Method and device for acquiring data for diffusion-weighted magnetic resonance imaging
First Claim
1. Method of acquiring data for the illustration of an image which shows the spatial distribution of the magnetic resonance behavior of an object within a selected object area which is disposed in a stationary and the most homogenous possible longitudinal magnetic field and is subjected to a sequence of HF-pulses and magnetic field gradient pulses in different spatial directions, such that a sequence of useful echoes (E), encoded in dependence upon the location, of the magnetisation which is transversal with respect to the stationary magnetic field is produced which useful echoes are acquired as a data record for the reconstruction of the image to be illustrated,wherein between an HF-pulse which excites the transversal magnetisation and the production of the useful echoes (E) a diffusion-weighting sequence is introduced which leads to an attenuation in the transversal magnetisation which is dependent upon the diffusion procedures in the selected object area, and wherein from this diffusion-weighted transversal magnetisation a navigator signal is produced by echo-generation (N1, N2, N3) and its characteristic is used as information for the correction of image artifacts which are produced by movement of the object characterised in that prior to the production of the useful echoes (E) at least one of those interference variables in the phase characteristic of the navigator signal (N1, N2, N3), which would cause the said image artefacts, is measured, and that the result of this measurement is utilised in order to change the phase characteristic of the transversal magnetisation, from which the useful echoes are generated, for the purpose of compensating for the measured variable.
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Abstract
The invention relates to a magnetic resonance imaging method which is characterized in that the transversal magnetization excited in the object to be imaged is diffusion-weighted before the useful echo (E) used for the reconstruction of an image is induced. When the object is moved, phase changes in the diffusion-weighted transversal magnetization can occur that lead to artifacts in the reconstructed image. These disturbing phase changes are measured by analyzing a navigation signal (N1, N2) that is generated before the useful signal is generated. The result of the measurement is used to change the phase characteristics of the transversal magnetization online by a correctional intervention (C0, C1, C2) in such a way that the measured phase changes are compensated. The invention further relates to a magnetic resonance device for carrying out said method.
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Citations
32 Claims
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1. Method of acquiring data for the illustration of an image which shows the spatial distribution of the magnetic resonance behavior of an object within a selected object area which is disposed in a stationary and the most homogenous possible longitudinal magnetic field and is subjected to a sequence of HF-pulses and magnetic field gradient pulses in different spatial directions, such that a sequence of useful echoes (E), encoded in dependence upon the location, of the magnetisation which is transversal with respect to the stationary magnetic field is produced which useful echoes are acquired as a data record for the reconstruction of the image to be illustrated,
wherein between an HF-pulse which excites the transversal magnetisation and the production of the useful echoes (E) a diffusion-weighting sequence is introduced which leads to an attenuation in the transversal magnetisation which is dependent upon the diffusion procedures in the selected object area, and wherein from this diffusion-weighted transversal magnetisation a navigator signal is produced by echo-generation (N1, N2, N3) and its characteristic is used as information for the correction of image artifacts which are produced by movement of the object characterised in that prior to the production of the useful echoes (E) at least one of those interference variables in the phase characteristic of the navigator signal (N1, N2, N3), which would cause the said image artefacts, is measured, and that the result of this measurement is utilised in order to change the phase characteristic of the transversal magnetisation, from which the useful echoes are generated, for the purpose of compensating for the measured variable.
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17. Device for the acquisition of data for the illustration of an image which shows the spatial distribution of the magnetic resonance behaviour of an object within a selected location area, having
a device (11, 11a, 21, 22a) for generating a homogenous magnetic field along a longitudinal axis in the object area to be examined, a device (15, 23) for generating HF-pulses which act upon the object area, devices (12, 13, 14, 22) for generating magnetic field gradients in different spatial directions in the object area, a device (50) for selecting the magnetic resonance signals emanating from the object area, and a control device (30, 40, 60) which upon activation controls the generation of the HF-pulses and the magnetic field gradients and the selection of the magnetic resonance signals in such a manner that the object area is subjected to a sequence of HF- and magnetic field gradient pulses, in order to produce a sequence of useful echoes (E), encoded in dependence upon the location, of the magnetisation which is transversal to the stationary magnetic field, which useful echoes form the data record for the reconstruction of the image to be illustrated, and in order to introduce between an HF-pulse, which excites the transversal magnetisation, and the production of the useful echoes (E), a diffusion-weighting sequence which leads to an attenuation in the transversal magnetisation which is dependent upon diffusion procedures in the selected object area, and in order from this division-weighted transversal magnetisation to produce a navigator signal by echo-generation (N1, N2, N3), the characteristic of said navigator signal being used as information for the correction of image artefacts which are produced by movement of the object, characterised by a configuration of the control device (30, 40, 60) such that upon activation thereof prior to the production of the useful echoes (E) at least one of those interference variables in the phase characteristic of the navigator signal (N1, N2, N3), which would cause the said image artefacts, is measured and the phase characteristic of the transversal magnetisation, from which the useful echoes are generated, is changed for the purpose of compensating for the respectively measured variable.
Specification