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Background and Objectives: Renal denervation (RDN) is an emerging surgical treatment for resistant hypertension. However, the current RDN using radiofrequency can cause undesirable thermal damage to the medial and luminal layers due to direct contact between the arterial lumen and energy source. The aim of this study is to evaluate the feasibility of the new laser-assisted RDN by exploring the potential treatment conditions., Methods: For ex vivo testing, six different treatment conditions (10 and 20 W applied for delivery of 300, 450, and 600 J) were tested on the porcine liver and renal artery (RA) by using a continuous wave 1064 nm laser wavelength. The ablated area in the liver tissue was measured to estimate the extent of the coagulated area. Histological evaluation was performed on the treated RA tissues to confirm the extent of thermal nerve damage., Results: The ablated depth, length, and area in the liver tissue increased with laser power and total energy. According to the histological results, 20 W groups yielded more significant damage to the RA nerves than 10 W groups at the total energy of 300 J (0.0 ± 0.0 mm for 10 W vs. 2.9 ± 1.0 mm for 20 W), 450 J (1.9 ± 0.6 mm for 10 W vs. 6.8 ± 1.5 mm for 20 W), and 600 J (2.9 ± 0.4 mm for 10 W vs. 7.3 ± 0.8 mm for 20 W). The treated RA exhibited insignificant medial injury in depth (medial thinning ≤ 25%), and no difference in the medial thinning was found among the six groups (p = 0.4)., Conclusion: The current study demonstrated that the 1064 nm laser at 20 W with delivery of 450 J could effectively damage the RA nerves with no or minimal injury to the surrounding tissue. The proposed laser-assisted RDN may enhance physiological effects with insignificant complications in in vivo situations. Further in vivo studies will be conducted to validate the current findings by evaluating the extent of blood pressure reduction and norepinephrine changes after the laser-assisted RDN on a large animal model., (© 2024 Wiley Periodicals LLC.)

Laser ablation (LA) has been evaluated for the minimally invasive thermal treatment of various cancers, but conventional unidirectional endoscopic ultrasound (EUS)-guided LA has limitations. Therefore, we developed a cylindrical laser diffuser to overcome the limitations of unidirectional EUS-guided LA. The purpose of this study was to compare the efficacies and safeties of EUS-guided LA using a novel cylindrical laser diffuser and radiofrequency ablation (RFA) in vivo in swine pancreas. EUS-guided RFA (15 W, 30 s, 450 J) and cylindrical interstitial LA (CILA) (5 W, 90 s, 450 J) were applied to normal pancreatic tissue in six anesthetized pigs (three per group). Laboratory tests were performed at baseline, immediately after ablation (day 0), and 2 days after procedures (day 2). Two days after procedures, all pigs were sacrificed, and histopathological safety and efficacy assessments were performed. Technically, EUS-guided RFA and CILA were performed successfully in all cases. No major complications, including perforation or acute pancreatitis, occurred during the experiment in either group. All animals remained in excellent condition throughout the experimental period, and laboratory tests provided no evidence of a major complication. Average necrotic volumes in the RFA and CILA groups were 424.2 mm 3 and 3747.4 mm 3 , respectively, and average necrotic volume was significantly larger in CILA group (p < 0.001). EUS-guided RFA and CILA had acceptable safety profiles in the normal swine pancreas model. Our findings indicate EUS-guided CILA has potential for the effective local treatment of pancreatic cancer as an alternative to EUS-guided RFA., (© 2024. The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.)

A Q-switched laser system has been used in a single-pulse mode for skin melasma treatments because of instant heat deposition in the target. Despite the efficient ablation of the melanophores in the skin, the single, high-fluence pulse often causes undesirable damage to the surrounding tissue, leading to high recurrence rates. This study aims to investigate the feasibility of dual-optical pulses with a temporal energy distribution on the melasma treatment in in vivo zebrafish models in comparison to that of the single optical pulse. Based on the optical detection, the dual-optical pulses had a temporal energy distribution ratio of 4:1 and an interval of 61 μs between the two consecutive pulses. According to the histological analysis, the dual pulses removed melanophores and induced a few apoptotic nuclei with minimal recurrence. This study demonstrated that the feasibility of dual-optical pulses (energy ratio = 4:1) could enhance the laser ablation performance in vivo., (© 2023 Wiley-VCH GmbH.)

The current study aims to demonstrate the feasibility of a novel balloon-integrated optical catheter (BIOC) to achieve endoscopic laser application for circumferential coagulation of a tubular tissue structure. Both optical and thermal numerical simulations were developed to predict the propagation of laser light and a spatio-temporal distribution of temperature in tissue. Ex vivo esophagus tissue was tested with 980 nm laser light at 30 W for 90 s for quantitative evaluations. In vivo porcine models were used to validate the performance of BIOC for circumferential and endoscopic laser coagulation of esophagus in terms of acute tissue responses post-irradiation. Optical simulations confirmed that a diffusing applicator was able to generate a circumferential light distribution in a tubular tissue structure. Both numerical and experimental results presented that the maximum temperature elevation occurred at 3-5 mm (muscle layer) below the mucosa surface after 90 s irradiation. In vivo tests confirmed the circumferential delivery of laser light to a deep muscle layer as well as no evidence of thermal damage to the esophageal mucosa. The proposed BIOC can be a feasible optical device to provide circumferential laser irradiation as well as endoscopic coagulation of tubular esophagus tissue for clinical applications., (© 2023. The Author(s) under exclusive licence to Biomedical Engineering Society.)

Pancreatic cancer (PC) is a leading cause of cancer death and its incidence and mortality have shown an increasing trend. Despite improvements in outcomes, another treatment option is required for PC. Laser ablation (LA) has been evaluated for the treatment of various types of cancer. The aim of this study was to assess the safety and feasibility of a novel cylindrical light diffuser in a xenograft model of PC. This study was performed using a customized high-power laser system. PANC-1 cells and BALB/c mice were used for experiments at a laser power of 5 W for 40 to 200 s at five different energy levels (n = 30). There was no acute bleeding or major complication. Using the cylindrical light diffuser, tumors were irradiated with similar size in each energy group. A correlation between laser dose and tumor necrosis was observed. Pearson's correlation for the relation between the amount of necrosis area and laser ablation energy on day 3 was 0.78 (p < 0.01). No statistical difference of necrosis area was exhibited when the necrosis area of each harvested tumor analyzed by dividing into 5 specimens for each energy. The study demonstrates that LA treatment using a cylindrical light diffuser induced remarkable tumor necrosis at histopathologic examinations. Laser ablation dosage and tumor response were strongly correlated, and the ablation procedure resulted in homogeneous tissue necrosis. No adverse event was encountered. These findings suggest that the devised cylindrical light diffuser offers a safe and effective means of treating pancreatic cancer., (© 2022. The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.)

Endoscopic submucosal dissection (ESD) is clinically used to remove early gastric cancer in stomach. The aim of the current study is to examine a therapeutic capacity of pulsed Ho:YAG laser for the development of laser-assisted ESD under various surgical parameters. Ex vivo porcine stomach tissue was ablated with 1-J Ho:YAG pulses at 10 Hz at different number of treatments (NT = 1, 2, and 3) and treatment speeds (TS = 0.5, 1, and 2 mm/s) without and with saline injection. Regardless of saline injection, straight tissue ablation showed that ablation depth increased with increasing NT and decreasing TS. At NT = 3 and TS = 0.5 mm/s, no saline injection yielded the maximum ablation depth (3.4 ± 0.3 mm), partially removing muscularis propria. However, saline injection confined the tissue ablation within a submucosal layer (2.1 ± 0.3 mm). Thermal injury was found to be 0.7~1.1 mm in the adjacent tissue with superficial carbonization. Circular tissue ablation (2 cm in diameter) at NT = 3 and TS = 0.5 mm/s presented that no saline injection yielded a reduction in the lesion area, whereas saline injection maintained the ablated lesion area. Histological analysis revealed that unlike no saline injection, saline injection ablated the entire mucosal layer without perforation in the muscular propria. The pulsed Ho:YAG laser can be a potential surgical tool for clinical ESD to incise a target lesion without adverse perforation. Further investigations will validate the efficacy and safety of the Ho:YAG laser-assisted ESD in in vivo porcine stomach models for clinical translation., (© 2020. Springer-Verlag London Ltd., part of Springer Nature.)

Endoscopic management of benign biliary stricture (BBS) remains challenging. Stenting is currently used for BBS management, but refractory BBS remains problematic. The aim of this study was to assess the safety and feasibility of a dilation balloon-equipped cylindrical light diffuser for BBS in a large animal model. A total of seven mini-pigs were used in the current study. Laser settings were chosen based on the findings of a previous animal study. Five animals were used in a preliminary study to establish process conditions. BBSs were created in the common bile ducts of the other two animals by intraductal radiofrequency ablation (RFA) via endoscopic retrograde cholangiography (ERC). At 4 weeks post-RFA, laser ablation was performed using a customized balloon-equipped cylindrical diffuser at 10 W for 10 s while maintaining balloon inflation for 10 s at 5 atm. A follow-up ERC was performed at 4 weeks post-laser ablation and the animals were sacrificed for histologic evaluation. BBS was observed in all animals by ERC at 4 weeks post-RFA. The mean bile duct stricture diameter in the two animals as determined by ERC was 0.8 mm. Laser ablations were performed without technical difficulty and no adverse event was encountered. At 4 weeks post-laser ablation, mean biliary stricture diameter had dilated to 1.6 mm on cholangiographic finding. On histologic examination, inflammatory cell infiltration in lamina propria and dense collagen deposition were observed, but there was no evidence of bile duct perforation. The devised balloon-equipped cylindrical laser light diffuser appears to be safe and feasible for the treatment of BBS. However, further studies and modifications are required before it can be applied clinically as a monotherapy.

Background: The therapeutic capacity of multiple cylindrical interstitial laser ablations (CILAs) of pancreatic tissue was evaluated with 1064 nm laser light in ex vivo and in vivo porcine pancreatic models., Methods: A diffusing applicator was sequentially employed to deliver 1064 nm laser light in a cylindrical distribution to ablate a large volume of pancreatic tissue. Ex vivo tissue was tested at various power levels (5, 7, and 10 W) under US imaging. An in vivo porcine model was used to evaluate the clinical feasibility of multiple CILAs on pancreatic tissue at 5 W via laparotomy ( N  = 3)., Results: Multiple CILAs symmetrically ablated a range of ex vivo tissue volumes (2.4-6.0 cm 3 ) at various power levels. Multiple CILAs warranted a therapeutic capacity of symmetrically ablating in vivo pancreatic tissue. Both ex vivo and in vivo pancreatic tissues after multiple CILAs at 5 W confirmed the absence of or minimal thermal injury to the peripheral tissue and carbonization., Conclusions: The current findings suggest that the collective thermal effects from multiple CILAs can help widely ablate pancreatic tissue with minimal thermal injury. Further in vivo studies will investigate the safety of the proposed CILA treatment as well as acute/chronic responses of pancreatic tissue for clinical translations.

Purpose: The aim of the current study was to identify the efficient fiber movements for 532-nm laser prostatectomy., Materials and Methods: 532-nm Lithium triborate (LBO) laser light was tested on 120 kidney tissues at three different translational speeds (TS 1, 2, and 4 mm/s) and four different rotational speeds (RS 0.5, 1.0, 1.6, and 2.1 rad/s). The applied power was 120 W at a 2-mm working distance and 60° sweeping angle. Ablation rate and dimensions of resulting ablation craters were measured., Results: Slower TSs and RSs created deeper and wider ablation craters with thinner coagulation, leading to more efficient ablation performance. Maximal ablation rate was achieved at a TS of 2 mm/s and RSs of 0.5 and 1.0 rad/s. An RS of 0.5 rad/s accompanied surface carbonization for all the TSs. Irrespective of TS, ablation rate became saturated at faster RSs than 1.0 rad/s. Faster TSs or RSs reduced tissue ablation, but increased thermal coagulation due to a shorter interaction time., Conclusions: Optimal ablation efficiency occurred at a TS of 2 mm/s and a RS of 1.0 rad/s with a thin coagulation of around 1.0 mm and no or minimal carbonization. Further studies will validate the current findings with prostate tissue and high-power levels for laser prostatectomy.

Intraoperative bleeding during laser treatment of benign prostate hyperplasia (BPH) often impedes cystoscopic vision, necessitating the use of conventional hemostatic devices. This study proposes an optical technique to improve the efficacy of photothermal hemostasis of bleeders during laser prostatectomy by temporally modulating a 532 nm laser beam. A perfused porcine kidney model is established to quantitatively investigate various optical pulse patterns and irradiation modes. Thermal simulations demonstrate a high success rate of complete hemostasis achieved by the modulated 532 nm pulse pattern. In comparison to the irradiation modes typically employed for hemostasis, the modulated 532 nm mode exhibits a short coagulation time and minimal thermal injury. ex vivo and in vivo cystoscopic observations validate the clinical feasibility of the proposed optical energy modulation method to regulate intraoperative bleeding., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Background and Objective: Laser ablation can be used to treat atrial fibrillation by thermally isolating pulmonary veins. In this study, we evaluated the feasibility of high-resolution (<1 mm) ultrasound thermal imaging to monitor spatial temperature distribution during laser ablation on ex vivo cardiac tissue., Study Design/materials and Methods: Laser ablation (808 nm) was performed on five porcine cardiac tissue samples. A thermocouple was used to measure the interstitial tissue temperature during the laser ablation process. Tissue-strain-based ultrasound thermal imaging was conducted to monitor the spatial distribution of the temperature in the cardiac tissue. The tissue temperature was estimated from the time shifts of ultrasound signals owing to the changes in the speed of sound and was compared with the measured temperature. The temperature estimation coefficient k of porcine cardiac tissue was calculated from the estimated thermal strain and the measured temperature. The degree of tissue coagulation (temperatures > 50°C) was derived from the estimated temperature and was compared with that of the tested cardiac tissue., Results: The estimated tissue temperature using strain-based ultrasound thermal imaging at a depth of 1 mm agreed with thermocouple measurements. During the 30-second period of the laser ablation process, the estimated tissue temperature increased from 25 to 70°C at a depth of 0.1 mm, while the estimated temperature at a depth of 1 mm increased up to 46°C. Owing to the uncertainty of the coefficient k, the k value of the porcine cardiac tissue varied from 160 to 220°C with temperature changes of up to 20°C. The estimated coagulation region in the ultrasound thermal imaging was 20% wider (+0.6 mm) but 9% shallower (-0.1 mm) than the measured region of the ablated porcine cardiac tissue., Conclusions: The current study demonstrated the feasibility of temperature monitoring with the use of ultrasound thermal imaging during the laser ablation on ex vivo porcine cardiac tissue. The high-resolution ultrasound thermal imaging could map the spatial distribution of the tissue temperature. The proposed method can be used to monitor the temperature and thermal coagulation to achieve effective laser ablation for atrial fibrillation. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc., (© 2019 Wiley Periodicals, Inc.)

Laser lights have been used by dermatologists for tattoo removal through photothermal interactions. However, most clinical studies used a visual scoring method to evaluate the tattoo removal process less objectively, leading to unnecessary treatments. This study aimed to develop a simple and quantitative imaging method to monitor the degree of tattoo removal in in vivo skin models. Sprague Dawley rat models were tattooed with four different concentrations of black inks. Laser treatment was performed weekly on the tattoos using a wavelength of 755 nm over six weeks. Images of non-treated and treated samples were captured using the same method after each treatment. The intensities of the tattoos were measured to estimate the contrast for quantitative comparison. The results demonstrated that the proposed monitoring method quantified the variations in tattoo contrast after the laser treatment. Histological analysis validated the significant removal of tattoo inks, no thermal injury to adjacent tissue, and uniform remodeling of epidermal and dermal layers after multiple treatments. This study demonstrated the potential of the quantitative monitoring technique in assessing the degree of clearance level objectively during laser treatments in clinics.

Laser treatment on a large size of prostate gland often encounters significant bleeding that can prolong the entire procedure and cause urinary complications. The current study investigates the feasibility of dual-wavelength (532 and 980 nm) application to achieve rapid hemostasis for 532-nm laser prostatectomy. Porcine kidney and bleeding phantom models were tested to quantify the degree of the irreversible tissue coagulation and to estimate the time for the complete hemostasis, respectively. The ex vivo kidney testing verifies that the dual-wavelength created up to 40% deeper and 25% wider coagulation regions than a single wavelength does. The bleeding phantom testing demonstrates that due to the enhanced thermal effects, the simultaneous irradiation yields the complete photocoagulation (~11 seconds) whereas 532 or 980 nm hardly stops bleeders. Numerical simulations validate that the combined optical-thermal characteristics of both the wavelengths account for the augmented thermal coagulation. The dual-wavelength-assisted coagulation can be a feasible treatment to entail the rapid hemostasis and to facilitate the laser prostatectomy in an effective manner., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Endovenous laser ablation (EVLA) has frequently been used to treat varicose veins for 20 years. In spite of 90˜95% occlusion rates, clinical complications such as burn and ecchymosis still occur due to excessive thermal injury to perivenous tissue. In the current study, a glass-capped diffusing applicator is designed to validate the feasibility of EVLA as an effective therapeutic device by applying circumferential light distribution. The proposed device is evaluated with a flat fiber as a reference in terms of temperature elevation, fiber degradation, and degree of coagulative necrosis after 532 nm-assisted EVLA at 100 J/cm. The diffusing fiber generates a 40% lower maximum temperature with a 90% lower transient temperature change in blood, compared to the flat fiber. Due to low irradiance (13.5 kW/cm 2 ) and wide light distribution, the diffuser tip experiences no significant thermal degradation while severe carbonization occurs at the flat fiber tip. Ex vivo tissue tests verify that the diffusing fiber induces circumferential and consistent tissue denaturation to the vein wall (107.8 ± 7.8 µm) along with 19% vessel shrinkage. The proposed glass-capped diffusing applicator can be a feasible therapeutic device for EVLA with minimal complications by entailing low maximum temperatures and uniform tissue denaturation in the venous tissue., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The photothermal effect of a marine-oriented xanthophyll carotenoid, astaxanthin (AXT), was characterized based on its potential absorption of visible laser light and conversion of optical light energy into heat for thermal treatment. As an antioxidant and anticancer agent, AXT extracted from marine material can be utilized for photothermal therapy due to its strong light absorption. The current study investigated the feasibility of the marine-based material AXT to increase the therapeutic efficacy of chemo-photothermal therapy (PTT) by assessing photothermal sessions in both cells and tumor tissues. A quasi-cw Q-switched 80 W 532 nm laser system was utilized to induce thermal necrosis in in vitro and in vivo models. An in vitro cytotoxicity study of AXT was implemented using squamous cell carcinoma (VX2) and macrophage (246.7) cell lines. In vivo PTT experiments were performed on 17 rabbits bearing VX2 tumors on their eyes that were treated with or without intratumoral injection of AXT at a dose of 100 μl (300 μg/ml) followed by laser irradiation at a low irradiance of 0.11 W/cm2. Fluorescence microscopy images revealed cellular death via apoptosis and necrosis owing to the dual chemo-photothermal effects induced by AXT. In vivo experimental results demonstrated that the AXT-assisted irradiation entailed a temperature increase by 30.4°C after tumor treatment for 4 min. The relative variations in tumor volume confirmed that the tumors treated with both AXT and laser irradiation completely disappeared 14 days after treatment, but the tumors treated under other conditions gradually grew. Due to selective light absorption, AXT-assisted laser treatment could be an effective thermal therapy for various drug-resistant cancers.

Background and Objective: Fiber-assisted laser surgery has been employed as a minimally invasive method in various medical fields. In spite of multiple sweeping on tissue during laser treatments, the rate of tissue removal gradually decreases and eventually leads to longer irradiation times as well as deeper thermal injury. The objective of the current study was to quantitatively investigate the effect of multiple fiber sweeps on ablation performance during ex vivo 532-nm laser nephrectomy., Materials and Methods: Porcine kidney tissue was used to evaluate variations in tissue ablation and coagulative necrosis after pre- and multiple-sweeping with a 532 nm wavelength at various fiber speeds (2, 4, and 6 mm/second). The distance between a fiber tip and tissue surface was initially set at 1.5 mm, and no further distance change was performed. Double-integrating spheres in conjunction with an adding-doubling method were employed to measure variations in optical properties of the tested tissue. The extent of ablation and coagulation was quantified to identify the role of multiple-sweeping at various fiber conditions., Results: Optical property measurements showed a 30% decrease in light absorption but a more than threefold increase in light scattering after irreversible thermal denaturation. Pre-sweeping yielded insignificant effects on tissue coagulation due to almost consistent coagulation depths with numbers of pre-sweeps. Ablation depths increased with more numbers of fiber sweeps and slower fiber speeds whereas coagulation depths thickened primarily with the slower speeds. Multiple-sweeping induced saturation in ablation volume with the increasing numbers of multiple-sweeps irrespective of the fiber speed., Conclusion: A combination of coagulation barriers, spatial distribution of power, and temporal interplay of optical energy could attribute to continuously lessen the amount of the ablated tissue with the multiple sweeps. Optical power modulation with varying fiber conditions (speed and distance) will be examined to optimize surgical parameters and to sustain the equivalent ablation performance of the first sweep with the multiple sweeping for laser nephrectomy. Lasers Surg. Med. 48:616-623, 2016. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

Laser-assisted lipolysis has been implemented to reduce body fat in light of thermal interactions with adipose tissue. However, using a flat fiber with high irradiance often needs rapid cannula movements and even undesirable thermal injury due to direct tissue contact. The aim of the current study was to explore the feasibility of a radially diffusing optical applicator to liquefy the adipose tissue for effective laser lipolysis. The proposed diffuser was evaluated with a flat fiber in terms of temperature elevation and tissue liquefaction after laser lipolysis with a 980-nm wavelength. Given the same power (20 W), the diffusing applicator generated a 30% slower temperature increase with a 25% lower maximum temperature (84±3.2°C in 1 min; p<0.001) in the tissue, compared with the flat fiber. Under the equivalent temperature development, the diffuser induced up to fivefold larger area of the adipose liquefaction due to radial light emission than the flat fiber. Ex vivo tissue tests for 5-min irradiation demonstrated that the diffuser (1.24±0.15  g) liquefied 66% more adipose tissue than the flat fiber (0.75±0.05  g). The proposed diffusing applicator can be a feasible therapeutic device for laser lipolysis due to low temperature development and wide coverage of thermal treatment.

Background and Objective: Artificial skin phantoms have been developed as an alternative tissue for human skin experiments due to convenient use and easy storage. However, fabricating both thin (∼100 μm) epidermis and relatively thick dermis is often cumbersome, and most developed phantoms have hardly reflected specific human skin types. The objective of this study was to fabricate skin phantoms with 3D printing technique to emulate various human skin types (I-VI) along with the corresponding optical and mechanical properties for laser tattoo removal., Study Design/materials and Methods: Both gelatin and agar powders were mixed with coffee and TiO2 particles to fabricate skin phantoms with materials properties for various skin types (I-VI). A 3D printer was employed to precisely control the thickness of each phantom for epidermis and dermis layers. A number of concentrations of the coffee and TiO2 particles were used to determine the degree of absorption and scattering effects in various skin types. The optical properties between 500 and 1,000 nm for the fabricated phantoms were measured by double-integrating spheres with an inverse adding-doubling (IAD) algorithm. Optical coherence tomography (OCT) and rheometer were also utilized to evaluate optical (absorption and reduced scattering coefficients) and mechanical properties (compression modulus) of the fabricated phantoms, respectively., Results: Visible color inspections presented that the skin phantoms for types I, III, and VI similarly emulated the color space of the human skin types. The optical property measurements demonstrated that the absorption (μa) and reduced scattering (μ(s')) coefficients decreased with wavelengths. Compared to the human skin type VI, a dermis phantom represented quite equivalent values of μa and μ(s') whereas an epidermis phantom showed up to 30% lower μa but almost identical μ(s') over the wavelengths. The OCT measurements confirmed that the thicknesses of the epidermis and the dermis phantoms were measured to be 138.50 ± 0.01 μm and 0.81 ± 0.04 mm, respectively. The mechanical properties of the phantoms mixed with the agar volume of 40% yielded a compression modulus of 83.7 ± 14.8 kPa, which well corresponded to that of human forearm skin (50-95 kPa)., Conclusion: The 3D printing technique was able to reliably fabricate the double-layered phantoms emulating a variety of skin types (I-VI) along with the comparable optical and mechanical properties. Further investigations will incorporate artificial chromophores into the fabricated skin phantoms to reliably evaluate the new therapeutic wavelengths for laser tattoo removal., (© 2016 Wiley Periodicals, Inc.)

Purpose: To investigate serial changes in the incidences of de novo urge urinary incontinence (UUI) after photoselective vaporization of the prostate (PVP) for BPH using a validated questionnaire, OABSS, and to determine predictors of postoperative de novo UUI (dnUUI)., Methods: A total of 84 men, for whom 12-month follow-up data were available and who did not complain of UUI based on the OABSS [score of OABSS question 4 (OABSS4) ≤1], were included in this study. Outcomes were evaluated at 1 week, and 1, 3, 6, and 12 months postoperatively using IPSS, OABSS, and uroflowmetry. The presence of de novo UUI was defined as OABSS4 ≥2 at the follow-up visit., Results: Maximum flow rate (Qmax), post-void residual urine volume, voiding symptom score, total IPSS, and QOL index improved from 1 week. Storage symptom score and total OABSS improved from 3 months. Incidences of postoperative dnUUI at 1 week, and 1, 3, and 6 months were 42.9, 27.4, 14.3, and 0.0 %, respectively. The decrease in QOL index in patients with dnUUI at each follow-up visit was lesser than in those without dnUUI. On multivariate regression analysis, older age, shorter time to Qmax on baseline uroflowmetry, higher storage symptom score, higher total OABSS, smaller bladder volume at first desire to void, and smaller maximum cystometric capacity (MCC) on baseline urodynamics were independent predictors of occurrence of dnUUI., Conclusions: Our data indicate that transient dnUUI occurs in a significant proportion of patients after PVP and it tends to decrease over time. Older-aged patients, patients with shorter time to Qmax, higher baseline storage symptom score, higher baseline total OABSS, smaller bladder volume at first desire to void, and smaller MCC may be prone to develop dnUUI postoperatively.

Background and Objectives: During laser vaporization of benign prostate hyperplasia (BPH), high precision of optical fiber handling is pivotal to minimize any post-operative complications. The aim of the study was to evaluate the feasible applications of a bundled fiber to treat BPH by directionally and selectively manipulating laser light onto the targeted tissue., Methods: A bundled optical fiber, consisting of four side-firing fibers, was fabricated to selectively emit laser beams in from one to four directions. Both transmission efficiency and light distribution were qualitatively and quantitatively characterized on the bundled fiber. In terms of interstitial application of the proposed fiber with 1064 nm on porcine liver tissue, the extent of thermal denaturation was estimated and compared at various laser parameterizations and for different directions of light., Results: From the laser source to the fiber tip, the fabricated fiber device demonstrated a total light transmission of 52%. Due to internal light reflection, a secondary beam was emitted backward from the fiber tip and was responsible for 25% of the transmission loss. According to tissue testing, the extent of tissue denaturation generally increased with laser power, irradiation time, and number of light directions. The geometrical shape of thermal coagulation correlated well with the direction of light emission. Thermal damage to the glass tube occurred during excessive heat accumulation generated by continuous irradiation., Conclusions: The proposed fiber can be beneficial for laser vaporization of BPH by providing a selective light direction irradiation along with minimal thermal damage. Further studies will extend the applicability of the bundled fiber to treat tubular tissue structure., (© 2014 Wiley Periodicals, Inc.)

Background and Objective: Laser light has been widely used as a surgical tool to treat benign prostate hyperplasia (BPH) over 20 years. Recently, application of high laser power up to 200 W was often reported to swiftly remove a large amount of prostatic tissue. The purpose of this study was to validate the feasibility of photoactive dye injection to enhance light absorption and eventually to facilitate tissue vaporization with low laser power., Materials and Methods: Chicken breast tissue was selected as a target tissue due to minimal optical absorption at the visible wavelength. Four biocompatible photoactive dyes, including amaranth (AR), black dye (BD), hemoglobin powder (HP), and endoscopic marker (EM), were selected and tested in vitro with a customized 532 nm laser system with radiant exposure ranging from 0.9 to 3.9 J/cm(2) . Light absorbance and ablation threshold were measured with UV-Vis spectrometer and Probit analysis, respectively, and compared to feature the function of the injected dyes. Ablation performance with dye-injection was evaluated in light of radiant exposure, dye concentration, and number of injection., Results: Higher light absorption by injected dyes led to lower ablation threshold as well as more efficient tissue removal in the order of AR, BD, HP, and EM. Regardless of the injected dyes, ablation efficiency principally increased with radiant exposure, dye concentration, and number of injection. Among the dyes, AR created the highest ablation rate of 44.2 ± 0.2 µm/pulse due to higher absorbance and lower ablation threshold. High aspect ratios up to 7.1 ± 0.4 entailed saturation behavior in the tissue ablation injected with AR and BD, possibly resulting from plume shielding and increased scattering due to coagulation. Preliminary tests on canine prostate with a hydraulic injection system demonstrated that 80 W with dye injection yielded comparable ablation efficiency to 120 W with no injection, indicating 33% reduced laser power with almost equivalent performance., Conclusion: Due to efficient coupling of optical energy, pre-injection of photoactive dyes promoted the degree of tissue removal during laser irradiation. Further studies will investigate spatial distribution of dyes and optimal injecting pressure to govern the extent of dye-assisted ablation in a predictable manner. In-depth comprehension on photoactive dye-enhanced tissue ablation can help accomplish efficient and safe laser vaporization for BPH with low power application., (© 2014 Wiley Periodicals, Inc.)

Optical fibers have been used as a minimally invasive tool in various medical fields. However, due to excessive heat accumulation, the distal end of a fiber often suffers from severe melting or devitrification, leading to the eventual fiber failure during laser treatment. In order to minimize thermal damage at the fiber tip, an optical feedback sensor was developed and tested ex vivo. Porcine kidney tissue was used to evaluate the feasibility of optical feedback in terms of signal activation, ablation performance, and light transmission. Testing various signal thresholds demonstrated that 3 V was relatively appropriate to trigger the feedback sensor and to prevent the fiber deterioration during kidney tissue ablation. Based upon the development of temporal signal signatures, full contact mode rapidly activated the optical feedback sensor possibly due to heat accumulation. Modulated light delivery induced by optical feedback diminished ablation efficiency by 30% in comparison with no feedback case. However, long-term transmission results validated that laser ablation assisted with optical feedback was able to almost consistently sustain light delivery to the tissue as well as ablation efficiency. Therefore, an optical feedback sensor can be a feasible tool to protect optical fiber tips by minimizing debris contamination and delaying thermal damage process and to ensure more efficient and safer laser-induced tissue ablation.

Laser light has been widely used as a surgical tool to treat benign prostate hyperplasia (BPH). Various surgical parameters still need to be tested and optimized to accomplish better clinical outcomes. The purpose of the current study is to investigate the effect of fiber core size on ablation performance at various laser power levels. Three optical fibers (600, 775, and 850 μm) were tested in vitro with a customized 532-nm laser system with power ranging from 120 to 180 W. Ablation performance was evaluated in light of total energy, irradiance, and volumetric energy density. Irrespective fiber size, crater dimension, and ablation volume linearly increased with the incident irradiance. However, each fiber created different geometry of ablation craters (i.e., deep columnar shape for 600 μm vs. shallow funnel shape for 850 μm). Smaller fiber size demonstrated the efficient energy usage for tissue removal. In-depth comprehension of fiber performance can help accomplish predictable and efficient surgical procedures for BPH therapy.

During laser treatment of prostate, urological surgeons occasionally experience fiber-cap failure due to concentration of thermal stress on the fiber tip. Upon the cap breakage, laser light becomes forward-propagating and may adversely affect the bladder tissue such as perforation. The purpose of the current study was to identify any bladder perforation with forward-propagating laser light (λ = 532 nm) at 80 and 120 W with an assumption of fiber-cap failure. Perforation time was measured and compared in terms of fiber distance. The results showed that 80 and 120 W perforated the tissue up to 2 and 2.5 cm, respectively with perforation threshold of 17.2 kW/cm(2), and the minimum perforation time was approximately 7 s. No perforation occurred at the distance of 3 cm for 1-min irradiation at both power levels, but severely carbonized lesions were generated around the irradiated tissue. Although equivalent ablation speed was found between the two power levels, 120 W created up to 20 % wider craters regardless of fiber distance. With consideration of dense collagen fibers in bladder structure and long surgical distance, direct incidence of laser perforation on bladder wall could be unlikely to happen upon fiber-cap failure during laser surgery.

Background and Objective: The optimal fiber manipulation during laser prostatectomy has been highlighted as a critical element to achieve desirable clinical outcomes. However, scientific understanding of the physical interplay between fiber movement and ablative tissue response is still lacking. The objective of this study was to quantitatively investigate the effect of angular movement of an optical fiber on tissue ablation performance., Study Design/materials and Methods: Porcine kidney was employed as a tissue model in vitro. A 180 W 532 nm surgical laser with 750 µm side-firing fibers was utilized to mimic clinical laser prostatectomy. The effect of fiber manipulation parameters on the tissue such as irradiance, number of overlapping pulses (OP), and beam path length (BPL) was assessed at various fiber sweeping (rotational) angles ranging from 0° to 120°. Morphological properties of the post-irradiated tissue were also evaluated in light of ablation depth, coagulative necrosis, and volumetric ablation density (VAD)., Results: As sweeping angle (SA) increased, both laser irradiance and number of OP decreased but BPL increased. Ablation depth was maximized (5.4 ± 1.0 mm) at SAs less than 30° but decreased at higher SAs. The SAs of 15° and 30° demonstrated the minimal thickness of denaturized tissue (0.74 ± 0.14 mm) and VAD (total laser energy/ablation volume (AV) ≈ 4.6 ± 0.46 J/mm(3) ). Decreasing depth and increasing tissue coagulation associated with increasing SA resulted from substantial reduction in both beam irradiance and number of OP, eventually impeding ablation process. Excessive tissue denaturation also occurred when no rotational motion was applied to the fiber possibly due to plume shielding., Conclusion: Inefficient tissue ablation could lead to adverse post-operative complications due to unwanted thermal injury to peripheral tissue. A SA of 30° was found to be desirable for effective tissue ablation, and further clinical investigations will validate the current findings., (Copyright © 2012 Wiley Periodicals, Inc.)

Purpose: The goal of this study is to identify the most efficient sweeping angle (SA) during photoselective vaporization of the prostate (PVP)., Materials and Methods: Experiments were conducted with GreenLight XPS™ laser at 120 and 180 W. Ten blocks of porcine kidney were used for each SA (0, 15, 30, 45, 60, 90, and 120 degrees). Vaporization efficiency was assessed by the amount of tissue removed per time. The coagulation zone (CZ) thickness was also measured., Results: Maximal vaporization rate (VR) was achieved at SA 15 and 30 degrees. Irrespective of power, VR increased and CZ decreased linearly with decreasing SA from 120 to 30 degrees. The CZ was the thinnest at SA 30 degrees., Conclusions: Optimal vaporization occurred at a SA of 15 degrees and 30 degrees with the lowest CZ at 30 degrees. Contrary to a previous recommendation for a wider SA (60 degrees or greater), a narrower SA (30 degrees) achieved the maximal tissue vaporization efficiency.

Background and Purpose: Photoselective vaporization of the prostate (PVP) has emerged as an effective debulking procedure for prostatic urinary obstruction. Surgical technique for the most efficient vaporization has, however, received little scientific investigation. We used an ex-vivo bovine prostate model to investigate how variation in the angle of laser fiber rotational movement ("sweeping") affects prostate tissue vaporization efficiency., Materials and Methods: Experiments were conducted using the GreenLight™ HPS 120W laser system. A single surgeon performed a clinical PVP video analysis, forming the basis of our study design. Sixty bovine prostate specimens were vaporized using an ex-vivo chamber equipped with computer-assisted axial movements. Specimens were vaporized at a fixed sweeping speed (0.5 sweeps/sec) and variable sweeping angles (0, 15, 30, 60, 90, and 120 degrees). The volume of tissue vaporized was calculated from cross sections and compared by a two-sample t test., Results: Clinical PVP video analysis of a single experienced surgeon showed a mean angle of 47.7 degrees with 25% of vaporization between 0 and 30 degrees. Ex-vivo analysis showed larger sweeping angles generated wider but more superficial vaporization defects, leading to smaller vaporized volumes. Specifically, vaporization volumes with angles of 0, 15, or 30 degrees were significantly greater than those with rotational angles of 45, 60, and 90 degrees (1.5-3.0 X; P<0.05). The depth of tissue coagulation significantly increased with greater rotational angles., Conclusions: Optimal PVP occurred at narrower angles of laser fiber sweeping in our ex-vivo model. Our findings highlight that PVP laser fiber movement can be tested in a scientific manner, identifying parameters to maximize vaporization efficiency.

Purpose: We studied vaporization parameters, and anatomical and histopathological outcomes of photoselective vaporization of the prostate with the novel GreenLight™ XPS™ 180 W, 532 nm lithium triborate laser and MoXy™ fiber in a survival model of living dogs. We compared these findings with those of the existing GreenLight HPS™ 120 W 532 nm lithium triborate laser photoselective vaporization of the prostate in living dogs., Materials and Methods: Eight dogs underwent antegrade photoselective vaporization of the prostate with the 180 W laser delivered through a new 750 μm (vs the existing 600 μm core diameter), 50% larger, spot sized, side firing fiber. Four dogs were sacrificed 3 hours and 8 weeks postoperatively, respectively. We recorded laser energy and time. Prostates were sectioned, measured and histologically analyzed after hematoxylin and eosin, triphenyltetrazolium chloride or Gomori trichrome staining and compared with a normal control., Results: Photoselective vaporization of the prostate with the 180 W laser bloodlessly created a 76% larger cavity (mean 11.8 vs 6.7 cm(3), p = 0.014), vaporized tissue at a 77% higher rate (mean 2.3 vs 1.3 cm(3) per minute, p = 0.03) and did so in 37% less time per volume vaporized (0.5 vs 0.8 minutes per cm(3), p = 0.003). Hematoxylin and eosin, and triphenyltetrazolium chloride staining histologically revealed a 33% thicker mean coagulation zone vs that of 120 W laser photoselective vaporization of the prostate (2.0 ± 0.4 vs 1.5 ± 0.3 mm, p <0.005). In prostates healed for 8 weeks postoperatively hematoxylin and eosin, and Gomori trichrome staining showed re-epithelialized cavities with negligible submucosal fibrosis compared with a normal prostate., Conclusions: GreenLight XPS 180 W 532 nm lithium triborate laser photoselective vaporization of the prostate with the MoXy fiber has a significantly higher vaporization rate and speed with a deeper hemostatic coagulation zone but favorable tissue interaction and healing equal to those of HPS 120 W laser photoselective vaporization of the prostate in dogs., (Copyright © 2011 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.)

Purpose: We investigated the effect of 120 to 200 W high power levels on in vitro vaporization of bovine prostate using a custom-made 532 nm lithium triborate laser system., Materials and Methods: Light (532 nm) delivered through a newly designed 750 microm core diameter side firing prototype fiber vaporized 114 bovine prostate tissue specimens in saline at 20C using a 2-dimensional scanning system. Various conditions were tested, including 120 to 200 W power, 1 to 5 mm working distance and 2 to 8 mm per second treatment speed., Results: Regardless of treatment speed 180 W was the optimal power to maximize tissue vaporization efficiency by removing 80% more tissue than at 120 W. At 120 and 180 W laser light vaporized tissue more efficiently at a 4 mm per second treatment speed and vaporized equally efficiently at up to 3 mm working distance. At the slowest treatment speed the mean thickness of the coagulation zone at 180 W was 20% thicker than at 120 W (1.31 vs 1.09 mm) but still thin, comparable to previous findings of 1 to 2 mm., Conclusions: In vitro the 532 nm lithium triborate laser showed that 180 W is the optimal power to maximize tissue vaporization efficiency with enhanced coagulation characteristics. These desirable outcomes must be validated in vivo., (2010 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.)

Background and Objective: Over a decade, laser prostatectomy has been performed to effectively treat benign prostate hyperplasia (BPH) with low post-operative complications. In this study, two laser wavelengths conventionally used for BPH treatment were compared to characterize the outcomes of in vitro tissue ablation., Study Design/materials and Methods: Two lasers with wavelengths including 532 nm (Q-switched) and 2.01 microm (continuous wave) were employed to ablate porcine kidney tissue in vitro. Ablation performance was evaluated by varying applied power, treatment speed, and fiber working distance. Optical transmission was measured as a function of working distance and compared with the corresponding ablation volume. Coagulation depth was quantified from gross tissue examination, and histology analysis confirmed coagulation features for both wavelengths., Results: Five hundred thirty-two nanometers yielded up to 30% (P<0.005) higher ablation efficiency than 2.01 microm. Regardless of wavelength, ablation rate increased with power and was maximized at treatment speed of 4 mm/seconds. A comparable ablation depth was found between the two wavelengths, but 532 nm generated relatively wider (up to 30%; P<0.005) craters. Both optical transmission and ablation volume revealed that energy loss by strong water absorption compromised ablation efficiency generated by 2.01 microm. Gross tissue and histology examination demonstrated that 532 nm created a thin coagulation zone whereas 2.01 microm induced approximately 20% (P<0.005) more thermal injury in association with carbonized tissue surface., Conclusions: Due to more light scattering and effective thermal confinement, 532 nm induced more efficient tissue ablation with a smaller coagulative necrotic zone. Comparable ablation depth may enable a potential tissue incision technique with 532 nm, possibly allowing both tissue removal and biopsy intraoperatively.

Introduction: Recommendations for efficient photoselective vaporization of the prostate (PVP) include a side-to-side rotational laser-fiber "sweeping" motion, yet scientific study of this technique is lacking. We investigated whether the speed of laser-fiber sweeping affects tissue vaporization efficiency., Methods: PVP was performed using the 120-W GreenLight high-performance system. Video analysis of a surgeon performing PVP was carried out to identify sweeping speeds used clinically. PVP efficiency was subsequently tested at four different sweeping speeds using two manipulations of an ex vivo bovine prostate model, including (1) excised prostate tissues (n = 40) in a vaporization chamber equipped with motorized laser-fiber movements; (2) retrograde endoscopic vaporization (n = 80) within whole lower urinary tracts. Vaporized cavity sizes and coagulative margins were measured by liquid-paraffin molding and histologic cross-sectioning approaches., Results: Video analysis of clinical PVP showed wide variability in sweeping speed, mostly ranging between 0.5 and 2.0 (mean 1.50) sweeps/second. Using either manipulation of the ex vivo bovine prostate model described above, PVP at lower sweeping speeds (0.5 and 1.0 sweeps/second) removed significantly more tissue (up to twofold) compared with higher sweeping speeds (1.5 and 2.0 sweeps/second), with significant albeit minimal reductions in coagulation margins., Conclusion: In this ex vivo prostate model, our results suggest that vaporization efficiency is compromised with faster laser-fiber sweeping. This finding counters principles of traditional transurethral resection of the prostate, in which faster axial movement toward the surgeon removes tissue more efficiently. This study highlights that PVP technique can be tested in a scientific manner, identifying optimal parameters for achieving maximal tissue vaporization efficiency.

Purpose: Efficiency, anatomic, and histopathologic outcomes of GreenLight HPS 120-W, 532-nm lithium triborate (LBO) laser photoselective vaporization of the prostate (PVP) in a survival model of living canines were studied and compared with the outcomes of the only benchmarked survival study of 60-W 532-nm potassium-titanyl-phosphate (KTP) laser PVP in living canines., Materials and Methods: Twelve dogs underwent anterograde PVP with the 120-W LBO laser and, 4 each, were euthanized 3 hours (acute), 3 days (early), or 8 weeks (chronic) postoperatively. Laser energy and time were recorded. Prostates were sectioned, measured, and histologically analyzed after hematoxylin and eosin (H&E), triphenyltetrazolium chloride (TTC), or Gomori trichrome (GT) staining and compared with a normal control., Results: LBO laser PVP at 120 W acutely created a 6.7 +/- 3.2 cm(3) cavity, hemostatically, and vaporized tissue 160% more efficiently (mean 1.3 cm(3)/min vs 0.5 cm(3)/min), 500% faster (mean 4.9 vs 29.1 min), and needed 121% less energy (mean 28.8 vs 63.6 kJ) than the 60-W KTP laser. Histologic staining with H&E and TTC demonstrated a coagulation zone of 1.5 +/- 0.3 mm for the 120-W LBO laser, comparable to the 1 to 2 mm for the 60-W KTP laser. H&E- and GT-stained, healed prostates at 8-weeks postoperatively showed reepithelialized cavities with minimal submucosal fibrosis compared with an identically stained normal and the benchmarked KTP laser PVP-treated prostates., Conclusion: Our in vivo canine survival study demonstrates GreenLight HPS 120-W, 532-nm LBO laser PVP has substantially more vaporization efficiency and speed, with equally favorable tissue interaction and healing vis-à-vis those benchmarked for the 532-nm wavelength by KTP laser PVP.

Purpose: We compared the outcomes of in vitro vaporization of bovine prostate using the lithium triborate GreenLight HPS and the GreenLight KTP PV photoselective vaporization laser., Materials and Methods: A total of 96 specimens of bovine prostate tissue in saline at 20C were vaporized with a 2-dimensional scanning system using a side firing fiber emitting a 532 nm wavelength at 80 W using the KTP laser, and at 80 and 120 W using the HPS laser at a working distance of 0.5 to 5 mm and a treatment speed of 2 to 8 mm per second. Dimensions of the vaporized tissue and resultant lesions were assessed., Results: At a minimum working distance of 0.5 mm and a treatment speed of 4 mm per second (determined by optimum vaporization volume/energy use) the HPS laser at 80 and 120 W vaporized 50% and 100% more tissue, respectively, than the KTP laser at the customary 80 W. At the same treatment speed the HPS laser vaporized equally efficiently at up to 3 mm working distance at each power level, whereas the KTP laser lost efficiency at working distances beyond 0.5 mm. The 2 lasers vaporized more tissue at slower (longer lasing) treatment speeds but even at the slowest treatment speed mean thickness of the coagulation zone with the HPS laser at 80 and 120 W was comparable to that of the 80 W KTP laser (0.80 and 1.07 mm, respectively, vs 0.81)., Conclusions: In vitro the lithium triborate GreenLight HPS 120 W laser vaporizes bovine prostate far more efficiently than the KTP photoselective vaporization laser but coagulates it equally well. These favorable outcomes must be validated in vivo.

The purpose of this study was to investigate the effect of liquid environments upon laser bone ablation. A long-pulsed Er,Cr:YSGG laser was employed to ablate bovine bone tibia at various radiant exposures under dry, wet (using water or perfluorocarbon) and spray environmental conditions. Energy loss by the application of liquid during laser irradiation was evaluated, and ablation performance for all conditions was quantitatively measured by optical coherence tomography (OCT). Microscope images were also used to estimate thermal side effects in tissue after multiple-pulse ablation. Wet using water and spray conditions equally attenuated the 2.79 microm wavelength laser beam. Higher transmission efficiency was obtained utilizing a layer of perfluorocarbon. Dry ablation exhibited severe carbonization due to excessive heat accumulation. Wet condition using water resulted in similar ablation volume to the dry case without carbonization. The perfluorocarbon layer produced the largest ablation volume but some carbonization due to the poor thermal conductivity. Spray induced clean cutting with slightly reduced efficiency. Liquid-assisted ablation provided significant beneficial effects such as augmented material removal and cooling/cleaning effects during laser osteotomy.

The objective of this study was to understand the dominant mechanism(s) for dental enamel ablation with the application of water spray. A free-running Er,Cr:YSGG (yttrium, scandium, gallium, garnet) laser was used to ablate human enamel tissue at various radiant exposures. During dental ablation, distilled water was sprayed on the sample surface, and these results were compared to ablation without a spray (dry ablation). In order to identify dominant ablation mechanisms, transient acoustic waves were compared to ablation thresholds and the volume of material removed. The ablation profile and depth were measured using optical coherence tomography (OCT). Irregular surface modification, charring and peripheral cracks were associated with dry ablation, whereas craters for spray samples were relatively clean without thermal damage. In spite of a 60% higher ablation threshold for spray associated irradiations owing to water absorption, acoustic peak pressures were six times higher and ablation volume was up to a factor of 2 larger compared to dry ablation. The enhanced pressure and ablation performance of the spray-assisted process was the result of rapid water vaporization, material ejection with recoil stress, interstitial water explosion and possibly liquid-jet formation. With water cooling and abrasive/disruptive mechanical effects, the spray ablation can be a safe and efficient modality for dental treatment.