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Holmium:YAG laser has been the lithotrite of choice for around 30 years in kidney stone surgery. Lasers have evolved over the years to offer higher power, increased pulse frequencies and longer pulse durations. The drivers for change have been to improve stone ablation and to minimise retropulsion. We report on a new prototype Holmium laser that fires multiple “micro-pulses” in “pulse packets” and discuss the stone phantom ablation rate results utilizing a bench model. The prototype laser demonstrated impressive stone ablation rates in our bench testing across a range of power settings. We will discuss the details of these results supporting that pulse-modulation with packets of micro-pulses are a promising technological development. (Disclaimers: Bench Test results may not necessarily be indicative of clinical performance. The testing was performed by or on behalf of BSC.

Stone retropulsion during laser lithotripsy results from various physical phenomena such as recoil momentum, bubble dynamics, and subsequent jet formation. Considerable stone retropulsion has been observed whereby the optical energy is converted into both mechanical and thermal energy as a distinctive bubble generation and collapse. It is hypothesized that by reducing the peak power and lengthening the pulse duration, we can reduce this conversion of optical energy into mechanical energy. This should maximize the thermal effects on the stone leading to enhanced ablation efficiency as well as less stone “chasing”. We are reporting on a new prototype Holmium laser with low pulse power and long temporal pulse durations in an attempt to minimize stone retropulsion.

Welcome and Introduction to SPIE Photonics West BiOS conference 11619: Advanced Photonics in Urology.

Cystoscope cleaning and sterilization are one of the most important procedures to prevent infection in urological surgery. The current cleaning techniques have demonstrated lengthy process times or insufficient decontamination of flexible cystoscopes. Thus, high-level disinfection and sterilization are still needed to enhance cleaning efficacy. The current study demonstrated the feasibility of a combination of 405-nm laser and infrared (IR) lights to inactivate bacterial biofilms inside the working channels. Staphylococcus strains in suspension (concentration ~ 108 CFU/mL) were incubated in 24 hours at 37 0C to form biofilms on multi-well plates. Each sample initially experienced 5-minute IR dehydration (intensity = 1.5 W/cm2), and 405-nm laser system was then used for bacterial disinfection at various conditions: 19.1, 38.2, 57.3, and 76.4 J/cm2. An IR camera was deployed for real-time monitoring temperature on the biofilm surface. MTT assay was employed to assess cell viability after the treatment. The results showed that staphylococcus bacteria in liquid suspension were more resistant to 405-nm laser light than those in hard surfaces. In addition, the 405-nm laser treatment resulted in less decontaminating effectiveness while the 405-nm laser in conjunction with IR light could induce bacterial reduction up to 75% possibly due to effect low temperature dehydration. The proposed technique can be a useful modality for cystoscope cleaning and sterilization to prevent any secondary infection in the urinary tract during urological procedures. Further experiments will be conducted to validate reprocessing efficacy on various types of bacterial biofilm models along with high-level disinfectants to find the optimal cleaning doses.

Temperature variations are often monitored by using sensors operating at the site of treatment during Laser-induced Interstitial Thermotherapy (LITT). Currently, temperature measurements during LITT have been performed with thermocouples (TCs). However, TCs could directly absorb laser light and lead to self-heating (resulting in an over-estimation). Fiber Bragg grating (FBG) sensors can instead overcome this limitation of the TCs due to its insensitivity to electromagnetic interference. The aim of the current study was to quantitatively evaluate the FBG temperature sensor with a K-type thermocouple to real-time monitor temperature increase in ex vivo tissue during diffuser-assisted LITT. A 4-W 980-nm laser was employed to deliver optical energy in continuous mode through a 600-µm core-diameter diffusing applicator. A goniometric measurement validated the uniform light distribution in polar and longitudinal directions. The FBG sensor showed a linear relationship (R2 = 0.995) between wavelength shift and temperature change in air and tissue along with a sensitivity of ~ 0.0114 nm/˚C. Regardless of sensor type, the measured temperature increased with irradiation time and applied power but decreased with increasing distance from the diffuser surface. The temperature elevation augmented the degree of thermal coagulation in the tissue during LITT (4.0±0.3-mm at 99˚C after 120-s). The temperature elevation augmented the degree of thermal coagulation in the tissue during LITT s irradiation). The FBG-integrated diffuser was able to monitor the interstitial temperature in tubular tissue (porcine urethra) real-time during laser treatment. However, the thermal coagulation thickness of the porcine urethra was measured to be 1.5 mm that was slightly thicker (~20%) than that of the bovine liver after 4-W 980-nm laser for 48 s. The FBG temperature sensor can be a feasible tool to real-time monitor the temporal development of the temperature during the diffuser-assisted LITT to treat urethral disease.

For last two decades, endovenous laser therapy (EVLT) is one of the most widely accepted surgical options for treating incompetent great and small saphenous veins. However, due to excessive heating during EVLT, the major complications include pain and burning that often increase the risk of dermatitis disease. The aim of the current study was to quantitatively compare commercially-available radial fibers with newly-developed diffusing applicators for 1470 nm-EVLA in terms of temperature elevation and vein deformation. Rabbit veins were used as an ex vivo model for EVLA. A 5-W 1470 nm laser system in conjunction with the radial and diffusing fibers was employed to thermally coagulate the venous tissue. A goniometric measurement validated uniform and isotropic distribution of laser light in polar and longitudinal directions (i.e., normalized intensity = 0.84±0.08). The diffusing applicator induced a 20 % lower maximum temperature than the radial fiber did (maximum temperature = 79.2 °C for radial vs. 63.3 °C for diffusing). Due to higher irradiance, the radial fiber was associated with a transient temperature change of 5.9 °C/s, which was 1.5-fold faster than the diffusing applicator (i.e., 2.4 °C/s). However, the degree of cross-sectional area reduction in the veins was almost comparable for both the fibers (i.e., 53% for radial vs. 48% for diffusing). Due to longer irradiation length, the diffusing applicator demonstrated wider treatment coverage and less fiber speed-dependent. On account of easy pullback technique and uniform thermal effect, the proposed cylindrically diffusing applicator can be a feasible optical device to effectively treat varicose veins. Further in vivo studies will be performed to identify the complete removal of the vein disease and healing response of the venous tissue.

Previous studies have shown that photothemal therapy combined with high intensity focused ultrasound (HIFU) can provide a promising method to achieve rapid thermal coagulation during surgical procedures. The current study investigated the feasibility of the laser-integrated high intensity focused ultrasound (HIFU) application to treat bladder tumors by enhancing thermal effects and therapeutic depth in vitro. To generate thermal coagulation, a single element HIFU transducer with a central frequency of 2.0 MHz was used to transmit acoustic energy to 15 fresh porcine bladders injected with an artificial tumor (100 µl gelatin and hemoglobin solution) in vitro. Simultaneously, an 80-W 532-nm laser system was also implemented to induce thermal necrosis in the targeted tissue. The intensity of 570 W/cm2 at the focus of HIFU and laser energy of 0.9 W were applied to all the samples for 40 s. The temperature rise increased up to about 1.6 or 3 folds (i.e., ΔT=32±3.8 K for laser-integrated HIFU, ΔT=20±6.5 K for HIFU only, and ΔT=11±5.6 K for laser only). The estimated lesion depth also increased by 1.3 and 2 folds during the dual-thermal treatment, in comparison with the treatment by either HIFU or laser. The results indicated that the laser-integrated HIFU treatment can be an efficient hyperthermic method for tumor coagulation.

Optical fibers have frequently been used for photothermal laser therapy due to its efficiency to deliver laser energy directly to tissue. The aim of the current study was to develop a diffusing optical fiber to achieve radially uniform light irradiation for endoscopically treating urethral stricture. The optical diffuser was fabricated by micro-machining helical patterns on the fiber surface using CO2 laser light at 5 W. Visible light emission (632 nm) and spatial emissions (including polar, azimuthal, and longitudinal emissions) of the fiber tip were evaluated to validate the performance of the fabricated diffuser. Prior to tissue tests, numerical simulation on heat distribution was developed to estimate the degree of tissue coagulation depth during interstitial coagulation. Due to a high absorption coefficient by tissue water, 1470 nm laser was used for photothermal therapy treatment of urethral stricture to obtain a more precise depth profile. For in vitro tissue tests, porcine liver tissue was irradiated with three different power levels (3, 6, and 9 W) at various irradiation times. Porcine urethral tissue was also tested with the diffuser for 10 sec at 6 W to validate the feasibility of circumferential photothermal treatment. The treated tissue was stained with hematoxylin and eosin (H and E) and then imaged with an optical transmission microscope. The spatial emission characteristics of the diffusing optical fiber presented an almost uniform power distribution along the diffuser tip (less than 10% deviation) and around its circumference (less than 5% deviation). The peak temperature in simulation model at the tissue interface between the glass-cap and the tissue was 373 K that was higher than that at the distal end. The tissue tests showed that higher power levels resulted in lower coagulation thresholds (e.g., 1 sec at 9 W vs 8 sec at 3 W). Furthermore, the coagulation depth was approximately 20% thinner than the simulation results (p

High Intensity Focused Ultrasound (HIFU) technology provides a feasible method of achieving thermal coagulation during surgical procedures. One of the potential clinical benefits of HIFU can induce immediate hemostasis without suturing. The objective of this study was to investigate the efficiency of a HIFU system for blood coagulation on severe vascular injury. HIFU treatment was implemented immediately after bleeding in artery. The ultrasound probe was made of piezoelectric material, generating a central frequency of 2.0 MHz as well as an ellipsoidal focal spot of 2 mm in lateral dimension and 10 mm in axial dimension. Acoustic coagulation was employed on a perfused chicken artery model in vitro . A surgical incision (1 to 2 mm long) was made with a scapel on the arterial wall, and heparinized autologous blood was made to leak out from the incision with a syringe pump. A total of 5 femoral artery incisions was treated with the HIFU beam. The intensity of 4500 W/cm 2 at the focus was applied for all treatments. Complete hemostasis was achieved in all treatments, along with the treatment times of 25 to 50 seconds. The estimated intraoperative blood loss was from 2 to 5 mL. The proposed HIFU system may provide an effective method for immediate blood coagulation for arteries and veins in clinical applications.

Q-switched Tm:YAG laser ablation mechanisms on urinary calculi are still unclear to researchers. In this study, dependence of water content in calculus phantom on calculus ablation performance was investigated. White gypsum cement was used as a calculus phantom model. The calculus phantoms were ablated at single pulse and contact mode in three different conditions: dry calculus in air, wet calculus in air, and wet calculus in water. Ablation volume was obtained on average 0.006, 0.008, and 0.008 mm 3 in dry calculus in air, wet calculus in air, and wet calculus in water groups, respectively. There were three proposed ablation mechanisms that could explain the effect of water content in calculus phantom on calculus ablation performance, including shock wave due to bubble collapse, spallation, and microexplosion. Shock wave generation due to bubble collapse in wet calculus in water condition had negligible effect on calculus ablation as captured by a needle hydrophone and cannot be a primary mechanism for calculus ablation in this study. Increased absorption coefficient of wet calculus can cause stronger spallation process compared with that caused by dry calculus; and as a result, higher calculus ablation was observed in both wet calculus in air and wet calculus in water. Vaporization of interstitial water in porous calculus phantom can also help enhance calculus ablation efficiency. There were some limitations in this study including use of small sample size and lack of employing real urinary calculus, which should be addressed in future experiment.

A novel MoXy TM fiber delivery device with Active Cooling Cap (ACC TM ) is designed to transmit up to 180W of 532 nm laser light to treat benign prostatic hyperplasia (BPH). Under such high power tissue ablation, effective cooling is key to maintaining fiber power transmission and ensuring the reliability of the fiber delivery device To handle high power and reduce fiber degradation, the MoXy fiber features a larger core size (750 micrometer) and an internal fluid channel to ensure better cooling of the fiber tip to prevent the cap from burning, detaching, or shattering during the BPH treatment. The internal cooling channel was created with a metal cap and tubing that surrounds the optical fiber. In this study MoXy fibers were used to investigate the effect of power levels of 120 and 200 W on in-vitro bovine prostate ablation using a 532 nm XPS TM laser system. For procedures requiring more than 100 kJ, the MoXy fiber at 200W removed tissue at twice the rate of the current HPS fiber at 120W. The fiber maintained a constant tissue vaporization rate during the entire tissue ablation process. The coagulation at 200W was about 20% thicker than at 120W. In conclusion, the new fibers at 200W doubled the tissue removal rate, maintained vaporization efficiency throughout delivery of 400kJ energy, and induced similar coagulation to the existing HPS fiber at 120W.

Photoselective vaporization of the prostate (PVP) is considered a minimally invasive procedure to treat benign prostatic hyperplasia (BPH). During the PVP, the prostate gland is irradiated by the 532-nm laser and the fiber is swept and dragged along the urethra. In this study the speed of sweeping fiber during the PVP is being investigated. In vitro porcine kidney model was used (N=100) throughout the experiment. A Q-switched 532-nm laser, equipped with sidefiring 750-Um fiber, was employed and set to power levels of 120 and 180 W. The speed of fiber sweeping was the only variable in this study and varied at 0 (i.e. no sweeping), 0.5, 1.0, 1.5, and 2.0 sweep/s. Ablation rate, depth, and coagulation thickness were quantified. Based on the current settings, ablation rate decreased as sweeping speed increased and was maximized between 0 to 1.0 sweep/s for 120-W power level and between 0 to 0.5 sweep/s for 180-W power level. Ablation rate at 180 W was higher than that at 120 W, regardless of sweeping speed. Ablation depth at both 120 and 180 W was maximized at 0 sweep/s and decreased 35% at 0.5 sweep/s. The overall coagulation thickness was less than 1.5 mm and comparable from 0 to 1.5 sweep/s (0.8~0.9 mm) and increased at 2.0 sweep/s (~1.1 mm). This study demonstrated that tissue ablation performance was contingent upon sweeping speed and maximized at slow sweeping speed due to longer laser-tissue interaction time and larger area coverage by the 532-nm light.

A previous in vitro study demonstrated that 180W was the optimal power to reduce photoselective vaporization of the prostate (PVP) time for larger prostate glands. In this study, we investigated anatomic and histologic outcomes and ablation parameters of 180W laser performed with a new 750-μm side-firing fiber in a survival study of living canines. Eight male canines underwent anterograde PVP with the 180W 532-nm laser. Four each animals were euthanized 3 hours or 8 weeks postoperatively. Prostates were measured and histologically analyzed after hematoxylin and eosin (H&E), triphenyltetrazolium chloride (TTC), or Gomori trichrome (GT) staining. Compared to the previous 120W laser, PVP with the 180W laser bloodlessly created a 76% larger cavity (mean 11.8 vs. 6.7 cm 3 ; p =0.014) and ablated tissue at a 77% higher rate (mean 2.3 vs. 1.3 cm 3 /min; p =0.03) while H&E- and TTC-staining demonstrated its 33% thicker mean coagulation zone (2.0±0.4 vs. 1.5±0.3 mm). H&E-stained cross-sectional prostatic tissue specimens from the 3-hour (acute) group showed histologic evolution of concentric non-viable coagulation zone, partially viable hyperemic transition zone of repair, and viable non-treated zone. H&E- and GT-stained specimens from the 8-week (chronic) group revealed healed circumferentially epithelialized, non-edematous, prostatic urethral channels with no increase in collagen in the subjacent prostatic tissue vis-a-vis the normal control. Our canine study demonstrates that 180W 532-nm laser PVP with its new fiber has a significantly higher ablation rate with a more hemostatic coagulation zone, but equally favorable tissue interaction and healing, compared with our previous 120W canine study.

Laser prostatectomy with various lasers has been shown to be effective in the treatment of benign prostate hyperplasia. However, the impact of laser parameters on tissue ablation is still in question. The aim of this study is to experimentally characterize laser-tissue interactions in terms of wavelength by comparing visible (λ= 532 nm) and infrared (λ= 2.01 μm) spectra. Porcine kidney tissue was used as it has thermal properties and glandular structure similar to human prostatic tissue. Q-switched 532 nm (GreenLight TM HPS) and continuous-wave (CW) 2.01 μm (custom-made Tm:YAG) lasers were employed to remove soft tissue under various settings (power, working distance, and treatment speed). For both laser systems, ablation rate increased with power and was maximized at 4 mm/s. The 532 nm laser generated approximately 30% (p

Laser therapy for obstructive benign prostatic hyperplasia (BPH) has gained broad adoption due to effective tissue removal, immediate hemostasis, and minor complications. The aim of this study is to quantitatively compare ablation characteristics of PV (Photoselective Vaporization) and the newly introduced HPS (High Performance System) 532 nm lasers. Bovine prostatic tissues were ablated in vitro , using a custom-made scanning system. Laser-induced volume produced by two lasers was quantified as a function of applied power, fiber working distance (WD), and treatment speed. Given the same power of 80 W and speed of 4 mm/s, HPS created up to 50 % higher tissue ablation volume than PV did. PV induced a rapid decrease of ablation volume when WD increased from 0.5 mm to 3 mm while HPS yielded almost constant tissue removal up to 3 mm for both 80 W and 120 W. As the treatment speed increased, both lasers reached saturation in tissue ablation volume. Lastly, both PV and HPS lasers exhibited approximately 1 mm thick heat affected zone (HAZ) in this study although HPS created twice deeper ablation channels with a depth of up to 4 mm. Due to a smaller beam size and a higher output power, HPS maximized tissue ablation rate with minimal thermal effects to the adjacent tissue. Furthermore, more collimated beam characteristics provides more spatial flexibility and may even help to decrease the rate of fiber degradation associated with thermal damage from debris reattachment to the tip.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this study, we investigated the role of water spray. To ablate human enamel tissue, a long-pulsed Er,Cr:YSGG laser was used at various radiant exposures. During dental ablation, distilled water was sprayed to the sample surface. Desiccated samples were also tested with direct irradiation for comparison. In order to identify dominant ablation mechanisms, transient acoustic waves were measured using a piezoelectric microphone. Enamel ablation efficiency was evaluated with Optical Coherence Tomography (OCT). Material removal was up to four times larger at the best flow rate with respect to ablation without spray. In spite of 60 % higher damage threshold by water absorption, spray ablation enhanced both the laser-induced acoustic transients up to six times and the ablation efficiency up to twice over the entire range of radiant exposures tested, compared to dry ablation. The improved pressure and ablation performance of the spray-assisted process with cooling effect were thought to be induced by recoil stress, rapid water vaporization, interstitial water explosion, and/or liquid-jet formation. Spray ablation along with water cooling and abrasive mechanical effects can be a safe and efficient modality for dental treatment.

Stone retropulsion during Ho:YAG ( λ = 2.12 μm) laser lithotripsy with various pulse durations (τ p : 250 ~ 495 μsec) was investigated. Depending on pulse energy, optical pulse durations were divided into two regimes: short pulse (250~350 μsec) and long pulse (315~495 μsec). Retropulsion distance was measured as a function of pulse energy from 0.4 J to 1.2 J. Calculus phantoms made from plaster of Paris were ablated with a free running Ho:YAG laser using various optical fibers (200, 400, 600 μm) in water. In order to examine the ablation efficiency of two different pulse durations, a single pulse was applied, and the dynamics of the recoil action of a calculus phantom was monitored using a high-speed camera. The correlation among laser-induced topography, ablation volume, and retropulsion was evaluated. Higher pulse energy and larger fibers resulted in larger ablation volume and retropulsion. At a given pulse energy, optical pulses with different durations yielded comparable ablation volumes. The shorter duration pulses induced more retropulsion than longer pulses did at the same pulse energy. Larger retropulsion with the shorter pulse is thought to be induced by higher temperature at the vapor-solid interface, subsequently resulting in faster plume ejection with higher recoil momentum. The results suggest that a longer pulse could minimize retropulsion of the stone during lithotripsy.