JPH04338457A - High frequency signal frequency switching system for exciting nuclear magnetic resonance - Google Patents

Abstract

PURPOSE:To control the frequency and phase of an output wave independently by generating output wave data from the sum of a reference oscillation output and frequency data. CONSTITUTION:An multiplier 3 computes a product of 20 bit reference data of counter 20 and 17 bit frequency data of a frequency data latch 7. A CPU 9 sends 8 bit phase data to a phase data latch 8 and an adder 4 adds the 8 bit phase data of the phase data latch 8 to a high order 8 bit of 12 bit frequency information of the multiplier 3 and the 12 bit frequency phase information is converted to an amplitude value with an ROM table 5. The ROM table 5 outputs sine wave data of one cycle with 12 bit resolutions to a 12 bit address and finally, the 12 bit sine wave data of the ROM table 5 are converted to voltages with a DA converter 6. Thus, the moment of starting counting with the counter 2 gives a phase reference (zero).

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is characterized in that the intensity of nuclear magnetic resonance signals obtained by selectively exciting nuclear magnetic resonance substances such as hydrogen nuclei in specific parts of a test object such as a living body depends on the parts inside the living body. The selection of inspection equipment that measures two-dimensional or three-dimensional nuclear magnetic resonance signal intensity images inside living organisms or resonance spectra of specific parts by utilizing the differences in concentration and properties of nuclear magnetic resonance substances. This invention relates to a high-frequency signal frequency switching method for nuclear magnetic resonance excitation of a high-frequency signal generator for nuclear magnetic resonance excitation that controls the phase of high-frequency power having a highly accurate frequency spectrum shape necessary for accurately performing nuclear magnetic resonance excitation. .

0002

[Prior Art] Direct Digital Frequency has conventionally been used to switch the frequency of a high-frequency signal for nuclear magnetic resonance excitation in a high-frequency signal generator for nuclear magnetic resonance excitation.
For ency Synthesizer, please refer to Ro
dger H. Hosking; Direct
Digital Frequency Synthes
is, Rockland Systems Corpo
ration, West Nyack, New Y
ork. or P. H. Saul D. G. Tay
lor ；A High Speed Direct
Frequency Synthesizer, Pl
essy Research & Technology
yResearch Review 1989. It is discussed in

The principle of operation is that the value of a latch (phase adder) that stores the phase of the output wave is increased by the frequency setting value every unit time determined by the clock oscillator, and the output is stored in the ROM.
It uses a table to convert data into a sine wave.

0004

[Problems to be Solved by the Invention] In the above prior art, the phase increment proportional to the output frequency linearly increases the phase for each cycle of the clock oscillator, and this phase is transferred between the ROM table storing the sine wave and the DA. Since it uses a converter to convert to the corresponding voltage, no consideration is given to phase control; the phase of the output frequency is uniquely determined by the time at which the frequency is set, and when the frequency is switched, the phase also changes. There was a problem that it would switch every time.

An object of the present invention is to independently control the frequency and phase of the output wave.

[0006]

The above object is achieved by generating output wave data by the product of a reference oscillation output and frequency data and the sum of phase data.

[0007]

[Operation] The clock oscillator and counter oscillate at a frequency ωt that is the reference of the output wave. This ωt is multiplied by the frequency data α using a multiplier to determine the frequency (αωt) of the output wave. Further, phase data β is added using an adder to determine the frequency and phase (αωt+β) of the output wave. Since the ROM table generates a sine wave function, the output data is sin
It is converted as (αωt+β). This digital data is converted into a corresponding voltage using a DA converter. In this way, the phase reference is ωt determined by the clock oscillator and counter, and the phase data is calculated independently of the frequency data, so the phase of the output wave can be set independently of frequency and time. .

[0008]

[Embodiment] An embodiment of the present invention will be explained below with reference to FIG.

FIG. 1 shows a block diagram of the present invention. This digital frequency synthesizer has a frequency resolution of 10Hz and settings from 10Hz to 1310710Hz.
It oscillates a SIN waveform with a phase setting of approximately 1.4 degrees.

Clock oscillator 1 is 10485760H
z oscillates. Counter 2 is a 20-bit binary counter with a 20-bit output, forms a loop counter with clock oscillator 1, and outputs reference frequency data of 10 Hz. On the other hand, the CPU 9 sends 17 bits (0 to 131071) of frequency data to the frequency data latch 7. The multiplier 3 calculates the product of the 20-bit reference frequency data of the counter 2 and the 17-bit frequency data of the frequency data latch 7. The output of multiplier 3 will be 37 bits, but since the frequency resolution is 10 Hz, any overflow exceeding 20 bits will be truncated, and in order to obtain the necessary and sufficient resolution and spurious intensity in the final output, the frequency resolution will be 10 Hz.
Since 2 bits of data is sufficient, the lower 8 bits are also discarded. Therefore, the calculation after multiplier 3 is 3 of multiplier 3.
12 bits between bits 9 and 20 of the 7-bit output are used. Further, the CPU 9 sends 8-bit phase data (the phase resolution is approximately 1.4 degrees) to the phase data latch 8. The adder 4 adds the 8-bit phase data of the phase data latch 8 to the upper 8 bits of the 12-bit frequency information of the multiplier 3. Here too, any overflow exceeding 12 bits is truncated. 1 obtained as above
The 2-bit frequency phase information is converted into an amplitude value using the ROM table 5. The ROM table 5 outputs one cycle of sine wave data with 12-bit resolution for a 12-bit address. Finally, the 12-bit sine wave data in the ROM table 5 is converted into voltage by the DA converter 6.

With the above configuration, the time point at which the counter 2 starts counting becomes the phase reference (zero). Therefore, even if the output frequency is switched at any given time, the phase at that frequency is determined by the phase reference of the counter 2 and has a phase unique to the frequency switched at that time. Furthermore, even if the phase of the output is switched according to the phase data, the phase reference is stored in the counter 2, so if it is desired to return the phase of the output to its original state, it can be easily done by clearing the phase data.

According to this embodiment, there is an advantage that even if the frequency of the digital frequency synthesizer is switched, the phase reference does not change.

[0013]

According to the present invention, even if the frequency of a reference signal generator that generates one frequency is switched at any time, the phase at that frequency has a phase specific to that frequency determined by a certain phase reference. The phase of the nuclear magnetic resonance signal obtained by selectively exciting the magnetic resonance substance in an inspection device that measures the nuclear magnetic resonance signal intensity image or the resonance spectrum of a specific region can be controlled, so the phase of the nuclear magnetic resonance signal can be controlled. This has the effect of being able to implement various signal measurement methods that effectively utilize information.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a block diagram of an embodiment of the present invention.

[Explanation of symbols]

1... Clock oscillator, 2... Counter, 3... Multiplier, 4...
Adder, 5...ROM table, 6...DA converter, 7
...Frequency data latch, 8...Phase data latch, 9...C
P.U.

Claims (3)

[Claims] Claim 1: By amplitude-modulating a high-frequency signal for exciting nuclear magnetic resonance with a pre-designed low-frequency signal waveform, a high-frequency signal with only spectral components within a specified frequency band is generated, and this is used to generate electric power. A high frequency for nuclear magnetic resonance excitation that selectively excites only the nuclear magnetic resonance of nuclear spins whose nuclear magnetic resonance frequency is within the specific frequency band by amplifying the signal and irradiating it to the subject as a nuclear magnetic resonance excitation signal. In a reference signal generator that determines the high frequency of a signal generator, even if the frequency of the reference signal generator that generates one frequency is changed at any time, the phase at that frequency remains the same as that frequency determined by a certain phase reference. A high-frequency signal frequency switching method for nuclear magnetic resonance excitation characterized by having a unique phase. 2. In the reference signal generator for determining the frequency of the radio frequency of the radio frequency signal generator for nuclear magnetic resonance excitation according to claim 1, the reference signal generator for generating one frequency has a frequency equal to the switching resolution of the set frequency. A high-frequency signal frequency switch for nuclear magnetic resonance excitation, comprising a digital frequency synthesizer that multiplies the output of a reference oscillation loop counter that oscillates by a constant that sets the frequency, converts the product into a sine wave function, and then converts it from digital to analog. method. 3. In the digital frequency synthesizer according to claim 2, the output of the reference oscillation loop counter is multiplied by a constant for setting the frequency, and then the sum of the product and the constant for setting the phase offset is converted into a sine wave function and then DA converted. 1. A high-frequency signal frequency switching system for nuclear magnetic resonance excitation, characterized in that the phase of the high-frequency wave of a high-frequency signal generator for nuclear magnetic resonance excitation can be arbitrarily set.