Emil N. Sobol

Thermo-optical response of cartilage during feedback-controlled laser-assisted reshaping

Cartilage undergoes characteristic deformation following laser irradiation below the ablation threshold. Measurements of surface temperature and integrated scattered light intensity were performed during laser irradiation. Porcine auricular cartilage (1 - 2 mm thickness) was irradiated with an Nd:YAG laser (lambda equals 1.32 micrometer) with varying dose (J/cm2). Surface temperature was monitored using a single element HgCdTe infrared detector, responsive between 10 - 14 micrometer. A HeNe laser beam (lambda equals 632.8 nm) was incident on the back surface of the cartilage specimen and fractional integrated back scattered light intensity was measured using an integrating sphere and a silicon photodiode. Laser irradiation (2 W, 5.83 W/cm2, 50 Hz PRR) was allowed to proceed until surface temperature reached 70 degrees Celsius. Cartilage deformation was observed in each instance. Integrated scattered light intensity reached a plateau before the peak temperature (70 degrees) was reached. At increased laser power (10 W, 39.45 W/cm2, 50 Hz PRR), a feedback controlled cryogen spray was used to maintain surface temperature below 50 degrees Celsius. A similar plateau response was also noted in integrated scattered light intensity. This signal may be used to optimize the process of stress relaxation in laser cartilage reshaping. Several clinical applications are discussed.

Laser reshaping of nasal septum cartilage: clinical results for 40 patients

Clinical results on sparing laser reshaping of nasal septum cartilage are reported for the first time. Forty patients have been treated with holmium laser to correct a deformed cartilage. The laser reshaping is a bloodless, painless procedure which takes few minutes to straighten nasal septum. The stability of the new shape and possible side effects have been examined during twelve months. The headache and other negative symptoms have disappeared, as a result of laser treatment for the most of patients. Rhinoscopic examination show an excellent long-term reshaping effects for nasal septum of 23 patients, and, also, good results for other 12 patients. For 5 patients only a little effect takes place. Our rhinomanometric examinations demonstrate a pronounced improvement of the breathing for 35 patients. No visible undesirable side effects were observed for all patients underwent to laser reshaping procedure.

Kinetics of water transfer and stress relaxation in cartilage heated with 1.56 μm fiber laser

In this work we have used for the first time 1.56 micrometer fiber laser to study mechanisms of IR laser induced stress relaxation in cartilage. We have applied several in-situ monitoring techniques: local temperature measurements (IR radiometry and thermocouple), IR-light absorption, direct stress measurements, micro-balancing, visible light scattering and optical coherent tomography. We have measured temporal behavior of 1.56 micrometer laser light transmission through the cartilage sample at different intensities with synchronous temperature and stress monitoring. The observed bleaching effect (self-induced transparency) is caused by water release from irradiating zone, water evaporation from the cartilage surface and, also, by temperature shift and decrease of intensity of water absorption bands.

In-vivo study and histological examination of laser reshaping of cartilage

The results of recent study of cartilage reshaping in vivo are reported. The ear cartilage of piglets of 8-12 weeks old have been reshaped in vivo using the radiation of a holmium laser. The stability of the shape and possible side effects have been examined during four months. Histological investigation shown that the healing of irradiated are could accompany by the regeneration of ear cartilage. Finally, elastic type cartilage has been transformed into fibrous cartilage or cartilage of hyaline type.

Theoretical modeling of heating and structure alterations in cartilage under laser radiation with regard to water evaporation and diffusion dominance

We develop a theoretical model to calculate the temperature field and the size of modified structure area in cartilaginous tissue. The model incorporates both thermal and mass transfer in a tissue regarding bulk absorption of laser radiation, water evaporation from a surface and temperature dependence of diffusion coefficient. It is proposed that due to bound- to free-phase transition of water in cartilage heated to about 70 degrees Celsius, some parts of cartilage matrix (proteoglycan units) became more mobile. The movement of these units takes place only when temperature exceed 70 degrees Celsius and results in alteration of tissue structure (denaturation). It is shown that (1) the maximal temperature is reached not on the surface irradiated at some distance from the surface; (2) surface temperature reaches a plateau quicker that the maximal temperature; (3) the depth of denatured area strongly depends on laser fluence and wavelength, exposure time and thickness of cartilage. The model allows to predict and control temperature and depth of structure alterations in the course of laser reshaping and treatment of cartilage.

Laser-induced activation of regeneration processes in spine disc cartilage

The effect of laser radiation on the regeneration processes in spine disk cartilage has been studied in-vivo. We used rabbits as a model and a Holmium (2.09 micrometer) and an Erbium fiber (1.56 micrometer) lasers for irradiation the discs which were preliminary opened to remove annulus fibrosus and the nucleus pulposus of the intervertebral disc. The irradiated zone has been examined using an optical coherent tomography in one month after the operation and conventional histological technique in two months after the laser operation. It has been shown that laser radiation promotes the growth of the new cartilaginous tissue of fibrous and hyaline types.

Feedback-controlled cartilage reshaping with an Nd:YAG laser: effects of pH variation

In this study, we examined the effect of variation of pH environment on the thermal, mechanical and optical response of cartilage to laser-mediated heating. Our previous studies have demonstrated that cartilage undergoes accelerated stress relaxation during laser irradiation at fluences below the ablation threshold. Characteristic changes in integrated backscattered light intensity, radiometric surface temperature and internal stress are consistently observed during irradiation at physiologic pH. A peak in integrated backscattered light intensity occurs when surface temperature reaches approximately 65 degrees Celsius. Internal stress increases, plateaus, and subsequently decreases in a similar manner. In this study, porcine nasal septal cartilage specimens were immersed for 24 hours in physiologic buffer solution titrated to pH 1.1., 7, and 11. Cartilage samples were then irradiated (equals 1.3 micrometer, 4 W, spot size 4 - 5 mm) and integrated backscattered light intensity, radiometric surface temperature and internal stress were recorded. While specimens at pH 7 and 11 demonstrated qualitatively similar behavior, notable differences at pH 1.1 were observed, including: (1) temporal decoupling of the internal stress and light scattering responses; (2) rapid increases in integrated backscattered light intensity measurements during the early phases of laser irradiation; and (3) prolonged elevation in integrated backscattered light intensity and internal stress following laser irradiation. In addition, during successive laser irradiation to the same specimen, we observed a temporal decoupling between integrated backscattered light intensity and internal stress at pH 7 and 11. This was not observed at pH 1.1. These observations are discussed in the context of cartilage structure and chemical interactions within the extracellular matrix. Mechanisms for the observed differences are proposed, including interactions by the cartilage proteoglycan moieties, which are sensitive to changes in the pH environment and provide cartilage tissue with its characteristic viscoelastic properties.

Cartilage reshaping under nonablative laser radiation: research and clinical applications in ENT

We developed a new surgical procedure to correct cartilaginous deformities of the nasal septum using transmucosal laser irradiation without the need for sedation or traditional septoplasty techniques in particular the creation of mucoperichondrial flaps. Since 1988, at the Sechenov Medical Academy of Moscow, 150 patients have underwent laser septal cartilage reshaping using a Holmium:YAG laser. Minimal re-relaxation of shaped septa was observed. Rhinomanometric findings confirmed subjective assessments of improved breathing and relief of nasal obstruction. Laser septoplasty involves photothermal non-destructive heating of the septal cartilage allowing plastic deformation of this tissue. It is performed in an outpatient setting requiring only about ten minutes to complete without the need for sedation or splints. No visible undesirable side effects were observed for all patients underwent to laser reshaping procedure. It is shown that the laser reshaping is a simple bloodless, painless procedure. Potential applications in aesthetic, reconstructive, and pediatric head and neck surgery are discussed.

Acoustic control of laser shaping of cartilage

The aim of this work is to control shaping of cartilage under laser heating with acoustic and opto-acoustic approaches. Generation of acoustic signal in cartilage is due to water movement through porous cartilage matrix.

Optical properties of nasal septum cartilage

Optical parameters (scattering coefficient s, absorption coefficient k and scattering anisotropy coefficient g) of hyaline cartilage were studied for the first time. Optical properties of human and pig nasal septum cartilage, and of bovine ear cartilage were examined using a spectrophotometer with an integrating sphere, and an Optical Multi-Channel Analyser. We measured total transmission Tt, total reflection Rt, and on-axis transmission Ta for light propagating through cartilage sample, over the visible spectral range (14000 - 28000 cm-1). It is shown that transmission and reflection spectra of human, pig and bovine cartilage are rather similar. It allows us to conclude that the pig cartilage can be used for in-vivo studies instead of human cartilage. The data obtained were treated by means of the one-dimensional diffusion approximation solution of the optical transport equation. We have found scattering coefficient s, absorption coefficient k and scattering anisotropy coefficient g by the iterative comparison of measured and calculated Tt, Rt and Ta values for human and pig cartilage. We found, in particular, that for 500 nm irradiation s equals 37,6 plus or minus 3.5 cm-1, g equals 0,56 plus or minus 0.05, k approximately equals 0,5 plus or minus 0.3 cm-1. The above data were used in Monte Carlo simulation for spatial intensity profile of light scattered by a cartilage sample. The computed profile was very similar to the profile measured using an Optical Multi-Channel Analyzer (OMA).