Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Reexamination Certificate
2001-02-24
2002-09-24
Arana, Louis (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
C324S307000
Reexamination Certificate
active
06456073
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a data acquisition method of compensation for magnetic field drift, a method of compensation for magnetic field drift, and an MRI (magnetic resonance imaging) apparatus, and more particularly to a data acquisition method of compensation for magnetic field drift, a method of compensation for magnetic field drift, and an MRI apparatus, allowing improvement of the image quality by compensating for the magnetic field drift and reduction of overall scanning time.
In the method of compensation for magnetic field drift in an MRI apparatus, disclosed in the Japanese Unexamined Patent Publication No. H1-141656, data for magnetic field drift compensation is gathered for each view of imaging data to be acquired, and based on thus gathered data for magnetic field drift compensation the current flowing through the primary field coil may be adjusted in order to compensate for the magnetic field drifting.
In the magnetic field drift compensation according to the Prior Art technique above, magnetic field drift will be compensated for by measuring the magnetic field drift during gathering data for imaging. This technique allows compensation to be improved more accurately than gathering independent data for magnetic field drift compensation separated apart from data gathered for imaging.
There is however a drawback that the repetition time TR becomes longer, because the repetitive unity of pulse sequences includes a pulse sequence for gathering the imaging data, plus a pulse sequence for gathering data for compensation for magnetic field drift. Thus, when the desired contrast of image changes, the scanning time as whole will be longer.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to provide a data acquisition method for magnetic field drift compensation, a method of magnetic field drift compensation, and an MRI apparatus, allowing improvement of the image quality by compensating for the magnetic field drift and reduction of overall scanning time.
In accordance with a first aspect of the present invention, a data acquisition method of magnetic field drift compensation is provided, characterized by N>M≧2, where: N is the number of repetition of pulse sequences for gathering imaging data, M is the total number of repetition of pulse sequences for gathering data for magnetic field compensation; and acquiring data for magnetic field compensation by interposing at least one or more pulse sequences for gathering data for magnetic field drift compensation between two pulse sequences for gathering imaging data.
In the data acquisition method of magnetic field drift compensation in accordance with the first aspect as have been mentioned above, the total number of pulse sequences for gathering data for magnetic field drift compensation, M, will be smaller than the repetition of pulse sequences for gathering imaging data, N, and a pulse sequence for gathering data for magnetic field drift compensation will be inserted between pulse sequences for gathering imaging data. For instance, When N=256, then M=128, one pulse sequence for gathering data for magnetic field drift compensation will be inserted between two pulse sequences for gathering imaging data. In this manner, the magnetic field drift can be measured during imaging data acquisition, so that the compensation accuracy will be improved, when compared with independent data acquisition of compensation for magnetic field drift separately. In addition, overall scanning time required may be shorter than adding a pulse sequence for gathering compensation data for magnetic field drift to each pulse sequence for gathering imaging data.
In accordance with a second aspect of the present invention, in the data acquisition method of magnetic field drift compensation of the arrangement described above, a method is provided, characterized in that the integral of gradient field in the imaging data acquisition pulse sequence will be equal to the integral of gradient field in the pulse sequence for data acquisition of compensation for drift in magnetic field, for each of axis in order to hold the steady state of spins.
In the data acquisition method of magnetic field drift compensation in accordance with the second aspect as have been described above, the integration of gradient field in the imaging data acquisition pulse sequence will be equal to the integration of gradient field in the pulse sequence for data acquisition of compensation for drift in magnetic field, such that the gradient field of the pulse sequences for data acquisition of compensation for drift in magnetic field, when inserted between the imaging data acquisition pulse sequences, will not affect to the imaging data acquisition pulse sequence.
In accordance with a third aspect of the present invention, in the data acquisition method of magnetic field drift compensation of the arrangement described above, a method is provided, characterized in that the imaging data acquisition pulse sequences are pulse sequences of the gradient echo method having read gradient for convergence of gradient echo, and the data acquisition pulse sequences of magnetic field drift compensation are pulse sequences without read gradient and phased gradient for convergence of gradient echo during imaging data acquisition pulse sequences.
In the data acquisition method of magnetic field drift compensation in accordance with the third aspect as have been described above, compensation data for magnetic field drift can be acquired, in a manner preferable to the imaging data acquisition by pulse sequences of the gradient echo method.
In accordance with a fourth aspect of the present invention, in the data acquisition method of magnetic field drift compensation of the arrangement described above, a method is provided, characterized in that the pulse sequences for acquiring imaging data are pulse sequences by the spin echo method having diffused read gradient between a 90° RF pulse and a 180° RF pulse, and the pulse sequences for acquiring compensation data for magnetic field drift are pulse sequences without diffuse read gradient in the imaging data acquisition pulse sequences, and corresponding read gradient and phase gradient after 180° RF pulses.
In the data acquisition method of magnetic field drift compensation in accordance with the fourth aspect as have been described above, compensation data for magnetic field drift can be acquired, in a manner preferable to the acquisition of imaging data by the pulse sequences of the spinning echo method.
In accordance with a fifth aspect of the present invention, in the data acquisition method of magnetic field drift compensation of the arrangement described above, a method is provided, characterized in that the pulse sequences for acquiring imaging data are pulse sequences of high-speed spinning echo method, having diffuse read gradient between a 90° RF pulse and a 180° RF pulse, and between a 180° RF pulse and another 180° RF pulse, the pulse sequences for acquiring magnetic field drift compensation data are pulse sequences without diffuse read gradient in the imaging data acquisition pulse sequence, and corresponding read gradient and phase gradient after a 180° RF pulse.
In the data acquisition method of magnetic field drift compensation in accordance with the fifth aspect as have been described above, compensation data for magnetic field drift can be acquired, in a manner preferable to the imaging data acquisition by pulse sequences of the high-speed spinning echo method (the multi-echo method also).
In accordance with a sixth aspect of the present invention, a method is provided, characterized by the step of adjusting the current of primary field coil based on the compensation data for magnetic field drift gathered in accordance with the data acquisition method of magnetic field drift of the arrangement described above.
In the method of compensation for magnetic field drift in accordance with the sixth aspect of the present invention, the current flowing through the primar
Kosugi Susumu
Uetake Nozomu
Arana Louis
GE Medical Systems Global Technology Company LLC
Kojima Moonray
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