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.
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.
We have investigated the application of AO sensing for quantitative three-dimensional mapping of tissue-mimicking
phantoms. An Intralipid phantom, which contains a turbid absorber, confined in a silicone tube, was used. Multiply
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. By moving the ultrasound transducer, we could build up a volumetric map of modulation
depth values. We have experimentally determined the acousto-optical modulation depth as a function of the absorption
coefficient in phantom voxels of a few millimeters in size.
We have investigated if the application of microsecond length pulses of ultrasound and laser light for AO sensing
could result in an improvement of the detection of changes 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 and subsequent image contrast processing. This
approach has proved that a spatial resolution of the system of a few millimeters can be obtained and thus, smaller
changes in the absorber concentration can be measured. Based on a comparison of experimental data and Monte-
Carlo simulations, the quantitative correlation between local absorbances of the phantom and the measured signal
has been shown.
KEYWORDS: Modulation, Photons, Signal to noise ratio, Acousto-optics, Absorbance, Speckle, Sensors, Monte Carlo methods, Spectroscopy, Systems modeling
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.
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