Development of a preclinical CCD-based temperature modulated fluorescence tomography platform.

In preclinical research, fluorescence molecular tomography (FMT) is the most sensitive imaging modality to interrogate whole-body and provide 3D distribution of fluorescent contract agents. Despite its superior sensitivity, its mediocre spatial-resolution has been the main barrier to its clinical translation. This limitation is mainly due to the high scattering of optical photons in biological tissue together with the limited boundary measurements that lead to an undetermined and ill-posed inverse problem. To overcome the limitations of FMT, we previously introduced a novel method termed, Temperature Modulated Fluorescence Tomography (TMFT). TMFT utilizes thermos-sensitive fluorescent agents (ThermoDots) as a key component and localizes them with high-intensity focused ultrasound (HIFU). Scanning the focused HIFU beam having a diameter Ø = 1.3 mm across the tissue while monitoring the variation in the measured fluorescence signals reveals the position of the ThermoDots with high spatial accuracy. We have formerly built a prototype TMFT system that uses optical fibers for detection. In this paper, we present an upgraded version using a CCD camera-based detection that enables non-contact imaging. In this version, the animal under investigation is placed on an ultrasound transparent membrane, which eliminates the need for its immersion in optical matching fluids that were required by the fiber-based system. This CCD-based system will pave the way for convenient and wide-spread use of TMFT in preclinical research. Its performance validation on phantom studies demonstrates that high spatial-resolution (∼1.3 mm) and quantitative accuracy in recovered fluorophore concentration (<3% error) can be achieved.