The demand for Magnetic Resonance Imaging (MRI) in Ontario has been increasing annually, resulting in longer wait times for patients. This big data study links multiple administrative data sets to characterize and explore drivers of growth in MRI imaging in Ontario between 2008 and 2017. Our retrospective population-based big data study shows an increasing trend in the use of MRI scans, outpacing capacity. Demand increased the greatest amongst family physicians, and there were also wide variations in MRI referral rates among this group. Subgroup analysis demonstrates that family physicians practicing sports medicine ordered more extremities and spine MRIs. Multiple physician characteristics, including years of practice and physician demographics, also impacted the use of MRIs. Overall, 8% family physicians were consistent higher testers, who contributed to nearly 25% of extremities, spine, and brain MRI tests. These findings may help better target interventions to reduce variations in care and overuse.