Reconfigurable animal bed–EPR resonator assembly for multimodal co-registration

A modular animal bed-resonator assembly (ABRA) platform is presented for multimodal preclinical co-registration of electron paramagnetic resonance imaging (EPRI) and magnetic resonance imaging (MRI). The reconfigurable "Lego-style" design enables effortless exchange and repositioning of resonator components to support a wide range of frequencies and achieve critical coupling conditions, tailored to the animal's type and size. The ABRA platform also addresses the need for stable EPRI of deep-lying organs in small animal disease models, such as pancreatic cancer, using advanced rapid-scan (RS) technology. RS EPRI enhances sensitivity by enabling higher excitation powers without saturating the spin system. However, the use of increased power exacerbates the challenge of maintaining critical coupling throughout the experiment. To improve data acquisition stability, the EPR resonator and coupling loop are constructed from coaxial cable segments, with the electric field uniformly confined between the inner and outer conductors to minimize undesired electric interactions with the animal. Shielding, along with the absence of touch-sensitive components such as lumped capacitors, contributes to stable data acquisition. Fiducial markers integrated into the bed, visible in both modalities, facilitate automated spatial alignment. The 3D-printed bed is designed to be compatible with affordable preclinical small-bore 1 T MRI systems. Co-registration is performed using a standard MATLAB-based image processing workflow that includes segmentation, fiducial selection, and rigid-body transformation. In vivo evaluation of tuning and coupling performance was conducted using mice bearing pancreatic adenocarcinoma or non-tumor-bearing mice. Imaging results, including co-registration performance, are reported for the non-tumor-bearing mice. The ABRA components and data processing using standard MATLAB tools can be easily replicated in laboratories with minimal engineering expertise.