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Abstract

X-ray induced luminescence imaging employs lanthanide-doped nanophosphors that emit near-infrared light in the presence of ionizing radiation. This nascent modality has potential applications in molecular imaging or theranostic medicine. The penetrating nature of x-rays, which activate the imaging probes, allows for imaging at depths beyond conventional optical fluorescence imaging in a diffuse environment like mammalian tissue. The x-ray induced luminescent properties of europium-doped nanophosphors are initially characterized with experimental measurements within a small animal irradiator. Measurements in optical gel phantoms are used to calibrate an imaging model that is then used for simulations that evaluate the sensitivity of the nanoparticles with respect to concentration, dose, and imaging depth. Shaping the incoming x-ray beam geometry constrains the x-ray induced luminescence to a known region within the object, thus reducing the ill-posedness of reconstructing nanophosphor distributions at depth from a detected surface radiance measurement. A selective-plane geometry is presented which allows for a two-dimensional deconvolution-based reconstruction and is experimentally demonstrated in optical gel phantom measurements. A benchtop system with a pencil beam geometry is presented which allows for dual-modality imaging of x-ray induced luminescence and of x-ray fluorescence. The x-ray induced luminescence reconstruction reduces to a one-dimensional deconvolution and the reconstructed x-ray fluorescence image serves as prior information that enhances the x-ray induced luminescence reconstruction. Experimental measurements demonstrate that the x-ray luminescence/x-ray fluorescence joint reconstruction combines the high resolution of the x-ray fluorescence imaging with the high sensitivity of the x-ray luminescence imaging.

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