Last researches on Osteoporosis disease show's that the correlation between BMD information that come from DXA,
and the fractual risk are not enough correlated. For this reason, new techniques that could be more sensitive and give
different information's on the bone are being looking for. The key for success is to find a technique that could be
detected changes in the micro-structure inside the trabecular bone, and supply more information on this structure.
We have shown that pulse ultrasound light tomography could work in well reflection configuration and on living tissue
to measure locally the "reduce scattering coefficient" inside the body. This technique could work deep inside the body
(few cm) and could supply very good resolution. In the beginning on this research we show clinical results that justified
planning more accurate and larger clinical study. The system suffers from mechanical and body interface problems that
only very skill and professional physician could get a good results. This system also suffers from low signal to noise
ratio, and irrevocable data on the same people. In this lecture we will present an upgrade and improved system. The
mechanical and body interface changes will present and discusses. A good repeated data will be presented on phantoms
and on peoples. Finally, large clinical data that operated in clinical technician on 60 Ultra distal bone peoples will
present in compare to DXA data that was measure on the same peoples on the same place.
Ultrasound modulated light tomography (UMLiT) is a very attractive method for optical imaging of turbid media. Different schemes have been developed for effectively discriminating between the non-modulated and modulated photons and locate absorbing inhomogeneities. L. Wang has shown the possibility of using chirped ultrasound as well as Radon transformed-based tomography for three-dimensional imaging, C. Boccara has demonstrated the use of ultrafast cameras in order to increase the signal to noise ratio. Our group has shown the use of pulsed ultrasound for three-dimensional localization. However, although there have been a strong effort towards imaging objects in phantoms, very few experiments have shown quantitative results probing the limits of the technique in terms of resolution and sensitivity. We will present experimental results obtained in a reflection configuration. In a first series of experiments we present results obtained on living mice and rabbits, showing two and three-dimensional representations. In a second series of experiments, we have prepared different Agar-based phantoms in which small absorption inhomogeneities have been introduced. The background effective attenuation was 0.05 cm-1. Several 5 mm diameter inclusions have been introduced in the phantom in different geometries with an effective absorption varying from twice to ten times the background. These inclusions could be detected up to a depth of 4 cm.
There have been several attempts to detect bone structural changes using optical techniques. H.G. Eberle et al. have used ultrafast optical techniques on the finger in trans-illumination and have shown an excellent correlation between their measurements of the scattering coefficient and bone mineral density obtained using dual X-ray absorption (DXA) imaging. Encouraged by these results, we have developed a system based on the combination of cw laser light and low-frequency ultrasound to probe the bone structure. The physical principle of this system is the detection of laser light diffusing in the bone tissue modulated ("tagged") by a low-frequency ultrasound pulse, which allows a local measurement of the attenuation coefficient. The basic assumption of the technique is that the main factor of attenuation changes in the bone of elderly patients is a scattering change due to osteoporosis, and therefore attenuation measurements directly reflect the scattering properties of the bone. We present a preliminary series of clinical experiments showing that this technique allows determining the bone scattering modification inside the trabecular bone. In this series of clinical experiments, the scattering coefficient determined using the optical technique is compared with the bone mineral density obtained using dual X-ray absorption in a group of 9 patients. A correlation of 0.84 (p=0.05) was found, showing the potential of this technique for the assessment of osteoporosis.
Arsenic based chalcogenide glasses present several advantages for nano-structured optical devices in the infrared. First they possess a good transparency in this optical window, second their amorphous nature is ideal for coating based applications or for hybrid integration, third their photo-structural transformation properties give the possibility of creating high-resolution patterns on films and finally their high index make them particularly suitable for the fabrication of photonic crystal devices. We have demonstrated the fabrication of two-dimensional and three-dimensional (wood-pile) photonic crystal structures for typically 500 nm period structures using interferometric lithography to create the periodic pattern. We show here different techniques in order to obtain specific patterns on the chalcogenide glass using a combination of illumination, etching and redeposition techniques. Moreover, in order to create very steep contrast, we have used the fact that silver ions can freely propagate in the glass under light action, providing a very effective contrast between illuminated and non-illuminated regions. 130 nm patterns with a 500 nm periodicity have been obtained using silver doping of chalcogenide glasses. We will finally show different examples of pattern sculpturing using different illumination and film preparation conditions.
Ultrasound can be used in order to locally modulate, or tag, light in a turbid medium. This tagging process is made possible due to the extreme sensitivity of laser speckle distribution to minute changes within the medium. This hybrid technique presents several advantages compared to all-optical tomographic techniques, in that the image resolution is fixed by the ultrasound focus diameter. To our best knowledge, only in vitro experiments have been performed, either on tissue-like phantoms or meat. However a strong difference exists between these sample and living tissues. In living tissues, different kind of liquids flow through the capillaries, strongly reducing the sspeckle autocorrelation time. We have performed experiments on both mice and humans, showing that the autocorrelation time is much shorter than what was previously thought. We show however that it is possible to obtain signal with acceptable signal to noise ratio down to a few cm depth. We will also discuss the origin and characteristics of the speckle noise.
Probing photon density in diffusive media is very important in order to model and understand their propagation. It is possible to detect photons outside the medium, but their non-invasive detection inside it is still an unsolved problem. An elegant, semi-invasive approach to perform this task is to scan a small absorbing sphere inside the turbid medium and measure the light outside the sample when the sphere is present and when it is not. However this method requires the medium to be liquid and such a procedure cannot be performed in the case of biological tissues. Ultrasound tagging of light has been introduced initially for transillumination imaging in turbid media, and then extended to the case of reflection imaging. Here we present results showing that it is possible to map the photon density inside solid turbid media by locally tagging photons using an ultrasonic field. We experimentally retrieve the well-known banana-shaped photons distribution when the source and the detectors are in a back-scattering configuration, using a gel-based homogeneous phantom. We also present experiments where hemoglobin has been introduced inside the gel. By fitting the experimental results with the theoretical formula, we are able to quantitatively retrieve the amount of hemoglobin introduced inside the gel, not only from data obtained by scanning the ultrasound waist inside the phantom, the in put and output fibers staying fixed.
AsSeTe/AsSe chalcogenide glasses are photosensitive materials with large refractive index. These properties make these glasses suitable for the fabrication of photonic crystals, waveguide components and MOEMS. We present in this article fabrication of 3D photonic crystals, composed from AsSeTe and air, with sub-micron feature size. The method of fabrication is relatively simple and cheap using only vapor deposition and optical holographic lithography. The interferometric alignment allows to eliminate requirement for a mask aligner.
Optical gain media filled with strong scatterers present a laser-like emission when optically pumped.Different regimes can be evidenced where amplified spontaneous emission together with multiple scattering play the main role. A mapping technique where both the concentrations of dye molecules and scatterers are independently varied allows to differentiate between those regimes. A simple model based on photon diffusion is presented and threshold for lasing emission is derived, and is compared with the experiment. Qualitative agreement is found, showing that the threshold critically depends on the samples macroscopic size.
Epitaxial methods allow the fabrication of nonlinear interferomethc structures which include the mirrors and the GaAs Multiple Quantum Wells (MQW) nonlinear medium in a single crystal. This results in very compact nonlinear microcavities with typically 5im overall thickness. Optical bistability is observed in these structures at mW optical power. We review our latest experimental results on these structures including the observation of high contrast switching in the reflection mode the direct measurement of dispersive optical nonlinearities in MQWs evidencing their saturation behavior at high intensities. Finally we report external-beam switching experiments which allow to assess the potential of these structures as all-optical gates.
GaAs/A1GaAs epitaxial structures allow the fabrication of monolithic bistable devices with very
appealing characteristics for all-optical switching applications, such aslow threshold power and good thermal
stability. They rely upon the excitonic and band-gap resonant nonlinearities in bulk GaAs or MQW. Very
compact devices of a few micron size with A1As/A1GaAs integrated Bragg reflectors can be grown during
a single epitaxial process. We report linear and nonlinear reflectivity measurements on such a monolithic
étalon with a MQW active layer grown by MOVPE. A bistability power threshold lower than 3 mW at
836 nm was observed with a reflective contrast ratio as high as 30: 1 .We show evidence that the refractive
index dependence on optical intensity is strongly sublinear, indicating that a substantial degree of saturation
occurs at intensity levels of iO W/cm2. We discuss the origin of this saturation and its implications on the
design of future devices.