Abstract: A method and apparatus are provided which reduce coupling between a Z-axis gradient coil and an rf coil in magnetic resonance imaging systems and an rf shield disposed between the Z-axis gradient coil and the remaining gradient coils. The reduction in coupling is accomplished by novel windings of conductor forming the Z-axis gradient coil.

Abstract: An RF coil assembly is presented that incorporates balun networks to eliminate standing waves from cables used to apply a voltage to multiple drive ports of the coil. Each drive port is driven by an applied voltage that is shifted 90 degrees in the tangential direction. Further, all drive ports are located on one end-ring of the coil, e.g. the superior end-ring. The inequality of the efficiency of the drive ports is reduced such that a substantially circular polarization in the volume of the coil is maintained. The present invention reduces asymmetrical loading by a patient as a result of patient asymmetry and patient contact with the opposite end-ring of the coil that normally negatively affects circular polarization and conventional coil configurations.

Abstract: A magnetic resonance imaging assembly is provided. The assembly includes a magnet assembly defining a scanning bore along a z-direction. The assembly further includes a surface coil assembly positioned within the scanning bore. The surface coil assembly receives an imaging field. The surface coil assembly comprises a first surface coil positioned along the z-direction. The first surface coil is induced with a first coil current comprised of a first coil amplitude and a first coil phase. The surface coil assembly includes a second surface coil positioned along said z-direction. The second surface coil is induced with a second coil current comprised of a second coil amplitude and a second coil phase. The second coil phase is varied from the first coil phase to correct asymmetries within the imaging field.

Abstract: A method and apparatus are provided which reduce coupling between a Z-axis gradient coil and an rf coil in magnetic resonance imaging systems and an rf shield disposed between the Z-axis gradient coil and the remaining gradient coils. The reduction in coupling is accomplished by novel windings of conductor forming the Z-axis gradient coil.

Abstract: A method and apparatus are disclosed for combining the respective readout signals for a loop and butterfly coil pair of a quadrature phased array used for magnetic resonance imaging. The technique used to combine the signals introduces a 180 degree phase shift, or multiple thereof, to the loop coil signal, thereby allowing the loop coil signal to be decoupled from other loop coil signals by a low input impedance preamplifier in series with the signal.

Abstract: The present invention provides a system and method wirelessly transmitting MR signals from receive coils of an RF coil assembly to a remotely located receiver system. By utilizing wireless telemetry, ghosting, SNR problems, and standing waves on shields typically associated with cabled receive coils are avoided. Furthermore, by incorporating a rechargeable battery in place of DC cables, the coaxial cable conducting large currents can be eliminated. The present invention incorporates a transmitter that transmits a modulated MR signal to a receiver at the end of the bore of the magnet of the MRI system. Modulating the MR signals with a carrier frequency enables wireless transmission of the modulated signal to the remote receiver. Preferably, the modulated signal is transmitted using a 900 MHz carrier frequency. The receiver then demodulates the received signal and transmits the resulting signal to a system control for subsequent processing and image reconstruction.

Abstract: A method and apparatus are provided which reduce coupling between a Z-axis gradient coil and an rf coil in magnetic resonance imaging systems and an rf shield disposed between the Z-axis gradient coil and the remaining gradient coils. The reduction in coupling is accomplished by novel windings of conductor forming the Z-axis gradient coil.

Abstract: A method and apparatus are disclosed for combining the respective readout signals for a loop and butterfly coil pair of a quadrature phased array used for magnetic resonance imaging. The technique used to combine the signals introduces a 180 degree phase shift, or multiple thereof, to the loop coil signal, thereby allowing the loop coil signal to be decoupled from other loop coil signals by a low input impedance preamplifier in series with the signal.

Abstract: A combination gradient coil/RF shield is provided for magnetic resonance imaging systems. The coil may be adapted from any of the existing gradient coil structures, but is preferably an X-axis or Y-axis coil, with an inner Z-axis coil being inherently decoupled from the RF magnetic field due to its design. Capacitive circuits are provided between conductive paths of the selected gradient coil to adapt the gradient coil to the RF frequencies used during operation, such as 64 MHz. The technique permits the gradient coil assembly to be affectively moved closer to the patient while providing an enhanced distance between the RF coil and the RF shield defined by the adapted gradient coil.

Abstract: A multi-channel phased array coil for use in a magnetic resonance (MR) system is disclosed herein. The phased array coil includes N coils configured in an array, each of the N coils having a geometric shape and overlapping with (N−1) coils to form an overlap area within the array. The geometric shape of each of the coils and the overlap area are configured to cause a mutual inductance between every pair of the coils to be less than 10 percent of the self-inductance of each of the N coils. At least four coils are provided in the phased array coil.

Abstract: An RF shielding technique is provided for open MRI systems. The RF shield includes a first portion disposed over a gradient field generating set, and a skirt-like second portion that wraps around lateral structures, such as the primary magnet and support. The two portions are joined to one another to form an integral RF shield that limits loss of RF energy both through the gradient field elements and through the primary magnet and support structures.

Abstract: A technique is disclosed for shielding rf magnetic fields in MRI systems. An rf shield is embedded in a gradient coil structure including X-, Y- and Z-axis coils. The rf shield is positioned between an inner gradient coil which is inherently decoupled from the rf field, and the remaining coils which require rf shielding. The inner gradient coil may be a Z-axis coil wound as a solenoid, the field of which is generally orthogonal with respect to the rf magnetic field. The rf shield is thereby placed at an enhanced distance from the rf coil, providing greater efficiency and permitting energy levels to be reduced to obtain the desired rf magnetic field strength.

Abstract: A technique is disclosed for shielding rf magnetic fields in MRI systems. An rf shield is embedded in a gradient coil structure including X-, Y- and Z-axis coils. The rf shield is positioned between an inner gradient coil which is inherently decoupled from the rf field, and the remaining coils which require rf shielding. The inner gradient coil may be a Z-axis coil wound as a solenoid, the field of which is generally orthogonal with respect to the rf magnetic field. The rf shield is thereby placed at an enhanced distance from the rf coil, providing greater efficiency and permitting energy levels to be reduced to obtain the desired rf magnetic field strength.

Abstract: A quadrature coil suitable for use with an open frame MRI system provides crossing pairs of arrays of parallel conductor elements, respectively. Compact configuration is provided through use of an isolating circuit for incorporating parasitic capacitances at the resonance frequency of the coil into a blocking parallel resonance. Termination of the parallel conductor elements may be accomplished by equal impedance node connectors formed from branching pairs of conductors or a triangular least resistance connection form. RF shields are provided by pairs of conductive sheets containing eddy current reducing slots aligned with the parallel conductors elements of the coil.

Abstract: A combination gradient coil/RF shield is provided for magnetic resonance imaging systems. The coil may be adapted from any of the existing gradient coil structures, but is preferably an X-axis or Y-axis coil, with an inner Z-axis coil being inherently decoupled from the RF magnetic field due to its design. Capacitive circuits are provided between conductive paths of the selected gradient coil to adapt the gradient coil to the RF frequencies used during operation, such as 64 MHz. The technique permits the gradient coil assembly to be affectively moved closer to the patient while providing an enhanced distance between the RF coil and the RF shield defined by the adapted gradient coil.

Abstract: An RF shielding technique is provided for open MRI systems. The RF shield includes a first portion disposed over a gradient field generating set, and a skirt-like second portion that wraps around lateral structures, such as the primary magnet and support. The two portions are joined to one another to form an integral RF shield that limits loss of RF energy both through the gradient field elements and through the primary magnet and support structures.

Abstract: A magnetic resonance imaging (MRI) coil system is provided which comprises an RF coil element comprising a plurality of electrically conductive members spaced to form a generally tubular structure and defining an imaging volume. The coil element is adapted to receive a RF signal and apply a magnetic field to the imaging volume. A signal generator generates the RF signal, and a power splitter is adapted to distribute the RF signal across each of the plurality of electrically conductive members in signals of equal power. A phase shifter receives the split signals from the signal splitter and equally phase shifts each of the split RF signals across each of the plurality of electrically conductive members such that each conductor carries the signal at a different phase angle with respect to each other conductor. An amplifier is coupled to each of the conductors for independently controlling the current amplitude of the signal carried on the respective conductor.

Abstract: A radio frequency (RF) coil system for resonance imaging/analysis comprising a primary coil element having a plurality of axial conductors spaced to form a generally tubular structure having two ends and defining a coil volume, and a first pair of spoiler coils. The first pair of spoiler coils each comprising a plurality of axial conductors spaced to form a generally tubular structure and defining a coil volume. Each of the spoiler coils is positioned adjacent to and overlapping an end of the primary coil. Each of the primary and spoiler coils is also adapted to carry an RF signal, wherein the signal in the spoiler coils is 180 degrees out of phase with the signal in the primary coil. The counter-phased spoiler coils act to rapidly drive down the RF magnetic field generated by the primary coil in the region of the ends of the primary coil to reduce the occurrence of aliasing artifacts from outside the imaging field of view.

Abstract: A gasket having an integral support is provided that is suitable for use in connection with a heat shield in a gasket-heat shield assembly. The integral support may include a receiving cavity designed to accurately position and retain a portion of the heat shield. The integral support and gasket may further incorporate additional integral features to improve the positioning and connection of the heat shield to the gasket. A method for assembling a gasket-heat shield assembly is also disclosed.

Abstract: A short radio frequency coil for magnetic resonance imaging of the head to provide a homogeneous magnetic field including parallel conductors forming a first cylindrical portion with end rings supporting the conductors which then continue at an angle to form the frustum of a cone and further continuing to form a reduced diameter second cylindrical portion. A third conductive end ring of reduced diameter positioned at the open end of the second cylindrical portion supports the end of the conductors and provides a reduced diameter opening. An asymmetrical coil surrounds portions of the radio frequency coil including the first cylindrical and frustum of a cone portions.