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.

Detachable microsphere scalpel tips for potential use in ophthalmic surgery with the erbium:YAG laser.

Vitreoretinal surgery is performed using mechanical dissection that sometimes results in iatrogenic complications, including vitreous hemorrhage, retinal breaks, incomplete membrane delamination, retinal distortion, microscopic damage, etc. An ultraprecise laser probe would be an ideal tool for cutting away pathologic membranes; however, the depth of surgery should be precisely controlled to protect the sensitive underlying retina. The ultraprecise surgical microprobe formed by chains of dielectric spheres for use with the erbium:YAG laser source (λ=2940 nm), with extremely short optical penetration depth in tissue, was optimized. Numerical modeling demonstrated a potential advantage of five-sphere focusing chains of sapphire spheres with index n=1.71 for ablating the tissue with self-limited depth around 10 to 20 µm. Novel detachable microsphere scalpel tips formed by chains of 300 µm sapphire (or ruby) spheres were tested on ophthalmic tissues, ex vivo. Detachable scalpel tips could allow for reusability of expensive mid-infrared trunk fibers between procedures, and offer more surgical customization by interchanging various scalpel tip configurations. An innovative method for aiming beam integration into the microsphere scalpel to improve the illumination of the surgical site was also shown. Single Er:YAG pulses of 0.2 mJ and 75-µs duration produced ablation craters in cornea epithelium for one, three, and five sphere structures with the latter generating the smallest crater depth (10 µm) with the least amount of thermal damage depth (30 µm). Detachable microsphere laser scalpel tips may allow surgeons better precision and safety compared to mechanical scalpels when operating on delicate or sensitive areas like the retina.

Continuous-wave laser stimulation of the rat prostate cavernous nerves using a compact and inexpensive all single mode optical fiber system.

BACKGROUND AND PURPOSE: Laser stimulation of the rat cavernous nerve (CN) recently has been demonstrated as an alternative to electrical stimulation for potential application in nerve mapping during nerve-sparing radical prostatectomy. Advantages include noncontact stimulation and improved spatial selectivity. Previous studies, however, have used large and/or expensive laser sources for stimulation. This study demonstrates the feasibility of optical stimulation of the rat CN, in vivo, using a compact, inexpensive all-single-mode fiberoptic system. MATERIALS AND METHODS: A 1455-nm wavelength infrared diode laser beam was coupled into a 9-µm-core single-mode fiber for delivery through a 10F laparoscopic probe and used for laser stimulation of the CN in a total of eight rats, in vivo. RESULTS: Laser stimulation of the CN was observed at threshold temperatures of 41°C, with intracavernous pressure response times as short as 4 s, and magnitudes up to 50 mm Hg, compared with baselines of 10 mm Hg. CONCLUSION: This novel, all-single-mode-fiber laser nerve stimulation system introduces several advantages including: (1) lower cost laser; (2) more robust fiberoptic design, eliminating alignment and cleaning of bulk optical components; and (3) improved Gaussian spatial beam profile for simplified alignment of the laser beam with the nerve. With further development, laser nerve stimulation may be useful for identification and preservation of the CN during prostate cancer surgery.

Noninvasive laser vasectomy: preliminary ex vivo tissue studies.

BACKGROUND AND OBJECTIVES: Male sterilization (vasectomy) is more successful, safer, less expensive, and easier to perform than female sterilization (tubal ligation). However, female sterilization is more popular, primarily due to male fear of vasectomy complications (incision, bleeding, infection, and scrotal pain). The development of a completely noninvasive vasectomy technique may eliminate these concerns. MATERIALS AND METHODS: Ytterbium fiber laser radiation with a wavelength of 1,075 nm, average power of 11.7 W, 1-second pulse duration, 0.5 Hz pulse rate, and 3-mm-diameter spot was synchronized with cryogen cooling of the scrotal skin surface in canine tissue for a treatment time of 60 seconds. RESULTS: Vas thermal lesion dimensions measured 2.0+/-0.3 mm diameter by 3.0+/-0.9 mm length, without evidence of skin damage. The coagulated vas bursting pressure measured 295+/-72 mm Hg, significantly higher than typical vas ejaculation pressures of 136+/- 29 mm Hg. CONCLUSIONS: Noninvasive thermal coagulation and occlusion of the vas was produced in an ex vivo canine tissue model. However, chronic in vivo animal studies will be necessary to optimize the laser/cooling treatment parameters and confirm long-term vas occlusion with absence of sperm in the ejaculate, before clinical application.

New laser treatment approaches for benign prostatic hyperplasia.

The recent introduction of higher power 100 W holmium:yttrium-aluminum-garnet (Ho:YAG) and 80 W potassium titanyl phosphate lasers for rapid incision and vaporization of the prostate has resulted in renewed interest in the use of lasers for treatment of benign prostatic hyperplasia (BPH). Although long-term studies are still lacking, short-term results demonstrate that these procedures are at least as safe and effective in relieving BPH symptoms as transurethral resection of the prostate and may provide reduced morbidity. Other laser techniques, such as interstitial laser coagulation and contact laser vaporization of the prostate, have lost popularity due to complications with increased catheterization time, irritative symptoms, and infection rates. Although Ho:YAG laser enucleation of the prostate is more difficult to learn and a slower procedure than potassium titanyl phosphate laser vaporization, the Ho:YAG laser is currently the most proven laser technique for BPH treatment. This article reviews the latest developments in laser treatment of BPH over the past 2 years and provides a view toward the future of lasers in the treatment of BPH.

Comparison of germanium oxide fibers with silica and sapphire fiber tips for transmission of erbium: YAG laser radiation.

BACKGROUND AND OBJECTIVES: Endoscopic applications of the Erbium:YAG laser have been limited due to the lack of a suitable optical fiber delivery system. The purpose of this study was to compare the transmission of Er:YAG laser radiation through germanium oxide trunk fibers with silica and sapphire fiber tips for potential use in contact tissue ablation during endoscopy. STUDY DESIGN/MATERIALS AND METHODS: Er:YAG laser radiation with a wavelength of 2.94 microm, pulse length of 300 microseconds, pulse energies from 5 to 1,360 mJ, coupled into pulse repetition rates of 3-10 Hz, was through 1-m-long germanium oxide fibers with either 1-cm-long, 550-microm-diameter silica or sapphire tips. RESULTS: Transmission through the germanium oxide/sapphire fibers measured 65+/-5% compared with 55+/-4% for the germanium oxide/silica fibers (P<0.05). The damage threshold for the hybrid fibers averaged 309+/- 44 mJ and 126+/-43 mJ, respectively (n = 7 fibers each) (P<0.05). The highest pulse energies transmitted through the fibers were 700 mJ and 220 mJ, respectively. CONCLUSIONS: Improved index-matching of the trunk fiber and fiber tip at 2.94 microm resulted in higher transmission and damage thresholds for the germanium oxide/sapphire fibers. The germanium oxide/sapphire fiber may represent a promising mid-infrared optical fiber delivery system for use in endoscopic applications of the Er:YAG laser requiring a flexible, biocompatible, and robust fiber delivery system for contact tissue ablation.

Erbium:YAG laser lithotripsy using hybrid germanium/silica optical fibers.

BACKGROUND AND PURPOSE: Previous studies have demonstrated that the erbium:YAG laser is two to three times more efficient for laser lithotripsy than the holmium:YAG laser. However, the lack of a suitable optical fiber delivery system remains a major obstacle to clinical application of Er:YAG laser lithotripsy. This paper describes the initial testing of a hybrid germanium oxide/silica optical fiber for potential endoscopic use with the Er:YAG laser. MATERIALS AND METHODS: Er:YAG laser radiation with a wavelength of 2.94 microm, a pulse energy of 10 to 600 mJ, a pulse length of 220 microsec, and pulse-repetition rates of 3 to 10 Hz was focused into either 350- or 425- microm-core hybrid germanium/silica fibers in contact with human uric acid or calcium oxalate monohydrate stones. RESULTS: Average Er:YAG pulse energies of 157 +/- 46 mJ (66 J/cm(2)) (N = 8) were delivered at 10 Hz through the 425-microm hybrid fibers in contact with urinary stones before fiber damage was observed. A maximum pulse energy of 233 mJ (98 J/cm(2)) was also measured through the hybrid fiber in contact with the stones. These values are significantly greater than the stone ablation thresholds of 15 to 23 mJ (6-10 J/cm(2)) and the fiber damage thresholds measured for germanium oxide, 18 +/- 1 mJ (13 J/cm(2)), and sapphire, 73 mJ (51 J/cm(2)), optical fibers during Er:YAG laser lithotripsy (P < 0.05). CONCLUSIONS: A prototype hybrid germanium/silica optical fiber demonstrated better performance than both germanium oxide and sapphire fibers for transmission of Er:YAG laser radiation during in vitro lithotripsy.

Transmission of Q-switched erbium:YSGG (lambda=2.79 microm) and erbium:YAG (lambda=2.94 microm) laser radiation through germanium oxide and sapphire optical fibres at high pulse energies.

The erbium:YSGG and erbium:YAG lasers are used for tissue ablation in dermatology, dentistry and ophthalmology. The purpose of this study was to compare germanium oxide and sapphire optical fibres for transmission of sufficient Q-switched erbium laser pulse energies for potential use in both soft and hard tissue ablation applications. Fibre transmission studies were conducted with Q-switched (500 ns) Er:YSGG (lambda=2.79 microm) and Er:YAG (lambda=2.94 microm) laser pulses delivered at 3 Hz through 1-m-long, 450-mum germanium oxide and 425-mum sapphire optical fibres. Transmission of free-running (300 micros) Er:YSGG and Er:YAG laser pulses was also conducted for comparison. Each set of measurements was carried out on seven different sapphire or germanium fibres, and the data were then averaged. Fibre attenuation of Q-switched Er:YSGG laser energy measured 1.3+/-0.1 dB/m and 1.0+/-0.2 dB/m for the germanium and sapphire fibres, respectively. Attenuation of Q-switched Er:YAG laser energy measured 0.9+/-0.3 dB/m and 0.6+/-0.2 dB/m, respectively. A maximum Q-switched Er:YSGG pulse energy of 42 mJ (26-30 J/cm(2)) was transmitted through the fibres. However, fibre tip damage was observed at energies exceeding 25 mJ (n=2). Both germanium oxide and sapphire optical fibres transmitted sufficient Q-switched Er:YSGG and Er:YAG laser radiation for use in both soft and hard tissue ablation. This is the first report of germanium and sapphire fibre optic transmission of Q-switched erbium laser energies of 25-42 mJ per pulse.

High-intensity focused ultrasound ablation of the epididymis in a canine model: a potential alternative to vasectomy.

BACKGROUND AND PURPOSE: High-intensity focused ultrasound (HIFU) is a noninvasive technology capable of inducing thermal coagulative necrosis of subsurface structures without injuring intervening tissues. We have previously reported on the feasibility of HIFU vasectomy in a canine model. In this study, we evaluated the feasibility of HIFU ablation of the canine epididymis as an alternative to vasectomy. The epididymis may be a better target than the vas deferens because it is larger, more easily positioned in the HIFU focal zone, and more susceptible to occlusive injury at lower energy levels, thus reducing collateral damage. MATERIALS AND METHODS: A hand-held HIFU clamp was used to grasp the epididymides of anesthetized dogs (eight surgically exposed and six grasped transcutaneously). An ultrasound transducer in the clamp focused energy on a 1 x 3 x 8-mm target zone centered between the clamp jaws. Ultrasonic energy (6-19 W) was delivered to this target zone for various times (16-150 seconds). The vas, epididymis, and testis were harvested for histologic examination 2 weeks after ablation. RESULTS: Seven of the eight epididymides ablated after surgical exposure demonstrated histologic findings associated with occlusion (fibrosis, hemorrhage, and proximal duct dilatation). Five of the six epididymides ablated transcutaneously also demonstrated histologic evidence of occlusion. Skin burns were evident overlying three epididymides, and one testicular injury was noted adjacent to an ablated region of the epididymis. CONCLUSION: High-intensity focused ultrasound ablation of the epididymis causes injury and histologic changes associated with epididymal occlusion. Further investigations are under way to optimize ablation parameters and to confirm azoospermia with ejaculate studies. Refinement of this technology may provide a rapid noninvasive alternative to conventional vasectomy.