Siemens Aktiengesellschaft

Volker Weissenberger

Peter Heubes

Joerg Ulrich Fontius

In a method for determining a compensation setting for an eddy current field that is caused by a temporally variable gradient field of a magnetic resonance apparatus, at least two magnetic resonance data sets arising from different spatial positions are generated using the gradient field, and from the magnetic resonance data sets, the compensation setting of a filter is calculated, with which a control quantity of the gradient field can be pre-distorted, such that the sum from the gradient field and at least one component of the eddy current field exhibits a desired time curve, and the gradient field used for the magnetic resonance data sets is generated with a predetermined initial setting of the filter that at least approximately takes into account the component of the eddy current field.

Method for determining a compensation setting for an eddy current field

In a method for the compensation of disturbances due to vibrations in a magnetic resonance tomography apparatus s having a cryo-head seated on a cryostat for cooling a superconducting magnet and having a compensation device for correcting the magnetic field fluctuations generated due to the vibrations of the cryo-head, the compensation device sets the synthesizer frequency and/or the gradient currents according to the time curve of the field terms of the 0and/or 1orders acquired in a tune-up.

Method for vibration compensation in a magnetic resonance tomography apparatus

In an operating method for a magnetic resonance tomography apparatus a sequence of digital signals is transmitted to the digital-analog converter. An analog signal is emitted from the digital-to-analog converter for each digital signal to a coil system for producing a gradient magnetic field. A signal processor produces a processed digital signal which is supplied to the digital-to-analog converter to produce the analog signal. A difference between the incoming digital signal and the processed digital signal Is determined by the signal processor and is added to the next incoming digital signal or at least for a portion thereof.

Operating method for a magnetic resonance tomography apparatus

In a method for acquiring eddy currents that are caused by switched magnetic field gradients and that contain cross-terms, at least the cross-terms can be determined from the selected slice within a short time, by the steps of introducing a spatially expansive phantom into the examination region of the magnetic resonance apparatus, activating a measuring gradient pulse that exhibits a prescribable pulse width, and after the deactivation of the measuring gradient pulse generating at least two imaging sequence blocks following one another at the spacings (t , t , t ) with at least two-dimensional, complex data set being generated from their imaging signals, the phase information contained therein being proportional to the magnetic field strength.

Method of acquiring eddy currents that are caused by switched magnetic field gradients of a magnetic resonance apparatus and that contain cross-terms

In a method for avoiding image occlusions in nuclear magnetic resonance tomography apparatus that are operated with multi-echo sequences, at a time t.sub.0, a cross-magnetization in spins is generated in an examination subject with an excitation radio-frequency pulse. At times t.sub.1, t.sub.3, t.sub.5 . . . , at least two refocusing radio-frequency pulses that re-phase the cross-magnetization follow and read-out intervals follow at times t.sub.2, t.sub.4, t.sub.6 . . . The following condition is satisfied in at least one direction for the gradients G activated during the pulse sequence: ##EQU1## Even given quadratic gradient terms, thus, no phase difference occurs between a primary and a stimulated echo path. The presence of such a phase difference causes an image occlusion, and thus such occlusions are avoided by eliminating such a phase difference.

Method for avoiding image occlusions in nuclear magnetic resonance

In a method for the compensation of eddy currents caused by gradients in nuclear magnetic resonance apparatus a gradient pulse is activated and a nuclear magnetic resonance signal is excited in a slice of a spatially extended phantom, the nuclear magnetic resonance signal is acquired after the end of the gradient pulse and during the decay time of the eddy currents caused by said gradient pulse and the eddy current magnetic field is identified from the phase curve of this nuclear magnetic resonance signal. A filter for the gradient system that generates the gradient pulse is calculated on the basis of the eddy current magnetic field identified in this way.

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Moehrendorf, Germany

Volker Weissenberger