In this paper we present systems for dual modality imaging, combining fluorescence-enhanced diffuse optical tomography and X-ray computed tomography. Fluorescence diffuse optical tomography is carried out in a cylindrical geometry, which ensures optimal sampling and a straight forward integration with the X-ray modality. Specific acquisition protocols and reconstruction software have been developed to this end. The X-ray computed tomography serves two purposes. First, it provides the anatomical information in the registered dual modality images. Second, it provides the actual shape and boundaries of the animal as a priori input to the fluorescence reconstruction algorithm. To evaluate the performance of the optical imaging system, experiments have been conducted on phantoms, mice with inserted fluorescing capillaries, and finally on mice bearing tumors, ex-vivo and in-vivo. Experiments on mice with capillaries inserted in different region of interest, allow estimating the detection limits of fluorophore concentrations. The fluorescence reconstructions are shown to be geometrically consistent with the X-ray images. Finally we demonstrate the capability of the bimodal system to localize real tumours in mice in-vivo. These results show that dual modality fluorescence-enhanced diffuse optical tomography and X-ray computed tomography imaging in cylindrical geometry has a high potential for small animal tumour evolution studies. 1. Introduction Three-dimensional near-infrared fluorescence-enhanced Diffuse Optical Tomography (fDOT) has been proven to be an efficient noninvasive tool for preclinical cancer research [1, 2]. With it, the biodistribution of fluorescent probes targeting molecular markers of tumor development can be quantitatively estimated. Moreover, fDOT can be used to assess the influence of anti-cancer treatments on the molecular level, which makes it a relevant technique not only in fundamental research but also in drug development [3–5]. fDOT, as a molecular imaging modality analog to PET, does not readily provide anatomical information. However, structure can be obtained by combining fDOT with a second modality providing morphological information, such as MRI [6, 7], ultrasound [8, 9], or XCT [10–13]. In this way, obtaining in vivo anatomical and molecular information simultaneously becomes possible. In the present work, XCT has been chosen as the second imaging modality because it provides high resolution, is relatively cheap, and its integration with optical tomography in a single instrument is straightforward. The dual-modality-approach
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