The quest for open MRI magnets has so far been satisfied by designs that can be re-conduced to “C” or “H” configurations, whose cavities can be described as “two sided,” meaning that two surfaces only are actively generating the magnetic field in the region of interest. The low efficiency of these magnets can be increased giving an active role to the “third wall” of the cavity. We present here a configuration involving only planar coils. This layout avoids excessive folding and torsion of the wire and reduces the effect of the mechanical forces produced by the magnetic field.
A study of the motor cortex during the programming, execution and mental representation of voluntary movement is of great relevance; its evaluation in conditions close to reality is necessary, given the close integration of the visuomotor, sensory feedback and proprioceptive systems, as of yet, a functional Magnetic Resonance Imaging (fMRI) scanner allowing a human subject to maintain erect stance, observe the surroundings and conserve limb freedom is still a dream. The need for high field suggests a solenoid magnet geometry that forces an unnatural posture that affects the results, particularly when the motor cortex is investigated. In contrast in a motor functional study, the scanner should allow the subject to sit or stand, with unobstructed sight and unimpeded movement. Two approaches are presented here to solve this problem. In the first approach, an increased field intensity in an open magnet is obtained lining the "back wall" of the cavity with a sheet of current: this boosts the field intensity at the cost of the introduction of a gradient, which has to be canceled by the introduction of an opposite gradient; The second approach is an adaptation of the "double doughnut" architecture, in which the cavity widens at the center to provide additional room for the subject. The detailed design of this kind of structure has proven the feasibility of the solution.
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