Abstract: An RF shield is provided to prevent coupling between the gradient coils and the RF coil of an MR imaging system, wherein the RF field rotates around the RF coil axis. The shield includes a number of coaxial conductive cylinders, and further includes a plurality of cylinders formed of dielectric material, each dielectric cylinder positioned between adjacent conductive cylinders. Each conductive cylinder is formed from sheets of copper, each sheet having a pattern of conductive loops formed therein, and each loop having an associated gap to prevent induction of eddy currents therein by gradient magnetic fields produced by the MR system gradient coils.

Abstract: The invention is directed to a gradient coil assembly for MR imaging which includes a gradient coil set comprising inner and outer gradient coils, the inner gradient coil located within the outer gradient coil and surrounding or otherwise proximate to an imaging volume. The system further includes means for selectively energizing the inner and outer gradient coils to generate a resultant gradient field in the imaging volume. The energized inner and outer gradient coils are also disposed to collectively generate an eddy current field component in a region between the outer coil and a conductive structure spaced-apart therefrom when the inner gradient coil is displaced along an axis from a specified position with respect to the outer gradient coil.

Abstract: A whole body RF coil provided for use with an open MR magnet system comprises first and second RF coil components selectively spaced apart from each other on opposite sides of an imaging space disposed to receive a subject, each of the RF coil components comprising a plurality of electrically conductive inner and outer arc segments which respectively lie on corresponding inner and outer circular paths. The RF coil is constructed to allow the subject to pass through the inner and outer circular paths of a selected one of the coil components or alternatively between the spaced apart RF coil components, into imaging space. The first and second RF coils are each energized in quadrature to generate respective corresponding first and second magnetic fields which collectively provide a resultant field comprising the B.sub.1 field component required for imaging.

Abstract: In a magnetic resonance imaging (MRI) system, a method is provided for reducing oblique Nyquist ghost artifact in an image produced by an oblique EPI scan. Prior to commencing the EPI scan, referencing pre-scans are conducted to generate pre-scan echo trains respectively corresponding to the physical gradient axes. Distortion compensating parameters are derived from the pre-scan echo trains for reducing Nyquist ghost by alternatively modifying the data acquisitions stage of the oblique EPI scan, or the post-data acquisition image processing stage thereof. In one mode of operation, the pre-scan echo trains are generated while a subject is in the MRI system. In another mode of operation, pre-scan echo trains are generated while no subject is present in the MR system, so that the distortion compensating parameters represent characteristics of the MR system only, and thus may be used for EPI scans of different protocols.

Abstract: An amplification device is provided for driving a gradient coil in an MR system, wherein the gradient coil is required to generate a rapidly changing gradient magnetic field during a first time period, and a substantially constant field during an immediately following second time period. The device includes a adjustable bus, for providing first and second voltage levels, and a switching or PWM amplifier. A switch is coupled between the bus and the switching amplifier for applying the first voltage to the amplifier during the first time period, and the second voltage to the amplifier during the second time period. The switching amplifier comprises an inverter for generating a PWM voltage in response to its input, and an LC filter for converting the PWM wave into a DC voltage. The switching amplifier generates a substantially higher coil driving voltage during the first period, in response to the first voltage level, than during the second period in response to the second voltage level.

Abstract: A method for correcting MR data elements acquired in the presence of an imperfectly linear gradient field, each element comprising nominal first and second quadrature components. The quadrature components are multiplied by an artifact correction factor to provide respective first and second quantities. A Gradwarp geometric correction operation is applied to respective quantities to provide a corrected first and second quadrature component, corresponding to each data element. For a given data element, the arctangent function is applied to the result obtained by dividing the first corrected component by the second corrected component to provide a corrected phase component for use in forming an image.

Abstract: A method is provided for fabricating a gradient coil for an MR imaging system having an open magnet. The method includes forming a structure from thin conductive material such as copper, the structure generally comprising a section of a cylinder and a section of an annulus joined to an edge of the cylinder section as a flange. During a first cutting operation, a plurality of first groove segments are cut through the material, each of the first groove segments lying in one of a plurality of cutting zones selectively positioned around the structure, a strip of material positioned between two adjacent groove segments comprising a coil turn segment. The coil turn segments of a cutting zone are rigidly joined to one another and to a support frame comprising the outer edge of the structure by suitable means. Thereafter, a second cutting operation is performed, whereby a plurality of second groove segments are cut through the material to completely form the gradient coil.

Abstract: A method is provided for rapidly measuring change in T.sub.2 * in a region of an MR imaging subject, the method employing a double gradient echo sequence with spiral readout. In this technique, two gradient echoes are acquired after a single RF excitation. A first readout trajectory spirals out from the center of k-space, i.e., k.sub.r =0, to some maximum radius, and then a second readout trajectory spirals back towards the center of k-space. A gradient echo is formed each time a k-space trajectory passes through the center of k-space. The signal intensity of the two echoes allows the calculation of the T.sub.2 * values on a pixel by pixel basis. The ability to measure changes in T.sub.2 * allows measurement of change in perfusion to be quantified.

Abstract: An arrangement is provided for supporting the inner and outer gradient coils of one or more gradient coil sets, the coils of each gradient coil set providing one of the orthogonal gradient magnetic fields for an MR imaging system. The arrangement includes an inner cylindrical coil form disposed to supportably carry an inner gradient coil of a coil set, an outer cylindrical coil form in coaxial spaced-apart relationship with the inner coil form disposed to supportably carry an outer gradient coil of the coil set, and a stiffening cylinder positioned between the inner and outer coil forms to divide the space therebetween into first and second volumes. A thermally conductive adhesive material, such as an epoxy containing alumina particulate material, is inserted into the first and second volumes to bond both the inner and outer coil forms to the stiffening cylinder, in order to hold the inner and outer gradient coils respectively carried by the coil forms in rigid fixed relationship with respect to one another.

Abstract: A system is provided for MR imaging wherein a volume within an imaging subject positioned with respect to the system contains both water molecules and fat tissue proximate to one another. The water molecules and fat tissue are selectively saturated by first determining whether application of a first RF excitation pulse of a first RF frequency to the volume, in association with a gradient magnetic field having a selected polarity with respect to an axis, would saturate fat tissue in a band lying closer to or farther from a selected location than a band of saturated water molecules. The first frequency comprises the sum of a center frequency and a first offset frequency having a magnitude and polarity determined by the gradient magnetic field.

Abstract: A power coupling assembly for superconducting magnets includes a conduit with insulating tubes around each power lead, with the tubing passing through a plug at the upper end of the conduit and extending only part way to the lower end. Cryogen gas flowing from the magnet chamber into the conduit is forced to flow through the multiple tubes to cool the leads.

Abstract: A flexible heat transfer assembly between a cryogenic refrigerator cold head sleeve and magnetic resonance imager thermal shields includes a plurality of rope-lay stranded copper ropes, each containing a large number of section.

Abstract: A method for MR imaging in an inhomogeneous magnetic field substantially without inhomogeneity induced artifacts is disclosed. The method includes acquiring more than one line of K-space per pulse sequence. The K-space data is acquired in partial line segments. The method allows shorter imaging times and higher image quality than conventional imaging methods for inhomogeneous fields.

Abstract: A Belleville spring/ball combination is utilized in a rotating anode target bearing assembly in an X-ray tube for thermal and electrical conduction as well as self-centering of the target shaft and noise reduction.

Abstract: A flexible castellated joint is included in the shim lead assembly electrically connecting the cryostat pressure vessel and the outer vacuum vessel in a superconducting magnet to accommodate relative motion between the two vessels during transportation of the superconducting magnet.

Abstract: Apparatus and method for forming long lengths of laminated superconducting tape by passing three foils over idler pulleys, through a solder bath and between pinch rollers having a portion which extend above the solder bath to enable cleaning of the pinch rollers during the formation of the superconducting tape with means to adjust the pressure applied by the pinch rollers, and to adjust the laminated tape takeup tension independently from the foil process tension.

Abstract: An adjustable alignment assembly for a cryogen venting system for a superconducting magnet including a radially adjustable floating flange connection with a cryogenic seal to enable precise alignment of the cryostat vent pipe with the ceiling vent pipe of the room in which the superconducting magnet is installed.

Abstract: A flexible elongated slatted grid structure is suspended between a pair of spaced apart grid support frames each of which is adapted for rotation about a transverse axis intermediate the suspended ends of the grid. Mechanical adjustment means provides equal but opposite angular motion of the frames to curve the grid along a circular path.

Abstract: Power couplings are provided from outside the shell of a superconducting magnet through the intervening space and through the cryogen pressure vessel to the magnet coils within the vessel. The multi-pin shim magnet connector is replaceable without cutting the vessel open and the shim and main magnet main coil connectors include central apertures through which cryogen boil-off gas is flowed before venting to cool the connectors and reduce boil-off.

Abstract: An open architecture Magnetic Resonance Imaging Magnet with a pair of spaced annular superconducting magnet assemblies utilizing a cantilevered main magnet coil and correction magnet coil within each assembly.