Abstract: A portable magnetic resonance imager has a probe. One or more magnets are disposed in the probe, creating at least one magnetic field to precess protons at a target. A magnetometer disposed in the probe has a light source and a nitrogen vacancy diamond. The light source projects a light on the nitrogen vacancy diamond. The nitrogen vacancy diamond fluoresces in response to the light. A photodetector detects the fluorescence and produces a signal in response thereto indicative of the decaying of precessing protons having precessed in the presence of the one or more magnets.