Purpose: X-ray-induced luminescence computed tomography (XLCT) based on X-ray-excitable nanophosphors has been recently proposed as a new modality for molecular imaging. Here, we demonstrate a novel XLCT modality using a novel X-ray excitable rare-earth nanophosphor capable of emitting light in shortwave infrared (SWIR, alternatively referred to as NIR-II, 1000-2300 nm) spectral region where an emerging optical imaging modality namely SWIR imaging has been widely investigated for deep tissue imaging.
Methods: XLCT offers two main advantages compared to other modalities. First, autofluorescence, problematic for fluorescence imaging can be avoided. Second, deep-tissue in vivo imaging with high optical contrast and spatial resolution becomes achievable. In this study, novel rare-earth nanophosphors were utilized as agents that absorb X-ray energy and emit light with a wavelength of ~1100 nm. A steady-state radiative transfer equation was used to model the emitting light interacts with the tissue, while a compressed sensing based method was adopted to reconstruct three-dimensional (3D) nanophosphor distribution within the imaging domain.
Results: Numerical simulations and experiments were performed to quantify the performance of our proposed novel X-ray-induced shortwave infrared luminescence computed tomography technique. The results show that the 3D distribution of the nanophosphor targets at a depth of up to 1.5 cm can be mapped with a sub-millimeter spatial resolution.
Conclusion: A novel X-ray molecular imaging technique, namely, X-ray-induced induced shortwave infrared luminescence computed tomography (SWIR-XLCT), has been developed and investigated. It has the potential for in vivo molecular imaging with a high spatial resolution.