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Laser-Induced Breakdown Spectroscopy As a Potential Tool for Autocarbonization Detection in Laserosteotomy

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Laser-Induced Breakdown Spectroscopy As a Potential Tool for Autocarbonization Detection in Laserosteotomy Laser-induced breakdown spectroscopy as a potential tool for autocarbonization detection in laserosteotomy Hamed Abbasi Georg Rauter Raphael Guzman Philippe C. Cattin Azhar Zam Hamed Abbasi, Georg Rauter, Raphael Guzman, Philippe C. Cattin, Azhar Zam, “Laser-induced breakdown spectroscopy as a potential tool for autocarbonization detection in laserosteotomy,” J. Biomed. Opt. 23(7), 071206 (2018), doi: 10.1117/1.JBO.23.7.071206. Journal of Biomedical Optics 23(7), 071206 (July 2018) Laser-induced breakdown spectroscopy as a potential tool for autocarbonization detection in laserosteotomy Hamed Abbasi,a,* Georg Rauter,b Raphael Guzman,c Philippe C. Cattin,d and Azhar Zama,* aBiomedical Laser and Optics Group, Department of Biomedical Engineering, University of Basel, Allschwil, Switzerland bBio-Inspired Robots for Medicine-Laboratory, Department of Biomedical Engineering, University of Basel, Allschwil, Switzerland cDepartment of Neurosurgery, University Hospital Basel, Basel, Switzerland dCenter for Medical Image Analysis and Navigation, Department of Biomedical Engineering, University of Basel, Allschwil, Switzerland Abstract. 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 pos- sible 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 autocarbo- nization 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. © 2018 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.JBO.23.7.071206] Keywords: laser-induced breakdown spectroscopy; laserosteotome; carbonized bone; smart surgery; feedback; differentiation. Paper 170634SSR received Sep. 29, 2017; accepted for publication Feb. 12, 2018; published online Mar. 2, 2018. 1 Introduction Lack of real-time information about depth of the cut can be Over the past several years, there has been a particular interest in solved by combining the laser surgery system with a coaxial real-time optical coherence tomography setup,16,17 and lack of the development of laser surgery systems due to the advantages information about the properties of the ablated tissue can be offered by laser-based cutting, including minimal invasiveness, improved by connecting the system to an optical detection noncontact interaction, precise and small cuts, functional cut 18 – setup. Therefore, having a real-time feedback method to detect geometry as well as less trauma.1 6 Moreover, in comparison to the possible carbonization in case of any possible error in the other mechanical procedures, such as conventional surgery, bone irrigation system is needed. showed faster healing after interventions with laserosteotomes.7 The potential optical detection methods to investigate Studying the effect of different laser parameters on quality the properties of the tissues include optoacoustic-based and efficiency of laser cutting in both soft and hard tissues is 19,20 8–13 measurements and also spectroscopy-based measurements, a topic of present interest. Although laserosteotomy has – including diffuse reflectance,21,22 laser-induced breakdown,23 25 become a generally accepted technique in various surgical appli- Raman,26,27 and fluorescence spectroscopy.28,29 Among the cations, this technique has two main drawbacks: lack of real- above-mentioned optical methods, laser-induced breakdown time information about depth of the cut and lack of information spectroscopy (LIBS) showed its potential to detect the type about the properties of the ablated tissue; as a result, critical of tissue with high accuracy. In LIBS, the light emitted from structures of the body under or near the focal spot of the the ablation spot, which corresponds to the recombination spec- laser beam are prone to iatrogenic damage. In addition, to be tra of ionized atoms and molecules, is collected with a spectrom- a practical tool, clinical lasers have to be safe and effective eter to resolve the atomic composition of the ablated sample. in removing tissue with limited collateral damage. To reduce LIBS has been applied to differentiate between different tissue the thermal damage to the surrounding tissue, it is vital to pairs with a high sensitivity and specificity (normally ranging use a cooling system to avoid carbonization. Carbonization hap- from 70% to 100%), such as cartilage and cortical bone,30 pens when the tissue is heated up and all the water content is nerve and gland,31 nerve and fat32 as well as differentiation evaporated. Carbonization occurs not only in hard tissues but between oral soft and hard tissues.33 Due to the compelling per- also in soft tissues. Carbonization not only reduces the ablation formance of LIBS in tissue characterization, we assume that 14,15 efficiency but also prolongs healing. applying LIBS also for detecting carbonization in laser surgery will be possible while tissue characterization can be performed in parallel. *Address all correspondence to: Hamed Abbasi, E-mail: hamed.abbasi@ unibas.ch; Azhar Zam, E-mail: [email protected] 1083-3668/2018/$25.00 © 2018 SPIE Journal of Biomedical Optics 071206-1 July 2018 • Vol. 23(7) Abbasi et al.: Laser-induced breakdown spectroscopy as a potential tool for autocarbonization detection in laserosteotomy The aim of this study is to differentiate between normal and carbonized hard porcine bone samples by monitoring the laser- driven plasma generated during a nanosecond pulse ablation using a frequency-doubled nanosecond Nd:YAG laser. A high-resolving power echelle spectrometer connected to an intensified CCD (ICCD) was employed to detect carbonization. The ICCD was capable of collecting LIBS signals with high temporal resolution (ps) and also short integration time (ns) to measure spectra for the classification of the samples. The ana- lytical approach of calculating ratios of values of specific pairs of emission lines was taken to perform the differentiation Fig. 1 Schematics of the LIBS setup: A, laser (flash-lamp-pumped between two groups of samples: normal (noncarbonized) and Nd:YAG), B, second-harmonic generator; C, harmonic separator; carbonized porcine bone. Then the sensitivity, specificity, and D, beam blocker; E, laser beam; F, focusing lens; G, bone sample; H, generated plasma; I, light collector; J, fiber optic; K, spectrometer accuracy of the method were calculated afterward. Based on (echelle); and L, computer. the results of the current study, we aim at proceeding LIBS- based carbonization detection also in real time. A successful real-time autodetection of carbonization in laserosteotomy Quantel, France) running in its second harmonics of 532 nm will increase the safety of laserosteotomes. Additionally, this with 5-ns pulse duration was used to ablate both normal and proof of principle study is intended to pave the way for in carbonized bone samples. The 1064-nm mode of the beam vivo experiments with an LIBS-based autocarbonization detec- was separated and blocked using a nonlinear crystal, and a beam tion system in laser surgery. blocker installed right after the harmonic generator, respectively. The laser was operated at 108 mJ per pulse and 1-Hz repetition 2 Materials and Methods rate. The initial output beam of the laser with 6.5-mm diameter was directly focused onto the sample’s surface using an 2.1 Sample Preparation uncoated CaF2 planoconvex lens (LA5458, Thorlabs) with a focal length of 80 mm. Fresh porcine femur bone was used as a sample in this experi- ment. The bone samples were kept in a freezer between the slaughtering of the pig to the starting day of the experiment. 2.4 Spectroscopy Setup The temperature of the freezer was set to −18°C. Four hours An echelle spectrometer with a wavelength range of 200 to before starting the experiment, the bones were moved from 975 nm connected to an ICCD was used to reveal the spectral the freezer to the refrigerator (þ4°C). Soft tissues were removed from the bone’s surface using a surgical scalpel. Five bisected distribution of the laser-generated plasma light. The spectral res- olution (λ∕Δλ) of the spectrometer was more than 4000. The bones with the height of ca. 3 cm were used as samples. One half CCD was cooled down to −30°C to reduce the background of each sample was irradiated by a microsecond Er:YAG laser noise level. A fiber optic with a 50-μm core connected to a (DPM-15, 3mikron, Pantec, Liechtenstein) with a pulse energy – F of 90 mJ and a 10-Hz repetition rate for 30 s without any cooling UV NIR light collector with an -number of 2 was used to guide the plasma light into the spectrometer. A gate delay of water to create a carbonized layer on the bone’s surface; the 1 μs between the laser shot and opening of the intensifier other half of the bone remained untouched as a noncarbonized reference sample. To confirm bone carbonization and assess the was applied to remove the continuum emission of the plasma. The gate width was set to 200 μs. Both gate delay and width carbon bonding, Raman spectroscopy was employed. Er:YAG were applied using the internal delay generator of the ICCD. bone ablation at 3 μm is based on absorption of the laser beam mainly by the water content of the bone.
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