Picker International, Inc.

Paul T Orlando

George J Misic

John Lester Patrick

G Neil Holland

David A Lampman

John L Patrick, Iii

Xueming Zou

Gregory C Hurst

Nicholas J Mastandrea

Mehrdad Mehdizadeh

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

A toroidal vacuum dewer (22) holds a superconducting magnet assembly (10) which generates a substantially temporally constant magnetic field through a central bore (12). A whole body gradient coil (30) and a whole body RF coil assembly (32) are mounted to a cylindrical member (24) of the dewar. An insertable gradient coil assembly (40) is selectively insertable into and removable from the bore. The insertable gradient coil assembly includes gradient coils for selectively generating magnetic field gradients along three mutually orthogonal axes, e.g. x, y, and z-axes. A flexible cable (42) connects the insertable gradient coil with a series of current amplifiers (44). The current amplifiers selectively generate current pulses which are fed along feed conductors (84) of the coil assembly and which return along return conductors (86) of the cable. The feed and return conductors are configured such that the net feed and the net return current traverse the same effective path in opposite directions. Stated more mathematically,

Feed cable system for coils in high magnetic fields

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

In a magnetic resonance imaging apparatus, a first frequency radio signal source (20a) is connected in quadrature with a four fold symmetric birdcage coil (24) at 90.degree. spaced connection points (80a,b). A source of a second radio frequency signal is directly connected with the birdcage coil by first and second inductive couplings (70a,b). The birdcage coil includes tank circuits (52) and capacitors (58, 60) in the end connectors. The capacitance of the end connectors is simultaneously adjustable by a tuning ring (62) to adjust a first resonance frequency of the coil and the capacitance of the tank circuits is selectively adjustable to adjust a second resonant frequency of the birdcage coil. In this manner, the birdcage coil is simultaneously tuned to two frequencies and can operate in quadrature at either one. PIN diodes (92) are provided for de-tuning the coil such that it operates in a third mode in which no resonance frequency exists such that the birdcage coil does not interfere with reception of resonance signals by a surface coil (42). When operating in quadrature, additional PIN diodes (114) are provided for connecting the RF feed point to one node (102a) of a 90.degree. phase shift circuit (100) in the transmit mode and to the opposite node (102b) of the 90.degree. phase shift circuit in the receive mode.

NMR spectroscopy and imaging coil

A resonance exciting coil (C) excites magnetic resonance in nuclei disposed in an image region in which a main magnetic field and transverse gradients have been produced. A flexible receiving coil (D) includes a flexible plastic sheet (40) on which one or more loops (20) are adhered to receive signals from the resonating nuclei. Velcro straps (46) strap the flexible sheet and the attached coil into close conformity with the surface of the portion of the patient to be imaged. An impedance matching or coil resonant frequency adjusting network (50) is mounted on the flexible sheet for selectively adjusting at least one of an impedance match and the peak sensitivity resonant frequency of the receiving coil. A preamplifier (52) amplifies the received signals prior to transmission on a cable (24). A selectively variable voltage source (70) applies a selectively adjustable DC bias voltage to the cable for selectively adjusting at least one of the impedance match and the LC resonant frequency of the receiving coil. The received signals are amplified by an amplifier (82) and processed by an image processor (30) to form man-readable images of the examined region of the patient for display on a video display (32) or the like.

Surface coil system for magnetic resonance imaging

During a transmit cycle portion, a radio frequency transmitter (C) continuously generates an AC biasing signal and selectively generates a radio frequency signal. The AC biasing signal gates a first switch (10) and a second switch (32) such that the radio frequency signals from the transmitter are conducted to a magnetic resonance probe (E) but are blocked from being conducted to a receiver (F). A first filter (20) prevents the bias signals from being applied to the probe. The second switch includes a pair of crossed diodes (34, 36) which are gated conductive by the AC bias signal. A filter (72) passes the radio frequency signals but not the bias signals to ground to prevent the radio frequency signals from reaching the receiver. A filter (80) allows the bias signals to be applied across a load (88) such that the transmitter sees the load at the bias signal frequency. Another filter (40) prevents the bias signal from reaching the transmitter. An additional switch (50) provides further isolation between the receiver and the transmitter during the transmit cycle portion. During the receive cycle portion, radio frequency signals received by the probe pass through the filters (20,40) directly to the receiver but are blocked by switch (10) from passing to the transmitter.

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Mentor, OH, United States of America

Paul T Orlando