Magnetic resonance imaging apparatus with means to screen rf fields
OwnerIan Robert Young, Michael Charles Keogh Wiltshireinventors
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Abstract
In magnetic resonance imaging apparatus, an array of coils (7, 8, 9, 10) is used to receive magnetic resonance signals from a desired region of a patient. Screens 11 to 13 and 14 and 15 are provided between the coils and at the ends of the array of coils to control the sensitive region A of each coil but, in accordance with the invention, the screening properties of the screens is controllable so that for example the screens may be made inoperative beneath the plane of the array of coils so that each has the field of view B, in order to vary the properties produced by the array. Other uses of screens are described.
Claims13
Magnetic resonance apparatus, in which resonance is excited in use in magnetic resonant active nuclei in a region of an object (1) in the presence of a main magnetic field, which magnetic resonance apparatus includes a structure with magnetic properties forming a screen (11-15, 37-40, 22) to screen r.f. flux, the structure comprising an array of capacitive elements, the array exhibiting a predetermined magnetic permeability in response to incident electromagnetic radiation lying within a predetermined frequency band, wherein each capacitive element includes a conducting path and is such that a magnetic component of the electromagnetic radiation lying within the predetermined frequency band induces an electrical current to flow around said path and through said associated element, wherein the spacing of the elements is less than the wavelength of the radiation within the predetermined frequency band, and wherein the size of the elements and their spacing apart are selected such as to provide a magnetic permeability appropriate to that of a screen to electromagnetic radiation in that predetermined frequency band.
Dependencies are inferred from the claim text.