Benchtop 2D multi-pinhole x-ray fluorescence imaging system using a high energy resolution pixelated cadmium zinc...

X-ray fluorescence (XRF) imaging is a promising modality for quantitative molecular imaging that allows for the in vivo biodistribution detection of specific elements within biological systems. Despite its potential, challenges such as detection limit and scan time have hindered its widespread adoption in preclinical in vivo imaging.

This study aims to address these challenges by developing a benchtop 2D multi-pinhole XRF imaging system with an up-to-date cadmium zinc telluride (CZT) detector system without tomographic reconstruction.

The benchtop 2D multi-pinhole XRF imaging system was implemented by integrating a High Energy x-ray Imaging Technology (HEXITEC) 2 × 2 CZT detector system with a lead collimator containing four tungsten pinholes. 140 kV fan beam x-rays irradiated a small-animal-sized polymethyl methacrylate (PMMA) phantom filled with gold nanoparticle (GNP) solutions at concentrations of 0.156, 0.313, 0.625, 1.25, 2.5, and 5.0 mg/mL. A GNP-loaded phantom with varying concentrations was used to establish a calibration curve relating GNP concentrations to K-shell XRF photon counts and to evaluate the detection limit of the system.

The multi-pinhole collimator generated four well-aligned, nonoverlapping projections, each centered on a CZT module, resulting in a fourfold increase in photon detection efficiency compared with a single-pinhole collimator. The detector exhibited excellent spectral performance with an energy resolution of 1.38 ± 0.32 keV full width at half maximum (FWHM) at 59.5 keV. As a result, two gold $K_{\alpha }$ XRF peaks (67.0 and 68.8 keV) were well resolved. Reconstructed XRF images, generated by combining four projections using the maximum likelihood expectation maximization algorithm, showed a strong linear relationship between GNP concentrations and XRF photon counts (R² > 0.99). The benchtop 2D multi-pinhole XRF imaging system demonstrated in this study achieved a detection limit of 0.105 mg/mL with a scan time of 10 min and an imaging dose of 51.5 cGy.

By successfully integrating a multi-pinhole collimator with the HEXITEC 2 × 2 CZT detector system, the benchtop 2D multi-pinhole XRF imaging system substantially improved system sensitivity, achieving a detection limit of 0.1 mg/mL for GNPs, a biologically relevant concentration, in a small-animal-sized phantom. This detection limit was attained with a 10-min scan time and an imaging dose of 51.5 cGy, both within the acceptable range for in vivo imaging applications. These results highlight the potential of the benchtop 2D multi-pinhole XRF imaging system for preclinical in vivo applications.