University of California

Lawrence E Crooks

Mitsuaki A Arakawa

John C Hoenninger, Iii

Leon Kaufman

Joseph W Carlson

James D Hale

David A Feinberg

William H Harrison

David M Kramer

Jerome R Singer

John H Fehn

John Van Heteren

Douglas A Ortendahl

James W Jones

Ching Yao

Kristen Hake

Heckor Avram

Joel Wummer

Keiji Furui

Thomas McDermott

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.

Switched field magnetic resonance imaging

A control interface for a magnetic resonance imaging (MRI) system provides extended, improved linker syntax/techniques that maximize reuse of program segments, allow optimal compromise between detailed representation and efficient sequence program design and maintenance, and permit uniform application of the loop syntax to link commands for MRI sequencers with a wide range of hardware implementations. The control interface provides, among other features, generalized loops at the link level; loop symbols representing loop identity can be associated with scope and/or range (with some kind of limited grammar in the link command itself that supports identification of scope and/or range); parameter tables that can be associated with loop symbols (any given table can be associated with N loop symbols in order to provide multidimensional sequences); multiple levels of loop nesting; and directed limited syntax that provides limited grammar, and range and syntax checking and requires the user to explicitly enter information into the interface.

Control interface for an MRI system

A multi-rate sample MRI (magnetic resonance imaging) digital receiver maintains synchronization of digitally processed signals. This multi-rate sample data system is used to demodulate and filter a digitized MRI RF signal. A phase/timing relationship is established between the signal received and processed by the digital receiver, and the physical nuclear magnetic resonance (NMR) process the body being imaged is undergoing. Once established, the phase/timing relationship is maintained for the duration of the particular NMR experiment being performed. Special logic in the digital system ensures that the data output is synchronized with an external synchronous signal controlling data acquisition within the MRI system. Optimum signal processing is performed to minimize the time between the end of the acquisition control signal and the last output from the digital signal processing system.

Synchronized digital signal processor for MRI reception

An all digital controlled current driver is used for each pulsed electromagnet (e.g., gradient coils) in a magnetic resonance imaging (MRI) system. Such an all digital current controller may be advantageously employed in either closed loop or open loop gradient coil control circuits. The elimination of analog components decreases cost, increases operating efficiency and improves operating characteristics of the MRI system.

MRI gradient drive current control using all digital controller

A local frequency generator employing a single crystal oscillator, latches and direct digital synthesizer circuits digitally produces all signals needed in the transmitter channel of a MRI system to generate MRI transmitter RF pulses. The local frequency generator is operable in both the single side band and double side band modes and has the capability of switching between the modes. The generator is constructed with a phase resetting capability for providing the plural output frequencies needed for making plural MRI slices.

MRI multi-frequency DSB and SSB RF synthesizer

The effective Q of a capacitively coupled RF coil in a magnetic resonance imaging (or magnetic resonance spectroscopic imaging) system is controllably lowered from its intrinsic maximum value by controlling the impedance reflected across the coil via a tuning/matching network associated and located with the coil. The Q may be advantageously lowered during transmit time as compared with receive times (during which the Q may be relatively increased) by effecting controlled impedance mismatches within the RF feed network used to supply RF signals to/from the RF coil.

Q control for capacitively coupled MRI/MRSI RF coil

Static B.sub.o field strength is measured during each TR interval of an MRI sequence providing field calibration data used to compensate for rapid variations in B.sub.o during the MRI sequence.

MRI compensated for spurious rapid variations in static magnetic field

At least one extra NMR measurement cycle is performed without any imposed magnetic gradients during readout and recordation of the NMR RF response. Calibration data derived from this extra measurement cycle or cycles can be used for resetting the RF transmitter frequency and/or for phase shifting other conventionally acquired NMR RF response data to compensate for spurious changes in magnetic fields experienced during the NMR data measuring processes. Some such spurious fields may be due to drifting of the nominally static magnetic field. Another source of spurious fields are due to remnant eddy currents induced in surrounding conductive structures by magnetic gradient pulses employed prior to the occurrence of the NMR RF response signal. Special procedures can be employed to permit the compensation data itself to be substantially unaffected by relatively static inhomogeneities in the magnetic field and/or by differences in NMR spectra of fat and water types of nuclei in imaged volumes containing both.

MRI compensated for spurious NMR frequency/phase shifts caused by

In a gradient coil set for a magnetic resonance system, the y gradient coils are located substantially closer to the patient than are the x and z gradient coils. As a result, one may design the y gradient coils to produce a stronger y gradient, to have reduced inductance or otherwise better tailor the magnetic/electrical properties of the gradient coil set for MRI imaging sequences. In the exemplary embodiment, at least portions of the y gradient coils have a first spacing from the z-axis while the x and z gradient coils have a second substantially larger spacing from the z-axis. Furthermore, while the x and z gradient coils are centered about the z-axis in the patient access space, alternate sides of the y gradient coil set are centered about respectively off-set centers vertically displaced from the z-axis center of the patient access area. The result is a substantially rectangular or elliptical patient access opening with horizontal dimensions defined by the x, z coils sets and vertical dimensions defined by the y coil set.

Magnetic gradient coil set for nuclear magnetic resonace system having

An RF coil for a magnetic resonance imaging device using nuclear magnetic resonance phenomena includes self-tracking ganged coupling capacitors which provide impedance matching and also tune out coil inductance to establish resonance at the RF operating frequency. At least one variable capacitor connected in parallel with the RF coil is mechanically ganged to at least one variable capacitor connected in series to the RF coil. The parallel and series capacitances are initially set to achieve resonance at a desired operating frequency. As the shaft of one variable capacitor is rotated in a first direction through a given angle, the shaft of the other variable capacitor rotates in the opposite direction through the same angle, thereby varying the ratio (but not the sum) of parallel and series capacitances. A servo controller connected to a standing wave ratio detector automatically adjusts the ratio of parallel to series capacitances to optimize impedance matching between the source and the RF coil.

RF coil for MRI with self-tracking ganged coupling capacitors

A detuning/decoupling arrangement for a Magnetic Resonance Imaging (MRI) system RF coil arrangement (of the typing using the nuclear magnetic resonance, or NMR, phenomenon) uses switching diodes to selectively connect and disconnect portions of an RF resonant circuit in response to a DC control signal. The DC control signal selectively forward biases and reverse biases the switching diodes. The DC control current is fed to the resonant circuit along the same RF transmission line used to feed RF signals to/from the circuit. An in-line coaxial shielded RF choke connected to the RF transmission line isolates the DC control signals from the RF signals flowing on the same transmission line--reducing the number and complexity of isolation devices required on the ends of the transmission line to separate the RF and DC signals.

MRI transmit coil disable switching via RF in/out cable

A quadrature detection MRI radio frequency coil includes plural axially-extending conductive legs. At least two of the legs include breaks in conductivity at their mid-point with circumferentially extending inner-bridge conductors connected thereacross to which RF input/output feed connections are conveniently made so as to achieve a center fed coil structure, open at both ends. Other axially-extending legs may also include conductive breaks with capacitive coupling thereacross and circumferentially extending outer-bridges between the outer or distal ends of the legs may also include breaks in conductivity with capacitive coupling thereacross.

Center fed QD MRI RF coil

In a multi-slice magnetic resonance imaging system which employs a train of plural RF NMR nutation pulses, the frequency spectrum and/or magnetic gradient employed for succesive pulses is controlled so as to effect more nearly equal full-width-half-magnitude (FWHM) or other spatial dimensions of actual nuclei nutation variation versus distance curves for all of the slice selective nutation pulses. The result is a reduction of any 'gap' of non-imaged volume disposed between the succession of selected MRI slice volumes.

Contiguous slices in multi-slice MRI

NMR imaging apparatus and method is arranged so as elicit NMR image response data in a predetermined order which provides the more significant lower spatial frequency image data during an initial portion of a relatively long complete image data acquisition cycle. The remaining higher spatial frequency image data is captured during subsequent portions of the overall image data acquisition cycle. In this manner, apparent motion artifact in the resulting image is reduced. Furthermore, such a special data acquisition sequence permits image reconstruction processes to produce a recognizable image at an earlier time in the complete data gathering cycle thus permitting a more timely image display for the apparatus operator to use in monitoring and/or controlling the NMR imaging procedure.

Apparatus and method for initially capturing most significant low

An assembler/linker process utilizes predetermined control program segments ('templates' defining a sub-sequence of magnetic resonance imaging (MRI) states) together with predetermined program-change tables of MRI parameter values. At least some of the program segments are referenced by predetermined symbolic addresses and include pointer-references to corresponding ones of the table entries. The assembler/linker process machine replicates a predetermined set of such slice/specific program segments in a predetermined order while also simultaneously indexing corresponding symbolic addresses and referenced table entries in a predetermined sequence so as to maintain proper correspondence between slice-specific main programs and subroutines for each replicated program segment. In addition, certain of the replicated program segments may be defined having predetermined symbolic addresses which are not indexed thus further conserving the number of program instructions which need to be replicated and stored in the assembly/linkage process. A subset of slice-specific program segments can be further designated for replication as a unit before following program segments are utilized. A unique linker language level syntax is also provided for an ordered string of input digital data used to control the assembler/linker replication process.

Growing community of inventors

Richmond, CA, United States of America

Lawrence E Crooks