Nhng tin b trong Quang hc, Quang ph vÃ ng dng VI ISSN 1859 - 4271

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Advances in Optics, Photonics, Spectroscopy & Applications VI ISSN 1859 - 4271Fig. 8: The fit is consistent with the scatterers Brownian motionin glycerol with 12% water at 19°.V. DEVELOPMENT OF A SPECIFIC SENSORWe have demonstrated that we could obtain an adequate SNR by using a multi-detectorsensor (i.e. a camera). However, the measurements could be easier, faster and more reliable witha custom designed sensor. We designed in our laboratory an ASIC camera in which each pixel isan opto-electronic processor with its own <strong>ph</strong>otodiode. All pixels measure and compute theresults in parallel. The early prototype, designed as a proof of concept, only has 400 pixels, butthe final sensor will have approximately a million detectors. The silicon process we chose hashigh quantum efficiency, typically more than 50%. So, we can expect a fast acquisition coupledto a very good SNR.Fig. 9: view of a pixel, with the <strong>ph</strong>otodiode (small rectangle) associated to a dedicated processorimplemen<s<strong>trong</strong>>tin</s<strong>trong</strong>>g our measurement protocol.At the present time, we are tes<s<strong>trong</strong>>tin</s<strong>trong</strong>>g and characterizing the circuit’s individual functions andcompare it to the electronic software simulations. We soon expect to be able to use it on realbiological tissues.(a)(b)Fig. 10: measurement of the circuit’s ability to lock-in, measure correlation,compared to thetheoretical expectations (part b).142
Những tiến bộ <strong>trong</strong> <strong>Quang</strong> học, <strong>Quang</strong> <strong>ph</strong>ổ và Ứng dụng VI ISSN 1859 - 4271VI. CONCLUSIONWe have shown that time-resolved measurements of the diffuse light transmitted throughthick scattering slabs can be performed with CCD cameras, thanks to the interferometric methodwe have developed in our laboratory. Time-resolved correlations can also be measured at a fixed<strong>ph</strong>oton transit time, and this provides valuable information about biological tissues perfusion. Atfirst, we tried ultra fast CCD cameras, but we were disappointed by the high level of electronicnoise in their images. Standard CCD cameras, with their high pixels count, allow us to attain aquite good sensitivity for a reasonably low acquisition time. We expect to outperform thesecameras with a custom designed ASIC, in which each pixel is coupled to a fixed-functionprocessor implemen<s<strong>trong</strong>>tin</s<strong>trong</strong>>g our measurement protocol.REFERENCESAll the calculations, the experimental setups and analysis of the noise sources are explained infull details in Katarzyna Zarychta’s PhD thesis “MESURES RESOLUES EN TEMPS DETRANSIT DE LA LUMIERE DIFFUSE AVEC UNE CAMERA CCD”, Université Paris 13,December 13th 2010 (in french).[1] J.-M. Tualle, E. Tinet and S. Avrillier, “A new and easy way to perform time-resolved measurementsof the light scattered by a turbid medium”, Opt. Comm., 189/4-6, 211-220, (2001).[2] J-M. Tualle, H. L. Nghiêm, C. Schäfauer, P. Berthaud, E. Tinet, D. Ettori and S.Avrillier, “Timeresolvedmeasurements from speckle interferometry”, Optics Letters, 30, Issue 1, 50-52, (2005).[3] J.-M Tualle, H. L Nghiêm, M. Cheikh, D. Ettori, E. Tinet and S. Avrillier, “Time-resolved diffusingwave spectroscopy beyond 300 transport mean free paths”, JOSA A, 23/6, 1452-1457, (2006).[4] M. Cheikh, H. L Nghiêm, D. Ettori, E. Tinet, S. Avrillier, and J.-M Tualle, “Time-resolved diffusingwave spectroscopy applied to dynamic heterogeneity imaging”, Optics Letters, 31 (15), 2311-2313,(2006).[5] T. Spirig, P. Seitz, O. Vietze, and F. Heitger, “The lock-in CCD- two-dimensional synchronousdetection of light”, IEEE J. Quantum Electron. 31 (9), 1705-1708 (1995).[6] P. Gleyzes, A.C. Boccara, and H. Saint-Jalmes, “Multichannel Nomarski microscope withpolarization modulation: performance and applications”, Opt. Lett. 22 (20), 1529-1531 (1997).[7] M. Gross, P. Goy, B. C. Forget, M. Atlan, F. Ramaz, A. C. Boccara, and A. K. Dunn, “Heterodynedetection of multiply scattered monochromatic light with a multipixel detector,” Opt. Lett. 30, 1357-1359 (2005) http://www.opticsinfobase.org/abstract.cfm?URI=ol-30-11-1357[8] D. Ettori, K. Zarychta, E. Tinet, S. Avrillier, J.-M. Tualle, “Time-resolved measurement of thescattered light with an interferometric method based on the use of a camera”, in Diffuse OpticalImaging of Tissue, R. Cubeddu ed., Vol. 6629 of Proceedings of SPIE-OSA Biomedical Optics(Optical Society of America, 2007), paper 6629_20.[9] M. A. Webster, T. D. Gerke, A. M. Weiner, and K. J. Webb, "Spectral and temporal speckle fieldmeasurements of a random medium," Opt. Lett. 29, 1491-1493 (2004)http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-29-13-1491[10] B. Varghese and V. Rajan, T.G. Van Leeuwen, W. Steenbergen, "Path-length-resolvedmeasurements of multiple scattered <strong>ph</strong>otons in static and dynamic turbid media using <strong>ph</strong>asemodulatedlow-coherence interferometry", J. Biomed. Opt. 12, 024020 (2007).[11] A.K. Dunn, H. Bolay, M.A. Moskowitz, and D.A. Boas, "Dynamic Imaging of Cerebral Blood FlowUsing Laser Speckle", Journal of Cerebral Blood Flow and Metabolism 21,195–201 (2001).143
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