Lloyd P. Tate

Development of a model to evaluate laser penetration in the equine using the Nd:YAG laser as a standard

The Nd:YAG laser is a frequently used laser in correcting equine upper respiratory disorders. Evaluation of this laser and several other lasers ability to penetrate tissue has been based on in vitro studies using portions of the arytenoid cartilage. The parameters measured have routinely been depth and width of crater created from irradiation of tissue. This investigation was performed on cadaver acquired tissue with anticipation of developing a model to conduct future in vivo studies of a similar nature to evaluate and compare different lasers. To perform this power setting, tissue selection and means of acquiring measurements needed to be standardized. Due to its accessibility and anatomic similarity to the arytenoid used in previous studies the rostral nasal septum was chosen as the second tissue for comparison with the arytenoid. Evaluation of the selected energies delivered to the tissues by the Nd:YAG laser were evaluated to set a standard by determining depth and top and bottom diameters of the area ablated. Methods of measurement consisting of standard histologic preparation followed by microscopic evaluation was compared to computer tomography acquired determinations. Statistical analysis supported the hypothesis that the nasal septum is a viable substitute for the arytenoid cartilage for future in vivo studies. It is also easily accessible compared to the arytenoid and evaluation of laser induced lesion parameters either in situ or separate from the animal should not be detrimental to the animal.

Transendoscopic Nd:YAG ablation of cystic lesions in 27 large animals: 1986-1995

Hospital medical surgery records and laser logs were examined to determine the population of large animals presented to the College of Veterinary Medicine treated by laser and conventional means for cystic lesions. Cystic lesions were most frequently found in 2 anatomical locations: endometrial cysts and upper respiratory cysts. The majority of endometrial cysts were considered to be acquired, whereas the most frequently encountered upper respiratory cysts were believed to be congenital due to the fact they were most frequently seen in young animals. Nine mares, totaling 42 endometrial cysts, were presented to the Veterinary Teaching Hospital (VTH), all of which had been treated by transendoscopic Nd:YAG laser ablation. Eighteen of the respiratory cysts in the same time period were presented to the VTH, of which 10 received conventional surgery and 8 were laser photoablated. Respiratory cysts treated by conventional surgery were generally found in locations inaccessible to visualization by transendoscopic technique, and thus required a surgical approach under general anesthesia. All mares with endometrial cysts were presented with a history of conception failure. After laser ablation, a majority of the mares were able to carry a foal to term and none represented with recurrence of endometrial cysts. Horses that presented with upper respiratory cysts also did not experience recurrence of cysts; although several horses, 1 treated by laser ablation and 4 treated by conventional surgery for frontal and/or maxillary sinus cysts, had transitory sinusitis. Transendoscopic Nd:YAG photoablation of cysts appears to be a very satisfactory means of treating this particular form of lesion in large animals with minimal complications and it can be performed with the animal in a standing position as an outpatient.

Six years of transendoscopic Nd:YAG application in large animals

Noncontact transendoscopic application of a high-powered Nd:YAG laser was used over six years to treat partial upper respiratory obstruction in 112 large animal cases. Laser irradiation was applied to the standing animal, which has developed into a successful alternative to surgical intervention under general anesthesia for treatment of entrapment of the epiglottis and various nasal pharyngeal masses. Treatment of laryngeal hemiplegia and bleeding disorders of the gutteral pouch were treated by a combined therapy consisting of a surgical approach under anesthesia followed by laser irradiation.

A guide for calculation of spot size to determine power density for free fiber irradiation of tissue

Transendoscopic laser treatment for upper airway disorders has been performed in the horse for over twenty years. Endoscopic laser transmission utilizing flexible fiber optics is limited to certain discreet wavelengths. Initially, the laser of choice was the Nd: YAG laser (1064nm), but in the early 1990s, diode lasers (810nm, 980nm) were introduced to veterinary medicine and are currently used in private practice and universities. Precise application of laser irradiation is dependent on the user knowing the lasers output as well as the amount of energy that is delivered to tissue. Knowledge of dosimetry is important to the veterinarian for keeping accurate medical records by being able to describe very specific treatment regimes. The applied energy is best described as power density or energy density. Calculation of this energy is dependent upon the users ability to determine the lasers spot size when irradiating tissue in a non-contact mode. The charts derived from this study provide the veterinarian the ability to estimate spot size for a number of commonly used lasers with the fiber positioned at various distances from the target.

Preliminary report: comparison of 980-nm, 808-nm diode laser enhanced with indocyanine green to the Nd:YAG laser applied to equine respiratory tissue

The Neodynium: Yttrium Aluminum Garnet (Nd:YAG) laser has been the mainstay of performing upper respiratory laser surgery in the equine since 1984. The 808-nm diode laser has also been applied transendoscopically as well as the 980-nm diode laser over recent years. It has been shown that Indocyanine Green (ICG) enhances the performance of the 808- nm laser because it is absorbed at 810 nm of light. The 808- nm lasers tissue interaction combined with ICG is equivalent to or greater than the Nd:YAG lasers cutting ability. The 980-nm diode laser performance was similar to that of the Nd:YAG as determined by the parameters of this study. This study compared the depths and widths of penetration achieved with the 808-nm diode laser after intravenous injection of ICG on equine respiratory tissue. It also compared depths and widths of penetration achieved by the non-contact application of the 980-nm diode laser delivering the same energy of 200 joules. The depths and widths of penetration of both diode lasers were compared to themselves and to the Nd:YAG laser with all factors remaining constant.

The Effect of Photodynamic Therapy on Cisterna Chyli Patency in Rats

OBJECTIVEnTo radiographically and histologically evaluate the effects of photodynamic therapy on the cisterna chyli in rats.nnnSTUDY DESIGNnExperimental study.nnnANIMALSnAdult male Sprague-Dawley rats (nu2009=u200960).nnnMETHODSnCecal lymph nodes were injected with the photodynamic compound verteporfin. A 690u2009nm, 500u2009mW diode laser was then directed at the area of the cisterna chyli for either 0, 1.5, or 3u2009minutes. Cisterna chyli patency was evaluated using lymphography, and histologic changes were evaluated on postoperative Days 1, 3, 5, 7, and 14.nnnRESULTSnHistologically, minimal to marked injury to the cisternal and/or pericisternal tissues was present in all treated rats at all time periods. Radiographically, 8/20 cisternae were occluded in the 1.5-minute treatment group (including 1/4 on Day 1, 2/4 on Day 3, 3/4 on Day 5, 0/4 on Day 7, and 2/4 on Day 14), and 9/20 cisternae were occluded in the 3-minute treatment group (including 0/4 on Day 1, 1/4 on Day 3, 3/4 on Day 5, 3/4 on Day 7, and 2/4 on Day 14). There was minimal to no histologic evidence of tissue injury in control rats. All control cisternae were radiographically open.nnnCONCLUSIONSnFurther investigations into the timing of laser application and light dose, or alternative photodynamic agents are required to limit injury to adjacent tissues and to improve the effectiveness of cisternal photoablation.

Pilot study: intravenous use of indocyanine green as an enhancer for 808-nm diode laser application in the equine

The 808-nm diode laser, delivering 20 - 40 watts of power, has been produced for medical applications by several manufacturers over the past 10 years. This lasers power output is less than most Neodymium:yttrium aluminum garnet (Nd:YAG) lasers and other high power cutting lasers that use fiberoptic delivery systems. The 808-nm diode laser has not gained popularity in equine transendoscopic laser surgery. Indocyanine green (ICG) is absorbed at 810-nm of light which when concentrated in tissue should be an excellent absorber for the energy produced by the 808-nm diode laser. This study compares the depths and widths of penetration achieved with the 808-nm diode laser after intravenous injection of ICG in equine respiratory tissue. Indocyanine green was administered at two doses: 1.5 mg/kg and 3 mg/kg. The 808-nm diode laser was set to deliver 200 joules of energy. The depths and widths of penetration were also compared to the Nd:YAG laser applied at the same energy setting.

Nd:YAG photovaporization of residual equine guttural-pouch mycotic lesions after internal carotid occlusion

Hospital records reviewed over a 12-year period determined that 6 horses had been presented for guttural pouch mycosis. All had a history of epistaxis and several had accompanying neurologic signs, including dysphagia. Initially, conformation of the disease was obtained by radiographic and endoscopic examinations. Surgical treatment was directed at controlling and preventing additional hemorrhage by occluding the arterial source of the hemorrhage. Direct treatment of the mycotic plaque present within the guttural pouch was conducted using transendoscopic technique to direct irradiation from the Nd:YAG laser. The protocol described for the laser application was successful in resolving the lesions and was less complicated and stressful than previously reported topically applied chemical protocols.

Review of treatment of upper airway obstruction caused by various masses both malignant and nonmalignant in the horse using transendoscopic Nd:YAG laser application for treatment

A computer search and review of surgery logs, laser logs and case records was conducted to determine the number of horses that were presented and treated for upper respiratory abnormalities. This report concentrated on equine cases that had malignant and nonmalignant disease and whether the use of a laser affected the outcome. The report concluded that neoplastic or malignant cases were presented late in the course of the disease to be successfully treated but their demographics were helpful in distinguishing them from nonmalignant cases that had similar endoscopic findings and clinical signs. Having laser capability for treatment of nonmalignant diseases improved the success rate achieved with some diseases and influenced the selection of treatment, conventional surgery versus standing transendoscopic laser irradiation of the lesions.

Carbon dioxide (CO2) laser treatment of bovine penile persistent frenulum and fibropapillomas

Persistent Frenulum and Fibropapillomas are commonly encountered diseases of young bulls. Both are amenable to simple resection with ligation of bleeders followed by mucosa suturing. Sexual rest for several weeks is generally required. Carbon dioxide laser was applied in resection of both these two maladies in six bulls (2 Persistent Frenulum, 4 with fibropapillomas) without the need for ligation of bleeders or mucosal suturing. No immediate postsurgery complications occurred related to the laser being used and potential recurrence of fibropapilloma neoplasia did not occur. The CO2 laser, compared to the steel scalpel, provided better visibility and improved hemostatic capabilities for performing the resection. The CO2 laser incisions healed completely by two weeks postirradiation, and the bulls required only one week sexual rest to allow healing to progress prior to entering an active breeding program.