Abstract: A magnetic resonance imaging scanner (10) includes a main magnet (20) generating a spatially uniform main magnetic field at least over a field of view, a plurality of gradient coils (30) selectively generating magnetic field gradients at least over the field of view, and a radio frequency coil (32, 34) for performing at least one of exciting and detecting magnetic resonance at the selected resonance frequency in an imaging subject disposed in the field of view. A radio frequency trap (60, 60?) connected with the radio frequency coil (32, 34) includes helically grooved dielectric formers (62, 62) around which a coaxial cable (64) is wrapped. A plurality of electrically conductive tuning elements such as screws or rods (84, 90) are selectively inserted into the dielectric formers (62, 62) to tune the radio frequency trap (60, 60) to a selected resonance frequency by adjusting the inductance of the trap.

Abstract: A multi-channel RF cable trap (70) blocks stray RF current from flowing on shield conductors (114) of coaxial RF cables (60) of a magnetic resonance apparatus. An inductor (116) is formed by a curved semi-rigid trough (80) constructed of an insulating material coated with an electrically conducting layer. Preferably, the inductor (116) and the cable follow an “S”-shaped path to facilitate good electromagnetic coupling therebetween. The RF cables (60) are laid in the trough (80) and the shield conductors inductively couple with the inductor (116). A capacitor (82) and optional trim capacitor (83) are connected across the the trough of the inductor (116) to form a resonant LC circuit tuned to the resonance frequency. The LC circuit inductively couples with the shield conductors (114) to present a high, signal attenuating impedance at the resonance frequency. The resonant circuit is preferably contained in an RF-shielding box (84) with removable lid.

Abstract: A multi-channel RF cable trap (70) blocks stray RF current from flowing on shield conductors (114) of coaxial RF cables (60) of a magnetic resonance apparatus. An inductor (116) is formed by a curved semi-rigid trough (80) constructed of an insulating material coated with an electrically conducting layer. Preferably, the inductor (116) and the cable follow an “S”-shaped path to facilitate good electromagnetic coupling therebetween. The RF cables (60) are laid in the trough (80) and the shield conductors inductively couple with the inductor (116). A capacitor (82) and optional trim capacitor (83) are connected across the the trough of the inductor (116) to form a resonant LC circuit tuned to the resonance frequency. The LC circuit inductively couples with the shield conductors (114) to present a high, signal attenuating impedance at the resonance frequency. The resonant circuit is preferably contained in an RF-shielding box (84) with removable lid.

Abstract: A magnetic resonance apparatus includes a main magnetic field source (12) for providing a magnetic field (B0) along a main field axis. A transmitter (34) and transmit coils (30, 32) excite a nuclei of an object to resonate. The resonating nuclei generate magnetic resonance signals detected by a volume coil (50) including a pair of end rings (70, 72) separated along a coil axis (Y). The end rings (70, 72) are electrically interconnected by a plurality of rungs (74) disposed about the rings. A conductive loop (80) is concentrically disposed between and inductively coupled to the end rings. The loop includes an electrical conductor (82) preferably surrounding the rungs (74), and positioned parallel to the end rings (70, 72). A capacitive element (84), in electrical communication with the conductor (82), is selected or adjusted to tune the loop (80) to signals at a selected frequency.

Abstract: A multi-channel balun (70, 72) blocks stray RF current from flowing on shield conductors of coaxial RF cables of a magnetic resonance apparatus. The balun comprises a parallel combination of an even number of helical coils of shielded transmission cable (L10, L12; L14, L16, L18, L20) wound in alternate directions such that voltages iduced by their external RF fields cancel. One capacitor (C10; C16, C18) is connected in parallel symmetrically with each pair of helical coils, with trim capacitors (C12; C22) fixed in the coil plug (86, 90) to retune the balun as required. The multi-channel balun (70, 72) accommodates magnetic resonance systems with an odd or even number of channels without requiring shielding. Preferably, the balun (70, 72) is constructed on a single circuit board in a close-packed relationship that is compact and space efficient, yet provides better decoupling from the transmit field.

Abstract: A tunable radio frequency birdcage coil (30) is oriented vertically in a bore-type magnetic resonance apparatus. The birdcage coil (30) includes a pair of end rings (60, 62) disposed in parallel planes along a coil axis which is orthogonal to the main magnetic field. A plurality of rungs (64) electrically interconnect the end rings (60, 62) to form a generally cylindrical volume. The end rings (60, 62) and rungs (64) are mounted on a hinged (68) dielectric former (66). Conductive connectors (70) releasably fasten the end rings (60, 62) so that the coil (30) may be opened and closed to receive a portion of a subject to be examined. A conductive loop (80) is inductively coupled and positioned parallel to the end rings (60, 62). The conductive loop (80) is slidably adjustable along the coil axis for matching and tuning end-ring modes of the coil. The coil is oriented to provide a subject disposed therein with an open view for fMRI applications.

Abstract: An endocavity RF coil assembly for an MRI apparatus includes a reusable probe (30). The reusable probe has a hollow outer cover (60) having a closed distal end and (62) an open proximate end (64). The distal end (62) is formed to fit into a cavity of a subject being examined. An active RF coil element (72) is rigidly formed about an internal sleeve (70) which is located within the distal end (62) of the outer cover (60). A tuning and matching circuit is disposed within the outer cover (60) on the proximate end (64) side of the active RF coil element (72). The tuning and matching circuit is arranged on a printed circuit board (74) and attached to the active RF coil element (72). An over-molded form (90) is connected to the proximate end (64) of the outer cover (60). The over-molded form (90) is arranged such that it seals the proximate end (64) of the outer cover (60) closed.

Abstract: A multimode radio frequency coil (50.sub.1) receives resonance signals from a region of interest while allowing arbitrary placement of the coil. A peripheral electrical conductor (62) is divided into four symmetric segments by capacitors (76), (78), (80), (82). A pair of crossing conductors (64, 66) are connected between 90.degree. offset diagonally opposite portions of the peripheral loop (62). The crossing conductors include capacitors (68, 70) when not connected and include capacitors (68, 70, 86, 88) when connected at their midpoints. With this configuration, the coil supports orthogonal modes (72, 74) within the plane of the coil and, additionally, a third orthogonal mode (84) perpendicular to the plane of the coil. To image an extended region, a plurality of coils are overlapped to minimize mutual inductance relative to a first mode. An adjustable capacitor (90) across one of the coils adjusts mutual inductance relative to the second mode.

Abstract: A vertical B.sub.0 temporally constant magnetic field is defined between a pair of pole faces (12, 14) that are interconnected by a C-shaped ferrous magnetic flux path (16). A quadrature radio frequency coil array (50) is disposed in a plane orthogonal to the B.sub.0 field. The coil array includes a plurality of coils (50.sub.1, 50.sub.2, . . . ) that are disposed in a partially overlapping relationship. Each of the coils has a peripheral loop (60), preferably defined by four linear legs (60.sub.1, 60.sub.2, 60.sub.3, 60.sub.4) of equal length which define a square. A pair of crossing elements (62.sub.1, 62.sub.2) are connected with mid-points of opposite sides of the square, the opposite mid-points are 180.degree. out-of-phase with each other at the magnetic resonance frequency and 90.degree. out-of-phase with neighboring mid-points of the square. The crossing elements cross but are not connected, in a symmetric relationship. Each of the crossing elements has a radio frequency pick-up (64.sub.1, 64.sub.

Abstract: An RF device (A) under test is connected with ports or jacks (14, 16) of an S-parameter test set (B). An RF input jack (18) is connected with an RF tracking signal output (20) of a spectrum analyzer (C) to receive an RF tracking signal. An output jack (22) is connected with a receiver input (24) of the spectrum analyzer. A mode control (30) internal to the test set is controlled by a programmable control sequence generator (34) of the spectrum analyzer. The mode control controls a switch array (32), preferably PIN diodes, which interconnect the RF input jack (18), the RF output jack (22), the two jacks (14, 16) that are connected to the device under test, and a 50 Ohm termination (54) in four modes to make reflection measurements and two transmission measurements. DC bias jacks (26, 28) are connected with a DC power for injecting a DC component into the RF signals applied to the device under test.