Comparison of KTP, Thulium, and CO2 laser in stapedotomy using specialized visualization techniques: thermal effects

Abstract

High-speed thermal imaging enables visualization of heating of the vestibule during laser-assisted stapedotomy, comparing KTP, CO2, and Thulium laser light. Perforation of the stapes footplate with laser bears the risk of heating of the inner ear fluids. The amount of heating depends on absorption of the laser light and subsequent tissue ablation. The ablation of the footplate is driven by strong water absorption for the CO2 and Thulium laser. For the KTP laser wavelength, ablation is driven by carbonization of the footplate and it might penetrate deep into the inner ear without absorption in water. The thermal effects were visualized in an inner ear model, using two new techniques: (1) high-speed Schlieren imaging shows relative dynamic changes of temperatures up to 2 ms resolution in the perilymph. (2) Thermo imaging provides absolute temperature measurements around the footplate up to 40 ms resolution. The high-speed Schlieren imaging showed minimal heating using the KTP laser. Both CO2 and Thulium laser showed heating below the footplate. Thulium laser wavelength generated heating up to 0.6 mm depth. This was confirmed with thermal imaging, showing a rise of temperature of 4.7 (±3.5) °C for KTP and 9.4 (±6.9) for Thulium in the area of 2 mm below the footplate. For stapedotomy, the Thulium and CO2 laser show more extended thermal effects compared to KTP. High-speed Schlieren imaging and thermal imaging are complimentary techniques to study lasers thermal effects in tissue.

Capturing Thermal, Mechanical, and Acoustic Effects of the Diode (980 nm) Laser in Stapedotomy

“…This technique provides a good insight in the thermodynamic processes inside the inner ear, which give a good prediction of potential damage to inner ear function. When comparing the results of the diode lasers to the lasers that have previously been evaluated by our research group, the same amount of heating was seen in the experiments with the diode laser as was seen in the KTP laser, around 4IC (12). Most researchers use thermocouples to measure heat (16Y18).…”

“…This technique also enables the visualization of temperature effects inside a physiologic medium like water and can be combined with a regular high-speed camera at high magnification using standard close-up optics. The same test setup was previously described and used to visualize thermal effects of the KTP, CO 2 , and thulium laser (12).…”

“…A special optical technique based on color Schlieren imaging was used to study the thermal effects (11,12). This technique visualizes inhomogeneities in the refractive index of a transparent medium induced by, for example, temperature gradients.…”

Audiometric Results after Stapedotomy Operations in Patients with Otosclerosis and Preoperative Small Air-Bone Gaps

“…Even though inner ear damage as a result of mechanical trauma is less likely, the potentially harmful effects of laser use should not be underestimated. CO 2 laser, as well as KTP and to a larger extent Thulium laser have some thermal effects as showed by Kamalski et al [2014].…”

A Nonrandomized Comparison of the Thulium Laser and the CO2 Laser in Primary Stapedotomy for Otosclerosis

“…This means that energy absorption (heat production) for the CO 2 laser, when passing through the footplate, occurs right at the surface beneath the footplate, resulting in minute amounts of water vapor (8;9). The CO 2 laser will not penetrate any further than 0.3 mm (at the power levels used in ear surgery) (8). The thulium laser, because of its lesser absorption, has its energy absorption reaching deeper below the footplate.…”