Abstract: Methods and apparatuses are disclosed for dynamic adjustment of the receiver gain during magnetic resonance imaging (MRI) scan. To account for distortions introduced by the receiver that may be different at various receiver gains, a reference radio frequency (rf) signal is applied to the receive chain by an additional antenna. In some disclosed embodiments the reference signal is adjusted such that its frequency lies at the border of the frequency band detected by the MR scan. Comparing the a priori known amplitude and phase of the reference signal with the amplitude and phase of the received reference signal allows determination of the distortions introduced at the respective receiver gain which are subsequently corrected. In some disclosed embodiments, the reference signal is used to synchronize the modulation and demodulation units of a wireless transceiver system.

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: A magnetic resonance imaging method is known for the reduction of image errors in magnetic resonance images which are caused by quantization errors in a DAC (26) for generating a phase encoding gradient waveform in an MRI measuring sequence (ms1, ms2) for generating magnetic resonance signals (S(t), S.sub.1 (t)). The known method has the drawback that inter alia the effect of differential non-linearity of the DAC (26) on the image errors is not taken into account. The invention proposes an MRI method in which such image errors are also reduced. To achieve this, prior to and/or during application of the measuring sequences (ms1, ms2), deviations of phase encoding gradient areas relative to desired areas are determined and image data in an image matrix derived from the resonance signals are corrected on the basis of said deviations.

Abstract: A known magnetic resonance device (1) operates with a coil array (c1 to cn) which serves as a detection coil whereby magnetic resonance signals are detected so as to form partial images of a sub-volume of an object (5) to be measured. A signal processing unit (9) forms an overall image from the partial images. Because the known device utilizes separate detection and signal acquisition channels, it is comparatively expensive and complex. In accordance with the invention, a simpler and less expensive magnetic resonance device (1) is obtained in that the device comprises a signal combination device (28) which shifts frequency ranges (s1 to sn) of individual coil elements in the coil array in respect of frequency and which forms, from the shifted frequency ranges (o1 to on) a sum signal (sm) in which the frequency ranges are separated from one another.

Abstract: Notably for MR spectroscopy it is important than an MR receiver for resonance signals has a large dynamic range in order to enable the reproduction of comparatively strong as well as comparatively to the weak signals in a spectrum. Therefore, the MR receiver should be linear to a high degree. Otherwise, for example in proton spectra metabolites are liable to be masked by peaks in tne spectrum which are caused by harmonic distortion and notably intermodulation distortion. An MR method is proposed for increasing the dynamic range of the MR receiver by software compensation of non-linearities in the MR receiver by means of a counter-distortion function.

Abstract: An MRI apparatus is proposed with an optimally adjusted gain of the detection chain, said MRI apparatus being used for generating pulse and gradient sequences which comprise an excitation pulse having a predetermined excitation angle and a phase encoding gradient. In order to obtain a data set wherefrom an MR image is reconstructed, the pulse and gradient sequence is repeated a number of times, for example 128 times, while varying the value of the time integral of the phase encoding gradient, for lower profile numbers there being chosen an excitation angle which is smaller or greater than the predetermined excitation angle in order to prevent overdriving of the detection chain. The detection chain of such an apparatus is optimally used for obtaining a data set for an MR image.

Abstract: A magnetic resonance imaging device and method are disclosed in which, during acquisition of measuring data the receiver gain is switched over in dependence of the signal strength, so that in principle every data set of the various measuring cycles has an optimum signal to noise ratio.

Abstract: A multiprocess computer executes operating system routines and user processes. One specific peripheral apparatus has a preferential status in that it may emit attention interrupts and/or completion interrupts that relate to an I/O-operation. Only those interrupts find preferential treatment in that the associated interrupt has a higher priority level than the one(s) corresponding to the majority of the operating system routines. In contradistinction to all other user process interrupts the above attention and completion interrupts are executed in their own hardware and software context, to which effect the latter context is temporarily activated, and after execution of the interrupt procedure restored to its previous status. In this way dialog with the peripheral may be executed real-time, while the "own" context greatly facilitates programming. An upgraded driver program is also presented.

Abstract: The measurement of localized spectra by means of stimulated echoes is known per se. Using three 90.degree. pulses, stimulated echoes are then generated; these pulses are selective or not. However, this technique it is not suitable for measuring good proton spectra of metabolites because the response of the non-bound protons is much greater than the response of the bound protons. In accordance with the invention, a fourth (spatially selective) 180.degree. refocusing pulse is added to a pulse sequence consisting of a 90.degree. non-spatially selective but frequency-selective pulse and two subsequent 90.degree. spatially selective pulses. Thus, a refocused stimulated echo is generated in which the response of the non-bound protons is suppressed and which contains only signals from the chemically bound protons. The proposed methods are particularly suitable for measurements on lactate because of the excellent spectral editing properties.

Abstract: A magnetic resonance apparatus is provided with a detection system comprising a coil, which may be part of a shim coil system. Signals detected by this system are used for a dynamic control of a shim coil system in order to mitigate dynamically adverse influences of eddy currents on the magnetic field homogenity in at least a region of interest within the coil system of the apparatus.

Abstract: The invention relates to a magnetic resonance imaging device comprising a transmitter/receiver which, with the exception of a few components is all digital. The transmitter comprises a digital frequency synthesizer, a single sideband modulator and a selective power amplifier, the single sideband modulator being controlled by a phase locked loop oscillator. The receiver comprises a selective pre-amplifier, a frequency mixing stage which is connected either to an output of the phase locked loop oscillator or to an output of the single sideband modulator, and an analog-to-digital converter which samples the output signal of the frequency mixing stage. The demodulation frequency for the receiver is chosen so that, after demodulation, a frequency band is obtained which is situated to one side of 0 Hz.

Abstract: The invention relates to a method of making NMR images (density distributions, location-dependent spectroscopy) utilizing two alternating gradient fields whose gradient directions are mutually perpendicular. Thus, a two-dimensional "plane" in the 3-D image frequency space can be filled with a uniform density of measurement points. Per FID signal more signal samples can be taken, resulting in a substantial reduction of the entire measurement procedure for a 3-D image. This method is very suitable for imaging of 3-D density distributions, 2-D or 3-D spectroscopy etc. The periods and the amplitudes of the alternating gradient fields are preferably the same; however, these fields are preferably phase-shifted 90.degree. with respect to one another.

Abstract: The invention relates to a method and system for determining an image of a nuclear magnetization distribution in a body. In known methods, particularly in nuclear spin echo techniques, a resonance signal is generated which has high dynamics. In the method according to the invention dephasing is effected which is non-linear place-dependent or which is frequency-dependent within a spectroscopy distribution, as a result of which the generated resonance signal will have a much smaller amplitude. Since the non-linear dephasing applied within the distribution is known, a correction can be made for this after the determination of the measuring signals.

Abstract: NMR images formed by means of Fourier zeugmatography contain disturbing artefacts which are caused by coherent interference signals (for example, off-set signals, non-ideal 180.degree. reversing pulses). In accordance with the invention, an additional phase difference (.DELTA..phi.=.pi. in the case of even rows, and .DELTA..phi.=.pi.. (m-1)/m rad/sec in the case of m odd rows) is generated and the signal samples taken from the resonance signals are stored in adjacently situated rows of an image frequency matrix. The values in every second row of the matrix are changed to cancel said additional phase-difference, so that the contributions of the coherent interference signals to the matrix are influenced by the additional phase shift; if the additional phase shift is .pi. rad/sec, the values of every second row of interference signals in the direction of the columns are simply inverted.

Abstract: NMR images formed by means of Fourier zeugmatography contain disturbing artefacts which are caused by coherent interference signals (for example, offset signals, non-ideal 180.degree. reversing pulses). In accordance with the invention, alternating phase (90.degree.) excitation pulses are used in the successive measurement cycles and the signal samples taken during the measurement cycles are stored in adjacent rows of an image frequency matrix. The values in every second row of the matrix are inverted, so that the contributions of the coherent interference signals change their sign in every row in the direction of the columns. During the Fourier transformation of the columns, therefore the artefacts caused by the interference signals are shifted towards the edge of the image.

Abstract: During measurement cycles for generating and sampling FID signals in NMR imaging devices, a 180.degree. pulse and subsequently a 90.degree. excitation pulse are added to the pulse sequence. The 180.degree. pulse produces an additional echo signal. During (the maximum of) the echo signal, the 90.degree. pulse is generated. The waiting period occurring before the beginning of a next measurement cycle can thus be substantially reduced without giving rise to a significant signal loss in the echo signals to be generated during said cycle. In addition to a reduction of the measurement time, NMR images with different contrasts (other intensity distribution) can be provided.