Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Patent
1989-05-30
1991-03-12
Tokar, Michael J.
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
324314, G01R 3320
Patent
active
049995812
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic resonance imaging system and, more particularly, to a magnetic resonance imaging system in which correction is performed for acquired magnetic resonance data by hardware, thereby reducing a load on software processing except for Fourier transform processing for image reconstruction and improving throughput of the system.
DISCUSSION OF BACKGROUND
As is well known, magnetic resonance imaging is a technique capable of obtaining chemical and physical microscopic information about molecules by utilizing a phenomenon in which when atomic nuclei having a specific spin and a magnetic moment based on the spin are placed in a uniform static magnetic field, the atomic nuclei resonantly absorb an energy of an RF magnetic field rotating at a predetermined frequency in a plane perpendicular to the direction of the static magnetic field.
As a method of visualizing a spatial distribution of specific atomic nuclei (e.g., hydrogen atomic nuclei contained in water and fat) in an object to be examined by using the magnetic resonance imaging, a projecting reconstruction method by Lauterbur, a Fourier method by Kumar, Welti, or Ernst, a spin warp method as a modification of the Fourier method by Hutchison et al., an echo planar method by Mansfield, and the like have been proposed.
When the magnetic resonance imaging is to be performed on the basis of these methods, in order to obtain a reconstructed image with high precision and high image quality from acquired magnetic resonance data, correction is performed for various error factors.
For example, correction of a base line of a magnetic resonance signal (echo), correction of a sampling point of magnetic resonance data, and phase correction of a detection reference signal can be considered as the correction performed upon acquisition of magnetic resonance data and reconstruction of a magnetic resonance image. As a method of performing these correction operations, a method of performing base line correction, shifting of a sampling point based on an interpolation operation, and phase correction can be performed by software processing for the acquired magnetic resonance data, as pre-processing prior to image reconstruction processing. By Fourier-transforming the corrected magnetic resonance data by the above correction processing, image reconstruction can be properly performed.
Especially in a so-called half encoding method in which data of a half of a Fourier space is obtained on the basis of measurement data of the other half by utilizing the fact that data point-symmetrical about the origin of the Fourier space are complex conjugate with each other, a magnetic resonance data error greatly adversely affects a reconstructed image. Therefore, the above correction processing is essential.
FIG. 1 shows a procedure of magnetic resonance data acquisition and image reconstruction including the above correction processing based on the half encoding method.
First, magnetic echo data (to be referred to as "zero-encoded MR data" hereinafter) which are not phase-encoded are acquired from an object to be examined or a proper phantom by a magnetic, resonance excitation sequence excluding application of a gradient magnetic field for phase encoding (step S1). On the basis of the acquired zero-encoded MR data, an offset value of an echo signal is obtained, and the offset is corrected (step S2). On the basis of the acquired zero-encoded MR data, a peak point position of a norm of the echo signal is detected (step S3). On the basis of the detected peak point position, a shift amount .DELTA.ts for correcting a sampling point position is obtained (step S4). On the basis of the zero-encoded MR data at the peak point position, a correction phase angle .DELTA..phi.c for a detection reference signal is obtained (step S6). After the above preliminary measurements and correction value determination processing are performed, main measurements and image reconstruction processing are performed as follows.
By
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Kabushiki Kaisha Toshiba
Tokar Michael J.
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