Time-resolved fluorescence intensity issued from a heterogeneous slab: Sensitivity characterization

Optical imaging using fluorescent contrast agents has become an interesting tool to differentiate diseased lesions from normal tissue. However, several sensitivity characterizations may strongly influence the time-dependent fluorescence measurements. Herein, we present a numerical model based on the finite element method that allows the simulation of time-resolved reflectance and transmittance signals from heterogeneous media mimicking breast tissues with an embedded fluorescent object (tumor). The influence, on the computed signals, of several tumor depths, as well as various fluorophore concentrations and several fluorescent markers targeting are analyzed. The results show the possibility of uncoupling location depth from the shape of the target. Therefore, the analysis of the time to reach half the maximum intensity is validated as a good localization scheme. Then, the transmitted data show that the maximal detected intensity at the bottom of the medium is very sensitive to the dye concentration but not to the tumor shape. Moreover, the strong competition between concentration determination and fluorophore distribution is presented. These results will lead to a better detection and localization of tumors

Effets de la fluorescence résiduelle dans les tissus biologiques sur les signaux de fluorescence résolus temporellement par la méthode des éléments finis

RésuméUn modèle numérique basé sur la méthode des éléments finis est proposé afin d’analyser l’influence, sur les signaux de fluorescence résolus dans le temps, de la fluorescence résiduelle présente dans les milieux environnant une lésion tumorale. Nous appliquons une méthode de soustraction des données dans le cas d’une concentration imparfaite des agents de fluorescence au sein de la tumeur. Nous montrons ainsi les limites de la méthode de soustraction pour un faible contraste de fluorescence tumeur/milieu ambiant. En particulier, nous analysons l’extraction du temps de demi-montée et du maximum de l’intensité de fluorescence en fonction de la profondeur de la cible fluorescente. A computational model based on finite element method is derived to examine how the simulated time-dependent signals are related to the presence of residual fluorescence in biological media surrounding a fluorescent object. We apply a subtraction technique on recorded data when imperfect uptake of fluorescing agent into the tumor is considered. We show the limits of the subtracting method for low target: background fluorescent absorption contrast by extracting the time to reach the half maximum and analyzing the maximum of the time-resolved signals versus target depth

A new method to determine arterial distensibility in small arteries

Several methods allow to measure arterial distensibilty. One of them consists in estimating the direct distensibility (D) from diameter and distending blood pressure. Herein, we propose a new method to assess the distensibility in small arteries which is based on spectral analysis of time motion mode ultrasound images of radial arteries. A Fourier transform was performed on intensity of upper and lower walls. Spectral amplitude at heart frequency from both wall spectra was estimated and summed (SumAmp). SumAmp was then compared with direct distensibility. A significant correlation was found between SumAmp and D (r = 0.7, p = 0.02)

Mesures et analyses biomécaniques des interactions macrocirculation/microcirculation sanguines

L'étude de paramètres de type distensibilité des vaisseaux constituant le système cardiovasculaire est très pertinente pour le diagnostic de certaines pathologies. Nous proposons d'estimer la corrélation entre les propriétés biomécaniques des vaisseaux sanguins de gros calibre et ceux de petit calibre. Un protocole de mesure est présenté intégrant l'acquisition de signaux d'impédance bioélectrique et de fluxmétrie laser Doppler. Une analyse de ces données est effectuée à partir de diverses techniques de traitement du signal (analyses de flux, de pressions, etc), et d'une étude statistique