Sub-millimetric ultra-low-field MRI detected in situ by a dressed atomic magnetometer

Magnetic resonance imaging (MRI) is universally acknowledged as an excellent tool to extract detailed spatial information with minimally invasive measurements. Efforts toward ultra-low-field (ULF) MRI are made to simplify the scanners and to reduce artifacts and incompatibilities. Optical atomic magnetometers (OAMs) are among the sensitive magnetic detectors eligible for ULF operation; however, they are not compatible with the strong field gradients used in MRI. We show that a magnetic-dressing technique restores the OAM operability despite the gradient, and we demonstrate submillimetric resolution MRI with a compact experimental setup based on an in situ detection. The proof-of-concept experiment produces unidimensional imaging of remotely magnetized samples with a dual sensor, but the approach is suited to be adapted for 3-D imaging of samples magnetized in loco. An extension to multisensor architectures is also possible.