Optimizing x-ray based multimodal imaging: investigating dose dependency and modulation of fluorescence emission from GdF 3 nanoparticles doped with terbium using spectral photon counting CT

Abstract Objective. Spectral photon counting computed tomography (SPCCT) represents a major advancement in diagnostic imaging, with the potential to significantly enhance image contrast and resolution by leveraging photon-counting detectors. The integration of high atomic number nanoparticles (NPs), such as gadolinium fluoride (GdF 3 ), expands the scope of SPCCT by enabling combined high-resolution imaging and therapeutic strategies. This study investigates the interactions between SPCCT irradiation and acquisition parameters and surface-functionalized GdTbF 3 NPs, with the goal of optimizing the x-ray-induced activation and imaging protocols. These optimizations are crucial toward in vivo application of x-ray induced photodynamic therapy (X-PDT). Approach. Nanoparticles, synthesized with and without surface modifications, were evaluated for their biocompatibility ( in vivo ) and imaging properties ( in vitro and in vivo ). SPCCT enabled K-edge imaging to achieve specific gadolinium NP distribution and quantification. Main results. In vitro experiments revealed a linear relationship between NP concentration and fluorescence intensity, confirming their potential as contrast agent for both K-edge imaging and fluorescence X-PDT. Optimization of emission activation conditions by varying tube voltage (kVp) and tube current (mA) demonstrated that fluorescence intensity increased proportionally with the tube current-time product (mAs). In vivo experiments in mice, following subcutaneous injections of functionalized GdTbF 3 @PEG NPs, showed a clear concentration-dependent increase in fluorescence intensity. K-edge imaging further confirmed the specificity and distribution of the NPs. Significance. These findings demonstrate the dual capability of GdTbF 3 NPs to act both as efficient contrast agents for x-ray-based imaging and as luminescent probes under x-ray excitation, highlighting their potential for multimodal imaging and X-PDT.