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1.
Lasers Surg Med ; 2021 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-34481417

RESUMO

OBJECTIVES: Laser surgery requires efficient tissue classification to reduce the probability of undesirable or unwanted tissue damage. This study aimed to investigate acoustic shock waves (ASWs) as a means of classifying sciatic nerve tissue. MATERIALS AND METHODS: In this study, we classified sciatic nerve tissue against other tissue types-hard bone, soft bone, fat, muscle, and skin extracted from two proximal and distal fresh porcine femurs-using the ASWs generated by a laser during ablation. A nanosecond frequency-doubled Nd:YAG laser at 532 nm was used to create 10 craters on each tissue type's surface. We used a fiber-coupled Fabry-Pérot sensor to measure the ASWs. The spectrum's amplitude from each ASW frequency band measured was used as input for principal component analysis (PCA). PCA was combined with an artificial neural network to classify the tissue types. A confusion matrix and receiver operating characteristic (ROC) analysis was used to calculate the accuracy of the testing-data-based scores from the sciatic nerve and the area under the ROC curve (AUC) with a 95% confidence-level interval. RESULTS: Based on the confusion matrix and ROC analysis of the model's tissue classification results (leave-one-out cross-validation), nerve tissue could be classified with an average accuracy rate and AUC result of 95.78  ± 1.3% and 99.58  ± 0.6%, respectively. CONCLUSION: This study demonstrates the potential of using ASWs for remote classification of nerve and other tissue types. The technique can serve as the basis of a feedback control system to detect and preserve sciatic nerves in endoscopic laser surgery.

2.
J Biomed Opt ; 26(9)2021 09.
Artigo em Inglês | MEDLINE | ID: mdl-34519191

RESUMO

SIGNIFICANCE: The highest absorption peaks of the main components of bone are in the mid-infrared region, making Er:YAG and CO2 lasers the most efficient lasers for cutting bone. Yet, studies of deep bone ablation in minimally invasive settings are very limited, as finding suitable materials for coupling high-power laser light with low attenuation beyond 2 µm is not trivial. AIM: The first aim of this study was to compare the performance of different optical fibers in terms of transmitting Er:YAG laser light with a 2.94-µm wavelength at high pulse energy close to 1 J. The second aim was to achieve deep bone ablation using the best-performing fiber, as determined by our experiments. APPROACH: In our study, various optical fibers with low attenuation (λ = 2.94 µm) were used to couple the Er:YAG laser. The fibers were made of germanium oxide, sapphire, zirconium fluoride, and hollow-core silica, respectively. We compared the fibers in terms of transmission efficiency, resistance to high Er:YAG laser energy, and bending flexibility. The best-performing fiber was used to achieve deep bone ablation in a minimally invasive setting. To do this, we adapted the optimal settings for free-space deep bone ablation with an Er:YAG laser found in a previous study. RESULTS: Three of the fibers endured energy per pulse as high as 820 mJ at a repetition rate of 10 Hz. The best-performing fiber, made of germanium oxide, provided higher transmission efficiency and greater bending flexibility than the other fibers. With an output energy of 370 mJ per pulse at 10 Hz repetition rate, we reached a cutting depth of 6.82 ± 0.99 mm in sheep bone. Histology image analysis was performed on the bone tissue adjacent to the laser ablation crater; the images did not show any structural damage. CONCLUSIONS: The findings suggest that our prototype could be used in future generations of endoscopic devices for minimally invasive laserosteotomy.


Assuntos
Terapia a Laser , Lasers de Estado Sólido , Óxido de Alumínio , Animais , Endoscópios , Fibras Ópticas , Ovinos
3.
Biomed Opt Express ; 12(4): 2118-2133, 2021 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-33996219

RESUMO

This work presents a long-range and extended depth-of-focus optical coherence tomography (OCT) system using a Bessel-like beam (BLB) as a visual feedback system during laser osteotomy. We used a swept-source OCT system (λ c = 1310 nm) with an imaging range of 26.2 mm in the air, integrated with a high energy microsecond Er:YAG laser operating at 2.94 µm. We demonstrated that the self-healing characteristics of the BLB could reduce the imaging artifacts that may arise during real-time monitoring of laser ablation. Furthermore, the feasibility of using long-range OCT to monitor a deep laser-induced incision is demonstrated.

4.
Biomed Opt Express ; 12(1): 444-461, 2021 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-33659082

RESUMO

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.

5.
Lasers Surg Med ; 53(3): 377-389, 2021 03.
Artigo em Inglês | MEDLINE | ID: mdl-32614077

RESUMO

BACKGROUND AND OBJECTIVES: Using lasers instead of mechanical tools for bone cutting holds many advantages, including functional cuts, contactless interaction, and faster wound healing. To fully exploit the benefits of lasers over conventional mechanical tools, a real-time feedback to classify tissue is proposed. STUDY DESIGN/MATERIALS AND METHODS: In this paper, we simultaneously classified five tissue types-hard and soft bone, muscle, fat, and skin from five proximal and distal fresh porcine femurs-based on the laser-induced acoustic shock waves (ASWs) generated. For laser ablation, a nanosecond frequency-doubled Nd:YAG laser source at 532 nm and a microsecond Er:YAG laser source at 2940 nm were used to create 10 craters on the surface of each proximal and distal femur. Depending on the application, the Nd:YAG or Er:YAG can be used for bone cutting. For ASW recording, an air-coupled transducer was placed 5 cm away from the ablated spot. For tissue classification, we analyzed the measured acoustics by looking at the amplitude-frequency band of 0.11-0.27 and 0.27-0.53 MHz, which provided the least average classification error for Er:YAG and Nd:YAG, respectively. For data reduction, we used the amplitude-frequency band as an input of the principal component analysis (PCA). On the basis of PCA scores, we compared the performance of the artificial neural network (ANN), the quadratic- and Gaussian-support vector machine (SVM) to classify tissue types. A set of 14,400 data points, measured from 10 craters in four proximal and distal femurs, was used as training data, while a set of 3,600 data points from 10 craters in the remaining proximal and distal femur was considered as testing data, for each laser. RESULTS: The ANN performed best for both lasers, with an average classification error for all tissues of 5.01 ± 5.06% and 9.12 ± 3.39%, using the Nd:YAG and Er:YAG lasers, respectively. Then, the Gaussian-SVM performed better than the quadratic SVM during the cutting with both lasers. The Gaussian-SVM yielded average classification errors of 15.17 ± 13.12% and 16.85 ± 7.59%, using the Nd:YAG and Er:YAG lasers, respectively. The worst performance was achieved with the quadratic-SVM with a classification error of 50.34 ± 35.04% and 69.96 ± 25.49%, using the Nd:YAG and Er:YAG lasers. CONCLUSION: We foresee using the ANN to differentiate tissues in real-time during laser osteotomy. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

6.
Biomed Opt Express ; 11(4): 1790-1807, 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-32341848

RESUMO

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.

7.
Opt Lett ; 45(3): 656-659, 2020 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-32004276

RESUMO

We report experimental demonstration of graphene mode-locked operation of ${{\rm Tm}^{3 + }}\!:\!{{\rm YLiF}_4}$Tm3+:YLiF4 (YLF) and ${{\rm Tm}^{3 + }}\!:\!{{\rm KY}_3}{{\rm F}_{10}}$Tm3+:KY3F10 (KYF) lasers near 2.3 µm. To scale up the intracavity pulse energy, the cavity was extended, and double-end pumping was employed with a continuous-wave, tunable ${{\rm Ti}^{3 + }}\!:\!{\rm sapphire}$Ti3+:sapphire laser delivering up to 1 W near 780 nm. The extended ${{\rm Tm}^{3 + }}\!:\!{\rm KYF}$Tm3+:KYF laser cavity was purged with dry nitrogen to eliminate pulsing instabilities due to atmospheric absorption lines, but this was not needed in the case of the ${{\rm Tm}^{3 + }}\!:\!{\rm YLF}$Tm3+:YLF laser. Once initiated by graphene, stable uninterrupted mode-locked operation could be maintained with both lasers. With the extended cavity ${{\rm Tm}^{3 + }}\!:\!{\rm YLF}$Tm3+:YLF laser, 921 fs pulses were generated at a repetition rate of 17.2 MHz at 2304 nm. 739 fs pulses were obtained at the repetition rate of 54 MHz from the ${{\rm Tm}^{3 + }}\!:\!{\rm KYF}$Tm3+:KYF laser at 2340 nm. The corresponding pulse energy and peak power were 2.4 nJ and 2.6 kW for the ${{\rm Tm}^{3 + }}\!:\!{\rm YLF}$Tm3+:YLF laser, and 1.2 nJ and 1.6 kW for the ${{\rm Tm}^{3 + }}\!:\!{\rm KYF}$Tm3+:KYF laser. We foresee that it should be possible to generate shorter pulses at higher pump levels.

8.
Biomed Opt Express ; 11(12): 7253-7272, 2020 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-33408994

RESUMO

The microsecond Er:YAG pulsed laser with a wavelength of λ = 2.94 µm has been widely used in the medical field, particularly for ablating dental tissues. Since bone and dental tissues have similar compositions, consisting of mineralized and rigid structures, the Er:YAG laser represents a promising tool for laserosteotomy applications. In this study, we explored the use of the Er:YAG laser for deep bone ablation, in an attempt to optimize its performance and identify its limitations. Tissue irrigation and the laser settings were optimized independently. We propose an automated irrigation feedback system capable of recognizing the temperature of the tissue and delivering water accordingly. The irrigation system used consists of a thin 50 µm diameter water jet. The water jet was able to penetrate deep into the crater during ablation, with a laminar flow length of 15 cm, ensuring the irrigation of deeper layers unreachable by conventional spray systems. Once the irrigation was optimized, ablation was considered independently of the irrigation water. In this way, we could better understand and adjust the laser parameters to suit our needs. We obtained line cuts as deep as 21 mm without causing any visible thermal damage to the surrounding tissue. The automated experimental setup proposed here has the potential to support deeper and faster ablation in laserosteotomy applications.

9.
Opt Lett ; 42(19): 3964-3967, 2017 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-28957173

RESUMO

We report what is to our knowledge a new source of femtosecond pulses in the mid-infrared, based on a Kerr-lens mode-locked (KLM) Tm3+:YLF laser at 2303 nm. An undoped ZnSe substrate was included in the resonator to provide enhanced nonlinear phase modulation during KLM operation. The Tm3+:YLF laser was end-pumped with a continuous-wave Ti3+ : sapphire laser at 780 nm. With 880 mW of pump power, we generated 514-fs pulses at a pulse repetition rate of 41.5 MHz with an average power of 14.4 mW. The spectral width (full width at half-maximum) was measured as 15.4 nm, giving a time-bandwidth product of 0.44. We foresee that the wide availability of this gain medium, as well as the straightforward pumping scheme near 800 nm, will make 2.3-µm, mode-locked Tm3+:YLF lasers versatile sources of ultrashort pulses in the mid-infrared.

10.
Opt Lett ; 42(9): 1656-1659, 2017 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-28454128

RESUMO

We report, what is to our knowledge, the first passively Q-switched operation of a 2.3-µm Tm3+:YLF laser by using a Cr2+:ZnSe saturable absorber. In the experiments, a tunable Ti3+:sapphire laser was used to end pump the Tm3+:YLF gain medium inside an x cavity. A Cr2+:ZnSe saturable absorber was also included in the cavity to initiate passive Q switching. At all pump power levels above lasing threshold, passively Q-switched operation of the Tm3+:YLF laser could be obtained at 2309 nm with pulse durations and repetition frequencies in the ranges of 1.2-1.4 µs and 0.3-2.1 kHz, respectively. Analysis of power dependent repetition rate data further gave an estimated value of 3.1% for the round-trip saturable loss of the Cr2+:ZnSe saturable absorber.

11.
Opt Express ; 25(3): 2834-2839, 2017 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-29519000

RESUMO

We demonstrate, what is to our knowledge, the shortest pulses directly generated to date from a solid-state laser, mode locked with a graphene saturable absorber (GSA). In the experiments, a low-threshold diode-pumped Cr3+:LiSAF laser was used near 850 nm. At a pump power of 275 mW provided by two pump diodes, the Cr3+:LiSAF laser produced nearly transform-limited, 19-fs pulses with an average output power of 8.5 mW. The repetition rate was around 107 MHz, corresponding to a pulse energy and peak power of 79 pJ and 4.2 kW, respectively. Once mode locking was initiated with the GSA, stable, uninterrupted femtosecond pulse generation could be obtained. In addition, the femtosecond output of the laser could be tuned from 836 nm to 897 nm with pulse durations in the range of 80-190 fs. We further performed detailed mode locking initiation tests across the full cavity stability range of the laser to verify that pulse generation was indeed started by the GSA and not by Kerr lens mode locking.

12.
Opt Lett ; 40(17): 4110-3, 2015 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-26368724

RESUMO

We report, for the first time to our knowledge, a mode-locked femtosecond Cr:LiSAF laser initiated with a high-quality monolayer graphene saturable absorber (GSA), synthesized by chemical-vapor deposition. The tight-focusing resonator architecture made it possible to operate the Cr:LiSAF laser with only two 135 mW, 660 nm low-cost single-mode diode lasers. At a pump power of 270 mW, the laser produced nearly transform-limited 68 fs pulses with an average power of 11.5 mW at 850 nm. The repetition rate was around 132 MHz, corresponding to a pulse energy and peak power of 86 pJ and 1.26 kW, respectively. Once mode locking was initiated with the GSA, stable, uninterrupted femtosecond pulse generation could be sustained for hours. The saturation fluence and the modulation depth of the GSA were further determined to be 28 µJ/cm2 and 0.62%, respectively.

13.
Opt Lett ; 39(2): 327-30, 2014 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-24562138

RESUMO

We present efficient and robust Kerr-lens mode locking (KLM) of a diode-pumped Cr:LiSAF laser using a gain-matched output coupler (GMOC). An inexpensive, battery-powered 660 nm single-spatial-mode diode was used as the pump source. GMOC enhances the effective self-amplitude modulation depth by reducing the gain-filtering effect in broadband KLM operation to provide significant improvement in efficiency and robustness. Pulsing can be initiated without careful cavity alignment and is sustained for hours. 13 fs pulses with an average power of 25 mW have been generated using only 120 mW of pump power. The corresponding pulse energy and peak power is 200 pJ and 15 kW for the 126 MHz repetition rate cavity. Optical-to-optical conversion efficiency of the system is 21%, which represents an order of magnitude improvement in reported efficiencies for such diode-pumped ultrashort-pulse KLM Cr:LiSAF lasers. The obtainable pulse width is currently limited by the dispersion bandwidth of the available optics and can be potentially reduced to below 7 fs.

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