A. Bratchenia

Acousto-optic-assisted diffuse optical tomography.

We introduce and experimentally demonstrate acousto-optic-assisted diffuse optical tomography (DOT) using a holography-based acousto-optic setup. The method is based on probing a scattering medium with a localized acoustical modulation of the phase of the scattered light. The optical properties of the scattering medium are recovered with ultrasound-limited resolution by applying DOT reconstruction methods on a set of the measured intensities of light, modulated at different locations throughout the medium.

Feasibility of quantitative determination of local optical absorbances in tissue-mimicking phantoms using acousto-optic sensing

We have investigated the application of ultrasound modulation of coherent light for quantitative determination of local absorbances in tissue-mimicking phantoms. An Intralipid-based phantom model, which mimics a blood vessel in human tissue, was used. The detection technique was based on homodyne parallel speckle detection in transmission mode. Based on a comparison of experimental data and Monte Carlo simulations, a quantitative correlation between local absorbances of the phantom and the measured signal has been shown. The use of microsecond pulses of ultrasound and laser light resulted in a spatial resolution of the system of a few millimeters

Millimeter-resolution acousto-optic quantitative imaging in a tissue model system

We have investigated the application of ultrasound modulated coherent light for quantitative determination of the ratio of dye concentrations and total concentration of absorbers in a blood vessel-mimicking sample. A 3-mm-diam tube containing the mixture of dyes inside an Intralipid-based gel with optical properties similar to tissue was interrogated by two different laser wavelengths in combination with intense microsecond ultrasound bursts. The use of calibration curves allowed us to extract quantitative information on the ratio of dye concentrations with the accuracy of better than 15%, as well as on the total concentration. Furthermore, we demonstrated the feasibility to obtain a quantitative 3-D map of the absorbing structure with a spatial resolution of better than 3 mm. These findings give an outlook to apply this technique for noninvasive 3-D mapping of oxygen saturation and total concentration of hemoglobin in tissue.

Towards quantitative acousto-optic imaging in tissue

We have investigated the possibilities and limitations of the application of ultrasound modulated coherent light to obtain quantitative information of local absorbers in light-scattering objects, among which tissue. For all objects studied, the combined use of microsecond ultrasound and light pulses enabled us to construct a 3D map of local absorbers with a spatial resolution of ∼2 mm. Moreover, in relatively homogeneous model systems, mimicking a blood vessel embedded in tissue, the use of a calibration procedure allowed for a determination of the local absorbance. Speckle decorrelation times for real tissue containing blood vessels, in which appreciable motion of scatterers can exist, were found to be smaller than 1ms. These relatively short times present a major challenge for acousto-optics to be applied in living tissue systems.

Acousto-optic spectroscopy as a tool for quantitative determination of chemical compounds in tissue: a model study

We have made a comparison of various detection strategies for detection of acoustically modulated light in a scattering medium. Furthermore we have investigated the possibility to determine the local absorbance in a model system mimicking a blood vessel in tissue.

Quantitative acousto-optic imaging in tissue-mimicking phantoms

We have investigated the application of acousto-optic sensing for quantitative imaging of tissue-mimicking phantoms. An Intralipid phantom, which contains a turbid absorber, confined in a silicone tube, was used. Scattered pulsed laser light was modulated by ultrasonic bursts focused in a predefined volume in the medium. By varying the delay time between ultrasound burst initiation and light pulse firing we could perform a scan in the ultrasound-propagation plane. The use of calibration procedures allowed us to establish a quantitative correlation between local absorbances in the phantom and the measured signal and to obtain information on the ratios of dye concentrations inside the tube.