Biomedical subjects

Juliette Selb

Publications and source records attributed to Juliette Selb.

3 recordsLinked to original sources

PubMed2003

High-contrast fast Fourier transform acousto-optical tomography of phantom tissues with a frequency-chirp modulation of the ultrasound.

We report new results on acousto-optical tomography in phantom tissues using a frequency chirp modulation and a CCD camera. This technique allows quick recording of three-dimensional images of the optical contrast with a two-dimensional scan of the ultrasound source in a plane perpendicular to the ultrasonic path. The entire optical contrast along the ultrasonic path is concurrently obtained from the capture of a film sequence at a rate of 200 Hz. This technique reduces the acquisition time, and it enhances the axial resolution and thus the contrast, which are usually poor owing to the large volume of interaction of the ultrasound perturbation.

Fourier Analysis↗

PubMedDate not supplied

Improved sensitivity to cerebral hemodynamics during brain activation with a time-gated optical system: analytical model and experimental validation.

Time domain (TD) diffuse optical measurement systems are being applied to neuroimaging, where they can detect hemodynamics changes associated with cerebral activity. We show that TD systems can provide better depth sensitivity than the more traditional continuous wave (CW) systems by gating late photons, which carry information about deep layers of the brain, and rejecting early light, which is sensitive to the superficial physiological signal clutter. We use an analytical model to estimate the contrast due to an activated region of the brain, the instrumental noise of the systems, and the background signal resulting from superficial physiological signal clutter. We study the contrast-to-noise ratio and the contrast-to-background ratio as a function of the activation depth and of the source-detector separation. We then present experimental results obtained with a time-gated instrument on the motor cortex during finger-tapping exercises. Both the model and the experimental results show a similar contrast-to-noise ratio for CW and TD, but that estimation of the contrast is experimentally limited by background fluctuations and that a better contrast-to-background ratio is obtained in the TD case. Finally, we use the time-gated measurements to resolve in depth the brain activation during the motor stimulus.

Artifacts↗

PubMedDate not supplied

Time-gated optical system for depth-resolved functional brain imaging.

We present a time-domain optical system for functional imaging of the adult head. We first describe the instrument, which is based on a Ti:Sapphire pulsed laser (wavelength 750-850 nm) and an intensified CCD camera enabling parallel detection of multiple fibers. We characterize the system in terms of sensitivity and signal-to-noise ratio, instrument response function, cross-talk, stability, and reproducibility. We then describe two applications of the instrument: the characterization of baseline optical properties of homogeneous scattering media, and functional brain imaging. For the second application, we developed a two-part probe consisting in two squares of 4 x 4 sources and 3 x 3 detectors. The laser source is time-multiplexed to define 4 states of 8 sources that can be turned on during the same camera frame while minimizing cross-talk. On the detection side, we use for each detector 7 fibers of different lengths creating an optical delay, and enabling simultaneous detection in 7 windows (by steps of 500 ps) for each detector. This multiple window detection allows depth sensitivity. The imaging probe was tested on dynamic phantoms and a preliminary result on an adult performing a motor task shows discrimination between superficial and cortical responses to the stimulus on both hemispheres.

Adult↗