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.

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.

Optical coherence tomography for use in infrared laser sealing of blood vessels.

Infrared lasers may provide faster sealing of vascular tissues with less collateral thermal damage and lower device temperatures than radiofrequency and ultrasonic devices currently used for surgery. Optical coherence tomography is tested to image native and thermally coagulated blood vessels, as a potential feedback system.

Novel Optical Linear Beam Shaping Designs for use in Laparoscopic Laser Sealing of Vascular Tissues.

Suture ligation of vascular tissues is slow and skill intensive. Ultrasonic (US) and radiofrequency (RF) devices enable more rapid vascular tissue ligation to maintain hemostasis, than sutures and mechanical clips, which leave foreign objects in the body and require exchange of instruments. However, US and RF devices are limited by excessive collateral thermal damage to adjacent tissues, and high jaw temperatures that require a long time to cool. A novel alternative method using infrared (IR) laser energy is being developed for more rapid and precise sealing of vessels. This study describes design, modeling, and initial testing of several optical beam shaping geometries for integration into the standard jaws of a laparoscopic device. The objective was to transform the circular laser beam into a linear beam, for uniform, cross-irradiation and sealing of blood vessels. Cylindrical mirrors organized in a staircase geometry provided the best spatial beam profile.Clinical Relevance-This study explored several optical designs for potential integration into the standard jaws of a laparoscopic vessel sealing device, transforming a circular laser beam into a linear beam for sealing of vascular structures.

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.

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

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).

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.

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.

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.

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, lowpower, 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 mum. The red diode laser may represent an inexpensive, compact, and safer alternative laser for use in laser suture lysis during ophthalmic surgery.

Noninvasive thermal coagulation of deep subsurface tissue structures using a laser probe with integrated contact cooling.

Cooling methods are used during cosmetic laser surgery to preserve a superficial layer of the skin surface. This study investigates contact cooling for sparing a deeper layer of the tissue surface during laser irradiation of subsurface tissues, with the goal of developing noninvasive laser therapy applications beyond cosmetic surgery. A laser probe was designed and tested for simultaneous laser irradiation and contact cooling of liver tissue, ex vivo. Gross and histologic examination was used to quantify thermal lesion dimensions. Liver lesions of 5.8-mm-diameter were created, while preserving the tissue surface to a depth of 1.5 mm. In vivo animal studies are planned to optimize the laser and cooling parameters for potential clinical applications.