A method of performing proton resonance frequency, PRF, based magnetic resonance, MR temperature measurement, the method comprising the steps of: acquiring a plurality of reference phase images of an MR imaging region, each of the reference phase images corresponding to a phase background resulting from a different arrangement of one or more devices in or near the MR imaging region, wherein the movements of said one or more devices perturb the local magnetic field and thereby change the phase background in the MR imaging region; acquiring a first phase image of the MR imaging region subsequent to the acquisition of the plurality of reference phase images; selecting, from the plurality of reference phase images, a first reference phase image which was acquired with an arrangement of said one or more devices which most closely corresponds to the arrangement of said one or more devices during the acquisition of the first phase image; calculating a first phase shift by calculating a difference between the first phase image and the first reference phase image; acquiring a second phase image of the MR imaging region subsequent to the acquisition of the first phase image; selecting, from the plurality of reference phase images, a second reference phase image which was acquired with an arrangement of said one or more devices which most closely corresponds to the arrangement of said one or more devices during the acquisition of the second phase image; characterised in that the method further comprises: calculating a second phase shift by summing (i) the first phase shift and (ii) either an incremental phase shift of a difference between the second phase image and the second reference phase image as compared to a difference between the first phase image and the first reference phase image, or an incremental phase shift of a difference between the second phase image and the first phase image as compared to a difference between the second reference phase image and the first reference phase image; and determining at least one temperature change based on at least the second phase shift. acquiring a plurality of reference phase images of an MR imaging region, each of the reference phase images corresponding to a phase background resulting from a different arrangement of one or more devices in or near the MR imaging region, wherein the movements of said one or more devices perturb the local magnetic field and thereby change the phase background in the MR imaging region; acquiring a first phase image of the MR imaging region subsequent to the acquisition of the plurality of reference phase images; selecting, from the plurality of reference phase images, a first reference phase image which was acquired with an arrangement of said one or more devices which most closely corresponds to the arrangement of said one or more devices during the acquisition of the first phase image; calculating a first phase shift by calculating a difference between the first phase image and the first reference phase image; acquiring a second phase image of the MR imaging region subsequent to the acquisition of the first phase image; selecting, from the plurality of reference phase images, a second reference phase image which was acquired with an arrangement of said one or more devices which most closely corresponds to the arrangement of said one or more devices during the acquisition of the second phase image; characterised in that the method further comprises: calculating a second phase shift by summing (i) the first phase shift and (ii) either an incremental phase shift of a difference between the second phase image and the second reference phase image as compared to a difference between the first phase image and the first reference phase image, or an incremental phase shift of a difference between the second phase image and the first phase image as compared to a difference between the second reference phase image and the first reference phase image; and determining at least one temperature change based on at least the second phase shift. calculating a second phase shift by summing (i) the first phase shift and (ii) either an incremental phase shift of a difference between the second phase image and the second reference phase image as compared to a difference between the first phase image and the first reference phase image, or an incremental phase shift of a difference between the second phase image and the first phase image as compared to a difference between the second reference phase image and the first reference phase image; and determining at least one temperature change based on at least the second phase shift.