Time-domain reflectance diffuse optical tomography with Mellin-Laplace transform for experimental detection and depth localization of a single absorbing inclusion.

International audienceWe show how to apply the Mellin-Laplace transform to process time-resolved reflectance measurements for diffuse optical tomography. We illustrate this method on simulated signals incorporating the main sources of experimental noise and suggest how to fine-tune the method in order to detect the deepest absorbing inclusions and optimize their localization in depth, depending on the dynamic range of the measurement. To finish, we apply this method to measurements acquired with a setup including a femtosecond laser, photomultipliers and a time-correlated single photon counting board. Simulations and experiments are illustrated for a probe featuring the interfiber distance of 1.5 cm and show the potential of time-resolved techniques for imaging absorption contrast in depth with this geometry

Depth probing of diffuse tissues controlled with elliptically polarized light

5 pagesInternational audiencePolarization gating is a popular technique in biomedical optics. It is widely used to inspect the surface of the tissues (under colinear or cocircular detection) or instead to probe the volume (cross-linear detection), without information on the probed depth. Elliptical polarization is introduced to explore the possibility of probing diffuse tissues at selective depths. A thorough Monte Carlo simulation study shows complete correlation between the probed depths and the ellipticity of the polarized light, for a medium with known optical properties. Within a wide range of optical parameters, a linear relation between the backscattered intensity and the depth extension of the probed volume was found whatever the polarization used, but with a controlled extension depending on the ellipticity

Toward noninvasive assessment of flap viability with time-resolved diffuse optical tomography: a preclinical test on rats

The noninvasive assessment of flap viability in autologous reconstruction surgery is still an unmet clinical need. To cope with this problem, we developed a proof-of-principle fully automatized setup for fast time-gated diffuse optical tomography exploiting Mellin–Laplace transform to obtain three-dimensional tomographic reconstructions of oxy- and deoxy-hemoglobin concentrations. We applied this method to perform preclinical tests on rats inducing total venous occlusion in the cutaneous abdominal flaps. Notwithstanding the use of just four source-detector couples, we could detect a spatially localized increase of deoxyhemoglobin following the occlusion (up to 550 μM in 54 min). Such capability to image spatio-temporal evolution of blood perfusion is a key issue for the noninvasive monitoring of flap viability

imagerie optique in vivo : explorer le contraste optique endogène en profondeur des tissus

National audienceLe contraste optique endogène des tissus biologiques porte des informations anatomiques et fonctionnelles riches. En effet, lors de sa pénétration dans les tissus, la lumière interagit (par absorption et diffusion) avec différents chromophores tels que l’hémoglobine (forme oxy et desoxy), l’eau, les lipides, dont la concentration et ses variations temporelles traduisent respectivement la composition du tissus et l'activation de processus métaboliques. Cependant, les tissus biologiques sont diffusant pour la lumière. Ce phénomène limite l'utilisation de la microscopie optique à des profondeurs de pénétration inférieure à 1 mm. Pour extraire le contraste optique en profondeur dans les tissus, plusieurs méthodes d'imagerie ont été mises au point. Nous présenterons en parallèle ici deux approches émergentes pour des applications in vivo : la tomographie optique diffuse résolue en temps et l'imagerie photo-acoustique. Ces méthodes prometteuses s'appuient sur des acquisitions tomographiques pour reconstruire le contraste optique en régime diffusif et peuvent discriminer différents chromophores par leur signature spectrale en sondant les tissus à plusieurs longueurs d'onde dans le proche infrarouge. Nous comparerons brièvement dans cet exposé leur principe physique, leur contraste et résolution, et discuterons leurs régimes d'applications biomédicales

Time-Resolved Reflectance Diffuse Optical Tomography by using Mellin-Laplace Transform

International audienceIn this paper, we show how the Mellin-Laplace Transform helps to obtain robust and relevant reconstructions of deep optical heterogeneity from time-resolved diffuse optical tomography measurements

Time-resolved measurements in diffuse reflectance: effects of the instrument response function of different detection systems on the depth sensitivity

International audienceWe demonstrate the loss of depth sensitivity induced by the instrument response function on reflectance time-resolved diffuse optical tomography through the comparison of 3 detection systems: on one hand a photomultiplier tube (PMT) and a hybrid PMT coupled with a time-correlated single-photon counting card and on the other hand a high rate intensified camera. We experimentally evaluate the depth sensitivity achieved for each detection module with an absorbing inclusion embedded in a turbid medium. The different interfiber distances of 5, 10 and 15 mm are considered. Finally, we determine a maximal depth reached for each detection system by using 3D tomographic reconstructions based on the Mellin-Laplace transform

Diffuse reflectance spectroscopy: a clinical study of tuberculin skin tests reading

International audienceDiffuse reflectance spectroscopy is a technique widely used to determine optical properties of tissues: scattering and absorption coefficients. In this study, we present the development of a low-cost optical instrument usable in a clinical environment based upon the spatially resolved diffuse reflectance spectroscopy approach. This instrument has been used in a clinical study to support the diagnosis of tuberculosis. The idea is to establish a new scanning method for an early detection of inflammation due to a reagent injection, before the onset of visual signs. Results comparing the instrumental and classical clinical readings are presented

Time-Resolved Reflectance DOT: Experimental Results for Imaging Absorption Contrast in Depth

International audienceDetecting and localizing precisely contrast in depth is the major challenge of reflectance Diffuse Optical Tomography. We present a dedicated time-resolved instrumentation and first experimental results using a Mellin-Laplace Transform based method