Abstract: The invention relates to a method of reconstructing three-dimensional images from cone beam projection data of an object to be examined which is arranged in an examination zone. In practice cone beam projections are usually cut off, because the object to be examined usually cannot be imaged completely in all imaging positions. An image which is reconstructed exclusively from the acquired projection data, therefore, does not have the highest possible image quality. In order to continue the projection data beyond the sensitive detector surface and hence obtain images of higher image quality, therefore, the invention proposes a method which includes the following steps: (a) acquiring the cone beam projection data, (b) determining the contour of the sensitive detector surface, (c) determining pseudo-projection data in an overall outer zone from the projection data acquired, and (d) reconstructing a three-dimensional image from the projection data and the pseudo-projection data.

Abstract: The Overhauser effect is a technique for increasing the signal-to-noise ratio of nuclear magnetic resonance signals. Electron spin resonance is set up for example in a contrast agent 14 injected into a patient by means of a transmitter 3 at the end of a probe 1 to excite an area 15. The excited electrons couple to MR active nuclei and increase the population in the higher energy level. Then, when an NMR signal is transmitted and received via coil 5, more MR active nuclei return to the ground state and create a bigger, enhanced, signal detected by the coil 5, hence promoting increased signal-to-noise ratio on an image formed on the monitor 9. In the invention, the Overhauser effect may be applied to an intra-operative situation by means of probe 1 which is inserted, for example, into a patient in a region of interest.

Abstract: A magnetic resonance imaging apparatus has a patient support (1) moveable on runners (2) along a beam (3) into a bore (4). The r.f. coil (7) 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 (7) may also be variable in a lateral direction to accommodate patients of different size.

Abstract: In magnetic resonance apparatus, particularly magnetic resonance imaging apparatus, it is found that magnetic resonance signals generated in an alias region (D) will be aliased into the signals received by the primary receive coil (4) from the desired signal region (A-B). An additional receive coil 5 is provided to receive the signals from the alias region, and processing means (6) reduces the effect of these alias signals on the resulting desired data.

Abstract: A magnetic resonance imaging probe includes a dipole including a first arm and a second arm. The second arm includes an elongate loop coil. In one embodiment, the loop coil is an open coil. In another embodiment, the coil is a twisted coil. The first and second arms are electrically connected to provide a dipole output. The second arm is electrically connected to a loop output.

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 5may 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: 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 employing magnetic gradient fields in a phase-encode and in a read-out direction for spatially encoding excited MR active nuclei in a region of interest of a patient, in which a reduced number of readings in the read-out direction is taken, thereby creating an aliased reduced field of view image, at least two r.f. receive coils are used together with sensitivity information concerning those coils in order to unfold the aliased image to produce a full image while taking advantage of the reduced time of collection of data. In accordance with the invention, sensitivity information is collected at a lower resolution than that at which the image information is collected.

Abstract: In magnetic resonance imaging apparatus employing magnetic gradient fields in a phase-encode direction for spatially encoding excited MR active nuclei in a region of interest of a patient, in which a reduced number of readings in the phase-encode direction is taken, thereby creating an aliased reduced field of view image, a pair of r.f. receive coils is used together with sensitivity information concerning those coils in order to unfold the aliased image to produce a full image while taking advantage of the reduced time of collection of data. In accordance with the invention, the phase sensitivity pattern of each coil over the region of interest is different from that of the other coil.

Abstract: A non-selective inversion pulse is applied to a plurality of slices, r.f. resonance in MR active nuclei is excited in each of those slices individually, and the slice excitation order is cycled so that the time for the non-selective inversion pulse to any particular phase-encode gradient of all the slices is the same, the time of the zero phase-encode gradient corresponding to that for zero signal from cerebro spinal or other moving fluids.

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: 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.