Simultaneous sealing and bisection of porcine renal blood vessels, ex vivo, using a continuous-wave, infrared diode laser at 1470 nm.

Electrosurgical and ultrasonic devices are used in surgical procedures for hemostatic sealing and bisection of vascular tissues. Previous benchtop studies alternatively demonstrated successful infrared laser sealing and cutting of blood vessels, in a sequential, two-step approach. This study describes a smaller, laparoscopic device compatible design, and simultaneous approach to sealing and bisection of vessels, with potential optical feedback. A 1470-nm infrared diode laser sealed and bisected 40 porcine renal arteries, ex vivo. A reciprocating, side-firing, optical fiber, housed in a transparent square quartz optical chamber (2.7 × 2.7 × 25 mm outer dimensions), delivered laser energy over an 11 mm scan length, with a range of incident powers (41-59 W) and treatment times (5-21 s). Vessel diameters ranged from 2.5 to 4.8 mm. Vessel burst pressure measurements were performed on each cut end (n = 80) with success indicated by pressures exceeding 360 mmHg. All vessel ends were successfully sealed and bisected (80/80). The highest incident power, 59 W, yielded short treatment times of 5-6 s. Peak temperatures on the external chamber surface reached 103 oC. Time to cool down to body temperature measured 37 s. Infrared lasers simultaneously seal and bisect blood vessels, with treatment times comparable to, and temperatures and cooling times lower than reported for conventional devices. Future work will focus on integrating the fiber and chamber into a standard 5-mm-outer-diameter laparoscopic device. Customization of fiber scan length to match vessel size may also reduce laser energy deposition, enabling lower peak temperatures, treatment times, and cooling times.

A Real-Time Fluorescence Feedback System for Infrared Laser Sealing of Blood Vessels.

This study explores UV light induced fluorescence from blood vessels for indicating successful infrared laser sealing of vascular tissues. A light emitting diode (LED) with center wavelength of 340 nm and 0.1 mW power was used with a Y-shaped fiber bundle of seven 200-µm-core fibers. The central excitation fiber was connected to the LED, while the detection ring of six fibers was connected to a spectrometer. The fiber bundle was aligned with porcine renal arteries compressed between optical windows. Fluorescence was acquired before and after vessel sealing, with a 1470 nm laser for 5 s at 30 W (sealing, n = 10) or 5 W (control, n = 10). Signal increase in the 470-520 nm spectrum was correlated with vessel burst pressures (BP). Integrated fluorescence increased 71 ± 25% at 30 W vs. 19 ± 14% at 5 W (p < 0.05), corresponding to a successful BP of 639 ± 189 mmHg vs. failed seal BP of 39 ± 41 mmHg (p < 0.05). Real-time measurements showed a gradual increase in fluorescence with the signal reaching a plateau at 3-4 s, indicating that shorter seal times are possible. The increase in fluorescence signal during laser vessel sealing may provide a non-destructive, real-time, optical method for indicating hemostatic seals.

Comparison of quartz and sapphire optical chambers for infrared laser sealing of vascular tissues using a reciprocating, side-firing optical fiber: Simulations and experiments.

INTRODUCTION: Infrared (IR) lasers are being tested as an alternative to radiofrequency (RF) and ultrasonic (US) surgical devices for hemostatic sealing of vascular tissues. In previous studies, a side-firing optical fiber with elliptical IR beam output was reciprocated, producing a linear IR laser beam pattern for uniform sealing of blood vessels. Technical challenges include limited field-of-view of vessel position within the metallic device jaws, and matching fiber scan length to variable vessel sizes. A transparent jaw may improve visibility and enable custom treatment. METHODS: Quartz and sapphire square optical chambers (2.7 × 2.7 × 25 [mm3 ] outer dimensions) were tested, capable of fitting into a 5-mm-OD laparoscopic device. A 1470 nm laser was used for optical transmission studies. Razor blade scans and an IR beam profiler acquired fiber (550-µm-core/0.22NA) output beam profiles. Thermocouples recorded peak temperatures and cooling times on internal and external chamber surfaces. Optical fibers with angle polished distal tips delivered 94% of light at a 90° angle. Porcine renal arteries with diameters of 3.4 ± 0.7 mm (n = 13) for quartz and 3.2 ± 0.7 mm (n = 14) for sapphire chambers (p > 0.05), were sealed using 30 W for 5 s. RESULTS: Reflection losses at material/air interfaces were 3.3% and 7.4% for quartz and sapphire. Peak temperatures on the external chamber surface averaged 74 ± 8°C and 73 ± 10°C (p > 0.05). Times to cool down to 37°C measured 13 ± 4 s and 27 ± 7 s (p < 0.05). Vessel burst pressures (BP) averaged 883 ± 393 mmHg and 412 ± 330 mmHg (p < 0.05). For quartz, 13/13 (100%) vessels were sealed (BP > 360 mmHg), versus 9/14 (64%) for sapphire. Computer simulations for the quartz chamber yielded peak temperatures (78°C) and cooling times (16 s) similar to experiments. CONCLUSIONS: Quartz is an inexpensive material for use in a laparoscopic device jaw, providing more consistent vessel seals and faster cooling times than sapphire and current RF and US devices.

Nondestructive optical feedback systems for use during infrared laser sealing of blood vessels.

OBJECTIVES: High-power infrared lasers are capable of sealing blood vessels during surgery. A real-time diagnostic feedback system utilizing diffuse optical transmission is characterized by nondestructive identification of vessel seals. MATERIALS AND METHODS: For real-time diffuse optical transmission experiments, two approaches were studied. First, a low-power (1.2 mW) visible aiming beam (635 nm) was used for diagnostics, co-aligned with the therapeutic high-power infrared beam (1470 nm). Second, the 1470 nm beam was used simultaneously for both therapy and diagnostics. For both studies, the 1470-nm laser delivered 5 W for 5 seconds for unsuccessful seals (control) versus 30 W for 5 seconds for successful seals, using a linear beam profile (8.4 × 2 mm). Diffuse optical transmission signals were correlated with vessel burst pressures measured using a standard burst pressure setup. RESULTS: Diffuse optical transmission studies using the low-power, 635-nm aiming beam were promising. A decrease in the visible transmitted signal of 59 ± 11% was measured for successful seals versus 23 ± 8% for failed seals (p = 5.4E-8). The use of the high-power, 1470-nm infrared laser for simultaneous therapeutics and diagnostics proved inconsistent and unreliable, due in part to the dynamic and rapid changes in water content and absorption during the seal. CONCLUSIONS: A low-power, visible aiming beam, integrated with the therapeutic high-power infrared diode laser, may be used as a real-time diagnostic system for indicating successful laser seals, based on significant changes in optical scattering and diffuse optical transmission between native and coagulated compressed vessels. With further development, this simple and inexpensive optical feedback system may be integrated into a laparoscopic device for laser de-activation upon successful vessel sealing.

Comparison of fiber-optic linear beam shaping designs for laparoscopic laser sealing of vascular tissues.

Infrared lasers may provide faster and more precise sealing of blood vessels and with lower device jaw temperatures than ultrasonic and electrosurgical devices during surgery. Our study explores three beam shaping methods using optical fibers for transformation of a circular laser beam into a linear beam, necessary for integration into a standard 5-mm-diameter laparoscopic device, and for uniform irradiation perpendicular to the vessel length. In the first design, a servo motor connected to a side-firing, 550-µm-core fiber, provided linear translation of a 2.0-mm-diameter circular beam, back, and forth, over either 5 or 11 mm scan lengths for sealing of small or large vessels. The second design used external beam splitters to divide laser power equally into three side-firing fibers, stacked side-by-side, producing a linear beam of 4 × 2 mm. The third design used external beam splitters with three forward-firing fibers and a slanted jaw surface, to produce a linear beam of 5 × 1.5 mm. Laser seals were performed, ex vivo, on 41 porcine renal arteries of 1- to 6-mm diameter (n ≥ 10 samples for each design). Each vessel was compressed to a fixed 0.4-mm-thickness, matching the optical penetration depth at 1470 nm. Vessels were irradiated with fluences of 636 to 800 J/cm2, which, based on previous studies, is sufficient for sealing, but not cutting. A burst pressure setup was used to evaluate vessel seal strength. Reciprocating fiber and fiber bundles produced mean burst pressures of 554 ± 142, 524 ± 132, 429 ± 99, and 390 ± 140 mmHg, respectively. All designs consistently sealed blood vessels, with burst pressures above hypertensive (180 mmHg) blood pressures. The reciprocating fiber produced the most uniform linear beam profile and aspect ratio but will require integration of the servo motor into a handpiece. Fiber bundle designs produced shorter, less uniform beams, but enable optical components to be assembled outside the handpiece.

Computational Simulations for Infrared Laser Sealing and Cutting of Blood Vessels.

Blood vessel burst pressures were simulated and predicted for sealing and cutting of vessels in a two-step process, using low (<25 W), medium (~100 W), and high (200 W) power lasers at a wavelength of 1470 nm. Monte Carlo optical transport, heat transfer, Arrhenius integral tissue damage simulations, and vessel pressure equations were utilized. The purpose of these studies was to first validate the numerical model by comparison with experimental results (for low and medium power) and then to use the model to simulate parameters that could not be experimentally tested (for high power). The goal was to reduce the large range of parameters (power, irradiation time, and linear beam dimensions) to be tested in future experiments, for achieving short vessel sealing/cutting times, minimal bifurcated seal zones (BSZ), and high vessel burst pressures. Blood vessels were compressed to 400 µm thickness. A wide range of linear beam profiles (1-5 mm widths and 8-9.5 mm lengths), incident powers (20-200 W) and clinically relevant irradiation times (0.5-5.0 s) were simulated and peak seal and cut temperatures as well as thermal seal zones, ablation zones, and BSZ computed. A simplistic mathematical expression was used to estimate vessel burst pressures based on seal width. Optimal low-power parameters were: 24W/5s/8×2mm (sealing) and 24W/5s/8×1mm (cutting), yielding a BSZ of 0.4 mm, corresponding to experimental burst pressures of ~450 mmHg. Optimal medium-power parameters were: 90W/1s/9.5×3mm (sealing) and 90W/1s/9.5×1mm (cutting), yielding a BSZ of 0.9 mm for burst pressures of ~1300 mmHg. Simulated only optimal high-power parameters were: 200W/0.5s/9×3 mm (sealing) and 200W/0.5s/9×1mm (cutting), yielding a BSZ of 0.9 mm and extrapolated to predict a seal strength of ~1300 mmHg. All lasers produced seal zones between 0.4-1.5 mm, corresponding to high vessel burst pressures of 300-1300 mmHg (well above normal systolic blood pressure of 120 mmHg). Higher laser powers enable shorter sealing/cutting times and higher vessel strengths.

High power holmium:YAG versus thulium fiber laser treatment of kidney stones in dusting mode: ablation rate and fragment size studies.

OBJECTIVES: The experimental Thulium fiber laser (TFL) is currently being studied as a potential alternative to the gold standard Holmium:YAG laser for lithotripsy. Recent advances in both Holmium and TFL technology allow operation at similar laser parameters for direct comparison. The use of a "dusting" mode with low pulse energy (0.2-0.4 J) and high pulse rate (50-80 Hz) settings, is gaining popularity in lithotripsy due to the desire to produce smaller residual stone fragments during ablation, capable of being spontaneously passed through the urinary tract. METHODS: In this study, Holmium and TFL were directly compared for 'dusting' using three laser groups, G1: 0.2 J/50 Hz/10 W; G2: 0.2 J/80 Hz/16 W; and G3: 0.4 J/80 Hz/32 W. Holmium laser pulse durations ranged from 200 to 350 µs, while TFL pulse durations ranged from 500 to 1,000 µs, due to technical limitations for both laser systems. An experimental setup consisting of 1 × 1 cm cuvette with 1 mm sieve was used with continuous laser operation time limited to ≤5 minutes. Calcium oxalate monohydrate stone samples with a sample size of n = 5 were used for each group, with average initial stone mass ranging from 216 to 297 mg among groups. RESULTS: Holmium laser ablation rates were lower than for TFL at all three settings (G1: 0.3 ± 0.2 vs. 0.8 ± 0.2; G2: 0.6 ± 0.1 vs. 1.0 ± 0.4; G3: 0.7 ± 0.2 vs. 1.3 ± 0.9 mg/s). The TFL also produced a greater percentage by mass of stone dust (fragments <0.5 mm) than Holmium laser. For all three settings combined, one out of 15 (7%) stones treated with Holmium laser were completely fragmented in ≤5 minutes compared to nine out of 15 (60%) stones treated with TFL. CONCLUSIONS: These preliminary studies demonstrate that the TFL is a promising alternative laser for lithotripsy when operated in dusting mode, producing higher stone ablation rates and smaller stone fragments than the Holmium laser. Clinical studies are warranted. Lasers Surg. Med. 51:522-530, 2019. © 2019 Wiley Periodicals, Inc.

Computer simulations of thermal tissue remodeling during transvaginal and transurethral laser treatment of female stress urinary incontinence.

BACKGROUND AND OBJECTIVES: A non-surgical method is being developed for treating female stress urinary incontinence by laser thermal remodeling of subsurface tissues with applied surface tissue cooling. Computer simulations of light transport, heat transfer, and thermal damage in tissue were performed, comparing transvaginal and transurethral approaches. STUDY DESIGN/MATERIALS AND METHODS: Monte Carlo (MC) simulations provided spatial distributions of absorbed photons in the tissue layers (vaginal wall, endopelvic fascia, and urethral wall). Optical properties (n,µa ,µs ,g) were assigned to each tissue at λ = 1064 nm. A 5-mm-diameter laser beam and incident power of 5 W for 15 seconds was used, based on previous experiments. MC output was converted into absorbed energy, serving as input for finite element heat transfer simulations of tissue temperatures over time. Convective heat transfer was simulated with contact probe cooling temperature set at 0°C. Variables used for thermal simulations (κ,c,ρ) were assigned to each tissue layer. MATLAB code was used for Arrhenius integral thermal damage calculations. A temperature matrix was constructed from ANSYS output, and finite sum was incorporated to approximate Arrhenius integral calculations. Tissue damage properties (Ea ,A) were used to compute Arrhenius sums. RESULTS: For the transvaginal approach, 37% of energy was absorbed in the endopelvic fascia target layer with 0.8% deposited beyond it. Peak temperature was 71°C, the treatment zone was 0.8-mm-diameter, and 2.4 mm of the 2.7-mm-thick vaginal wall was preserved. For transurethral approach, 18% energy was absorbed in endopelvic fascia with 0.3% deposited beyond the layer. Peak temperature was 80°C, treatment zone was 2.0-mm-diameter, and 0.6 mm of 2.4-mm-thick urethral wall was preserved. CONCLUSIONS: Computer simulations suggest that transvaginal approach is more feasible than transurethral approach. Lasers Surg. Med. 49:198-205, 2017. © 2016 Wiley Periodicals, Inc.

Infrared laser sealing of porcine vascular tissues using a 1,470 nm diode laser: Preliminary in vivo studies.

INTRODUCTION: Infrared (IR) lasers are being explored as an alternative to radiofrequency (RF) and ultrasonic (US) devices for rapid hemostasis with minimal collateral zones of thermal damage and tissue necrosis. Previously, a 1,470 nm IR laser sealed and cut ex vivo porcine renal arteries of 1-8 mm diameter in 2 seconds, yielding burst pressures greater than 1,200 mmHg and thermal coagulation zones less than 3 mm. This preliminary study describes in vivo testing of a handheld laser probe in a porcine model. METHODS: A handheld prototype with vessel/tissue clasping mechanism was tested on 73 blood vessels less than 6 mm diameter using 1,470 nm laser power of 35 W for 1-5 seconds. Device power settings, irradiation time, tissue type, vessel diameter, and histology sample number were recorded for each procedure. The probe was evaluated for hemostasis after sealing isolated and bundled arteriole/venous (A/V) vasculature of porcine abdomen and hind leg. Sealed vessel samples were collected for histological analysis of lateral thermal damage. RESULTS: Hemostasis was achieved in 57 of 73 seals (78%). The probe consistently sealed vasculature in small bowel mesentery, mesometrium, and gastrosplenic and epiploic regions. Seal performance was less consistent on hind leg vasculature including saphenous arteries/bundles and femoral and iliac arteries. Collagen denaturation averaged 1.6 ± 0.9 mm in eight samples excised for histologic examination. CONCLUSIONS: A handheld laser probe sealed porcine vessels, in vivo. Further probe development and laser parameter optimization is necessary before infrared lasers may be evaluated as an alternative to RF and US vessel sealing devices. Lasers Surg. Med. 49:366-371, 2017. © 2016 Wiley Periodicals, Inc.

Collateral damage to the ureter and Nitinol stone baskets during thulium fiber laser lithotripsy.

BACKGROUND: The experimental Thulium fiber laser (TFL) is currently being studied as a potential alternative lithotripter to the clinical gold standard Holmium:YAG laser. Safety studies characterizing undesirable Holmium:YAG laser-induced damage to ureter tissue and stone baskets have been previously reported. Similarly, this study characterizes TFL induced ureter and stone basket damage. METHODS: A TFL beam with energy of 35 mJ per pulse, pulse duration of 500 µs, and variable pulse rates of 50-500 Hz, was delivered through 100-µm-core optical fibers, to either porcine ureter wall, in vitro, or a standard 1.9-Fr Nitinol stone basket wire. Ureter perforation times were measured and gross, histological, and optical coherence tomography images of the ablation area were acquired. Stone basket damage was graded as a function of pulse rate, number of pulses, and working distance. RESULTS: TFL operation at 150, 300, and 500 Hz produced mean ureter perforation times of 7.9, 3.8, and 1.8 seconds, respectively. Collateral damage widths averaged 510, 370, and 310 µm. Nitinol wire damage decreased with working distance and was non-existent at distances greater than 1.0 mm. In contact mode, 500 pulses delivered at pulse rates ≥300 Hz (≤1.5 seconds) were sufficient to cut Nitinol wires. CONCLUSIONS: The TFL, operated in low pulse energy and high pulse rate mode, may provide a greater safety margin than the standard Holmium:YAG laser for lithotripsy, as evidenced by longer TFL ureter perforation times and shorter non-contact working distances for stone basket damage than previously reported with Holmium:YAG laser.

Selective laser vaporization of polypropylene mesh used in treatment of female stress urinary incontinence and pelvic organ prolapse: preliminary studies using a red diode laser.

BACKGROUND AND OBJECTIVES: The most common mesh-related complication experienced by patients undergoing transvaginal polypropylene synthetic slings for stress urinary incontinence (SUI) and transvaginal pelvic organ prolapse (POP) repair with mesh is vaginal mesh erosion. More than half of the patients who experience erosion from synthetic mesh require surgical excision which is technically challenging and risks damage to healthy adjacent tissue. This study explores selective laser vaporization of polypropylene suture/mesh materials commonly used in SUI and POP. MATERIALS AND METHODS: A compact, 7 Watt, 647-nm, red diode laser was operated with a radiant exposure of 81 J/cm(2) , pulse duration of 100 milliseconds, and 1.0-mm-diameter laser spot. The 647-nm wavelength was selected because its absorption by water, hemoglobin, and other tissue chromophores is low, while polypropylene absorption is high. Laser vaporization of ∼200-µm-diameter polypropylene suture/mesh strands, in contact with fresh urinary tissue samples was performed, ex vivo. Temperature mapping of suture/mesh samples with a thermal camera was also conducted. RESULTS: Selective vaporization of polypropylene suture and mesh using a single laser pulse was achieved with peak temperatures of 180 and 232°C, respectively, while direct laser irradiation of tissue alone resulted in only a 1°C temperature increase. CONCLUSIONS: Selective laser vaporization of polypropylene suture/mesh materials is feasible without significant thermal elevation in the adjacent tissue. This technique may be useful for treatment of eroded mesh after SUI or POP procedures that require surgical revision.

Reciprocating Side-Firing Fiber for Laser Sealing of Blood Vessels.

Infrared lasers may provide faster and more precise sealing of blood vessels and with lower jaw temperatures than ultrasonic and electrosurgical devices. This study explores an oscillating or reciprocating side-firing optical fiber method for transformation of a circular laser beam into a linear beam, necessary for integration into a standard 5-mm-diameter laparoscopic device, and for uniform irradiation perpendicular to the vessel length. A servo motor connected to a side-firing, 550-µm-core fiber, provided linear translation of a 2.0-mm-diameter circular beam over either 5 mm or 11 mm scan lengths for sealing small or large vessels, respectively. Laser seals were performed, ex vivo, on a total of 20 porcine renal arteries of 1-6 mm diameter (n = 10 samples for each scan length). Each vessel was compressed to a fixed 0.4-mm-thickness, matching the 1470-nm laser optical penetration depth. Vessels were irradiated with fluences ranging from 636 J/cm2 to 716 J/cm2. A standard burst pressure (BP) setup was used to evaluate vessel seal strength. The reciprocating fiber produced mean BP of 554 ± 142 and 524 ± 132 mmHg, respectively, and consistently sealing blood vessels, with all BP above hypertensive (180 mmHg) blood pressures. The reciprocating fiber provides a relatively uniform linear beam profile and aspect ratio, but will require integration of servo motor into a handpiece.

Real-Time, Nondestructive Optical Feedback Systems for Infrared Laser Sealing of Blood Vessels.

High-power infrared (IR) diode lasers are capable of sealing blood vessels during surgery. This study characterizes an optical feedback system for real-time, nondestructive identification of vessel seals. A low power, red aiming beam (635 nm) was used for diagnostics, co-aligned with a therapeutic high-power IR beam (1470 nm). The IR laser delivered either 30 W for 5 s for successful seals or 5 W for 5 s for unsuccessful seals (control). All studies used a linear beam measuring 8.4 × 2.0 mm. Optical signals for successful and failed seals were correlated with vessel burst pressures (BP) using destructive testing via a standard BP setup. Light scattering increased significantly as vessels were coagulated. Successful seals correlated with a percent decrease in optical transmission signal of 59 ± 11 % and seal failures to a transmission decrease of 23 ± 8% (p < 0.01). With further development, the real-time optical feedback system may be integrated into a laparoscopic device to de-activate the laser upon successful vessel sealing.

Optical Coherence Tomography Feedback System for Infrared Laser Sealing of Blood Vessels.

Infrared (IR) lasers have recently been tested as an alternative to electrosurgical and ultrasonic laparoscopic devices for optical sealing of blood vessels. IR laser technology previously demonstrated faster sealing times, reduced thermal spread, and lower device temperatures during experimental studies. However, current commercial laparoscopic devices incorporate electrical impedance and/or temperature sensors as real-time, closed-loop, feedback to indicate successful blood vessel seals. This preliminary study explores an infrared laser system for sealing and optical coherence tomography (OCT) as a potential feedback system for successful vessel seal verification. A 1470-nm diode laser delivered an incident power of 30 W for an irradiation time of 5 s using an 8 × 2 mm linear beam, for creating strong seals in porcine renal blood vessels under compression. After sealing the blood vessels, OCT was performed on unsealed and sealed vessel regions for comparison. Standard vessel burst pressure (BP) measurements confirmed successful seals after OCT. Integrated reflectance intensity in OCT A-scans decreased by an average of 20 ± 6% in sealed versus native vessels of 2.4 ± 0.4 mm diameter. Vessel BP measured 532 ± 239 mmHg, with all vessels (n = 25) recording a successful BP > 180 mmHg (hypertensive blood pressure). Unsealed vessels demonstrated significantly deeper imaging marked by a continuous decay in reflected intensity, while sealed vessels showed subsurface reflectance intensity peaks, immediately followed by a rapid decay in reflectance intensity. These markers are consistent with increased light scattering and decreased optical penetration depth upon thermal coagulation of tissues. A-line OCT data consistently differentiated between sealed and unsealed blood vessel regions. Future work will involve OCT integration into the laparoscopic device for real-time optical feedback during IR laser sealing.

Contact focusing multimodal microprobes for ultraprecise laser tissue surgery.

Focusing of multimodal beams by chains of dielectric microspheres assembled directly inside the cores of hollow waveguides is studied by using numerical ray tracing. The device designs are optimized for laser surgery in contact mode with strongly absorbing tissue. By analyzing a broad range of parameters it is demonstrated that chains formed by three or five spheres with a refractive index of 1.65-1.75 provide a two-fold improvement in spatial resolution over single spheres at the cost of 0.2-0.4 attenuation in peak intensity of the central focused beam. Potential applications include ultra precise laser ablation or coagulation in the eye and brain, cellular surgery, and the coupling of light into photonic nanostructures.

Noninvasive laser coagulation of the human vas deferens: optical and thermal simulations.

BACKGROUND AND OBJECTIVES: Successful noninvasive laser coagulation of the canine vas deferens, in vivo, has been previously reported. However, there is a significant difference between the optical properties of canine and human skin. In this study, Monte Carlo (MC) simulations of light transport through tissue and heat transfer simulations are performed to determine the feasibility of noninvasive laser vasectomy in humans. MATERIALS AND METHODS: A laser wavelength of 1,064 nm was chosen for deep optical penetration in tissue. MC simulations determined the spatial distribution of absorbed photons inside the tissue layers (epidermis, dermis, and vas). The results were convolved with a 3-mm-diameter laser beam, and then used as the spatial heat source for the heat transfer model. A laser pulse duration of 500 milliseconds, pulse rate of 1 Hz, and cryogen spray cooling were incident on the tissue for 60 seconds. Average laser power (5-9 W), cryogen pulse duration (60-100 milliseconds), cryogen cooling rate (0.5-1.0 Hz), and increase in optical transmission due to optical clearing (0-50%) were studied. RESULTS: After application of an optical clearing agent (OCA) to increase skin transmission by 50%, an average laser power of 6 W, cryogen pulse duration of 60 milliseconds, and cryogen cooling rate of 1 Hz resulted in vas temperatures of approximately 58°C, sufficient for thermal coagulation, while 1 mm of the skin surface (epidermis and dermis) remained at a safe temperature of approximately 45°C. CONCLUSIONS: MC and heat transfer simulations indicate that it is possible to noninvasively thermally coagulate the human vas deferens without adverse effects (e.g., scrotal skin burns), if an OCA is applied to the skin prior to the procedure.

High-frequency ultrasound imaging of noninvasive laser coagulation of the canine vas deferens.

BACKGROUND AND OBJECTIVES: A noninvasive approach to vasectomy may eliminate male fear of complications related to surgery (e.g., hematoma, infection, acute and chronic pain, sterilization failure) and increase its acceptance. Noninvasive laser thermal occlusion of the canine vas deferens has recently been reported. In this study, high-frequency ultrasound is used to confirm successful laser thermal coagulation and scarring of the vas in a short-term canine model. MATERIALS AND METHODS: Bilateral noninvasive laser coagulation of the vas was performed in a total of nine dogs using a laser wavelength of 1,075 nm, incident power of 9.0 W, pulse duration of 500 milliseconds, pulse rate of 0.5 Hz, and 3-mm-diameter spot. Cryogen spray was used to cool the scrotal skin surface and prevent burns during the procedure. A clinical ultrasound system with a 13.2-MHz high-frequency transducer was used to image the vas before and after the procedure. Burst pressure measurements were performed on excised vas to confirm thermal occlusion. RESULTS: Day 0 and 28 burst pressures averaged 291 ± 31 mmHg and 297 ± 26 mmHg, respectively, significantly greater than ejaculation pressures of 136 ± 29 mmHg. Ultrasound showed a hyperechoic vas segment after thermal coagulation (Day 0) and scarring (Day 28). Doppler ultrasound showed normal blood flow through the testicular artery, indicating no collateral thermal damage to proximal structures. CONCLUSIONS: High-frequency ultrasound may be used as a noninvasive diagnostic tool to assist in determining successful short-term laser thermal coagulation and scarring of the vas.

Sealing and Bisection of Blood Vessels using a 1470 nm Laser: Optical, Thermal, and Tissue Damage Simulations.

A 1470-nm laser previously demonstrated faster sealing and cutting of blood vessels with lower thermal spread than radiofrequency and ultrasonic surgical devices. This study simulates laser sealing and cutting of vessels in a sequential two-step process, for low (< 25 W), medium (~ 100 W), and high (200 W) power lasers. Optical transport, heat transfer, and tissue damage simulations were conducted. The blood vessel was assumed to be compressed to 400 µm thickness, matching previous experimental studies. A wide range of linear beam profiles (1-5 mm widths and 8-9.5 mm lengths), incident powers (20-200 W) and irradiation times (0.5-5.0 s), were simulated. Peak seal and cut temperatures and bifurcated thermal seal zones were also simulated and compared with experimental results for model validation. Optimal low power laser parameters were: 24W/5s/8×2mm for sealing and 24W/5s/8×1mm for cutting, yielding thermal spread of 0.4 mm and corresponding to experimental vessel burst pressures (BP) of ~450 mmHg. Optimal medium-power laser parameters were: 90 W/1s/9.5×3mm for sealing and 90W/1s/9.5×1mm for cutting, yielding thermal spread of 0.9 mm for BP of ~1300 mmHg. Optimal high-power laser parameters were: 200W/0.5s/9×3mm for sealing and 200W/0.5s/9×1mm for cutting, yielding thermal spread of 0.9 mm and extrapolated to have BP of ~1300 mmHg. All lasers produced seal zones between 0.4-1.5 mm, correlating to high BP of 300-1300 mmHg. Higher laser powers enable shorter sealing and cutting times and higher vessel seal strengths.

Dynamic properties of surfactant-enhanced laser-induced vapor bubbles for lithotripsy applications.

SIGNIFICANCE: Water is a primary absorber of infrared (IR) laser energy, and urinary stones are immersed in fluid in the urinary tract and irrigated with saline during IR laser lithotripsy. Laser-induced vapor bubbles, formed during lithotripsy, contribute to the stone ablation mechanism and stone retropulsion effects. AIM: Introduction of a surfactant may enable manipulation of vapor bubble dimensions and duration, potentially for more efficient laser lithotripsy. APPROACH: A surfactant with concentrations of 0%, 5%, and 10% was tested. A single pulse from a thulium fiber laser with wavelength of 1940 nm was delivered to the surfactant through a 200-µm-core optical fiber, using a wide range of laser parameters, including energies of 0.05 to 0.5 J and pulse durations of 250 to 2500 µs. RESULTS: Bubble length, width, and duration with surfactant increased on average by 29%, 17%, and 120%, compared with water only. CONCLUSIONS: Our study demonstrated successful manipulation of laser-induced vapor bubble dimensions and duration using a biocompatible and commercially available surfactant. With further study, use of a surfactant may potentially improve the "popcorn" technique of laser lithotripsy within the confined space of the kidney, enable non-contact laser lithotripsy at longer working distances, and provide more efficient laser lithotripsy.

Thulium fiber laser lithotripsy using tapered fibers.

INTRODUCTION: The Thulium fiber laser has recently been tested as a potential alternative to the Holmium:YAG laser for lithotripsy. This study explores use of a short taper for expanding the Thulium fiber laser beam at the distal tip of a small-core fiber. METHODS: Thulium fiber laser radiation with a wavelength of 1,908 nm, 10 Hz pulse rate, 70 mJ pulse energy, and 1-millisecond pulse duration was delivered through a 2-m-length fiber with 150-microm-core-input-end, 300-microm-core-output-end, and 5-mm-length taper, in contact with human uric acid (UA) and calcium oxalate monohydrate (COM) stones, ex vivo (n = 10 each). Stone mass loss, stone crater depths, fiber transmission losses, fiber burn-back, irrigation rates, and deflection through a flexible ureteroscope were measured for the tapered fiber and compared with conventional fibers. RESULTS: After delivery of 1,800 pulses through the tapered fiber, mass loss measured 12.7+/-2.6 mg for UA and 7.2+/-0.8 mg COM stones, comparable to conventional 100-microm-core fibers (12.6+/-2.5 mg for UA and 6.8+/-1.7 mg for COM stones). No transmission losses or burn-back occurred for the tapered fiber after 36,000 pulses, while a conventional 150-microm fiber experienced significant tip degradation after only 1,800 pulses. High irrigation rates were measured with the tapered fiber inserted through the working port of a flexible ureteroscope without hindering its deflection, mimicking that of a conventional 150 microm fiber. CONCLUSIONS: The short tapered distal fiber tip allows expansion of the laser beam, resulting in decreased fiber tip damage compared to conventional small-core fibers, without compromising fiber bending, stone vaporization efficiency, or irrigation rates.