| 摘要 |
The axial dimensions of the usual "saddle" coils used to create transverse magnetic gradients in the static magnetic field of a magnetic resonance imaging system are substantially foreshortened. The outer arc of the saddle coil is moved axially inward while still leaving it at a position which produces negligible net transverse gradient contribution. While this new position of the outer arc can be expected to produce a significant second (third) derivative of the transverse gradient with respect to Z (the orientation of the static magnetic field) at the predetermined observation point, the inner arc of the saddle coil may be moved slightly away from the observation point so as to produce a second (third) derivative which substantially cancels that of the relocated outer arc. In this manner, the desired condition of having a net zero second (third) derivative may still be maintained even though the axial dimension of the saddle coil has been substantially reduced (e.g., to about 44% of the traditional axial length in one exemplary embodiment). Such a more compact coil may permit realization of lowered inductance (and thus permit faster gradient switching during MRI procedures) or, additional coil turns may be employed while still retaining the same inductance but thus permitting the regeneration of larger gradients or, the use of lower currents (thereby saving on power amplifiers, power dissipation, etc.).
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