A portable magnetic resonance imaging ("MRI") system, comprising: a magnet assembly comprising: a plurality of permanent magnets, each extending from a proximal end to a distal end along a longitudinal axis of the magnet assembly; a support configured to hold the plurality of permanent magnets in an annular arrangement so as to define a region configured to receive an object to be imaged and such that the permanent magnets generate a magnetic field that includes spatial inhomogeneities of a known profile in a plane transverse to the longitudinal axis of the magnet assembly; a rotator coupled to the magnet assembly and configured to rotate the magnet assembly about its longitudinal axis through a plurality of different rotation angles; a radio frequency coil for generating RF energy and receiving magnetic resonance signals from an object positioned in the magnet assembly; and a controller configured to: direct the rotator to rotate the magnet assembly through the plurality of different rotation angles and to direct the RF coil to generate RF energy and receive responsive magnetic resonance signals at each rotation angle to acquire imaging data by reading out magnetic resonance signals while the magnet assembly is at each of the plurality of different rotation angles, the phase of magnetic resonance signals being modulated by the spatial inhomogeneities of the magnetic field, thereby providing spatial encoding of magnetic resonance signals; and reconstruct an image of the object using the magnetic resonance signals and knowledge about the profile of the inhomogeneous magnetic field. a magnet assembly comprising: a plurality of permanent magnets, each extending from a proximal end to a distal end along a longitudinal axis of the magnet assembly; a support configured to hold the plurality of permanent magnets in an annular arrangement so as to define a region configured to receive an object to be imaged and such that the permanent magnets generate a magnetic field that includes spatial inhomogeneities of a known profile in a plane transverse to the longitudinal axis of the magnet assembly; a plurality of permanent magnets, each extending from a proximal end to a distal end along a longitudinal axis of the magnet assembly; a support configured to hold the plurality of permanent magnets in an annular arrangement so as to define a region configured to receive an object to be imaged and such that the permanent magnets generate a magnetic field that includes spatial inhomogeneities of a known profile in a plane transverse to the longitudinal axis of the magnet assembly; a rotator coupled to the magnet assembly and configured to rotate the magnet assembly about its longitudinal axis through a plurality of different rotation angles; a radio frequency coil for generating RF energy and receiving magnetic resonance signals from an object positioned in the magnet assembly; and a controller configured to: direct the rotator to rotate the magnet assembly through the plurality of different rotation angles and to direct the RF coil to generate RF energy and receive responsive magnetic resonance signals at each rotation angle to acquire imaging data by reading out magnetic resonance signals while the magnet assembly is at each of the plurality of different rotation angles, the phase of magnetic resonance signals being modulated by the spatial inhomogeneities of the magnetic field, thereby providing spatial encoding of magnetic resonance signals; and reconstruct an image of the object using the magnetic resonance signals and knowledge about the profile of the inhomogeneous magnetic field. direct the rotator to rotate the magnet assembly through the plurality of different rotation angles and to direct the RF coil to generate RF energy and receive responsive magnetic resonance signals at each rotation angle to acquire imaging data by reading out magnetic resonance signals while the magnet assembly is at each of the plurality of different rotation angles, the phase of magnetic resonance signals being modulated by the spatial inhomogeneities of the magnetic field, thereby providing spatial encoding of magnetic resonance signals; and reconstruct an image of the object using the magnetic resonance signals and knowledge about the profile of the inhomogeneous magnetic field.