Abstract: A system and method are presented that facilitate imaging of the joints of the upper and lower extremities including, for example, the hip and shoulder as well as sections of the spine, among others. One embodiment of the invention includes a short bore cylindrical magnet with an imaging volume smaller than that of a comparable whole body system, an articulated table that allows placement of the joint to be imaged in the center of the magnet homogeneous volume while maintaining a high degree of patient comfort and openness. The gradient and RF coils may be positioned above and below the patient instead of 360 degrees surrounding the patient. A smaller RF and gradient coil is made feasible because of the reduced imaging volume.

Abstract: The invention provides various systems, machine readable programs and methods for performing imaging using a MR scanner. The MR scanner includes at least one local radio-frequency transmit coil and at least one local gradient coil. The local radio-frequency transmit coil(s) and local gradient coil(s) cooperate to define an imaging volume. The MR scanner further includes a control system for performing an imaging operation on a patient's anatomy disposed within the imaging volume. The control system permits a selective simultaneous increase of the gradient magnetic field strength and peak B1 field strength by substantially the same factor, f.

Abstract: Methods, systems and machine readable programs are disclosed herein for providing improved magnetic resonance images, particularly with respect to fat and water separation.

Abstract: A system and method are presented that facilitate imaging of the joints of the upper and lower extremities including, for example, the hip and shoulder as well as sections of the spine, among others. One embodiment of the invention includes a short bore cylindrical magnet with an imaging volume smaller than that of a comparable whole body system, an articulated table that allows placement of the joint to be imaged in the center of the magnet homogeneous volume while maintaining a high degree of patient comfort and openness. The gradient and RF coils may be positioned above and below the patient instead of 360 degrees surrounding the patient. A smaller RF and gradient coil is made feasible because of the reduced imaging volume.

Abstract: An MRI RF coil has two resonant rings disposed along an axis. The resonant rings are inductively coupled, but are otherwise electrically isolated from one another. In an assembly having two such MRI RF coils, a decoupling element (e.g., a decoupling capacitor or inductor) electrically connected between one ring of one coil and one ring of the other coil decouples the 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: To generate a magnetic resonance image of a region comprised of two species of nuclei that have non-identical Larmor frequencies, the nuclei are excited and two read-out gradient pulses are generated. The relative phase offset between the two species of nuclei is different at the center of the first pulse than at the center of the second pulse. Data acquired during the two read-out pulses are processed in accordance with these relative phase offsets.

Abstract: A circuit for amplifying signals received by the receive coil of a magnetic resonance (MR) system includes a preamplifier employing an active circuit device, such as a GaAs-MESFET or HEMT. The preamplifier is located proximate to the receive coil in order to maintain as high a signal-to-noise ratio as possible for the preamplifier output signals. A capacitance is coupled to the receive coil to form an input impedance matching network for the input of the preamplifier. The preamplifier output is coupled through a fiber optic cable to remotely located MR signal processing electronics, which further processes signals received by the MR receive coil and amplified by the preamplifier.

Abstract: An in-situ method of extracting contaminants from a soil volume comprises applying a radiofrequency (RF) excitation signal to heat the soil with an array of electrodes. The electrodes are inserted into the contaminated volume or inserted into a matrix of holes drilled into the volume. A first row of electrodes is electrically coupled to a shield of a coaxial cable, with a second row electrically coupled to the central conductor of the coaxial cable. RF energy is applied to pairs of electrode rows through the coaxial cable and a matching network is installed in front of the electrode-row pair to maximize power flow into the electrode-row pair. This results in very evenly distributed voltages which results in even heating. A balanced-to-unbalanced transformer (balun) is installed at the input to the matching network to prevent the deposition of RF energy outside the target volume and creation of voltages that could be hazardous to personnel.

Abstract: A magnetic field gradient apparatus for use in a magnetic resonance (MR) imaging system employing open magnets allows access to a patient while the patient is being imaged. The magnetic field gradient apparatus employs two gradient coil assemblies and a gradient coil amplifier. Each gradient coil assembly has a gradient coil carrier with at least one gradient coil disposed on it. Each gradient coil carrier is comprised of a cylinder with a flange at one end. The gradient coil assemblies are positioned in the bore of each ring of the open magnet and spaced apart from each other allowing access to the patient. The gradient coil amplifier provides current through the gradient coils to create a magnetic field gradient which has high linearity inside an imaging volume. A coil is disposed on cylinders which surround each gradient coil assembly and fit inside the bore of each ring which acts as an active shield and minimizing eddy currents in conductors outside the gradient coil assemblies.

Abstract: A tracking system in which radiofrequency signals emitted by an invasive device such as a catheter, are detected and used to measure the position and orientation of the invasive device. The invasive device has a transmit coil attached near its end and is driven by a low power RF source to produce a dipole electromagnetic field that can be detected by an array of receive coils distributed around a region of interest. The position and orientation of the device as determined by the tracking system are superimposed upon independently acquired Medical Diagnostic images, thereby minimizing the radiographic exposure times. One or more invasive devices can be simultaneously tracked.

Abstract: A magnetic resonance (MR) imaging system for use in a medical procedure employs an open main magnet allowing access to a portion of a patient within an imaging volume, for producing a main magnetic field over the imaging volume; a set of open gradient coils which provide magnetic fields gradients over the imaging volume without restricting access to the imaging volume; a radiofrequency coil set for transmitting RF energy into the imaging volume to nutate nuclear spins within the imaging volume and receive an MR response signal from the nuclear spins; and a pointing device for indicating the position and orientation of a plane in which an image is to be acquired; an image control means for operating power supplies for the gradient coils and the RF coils to acquire an MR signal from the desired imaging plane; and a computation unit for constructing an image of the desired imaging plane.

Abstract: A gradient amplifier for use in magnetic resonance imaging equipment employs a low voltage DC power supply connected in series between a pair of higher voltage DC power supplies, the latter supplies serving to provide increased power for rapid gradient switching and the former supply providing correction current to produce the desired voltage output. The high voltage DC power supplies preferably comprise multiple DC units which can be combined to provide finer steps of control prior to correction by the lower voltage supply. The low voltage DC power supply preferably comprise one or more linear amplifiers connected in series, or one or more switchmode amplifiers connected in series. The DC power supplies are controlled in an open loop manner from a gradient signal that designates the desired current for the gradient coil and the amplifiers are operated in a closed loop responding to to a feedback signal from the gradient coil.

Abstract: An apparatus for microscopic imaging employing nuclear magnetic resonance is constructed from a cryogenic probe which is situated in a conventional magnetic resonance imaging system. The cryogenic probe employs a number of chambers and cryogenic liquids which cool a superconductor resonator to very low temperatures. A sample tube for containing a small specimen is heated to a temperature above its freezing point by flowing nitrogen gas over the specimen. A secondary resonant circuit is inductively coupled to the superconducting resonator. A transceiver passes RF signals to be transmitted into the specimen through the secondary resonant circuit causing the superconducting resonator to transmit the RF signal into the specimen. The resonator then acts as a receive coil and receives a signal from the specimen which is inductively passed to the secondary resonator circuit from which an image is generated.

Abstract: This invention relates to refrigerated superconducting eddy current free MR magnets having integrated gradient coils. In particular, the amount of resultant eddy currents produced by the magnet are substantially reduced while reducing the size and weight, and, therefore, the cost of the superconducting magnet required to produce an acceptable MR image.

Abstract: The invention relates to refrigerated superconducting MR magnets having integrated gradient coils. In particular, the amount of eddy currents produced by the magnet are substantially reduced while reducing the size and weight, and, therefore, the cost of the superconducting magnet required to produce an MR image.

Abstract: Apparatus for producing a magnetic field gradient for magnetic resonant imaging of the head of a subject employs two fingerprint coils disposed apart from each other, creating a generally cylindrical cavity in which subject's head is placed. A power supply provides current through the two fingerprint coils. The fingerprint coils are comprised of concentric current-carrying paths with each path being elongated along the length of the cylindrical cavity on only one end. The shape and geometry of the fingerprint coils create a magnetic field gradient that has high linearity inside the cavity, and monotonically decreases outside the cavity, thereby minimizing artifacts introduced by the body of the subject.

Abstract: A gradient current speed-up circuit, for use in a higher-speed NMR imaging system having an associated gradient coil, has a gradient power amplifier receiving an input analog signal controlling the current in an amplifier output circuit connected in series between first and second portions of a single gradient coil. Semiconductor switching elements selectively connect the coil portion-amplifier-coil portion between first and second potential sources, and are turned on and off in selected patterns to cause a current to be suddenly applied to, and removed from, flow through the associated gradient coil and the amplifier output circuit.

Abstract: A method and apparatus for combining NMR response data of a sample from a plurality of closely spaced RF receiver coils of an NMR phased array in the time domain to form a composite NMR image wherein each of the RF receiver coils receives a different respective one of a plurality of NMR response signals, each of which is evoked from a portion of the sample within a field of a respective one of the receiver coils. The response signals are conditioned to develop a plurality of data point signals corresponding to the magnitude of each of the respective response signals from each of the receiver coils at successive time intervals. The data point signals are convolved by a time domain representation of a field map of the respective one of the receiver coils generating the corresponding one of the response signals. The convolved signals are combined on a time domain point-by-point basis to produce a time domain representation of the composite NMR image of the sample.

Abstract: A gradient current speed-up circuit, for use in a higher-speed NMR imaging system having an associated gradient coil, has a gradient power amplifier receiving an input analog signal controlling amplifier output current, and a transformer having a primary winding and a pair of secondary windings connected in series with the amplifier output and the coil. Semiconductor switching elements selectively connect the primary winding between first and second potential sources, and are turned on and off in selected patterns to cause a current to be suddenly applied to, and removed from, flow through the associated gradient coil; the amplifier output current is changed with the gradient coil current lags behind an amplitude commanded by a master input signal.