Picker International, Inc.

Emi, LLC

Koninklijke Philips Corporation N.v.

Ericsson Ab

Marconi UK Intellectual Property Limited

Marconi Optical Components Limited

Ian R Young

Michael Burl

Gordon D DeMeester

Colin G Harrison

Michael Charles Keogh Wiltshire

Joseph Vilmos Hajnal

John Frederick Eastham

John V M McGinley

Alasdair Stewart Hall

John Brian Pendry

Godfrey N Hounsfield

Gosta J Ehnholm

Ilmari V Kinanen

David John Gilderdale

Jukka Ilmari Tanttu

David James Larkman

John V McGinley

Hugh Clow

David R Bailes

Ramesh Mistry

Graham J Clarke

Peter A Luker

Philip R Evans

James Michael McNally

A material having magnetic permeability at r.f. frequency, for example a microstructured magnetic material has a magnetic permeability of negative value but unity magnitude over a particular r.f. frequency range. The singularity in the flux pattern has the result that magnetic resonant disturbances in a plane C,E normal to the line C,D are focussed into a plane D,F also normal to the line C,D and vice versa. This is particularly applicable to magnetic resonance apparatus, since the material can be used to transfer the r.f. magnetic flux distribution in a target region in a patient, for example at C,E to D,F where the flux may be directly measured by receive coils. Equally, transmit coils may generate flux to be focussed into the target region by the material. Magnetic resonance apparatus may be constructed which does not require gradient coils, and r.f. hypothermia may be carried out in a focussed way, minimising damage to surrounding tissue.

Material having magnetic permeability at R.F. frequency

Microstructure materials which can be tuned to a particular range of r.f. frequencies to display particular magnetic permeabilities have been proposed. A typical material is made of an array of capacitive elements e.g. spirals or rolls of conducting material on a non-conducting substrate. These materials can be used as a guide which is effective for the particular band of frequencies to which it is tuned. In one example, the rolls (to) guide magnetic flux along ducts () while rolls () guide magnetic flux along ducts (). Flux can thus be guided upwardly along duct (), along ducts (and), and down ducts (), or vice versa.

Guides for r.f. magnetic flux

Microstructured materials which can be tuned to a particular range of r.f. frequencies to display particular magnetic permeabilities have been proposed. A typical material is made of an array of capacitive elements e.g. spirals or rolls of conducting material on a non-conducting substrate. These materials can be used as screening material which is effective for the particular band of frequencies to which it is tuned. In one example, the rolls to are orientated normal to the face of the screen , which reflects or absorbs the magnetic vector of electromagnetic radiation impinging normal onto the reflector face.

Screens for RF magnetic flux

A magnetic resonance imaging apparatus has a patient support ( ) moveable on runners ( ) along a beam ( ) into a bore ( ). The r.f. coil ( ) is secured to the patient support so as to travel axially with the patient support when the patient enters the bore. The r.f. coil is also moveable laterally to enable off-centre as well as central regions of the patient to be imaged. The apparatus is particularly suited to continuous scan. The width of the central section of the coil ( ) may also be variable in a lateral direction to accommodate patients of different size.

Magnetic resonance imaging apparatus

A high temperature superconductor (HTSC) is magnetized between drive coils forming poles of a magnet connected by an iron yoke by relative movement of a vacuum insulated cryostat containing the HTSC and the magnetizing magnet, in order to magnetize a large area of HTSC using a magnet with a small region of magnetizing flux. Alternatively, the HTSC may be contained in an evacuated region of a cryostat containing the magnetizing magnet. An interconnecting chamber allows the HTSC to be moved between an operative region and a magnetizing region without substantial loss of vacuum.

Magnetizing magnet

The image produced by a magnetic resonance imaging apparatus using a receive coil has inaccuracies due to external circumstances which affect the signal produced by the coil Thus, noise spikes affect the signal, although more usually extensive shielding is provided. Also, changes of loading of the coil produced by movement of the patient vary the Q of the coil and hence the signal output. In accordance with a first aspect of the invention, a second coil superimposed on the coil is tuned to a frequency offset compared to the MR center frequency and is used to monitor coil loading to enable the signal from coil to be corrected, and in accordance with a second aspect of the invention an additional coil or preferably both, is/are provided in order to detect broadband noise and enable its suppression on the output of the coil

In magnetic resonance imaging apparatus having a resistive electromagnet with a bore r.f. excitation pulse substantially simultaneously excites a number of slices A to D which are phase encoded and frequency encoded in the usual way, the direction of the main field being along the bore of the electromagnet in the direction z. The receive coil consists of an array of coils to which view different spatial regions of the imaging volume and the outputs of which are combined in different ways in order to reduce the number of slice encoding steps in the z-direction needed to distinguish between the slices A to D. Each coil of the array etc. can form part of a two dimensional array in order to reduce the number of phase encoding steps in the phase encode direction.

Magnetic resonance imaging

A probe,, for use with magnetic resonance imaging apparatus, which is designed to be inserted into and removed from a patient and which comprises a former,upon which an r.f. coil,is mounted is characterised in that the former also carries at least one transducer or sensor,by which the targeting of energy relating to an interventional procedure to an area in the vicinity of the transducer may be controlled both as to position and strength.

Nuclear magnetic resonance apparatus

In a magnetic resonance imaging apparatus,there is a region of good i.e. uniform field between A and B but, where the field falls off, say, at D, the r.f. excitation pulse can produce an alias image of D which overlies the desired image of say, B. To reduce this effect, the r.f. excitation coil,comprises an array of small coils, the amplitude and phase of the excitation of which is controlled so that the r.f. field collapses rapidly outside the region of good field.

Anti-aliasing transmitter coil array for magnetic resonance

Magnetic resonance imaging apparatus uses magnetic field gradients X, Y, Z to spatially encode the magnetic signals arising from a patient on a couch,in bore,of a main magnet. Thermal stresses arising from aggressive gradients during multiple acquisitions result in imperfectly repeated gradients and resulting image artefacts. The invention uses a probe,provided with a gradient coil set similar to that for imaging, and fed by currents derived from the imaging gradient coils, connected so as to produce an opposing gradient surrounding an MR active substance in the probe. This enables a probe with a sufficiently large amount of MR active substance to produce a useful signal to be used to monitor the gradient, while overcoming the de-phasing problem. which would otherwise occur. Closed loop control of gradients thereby becomes possible.

NMR and ESR probes for closed loop control of gradient fields

A high temperature superconductor (HTSC),is magnetized between drive coils,forming poles of a magnet connected by an iron yoke,by relative movement of a vacuum insulated cryostat,containing the HTSC and the magnetizing magnet, in order to magnetize a large area of HTSC using a magnet with a small region,of magnetizing flux. Alternatively, the HTSC,may be contained in an evacuated region of a cryostat containing the magnetizing magnet. An interconnecting chamber allows the HTSC to be moved between an operative region and a magnetizing region without substantial loss of vacuum.

Interventional MRI imaging leads to the development of open magnets such as for example C-magnet,in which it is correspondingly more difficult to generate a large field in order to obtain a good signal-to-noise ratio. To overcome this, a pre-polarizing unit,is provided which utilizes a HTSC magnet, for example of YBCO, which is brought adjacent to the patient to assist in generating the main field, and then rapidly withdrawn to position,in order to enable the r.f. signals to be detected in the presence of the field of the C-magnet

Magnetic resonance pre-polarization apparatus

When imaging a region of a patient using a contrast agent, for example in magnetic resonance imaging apparatus including a superconducting magnet,it is usual to take an image before and after injection of a contrast agent from an injector,into the patient. The invention provides a second injector,which contains a sample of the patient's blood or saline or other injectable medium which leads directly to the region of interest being imaged in the patient via a catheter,which has an expandible tip which can be expanded to block off the vessel in question. The injector can then be used to inject a bolus of injectable medium into the region of interest, whereupon a further image can be taken, and the catheter can be collapsed to unblock the vein whereupon an image in the presence of the contrast agent can be taken. This enables a second pair of images of the region of interest without and with contrast agent to be prepared, and this can be useful when detecting small blood flows to enable additional sensitivity to be achieved.

Imaging using a contrast agent

A pair of annular magnets (,) generate a vertical magnetic flux field through an imaging volume (,). The flux is focused by a pair of Rose rings (,) of high cobalt steel. A high order shim set includes a plurality of permanently magnetized or magnetized iron rings (,) which cooperatively interact with the magnet assembly to optimize the homogeneity of the magnetic flux through the imaging volume. One of the permanent magnetic rings (,), is mounted with an opposite polarity relative to the others. The magnetized rings are mounted in a non-ferrous, electrically insulating support structure (,) such that gradient coils (,) can be positioned behind the permanent magnet rings. A flux return path (,) provides a low flux resistant path from adjacent the Rose ring at one side of the imaging volume remotely around the imaging volume to a position adjacent the Rose ring at the other side of the imaging volume.

MRI magnet with high homogeneity, patient access, and low forces on the driver coils

A patient bed (,) of an MR imaging apparatus is provided with a tube (,) through which pre-polarised fluid can be injected into a patient in order to improve contrast when imaging veins, arteries or other vessels in the body. Fluid is delivered from pump (,) into a high field polarising magnet (,) and along a tube (,) to the patient. Valve (,) is provided so that fluid in the tube (,) downstream of the pre-polarised fluid can be discarded rather than being injected in the patient, and is associated with a reservoir into which the fluid to be discarded and the pre-polarised fluid can be rapidly injected. Then, when the pre-polarised fluid is injected into the patient, its magnetisation has not deteriorated by as much as it would have done if the tube (,) had been directly connected into the patient.

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Sunbury-on-Thames, United Kingdom

Ian R Young