Abstract: The computer tomography device includes an X-ray source for emitting an X-ray beam and a detector system for measuring density profiles of cross-sections of an object. The detector system includes a two-dimensional matrix of detector elements. The detector elements positioned along a direction transversely of the cross-sections have the same effective surface and detector elements positioned parallel to the cross-sections have different effective surfaces. Furthermore, the computer tomography device includes an adjustable X-ray collimator for limiting the X-ray beam transversely of the cross-sections.

Abstract: A magnetic resonance imaging apparatus includes a main magnet having a frame (19) with two magnetic elements (1) arranged thereon. The magnetic elements (1) have substantially parallel faces (3) that face each other so as to define a gap (5) between the magnetic elements. The magnetic elements (1) have magnetic poles of opposite polarities for generating a static magnetic field in the gap (5). A patient support (45) is provided for supporting a patient (47) so that a part of the patient that is to be examined is located in the gap (5). In order to improve the accessibility of the patient (47) without increasing the width of the gap (5), a supporting member (37) is arranged so as to support the frame (19) in such a position that the normals (41) to the planes of the substantially parallel faces (3) of the magnetic elements (1) extend in a direction that encloses an angle between 30.degree. and 60.degree. with the vertical direction.

Abstract: A magnetic resonance imaging apparatus includes a main magnet having a frame (19) with two magnetic elements (1) arranged thereon. The magnetic elements (1) have substantially parallel faces (3) that face each other so as to define a gap (5) between the magnetic elements. The magnetic elements (1) have magnetic poles of opposite polarities for generating a static magnetic field in the gap (5). A patient support (45) is provided for supporting a patient (47) so that a part of the patient that is to be examined is located in the gap (5). In order to improve the accessibility of the patient (47) without increasing the width of the gap (5), a supporting member (37) is arranged so as to support the frame (19) in such a position that the normals (41) to the planes of the substantially parallel faces (3) of the magnetic elements (1) extend in a direction that encloses an angle between 30.degree. and 60.degree. with the vertical direction.

Abstract: In magnetic resonance imaging various error sources lead to deterioration of the image quality. One class of errors is formed by errors which vary only slowly over the time required to sample a data line but vary substantially over the time required to acquire data for the complete magnetic resonance image. These error sources are, for example external magnetic fields, motion due to respiration, drift in amplifiers or drift phenomena in permanent magnets due to temperature influences. It is proposed to utilize mutually intersecting data lines in the Fourier domain so as to estimate these error sources and to use these estimates to correct the data sets obtained before execution of image reconstruction.

Abstract: A method is proposed for reducing the residual artefacts, such as blurring, which occurs in the image when the known methods are used, for example due to phase errors. In accordance with the proposed method, a number of steps are performed per column in the data matrix so as to produce an ever better estimation for the data not known from sampling. After the reconstruction, the image will have a phase which at least approximates the phase estimated from the central part of the data matrix. In the case of phase errors, substantially no residual artefacts will remain and at the same time the signal-to-noise in the image will be superior to that obtained by means of the known methods.

Abstract: Phase error contributions in pixels of a complex image of a nuclear magnetization distribution in a body region due to inhomogeneities of the steady, uniform magnetic field which are caused by the magnetic susceptibility of, for example a patient to be examined and by eddy currents are eliminated by processing the resonance signals obtained in multiple cycles of different magnetic field characteristics according to the assumption that the phase error varies smoothly as a function of the location in the complex image. A corrected phase and the corresponding phase error of a given pixel are determined and then the corrected errors of the next adjacent pixels are sequentially determined and a corrected phase 0 or .+-..pi. assigned to the respective next adjacent pixel, if the phase difference between its phase and the known phase error of the preceding pixel is modulo 2.pi. in intervals (-.DELTA.,.DELTA.), (.+-..pi.-.DELTA.,.+-..pi.+.DELTA.

Abstract: In MRI (Magnetic Resonance Imaging), the signal-to-noise ratio with nuclear magnetic resonance signals received by a surface coil from an excited body is considerably larger than with corresponding signals received by a body coil in the relevant region. The sensitivity pattern of a surface coil is very non-uniform, however. By correction of a reconstructed image from MR signals received by a surface coil by a corresponding image from MR signals received by a body coil, in which event the surface coil has an arbitrary shape and occupies an arbitrary position with respect to the body, the non-uniformity in the surface coil image is brought back to the uniformity of the body coil image.

Abstract: In known spin echo imaging examination a waiting period is customarily observed between two successive spin echo measurements in order to allow for the magnetic moment to relax in the direction of the uniform magnetic field Bo. In addition to this waiting period, the use of 180.degree. pulses also leads to a comparatively long examination time which increases the risk of image artefacts due to motions of, for example a patient to be examined. This comparatively long examination time is also unfavorable in view of the radiation load. In order to avoid these drawbacks, a method is proposed in which the electromagnetic pulses used are exclusively excitation pulses in the form of .alpha..degree. pulses, where 0<.alpha.<90.

Abstract: The invention relates to the determination of an NMR distribution in which an alternating gradient field is applied while sampling the NMR signal (FID signal, nuclear spin echo signal). The frequency of the alternating gradient field is comparatively low (order of magnitude of 100 Hz) and the field has from a few to some tens of cycles during each measurement period. While an FID signal is being sampled, the image frequency field matrix is scanned using a zig-zag (oscillating) line pattern during each line when data is provided for elements in from a few to some tens of rows in the image frequency matrix. By applying preparation gradient fields, the image frequency matrix can be filled by means of successive zig-zag line patterns which have been shifted with respect to one another and which thus enable a uniform sampling density to be provided in the image frequency space.

Abstract: The method and device for NMR Fourier zeugmatography utilizes amplitude-modulated r.f. pulses (90.degree. and 180.degree. pulses) for the excitation of nuclear spins and the generating of nuclear spin echo signals. For three-dimensional Fourier zeugmatography, r.f. pulse having a large bandwidth (for example 10-50 kHz) are desired. The use of amplitude-modulated signals then implies an undesirably high peak power of the r.f. generator. In accordance with the invention, use is made of a frequency-modulated signal which can have a substantially constant amplitude and which preferably covers the desired frequency spectrum at a uniform speed.

Abstract: Disclosed is a method and the device for making NMR images which utilize additional measurements and additional calculations in order to achieve a substantial reduction of image artefacts caused by (respiratory) motions of the body. The additional measurements involve the sampling of the non-conditioned FID or echo signal which can (but need not) be performed during each measurement cycle without consuming a substantial amount of additional measurement time. The non-conditioned signal samples are used to derive a frequency spectrum which is a measure of the size of the object. By comparison of the frequency spectra of the various measurement cycles, standardization is obtained so that image signals produce an unambiguous image even though they have been derived from signal samples from measurement cycles performed in different states of motion (different object size).