High-activity ⁹⁹Mo microresin fabrication for submillimeter SPECT system matrix acquisition

<i>Objective.</i>High-resolution small-animal single-photon emission computed tomography (SPECT) systems require accurate system matrices for high-quality image reconstruction. Experimentally measured point-source system responses provide high fidelity but are time-consuming, and the short half-life of^99mTc limits long-duration acquisitions required for dense system-matrix sampling.<i>Approach.</i>We propose a hybrid ⁹⁹Mo/^99mTc point source based on ⁹⁹Mo-adsorbable ion-exchange resin microspheres to achieve high activity with an effectively extended usable half-life. High-activity ⁹⁹Mo was adsorbed onto sub-millimeter resin beads, and Monte Carlo simulations were performed to quantitatively evaluate the impact of ⁹⁹Mo-derived high-energy photons on^99mTc system-matrix acquisition for two representative high-resolution SPECT configurations: a multi-pinhole system and a self-collimating system.<i>Main results.</i>Resin microspheres with activities exceeding 10 mCi per bead were successfully fabricated. Simulation results demonstrate that, within the^99mTc photopeak energy window, the contribution of ⁹⁹Mo-derived high-energy photons produces minimal distortion of system-response centroids and spatial distributions. The proposed source supports extended acquisitions for dense system-matrix sampling (e.g. 100 × 100 × 100 positions) with significantly improved statistical stability compared to conventional^99mTc sources.<i>Significance.</i>This work provides a practical and reproducible solution for accurate system-matrix calibration in state-of-the-art high-resolution SPECT systems, particularly where long acquisition durations are required, facilitating consistent system characterization in preclinical imaging research.