Minimally-invasive laser surgeries could benefit from a fiber-optic laser-induced breakdown spectroscopy (FO-LIBS) setup for real-time tissue characterization. In FO-LIBS, the sample receives limited light irradiance due to the fiber's low damage threshold and diminished laser beam quality. Therefore, the plasma created with FO-LIBS is less luminant than that of free-space LIBS. Furthermore, only a small portion of plasma emission can be collected, as the lens's size at the fiber tip is restricted to fit inside the narrow channel of an endoscope. A high optical throughput Echelle spectrometer was developed to compensate for low-intensity light collection with FO-LIBS. The Echelle spectrometer was tested for tissue differentiation when combined with a flexible fiber bundle delivery setup and a small lens at the bundle's tip. The customized FO-LIBS setup, coupled with multivariate data analysis, successfully differentiated bone from surrounding soft tissue (muscle, fat, and bone marrow) with 100% cross-validated (CV) sensitivity and specificity. The CV sensitivity and specificity for differentiation between all tissues were 90.2% and 96.7%, respectively. The results demonstrate, to the best of our knowledge, the first flexible FO-LIBS system, which may provide a further step towards the development of a smart endoscopic laser scalpel.

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To obtain efficient laser ablation in bone, dehydration, early carbonization and carbonization need to be avoided. Achieving this can only be provided by using an automated control of the ablation laser and irrigation system. As a preliminary study, we demonstrated a laser-induced breakdown spectroscopy based early carbonization detection system by analyzing carbonized bone tissues. Carbonization of bone samples was generated in a controlled way, by applying different number of Er:YAG pulses (0–25) at different locations on bone sample. To detect number of applied pulses, leading to the detection of carbonization level, we used a feed-forward Artificial Neural Network (ANN) with multi-layer perceptron structure. The results of the ANN were compared with the actual label, and R-squared of 0.85, 0.88, 0.86, 0.83, and 0.84 (0.85 on average) were achieved.

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Minimally invasive laser surgeries that require the use of a flexible endoscope (flexiscope) could benefit from high-energy nanosecond laser pulses delivered through fibers for real-time tissue characterization and phenotyping. The damage threshold of the fiber's glass material limits the maximum amount of deliverable peak power. To transmit high-energy pulses without damaging the fiber material, large-diameter fibers are typically used, leading to a limited bending radius. Moreover, in a large-core fiber, self-focusing can damage the fiber even if the tip remains intact. In this work, we tested a fused-end fiber bundle combined with a beam shaper capable of delivering more than 20 MW (>100 mJ/5 ns). The fiber bundle was tested over more than eight hours of operation, with different bending radiuses down to 15 mm. The results demonstrate, to the best of our knowledge, the highest peak power delivered through a flexible fiber, for a frequency-doubled Q-switched Nd:YAG laser.

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The preparation of small-sized biological samples is traditionally performed manually utilizing mechanical tools such as scalpels. The main drawbacks of such methods are a lack of accuracy and repeatability of the resulting cuts and damage to the surrounding tissue due to the high interaction forces and the accompanying mechanical stresses. One way to circumvent these issues is to substitute the mechanical tools for laser light. When used in conjunction with a high-accuracy positioning system, such a preparation procedure enables repeatable cutting of arbitrary geometries while largely preserving the integrity of the surrounding tissue. In this paper, a system leveraging the potential of laser-based ablation for bio-sample preparation is proposed. It integrates and synchronizes all key components with extensive safety features and an intuitive user interface, allowing novice operators to perform sample preparations easily. As a first application, the proposed system has been utilized to create microdamages in mouse tail tendon fascicles. Promising results could be obtained, but careful tuning of the laser parameters and further optimization of the mechanical setup is still required to attain the high repeatability striven for.

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Echelle spectrometers offer high-resolution (ca. one Angstrom or higher) and wide range (ca. half a micron or wider), simultaneously, without having a mechanical moving part. However, they require a complicated optical set-up as compared to conventional one-dimensional-dispersion/diffraction spectrometers, e.g., Czerny-Turner. Therefore, the simulation of the Echellogram is required before building the spectrometer. This paper aims to develop an application for visualizing the Echellogram using MATLAB App Designer followed by simulation of the optical aberrations by Zemax OpticStudio to optimize the spectrometer parameters. The developed application provides an interactive graphical interface with a user-friendly dashboard to control and monitor the required parameters. This spectrometer is being used in laser-induced breakdown spectroscopy (LIBS) system application lied of robot-guided laser ablation of biological tissues.

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Preparation of biological samples for further processing or analysis is generally performed manually by means of standard mechanical tools such as scalpels or biopsy punches. While this approach is uncomplicated and swift, it entails constraints such as low, operator-dependent cutting accuracy and reproducibility. Tissue segments surrounding the cut may further suffer mechanical and thermal damage due to shear forces and friction between tool and sample. These hindrances affect procedures both in the laboratory environment as well as within clinical settings. A system has been developed leveraging robotic positioning and laser light for precise, controlled, and contactless tissue ablation, and providing a concise and intuitive graphical user interface. Additionally, sterility of the process is demonstrated, a paramount element for clinical application. The proposed process does not require sterilization of the robotic components or the lasers, easing a prospective integration into existing workflows. In the context of this work, mainly cartilage repair surgery is targeted. The proposed system allows for highly accurate and reproducible shaping of the cartilage lesion area as well as its corresponding engineered cartilage graft, possibly leading to better and faster integration at the defect site. Promising results could be obtained in a first test series with human cartilage samples, validating the functionality of the preparation system and the feasibility of the sterility concept.

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A novel real-time and non-destructive method for differentiating soft from hard tissue in laser osteotomy has been introduced and tested in a closed-loop fashion. Two laser beams were combined: a low energy frequency-doubled nanosecond Nd:YAG for detecting the type of tissue, and a high energy microsecond Er:YAG for ablating bone. The working principle is based on adjusting the energy of the Nd:YAG laser until it is low enough to create a microplasma in the hard tissue only (different energies are required to create plasma in different tissue types). Analyzing the light emitted from the generated microplasma enables real-time feedback to a shutter that prevents the Er:YAG laser from ablating the soft tissue.

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During the past half-century, laser osteotomy has been studied for a broad range of lasers, which almost covers the entire range of available laser systems in the market, from early unsuccessful experiments with CW lasers to newly developed ultrashort pulse lasers. Although a large variety of laser parameters including wavelength, pulse energy, pulse duration, and repetition rate have been investigated to find an optimum laser system as an alternative osteotomy tool, there is not a universal agreement on a specific type of laser to replace conventional mechanical saws. The only universal agreement is on the speed of cutting (ablation rate) which went to longpulse Er:YAG and CO2 lasers. Microsecond pulse Er:YAG and CO2 lasers perform osteotomy by inducing efficient photothermal effect to the bone with the help of high absorption peak of water in the bone. However, having a speedy cut is not the only effective parameter to pave the way for transferring lasers to the operating room. Other parameters including cutting with the lowest thermal damage, ability for deep cutting, and compatibility with integrating sensors are among the other determinant parameters. Moreover, being able to be delivered through the fiber optic and as a consequence fit inside the endoscope channel could extend their application from the open surgery to minimally invasive ones. This chapter besides proving the necessary information on the physics behind the laser-bone interaction provides a short review on the history of bone surgery with laser and state-of-the-art studies in this field.

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A cost-effective method employing a smartphone sensor to measure the laser-induced sound pressure level (SPL) has been introduced for lens-to-sample distance (LTSD) adjustment in micro laser-induced breakdown spectroscopy (µLIBS).

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In laserosteotomy, it is vital to avoid thermal damage of the surrounding tissue, such as carbonization, since carbonization does not only deteriorate the ablation efficiency but also prolongs the healing process. The state-of-the-art method to avoid carbonization is irrigation systems; however, it is difficult to determine the desired flow rate of the air and cooling water based on previous experiments without online monitoring of the bone surface. Lack of such feedback during the ablation process can cause carbonization in case of a possible error in the irrigation system or slow down the cutting process when irrigating with too much cooling water. The aim of this paper is to examine laser-induced breakdown spectroscopy as a potential tool for autocarbonization detection in laserosteotomy. By monitoring the laser-driven plasma generated during nanosecond pulse ablation of porcine bone samples, carbonization is hypothesized to be detectable. For this, the collected spectra were analyzed based on variation of a specific pair of emission line ratios in both groups of samples: normal and carbonized bone. The results confirmed a high accuracy of over 95% in classifying normal and carbonized bone.@en

In minimal invasive laser osteotomy precise information about the ablation process can be obtained with LIBS in order to avoid carbonization, or cutting of wrong types of tissue. Therefore, the collecting fiber for LIBS needs to be optimally placed in narrow cavities in the endoscope. To determine this optimal placement, the plasma plume expansion dynamics in ablation of bone tissue by the second harmonic of a nanosecond Nd:YAG laser at 532 nm has been studied. The laserinduced plasma plume was monitored in different time delays, from one nanosecond up to one hundred microseconds. Measurements were performed using high-speed gated illumination imaging. The expansion features were studied using illumination of the overall visible emission by using a gated intensified charged coupled device (ICCD). The camera was capable of having a minimum gate width (Optical FWHM) of 3 ns and the timing resolution (minimum temporal shift of the gate) of 10 ps. The imaging data were used to generate position-time data of the luminous plasma-front. Moreover, the velocity of the plasma plume expansion was studied based on the time-resolved intensity data. By knowing the plasma plume profile over time, the optimum position (axial distance from the laser spot) of the collecting fiber and optimal time delay (to have the best signal to noise ratio) in spatial-resolved and time-resolved laser-induced breakdown spectroscopy (LIBS) can be determined. Additionally, the function of plasma plume expansion could be used to study the shock wave of the plasma plume.

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Although laserosteotomes have become generally accepted devices in surgical applications, they still suffer from a lack of information about the type of tissue currently being ablated; as a result, critical structures of the body under or near the focal spot of the laser beam are prone to inadvertent ablation. The lack of information about the properties of the ablated tissue can be solved by connecting the laserosteotome to an optical detection setup which can differentiate various types of tissues, especially bone from connective soft tissues. This study examines the applicability of laser-induced breakdown spectroscopy (LIBS) as a potential technique to differentiate bone from surrounding soft tissue (fat and muscle). In this experiment, fresh porcine femur bone, muscle, and fat were used as hard and soft tissue samples. The beam of a nanosecond frequency-doubled Nd:YAG laser was used to ablate the tissue samples and generate the plasma. The plasma light emitted from the ablated spot, which corresponds to the recombination spectra of ionized atoms and molecules, was gathered with a collection optic (including a reflective light collector and a fiber optic) and sent to an Echelle spectrometer for resolving the atomic composition of the ablated sample. Afterwards, Discriminant Function Analysis (DFA) based on the ratio of the intensity of selected peak pairs was performed to classify three sample groups (bone, muscle, and fat). Lastly, the sensitivity, specificity, and accuracy of the proposed method were calculated. Sensitivity and specificity of 100 % and 99 % were achieved, respectively, to differentiate bone from surrounding soft tissue.

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The aim of this paper is to examine the effect of pig bone immersion in different levels of cooling water during laser ablation with a Er:YAG laser. The laser worked at 2940 nm wavelength and 10 Hz repetition rate in microseconds pulse duration regime. The bone was immersed in different levels of cooling water in a sample container for preventing carbonization. The bone samples were ablated with fixed deposited energy to investigate at which water level Er:YAG lasers start ablating bone through a layer of water. Results showed that the maximum level of water that laser can pass through to start the ablation nonlinearly depends on pulse energy.

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The aim of the present study is to investigate the effect of laser pulse duration on ablation efficiency of hard bones. The bones were ablated using a microsecond pulsed Er-YAG laser. The laser wavelength was 2.94 μm and the repetition rate was 10Hz. Three samples of porcine femur were used and several areas were ablated with a fixed pulse energy of 280mJ and different pulse durations. The ablation procedure was applied during five seconds for all the experiments, therefore, the same amount of energy (14 J) was deposited in each trial. The ablation efficiency was determined by measuring the ablated volume per second for each experiment.@en