Alexander A. Oraevsky

Time-resolved optoacoustic method and system for noninvasive monitoring of glucose

The present invention is directed to a method/system of monitoring in real time changes in concentration of glucose in tissues. Laser-induced profiles of absorbed optical energy distribution in tissues are determined via measurements of spatial (in-depth) profile of optically-induced acoustic (pressure) transients using a wide-band optoacoustic transducer. Such technique can be applied for monitoring of glucose concentration in various human or nonhuman tissues, cell cultures, solutions or emulsions.

Laser-based optoacoustic imaging in biological tissues

A new technique based on time-resolved detection of laser-induced stress transients is proposed to visualize the distribution of absorbed laser fluence in turbid and layered biological tissues.

Optoacoustic monitoring of drug and contrast agent diffusion through skid

Opto-acoustic tomography is proposed and evaluated as a method to visualize and quantify penetration of drugs and optical contrast agents in skin and nails. Opto-acoustic front surface transducer operating in backward mode was developed and tested. Experimental results demonstrated that monitoring of drug diffusion in tissue is feasible with spatial resolution limited only by duration of laser pulses. Axial in-depth resolution of 18 um was achieved with 12-ns long laser pulses. Penetration of skin moisturizing lotions in skin and other solutions was visualized with the opto-acoustic tomography.

Working theory and experiments on photomechanical disruption of melanosomes to explain the threshold for minimal visible retinal lesions for sub-ns laser pulses

The threshold radiant exposure [Hth (J/cm2)] at the retina which produces a minimal visible lesion (MVL) has been investigated as a function of the laser pulse duration (tp). By considering the optical absorption coefficient of the melanosomal interior, (mu) a.melanosome, one can calculate the threshold deposited energy, Qth equals (mu) a.melanosomeHth (J/cm3), for the MVL. The tp-dependence of Qth is adequately explained for tp > 16 microsecond(s) by the thermal relaxation of heated melanosomes in the retinal pigmented epithelium (RPE). However, at very short pulses (< 100 ps), there is an apparent on the order of 10-fold drop in the Qth which is possibly due to the onset of a photomechanical mechanism of damage. Thermoelastic expansion of the laser-heated melanin granules (approximately 10 nm in size) within the 1.5-micrometers melanosome is induced by laser pulses less than 50 ps in duration. This expansion occurs faster than the induced pressure can dissipate from the granules at the speed of sound. The stress relaxation time of a 10-nm melanin granule is about 7 ps. As the accumulated pressure attempts to propagate out of the granule as a pressure wave, the pressure wave suffers reflectance at the granule surface boundary due to the difference in acoustic impedances of the granule and surrounding intramelanosomal matrix. About 12% of the acoustic energy is estimated to be reflected back into the granule as a negative (tensile) pressure wave. This negative stress is hypothesized to elicit cavitation within the melanin granule. This mechanism of intragranule cavitation is a working hypothesis for the mechanism of the MVL in the sub- 50-ps regime. An experimental test of feasibility was conducted using a Q-switched laser and a liver/saline interface. A negative reflectance of about -22% was demonstrated at the liver/saline interface, indicating the ease with which negative stress can be generated at interfaces with mismatched acoustic impedances.