© CEA Tous droits réservés. Toute reproduction totale ou partielle sur quelque support que ce soit ou utilisation du contenu de ce document est interdite sans l’autorisation écrite préalable du CEA All rights reserved. Any reproduction in whole or in part on any medium or use of the information contained herein is prohibited without the prior written consent of CEA Abstract Fluorescence Diffuse Optical Tomography is a promising technique for cancer diagnostic. It provides a way to characterize and localize tumors with a good accuracy and without ionization of tissues[1]. This technique can be performed by continuous or time resolved measurements. Time-resolved imaging is based on the use of subnanosecond laser pulses for excitation combined to fast response detection, providing photon time of flight. This poster presents an optimization of the acquisition geometry for breast cancer diagnosis. The influence of the sources step and the relative position between the source-detectors and the inclusions are demonstrated by simulations. After setting the optimal parameters, experimental acquisition was performed on a breast phantom made of gelatin and other components reproducing both its optical and geometrical properties. A fluorescent inclusion was placed inside the phantom to simulate a marked tumor. The fluorescence yield is reconstructed by processing the first two moments of the temporal fluorescence signals obtained for each source detector combination. A novel reconstruction method was used to localize the fluorescent inclusion with a millimetric resolution. Conclusion [1]A.P. Gibson, J.C. Hebden, et S.R. Arridge, “Recent advances in diffuse optical imaging,” Phys. Med. Biol, vol. 50, 2005, pp. 1–43. [2]J. Hebden, H. Veenstra, H. Dehghani, E. Hillman, M. Schweiger, S. Arridge, et D. DELPY, “Three- dimensional time-resolved optical tomography of a conical breast phantom,” APPLIED OPTICS, vol. 40, Jul. 2001, pp [3]A. De Grand, S. Lomnes, D. Lee, M. Pietrzykowski, S. Ohnishi, T. Morgan, A. Gogbashian, R. Laurence, et J. Frangioni, “Tissue-like phantoms for near-infrared fluorescence imaging system assessment and the training of surgeons,” JOURNAL OF BIOMEDICAL OPTICS, vol. 11, Fév An analysis of the geometrical parameters showed that larger source steps provide better localization. The quality of the reconstruction is highly dependent on the relative position of the source and the inclusion. An optical time resolved system allowed us to achieve localization of a fluorescent inclusion inside a breast-mimicking phantom which is representative both on its optical absorption (µ a ) and diffusion (µ s ’) properties. The associated reconstruction algorithm uses the mean intensity and the time of flight of the photons to get a 3D estimation of the tumor localization. A general study of optimal geometric parameters for time resolved diffuse optical tomography. Jérôme Boutet, Ludovic Lecordier, Simon Rehn, Mathieu Debourdeau, Lionel Hervé, Jean-Marc Dinten LETI - CEA Minatec - 17 rue des Martyrs Grenoble Cedex 9, France. References Reconstruction: The algorithm had been able to reconstruct the fluorescence yield where expected with experimental measurements. Intensities contribution Reconstruction from intensity only fails due to poorer signal to noise and the fact that shallow fluorophores provide a similar intensity contribution as more concentrated deep fluorophores. Acquisition system and experimental results Experimental set-up based on a titanium sapphire laser producing 50 fs pulses at 775 nm. The detector, a time gated camera, is connected to the probe through an optical fiber network This phantom was made by a combination of gelatin [3], intrlipid and bovine hemoglobine. Concentration of the components were tuned to fit the absorption and diffusion coefficient of breasts (µa=0.03cm- 1|µs’=7cm-1) The cancerous region was simulated by a capillary tube containing 0.1 cm 3 solution of ICG dye. lens camera lens HRI filters Influence of geometrical parameters Influence of the step between sources :These series of simulations show that larger source steps provide better localization accuracy. However, we have to find a compromise between the quality of reconstruction and the size of the probe Simulated phantom and fluorescence obtained for increasing source step values We simulated a fluorescent inclusion inside the breast and compared different geometries to study the influence of the number, step and position of the sources and detectors Influence of the probe position: The best resolution is obtained for the shortest source-inclusion distance. Simulated phantom and fluorescence obtained for different source and detector positions. 1st line corresponds to an inclusion positioned at the centre of the breast. 2nd line to an inclusion at the external boundary. Time of flight contribution In reflection geometry, the time of flight is highly dependent on the distance between the inclusion and the surface. Thus, time of flight provide a good resolution along Z axis. 3D view of the reconstructed fluorescence map based on experimental acquisitions. Photo of the breast phantom mold and its fluorescent inclusion Signals: This algorithm uses the first two moments of the signals : mean intensity M 0 and mean time of flight M 1 /M 0 Discretized volume: We work on a tetrahedral breast-shaped mesh obtained by a Delaunay tessellation Algorithm: A novel reconstruction method was developed to achieve localization of the inclusion. This algorithm finds the best position and concentration of one fluorophore in the medium according to a Chi- square criterion. For each voxel of the discretized medium, we assume the voxel contains the fluorescent inclusion that we are looking for. Then, we calculate the fluorescence yield that best matches the signals and determine the value of the criterion for the considered voxel. At last, the set of voxels for which the criterion is optimal is displayed Detailed description: This algorithm will be presented during Scientific Session 16: Advances in Optical Imaging ~ September 25, 2009 from 1:00 PM to 2:30 PM. Reconstruction technique fs laser Discretized Breast volume Probability of localization of the inclusion as a function of Z axis. Simulated reconstruction of a fluorescent inclusion in a cubic medium with the use of Intensity only Simulated reconstruction of a fluorescent inclusion in a cubic medium with the use of the time of flight and intensities Contribution of the time of flight information in reflection geometry