The University of Queensland

Nmr Holdings No. 2 Pty Limited

Other

Bruker Analytische Messtechnik Gmbh

Univ of Queensland

David Michael Doddrell

Stuart Crozier

Huawei Zhao

Kurt Luescher

Wolfgang Udo Roffman

Ian Malcolm Brereton

Michael G Irving

Desmond Yau

Ben Lawrence

Max R Bendall

David T Pegg

Lawrence Kennedy Forbes

Deming Wang

Michael Thomas Gladwin

Graham John Galloway

Wolfgang Udo Roffmann

William M Brooks

Grahmam J Galloway

A radio frequency (RF) coil array is used in resonance imaging and/or analysis of a subject located within a cylindrical space in which a magnetic field is operatively applied in an axial direction (z). The coil array comprises a plurality of coil elements () angled relative to each other about the axis of the cylindrical space, each coil element having a pair of main conductors extending generally parallel to the direction of the magnetic field and located on diametrically opposite sides of the cylindrical space, and a pair of connection conductors connected between respective ends of the main conductors. Each coil element has its maximum sensitivity near the centre of the cylindrical space, so that the subject under study is located in a region of maximum sensitivity.

Coil array for magnetic resonance imaging

Asymmetric radio frequency (RF) coils for magnetic resonance applications are provided. Also provided are time harmonic methods for designing such coils as well as symmetric coils. In addition, methods for converting complex current density functions into discrete capacitive and inductive elements are provided.

Asymmetric radio frequency coils for magnetic resonance

A three-dimensional grid () is used as a phantom for mapping geometric distortion in magnetic resonance imaging (MRI) apparatus. This phantom provides an array of densely distributed control points in three-dimensional space. These points are each defined by three orthogonal planes. In the phantom image, the planes are determined by detecting boundary surfaces between portions of the phantom and its surrounding medium, enabling the positions of the control points to be measured to sub-voxel accuracy. The mapped distortion can then be used to automatically correct images produced by the MRI apparatus.

Method and apparatus for mapping and correcting geometric distortion in MRI

Asymmetric, compact superconducting magnets for magnetic resonance imaging are provided. The magnets have a homogeneous region (the 'dsv') which can be located close to one end of the magnet so as to reduce the sensation of claustrophobia experienced by patients undergoing MRI procedures. The magnets can be designed using a hybrid process in which current density analysis is performed to obtain an initial coil configuration which is then refined using non-linear optimization techniques to obtain a final coil configuration. The hybrid method can incorporate various constraints, including, the location and size of the dsv, the uniformity and strength of the Bfield, stray field strengths outside of the superconducting magnet, and field strengths within the magnet's coils. The hybrid technique can also be used to design compact symmetric superconducting magnets.

Asymmetric superconducting magnets for magnetic resonance imaging

Spatial encoding in magnetic resonance imaging (MRI) techniques is achieved by sampling the signal as a function of time in the presence of magnetic field gradients, e.g., X, Y, and Z gradients. The gradient magnets have in the past been assumed to generate a linear gradient, and typical image reconstruction techniques have relied upon this assumption. However, to achieve high speed performance, gradient magnets often sacrifice linearity for speed. This non-linearity, in turn, results in distorted images, the distortion often being sufficiently large to compromise the usefulness of MRI images for stereotaxy or longitudinal studies, where precise volumetric information is required. The disclosure provides practical methods for correcting distorted images resulting from such non-linearity in the gradient fields, as well as distortions resulting from translational, rotational, and/or winding/design errors in the field generating devices. The methods employ spherical harmonic expansions of the gradient fields and fast Fourier transform techniques to provide well-corrected images without undue computational burdens.

Correction of magnetic resonance images

Asymmetric, compact non-superconducting magnets for magnetic resonance imaging are provided. The magnets have a homogeneous region (the &ldquo;dsv&rdquo;) which can be located close to one end of the magnet so as to reduce the sensation of claustrophobia experienced by patients undergoing MRI procedures. The magnets can be designed using a hybrid process in which current density analysis is performed to obtain an initial coil configuration which is then refined using non-linear optimization techniques to obtain a final coil configuration. The hybrid method can incorporate various constraints, including, the location and size of the dsv, the uniformity and strength of the B field, stray field strengths outside of the non-superconducting magnet, and field strengths within the magnet's coils. The hybrid technique can also be used to design compact symmetric non-superconducting magnets.

Asymmetric magnets for magnetic resonance imaging

Asymmetric zonal shim coils and shim sets for magnetic resonance applications are provided. Also provided are Fourier-series based methods for designing such coils as well as symmetric coils.

Asymmetric zonal shim coils for magnetic resonance

Asymmetric, compact superconducting magnets for magnetic resonance imaging are provided. The magnets have a homogeneous region (the 'dsv') which can be located close to one end of the magnet so as to reduce the sensation of claustrophobia experienced by patients undergoing MRI procedures. The magnets can be designed using a hybrid process in which current density analysis is performed to obtain an initial coil configuration which is then refined using non-linear optimization techniques to obtain a final coil configuration. The hybrid method can incorporate various constraints, including, the location and size of the dsv, the uniformity and strength of the B.sub.0 field, stray field strengths outside of the superconducting magnet, and field strengths within the magnet's coils. The hybrid technique can also be used to design compact symmetric superconducting magnets.

Assymetric superconducting magnets for magnetic resonance imaging

An NMR probehead is proposed having a generally cylindrical casing extending along a probehead axis. The NMR probehead can be inserted into the room temperature bore of an NMR spectrometer magnet providing, in a measurement region, a homogeneous static magnetic field along the probehead axis. The NMR probehead comprises a cylindrical radio frequency (RF) resonator oriented along a resonator axis and generating essentially homogeneous RF magnetic fields transverse to the resonator axis. In accordance with the invention, the angle between the probehead axis and the resonator axis is different from 0.degree.. In this manner, the inclination of the resonator does not affect the useful RF magnetic field and the signal to noise ratio of the received NMR signal is independent of the inclination angle.

Radio-frequency coil for magnetic resonance imaging and spectroscopy

A compact magnet is disclosed for high field, superconducting magnets for use in magnetic resonance spectroscopy. The magnet has at least a first and a second group of coils with the or each coil in the first group having wound to provide a negative current density with respect to the other coils. The first group acts to enable the overall length of the magnet to be reduced while maintaining a homogenous field over a central region of the magnet.

Superconducting magnets

Procedures for designing magnets, including superconducting magnets, shim magnets, and gradient magnets for magnetic resonance systems, are provided. The procedures involve the use of a simulated annealing procedure in which weighted spherical harmonics are included in the procedure's error function. The procedure has resulted in the development of previously unknown magnet designs. In particular, superconducting magnets have been designed which include at least one coil in which the current flow is opposite to that in adjoining coils. Such reversed flow in combination with a relatively large number of coils, e.g., more than 6 coils, have enabled the development of short, yet homogeneous, whole body magnets for use in magnetic resonance imaging (MRI).

Magnets for magnetic resonance systems

The invention concerns a birdcage resonator used as a transmitter and/or receiver coil in an NMR apparatus. The resonator comprises two ring-shaped conductors each of which is interrupted along its outer periphery by capacitors, the ring-shaped conductors being connected together by axial conducting strips. A plurality of axial conducting strips have their ends located between each pair of peripherally neighbouring capacitors. It is preferred when RF energy is coupled in or out between two conducting strips and when the ring-shaped conductors are shielded by shielding rings in the direction towards the sample. The birdcage resonator in accordance with the invention exhibits an improved RF field homogeneity at higher Q compared to conventional birdcage resonators.

RF resonator for NMR

Temporal B.sub.o shifts in NMR spectroscopy and/or imaging systems arising from pulsed field gradient induced eddy currents result in the distortion of free induction decay signals. A method of compensation of this distortion through modulation of the sender and/or receiver signal in opposite concert with the induced B.sub.o shifts is introduced. The method has the advantage of having a fast response and of not altering the magnetic gradient field. (FIG. 4)

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Westlake, Australia

David Michael Doddrell