Ablation of porcine ligamentum flavum with Ho:YAG, q‐switched Ho:YAG, and quadrupled Nd:YAG lasers

Abstract

Background and ObjectivesLigamentum flavum (LF) is a tough, rubbery connective tissue providing a portion of the ligamentous stability to the spinal column, and in its hypertrophied state forms a significant compressive pathology in degenerative spinal stenosis. The interaction of lasers and this biological tissue have not been thoroughly studied. Technological advances improving endoscopic surgical access to the spinal canal makes selective removal of LF using small, flexible tools such as laser‐coupled fiber optics increasingly attractive for treatment of debilitating spinal stenosis. Testing was performed to assess the effect of Ho:YAG, Q‐switched Ho:YAG, and frequency quadrupled Nd:YAG lasers on samples of porcine LF. The objective was to evaluate the suitability of these lasers for surgical removal of LF.Study Design/Materials and MethodsLF was resected from porcine spine within 2 hours of sacrifice and stored in saline until immediately prior to laser irradiation, which occurred within an additional 2 hours. The optical absorbance of a sample was measured over the spectral band from 190 to 2,360 nm both before and after dehydration. For the experiments using the Ho:YAG (λ = 2,080 nm, t p = 140 µs, FWHM) and Q‐Switched Ho:YAG (λ = 2,080 nm, t p = 260 ns, FWHM) lasers, energy was delivered to the LF through a laser‐fiber optic with 600 µm core and NA = 0.39. For the experiment using the frequency quadrupled Nd:YAG laser (λ = 266 nm, t p = 5 ns FWHM), rather than applying the laser energy through a laser‐fiber, the energy was focused through an aperture and lens directly onto the LF. Five experiments were conducted to evaluate the effect of the given lasers on LF. First, using the Ho:YAG laser, the single‐pulse laser‐hole depth versus laser fluence was measured with the laser‐fiber in direct contact with the LF (1 g force) and with a standoff distance of 1 mm between the laser‐fiber face and the LF. Second, with the LF remaining in situ and the spine bisected along the coronal plane, the surface temperature of the LF was measured with an IR camera during irradiation with the Ho:YAG laser, with and without constant saline flush. Third, the mass loss was measured over the course of 450 Ho:YAG pulses. Fourth, hole depth and temperature were measured over 30 pulses of fixed fluence from the Ho:YAG and Q‐Switched Ho:YAG lasers. Fifth, the ablation rate and surface temperature were measured as a function of fluence from the Nd:YAG laser. Several LF staining and hole‐depth measurement techniques were also explored.ResultsAside from the expected absorbance peaks corresponding to the water in the LF, the most significant peaks in absorbance were located in the spectral band from 190 to 290 nm and persisted after the tissue was dehydrated. In the first experiment, using the Ho:YAG laser and with the laser‐fiber in direct contact with the LF, the lowest single‐pulse fluence for which LF was visibly removed was 35 J/cm2. Testing was conducted at 6 fluences between 35 and 354 J/cm2. Over this range the single‐pulse hole de...

Trans-Sacral Epiduroscopic-Assisted 1,414-nm Nd:YAG Laser Decompression for Lumbar Discal Cyst: A Report of 9 Cases

“…Our study confirmed that a SELD-assisted, 1,414-nm Nd:YAG laser can effectively treat lumbar discal cyst 7,12,14) . However, this study had some limitations.…”

“…Therefore, SELD Currently, trans-sacral, epiduroscopicassisted, 1,414-nm Nd:YAG laser decompression (SELD) is commonly used for spinal pathologies and has been used as a minimally invasive procedure because it is associated with better visualization, precise pathology targeting, minimal collateral tissue disruption, and less bleeding. These advantages make the surgery easier to perform, improve healing, and minimize the risk of patient discomfort 7,14,18) . To the best of our knowledge, however, no studies have assessed the efficacy of the SELD-assisted, 1,414-nm Nd:YAG laser for the treatment of lumbar discal cyst.…”

Automating neurosurgical tumor resection surgery: Volumetric laser ablation of cadaveric porcine brain with integrated surface mapping

“…This study, however, is unique in that it measures a large volumetric resection of tissue. Ablation properties are more commonly characterized through mass loss experiments or measurements of cross sectional width and depth of ablation craters recorded from thin slices of stained and fixed tissue . This requires, of course, that the sample be destroyed to obtain measurements.…”

“…However, within the setting of laser‐human tissue interactions (specifically the brain), much remains to be characterized. Characterization of the laser‐tissue interaction between these various pathologic and non‐pathologic tissue types (as performed in previous publications) will be essential to provide the ablation and coagulation inputs necessary to estimate the amount of tissue removed or cauterized with each cut and plan a cutting path. Once various tissues and tumor types are characterized, real‐time sensor feedback can then be used to create a controller that is capable of predicting ablation efficiency prior to each cut, as has been shown in simulation .…”

Programmable Control of the Pulse Repetition Rate in the Multiwave Strontium Vapor Laser System

“…Plenty of works are devoted to the study of parameters of laser radiation on the material [1][2][3][4]. However there are no separate studies on the effect of the pulse repetition rate on the ablation process and, in some cases, this parameter is a result of preselected durations and energies of the laser pulse.…”