The invention relates to a method of performing a magnetic resonance imaging (MRI) reference scan of an examination volume comprising a plurality of image points, the method being performed using a set of detector elements (142), the method comprising: phase sensitive acquisition of a first and a second complex echo signal originating from a first (214; 306; 310) and second (216; 308; 312) echo for each image point, wherein the acquisition is performed by each of the detector elements of the set of detector elements (142), determining for a detector element of the set of detector elements (142) a phase difference between the first and the second echo signal for each image point, —calculating from the phase difference a local magnetic field inhomogeneity value for each image point, deriving for each image point a coil sensitivity matrix, wherein the coil sensitivity matrix is derived by calculating complex ratios of the first or the second complex echo signals acquired by the set of elements.