Preliminary investigations on therapy thresholds for laser dosimetry, cryogen spray cooling duration, and treatment cycles for laser cartilage reshaping in the New Zealand white rabbit auricle

Abstract

Previous studies have demonstrated the feasibility of laser irradiation (λ=1.45 μm) in tandem with cryogen spray cooling (CSC) to reshape rabbit auricular cartilage using total energy density of 14 J/cm2. The aim of this study was to further explore and identify the dosimetry parameter space for laser output energy, CSC duration, and treatment cycles required to achieve shape change while limiting skin and cartilage injury. Ten New Zealand white rabbits were treated with the 1.45 μm diode laser combined with cryogen spray cooling (Candela Smoothbeam™, Candela Co., Wayland, MA). The ear's central portion was bent around a cylindrical jig and irradiated in consecutive spots of 6 mm diameter (13 J/cm2 or 14 J/cm2 per spot) along 3 rows encompassing the bend. CSC was delivered during irradiation in cycles consisting of 25-35 ms. At thin and thick portions of the ear, 4-7 and 6-10 treatment cycles were delivered, respectively. After surgery, ears were examined and splinted for 6 weeks. Treatment parameters resulting in acceptable (Grades 1 & 2) and unacceptable (Grade 3) skin injuries for thick and thin regions were identified and shape change was observed. Confocal and histological analysis of cartilage tissue revealed several outcomes correlating to laser dosimetry, CSC duration, and treatment cycles. These outcomes included expansion of cartilage layers (thickening), partial cartilage injuries, and full thickness cartilage injuries. We determined therapy thresholds for laser output energy, cryogen spray cooling duration, and treatment cycles in the rabbit auricular model. These parameters are a starting point for future clinical procedures aimed at correcting external ear deformities.

Cryosurgery to remove perichondrium for the rabbit ear hypertrophic scar model: a simplified method

“…Interestingly, in 1961, Joseph et al investigated structural changes of the rabbit ear during wound healing after the removal of skin only or in combination with cartilage, concluding that metaplastic bone formation was detected in all the samples of both groups (8). Replacement of cartilage with fibrous tissue was also defined in rabbit ears as a result of full-thickness cartilage injury (9). There exist numerous cases of localized bone tissue formation in humans, mostly associated with local injury and intense inflammatory reaction (10).…”

Laser‐assisted cartilage reshaping for protruding ears: A review of the clinical applications

“…Another laser wavelength, 1.32 µm, was evaluated on animals only, mostly by Li et al Due to the fact that the 1.32‐µm laser wavelength penetrates deep into cartilage, significant thermal damages were concurrent with clinically relevant shape change. For this reason, Li et al now prefer to use a 1.45 µm diode laser, closer to the 1.54 µm . However, the 1.45‐µm wavelength is still used experimentally, and clinical evaluations on humans will be necessary to confirm that cartilage reshaping is as efficient and safe as 1.54 µm.…”

“…For this reason, Li et al now prefer to use a 1.45 mm diode laser, closer to the 1.54 mm. [25][26][27] However, the 1.45-mm wavelength is still used experimentally, and clinical evaluations on humans will be necessary to confirm that cartilage reshaping is as efficient and safe as 1.54 mm. Whatever the wavelength used, two different technological approaches using different laser power densities and different mechanisms of cartilage reshaping persist in the literature.…”