPSs to verify the rationality of the quantitative photothermal model.
Results
The temperature rise and thermal damage degree of HPS following laser treatment were directly correlated to the laser doses, which grew with the increase of energy density and laser pulse width. For the different spot diameters, the temperature rise decreased with the increase of spot diameter, whereas the thermal damage degree worsened with the increase of spot diameter. Both simulation and experimental results show that the optimal treatment parameters of HPS were as follows: The laser energy density was 7.5 J/cm³, the pulse width was 4 ms, and the spot diameter was 7 mm.
Conclusion
The laser dose parameters optimized by the photothermal model have achieved good therapeutic effects in the rabbit ear HPS, indicating that the model can be used for quantitative evaluation of laser doses before clinical treatment.
Photodynamic therapy (PDT) is a promising treatment method that generates reactive oxygen species by exciting a photosensitizer in the presence of light. The positive treatment outcome of PDT is enhanced by the photosensitizer's ability to get out quickly from normal tissue. This study non-destructively evaluated the biocompatibility of novel synthesized phthalocyanine-gold nanoconjugates (Pc-Au NCs) as a drug delivery mediator for in vivo PDT. We first proposed a novel noncontact and safe biospeckle optical imaging technique to visualize the quantitative changes in the internal dynamics of biological tissue in response to PDT treatment. Second, laser-induced breakdown spectroscopy (LIBS) was utilized to emphasize the accumulation of gold nanoparticles (Au NPs) within the normal and cancerous tissue, which in turn verifies the cytotoxic and treatment effects of the Pc-Au NCs. The biospeckle images and LIBS spectra were obtained from tumor and normal tissues of male BALB/c malignancy-bearing mice before and after exposure to PDT. Then, they were statistically treated via different artificial intelligence techniques. For biospeckle analysis, the proposed method was established from the combination of second and higher-order statistical features extracted from the gray-level co-occurrence matrix (GLCM) and local contrast analysis (LCA), respectively, through principal component analysis (PCA). Regarding LIBS analysis, the powerful, most popular ensemble sequential learning algorithm Adaptive Boost was implemented on highly uncorrelated variables extracted from the raw spectra. The results, confirmed by the histological investigation, indicated the potential of the biospeckle and LIBS statistical properties in demonstrating the efficiency of the Pc-Au NCs as a drug delivery mediator for in vivo PDT.
Precise control of tissue temperature during Laser-Induced Thermotherapy (LITT) procedures has the potential to improve the clinical efficiency and safety of such minimally invasive therapies. We present a method to automatically regulate in vivo the temperature increase during LITT using real-time rapid volumetric Magnetic Resonance thermometry (8 slices acquired every second, with an in-plane resolution of 1.4 mmx1.4 mm and a slice thickness of 3 mm) using the proton-resonance frequency (PRF) shift technique. The laser output power is adjusted every second using a feedback control algorithm (proportional-integral-derivative controller) to force maximal tissue temperature in the targeted region to follow a predefined temperature–time profile. The root-mean-square of the difference between the target temperature and the measured temperature ranged between 0.5 °C and 1.4 °C, for temperature increases between + 5 °C to + 30 °C above body temperature and a long heating duration (up to 15 min), showing excellent accuracy and stability of the method. These results were obtained on a 1.5 T clinical MRI scanner, showing a potential immediate clinical application of such a temperature controller during MR-guided LITT.
Objectives:
To investigate quantitatively the cutting efficiency and the thermal effects in the surrounding soft tissues of incisions that are induced by a 940 nm-diode laser with different power settings.
Materials and methods:
Fifty-four gingival samples were prepared from the lower jaws of freshly slaughtered German-land race pigs and were randomly divided into 9 groups (n = 6) according to the adjusted output power (1, 1.5, 2, 2.5, 3, 3.5, 4, 5 and 6 W). Five incisions were implemented for each sample using a diode laser (940 nm) in continuous wave with an initiated tip resulting in 30 incisions for each experimental group utilizing a three-dimensional computer-controlled micropositioner. The samples were prepared for histometric evaluation using a transmitted light microscope. The cutting depth and width and the thermal damage were recorded for each sample and the efficiency factor γ was calculated.
Results:
The highest cutting efficiency (γz = 0.81 ± 0.03) exhibited the group with 5 W output power (p < 0.05), while the lowest (γz = 0.45 ± 0.11) showed the 1-W group (p < 0.05). Over 3.5 W there was a rapid increase in the size of thermal damage of the incisions, especially for 6 W, which presented the largest.
Conclusions:
The most effective power parameters of diode laser (940 nm) for soft tissue surgery were from 3 to 5 W. The outcomes of the current study may help to establish clinical protocols for the use of diode lasers (940 nm) in soft tissue surgery in contact mode assisting dental professionals to achieve optimal clinical results and avoid complications.
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