Abstract: A magnetic resonance method is described for forming a fast dynamic image from a plurality of signals acquired by an array of multiple sensors. The k-space is segmented into regions of different type of acquisition. In the region of a first acquisition type a first partial image is reconstructed by data of normal magnetic resonance imaging with a full set of phase encoding steps or by data of fast dynamic imaging with a number of phase encoding steps with a low reduction factor with respect to the full set thereof, and in the region of a second acquisition type a second partial image is reconstructed by data of fast dynamic imaging with a full reduction factor. The first and the second partial images are subsequently combined so as to form the full image of the scanned object.

Abstract: In a magnetic resonance imaging method flow quantities and diffusion quantities are measured in the presence of temporary magnetic gradient fields (gradient pulses). Signal amplitudes of the magnetic resonance signals and/or flow and diffusion quantities calculated from the magnetic resonance signals are corrected for non-linearities in the magnetic gradient fields.

Abstract: A magnetic resonance method is described for forming a fast dynamic image from a plurality of signals acquired by an array of multiple sensors. The k-space is segmented into regions of different type of acquisition. In the region of a first acquisition type a first partial image is reconstructed by data of normal magnetic resonance imaging with a full set of phase encoding steps or by data of fast dynamic imaging with a number of phase encoding steps with a low reduction factor with respect to the full set thereof, and in the region of a second acquisition type a second partial image is reconstructed by data of fast dynamic imaging with a full reduction factor. The first and the second partial images are subsequently combined so as to form the full image of the scanned object.

Abstract: A magnetic resonance method is described for fast dynamic imaging from a plurality of signals acquired by an array of multiple sensors. The k-space will be segmented into regions of different acquisition. In the region of a first acquisition type a first partial image will be reconstructed by data of normal magnetic resonance imaging with a full set of phase encoding steps or by data of fast dynamic imaging with a number of phase encoding steps being with a low reduction factor with respect to the fall set thereof and in the region of a second acquisition type a second partial image will be reconstructed by data of fast dynamic imaging with a full reduction factor. Thereafter the first and the second partial images will be formed to the full image of the scanned object.

Abstract: A magnetic resonance imaging method employs sub-sampled signal acquisition from a number of receiver coils such as surface coils. A full field-of-view magnetic resonance image is reconstructed on the basis of the sensitivity profiles of the receiver coils, for example on the basis of the SENSE technique. The reconstruction is carried out mathematically as an optimization, for example, requiring a minimum noise level in the magnetic resonance image. According to the invention, a priori information is also involved in the reconstruction and the a priori information is taken into account especially as a constraint in said optimization.

Abstract: The invention relates to a magnetic resonance imaging method which employs multiple magnetic resonance signals from an array of multiple sensors or coils for the reconstruction of images. The method is used in fast dynamic MR imaging. Prior to the formation of the fast dynamic image a normal magnetic resonance image with the fall set of phase encoding steps is acquired for each sensor or coil. Then a subset of phase encoding trajectories is extracted commensurate with the phase encoding trajectories obtained by the fast dynamic imaging and an image is reconstructed from the above mentioned subset. Subsequently, the signals of the fast dynamic image are compared with the signals of the reconstructed image, thus yielding an estimate of the fold-over artefacts of the fast dynamic image. The signals of the fold-over artefacts thus compensate the signals obtained by the fast dynamic imaging and deliver a corrected image without artefact parts.

Abstract: The invention relates to a method and a device for the imaging of a part of an object which is arranged in a steady magnetic field. The method according to the invention includes a step for filtering the shot noise from the measured MR signals. Filtering is performed by determining in a first step the value of a combination of a value of a parameter of a measuring point of the MR signal to be corrected and values of the parameter of measuring points in a vicinity of the measuring point. If the value of this combination exceeds a predetermined reference, the value zero is assigned to the value to be corrected. The invention is based on the idea that for a substantial part of the k space the corresponding MR signals behave as white noise. The reference is determined from the statistical distribution of the white noise. If the value of the combination exceeds the reference, it is assumed that a measuring point has been affected by shot noise.

Abstract: An image is processed taking into account the direction of a predominant structure of the image. Said predominant direction is derived from image information in the image. In particular, the covariance matrix having matrix elements depending on products of differences between pixel-values in separate directions is calculated. The eigenvectors of the covariance matrix correspond with the predominant direction of the image structure and the eigenvalues of the covariance matrix represent the strength of the structure in the image. The covariance matrix is computed locally, i.e. for separate regions in the images so as to take variations of the direction of predominant structures into account.

Abstract: A method of determining a velocity of moving matter by magnetic resonance, includes a application of a phase contrast method in at least one measuring direction so as to determine a velocity. Upon determination of the velocity by means of phase contrast MRA, the cyclic nature of the phase introduces an ambiguity in the velocity determination. This ambiguity is removed by performing an additional measurement in an additional direction and by combining the velocity measured in the additional direction with the previously determined velocity. It has also been found that there is an optimum direction for this additional measurement. The advantage of the method of the invention is that the velocities can be determined and corrected in the three basic directions. As a result, low flow velocities can be determined and corrected in the three basic directions. As a result, low flow velocities can be measured, so that slow liquid flows in small blood vessels can be made visible in an MR image.

Abstract: In an EPI or GRASE magnetic resonance method, phase errors caused by the alternation of the read gradient polarity (G.sub.x) are corrected by obtaining a set of reference measurements with both polarities at low values in the phase encoding (k.sub.y) direction. From these reference measurements the phase errors are estimated. Subsequently, the measurements covering the whole of k-space are corrected and a magnetic resonance image obtained in which artefacts due to the alternating polarity of the read gradient are suppressed.

Abstract: A method of determining a magnetic resonance (MR) distribution in a part of a body uses an arrangement of multiple surface coils. According to the method, component distributions are determined using separate ones of the surface coils and the component distributions are combined to form the MR distribution. This is done by first combining the component distributions to form a distribution I.sub.hom which is optimized with respect to homogeneity and a distribution I.sub.snr which is optimized with respect to signal-to-noise ratio (SNR). Then the distributions I.sub.hom and I.sub.snr are combined to form the MR distribution, preferably by determining a smoothed ratio of the distributions I.sub.hom and I.sub.snr and using that ratio to correct I.sub.snr for homogeneity. Also an apparatus to perform the method is disclosed.

Abstract: In a GRASE magnetic resonance method, most profiles in k-space with a certain k.sub.y value are measured with different magnetic field read gradient polarity and at different time intervals from the excitation RF-pulse. The two resulting sets of measurements, with positive and negative read gradient polarity, respectively, are used to correct read gradient polarity dependent phase errors, in order to obtain reconstructed images in which the effects of these phase errors are greatly reduced. In an improved version the measurements are used to reconstruct images with a predictable T.sub.2 weighting.

Abstract: In MRI data acquisition according to the GRASE (gradient and spin-echo) sequence, trajectories (562, 563) in k-space are arranged such that different coordinates (k.sub.x, k.sub.y) in that space have monotonic relations with parameters (t, .tau.) that are related to physical effects, such as magnetic field inhomogeneities, T.sub.2 *-effects and motion, that causes artefacts in the image. By doing so, the artefacts are reduced.

Abstract: Nuclear or electron spin magnetic resonance method using multiple radial scans through frequency-space. The problem of insufficient sample density at the higher image frequencies is solved by deriving an edge image, determining a correction image therefrom by using a priori knowledge about the pixel value distribution and using the correction image after Fourier transformation to frequency-space.

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: An MRI method is proposed where the profile distribution is automatically determined so that the information contents of the image are maximum, subject to the restriction that the total number of profiles used to obtain the image is predetermined. During the determination of the profile distribution, profiles will be selected which have a minium redundancy and a redundancy pattern r(k.sub.y) will be dynamically adapted as a function of the spatial frequency k.sub.y. The redundancy of a profile increases as the number of times that a profile has been measured increases and is high when a signal-to-noise ratio associated with the profile is very small.

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.