1. A method for producing an image of bioelectromagnetic activity in a subject with a magnetic resonance imaging (MRI) system, the steps comprising: a) acquiring T 1ρ -weighted image data from the subject using a pulse sequence which directs the MRI system to perform a spin-lock preparatory pulse sequence prior to acquiring NMR image data, the spin-lock preparatory pulse sequence including the application of a spin-lock RF field, B 1ρ , that establishes a spin-lock condition in transverse spin magnetization that is sensitive at the frequency of bioelectromagnetic fields produced in the subject; b) reconstructing an image with the acquired T 1ρ -weighted image data; and c) analyzing the amplitude of the T 1ρ -weighted image to detect locations in the subject of bioelectromagnetic activity.