Optimizing x-ray based multimodal imaging: investigating dose dependency and modulation of fluorescence emission from GdF3nanoparticles doped with terbium using spectral photon counting CT.

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 (GdF3), 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 GdTbF3NPs, with the goal of optimizing the x-ray-induced activation and imaging protocols. These optimizations are crucial towardin vivoapplication 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 vitroandin vivo). SPCCT enabled K-edge imaging to achieve specific gadolinium NP distribution and quantification.Main results. In vitroexperiments 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 vivoexperiments in mice, following subcutaneous injections of functionalized GdTbF3@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 GdTbF3NPs 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.