Universitaetsklinikum Freiburg

Universitätsklinikum Freiburg

Bruker Biospin Mri Gmbh

Albert-ludwigs-universitat Freiburg

Jürgen Hennig

Maxim Zaitsev

Martin Haas

Peter Ullmann

Guobin Li

Wolfgang Ruhm

Gerrit Schultz

Daniel Gallichan

Walter Witschey

Oliver Speck

Daniel N Splitthoff

Anna Welz

Andreas Schmidt

Stephan Berner

Jan-Bernd Hövener

A method to compensate for the magnetic field heterogeneity inside an object of investigation in a MR device obtains an uncorrected magnetic field distribution of the object and executes an MR sequence with a desired k-space coverage by applying RF pulses to generate a transverse magnetization within the object. MR signal data is recorded, magnetic field shimming parameters are dynamically updated and MR signal data are reconstructed to produce images or localized spectroscopic data. Artifacts in a reconstructed image resulting from an uncorrected magnetic field distribution are suppressed by temporally separating MR signals originating from at least two different sub-volumes within a volume of transverse magnetization by generating a nonlinear phase distribution within the object and by dynamically updating shimming parameters to compensate for the field inhomogeneity distributions within the different sub-volumes in the volume of transverse magnetization.

Method of dynamically compensating for magnetic field heterogeneity in magnetic resonance imaging

A method for position dependent change in the magnetization in an object, according to a requirement in a magnetic resonance measurement, wherein radio-frequency pulses are irradiated in conjunction with supplementary magnetic fields that vary in space and over time and are superposed on the static and homogeneous basic field of a magnetic resonance measurement apparatus along a z-direction, is characterized in that non-linear supplementary magnetic fields are used, whose spatial gradient of the z-component is not constant at least at one instant of the irradiation, and that the radio-frequency pulses to be irradiated are calculated in advance, wherein progressions over time of the field strengths of the supplementary magnetic fields in the region of the object that are calculated and/or measured position-dependently are included in this calculation. This enables change in the magnetization with an at least locally spatially higher resolution and/or shorter irradiation duration of the RF pulses and supplementary magnetic fields than is feasible with linear supplementary magnetic fields produced by conventional gradient systems. In particular, this is possible under the technical and physiological conditions that currently constrain the performance of the known methods using linear supplementary fields.

Method for position dependent change in the magnetization in an object in a magnetic resonance experiment

A magnetic resonance method for using radio frequency pulses for spatially selective and frequency selective or multidimensionally spatially selective excitation of an ensemble of nuclear spins with an initial distribution of magnetization in a main magnetic field aligned along a z-axis, wherein a spin magnetization with a given target distribution of magnetization is generated, and for refocusing the spin magnetization, is characterized in that the radio frequency pulse is used as a sequence of sub-pulses of independent duration, courses of gradients and spatial and/or spectral resolution, comprising one or more large angle RF pulses with tip angles greater than or approximately equal to 15&#xb0;, which generate a gross distribution of magnetization approximating the target distribution of magnetization or a desired modification of the distribution of magnetization with a mean deviation less than or approximately equal to 15&#xb0;, wherein the actual effect of the LAPs on the distribution of spin magnetization before the radio frequency pulse is used is calculated by integration of the Bloch equations without small angle approximation, and one or more small angle RF pulses=SAPs with tip angles less than or approximately equal to 15&#xb0; reducing the difference between the target distribution of magnetization and the gross distribution of magnetization caused by the LAPs.

Magnetic resonance selective excitation method of a target distribution of magnetization with complete full integration of bloch equations for RF large angle pulses (LAP)'s that are 15 degrees or greater, without small angle approximation

The pursuit for ever higher field strengths and faster data acquisitions has led to the construction of coil arrays with high numbers of elements. With the SENSE technique it has been shown, how the sensitivity of those elements can be used for spatial image encoding. A method in accordance with the present invention, largely abstains from using encoding gradients. The resulting sensitivity encoded free induction decay (FID) data is then not used for imaging, but for determining field inhomogeneity distribution. The method has therefore been termed SSH for Sense SHimming.

Sense shimming (SSH): a fast approach for determining B0 field inhomogeneities using sensitivity encoding

A magnetic resonance tomography apparatus, includes a gradient system that can generate at least one spatially varying and optionally time-varying magnetic field for at least one-dimensional local encoding of measuring signals in an area of a test sample to be imaged. The gradient system contains at least one subsystem which can generate a non-bijective spatially varying magnetic (NBSEM) field for local encoding, such that the function of the field strength of such an NBSEM within the area to be imaged has at least one local extreme value (maximum or minimum), such that the area to be imaged is divided along the hyper surface formed by the entirety of all local extreme values of the at least one NBSEM. The apparatus can produce images of the same quality with smaller magnetic field differences and permits easy realization.

Apparatus and method for NMR tomography acquisition with local magnetic field gradients in connection with local receiver coils

A nuclear magnetic resonance (NMR) tomography method for investigating a target object, wherein radio frequency (RF) pulses are irradiated into a target volume and/or RF pulses from the target volume are detected, wherein the target volume is determined by the frequency of the RF pulses and/or through magnetic field gradients, and wherein the target object is moved relative to the NMR tomograph during NMR data acquisition, is characterized in that the frequency of the RF pulses and/or the magnetic field gradients is/are changed during NMR data acquisition such that the target volume covered by the RF pulses is moved relative to the NMR tomograph at the same speed and direction of motion as the target object during NMR data acquisition. This provides a method for investigating a target object which moves relative to the NMR tomograph during NMR data acquisition, which can be carried out in a fast and simple manner.

Method for the acquisition of moving objects through nuclear magnetic resonance tomography

A nuclear magnetic resonance (NMR) spectroscopy or tomography method wherein a sequence of temporally mutually offset radio frequency (RF) pulses is applied onto a spin ensemble like a CPMG multi echo experiment, and wherein the magnetization produced after an initial excitation pulse is transferred to or close to the static pseudo steady state of the initially applied refocussing flip angle &#x3b1;1 is characterized in that magnetization is transferred through gradual change of the refocussing flip angle in subsequent refocussing intervals to or close to the static pseudo steady state of the respectively used refocussing pulse with refocussing flip angle &#x3b1;such that the echo amplitude of the nth echo generated in this fashion approaches the maximum possible value corresponding to the respective refocussing pulse with refocussing flip angle &#x3b1;. The RF energy required for excitation of the nuclear spins can thereby be considerably reduced without having to accept signal intensity losses.

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Freiburg, Germany

Jürgen Hennig