JP2009128352A - Method and apparatus for removing spurious signals of hf band magnetic resonance signals - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately remove spurious signals in every aspect and noises, thereby extracting accurate magnetic resonance signals, in a continuous wave HF band magnetic resonance apparatus in which signals are faint. <P>SOLUTION: The spurious signals usually appear in various aspects, but when an operation parameter of the apparatus is constant, the spurious signals continually appear as a periodic function using a modulated frequency of a static magnetic field for a fundamental wave, whereas the spurious signals are statistically not correlated with the magnetic resonance signals. The method focuses on that, and includes the steps of: separating a static magnetic field into strong and weak components; superimposing the weak component on a modulated magnetic field to shift the static magnetic field; averaging the spurious signals under condition that the signals disappear from a display screen; and storing a waveform. When the signals appear on the display screen by shifting the static magnetic field back, the stored and averaged spurious waveform is subtracted. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a signal extraction method in continuous wave HF band magnetic resonance.

Nuclear magnetic resonance and NMR of the condensate were reported by the Purcell and Bloch groups immediately after the Second World War. Over the course of several years, basic problems were solved both theoretically and experimentally. The same applies to electron spin resonance ESR.
E. M.M. Purcell, H.M. C. Torrey, and R.M. V. Pound, Phys. Rev. 69, 37-38, 1946. F. Bloch, W.M. W. Hansen, and M.M. Packard, Phys. Rev. 69, 127, 680, 1946. D. J. et al. E. Ingram, Spectroscopy at Radio and Microwave frequencies, Butterworths Scientific Publications, 1955.

Advances in technology were in line with chemical research requirements to determine molecular structure.
Shoko 38-007595 45-004233

Applications to chemistry, pharmacy, biochemistry, etc. expanded rapidly.
W. Kemp, NMR in Chemistry, McCillan Publishers, 1986. Japanese translation, Atsushi Yamazaki, “Introduction to the latest NMR for chemistry, biochemistry, pharmacy and medicine”, Baifukan, 1988. Kei Yamauchi, “Magnetic Resonance-ESR”, Science, 2006.

  In NMR, it was sought to improve the resolution from the beginning. At present, the VHF band 200-500 MHz and about 4.7-11.8T are standard. In the spectroscope, the pulse method and the Fourier transform method are standard. In the ESR, microwaves in the SHF band and 9 GHz to 36 GHz and about 0.3 to 1.2 T in the X to Q band were used from the beginning, but the current standard is 9 GHz.

  Current spectroscopic devices that use such a frequency band require special superconducting magnets in NMR, and large electromagnets with a gap of 60 mm and 1 T or more in ESR. Spectroscopes also require advanced technology. It is technically mature and has advanced functions and performance. In addition, NMR has been applied to MRI using a magnetic field of about 0.2-1T, and a new field has been opened for imaging technology. Magnetic field measurement and control are also important applications and are used in equipment that uses high-precision magnetic fields.

  As described above, the present apparatus is expensive because advanced technology is used for molecular structure analysis and other academic research or for medical diagnosis. On the other hand, the present invention does not particularly require the decomposition of the fine structure, but mainly aims at simple measurement of the total spin number of the sample, and aims at generalization, miniaturization, and cost reduction of application of the magnetic resonance phenomenon.

  An important problem in putting the HF band magnetic resonance apparatus into practical use is that the S / N ratio decreases. Therefore, spurious (pseudo signal) becomes a problem together with noise. The spurious changes depending on the operating conditions and state of the entire device and external factors, and also depends on the position and size of the window of the display device. An object of the present invention is to provide means for solving these problems and an apparatus using the same.

In order to achieve the object, each step according to claim 1,
Dividing the static magnetic field generation into two systems, strong and weak, separating the strong magnetic field generation system from the signal extraction system, incorporating the weak magnetic field generation system as part of the signal extraction system,
It is executed as a means to set the period and amplitude of the modulation magnetic field so that the non-signal area and the existence area of the signal area can be distinguished, and AD-convert the signal from the detector and perform signal extraction display by digital processing.

  The spurious elimination method according to the present invention is possible because there is no correlation between the signal, spurious and noise, that the spurious exists stably under certain operating conditions, and that the noise is a random process.

  When the system according to the present invention is used, in a continuous wave HF band magnetic resonance apparatus using a magnetic field modulation method, noise and spurious that cannot be avoided by the magnetic field modulation method are caused by a combination of an arbitrary amplitude axis and time axis of the display device screen. An accurate magnetic resonance signal can be obtained by reliably removing and reducing within a limited screen. This facilitates signal observation and increases data accuracy. Since the signal strength decreases in the HF band, the effect of implementing the present invention is great. The same applies to a sample with a low spin concentration, a sample with a minute amount, and the like.

A system according to the present invention will be described with reference to FIGS. 1a, 1b and 3a. A magnetic resonance apparatus as shown in FIG. 1a is known. The radio frequency coil within the probe 8 in Figure 3a and excited by high-frequency oscillator 9 applies a high-frequency magnetic field h ₁ of frequency f ₁ in the sample. f ₁ is set to a predetermined resonance frequency fr by the high-frequency oscillator controller 10. By the modulation source 5 to generate a modulated magnetic field h _m in the direction perpendicular to the high frequency magnetic field h _r by exciting a modulation coil 4.

When targeting protons, the main coil power supply 2 and the controller 3 supply a constant current to the strong magnetic field main coil 1 to superimpose the strong magnetic field component H _sf of the static magnetic field H ₀ in a direction parallel to the modulation magnetic field. Applied to the sample. H _sf is set to a value in the vicinity of the resonant magnetic field.

The magnetic field strength of magnetic resonance at 3-30 MHz in the HF band is 0.07-0.7 T for protons and 0.1-1 mT for electrons. Therefore, in the case of electrons, an electromagnet for producing H _sf is not required, so the system including the main coil is separated from the signal extraction system.

The weak magnetic field controller 7 supplies a direct current bias current to the modulation coil to superimpose the weak magnetic field component H _wf of the static magnetic field H ₀ on the modulation magnetic field. Superimposed magnetic field h ₀ of the static magnetic field and the modulated magnetic field is as shown in Figure 1b.

In such a configuration, if a magnetic field H _r (ω _r = γH _r , ω _r = 2πf _r ) corresponding to the resonance frequency fr exists within the range of the magnetic field of H ₀ ± H _m , the high frequency oscillator controller 10 By adjusting the high-frequency magnetic field H ₁ and operating the weak magnetic field controller 7 and the modulation power supply controller 6, the magnetic resonance signal is periodically observed with the period T _m of the modulation magnetic field. H ₁ , H _m and T _m are adjusted by the high frequency oscillator controller 10 and the modulation power supply controller 6 according to the relaxation time of the sample.

The resonance signal is received by the detector 11 via a high-frequency oscillator, taken into the CPU 15, processed by the storage device 13 and the averaging device 12, and displayed on the display device 14 such as a synchroscope. Time axis of the display device is synchronized with the modulated magnetic field H _m.

Next, a process for removing spurious will be described. The weak magnetic field component H _wf is increased by the weak magnetic field controller 7 toward the value H _r corresponding to the resonance frequency f _r in the static magnetic field H ₀ modulated by a sine wave as shown in FIG. As is apparent from the figure, the range of H _r −H _m <H ₀ <H _r + H _m is a signal output region, this region is called a signaled region, and the other region is called a non-signal region. Even if H ₀ is raised or lowered from the signaled area, it becomes a no-signal area.

In the magnetic field modulation method, spurious SP that its harmonics and the fundamental wave f _m are mixed inevitably with noise n. To remove these, the system operates or operates as follows. This will be described with reference to FIGS. 2a and 2b. FIG. 2a schematically illustrates the process described below. In the figure, A and C are non-signal areas, and B and D are sections of a signal area. FIG. 3a is a system in which all of the controllers 3, 6, 7, 10 that need to be operated are manually operated.

Start from the no-signal area A while putting the output of the detector into CH1 and watching the screen. A waveform in which spurious and noise are mixed is seen as shown in FIG. SP is a periodic function having _fm as a fundamental wave when only the modulation magnetic field is a spurious source, and FIG. 2B shows such a case. If the periodicity of the disturbance frequency f _e affects becomes periodic function of complex waveforms with the fundamental wave of f _m ± f _e. If the disturbance is not periodic, it becomes part of the noise.

When H _wf is raised by the weak magnetic field controller 7, the signal enters the signal region B, and a magnetic resonance signal SG (hereinafter referred to as a signal) appears as shown in FIG. 2b (ii). This SG will be at equal intervals on the _H 0 = _{H r,} the fundamental wave is a 2f _m. When the H ₀ ≠ H _r is the signal fundamental wave appear at irregular intervals in pairs it becomes f _m. When this is confirmed, H _wf is lowered and returned to the no-signal region C again as shown in FIG. 2b (iii). Although n is a time function, it is a random process and has no periodicity. Each means a waveform sampled in the display screen determined by the width of the time axis, the width of the amplitude axis, and the DC offset.

The signal extraction process according to the present invention will be described below with mathematical formulas.
With CH1, SP and n as instantaneous values, both FIG. 2b (i) and FIG. 2b (iii)
CH1 = SP + n
It is.
When this is confirmed, time averaging is performed by the averaging device 12. <A> represents the time average of instantaneous value A
<CH1> = <SP + n>
Because there is no correlation between SP and n
<CH1> = <SP> + <n>
n is a random process, because <n> = 0
<CH1> = <SP>
This noise-reduced spurious waveform, FIG.

When the averaging and storage are confirmed, H _wf is increased and returned to the signal area D again so that a signal appears as shown in FIG. This waveform is a mixture of spurious and noise in the signal.
CH1 = SG + SP + n
It is. After confirming this, <SP>, that is, operate the CPU to subtract the stored noise-reduced spurious waveform.
MAT = CH1- <SP>
make. According to the above formula
MAT = SG + SP + n- <SP>
But there is no correlation between SG and SP
MAT = SG + n
It becomes. That is, it is a waveform diagram 2b (vi) including a signal in which spurious is corrected and noise.

If this is further averaged,
<MAT> = <SG + n>
Because there is no correlation between SG and n
<MAT> = <SG>
Thus, only the signal is extracted as shown in FIG. 2b (vii). This <SG> is put in the storage device 13 and displayed on the display device for observation as necessary. Alternatively, necessary parameters of various samples are calculated and processed to obtain data.

  FIG. 2c shows a case where the time width is narrowed so that two signals are output, and FIG. 2d is a case where the zoom-up is performed so that only one signal is output. In either case, signals are extracted for different spurious signals by the same procedure as in FIG.

  The data in FIGS. 2b, 2c, and 2d of the example uses a small electromagnet for proton nuclear magnetic resonance at 17 MHz and about 0.4 T. However, the data is illustrated for explaining the operation mechanism and the effect of implementation. It is. The measurement conditions are not related to the content and will be omitted. The electron spin resonance at 17 MHz is about 0.6 mT, and although it does not require an electromagnet, it is clear that it can be applied similarly without changing the gist.

  Although a specific example has been described above, each element of the system may be hardware or software as long as their functions are organically combined as described above. Some of them may be replaced. The choice is based on technical and economic reasons according to the required specifications.

It is a conceptual diagram explaining operation | movement of the apparatus of this invention. It is a schematic diagram explaining the superimposed field of the same static magnetic field and a modulation magnetic field. It is a schematic diagram which shows the change of the static magnetic field of the Example. It is an experimental example explaining the process of Example 1 and signal extraction. Five signals appear. Two signals appear in the zoomed-in version of Examples II and I. A zoomed-in version of Examples III and II shows only one signal. It is a systematic diagram of the same all manual operation system. It is a systematic diagram of the same part CPU control system. It is a systematic diagram of the same all-CPU control system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main coil for strong magnetic fields 2 Main coil power supply 3 Main coil power supply controller 4 Modulation coil 5 Modulation power supply 6 Modulation power supply controller 7 Weak magnetic field controller 8 Probe 9 High frequency oscillator 10 High frequency oscillator controller 11 Detector 12 Averaging device 13 Storage device 14 Display device 15 CPU

Claims (3)

Shifting the resonance condition from the range of the modulation width so that the real-time waveform of the signal does not exist in the display screen, and then averaging and storing the spurious real-time waveform present in the display screen in the CPU; After returning the resonance condition to the range of the modulation width so that the real-time waveform of the signal exists in the display screen, the waveform obtained by subtracting the averaged spurious waveform stored from the real-time waveform of the signal is All the operations using the spurious removal method according to the process composed of the step of displaying on the display screen and the step of averaging the subtracted waveform and storing it in the CPU and displaying on the display are performed manually. Continuous-wave HF band magnetic resonance apparatus using magnetic field modulation   A continuous wave HF band magnetic resonance apparatus using a magnetic field modulation method in which the process is automated by CPU control and other operations are performed manually using a spurious removal method by the process constituted by the same steps as in the first step.   A continuous wave HF band magnetic resonance apparatus using a magnetic field modulation method in which all operations including the process are automated by CPU control, using the spurious removal method by the process configured by the same steps as those in claim 1

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