Laser assisted fixation of ear prostheses after stapedectomy

Time and frequency resolved XeCl laser-induced mechanical transients in otic capsule bone

OBJECTIVE

This study identifies the presence of photoacoustic waves during excimer laser treatment of porcine otic capsule bone.

BACKGROUND DATA

Pulsed ultraviolet lasers have been suggested for use in middle ear surgery due to their potential for fiberoptic delivery, decreased thermal trauma, and precise ablation characteristics. However, the short pulse width of excimer lasers (typically 10-150 ns) can create large thermoelastic stresses in the ablation specimen.

MATERIALS AND METHODS

A XeCl (lambda = 308 nm, tau = 12 ns) excimer laser was used to ablate wafers of bone with energies of 90, 35, 13, 5, and 1.8 mJ/pulse. Custom high-frequency polyvinyldifluoride (PVDF) piezoelectric film transducers were fabricated and attached to the slices of bone. During ablation photoacoustic signals were amplified using a low-noise preamplifier and recorded on a digitizing oscilloscope.

RESULTS

Photoacoustic waves were clearly identified. Stress wave amplitude increased with laser fluence.

CONCLUSION

A laser fluence must be found that compromises between an increased ablation rate and increased stress wave amplitude. The acoustic power levels generated during ablation are below maximum exposure limits.

Lasers in clinical urology: state of the art and new horizons

We present an overview of current and emerging lasers for Urology. We begin with an overview of the Holmium:YAG laser. The Ho:YAG laser is the gold standard lithotripsy modality for endoscopic lithotripsy, and compares favorably to standard electrocautery transurethral resection of the prostate for benign prostatic hyperplasia (BPH). Available laser technologies currently being studied include the frequency doubled double-pulse Nd:Yag (FREDDY) and high-powered potassium-titanyl-phosphate (KTP) lasers. The FREDDY laser presents an affordable and safe option for intracorporeal lithotripsy, but it does not fragment all stone compositions, and does not have soft tissue applications. The high power KTP laser shows promise in the ablative treatment of BPH. Initial experiments with the Erbium:YAG laser show it has improved efficiency of lithotripsy and more precise ablative and incisional properties compared to Ho:YAG, but the lack of adequate optical fibers limits its use in Urology. Thulium:YAG fiber lasers have also demonstrated tissue ablative and incision properties comparable to Ho:YAG. Lastly, compact size, portability, and low maintenance schedules of fiber lasers may allow them to shape the way lasers are used by urologists in the future.

Erbium lasers in dentistry

Erbium hard tissue lasers have the capability to prepare enamel, dentin, caries, cementum, and bone in addition to cutting soft tissue. The ability of hard tissue lasers to reduce or eliminate vibrations, the audible whine of drills, microfractures, and some of the discomfort that many patients fear and commonly associate with high-speed handpieces is impressive. In addition, these lasers can be used with a reduced amount of local anesthetic for many procedures. Today, these instruments have evolved from their initial use for all classes of cavity preparations to their ability for removing soft tissue, their usefulness in the disinfection of bacteria within endodontic canals, and most recently, as an alternative to the high speed handpiece for the removal of bone in oral and maxillofacial surgery. In addition, recent research has centered on the value of the erbium family of laser wavelengths in periodontics, including the removal of calculus.

Erbium: YAG laser lithotripsy mechanism

PURPOSE

We tested the hypothesis that the mechanism of long pulse erbium:YAG laser lithotripsy is photothermal.

MATERIALS AND METHODS

Human urinary calculi were placed in deionized water and irradiated with erbium:YAG laser energy delivered through a sapphire optical fiber. Erbium:YAG bubble dynamics were visualized with Schlieren flash photography and correlated to acoustic emissions measured by a polyvinylidene fluoride needle hydrophone. The sapphire fiber was placed either parallel or perpendicular to the calculus surface to assess the contribution of acoustic transients to fragmentation. Stones were irradiated using desiccated stone irradiated in air, hydrated stone irradiated in air and hydrated stone irradiated in water. Ablation crater sizes were compared. Uric acid stones were irradiated in water and the water was assayed for cyanide.

RESULTS

During the early phase of vapor bubble expansion, acoustic transients had minimal effects on calculus fragmentation. Fragmentation occurred due to direct absorption of laser energy transmitted to the calculus through the vapor channel between the sapphire fiber tip and calculus. The forward axial expansion of the bubble occurred more rapidly than the radial expansion. A parallel oriented fiber on the calculus surface produced no fragmentation but generated larger amplitude acoustic transients compared to perpendicular orientation. In perpendicular orientation the erbium:YAG laser did not generate any collapse acoustic waves but fragmentation occurred. Crater width was greatest for desiccated stones irradiated in air (p <0.03). Cyanide production increased as erbium:YAG irradiation of uric acid calculi increased, (r2 = 0.98).

CONCLUSIONS

The erbium:YAG laser fragments stones through a photothermal mechanism.

The Er:YAG laser in ear surgery: first clinical results

BACKGROUND AND OBJECTIVE

The goal of this study was to gain experiences about the possibilities and limits of the Er:YAG laser for ear operations.

STUDY DESIGN/PATIENTS AND METHODS

Eighty-three ear operations were performed with the aid of an Er:YAG laser: 32 stapedotomies, 15 tympanoplasties type III, 10 tympanoplasties type I, 18 ear operations in cholesteatoma, and 8 removals of hyperostosis in the outer ear canal.

RESULTS

The Er:YAG laser facilitated stapedotomies and removal of hyperostosis from the outer ear canal. In cases of beginning cholesteatoma, the Er:YAG laser allowed matrix removal of the ear ossicles left in situ. Furthermore, in tympanoplasty it was possible to achieve an osteosynthesis of the auditory ossicles, which was done for the first time during this study. No hearing loss attributable to laser dose was found during postoperative hearing tests.

CONCLUSION

The Er:YAG laser seems to become a useful tool in middle ear surgery.

Effects of pulsed laser systems on stapes footplate

BACKGROUND AND OBJECTIVE

The aim of the present study was to investigate the tissue ablation capacity of various pulsed lasers at the stapes footplate.

STUDY DESIGN/MATERIALS AND METHODS

Isolated human stapes and bovine compact-bone platelets were used to determine the effective laser parameters and appropriate application technique for achieving a perforation measuring 500-600 microns in diameter. Of interest were also the shape and quality of the perforations, the reproducibility of the perforation effect, and the thermically altered marginal zones occurring at the footplate. Three pulsed laser systems were used: excimer, holmium:YAG (Ho:YAG), and erbium:YSGG (Er:YSGG) lasers.

RESULTS

The tissue-ablating effect of pulsed laser systems permits a precise and controlled management of the stapes footplate through low and readily reproducible ablation rates. The extent of thermic side effects at the footplate is lower in comparison to the purely thermically acting cw and superpulse laser systems. The Er:YSGG laser exhibits the highest ablation rate at the stapes and is thus the most effective laser for perforation of the stapes footplate. Though somewhat less effective, the Ho:YAG laser also appears to be suitable for stapedotomy. On the other hand, we do not consider the applied excimer laser (308 nm) to be particularly appropriate at the stapes because of its low ablation rates.

CONCLUSION

Thus, the erbium laser could represent an alternative to the argon, KTP 532, and CO2 lasers, already clinically successful in stapes surgery. However, further studies are necessary to examine the transmission of thermic energy into the vestibule and the acoustic stress to the inner ear during laser stapedotomy, to be able to make a definitive statement about the safest and most effective laser system for stapes surgery.

Thermal Imaging of the Temporal Bone in CO2 Laser Surgery: An Experimental Model

The unique properties of lasers create an enormous potential for specific treatment of chronic ear disease. Despite the widespread acceptance and use of the laser, however, a complete understanding of the time- and space-dependent temperature distribution in otic capsule bone immediately after pulsed laser exposure has not been elucidated. Using a liquid nitrogen-cooled mercury-cadmium telluride infrared detector, the temperature distribution in human cadaveric otic capsule bone was determined immediately after pulsed (100 msec) carbon dioxide laser exposure (0.3 to 4.0 W; 200 urn spot diameter). The time- and space-dependent temperature increases and thermal diffusion were determined as a function of the laser power density and were found to vary linearly.

Holmium:YAG laser endoscopic sinus surgery: a randomized, controlled study

Although surgical lasers were introduced to the field of otolaryngology more than 20 years ago, their use in rhinologic surgery has remained relatively limited. With the development of the holmium:yttrium-aluminum-garnet (YAG) laser, a device is now available that offers those features necessary for effective sinus surgery:precise bone ablation, efficient soft tissue coagulation, and fiberoptic transmission. This solid-state laser of 2.1-microns wavelength can be coupled with endoscopic instrumentation for the surgical treatment of sinus disease. This study was conducted to determine the clinical efficacy of the holmium:YAG laser for endoscopic sinus surgery. A microscopic analysis of laser-treated sinus tissue was also performed in an attempt to determine the histologic basis of the observed clinical findings. In a prospective, randomized, controlled, single-blinded study, 32 consecutive patients underwent endoscopic sinus surgery using the holmium:YAG laser on one side of the nose and conventional endoscopic instrumentation on the other side. Patients rated symptoms for each side of the nose at 1 week, 1 month, 3 months, 6 months, and 2 years after surgery. Healing parameters were similarly rated by the surgeon. Until the study was completed, patients were not told which side of the nose had been treated with laser surgery. No intraoperative complications occurred. The mean intraoperative blood loss was 24.6 mL less on the laser-treated side of the nose than on conventionally treated side (P < .001). At 1 week after surgery, there was increased mucosal edema on the laser-treated side (P < .01). Crust formation was greater on the conventionally treated side at 1 week and was greater on the laser-treated side at 1 mouth (P < .01). Improvements in symptoms of pain, congestion, and drainage were equivalent for both treatment modalities (P < .001). Microscopic analysis demonstrated the ability of the holmium:YAG laser to remove tissue in relatively thin layers with ablation depths of 260 +/- 8.2 microns, 286 +/- 9.4 microns, and 341 +/- 20.4 microns per pulse at energy levels of 0.5, 1.0, and 1.5 J, respectively. A zone of thermal necrosis extending up to 1 mm beyond the site of laser impact was thought to correlate with the increased postoperative edema observed on the laser-treated side. Endoscopic sinus surgery with the holmium:YAG laser is as effective as nonlaser techniques in relieving the symptoms of chronic sinusitis. Laser surgery offers improved intraoperative hemostasis, but it causes increased postoperative tissue edema. The holmium:YAG laser provides the surgeon with an additional tool for the performance of safe, effective sinus surgery.

Flexible fiberoptic endoscopy and laser surgery in obliterated cochleas: human temporal bone studies

BACKGROUND AND OBJECTIVE

The use of conventional drilling procedures in cochlear implant surgery of ossified cochleae poses special risks to the facial nerve and the carotid artery. This study evaluated the alternate use of flexible fiberoptic endoscopy and mid-infrared laser surgery for recanalization of partially and artificially obliterated cochleae in freshly dissected human cadavers.

STUDY DESIGN/MATERIALS AND METHODS

A pulsed Holmium:YAG-laser (lambda = 2120 nm) was used in the free-running mode (1180 mJ, 250 microseconds pulse, 5 Hz). A 660 microns optic quartz fiber was positioned in the center of the round window niche and slowly--endoscopically guided--advanced in contact shooting over 1.5 cm, creating by vaporization and photoablation a passage through the artificial bony occlusion in the basal segment of the cochlea.

RESULTS

In all experiments, laser application (110-130 pulses) resulted in complete recanalization of the bony occlusions without damaging surrounding structures. The microendoscopy proved capable of guiding the laser fiber through the curved segment of the basal turn allowing identification of normal bone, bone cement, and laser-treated bone cement.

CONCLUSION

If partial ossification of the basal turn is present, this technique could give access to place analog as well as digital implants deep within the cochlea.

Temperature dependence of the absorption coefficient of water for midinfrared laser radiation

The dynamics of the water absorption peak around 1.94 microns was examined. This peak is important for the absorption of holmium and thulium laser radiation. To examine the effect of temperature on the absorption coefficient, the transmission of pulsed Ho:YAG, Ho:YAG, Ho:YSGG, and Tm:YAG laser radiation through water of 22 degrees C, 49 degrees C, and 70 degrees C was measured as a function of the thickness of the water layer. From these data the absorption coefficients were determined at the three wavelengths. We found that at all three wavelengths, the absorption coefficients decreased when increasing the temperature. Second, the absorption spectrum of water was measured from 1,850-2,150 nm with a spectrophotometer. It was found that the absorption peak at 1.94 microns (at 22 degrees C) shifts to shorter wavelengths with increasing temperatures, to 1.92 microns at 70 degrees C. A model was developed to predict the temperature distribution incorporating the dynamic change in absorption coefficient. The temperature distributions are compared to the predictions of a model assuming constant optical properties. It is shown in this study that the dynamics of the absorption coefficient has a significant influence on the expected zone of damage and ablation parameters in the 2-microns wavelength range.

Mechanical effects of erbium:YAG laser bone ablation

When intending to use pulsed erbium:YAG laser radiation for the ablation of small bones, e.g., the ossicular chain or footplate, not only temperature and thermal damage, but also mechanical side effects become important. In studies on desiccated bone the total recoil momentum caused by laser ablation was measured using a sensitive pendulum. The momentum depends linearly on the radiant energy of the laser pulse with a slope of 10(-4) kg m s-1/J. The temporal course of the recoil force during ablation observed by means of a piezoelectric transducer is nearly proportional to the laser pulse intensity. By evaluating recoil momentum and mass loss data, the average initial velocity of the plume was calculated to be 230 to 280 m s-1. The kinetic energy is approximately 1% of the input energy. The measurements support to the hypothesis of a thermally induced explosive process.

Infrared laser stapedotomy

A pulsed holmium: YAG laser (lambda = 1980 nm) was used to perform 0.4 mm stapedotomy fenestrations in human stapes footplates from freshly dissected cadavers under simulated surgical conditions. The energy was coupled into a 400 microns core diameter nylon fiber. Thermal gradients were then measured following laser applications and tissue responses examined by light microscopy. The results of this study suggest the feasibility of using a surgical holmium: YAG laser in middle ear surgery.