Laser Fibers:Application of a flexible CO2 laser fiber for neurosurgery

Keywords:laser fibers, medical fibers, Co2 Laser,  Time:16-02-2016

For example, Stellar et al.20 reported the first resection of a glioblastoma multiforme using a CO2 laser in 1970, and commented that its use for “additional otherwise hopeless human brain tumours is now warranted.” Perhaps the strongest endorsement came from Ascher and Heppner3 who identified numerous indications for the CO2 laser in both central and peripheral surgical cases, and remarked that the only contraindication to use of the laser “occurs if somebody uses the laser to solve his Ego problems.

Unfortunately, cumbersome ergonomics of the CO2 laser have limited its widespread use. Its long wavelength (10.6 µm) prevents its transmission using standard Medical fiber optic cables, and bulky articulating arms with mirrors are required to transmit sufficient energy to the surgical site in direct line of sight, restricting freedom of movement.18 Moreover, resecting a tumor requires constant refocusing of the CO2 beam if it is coupled to a microscope. Without fiber optic delivery, use of a CO2 laser through an endoscope is impossible. These shortcomings have kept most neurosurgeons from adopting the CO2 laser as a regular surgical tool, despite its many potential benefits. Dielectric mirrors are able to efficiently reflect light through a narrow range of incident angles with low absorption losses.10 The existence of an omnidirectional reflection band allows a dielectric surface to reflect light of any incident angle, known as omnidirectional reflectance.11 A hollow optical fiber has been created that is lined with an interior omnidirectional dielectric mirror that has a photonic bandgap for the transmission of CO2 laser light with low absorptive losses.22 This PBF assembly allows for the flexible delivery of CO2 laser energy in a range of power settings similar to those used for surgical fiber applications with rigid delivery systems, but with the advantage of using a laser delivery apparatus that is on a small scale and does not use a large, inconvenient assembly. This is the first histological study to assess a newly developed tool that allows for the flexible delivery of CO2 laser energy to brain tissue. The differences between a focused, line-of-sight, free-space optical beam and a handheld fiber with a 320-µm aperture and no focal plane are subtle but important. The purpose of this study was to demonstrate that these differences do not impact the qualitative nature of the laser-tissue interaction and to assess the handling characteristics of the PBF CO2 laser on the brain tissue of a large animal, simulating its use in humans. Specifically, experiments were conducted using a swine craniotomy model to compare cortical incisions created using the laser with other incisions created using conventional means, such as bipolar cautery using microscissors, as well as a scalpel.

Photonic Bandgap Fiber Setup The PBF used for these experiments (Fig. 1) consisted of a disposable hollow core fiber (BeamPath Neuro-L fiber, OmniGuide Inc.) connected to a CO2 laser source (Lumenis Compact Series 30C, Lumenis Ltd.). The fiber used had an outer diameter of 1.2 mm and produced a 320-µm laser spot size at the tip. Laser energy was adjusted from 2 to 20 W, in continuous wave or pulsed mode. Before use in experiments, the laser output power was checked to ensure proper calibration, and the fiber was positioned in a handpiece. Study Ethical Approval This study was conducted at the Neurosurgery Research Laboratories in the Division of Neurological Surgery of the Barrow Neurological Institute and St. Joseph’s Hospital and Medical Center, with experimental approval from the St. Joseph’s Hospital and Medical Center’s Institutional Animal Care and Use Committee. Laser Application to Cortex Six adult female swine were used for this study. Under deep general inhalant anesthesia using a cuffed endotracheal tube, a craniotomy was performed to widely expose both cerebral hemispheres. In 4 animals (8 hemispheres), a positioning device was used to hold either the laser handpiece, or a Malis CMC-III Bipolar Cut and Coagulation System (tips fixed at 0.5-mm separation; Codman and Shurtleff, Inc.) in 90° approximation to the most prominent portion of a cortical gyrus. Laser or bipolar cautery energy was then delivered for a specified power setting and time duration (Table 1). The lesion points were marked with India ink and fixed with acetic acid for later identification during histopathological assessment. The region of the gyrus containing the lesion was then resected with a wide margin and immediately placed in 10% formalin for histopathological analysis. In 2 animals (4 hemispheres), incision lines were created by freehand application of the laser fiber within its handpiece (2 and 7 W), Malis bipolar cautery (with and without microscissor incision of pia), or a No. 11 scalpel blade. Incisions were 1 cm in length, in the center of the gyrus. In 2 hemispheres, the gyri were resected with a margin around the incision line and immediately placed in 10% formalin for histopathological analysis. In the other 2 hemispheres, the gyri were resected with a margin around the incision line and immediately placed in a 2.5% glutaraldehyde solution for electron microscopy. At the conclusion of the experiments, the animals were killed while still under deep anesthesia.

Tissue samples fixed in formalin were stained with H & E for light microscopy and lesion zones were characterized and measured (Fig. 2A and B). For laser incisions, the total depth of the incision was measured to the deepest point of tissue effect (bottom of edematous zone), the desiccated depth was measured to the deepest point of desiccated tissue (between desiccated and edematous zones), and the crater depth was measured to the deepest point at which all tissue had been vaporized. For bipolar cautery lesions, total depth and desiccated depth were measured, but no craters were present.