Picker International, Inc.

Xueming Zou

John Lester Patrick

Nicholas J Mastandrea

Michael Andrew Morich

Paul T Orlando

Gordon D DeMeester

David A Lampman

Mark A Richard

James M McNally

A superconducting magnet (10) generates a uniform, static magnetic field through a central bore (12) along its longitudinal or z-axis. An insertable coil assembly (40) is inserted into the bore with a radio frequency shield (76, 84) for providing a radio frequency shield between the insertable coil assembly and a surrounding, whole body radio frequency coil assembly (32) and a whole body gradient magnetic field coil assembly (30). The insertable coil includes a gradient coil (44a) including conductors (52) mounted on a dielectric former (50) with a dielectric constant below 4.0. The conductors are relatively narrow and spaced relatively far apart to minimize capacitive coupling with a closely adjacent insertable radio frequency coil (70a). Filters (60, 64) are connected with the conductors of the gradient coil to prevent the gradient coil conductors from supporting radio frequency signals while permitting ready support of kHz frequency currents. An RF filter (106) connected between the insertable gradient coil and an insertable gradient coil control (100) prevents induced radio frequency signals from being transmitted to the insertable gradient coil.

Gradient and RF coil system without RF shield

A magnetic resonance imaging apparatus includes a magnet assembly (10) for generating a temporally constant primary magnetic field through a central bore (14). The central bore is surrounded by a gradient coil assembly (30) including a dielectric former (32) and gradient coils (34, 36, 38) for generating magnetic field gradient pulses across the examination region. A radio frequency coil assembly (50) including a birdcage coil (52) is mounted inside of the gradient coil assembly and surrounding the examination region. A radio frequency shield (60) includes a dielectric sheet (62) having a plurality of first metal foil strips (72) defined on each surface. The metal strips are defined by etching or cutting gaps (70) in a continuous sheet of copper foil, leaving bridges (74) across the gaps adjacent opposite ends of the foil strips. The foil strips on opposite faces of the dielectric sheet are offset by half the width of one strip such that each strip is capacitively coupled to two strips on the opposite surface. The radio frequency coil induces radio or megahertz frequency eddy currents to which the capacitive coupling appears as a short-circuit, allowing the induced radio frequency currents to pass circumferentially around the shield. The gradient coil assembly induces kilohertz frequency eddy currents to which the capacitive couplings appear as open circuits. The kilohertz eddy currents flow longitudinally along a strip, cross a bridge adjacent one end of the strip, and flow back longitudinally along an adjacent strip, and so forth.

Low eddy current radio frequency shield for magnetic resonance imaging

A primary gradient coil assembly (22) is mounted in the inner bore or cylinder (20) of a vacuum dewar (18) that surrounds a superconducting magnet assembly (10). A pair of end ring assemblies, such as electrically conductive lapped segment loops (38) are supported by the gradient coil assembly (22). The end ring segments are capacitively coupled. A plurality of removable radio frequency coil element assemblies (40) are selectively attached to and detached from the gradient coil assembly. Each of the removable RF coil element assembly includes a dielectric housing (50), a longitudinally extending conductor element (52), an electrical connector (44), and circuit components (54) which connects the longitudinal conductor element with the electrical connector. The connector is electrically connected, at radio frequencies, with the ring assembly (38). A mechanical interlock (60) mechanically locks and selectively releases the removable element assemblies (40) to the gradient coil assembly. Sets of different removable element assemblies are provided with different effective radii, i.e. different physical displacements of the electrical conductor elements (52) from the gradient coil assembly, different resonance frequencies, i.e. different reactive elements (58), and the like to adapt the different removable element assemblies for different imaging applications. The removable element assemblies may be completely removed when specialty RF coils, such as a head coil, biplanar gradient coil, or surface coil are used.

Magnetic resonance imager with removable element RF coil

The magnetic field assembly of a magnetic resonance imaging device includes an annular superconducting magnet (10) which is mounted within a toroidal vacuum vessel (24). A cylindrical member (26) defines a central bore through which the superconducting magnets generate a temporally constant primary magnetic field. A cylindrical, dielectric former (46) is mounted in the bore displaced a small distance from the cylindrical member. A radio frequency coil (32) is mounted within the cylindrical member defining a patient receiving examination region. An RF shield (34) is mounted around the exterior peripheral surface of the former. Primary gradient coils (40) are mounted around and potted to the exterior of the dielectric former around the RF shield. Gradient shield or secondary coils (44) are potted around an exterior of the cylindrical member within the vacuum chamber. As illustrated in FIG. 3 , when unshielded gradient coils are used, the primary gradient coils and the RF shield are mounted around the outer diameter of the cylindrical member (26).

Integrated MRI gradient coil and RF screen

Superconducting magnets (10) of a magnetic resonance imager create static magnetic fields through an examination region (12). Gradient magnetic field coils (30) under control of a gradient magnetic field control (42) generate gradient magnetic fields across the examination region (12), as a whole. A plurality of surface coils (36, 38) receive radio frequency signals from each of two distinct subregions within the examination region (12). The two receiver coils are connected with separate receivers (60.sub.1, 60.sub.2) which demodulate the received magnetic resonance signals. The magnetic resonance signals are reconstructed (76) into an image representation (80, 82) of the first and second subregions. In the embodiment of FIGS. 1 and 2, a radio frequency transmitter (40) and a whole body coil (32) generate and manipulate the magnetic resonance signals within the first and second subregions. In the embodiment of FIGS. 3 and 4, a plurality of transmitters (40.sub.1, 40.sub.2, . . . ) convey RF signals to the surface coils such that the surface coils operate in both a transmit and receive mode. Regardless whether a single transmitter or a series of transmitters is utilized, a sequence control (44) controls the transmitter(s) and the gradient control (42) to conduct conventional magnetic resonance imaging sequences in coordination in both subregions.

Simultaneous magnetic resonance imaging of multiple human organs

In a magnetic resonance system, four primary loop circuits (50, 52, 54, 56) are inductively coupled to a resonator coil (32) at 90.degree. intervals around its circumference. The loop circuits are over-coupled to the resonator coil, i.e. they present more than the characteristic resistance of the associated cabling system which causes the maximum current transfer between the loop circuits and the resonator coil to be offset (f.sub.N) in equal amounts in each direction from a natural resonance frequency (f.sub.0) of the resonator coil. In one embodiment, two adjacent primary loop circuits provide for quadrature radio frequency transmission to and from the resonator coil at a first frequency and the other two primary loop circuits provide for quadrature radio frequency transmission to and from the resonator coil at a second resonance frequency. Each of the primary loop circuits includes a tank circuit (62) for blocking the passage of the frequency of the other quadrature primary loop circuit pair. In another embodiment, the third and fourth primary loop circuits are connected with tuning capacitors for adjusting the resonance frequency of the resonator coil relative to radio frequency signals applied and received by the primary loop circuit 180.degree. opposite. This enables the frequency of each quadrature component of a quadrature RF signal to be adjusted separately. Analogously, this enables the resonance frequency of two linear RF signals to be adjusted independently.

Technique for driving quadrature dual frequency RF resonators for

A superconducting magnet (10) generates a uniform, static magnetic field through a central bore (12) along its longitudinal or z-axis. A biplanar gradient coil assembly (44) is inserted into the bore to create gradients across the static magnetic field along orthogonal x, y, and z-axes. A biplanar radio frequency coil assembly (50, 80) is inserted into the bore for transmitting radio frequency signals into a subject and receiving magnetic resonance signals from the subject. The radio frequency coil includes a first biplanar coil assembly (50) for generating RF signals in an x-direction and a second biplanar coil assembly (80) for generating RF signals in a y-direction. The two biplanar coil assemblies each include a plurality of conductors (52, 82) along a first plane and a second plurality of conductors (54, 84) along a parallel second plane. The conductors extend parallel to the z-direction. Capacitors (56, 58, 94) are connected in series with each of the conductors in order to control the current flow such that the current flow in each plane is uniform across the plane. The ends of the electrical conductors are connected together (66, 88) such that the current flows are equal and opposite in the two planes. A radio frequency transmitter (136) transmits RF signals to the quadrature biplanar coil assembly. A digital receiver (140) receives and demodulates radio frequency signals from the quadrature coil assembly. The demodulated signals are reconstructed (144) into an image representation for display on a video monitor (146).

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Chesterland, OH, United States of America

Xueming Zou