Abstract: The image produced by a magnetic resonance imaging apparatus using a receive coil 2 has inaccuracies due to external circumstances which affect the signal produced by the coil 2. 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 4 superimposed on the coil 2 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 2 to be corrected, and in accordance with a second aspect of the invention an additional coil 4 or 8, preferably both, is/are provided in order to detect broadband noise and enable its suppression on the output of the coil 2.

Abstract: In magnetic resonance imaging apparatus having a resistive electromagnet with a bore 6, 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 5a to 5d 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 5a etc. can form part of a two dimensional array in order to reduce the number of phase encoding steps in the phase encode direction.

Abstract: In a magnetic resonance imaging apparatus 1 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 4 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.

Abstract: Magnetic resonance imaging apparatus uses magnetic field gradients X, Y, Z to spatially encode the magnetic signals arising from a patient on a couch 2 in bore 1 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 4 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.

Abstract: A high temperature superconductor (HTSC) 5 is magnetized between drive coils 1,2 forming poles of a magnet connected by an iron yoke 9 by relative movement of a vacuum insulated cryostat 4 containing the HTSC and the magnetizing magnet, in order to magnetize a large area of HTSC using a magnet with a small region 3 of magnetizing flux. Alternatively, the HTSC 5 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.

Abstract: A high temperature superconductor (HTSC) 5 is magnetized between drive coils 1,2 forming poles of a magnet connected by an iron yoke 9 by relative movement of a vacuum insulated cryostat 4 containing the HTSC and the magnetizing magnet, in order to magnetize a large area of HTSC using a magnet with a small region 3 of magnetizing flux. Alternatively, the HTSC 5 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.

Abstract: Interventional MRI imaging leads to the development of open magnets such as for example C-magnet 1, 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 7 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 8, in order to enable the r.f. signals to be detected in the presence of the field of the C-magnet 1.

Abstract: When imaging a region of a patient using a contrast agent, for example in magnetic resonance imaging apparatus including a superconducting magnet 2, it is usual to take an image before and after injection of a contrast agent from an injector 5 into the patient. The invention provides a second injector 8 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 9, 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.

Abstract: A patient bed (1) of an MR imaging apparatus is provided with a tube (17) 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 (2) into a high field polarising magnet (3) and along a tube (4) to the patient. Valve (5) is provided so that fluid in the tube (4) 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 (4) had been directly connected into the patient.

Abstract: A radio frequency coil (12, 19) adapted for use in interventional magnetic resonance imaging consists of a loop of an elongated electric conductor arranged to form a twisted wire pair (12, 19) and means associated with it for operating the coil both in transmit and receive mode, in order that the coil does not image anything but tracks its own path on an MR image, without affecting the magnetization in the main bulk of the body being imaged.

Abstract: A magnet having a yoke and a pair of poles coupled to the yoke in a spaced apart relationship includes a pair of energization coils in proximity to each of the poles for creating a magnetic field of a desired strength. A pair of prepolarization coils are also disposed in proximity to each of the poles to vary the strength of the magnetic field during a nuclear magnetic resonance prepolarization procedure. In order to minimize the amount of eddy currents introduced to the yoke during the prepolarization procedure the poles are comprised of magnetically effective and substantially non-electrically conductive material. Magnetically effective material includes material having a low hystresis. To further reduce the amount of eddy currents introduced to yoke, a flux is created having a sense substantially opposite of that produced by the energization coil. Such opposing flux may be produced by the prepolarization coils and/or by a shield winding placed in proximity of the poles for that purpose.

Abstract: A tool or device for use in interventional MRI has a matrix of electrical conductors formed on or carried by the outer surface of the tool or device so that in use energisation of the conductors can be effect in order to enable the susceptibility of the tool or device to be varied and thus the apparent shape of the tool or device to be varied.

Abstract: An imaging system produces an image of an internal part of an object and a representation of a tool, which representation corresponds to the position of the tool with respect to the actual object. An imaging apparatus defines an examination region. After an image of the object is obtained, the object is moved to a treatment position fixed in relation to the examination region. The object is supported on a moveable table, which is in turn supported on a pair of rails. A reference frame mounted to the imaging apparatus carries radiation detectors for detecting radiation emitted by emitters on a surgical tool. The position of the tool with respect to the reference frame, and hence with respect to the actual object, can therefore be determined.

Abstract: A flexible catheter or other object for insertion into an object is designed for use in connection with magnetic resonance (MR) imaging techniques. The catheter carries a closed loop coil arrangement tuned to the RF excitation frequency used in operation of an MR imager. The coil arrangement includes turns which lie substantially in non-parallel planes when the axis of the catheter is in a straight line. The coil arrangement may include two coils which are constituted by different sections of an electrically conductive track carried on a flexible, insulating substrate. According to another embodiment, the coil arrangement may comprise two separate closed loop tuned coils each constituted by a narrow metallized track carried on a flexible, insulating substrate. In another embodiment, the coil comprises turns of a saddle form.

Abstract: A marker and probe for use in magnetic resonance imaging includes a vial for insertion within the body. The vial contains a material having a spin-lattice relaxation time less than that of the material of the body in a region being imaged. A coil arrangement having at least one coil tuned to the frequency of the magnetic resonance excited in the material during an excitation sequence is wound around the vial. The body is subjected to an T1 weighted examination sequence. The coil arrangement preferably has at least one turn which lies in a plane orthogonal to at least one other turn. Materials suitable for use in the vial include copper sulphate, iron chloride, or gadoliuium cholate. The vial consists of a material which does not exhibit a nuclear magnetic resonance spectrum.

Abstract: A magnetic resonance imaging system includes a magnet system which includes pole pieces and an energizing coil. The end portions of the pole pieces are made from a material which, does not support eddy currents, such as insulated iron powder. An object to be imaged is placed in the gap between the pole pieces. A gradient coil system imposes desired gradient fields in the gap between the pole pieces. The gradient magnetic field sequences are controlled such that, for each gradient pulse or a particular polarity there is applied a compensating pulse of the same magnitude, but the opposite polarity. Each compensating gradient has an integral which is relatively small. Remanent magnetism in the end portions of the pole pieces is thereby substantially avoided.