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Assessment of environmental disturbances to the static magnetic field in magnetic resonance installations

Department of Medical Physics, St George's Hospital, Blackshaw Road, London SW17 0QT, UK

View larger version (70K): [in a new window]   Figure 1. (a) Reference phase image and (b) subtracted phase image of cylindrical uniform test object, with region of interest (ROI) used for measurements indicated. The variation of the average ROI phase value over a series of subtracted phase images is shown in (c), both in the absence of any magnetic field disturbance, and in the presence of a magnetic field disturbance caused by bringing a strongly paramagnetic solution to the test object vicinity and then removing it.

View larger version (35K): [in a new window]   Figure 2. (a–g) Sections of several single-shot echo-planar imaging (EPI) images of hexane, showing the image shift along the phase encoding (PE) direction associated with a magnetic field disturbance. (d–f) A paramagnetic solution is brought to the vicinity of the test object, and (g) then removed. In the absence of any magnetic field disturbances any measured image shifts are under 0.005 ppm, as shown in (h) for the image associated with CH3. (i) The separation between the CH3 and CH2 images remains constant even when there is movement of a paramagnetic solution in the vicinity of the isocentre.