ABSTRACT:The coregistration of electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) images in three-dimensional (3D) data space typically involves a process of visual inspection and manual alignment of the images. This is due primarily to the use of separate scanners, which can result in a number of potential differences between the two image types, such as resolution, field-of-view, and image orientation. In this article, we describe recently developed methodology and software that enables automatic coregistration of EPR and NMR acquired images without the need for manual alignment. The technique requires the use of fiducial markers during both EPR and NMR image acquisition, which contain a solution of free radical spin probes, and allow adjustment of the positions and the fields-of-view of the measured images. In this work we present results for EPR/NMR image coregistration using an isoflurane-anesthetized mouse, injected with triarylmethyl radical (Oxo63) spin probes. The same spin probes were also used inside the fiducial markers and in plastic tubes used for phantom measurements. Using our MATLAB-based software, we were able to successfully coregister EPR/NMR images in approximately 60 s.