An apparatus for generating and changing a magnetic field in a field of view, said magnetic field having a, in particular ball-shaped or line-shaped, first sub-zone having a low magnetic field strength and a second sub-zone having a higher magnetic field strength, which apparatus comprises: - at least three pairs of first coils (136a -136d), wherein the coils are arranged along a ring around the field of view at equal or unequal distances from the center of the field of view, and wherein the two coils of each pair are opposingly arranged on opposite sides of the field of view, - at least one pair of second coils opposingly arranged on opposite sides of the field of view at the open sides of said ring,- generator means (110, 130) for generating current signals for provision to said first and second coils for generating the desired magnetic fields by said first and second coils, and - control means for controlling said generator means to generate i) selection field current signals for provision to said first coils (136a - 136d) so that the at least three pairs of first coils generate a gradient magnetic selection field having a pattern in space of its magnetic field strength such that a, in particular ball-shaped or line-shaped, first sub-zone having a low magnetic field strength and a second sub-zone having a higher magnetic field strength are formed in the field of view and ii) drive field current signals for provision to said second coils and to two pairs (136a, 136c) of first coils so that the at least one pair of second coils and said two pairs of first coils generate a homogeneous magnetic drive field for changing the position in space of the two sub-zones in the field of view. - at least three pairs of first coils (136a -136d), wherein the coils are arranged along a ring around the field of view at equal or unequal distances from the center of the field of view, and wherein the two coils of each pair are opposingly arranged on opposite sides of the field of view, - at least one pair of second coils opposingly arranged on opposite sides of the field of view at the open sides of said ring,- generator means (110, 130) for generating current signals for provision to said first and second coils for generating the desired magnetic fields by said first and second coils, and - control means for controlling said generator means to generate i) selection field current signals for provision to said first coils (136a - 136d) so that the at least three pairs of first coils generate a gradient magnetic selection field having a pattern in space of its magnetic field strength such that a, in particular ball-shaped or line-shaped, first sub-zone having a low magnetic field strength and a second sub-zone having a higher magnetic field strength are formed in the field of view and ii) drive field current signals for provision to said second coils and to two pairs (136a, 136c) of first coils so that the at least one pair of second coils and said two pairs of first coils generate a homogeneous magnetic drive field for changing the position in space of the two sub-zones in the field of view. i) selection field current signals for provision to said first coils (136a - 136d) so that the at least three pairs of first coils generate a gradient magnetic selection field having a pattern in space of its magnetic field strength such that a, in particular ball-shaped or line-shaped, first sub-zone having a low magnetic field strength and a second sub-zone having a higher magnetic field strength are formed in the field of view and ii) drive field current signals for provision to said second coils and to two pairs (136a, 136c) of first coils so that the at least one pair of second coils and said two pairs of first coils generate a homogeneous magnetic drive field for changing the position in space of the two sub-zones in the field of view.