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The purpose of this study was to assess the effect of age and number of previous injections of gadodiamide on the signal intensity of unenhanced T1-weighted (T1w) images of the dentate nucleus and globus pallidus in a large population.A large, single-center retrospective population survey was designed and received institutional review board approval. Between January 2014 and December 2014, T1w signal intensity ratios were obtained from a large population of 2500 consecutive enhanced brain magnetic resonance imaging (MRI) scans. Of these, 1906 MRI scans of patients not previously exposed to any gadolinium (Gd)-based contrast agent were used as control group and were compared with 892 MRI scans of patients with documented prior exposure to intravenous gadodiamide. A quantitative study was conducted to assess the T1w signal intensity of dentate nucleus-to-pons (Dn/Po) and globus pallidus-to-thalamus (Gp/Th) ratios. Multiple regression analysis was used to test the effect of age, time delay, and number of previous Gd-based contrast agent injections as predictor variables of T1w signal intensity ratios.In the Gd-exposed patients, multivariate regression analysis showed age (β = −0.285; P < 0.0001) and the number of previous injections of gadodiamide (β = 0.224; P < 0.0001) to be powerful predictors of Dn/Po ratio. Similarly, age (β = 0.269; P < 0.0001) and the number of previous injections of gadodiamide (β = 0.127; P < 0.0001) predicted Gp/Th ratio.In this study, we confirm that the number of previous gadodiamide injections is a powerful predictor of the signal intensity increase of the Dn/Po and Gp/Th ratios on unenhanced T1w images and demonstrate that aging influences the T1 signal intensity of DN and GP in Gd-naïve and in Gd-exposed subjects.