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
047868716
DESCRIPTION:
BRIEF SUMMARY
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 two-dimensional Fourier transformation method is reduced.
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.O 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.
The NMR imaging apparatus having the above-described arrangement is driven in the pulse sequence based on the two-dimensional Fourier transformation method as shown in FIG. 6 in order to perform a predetermined data collecting operation. The operation carried out at each time during the data collection is as follows.
The time T.sub.l . . . The z-gradient magnetic field g.sub.s is applied, and a 90.degree. pulse (an RF signal) is applied (see FIG. 6(b) and 6(a)). Thus, spins within a specific slice plane of the object alone are selectively excited.
The time T.sub.2 . . . In order to generate a spin echo signal during the subsequent time T.sub.4, the x-gradient magnetic field g.sub.dp is applied (see FIG. 6(d)) to give the spins a phase difference corresponding to the x-coordinate (prephase). Further, in order to obtain positional data (positional data in the y-direction) in a direction perpendicular to the gradient g.sub.pr which is applied when a signal readout operation is carried out, the y-gradient magnetic field g.sub.w(k) is applied (see FIG. 6(c)) during the time T.sub.w (<T.sub.2) to give the spins a phase corresponding to the y-coordinate (warp). Further, the z-gradient magnetic field g.sub.rp is applied during the time T.sub.w (see FIG. 6(b)) in order to remove the z-direction phase shift of the spins caused in the slicing operation (rephase).
The time T.sub.3 . . . In order to generate a spin echo, a 180.degree. pulse signal is applied (see FIG. 6(a)) to invert the whole spins (inversion).
The time T.sub.4 . . . In order to obtain positional data in the x-direction, the x-gradient magnetic field (projection magnetic field ) g.sub.pr is applied (see FIG. 6(d)), and a spin echo signal is detected (see FIG. 6(e)).
The spin echo signal detected during the time T.sub.4 corresponds to one of the lines obtained by subjecting to the two-dimensional Fourier transformation the distribution of intensities of signals from the spins in the object (determined by the spin density and the relaxation phenomenon). The selection of lines is effected by means of the product of the amount of application of the y-gradient, i.e., the magnitude of the y-gradient magnetic field g.sub.w(k), and the application time T.sub.w. Accordingly, all the view data which is necessary for reconstruction of an image, i.e., a series of data shown in FIG. 7, is collected by repeating the sequence shown in FIG. 6 while varying the y-gradient magnetic field g.sub.w(k). A series of data in the read-out direction shown in FIG. 7 is observed for each view as a spin echo signal, while one of the data in the warp direction is obtained for each view.
The scanning time in the Fourier transformation method is known to be substantially proportional to the number of samples in the
REFERENCES:
patent: 4625171 (1986-11-01), Sekihara et al.
patent: 4674046 (1987-06-01), Ozeki et al.
patent: 4710716 (1987-12-01), Keren et al.
Arana Louis M.
Chapman John
Kojima Moonray
Yokogawa Medical Systems Limited
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