1. A method comprising: applying a preparatory radiofrequency (RF) pulse at a first time instant to a Magnetic Resonance (MR) scanner configured to scan an object comprising a plurality of chemical species; applying a phase sensitive pulse sequence at a second time instant to the MR scanner, wherein the preparatory RF pulse and a time delay between the first and the second time instants null a first subset of chemical species from the plurality of chemical species; receiving an output signal from a second subset of chemical species from the plurality of chemical species in response to the phase sensitive pulse sequence; and estimating a static magnetic (B0) field map based on the output signal from the second subset of chemical species.