Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Patent
1987-01-23
1988-03-22
Levy, Stewart J.
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
324309, 324322, 364414, G01R 3320
Patent
active
047331879
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an NMR imaging apparatus which is provided with an improved data acquiring device and which is useful for enhancement of the speed of reconstruction of an image.
BACKGROUND OF ART
A conventional NMR imaging apparatus is, as shown in FIG. 4, composed of a static magnetic field coil 2 which is urged by a power source and driver 1 for generating a uniform and stable static magnetic field; a probe head (RF coil) 4 which is urged by the power source and driver 1 for generating an RF pulse, and which detects an NMR signal of an object to be examined and supplies it to a preamplifier and detector 3; a gradient magnetic field coil 5 which is urged by the power source and driver 1 for generating linear gradient magnetic fields in the three directions of x, y and z which overlap the static magnetic field; an A/D converter 14 for converting an output signal of the preamplifier and detector 3 into digital data; and a computer system 6 for controlling the power source and driver 1 and the preamplifier and detector 3 and for processing the digital data supplied from the A/D converter 14. The computer system 6 is composed of a central processing unit (CPU) 7, a sequence controller 8, an image display (CRT) 9, a memory (DISK) 10, an array processor (AP) 11 provided with a high-speed memory, an input/output device (I/O) 12, a system bus 13 for connecting these members 7 through 12 to each other, and an A/D converter 14 connected to the I/O 12.
FIG. 5 schematically shows the relationship between a slice and a view with respect to an object to be examined in the case of acquiring data by a multislice multiecho method (hereinunder an image at the same slice which has a different echo time will be defined as a slice in a broad sense), for example, by the Fourier method by means of such a conventional NMR imaging apparatus. In FIG. 5, the reference numeral 15 represents an object to be examined, and the symbol m represents the number of slices and n the number of views. Ordinarily, k items of sample data are acquired in one measurement, and such measurement is repeated j times per view in order to obtain the average measured data.
The operation of the NMR imaging apparatus is as follows. In the actual apparatus, the number m of slices is typically 32 and the number j of measurements for averaging is typically 8, but hereinunder it is assumed that the number m of slices is 2, the number n of views 256, the number of items of data 256, and the number j of measurements 2, for the purpose of simplifying the explanation.
When the sequence controller 6 drives the power source and driver 1 at a constant timing on the basis of a command from the CPU 7, the probe head 4 is energized and the current of the gradient magnetic filed coil 5 is turned on and off, as is required for measurement of an NMR signal. It goes without saying that a uniform and static magnetic field has been generated in advance by the static magnetic field coil 2. After the base band of an NMR signal received by the probe head 4 is converted into an audio frequency by the preamplifier and detector 3, the NMR signal is supplied to the A/D converter 14.
The pulse sequence at this time is carried out in such a manner as is indicated by (a), (b), (c) and (d) in FIG. 6. (a), (b), (c) and (d) in FIG. 6 represent the timing for energizing the probe head, and the timings for applying gradient magnetic field in the directions of x, y and z, respectively. In correspondence with these operations, an NMR signal such as a free induction decay signal (FID signal) indicated by (e) in FIG. 6 is detected.
NMR signals E.sub.m /(#n, j) are acquired in the order of detection as shown in the column A of FIG. 7, and are stored in the DISK 10 in that order. The measured value of an NMR signal E.sub.m (#n, j) is composed of k items of sample data. The data stored in the DISK 10 are arranged in such a manner that the data measured at a first time at one view are arranged in the order of slices, and the data measured at a second time in the
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patent: 4034191 (1977-07-01), Tomlinson et al.
patent: 4355282 (1982-10-01), Young et al.
patent: 4634979 (1987-01-01), Riederer et al.
patent: 4652827 (1987-03-01), Eguchi et al.
patent: 4665365 (1987-05-01), Glover et al.
Imanishi Yasuo
Shimazaki Toru
Watanabe Yoshihiko
Kojima Moonray
Levy Stewart J.
O'Shea Kevin D.
Yokogawa Medical Systems Limited
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