High-resolution optically-detected magnetic resonance imaging in an ambient magnetic field

Magnetic resonance imaging (MRI) in an ultralow magnetic field usually has poor spatial resolution compared to its high-field counterpart. The concomitant field effect and low signal level are among the major causes that limit the spatial resolution. Here, we report a novel imaging method, a zoom-in scheme, to achieve a reasonably high spatial resolution of 0.6 mm x 0.6mm without suffering the concomitant field effect. This method involves multiple steps of spatial encoding with gradually increased spatial resolution but reduced field-of-view. This method takes advantage of the mobility of ultralow-field MRI and the large physical size of the ambient magnetic field. We also demonstrate the use of a unique gradient solenoid to improve the efficiency of optical detection with an atomic magnetometer. The enhanced filling factor improved the signal level and consequently facilitated an improved spatial resolution.