Open-source hardware designs for MRI of mice, rats, and marmosets: Integrated animal holders and radiofrequency coils

BACKGROUND Small-animal MRI is an important investigative tool for basic and preclinical research. High-resolution anatomical and functional studies of the brain require artifact-free images that are acquired with a highly sensitive radiofrequency (RF) coil. NEW METHOD The animal holder plays an important role in mitigating image artifacts: motion artifacts are reduced by immobilizing the animal and geometric-distortion artifacts are reduced by accurately positioning the animal to improve static-field shimming. The RF coil, in turn, must provide high sensitivity over the whole brain and not physically interfere with the animal holder. To accomplish these tasks, the animal holder and RF coil should be designed in tandem. In this manuscript, animal holders and RF coils for mice, rats, and marmoset monkeys are described. Each animal holder includes components for anesthesia delivery and animal immobilization, as well as a compatible receive coil. RESULTS/COMPARISON WITH EXISTING METHOD(S) Animal holders were capable of accurate and reproducible positioning (for the marmoset, this was in the stereotactic plane), consequently reducing geometric distortion in echo-planar images. Ear bars were designed in conjunction with receive-coil formers, thereby maximizing the sensitive region of coils, while concurrently reducing motion to less than a pixel over EPI time series. Motion and SNR were quantified to facilitate direct comparison to existing animal holders and RF coils. All computer-aided-design (CAD) files of animal holders and RF coils are provided to promote dissemination. CONCLUSIONS The confluence of design between the animal holder and RF coil provides a pragmatic solution for routine imaging of small animals.