Universitaetsklinikum Freiburg

Bruker Biospin Mri Gmbh

Universitätsklinikum Freiburg

Martin Haas

Maxim Zaitsev

Jürgen Hennig

Peter Ullmann

Wolfgang Ruhm

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

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Freiburg, Germany

Martin Haas