2007 Virtual source patterns for fluorescence tomography N. Ducros 1 , A. Bassi 1 , C. D’Andrea 1,2 , G. Valentini 1 , M. Schweiger 3 , and S.R. Arridge 3 1 Instituto di Fotonica e Nanotecnologie (IFN-CNR); Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy. 2 Italian Institute of Technology (IIT), Piazza Leonardo da Vinci 32, I-20133 Milan, Italy. 3 Centre for Medical Image Computing, University College London, Malet Place, London WC1E 6BT, United Kingdom. nicolas.ducros@polimi.it Principle o We consider an absorbing and diffusing medium (so- called turbid medium) W injected with fluorescence markers. We note f the fluorescence distribution. o A portion ∂W e of the medium surface ∂W is illuminated with a source pattern s. The photon density f e propagates within the medium and excites the fluorescence markers that act as secondary sources of light. o The fluorescence light f f exiting the medium surface through ∂W f is recorded by a CCD camera. A fluorescence image m is obtained. o The measurement is repeated projecting different source patterns and rotating the medium (different views are considered). Results Conclusions o Easy approach o Any pattern (negative or even complex) can be considered o Wavelet bases can be easily integrated into the virtual pattern framework Future work o Application of the method to mouse measurements o Adaptation of the detection area to the specific view o Influence of the autofluorescence? Pattern-based approach o Classical approach – Point detectors and point sources Detector: coupling problems, complicated to deal with, and very poor information compression ability. Source: raster scanning of the point source is slow (many source positions to cover, hence many measurements to make). o Pattern-based approach – Source and detection patterns [1-5] Detector: use of CCD cameras, non contact, easy to manage, and high compression ability. The fluorescence image m can be compressed to few components with little degradation. We consider: Source: using DMDs allows for projecting any pattern of light. How to choose source patterns? From a basis, e.g., Fourier or wavelet. Problem: Negative patterns cannot be projected Solution: Adding a DC component to get positive patterns  This solution sacrifices the benefit of using multiple source patterns [5]. Reconstruction Scheme References [1] S. D. Konecky et al., “Quantitative optical tomography of sub-surface heterogeneities using spatially modulated structured light” Opt. Express, 17(17), 14780, 2009. [2] C. D’Andrea et al., “ Fast 3D optical reconstruction in turbid media using spatially modulated light," Biomedical Optics Express, 1(2), 471, 2010. [3] N. Ducros et al., “A full-wavelet approach for fluorescence diffuse optical tomography with structured illumination," Optics Letters, 35(21), 3676, 2010. [4] N. Ducros et al., “Multiple-view fluorescence optical tomography reconstruction using compression of experimental data," Optics Letters, 36(8), 1377, 2011. [5] N. Ducros et al., “Virtual source pattern method for fluorescence tomography with structured light,” Phys. Med. Biol., submitted 2012. Acknowledgment Royal Society International Joint Project 2009/R2, Cariplo Foundation (Grant 2009-2626) and MIUR under the project Futuro in Ricerca (prot. RBFR08XH0H 002). phantom Abstract In order to reduce both acquisition and reconstruction times, illumination and detection in fluorescence molecular tomography have recently evolved from a point-based to a pattern-based approach. However, the choice of the best set of source patterns to project onto the sample is still an open problem. Here, we introduce a novel method, namely the virtual source patterns method, which allows for considering patterns with negative intensities. This method is shown to significantly increase the contrast and to reduce the reconstruction error. 6 virtual patterns 8 actual patterns Actual patterns (scaling functions at scale i) Virtual patterns (wavelet functions at scale i-1) Virtual pattern method o The problem is linear in terms of illumination. For a source pattern of the form , we get the measurement o Any source pattern can be considered provided that a set of actual (positive) source patterns S = [s 1 ... s J ] and a set of mixing coefficients T = [t 1 ... t J ] exist and satisfy: The corresponding virtual measurements are given by: o In practice, how can one find S and T ? Fourier basis: the phasor method offers a solution [1].  Wavelet basis: wavelets functions at a given scale can be obtained from scaling functions at a finer scale [5]. View publication stats View publication stats