Computational Simulations for Infrared Laser Sealing and Cutting of Blood Vessels

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.

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.

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.

Basic performance of domestic surgical robot and the safety and effectiveness of integrated energy equipment

OBJECTIVES

Surgical robot system has broken the limitation of traditional surgery and shown excellent performance in surgery, and has been widely used in minimally invasive treatment in most areas of surgery. This study aims to verify the basic performance of the domestic surgical robot system and the safety and effectiveness of the integrated bipolar electrocoagulation and ultrasonic knife.

METHODS

The basic performance of the domestic surgical robot system was evaluated by completing the square knot and surgical knot, vertical and horizontal perforation and right ring perforation and suture, as well as picking up beans. Compared with laparoscopy, the safety and effectiveness of the domestic surgical robot after integrated interconnection bipolar electrocoagulation and ultrasonic scalpel were evaluated by detecting the vascular closure performance and the degree of histopathological damage in animals.

RESULTS

Compared with freehand knotting, domestic robot knotting speed and circumference were slightly worse, but better than laparoscopic knotting. There was no statistical significance in the tension difference of the surgical knots among the 3 methods (P>0.05), but the tension of the square knots made by the freehand and the domestic surgical robot was greater than that of the laparoscopy (P<0.05). The space required for both the left and right forceps heads of knots was smaller than that of laparoscopy (P<0.001), which successfully completed the 4 quadrant suture tasks, and the time of picking up beans was significantly less than that of laparoscopy (P<0.05). There was no significant difference in the temperature of the liver tissue after the bipolar electrocoagulation between the interconnected domestic surgical robot and the laparoscopy (P>0.05), and the acute thermal injury was observed under the light microscope. The temperature of the liver tissue treated by the domestic robotic ultrasound knife was higher than that of the laparoscopic ultrasound knife (P<0.05).

CONCLUSIONS

Domestic surgical robots are obviously superior to laparoscopy in suturing, knotting, and moving objects, and domestic surgical robots' interconnect bipolar electrocoagulation and ultrasonic knife have achieved success in animal experiments, and hemostasis is considered to be safe and effective.

Laser coagulation and hemostasis of large diameter blood vessels: effect of shear stress and flow velocity

Photocoagulation of blood vessels offers unambiguous advantages to current radiofrequency approaches considering the high specificity of blood absorption at available laser wavelengths (e.g., 532 nm and 1.064 µm). Successful treatment of pediatric vascular lesions, such as port-wine stains requiring microvascular hemostasis, has been documented. Although laser treatments have been successful in smaller diameter blood vessels, photocoagulation of larger sized vessels is less effective. The hypothesis for this study is that a primary limitation in laser coagulation of large diameter blood vessels (500-1000 µm) originates from shear stress gradients associated with higher flow velocities along with temperature-dependent viscosity changes. Laser (1.07 µm) coagulation of blood vessels was tested in the chicken chorio-allantoic membrane (CAM). A finite element model is developed that includes hypothetical limitations in laser coagulation during irradiation. A protocol to specify laser dosimetry is derived from OCT imaging and angiography observations as well as finite element model results. Laser dosimetry is applied in the CAM model to test the experimental hypothesis that blood shear stress and flow velocity are important parameters for laser coagulation and hemostasis of large diameter blood vessels (500-1000 µm). Our experimental results suggest that shear stress and flow velocity are fundamental in the coagulation of large diameter blood vessels (500-1000 µm). Laser dosimetry is proposed and demonstrated for successful coagulation and hemostasis of large diameter CAM blood vessels.

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.

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.

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.