Jean-Michel Tualle

Performance assessment of photon migration instruments: the MEDPHOT protocol

We propose a comprehensive protocol for the performance assessment of photon migration instruments. The protocol has been developed within the European Thematic Network MEDPHOT (optical methods for medical diagnosis and monitoring of diseases) and is based on five criteria: accuracy, linearity, noise, stability, and reproducibility. This protocol was applied to a total of 8 instruments with a set of 32 phantoms, covering a wide range of optical properties.

Time-resolved diffusing wave spectroscopy with a CCD camera

We show how time-resolved measurements of the diffuse light transmitted through a thick scattering slab can be performed with a standard CCD camera, thanks to an interferometric protocol. Time-resolved correlations measured at a fixed photon transit time are also presented. The high number of pixels of the camera allows us to attain a quite good sensitivity for a reasonably low acquisition time.

Real-time inversion using Monte Carlo results for the determination of absorption coefficients in multilayered tissues: application to noninvasive muscle oxymetry: I

A clinical study of the evolution of the space resolved reflectance with the subcutaneous layers thickness, at rest, on the vastus lateralis, is used to determine convenient sets of muscle and fat optical coefficients at 850 nm. The results are compared to the data available in the literature. When the same study will be completed at 780 nm, these coefficients will be used in 3 layers MC simulations to establish pre-calculated tables of the reflectance as a function of the fat thickness and of the muscle absorption coefficient. The goal of this study is eventually to perform real time inversion during effort in order to determine the muscle oxygenation with this very simple technique (part 2).

Gadolinium/terbium hybrid macromolecular complexes for bimodal imaging of atherothrombosis

Abstract. We developed a fluorescence imaging microscope system intended for the localization within artery slices of a gadolinium-based macromolecular biospecific magnetic resonance (MR) contrast agent used for the visualization of atherothrombosis. As the contrast agent is not initially fluorescent, we substitute some gadolinium ions for terbium ions to make them fluorescent while preserving their chemical characteristics. A long fluorescence emission time constant enables us to have a suitable signal-to-noise ratio, despite a low intensity, using pulsed illumination and time-gated imaging. Images of rat arteries show that the contrast agent is indeed localized on the specific regions of the tissues. We currently have a tool that allows us to understand and optimize the MR contrast agent.

Real-time inversion using Monte Carlo results for the determination of absorption coefficients in multilayered tissues: application to noninvasive muscle oximetry: II

A clinical study of the evolution of the space resolved near infrared reflectance with the subcutaneous layers thickness, at rest, on the vastus lateralis, is used to determine convenient sets of muscle and fat optical coefficients at 850 nm and 780 nm. These coefficients are then used to establish pre-calculated 3 layers MC simulations tables of the reflectance as a function of the fat thickness. Real time inversion during effort is then performed to determine the absolute muscle oxygenation.

New method to perform time-resolved measurements: coherence scanning

We explore in this paper a new method to perform time-resolved measurements of the diffuse light transmitted through a thick turbid medium. This method is based on the analysis of the speckle fluctuations due a wavelength modulated source. A time resolution of about 50 ps is already achieved, and we expect to improve this result soon. This method could allow the design of low cost setups to perform such measurements.

Time- and space-resolved reflectance from multilayered turbid media

Our purpose is to develop an optical technique for in-vivo and non-invasive diagnosis using backscattered light measurements. We have already demonstrated that optical coefficients of turbid media ((mu) a, (mu) s) can be derived from time and space-resolved reflectance in the case of semi-infinite geometry. This procedure was then applied to the investigation of multi-layered media: the upper layer was an aqueous solution of calibrated latex microspheres in water and the lower layer of the sample was a solid phantom. Two different types of phantoms were used. In the first set of experiments, we used an absorbing medium for under layer. In the second case, the lower layer was an absorbing and scattering phantom. Comparison with Monte-Carlo simulations were achieved for the resolution of the inverse problem.

Retrieving viscoelastic properties using time-resolved spatial speckle imaging

The assessment of materials viscoelastic properties often represents a means of diagnosis or characterization of biological tissues and biomaterials. In this paper, we introduce a new optical method for the evaluation of dynamical properties of viscoelastic media. The approach is based on time-resolved spatial speckle imaging, using a continuous wave CW illumination and a standard CCD detector. We demonstrate that an estimation of viscoelastic properties is possible, by analyzing intensity and contrast profiles of scattering spot images acquired over multiple exposure times. The accuracy of this approach is evaluated using simulated tissue mimicking media having well known optical and dynamical properties.

La tomographie optique diffuse

Les methodes optiques presentent de nombreux avantages pour le diagnostic medical. Elles permettent d’acceder a des informations essentielles sur les tissus telles que leur oxygenation (par spectroscopie) ou leur perfusion (par analyse des correlations du speckle optique). Elles demandent en revanche la resolution de problemes inverses complexes, resolution grâce a laquelle les mesures resolues en temps peuvent se reveler un atout. De nouveaux circuits integres a pixels « intelligents » pourraient par ailleurs faciliter l’analyse statistique en temps reel du speckle.

In vivo time-resolved multi-distance spectroscopy of human forehead: a step towards optical characterization of brain tissue

Multi-distance time-resolved spectroscopy of in-vivo human forehead was performed on five volunteers in the range 700-1000 nm. A Monte Carlo simulation based on a four-layer model was employed and compared with in vivo data.