Alexander I. Omelchenko

Speckle-contrast monitoring of tissue thermal modification

Measurements of the contrast value of time-averaged speckle-modulated images of cartilage tissue are used to study tissue thermal modification in the case of laser-light treatment. This modification is related to thermally induced internal stress relaxation in the matrix of the treated tissue. The specific feature of the evolution of time-averaged speckle contrast with a change in the current temperature of modified collagen tissue is the typical looplike form of the contrast-temperature dependencies associated with irreversible changes in tissue structure and correlated with changes in the tissue diffuse transmittance and the tissue internal stress mentioned by other researchers.

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 (Sc(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.

A prospective randomised study of laser reshaping of cartilage in vivo.

Abstract. Laser reshaping using low laser energy levels was performed on the cartilage of ten porcine ears. The ears were examined up to 4 months after laser reshaping and the stability of the reshaping was assessed by photography and casts obtained from alginate impressions of the ears. The cartilage was also studied histologically in three animals at 3 weeks, 8 weeks, and 4 months using haematoxylin and eosin (H&E), periodic-acid–Schiff (PAS) and alcian blue stains as well as Mib-1 antibody stain to detect cells in cycle. These ears were compared with the other control or non-irradiated ear. All the treated ears initially demonstrated a controlled alteration in their shape. Four were exposed to a pulse energy of 2 J/cm2 at 20 Hz with a spot diameter of 1.1 mm for 7 s and retained their shape for up to 14 days. However, the three exposed to the same levels of energy for 9 s showed tissue necrosis whereas the three which were treated for less than 4 s returned to their original shape after 24 h. Histological examination revealed that there was a dramatic eccentric proliferation of perichondrium away from the centre of irradiation with a noticeable absence of any inflammation. In all laser-irradiated areas there was a loss of staining with PAS and a dramatic increase in staining with alcian blue within the cartilage matrix. Viable chondrocytes were absent from the irradiated cartilage. Staining with a Mib-1 antibody that detects cells in cycle showed positive staining in a small fraction of proliferated perichondrial cells where new cartilage had been produced.

Laser shaping of cartilage

The carbon dioxide laser has been used for the first time to change the cartilages shape. After the laser irradiation the cartilage has the tendency to retain its new form. Different types of laser modified cartilage structures were studied. The inferred physical mechanism for cartilage shaping using the stresses relaxation process is presented. The clinical significance of the results for corrective laser surgery is discussed.

Stress relaxation and cartilage shaping under laser radiation

The problem of a purposeful change of the shape of cartilage is of great importance for otolaryngology, orthopaedics, and plastic surgery. In 1992 we have found a possibility of controlled shaping of cartilage under moderate laser heating. This paper presents new results in studies of that phenomenon. We have measured temperature and stress in a tissue undergoing to irradiation with a Holmium laser. Study of cartilage structure allowed us to find conditions for laser shaping without pronounced alterations in the structure of matrix.

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.

Mechanism of laser-induced stress relaxation in cartilage

The paper presents theoretical and experimental results allowing to discuss and understand the mechanism of stress relaxation and reshaping of cartilage under laser radiation. A carbon dioxide and a Holmium laser was used for treatment of rabbits and human cartilage. We measured temperature, stress, amplitude of oscillation by free and forced vibration, internal friction, and light scattering in the course of laser irradiation. Using experimental data and theoretical modeling of heat and mass transfer in cartilaginous tissue we estimated the values of transformation heat, diffusion coefficients and energy activation for water movement.

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.

Phenomenon of cartilage shaping using moderate heating and its applications in otorhinolaryngology

We have established that the phenomenon of cartilage shaping under the laser irradiation is connected with the bound-to-free transformation of water at a temperature around 70 degrees Celsius. The process of laser-induced stress relaxation in cartilage is accompanied and may be detected by the (1) mechanical, (2) thermal, and (3) optical effects. No pronounced structure effects were observed, for optimal conditions of the laser shaping of cartilage. The significance for otolaryngology of new laser applications for the shaping of cartilage is discussed.

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.