Laser Cartilage Reshaping Research Articles

Effect of anisotropy and drying of costal cartilage on its optical transmittance in laser reshaping of implants with 1, 2, and 3 mm in thickness.

Laser reshaping of cartilage is a prospective technique which can be applied for manufacturing the natural implants for otolaryngology and reconstructive surgery. Optical properties and optimal laser settings for laser reshaping of costal cartilage depend on its thickness, water content, and structural anisotropy of the tissue, in particular, the distinct orientation of collagen packing. The aim of the work is to study the effect of different collagen orientation, thickness, and drying of costal cartilage on its interaction with laser radiation. Costal cartilage was cut along and crosswise the distinct collagen orientation. The dried and normal cartilage was used for the comparative analysis. The collagen package was studied using atomic force microscopy. The dried tissue was analyzed with thermogravimetry-differential scanning calorimetry (TG-DSC) analysis to reveal the residual water content. The optical transmittance was measured for two wavelengths λ: 1,560 and 532 nm. The reshaping of cartilage of 1-3 mm in thickness was performed with infrared laser with λ = 1560 nm while, the radiation with λ = 532 nm was used to determine the location of the IR beam. The transmittance of 532 nm radiation does not depend on collagen orientation and tissue drying. The IR radiation transmits better along the distinct collagen direction in dried cartilage while in normal cartilage the intensity of transmitted IR radiation increases intermittently passing crosswise and does not change dramatically with time along the collagen orientation. The effect of structural anisotropy of costal cartilage reveals itself in the increasing scattering of IR radiation with λ = 1,560 nm passing crosswise the collagen orientation when tissue water content is decreased. The radiation with λ = 1,560 nm is effective to perform the reshaping for cartilage of 1-3 mm in thickness; however, for 3 mm, the residual mechanical stress should be taken into account. Lasers Surg. Med. 48:887-892, 2016. © 2016 Wiley Periodicals, Inc.

In vivo laser cartilage reshaping with carbon dioxide spray cooling in a rabbit ear model: a pilot study.

Similar to conventional cryogen spray cooling, carbon dioxide (CO2) spray may be used in combination with laser cartilage reshaping (LCR) to produce cartilage shape change while minimizing cutaneous thermal injury. Recent ex vivo evaluation of LCR with CO2 cooling in a rabbit model has identified a promising initial parameter space for in vivo safety and efficacy evaluation. This pilot study aimed to evaluate shape change and cutaneous injury following LCR with CO2 cooling in 5 live rabbits. The midportion of live rabbit ears were irradiated with a 1.45 µm wavelength diode laser (12 J/cm(2)) with simultaneous CO2 spray cooling (85 millisecond duration, 4 alternating heating/cooling cycles per site, 5 to 6 irradiation sites per row for 3 rows per ear). Experimental and control ears (no LCR) were splinted in the flexed position for 30 days following exposure. A total of 5 ears each were allocated to the experimental and control groups. Shape change was observed in all irradiated ears (mean 70 ± 3°), which was statistically different from control (mean 37 ± 11°, P = 0.009). No significant thermal cutaneous injury was observed, with preservation of the full thickness of skin, microvasculature, and adnexal structures. Confocal microscopy and histology demonstrated an intact and viable chondrocyte population surrounding irradiated sites. LCR with CO2 spray cooling can produce clinically significant shape change in the rabbit auricle while minimizing thermal cutaneous and cartilaginous injury and frostbite. This pilot study lends support for the potential use of CO2 spray as an adjunct to existing thermal-based cartilage reshaping modalities. An in vivo systematic evaluation of optimal laser dosimetry and cooling parameters is required.

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.

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 a total energy density of 14 J/cm(2). 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, USA). The ear's central portion was bent around a cylindrical jig and irradiated in consecutive spots of 6 mm diameter (13 or 14 J/cm(2) per spot) along three 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 and 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.

Ex vivo investigations of laser auricular cartilage reshaping with carbon dioxide spray cooling in a rabbit model

Laser cartilage reshaping (LCR) with cryogen spray cooling is a promising modality for producing cartilage shape change while reducing cutaneous thermal injury. However, LCR in thicker tissues, such as auricular cartilage, requires higher laser power, thus increasing cooling requirements. To eliminate the risks of freeze injury characteristic of high cryogen spray pulse rates, a carbon dioxide (CO2) spray, which evaporates rapidly from the skin, has been proposed as the cooling medium. This study aims to identify parameter sets which produce clinically significant reshaping while producing minimal skin thermal injury in LCR with CO2 spray cooling in ex vivo rabbit auricular cartilage. Excised whole rabbit ears were mechanically deformed around a cylindrical jig and irradiated with a 1.45-μm wavelength diode laser (fluence 12-14 J/cm(2) per pulse, four to six pulse cycles per irradiation site, five to six irradiation sites per row for four rows on each sample) with concomitant application of CO2 spray (pulse duration 33-85 ms) to the skin surface. Bend angle measurements were performed before and after irradiation, and the change quantified. Surface temperature distributions were measured during irradiation/cooling. Maximum skin surface temperature ranged between 49.0 to 97.6 °C following four heating/cooling cycles. Significant reshaping was achieved with all laser dosimetry values with a 50-70 °C difference noted between controls (no cooling) and irradiated ears. Increasing cooling pulse duration yielded progressively improved gross skin protection during irradiation. CO2 spray cooling may potentially serve as an alternative to traditional cryogen spray cooling in LCR and may be the preferred cooling medium for thicker tissues. Future studies evaluating preclinical efficacy in an in vivo rabbit model are in progress.

레이저에 의한 연골의 광학적 열적 특성변화 연구

Laser cartilage reshaping(LCR) is a promising method for reshaping cartilage by using laser irradiation to maintain permanently modifies its shape. However this method has not been fully understood due to the limited scientific researches. The purpose of this study is to analyze optical and thermal characteristics of cartilage during laser irradiation. After analyzing Monte Carlo simulation for the comparison of laser fluence distributions with different laser wavelengths the characterization of the spectral changes during Nd:YAG laser(<TEX>${\lambda}$</TEX> = 1444 nm) irradiation was investigated in the ranges of 900-1700 nm with double integrating spheres. The surface temperature distribution changes during laser irradiation were investigated with an infrared camera. The quantitative measurements of optical and thermal characteristics in cartilage after laser irradiation were correlated with the transition of water flux(from bound to free water) and this study may be useful for better understanding of biophysical transformation phenomena in cartilage after laser heating.

The effects of laser irradiation of cartilage on chondrocyte gene expression and the collagen matrix

Laser reshaping of cartilage is an emerging technology aimed at replacing conventional techniques for aesthetic and reconstructive surgery. Little is known about the mechanisms of wound healing following the photothermal heating during laser reshaping and, ultimately, how collagen remodels in the irradiated tissue. Healthy hyaline and elastic cartilage as found in the ear, nose, larynx, and trachea does not express collagen type I which is characteristic of fibro-cartilage and scar tissue. The aim of the study was to determine if collagen I and II gene expression occurs within laser irradiated rabbit septal cartilage. Nasal septum harvested from freshly euthanized New Zealand White rabbits were irradiated with an Nd:YAG laser. After 2 weeks in culture, the laser spot and surrounding non-irradiated regions were imaged using immunofluorescence staining and evaluated using reverse transcription polymerase chain reaction (RT-PCR) to determine the presence of collagen I and II, and ascertain collagen I and II gene expression, respectively. All laser irradiated specimens showed a cessation in collagen II gene expression within the center of the laser spot. Collagen II was expressed in the surrounding region encircling the laser spot and within the non-irradiated periphery in all specimens. Immunohistochemistry identified only type II collagen. Neither collagen I gene expression nor immunoreactivity were identified in any specimens regardless or irradiation parameters. Laser irradiation of rabbit septal cartilage using dosimetry parameters similar to those used in laser reshaping does not result in the detection of either collagen I gene expression or immunoreactivity. Only collagen type II was noted after laser exposure in vitro following cell culture, which suggests that the cellular response to laser irradiation is distinct from that observed in conventional wound healing. Laser irradiation of cartilage can leave an intact collagen matrix which likely allows chondrocyte recovery on an intact scaffold.

Viability of human septal cartilage after 1.45 µm diode laser irradiation

Chondrocyte viability following laser irradiation and reshaping has not been established for human nasal septal cartilage. Knowledge of the relationship between thermal injury and laser dosimetry is needed in order to optimize septal laser cartilage reshaping. The objective of this study was to determine the depth and width of thermal injury in human septal cartilage following laser irradiation. Excess fresh nasal septal cartilage sections from rhinoplasty or septoplasty operations were irradiated using a 1.45 microm diode laser 1.25-3.6 W (2.8 mm spot diameter) with 1 second fixed exposure time, and then at exposure times of 1-4 seconds for a fixed power of 1.25 W. An infrared camera recorded surface temperature profiles during irradiation, and the temperature data were incorporated into a rate process model to numerically estimate thermal damage. Calcein AM and ethidium homodimer-1 fluorescent dyes combined with confocal laser microscopy (CLM) were used to measure thermal damage. CLM demonstrated clear demarcation between dead and living cells following irradiation. The extent of non-viable chondrocyte distributions increased with power and exposure time. The maximum depths of injury were 1,012 and 1,372 microm after 3.6 W 1 second and 1.25 W 4 seconds irradiation respectively. The damage predictions made by the rate process model underestimated thermal injury when compared with CLM measurements. The assay system identified regions of non-viable chondrocytes in human septal cartilage and defined how thermal injury varies with dosimetry when using a 1.45 microm diode laser.

Temperature dependent change in equilibrium elastic modulus after thermally induced stress relaxation in porcine septal cartilage

Laser cartilage reshaping (LCR) is a promising method for the in situ treatment of structural deformities in the nasal septum, external ear and trachea. Laser heating leads to changes in cartilage mechanical properties and produces relaxation of internal stress allowing formation of a new stable shape. While some animal and preliminary human studies have demonstrated clinical feasibility of LCR, application of the method outside specialized centers requires a better understanding of the evolution of cartilage mechanical properties with temperature. The purpose of this study was to (1) develop a method for reliable evaluation of mechanical changes in the porcine septal cartilage undergoing stress relaxation during laser heating and (2) model the mechanical changes in cartilage at steady state following laser heating. Rectangular cartilage specimens harvested from porcine septum were heated uniformly by a radio-frequency (RF) electric field (500 kHz) for 8 and 12 seconds to maximum temperatures from 50 to 90 degrees C. Cylindrical samples were fashioned from the heated specimens and their equilibrium elastic modulus was measured in a step unconfined compression experiment. Functional dependencies of the elastic modulus and maximum temperature were interpolated from the measurements. Profiles of the elastic modulus produced after 8 and 12 seconds of laser irradiation (Nd:YAG, lambda = 1.34 microm, spot diameter 4.8 mm, laser power 8 W) were calculated from interpolation functions and surface temperature histories measured with a thermal camera. The calculated elastic modulus profiles were incorporated into a numerical model of uniaxial unconfined compression of laser irradiated cylindrical samples. The reaction force to a 0.1 compressive strain was calculated and compared with the reaction force obtained in analogous mechanical measurements experiment. RF heating of rectangular cartilage sample produces a spatially uniform temperature field (temperature variations < or = 4 degrees C) in a central region of the sample which is also large enough for reliable mechanical testing. Output power adjustment of the RF generator allows production of temperature histories that are very similar to those produced by laser heating at temperatures above 60 degrees C. This allows creation of RF cartilage samples with mechanical properties similar to laser irradiated cartilage, however with a spatially uniform temperature field. Cartilage equilibrium elastic modulus as a function of peak temperature were obtained from the mechanical testing of RF heated samples. In the temperature interval from 60 to 80 degrees C, the equilibrium modulus decreased from 0.08+/- 0.01 MPa to 0.016+/-0.007 MPa, respectively. The results of the numerical simulation of uniaxial compression of laser heated samples demonstrate good correlation with experimentally obtained reaction force. The thermal history and corresponding thermally induced modification of mechanical properties of laser irradiated septal cartilage can be mimicked by heating tissue samples with RF electric current with the added advantage of a uniform temperature profile. The spatial distribution of the mechanical properties obtained in septal cartilage after laser irradiation could be computed from mechanical testing of RF heated samples and used for numerical simulation of LCR procedure. Generalization of this methodology to incorporate orthogonal mechanical properties may aid in optimizing clinical laser cartilage reshaping procedures.

Analysis of Nd:YAG laser‐mediated thermal damage in rabbit nasal septal cartilage

Laser cartilage reshaping (LCR) involves the use of photo-thermal heating to reshape cartilage. Its clinical relevance depends on the ability to minimize thermal injury in irradiated regions. The present study seeks to understand the safety of LCR by determining shape change and resultant tissue viability as a function of laser dosimetry. Rabbit nasal septal cartilage were irradiated using a Nd:YAG laser (lambda = 1.32 microm, 5.4 mm spot diameter) with different exposure times of 4, 6, 8, 10, 12, and 16 seconds and powers of 4, 6, and 8 W. Temperature on the cartilage surface in the laser-irradiated region was collected using infrared thermography, this data was then used to predict tissue damage via a rate process model. A Live/Dead viability assay combined with fluorescent confocal microscopy was used to measure the amount of thermal damage generated in the irradiated specimens. Considerable thermal injury occurred at and below the laser-reshaping parameters that produced clinically relevant shape change using the present Nd:YAG laser. Confocal microscopy identified dead cells spanning the entire cross-sectional thickness of the cartilage specimen (about 500 microm thick) at laser power density and exposure times above 4 W and 6 seconds; damage increased with time and irradiance. The damage predictions made by the rate process model compared favorably with measured data. These results demonstrate that significant thermal damage is concurrent with clinically relevant shape change. This contradicts previous notions that there is a privileged laser dosimetry parameter where clinically relevant shape change and tissue viability coexist.

Laser‐assisted straightening of deformed cartilage: Numerical model

The potential application of laser cartilage reshaping (LCR) for correction of septal deviations has generated increasing clinical interest, because septoplasty is among the top five most common operations performed. However, few studies have investigated stress fields existing in the nasal septal cartilage during LCR of septal deviations. The objectives of this study were to: (1) formulate a finite-element model describing stress fields in mechanically straightened septal cartilage, (2) calculate stress fields in the septum after a given pattern of laser irradiation produced thermally induced stress relaxation in selected sites, and (3) investigate the dependence of the overall stress relaxation in a straightened septum as a function of the number, location, and size of laser irradiation sites. The cartilagenous nasal septum was modeled as 24 x 24 x 2-mm slab. The deviation was represented as a bulge running along the center of the septum with a maximum elevation of 2 mm above the surface. A straightening deformation was represented in form of displacement boundary condition applied to the bulge convex surface with maximum displacement amplitude at center of the septum. Laser irradiation applied in a pattern of one, two, and three lines parallel to the bulge was assumed. The effect of thermally induced stress relaxation was modeled as a simultaneous change in the cartilage mechanical properties and reduction of strain to zero occurring inside the laser heated zone. The finite-element method was used to calculate stress fields within cross-section of the straightened septum and the force of reaction to the straightening deformation before and after laser irradiation. Calculations were performed for the width and depth of thermally modified zones varying from 0.5 to 3 mm and from 0.5 to 2 mm, respectively. Irradiation of convex and concave sides of the deviation was studied. The straightening deformation produced a stress field with both regions of tension and compression present. Maximum stress values were obtained on the surface where the straightening deformation was applied. Reaction force decreased with increasing width and depth of the relaxation zones and depends on location and number of these zones. The maximum reduction of reaction force obtained with three zones (3 mm wide and 2 mm deep) optimally placed in regions of stress concentration was 98%. However, using the same pattern of stress relaxation zones but with a depth of only 1 mm produces a reaction force reaction of 91%. Irradiation of convex side of the deviation reduced reaction force approximately twice as much as irradiation of the concave side. The present numerical simulation of the stress field in laser-reshaped deviated septum shows highly non-homogeneous stress distributions before and after laser treatment. Using reasonable assumptions on how the mechanical behavior of cartilage changes after heating, the model allows estimation reaction force and its reduction following localized laser irradiation as a function of size and location of laser heated zones.

Long-term Viability and Mechanical Behavior Following Laser Cartilage Reshaping

To investigate the long-term in vivo effect of laser dosimetry on rabbit septal cartilage integrity, viability, and mechanical behavior. Nasal septal cartilage specimens (control and irradiated pairs) were harvested from 18 rabbits. Specimens were mechanically deformed and irradiated with an Nd:YAG laser across a broad dosimetry range (4-8 W and 6-16 seconds). Treated specimens and controls were autologously implanted into a subperichondrial auricular pocket. Specimens were harvested an average +/- SD of 208 +/- 35 days later. Tissue integrity, histology, chondrocyte viability, and mechanical property evaluations were performed. Tissue damage results were compared with Monte Carlo simulation models. All laser-irradiated specimens demonstrated variable tissue resorption and calcification, which increased with increased dosimetry. Elastic moduli of the specimens were significantly either lower or higher than controls (all P<.05). Viability assays illustrated a total loss of viable chondrocytes within the laser-irradiated zones in all treated specimens. Histologic examination confirmed these findings. Experimental results were consistent with damage profiles determined using numerical simulations. The loss of structural integrity and chondrocyte viability observed across a broad dosimetry range underscores the importance of spatially selective heating methods prior to initiating application in human subjects.

Long‐term in vivo stability of rabbit nasal septal cartilage following laser cartilage reshaping: A pilot investigation

To evaluate the long-term effect of laser cartilage reshaping on rabbit nasal septal cartilage viability and mechanical integrity in an in vivo model. In vivo animal investigation. Rabbit septal cartilage specimens were laser (Nd:YAG, lambda = 1.32 mum, spot size 5.4-mm diameter, 10 W, 10 seconds, 50 Hz PPR) reshaped and subsequently reimplanted into an interscapular subcutaneous pocket. Specimens were harvested at 8 and 12 months and evaluated using photography, flow cytometry, and histology. Grossly, specimens showed alteration in the physical integrity with varying degrees of tissue resorption. The non-irradiated control specimens demonstrated significantly increased stiffness. Histologically, there was marked depletion of the extracellular matrix and an overall reduction in tissue mass in laser irradiated tissues. However, flow cytometry data identified viable chondrocytes in laser-irradiated specimens that were identical to those observed in controls. Study results demonstrate that the rabbit nasal septal cartilage model can be effectively used to study laser reshaping, however alternative recipient sites with perichondrial lining, such as the pinna, may provide a more realistic physiologic environment for reshaped graft tissue. The dosimetry used in this pilot study likely led to significant thermal injury. Study results underscore the importance of elucidating the optimal laser dosimetry required to initiate permanent shape change while minimizing thermal damage.

Laser cartilage reshaping in an in vivo rabbit model using a 1.54 microm Er:Glass laser.

The potential applications for facial laser cartilage reshaping (LCR) have generated increasing clinical interest. This study aimed to evaluate in vivo LCR of the rabbit ear using a 1.54 micro m Er:Glass laser in combination with contact cooling. LCR was performed in vivo on 12 rabbit ears using a 1.54 micro m Er:Glass laser (Aramis, Quantel Medical, Clermont Ferrand, France) connected to a 4 mm chilled (+5 degrees C) handpiece placed in contact to the skin. Ear curvature was predetermined using a perforated cylindrical guide also used to standardize laser beam delivery. The treatment consisted of 15 spots (3 millisecond, 7 pulses, 12 J/cm(2), 2 Hz, 84/cm(2) cumulative fluence) applied on 10 contiguous parallel rows along the ear. After irradiation, the aluminum jig was replaced by a holder (10 mm diameter plastic tube) maintaining the curvature. This holder was secured with sutures and covered by an adhesive gauze bandage dressing to keep new form during 7 days. In order to assess thermal damage, biopsies were taken on irradiated areas and 1 week, 3 weeks and 6 weeks and studied using haematoxylin-erythrosin-safran (HES) and orcein staining and PCNA to detect cells in cycle. Using the laser with the parameters given above, no immediate visible effects were observed on the skin (no swelling, no bleaching). There were also no late visible side effects like crusting, or blistering. The laser treatment produced changes in the shape of every ear after the dressing was removed. A slight tendency to recover its initial shape was observed for each ear. However, the curvature was stabilized after 10 days and the average shape retention was 64+/-4% at 6 weeks, with a curvature radius of 7.25+/-0.75 mm, instead of 5 mm initially. Histological examination of the laser irradiated side at 1 week showed an intact epidermis. A reduced inflammation process was seen in the dermis. A modification of half of the layer of cartilage was observed at the opposite side where the laser irradiation was applied and proliferative cells were detected inside. At 3 weeks, an important chondroblastic proliferation was observed around the area of contracted cartilage. At 6 weeks, significant thickening of the cartilage layer was observed (from 300 to 490 micro m) and new chondrocytes were clearly seen. Rabbit ear cartilage can be reshaped with an Er:Glass laser. This technique could offer exciting possibilities that may help patients whose cartilage-lined joints have been affected by disease or trauma. This technique could be certainly utilized to correct alar cartilage deformities and septum deviation of cleft lips.

Measurement of the elastic modulus of porcine septal cartilage specimens following Nd: YAG laser treatment.

Laser cartilage reshaping is a temperature-dependent process that results in stress relaxation with subsequent formation of a new and stable specimen geometry. The objective of this study was to quantitatively measure changes in the elastic moduli of porcine cartilage following laser heating. The elastic modulus of porcine nasal septal cartilage specimen (25 x 5 x 2 mm) was measured before and after Nd: YAG laser (lambda=1.32 Irvinem, 21.22 W/cm2) irradiation and following rehydration in saline solution. Specimens were secured in a single beam cantilever configuration and displaced using a calibrated thin beam load cell attached to a motorised micropositioner. Elastic modulus was calculated using elastic beam theory. Measurements were recorded before and immediately after laser heating, and following rehydration in saline solution (40 minutes, 25 degrees C). Specimens heated in saline (100 degrees C and then re-hydrated) were used as controls to determine the effect of total thermal denaturation. The calculated moduli before and after irradiation were 4.86 +/- .145 MPa and 1.166 +/- .055 MPa respectively. Following rehydration in saline, the modulus returned to near-baseline values (5.119 +/- .163 MPa). In contrast, elasticity remained lower in specimens boiled and re-hydrated (3.25 +/- .130 MPa). These findings suggest that cartilage matrix does not undergo complete thermal denaturation during laser reshaping, given the return in tissue properties with rehydration.

Measurement of the elastic modulus of rabbit nasal septal cartilage during Nd:YAG (lambda = 1.32 microm) laser irradiation.

The objective of this study was to quantitatively measure changes in the elastic moduli of rabbit nasal septal cartilage during laser heating. While the efficacy of laser cartilage reshaping has been established for use in nasal surgery, few studies have investigated the temperature-dependent viscoelastic behavior of cartilage. Cyclic force versus displacement curves were generated during the Nd:YAG laser (lambda = 1.32 microm, 10 second exposure time, 21.22 W/cm2) irradiation of cartilage specimens secured in cantilevered geometry. Samples were irradiated three times with 30 second cooling intervals between each laser exposure. Measurements were recorded before, during, and after laser irradiation, and then following complete rehydration in normal saline (NS) for 1 hour at 25 degrees C. Elastic modulus was calculated assuming linear viscoelastic behavior. The elastic modulus in native tissue decreased during and after successive laser exposures from about 6 to 3.5 MPa. After rehydration, the modulus returned to near-baseline value. Surface temperature reached a maximum of 65 degrees C. The laser irradiation of cartilage using parameters similar to those used in reshaping does not produce significant irreversible changes in the mechanical properties of the tissue. Measurement of the elastic modulus is an effective means of characterizing alterations in cartilage mechanical behavior during and after laser heating.

Laser Reshaping of Cartilage

Laser Reshaping of Cartilage

Measurement of radiometric surface temperature and integrated backscattered light intensity during feedback-controlled laser-assisted cartilage reshaping

Cartilage undergoes characteristic mechanical stress relaxation following laser irradiation below the ablation threshold. Porcine auricular cartilage (1–2 mm thickness) was irradiated with a Nd:YAG laser (λ=1.32 μm) at two power levels (W/cm2). Surface temperature (S c (t) (°C)) (monitored using a single element HgCdTe infrared detector, 10-14 μm spectral range), and integrated back scattered light intensityI(t) were measured during laser irradiation. A HeNe laser beam (λ=632.8 nm) was incident on the back surface of the cartilage specimen and fractional integrated backscattered light intensity was measured using an integrating sphere anda silicon photodiode. Laser irradiation (5.83 W/cm2, 50 Hz pulse repetition rate (PRR)) continued until surface temperature reached approximately 70°C, during which cartilage mechanical stress relaxation was observed. Integrated back scattered light intensity reached a plateau at about 70°C). At higher laser power (39.45 W/cm2, 50 Hz PRR), a feedback-controlled cryogen spray was used to maintain surface temperature below 50°C. A similar plateau response was noted in integrated backscattered light intensity. This signal may be used to optimise the process of stress relaxation in laser cartilage reshaping. Several clinical applications involving reconstructive surgery are proposed.