Abstract: Methods and devices for delivering heat to a target region within a body lumen. In one aspect, the present invention provides a method of delivering heat to a body lumen. The method comprises positioning a catheter comprising an electrode array in the body lumen and selectively delivering a current to fewer than all of the electrodes in the electrode array to heat a target region of the body lumen.

Abstract: The present invention relates generally to in vivo evaluation of labeled lesions within a body lumen using a catheter having an array of radiation detectors. The present invention provides catheters and methods which detect radiotracers which have bound to vulnerable plaque. The radiation detectors can be coupled to a signal processor through a delay line so as to reduce the number of transmission lines traveling through the catheter to the outside of the body. The radiation detectors can be semiconductor detectors or optical detectors.

Abstract: An RF coil array arrangement for enhanced magnetic resonance imaging of the breast or spine regions of prone and supine patients within a vertically oriented B0 field is disclosed. Several RF coil array embodiments are disclosed that provide for both generating a nuclei nutation field pulse and acquiring nuclear magnetic resonance signals when functioning in an MRI apparatus environment that employs a vertical main magnetic field. A coil array may include one or more RF coils that are intended to be oriented such that their primary B field direction(s) are perpendicular to the vertical magnetic field of the MRI apparatus. Each coil array may further include one or more single loop or solenoidal coil(s) that are oriented having their central or longitudinal axis aligned parallel to the vertical main magnetic field so as to make advantageous use of non-axial field components associated with the coil(s) to further generate and receive desired NMR signal components.

Abstract: An inherently de-coupled sandwiched solenoidal array coil (SSAC) is disclosed for use in receiving nuclear magnetic resonance (NMR) radio frequency (RF) signals in both horizontal and vertical-field magnetic resonance imaging (MRI) systems. In its most basic configuration, the SSAC comprises two coaxial RF receive coils. The first coil of the array has two solenoidal (or loop) sections that are separated from one another along a common axis. The two sections are electrically connected in series but the conductors in each section are wound in opposite directions so that a current through the coil sets up a magnetic field of opposite polarity in each section. The second coil of the SSAC is disposed (“sandwiched”) between the two separated solenoidal sections of the first coil in a region where the combined opposing magnetic fields cancel to become a null.

Abstract: An asymmetric spin-echo (ASE) sequence having a variable asymmetry (&Dgr;TE) with respect to the RF pulse is used for imaging paramagnetic, diamagnetic or ferromagnetic instruments within tissues during interventional MRI procedures. The degree of asymmetry introduced determines an apparent size of the imaged instrument. In one embodiment of the invention, the amount of asymmetry is varied as a function of the phase encoding gradient steps. In this manner, the sequence is made sensitive to local gradients in the magnetic field but left insensitive to large scale variations such as those introduced by main magnetic field inhomogeneities.

Abstract: A magnetic resonance imaging sequence synergistically combines Half Fourier Transform complex conjugation with shared echo imaging. The Half Fourier Transform complex conjugation reduces data acquisition time and permits the data acquisition per scan to be accomplished with a single RF transmission loop. The shared echo imaging provides multiple images of an image plane from a single scan, yet with different contrast and a larger number of slices. In an alternative embodiment, phase correction is provided between the non-shared echo responses.

Abstract: An RF coil for an MRI system is self-supported by the formed conductor used to make the coil itself. A high-strength, high-conductive, stiff, internally self-supporting Cu-ag alloy may be used.

Abstract: Static magnet pole tips for a MRI system in which the static magnet pole tips are cut from a slug of spirally wound ferromagnetic material. The static magnet pole tips are cut from the spirally wound slug such that the static magnet pole tips have no or few semi-closed loops of ferromagnetic material. The static magnet pole tips can be used individually, or can be stacked for strength and symmetry.

Abstract: An RF coil tuning circuit is disclosed in which two banks of parallel capacitive branches are provided. Each capacitive branch includes a fixed value capacitor, a relay and a PIN diode connected in series. An impedance of the tuning circuit is adjusted to the optimum VSWR=1 condition by first switching the eight PIN diodes to learn which open/closed condition applies the fixed value capacitors in the optimum combination. Then, the PIN diodes are all closed and the optimum combination is applied using the open/closed states of the relays.

Abstract: A nuclear magnetic resonance imaging system is described. The nuclear magnetic resonance imaging system includes an RF transmit device formed as two rectangular coils arranged in planes orthogonal to one another and formed by two U-shaped loops. The U-shaped loops improve B.sub.1 field homogeneity in the vertical direction. The rectangular coils may be used in a four post MRI device to improve access to the body being imaged.

Abstract: A gradient coil assembly for a magnetic resonance imaging device is disclosed. The gradient coil assembly includes a web of interconnected fibs fixed to the gradient coil former to rigidize the gradient coil former. The rigidized gradient coil former is less susceptible to vibration, thus minimizing the acoustical noise generated by the gradient coil assembly during the MRI operation.

Abstract: Switched magnetic fields (in addition to the usual pulsed magnetic gradient fields) aiding and/or opposing the usual constant static magnetic field B.sub.o are utilized so as to increase the signal-to-noise ratio for given available imaging sequence times and/or to provide special imaging effects.

Abstract: Convenient side access to an image volume located within a two-pole, two-column main magnet of an MRI system is provided by rotating the symmetry axis of the magnet to be non-perpendicular with respect to the longitudinal axis of the patient transport and/or otherwise displacing the two column structures of the magnetic circuit so as to permit open and unobstructed access to the image volume along a direction perpendicular to the longitudinal axis of the patient transport.

Abstract: An electromagnet shim coil is utilized for temporarily altering the shape of a volume in which there is provided a substantially homogeneous NMR polarizing field. By temporarily energizing the electromagnet shim coil and thus altering the shape of the volume, magnetic resonance imaging can take place in other than a substantially spherical volume (e.g., in an elongated ellipsoidal-like volume extending axially along a patient so as to encompass a longer section of the spinal column). In the exemplary embodiment, the electromagnet shim coil takes the form of a pancake-like coil with windings positioned so as to create fourth power spherical harmonic in a transverse magnet-type of MRI system.

Abstract: An RF coil sub-assembly for a transverse magnet MRI system includes substantially co-planar serially-connected turns mounted on a common substrate. Preferably, half of the turns are directed clockwise, while the other half are directed counter clockwise to produce a plurality of equal commonly directed currents along spaced apart parallel conductors. A low-loss expanded dielectric spacer is used to mount the RF coils within a pre-existing depression formed by the annular magnetic shims of a transverse magnet structure thus substantially eliminating any obstruction to the image volume for at least the RF transmit coils.

Abstract: A quadrature detection (QD) head coil assembly for use in magnetic resonance imaging (MRI) having a pair of orthogonally situated zero-pitch solenoidal windings is disclosed. The turns of each winding are serially connected along the solenoid surface in a predetermined axially-extending area by using dog leg connectors. Return coil connections (i.e., an RF connection between the first and last turn of each coil) is effected substantially adjacent to the dog leg interconnections so as to minimize the area of any equivalent return loop and thus to minimize the magnitude of any inter-coil coupling via such return loops. To further minimize possible inter-coil coupling, the return loops for each of the quadrature detection coils are preferably oriented so as to primarily couple to magnetic fields that are orthogonal to the main field of both the QD coils. The use of zero- pitch turfs in each solenoidal coil winding also substantially reduces possible inter-coil coupling.

Abstract: An MRI RF coil utilizes a helical conductor having a plurality of turns and a non-uniform pitch between turns along at least a portion of the axial length of the coil. The non-uniform pitch is disposed so as to accommodate interventional procedures and/or interventional apparatus (e.g., stereotaxic frames) when used on a human patient in conjunction with magnetic resonance imaging. The non-uniform pitch portion of the coil may comprise a simple gap, an opening formed by deformation or angular disposition of some or all of the coil turns and/or by utilizing fringe field effects of the coil to accomplish at least some of the magnetic resonance imaging procedure.

Abstract: An MRI magnet member (e.g., a pole piece or tip) is laminated using relatively large bar-shaped laminations instead of the usual thin sheet material. One or more layers of such bar-shaped laminations are arrayed with small insulating gaps into which a low loss insulating liquid filler material is flowed and then cured to a hardened solid state. This simultaneously produces insulated pole tip laminations which have been robustly integrated together into a unitary structure. The resulting robust laminated pole tip is relatively easy to manufacture and is also capable of withstanding rather large magnetic forces and maintaining relatively uniform magnetic field distribution within an MRI imaging region while yet providing providing sufficient eddy current reduction so as to efficiently permit rapidly changing magnetic gradient coil currents to be established.

Abstract: MRI T1 relaxometry is performed using a single fixed strength magnetic background field for RF signal transmission and reception thus greatly simplifying RF circuitry design and/or adjustment Switched differing strength background magnetic fields are employed at other times in the relaxometry cycle so as to predominate the NMR T1 relaxation parameter value and thus permit relaxometry determinations of T1 values versus magnetic field strength (or the equivalent corresponding NMR RF frequency) at N data points using as few as N+1 measurement cycles. In one embodiment, the booster field is switched on for fixed time intervals .tau. while variable initial NMR nutation pulses .alpha. are utilized as the controlled relaxometry variable parameter. Process and apparatus are disclosed for thus efficiently achieving in vivo NMR relaxometry (including magnetic resonance imaging if desired).