Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Patent
1987-06-23
1988-11-22
Chapman, John
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
324312, G01R 3320
Patent
active
047868724
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to improvements in an NMR imaging method and apparatus for obtaining a cross-sectional image of an object of inspection by utilizing nuclear magnetic resonance. More particularly, the present invention pertains to an NMR imaging method and apparatus wherein the scanning time required to collect NMR signals by the Fourier transformation method is reduced.
2. Background Art
An NMR imaging apparatus has a magnet section including a static magnetic field coil for producing a uniform static magnetic field H.sub.0 and a gradient magnetic field coil for producing a magnetic field which extends in the same direction as the static magnetic field H.sub.0 and which has a linear gradient in each of the x, y and z directions, a transmission and reception section which is arranged to apply radio-frequency pulses (radio-frequency electromagnetic wave) to an object of inspection placed within the magnetic field formed by the magnet section and to detect an NMR signal from the object, a control and image processing section which is arranged to control the operation of the transmission and reception section and that of the magnet section and to process detected data to thereby display an image, and other sections or members.
In such an NMR imaging apparatus, the transmission and reception section is under the control of the control and image processing section so as to output radio-frequency pulses in a sequence in accordance with the saturation recovery (SR) method or the inversion recovery (IR) method and on the basis of the multislice method. The control and image processing section effects collection of data on the basis of the Fourier transformation method in order to reconstruct an image.
In the above-described radio-frequency pulse sequence, the recovery of excited spins depends on a natural relaxation process. Accordingly, the proportion of the data observation time with respect to the scanning time is low and the S/N per time is low. Further, since the spin excitation interval is determined in view of the recovery of spins, the scanning time is correspondingly long, so that the rate of incidence of artifacts due to the movement of the object's body is high. On the other hand, the multislice method enables a plurality of images to be obtained within the same scanning time. However, there is no change in the entire scanning time and, therefore, this method is helpless against artifacts due to the movement of the object's body.
To shorten the scanning time in the SR or IR method, it is necessary to reduce the number of times of phase encoding (spin warp), and this leads to a lowering in the spatial resolving power of the NMR image.
One example of methods which have heretofore been invented in order to solve these problems is the FR (Fast Recovery) method disclosed, for example, in Japanese Patent Laid-Open Nos. 231438/1984 and 29684/1985. The feature of this method resides in that a radio-frequency pulse sequence is applied without awaiting spins to recover to a thermal equilibrium state so as to forcedly direct the magnetization M (the sum total of spins) toward the z-axis direction. More specifically, the sequence according to the FR method is so designed that the scanning speed is given priority and scanning is thereby completed within a short period time. Thus, it is possible to shorten the scanning time itself.
The conventional NMR imaging apparatus suffers, however, from the following problems. Since the recovery of spins to a thermal equilibrium state is forcedly effected, the contrast of an NMR image which originally strongly depends on the relaxation time is deteriorated. More specifically, the prior art has the problem that as the scanning time is reduced (as the speed of scanning is increased), the contrast of the resultant NMR image is degraded.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide an NMR imaging method and apparatus which is so designed that the scanning time is reduced without any lowering in the q
REFERENCES:
patent: 4536712 (1985-08-01), Iwaoka et al.
patent: 4684890 (1987-08-01), Briguet et al.
patent: 4694250 (1987-09-01), Iwaoka et al.
patent: 4694251 (1987-09-01), Yoshitome et al.
Chapman John
Fess Lawrence G.
Kojima Moonray
Yokogawa Medical Systems Limited
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