{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2023,9,19]],"date-time":"2023-09-19T08:42:07Z","timestamp":1695112927641},"reference-count":32,"publisher":"Wiley","issue":"10","license":[{"start":{"date-parts":[[2015,9,28]],"date-time":"2015-09-28T00:00:00Z","timestamp":1443398400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/"}],"funder":[{"name":"Department of the Air Force","award":["FA8721-05-C-0002"],"award-info":[{"award-number":["FA8721-05-C-0002"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Lasers Surg Med"],"published-print":{"date-parts":[[2015,12]]},"abstract":"<jats:sec><jats:title>Background and Objectives<\/jats:title><jats:p>Ligamentum 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\u2010coupled fiber optics increasingly attractive for treatment of debilitating spinal stenosis. Testing was performed to assess the effect of Ho:YAG, Q\u2010switched 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.<\/jats:p><\/jats:sec><jats:sec><jats:title>Study Design\/Materials and Methods<\/jats:title><jats:p>LF was resected from porcine spine within 2\u2009hours of sacrifice and stored in saline until immediately prior to laser irradiation, which occurred within an additional 2\u2009hours. The optical absorbance of a sample was measured over the spectral band from 190 to 2,360\u2009nm both before and after dehydration. For the experiments using the Ho:YAG (<jats:italic>\u03bb<\/jats:italic>\u2009=\u20092,080\u2009nm, <jats:italic>t<\/jats:italic><jats:sub>p<\/jats:sub>\u2009=\u2009140\u2009\u00b5s, FWHM) and Q\u2010Switched Ho:YAG (<jats:italic>\u03bb<\/jats:italic>\u2009=\u20092,080\u2009nm, <jats:italic>t<\/jats:italic><jats:sub>p<\/jats:sub>\u2009=\u2009260\u2009ns, FWHM) lasers, energy was delivered to the LF through a laser\u2010fiber optic with 600\u2009\u00b5m core and NA\u2009=\u20090.39. For the experiment using the frequency quadrupled Nd:YAG laser (<jats:italic>\u03bb<\/jats:italic>\u2009=\u2009266\u2009nm, <jats:italic>t<\/jats:italic><jats:sub>p<\/jats:sub>\u2009=\u20095\u2009ns FWHM), rather than applying the laser energy through a laser\u2010fiber, 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\u2010pulse laser\u2010hole depth versus laser fluence was measured with the laser\u2010fiber in direct contact with the LF (1\u2009g force) and with a standoff distance of 1\u2009mm between the laser\u2010fiber face and the LF. Second, with the LF remaining <jats:italic>in situ<\/jats:italic> 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\u2010Switched 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\u2010depth measurement techniques were also explored.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>Aside 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\u2009nm and persisted after the tissue was dehydrated. In the first experiment, using the Ho:YAG laser and with the laser\u2010fiber in direct contact with the LF, the lowest single\u2010pulse fluence for which LF was visibly removed was 35\u2009J\/cm<jats:sup>2<\/jats:sup>. Testing was conducted at 6 fluences between 35 and 354\u2009J\/cm<jats:sup>2<\/jats:sup>. Over this range the single\u2010pulse hole depth was shown to be near linear (<jats:italic>R<\/jats:italic><jats:sup>2<\/jats:sup>\u2009=\u20090.9374, <jats:italic>M<\/jats:italic>\u2009=\u20091.6), ranging from 40 to 639\u2009\u00b5m (<jats:italic>N<\/jats:italic>\u2009=\u20093). For the case where the laser\u2010fiber face was displaced 1\u2009mm from the LF surface, the lowest single\u2010pulse fluence for which tissue was visibly removed was 72\u2009J\/cm<jats:sup>2<\/jats:sup>. Testing was conducted at 4 energy densities between 72 and 180\u2009J\/cm<jats:sup>2<\/jats:sup>. Over this range the single\u2010pulse hole depth was shown to be near linear (<jats:italic>R<\/jats:italic><jats:sup>2<\/jats:sup>\u2009=\u20090.8951, <jats:italic>M<\/jats:italic>\u2009=\u20091.4), ranging from 31 to 220\u2009\u00b5m (<jats:italic>N<\/jats:italic>\u2009=\u20093). In the second experiment, with LF <jats:italic>in situ<\/jats:italic>, constant flushing with room temperature saline was shown to drastically reduce surface temperature during exposure to Ho:YAG at 5\u2009Hz with the laser\u2010fiber in direct contact with the LF. Without saline, over 1\u2009minute of treatment with a per\u2010pulse fluence of 141\u2009mJ\/cm<jats:sup>2<\/jats:sup>, the average maximum surface temperature measured 110\u00b0C. With 10\u2009cc's of saline flushed over 1\u2009minute and a per\u2010pulse laser fluence of 212\u2009mJ\/cm<jats:sup>2<\/jats:sup>, the average maximum surface temperature was 35\u00b0C. In the third experiment, mass loss was shown to be linear over 450 pulses of 600\u2009mJ from the Ho:YAG laser (212\u2009J\/cm<jats:sup>2<\/jats:sup>, direct contact, <jats:italic>N<\/jats:italic>\u2009=\u20094; 108\u2009J\/cm<jats:sup>2<\/jats:sup>, 1\u2009mm standoff, <jats:italic>N<\/jats:italic>\u2009=\u20094). With the laser\u2010fiber in direct contact, an average of 53\u2009mg was removed (<jats:italic>R<\/jats:italic><jats:sup>2<\/jats:sup>\u2009=\u20090.996, <jats:italic>M<\/jats:italic>\u2009=\u20090.117) and with 1\u2009mm laser\u2010fiber standoff, an average of 44\u2009mg was removed (<jats:italic>R<\/jats:italic><jats:sup>2<\/jats:sup>\u2009=\u20090.9988, <jats:italic>M<\/jats:italic>\u2009=\u20090.097). In the fourth experiment, 30 pulses of the Ho:YAG and Q\u2010Switched Ho:YAG lasers at 1\u2009mm standoff, and 5\u2009Hz produced similar hole depths for the tested fluences of 9\u2009J\/cm<jats:sup>2<\/jats:sup> (151 and 154\u2009\u00b5m, respectively) and 18\u2009J\/cm<jats:sup>2<\/jats:sup> (470 and 442\u2009\u00b5m, respectively), though the Ho:YAG laser produced significantly more carbonization around the rim of the laser\u2010hole. The increased carbonization was corroborated by higher measured LF temperature. In all tests with the Ho:YAG and Q\u2010Switched Ho:YAG, an audible photo\u2010acoustic affect coincided with the laser pulse. In the fifth experiment, with the frequency quadrupled Nd:YAG laser at 15\u2009Hz for 450 pulses, ablation depth per pulse was shown to be linear for the fluence range of 0.18 \u2013 0.73\u2009J\/cm<jats:sup>2<\/jats:sup> (<jats:italic>R<\/jats:italic><jats:sup>2<\/jats:sup>\u2009=\u20090.989, <jats:italic>M<\/jats:italic>\u2009=\u20092.4). There was no noticeable photo\u2010acoustic effect nor charring around the rim of the laser\u2010hole.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusion<\/jats:title><jats:p>The Ho:YAG, Q\u2010Switched Ho:YAG, and frequency quadrupled Nd:YAG lasers were shown to remove ligamentum flavum (LF). A single pulse of the Ho:YAG laser was shown to cause tearing of the tissue and a large zone of necrosis surrounding the laser\u2010hole. Multiple pulses of the Ho:YAG and Q\u2010Switched Ho:YAG lasers caused charring around the rim of the laser\u2010hole, though the extent of charring was more extensive with the Ho:YAG laser. Charring caused by the Ho:YAG laser was shown to be mitigated by continuously flushing the affected LF with saline during irradiation. The Nd:YAG laser was shown to ablate LF with no gross visible indication of thermal damage to surrounding LF. Lasers Surg. Med. 47:839\u2013851, 2015. \u00a9 2015 The Authors. <jats:italic>Lasers in Surgery and Medicine<\/jats:italic> Published by Wiley Periodicals, Inc.<\/jats:p><\/jats:sec>","DOI":"10.1002\/lsm.22424","type":"journal-article","created":{"date-parts":[[2015,9,28]],"date-time":"2015-09-28T20:02:51Z","timestamp":1443470571000},"page":"839-851","source":"Crossref","is-referenced-by-count":7,"title":["Ablation of porcine ligamentum flavum with Ho:YAG, q\u2010switched Ho:YAG, and quadrupled Nd:YAG lasers"],"prefix":"10.1002","volume":"47","author":[{"given":"Matt R.","family":"Johnson","sequence":"first","affiliation":[{"name":"Lincoln Laboratory Massachusetts Institute of Technology 244 Wood Street Lexington 02420 Massachusetts"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Patrick J.","family":"Codd","sequence":"additional","affiliation":[{"name":"Department of Neurosurgery Harvard Medical School Massachusetts General Hospital 55 Fruit Street Gray 502 Boston 02114 Massachusetts"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Westin M.","family":"Hill","sequence":"additional","affiliation":[{"name":"Lincoln Laboratory Massachusetts Institute of Technology 244 Wood Street Lexington 02420 Massachusetts"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Tara","family":"Boettcher","sequence":"additional","affiliation":[{"name":"Lincoln Laboratory Massachusetts Institute of Technology 244 Wood Street Lexington 02420 Massachusetts"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[2015,9,28]]},"reference":[{"key":"e_1_2_6_2_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1533-2500.2012.00565.x"},{"key":"e_1_2_6_3_1","doi-asserted-by":"publisher","DOI":"10.1056\/NEJMcp0708097"},{"key":"e_1_2_6_4_1","doi-asserted-by":"publisher","DOI":"10.1002\/jor.1100070116"},{"key":"e_1_2_6_5_1","doi-asserted-by":"publisher","DOI":"10.1007\/s00586-009-0919-7"},{"key":"e_1_2_6_6_1","unstructured":"American Association of Neurologic Surgeons 2006 National Neurosurgical Procedural Statistics"},{"key":"e_1_2_6_7_1","doi-asserted-by":"publisher","DOI":"10.1155\/2014\/293582"},{"key":"e_1_2_6_8_1","doi-asserted-by":"publisher","DOI":"10.1038\/nrneurol.2012.110"},{"key":"e_1_2_6_9_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.nec.2006.06.007"},{"key":"e_1_2_6_10_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.wneu.2010.05.038"},{"key":"e_1_2_6_11_1","doi-asserted-by":"publisher","DOI":"10.1055\/b-002-54100"},{"key":"e_1_2_6_12_1","doi-asserted-by":"crossref","unstructured":"VenugopalanV.Pulsed laser ablation of tissue: Surface vaporization or thermal explosion? 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