Christopher M. Cilip

Thulium Fiber Laser Ablation of Urinary Stones Through Small-Core Optical Fibers

Complications during laser lithotripsy include optical fiber bending failure resulting in endoscope damage and low irrigation rates leading to poor visibility. Both problems are related to fiber diameter and limited by the holmium:YAG (Ho:YAG) laser (lambda = 2120 nm) multimode beam profile. This study exploits the thulium fiber laser (lambda = 1908 nm) beam profile for higher power transmission through smaller fibers. Thulium fiber laser radiation with 1 ms pulse duration, pulse rates of 10-30 Hz, and 70-mu m-diameter spot was coupled into silica fibers with 100, 150, and 200 mum core diameters. Fiber transmission, bending, and endoscope irrigation tests were performed. Damage thresholds for 100, 150, and 200 mum fibers averaged 40, 60, and > 80 W, respectively. Irrigation rates measured 35, 26, and 15 mL/min for no fiber, and 100 and 200 mum fibers. Thulium fiber laser energy of 70 mJ delivered at 20 Hz through a 100 mum fiber resulted in vaporization and fragmentation rates of 10 and 60 mg/min for uric acid stones. The thulium fiber laser beam profile provides higher laser power through smaller fibers than Ho:YAG laser, potentially reducing fiber failure and endoscope damage, and allowing greater irrigation rates for improved visibility.

Continuous-wave infrared optical nerve stimulation for potential diagnostic applications.

Optical nerve stimulation using infrared laser radiation has recently been developed as a potential alternative to electrical nerve stimulation. However, recent studies have focused primarily on pulsed delivery of the laser radiation and at relatively low pulse rates. The objective of this study is to demonstrate faster optical stimulation of the prostate cavernous nerves using continuous-wave (cw) infrared laser radiation for potential diagnostic applications. A thulium fiber laser (λ=1870 nm) is used for noncontact optical stimulation of the rat prostate cavernous nerves in vivo. Optical nerve stimulation, as measured by an intracavernous pressure (ICP) response in the penis, is achieved with the laser operating in either cw mode, or with a 5-ms pulse duration at 10, 20, 30, 40, 50, and 100 Hz. Successful optical stimulation is observed to be primarily dependent on a threshold nerve temperature (42 to 45 °C), rather than an incident fluence, as previously reported. cw optical nerve stimulation provides a significantly faster ICP response time using a lower power (and also less expensive) laser than pulsed stimulation. cw optical nerve stimulation may therefore represent an alternative mode of stimulation for intraoperative diagnostic applications where a rapid response is critical, such as identification of the cavernous nerves during prostate cancer surgery.

Application of an optical clearing agent during noninvasive laser coagulation of the canine vas deferens

Development of a noninvasive vasectomy technique may eliminate male fear of complications and result in a more popular procedure. This study explores application of an optical clearing agent (OCA) to scrotal skin to reduce laser power necessary for successful noninvasive laser vasectomy and eliminate scrotal skin burns. A mixture of dimethyl sulfoxide and glycerol was noninvasively delivered into scrotal skin using a pneumatic jet device. Near-infrared laser radiation was delivered in conjunction with cryogen spray cooling to the skin surface in a canine model, ex vivo and in vivo. Burst pressure (BP) measurements were conducted to quantify strength of vas closure. A 30-min application of OCA improved skin transparency by 26+/-3%, reducing average power necessary for successful noninvasive laser vasectomy from 9.2 W without OCA (BP=291+/-31 mmHg) to 7.0 W with OCA (BP=292+/-19 mmHg). Control studies without OCA at 7.0 W failed to coagulate the vas with burst pressures (82+/-28 mmHg) significantly below typical ejaculation pressures (136+/-29 mmHg). Application of an OCA reduced the laser power necessary for successful noninvasive thermal coagulation of the vas by approximately 25%. This technique may result in use of a less expensive laser and eliminate the formation of scrotal skin burns during the procedure.

Infrared laser thermal fusion of blood vessels: preliminary ex vivo tissue studies.

Abstract. Suture ligation of blood vessels during surgery can be time-consuming and skill-intensive. Energy-based, electrosurgical, and ultrasonic devices have recently replaced the use of sutures and mechanical clips (which leave foreign objects in the body) for many surgical procedures, providing rapid hemostasis during surgery. However, these devices have the potential to create an undesirably large collateral zone of thermal damage and tissue necrosis. We explore an alternative energy-based technology, infrared lasers, for rapid and precise thermal coagulation and fusion of the blood vessel walls. Seven near-infrared lasers (808, 980, 1075, 1470, 1550, 1850 to 1880, and 1908 nm) were tested during preliminary tissue studies. Studies were performed using fresh porcine renal vessels, ex vivo, with native diameters of 1 to 6 mm, and vessel walls flattened to a total thickness of 0.4 mm. A linear beam profile was applied normal to the vessel for narrow, full-width thermal coagulation. The laser irradiation time was 5 s. Vessel burst pressure measurements were used to determine seal strength. The 1470 nm laser wavelength demonstrated the capability of sealing a wide range of blood vessels from 1 to 6 mm diameter with burst strengths of 578±154, 530±171, and 426±174  mmHg for small, medium, and large vessel diameters, respectively. Lateral thermal coagulation zones (including the seal) measured 1.0±0.4  mm on vessels sealed at this wavelength. Other laser wavelengths (1550, 1850 to 1880, and 1908 nm) were also capable of sealing vessels, but were limited by lower vessel seal pressures, excessive charring, and/or limited power output preventing treatment of large vessels (>4  mm outer diameter).

Noninvasive laser vasectomy: Preliminary ex vivo tissue studies

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.

Application of optical coherence tomography and high-frequency ultrasound imaging during noninvasive laser vasectomy

A noninvasive approach to vasectomy may eliminate male fear of complications related to surgery and increase its acceptance. Noninvasive laser thermal occlusion of the canine vas deferens has recently been reported. Optical coherence tomography (OCT) and high-frequency ultrasound (HFUS) are compared for monitoring laser thermal coagulation of the vas in an acute canine model. Bilateral noninvasive laser coagulation of the vas was performed in six dogs (n=12 vasa) using a Ytterbium fiber laser wavelength of 1075 nm, incident power of 9.0 W, pulse duration of 500 ms, pulse rate of 1 Hz, and 3-mm-diameter spot. Cryogen spray cooling was used to prevent skin burns during the procedure. An OCT system with endoscopic probe and a HFUS system with 20-MHz transducer were used to image the vas immediately before and after the procedure. Vasa were then excised and processed for gross and histologic analysis for comparison with OCT and HFUS images. OCT provided high-resolution, superficial imaging of the compressed vas within the vas ring clamp, while HFUS provided deeper imaging of the vas held manually in the scrotal fold. Both OCT and high HFUS are promising imaging modalities for real-time confirmation of vas occlusion during noninvasive laser vasectomy.

Noninvasive laser coagulation of the canine vas deferens, in vivo

Development of a noninvasive vasectomy technique may eliminate male fear of complications (incision, bleeding, infection, and scrotal pain) and result in a more popular procedure. This study builds upon previously reported ex vivo tissue studies by exploring acute and short-term chronic in vivo canine studies. Isolation of the canine vas was achieved using a conventional vas ring clamp method. No perforation of the scrotal skin was necessary to occlude the vas. Laser radiation with a wavelength of 1075 nm, average power of 11.2 W, 500-ms pulse duration, 0.5 Hz pulse rate, and 3-mm-diameter spot was synchronized with cryogen spray cooling of the scrotal skin surface in a total of 8 dogs (n = 16 vasa) for a treatment time of 60 s. Burst pressure measurements were conducted at Days 0 and 21 (n = 8 vasa each day) to quantify the strength of vas closure. The vas was successfully thermally occluded in 15/16 (94%) procedures with 14/15 (93%) vas recording burst pressures above ejaculation pressure. One vas was not present, and another vas recorded a bursting pressure below ejaculation pressure. The coagulated vas bursting pressure averaged 283 ± 34 mm Hg at Day 0 and 260 ± 77 mm Hg at Day 21, significantly higher than reported vas ejaculation pressures of 136 ± 29 mm Hg. Minor scrotal skin burns were observed during the recovery period. Noninvasive thermal occlusion of the vas is feasible in an in vivo canine model. Elimination of minor skin burns and longer term chronic in vivo canine studies are needed to confirm azospermia after vas occlusion without recanalization.

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

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.

Selective laser suture lysis with a compact, low-cost, red diode laser

The argon (blue-green) laser is currently used for vaporization of sutures during ophthalmic surgery. However, previous studies have reported more effective laser suture lysis and a lower rate of complications using the krypton (red) laser. Red wavelengths are selectively absorbed by the nylon sutures, but are minimally absorbed by adjacent tissue, and not absorbed by hemoglobin, unlike the argon laser wavelengths. More compact and less expensive red diode lasers have recently become commercially available for surgical applications. This study explores the use of a compact, low-power, red diode laser for selective laser suture lysis. A 225 mW, 660-nm diode laser was used to vaporize 10-0 nylon sutures in human cornea samples with a single laser pulse, pulse energy of 150 mJ, pulse duration of 100 ms, and spot diameter of 55 μm. The red diode laser may represent an inexpensive, compact, and safer alternative laser for use in laser suture lysis during ophthalmic surgery.

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

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.