JP2016168087A - Temperature measurement method and magnetic field measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature measurement method that can measure temperature change in a subject by using a material with characteristics where resonant frequency is hard to change with a temperature change and the resonant frequency changes by magnetic variation are newly discovered.SOLUTION: A temperature measurement method includes: a step of converting a magnetic resonance signal f(t) detected from a subject into a frequency spectrum F(ω) by application of a high frequency magnetic field including the resonant frequency of water, and converting a magnetic resonance signal f(t) detected from the subject into a frequency spectrum F(ω) by application of a high frequency magnetic field including the resonant frequency of a phosphorus compound; a step of acquiring a frequency fcorresponding to the resonant frequency of water from the frequency spectrum F(ω), and acquiring a frequency fcorresponding to the resonant frequency of the phosphorus compound from the frequency spectrum F(ω); and a step of detecting a temperature change according to a difference between a variation amount Δfof the frequency fand a variation amount Δfof the frequency fby using correlation between a variation amount of the resonant frequency of water and a temperature.SELECTED DRAWING: Figure 8

Description

  The present disclosure relates to a noninvasive temperature measurement method and a magnetic field measurement method inside a subject, and more particularly, to a temperature measurement method and a magnetic field measurement method based on characteristics of a phosphorus compound.

  In recent years, MRI (Magnetic Resonance Imaging) capable of noninvasively measuring the temperature inside a subject has been developed. For example, Non-Patent Document 1 discloses a method for noninvasively measuring the temperature in the brain using the fact that the resonance frequency of water in a static magnetic field changes depending on the temperature.

Rounald J.T.Corbett et al., “Validation of a Noninvasive Method to Measure Brain Temperature In Vivo Using 1H NMR Spectroscopy”, Journal of Neurochemistry, 1995 Mar, 64 (3), 1224-30

  The resonant frequency of water varies depending on various factors besides temperature. Another factor is, for example, a magnetic field change. The temperature measurement method disclosed in Non-Patent Document 1 uses N-acetylaspartic acid (NAA) in order to eliminate such a change in resonance frequency due to a change in magnetic field. The resonance frequency of NAA is not easily affected by temperature changes and is easily affected by magnetic field changes. On the other hand, the resonance frequency of water is easily affected by both the temperature change and the magnetic field change as described above. Therefore, if attention is paid to the resonance frequency of water on the basis of the resonance frequency of NAA, the influence of a magnetic field change or the like can be reduced. Thereby, the temperature measurement method disclosed in Non-Patent Document 1 measures the temperature in the brain with high accuracy.

  However, since the absolute amount of NAA in the brain increases and decreases depending on the location and individual differences, in some cases, it may be difficult to detect the magnetic resonance signal of NAA. In addition, the temperature cannot be measured by this method for a part where there is no NAA other than the brain. Therefore, discovery of other substances having the same characteristics as NAA is desired. That is, the resonance frequency hardly changes due to a temperature change, and the resonance frequency changes due to a magnetic field change, and it is desired to discover other substances (hereinafter also referred to as “reference substances”) that are widely present in the living body.

  The present disclosure has been made in order to solve the above-described problems. The purpose of the present disclosure is to discover a characteristic in which the resonance frequency hardly changes due to a temperature change and the resonance frequency changes due to a magnetic field change. To provide a temperature measurement method capable of measuring a temperature change inside a subject using a substance. The purpose of other aspects is to measure the magnetic field change in the region including the subject using a substance that has been found to have a characteristic in which the resonance frequency does not change easily due to temperature changes and the resonance frequency changes due to magnetic field changes. It is to provide a simple magnetic field measurement method.

  According to an aspect, a temperature measurement method applies a first high-frequency magnetic field including a resonance frequency of water to a subject existing in a static magnetic field (including voxel signal collection by applying a selective high-frequency magnetic field), After applying the first high-frequency magnetic field, a step of applying a second high-frequency magnetic field including the resonance frequency of the phosphorus compound, and a magnetic resonance signal detected from the subject by the application of the first high-frequency magnetic field indicate the signal intensity for each frequency. A step of converting the magnetic resonance signal detected from the subject by application of the second high-frequency magnetic field into the second frequency spectrum while converting to the first frequency spectrum, and a signal intensity relatively high in the first frequency spectrum. The first frequency corresponding to the resonance frequency of water is acquired, and the signal intensity is relatively high from the second frequency spectrum, and the resonance frequency of the phosphorus compound is The difference between the amount of change in the first frequency and the amount of change in the second frequency is obtained using the correlation between the step of obtaining the second frequency corresponding to the number and the amount of change in the resonant frequency of water and the temperature. Detecting a temperature change according to the above.

  Preferably, the applying step applies the second high-frequency magnetic field continuously after the application of the first high-frequency magnetic field is stopped.

  Preferably, the detecting step subtracts the change amount of the second frequency from the change amount of the first frequency, and detects a temperature change according to the result of the difference.

Preferably, the phosphorus compound includes phosphocreatine.
According to another aspect, a magnetic field measurement method includes applying a high-frequency magnetic field including a resonance frequency of a phosphorus compound to a subject existing in a static magnetic field, and magnetism detected from the subject by applying the high-frequency magnetic field. Converting the resonance signal into a frequency spectrum indicating the signal intensity for each frequency; obtaining a frequency having a relatively high signal intensity from the frequency spectrum and corresponding to a resonance frequency of the phosphorus compound; Detecting a magnetic field change according to the frequency change amount using a correlation between the change amount of the resonance frequency and the magnetic field strength.

  In one aspect, it is possible to measure a temperature change inside a subject using a substance in which a resonance frequency is hardly changed by a temperature change and a characteristic in which the resonance frequency is changed by a magnetic field change is newly found.

  The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the present invention taken in conjunction with the accompanying drawings.

It is the figure which showed the external appearance of MRI according to 1st Embodiment. It is the figure which showed the chemical shift of water, NAA, and organic phosphoric acid when changing temperature and making a magnetic field constant. It is the figure which showed the time change of the chemical shift of water, NAA, and inorganic phosphoric acid when changing temperature and making a magnetic field constant. It is the figure which showed the time change of the resonant frequency of organic phosphoric acid and NAA when temperature is made constant and a magnetic field is changed. It is the figure which showed the time change of the resonant frequency of inorganic phosphoric acid and NAA when temperature is fixed and a magnetic field is changed. It is the figure which showed the main structures of MRI according to 1st Embodiment. It is a figure which shows the timing of the high frequency magnetic field applied to a subject. It is the conceptual diagram which showed roughly the temperature measurement method by the computer system according to 1st Embodiment. It is a figure which shows the frequency spectrum of the phosphorus compound in a human head as a graph. It is a figure which shows the temperature measurement result by the temperature measuring method according to 1st Embodiment. It is the figure which showed the temperature distribution in the brain detected with the temperature measurement method according to 1st Embodiment. It is a flowchart showing a part of process which the computer system according to 1st Embodiment performs. It is a block diagram which shows the main hardware constitutions of the computer system according to 1st Embodiment. It is the conceptual diagram which showed roughly the magnetic field measuring method by the computer system according to 2nd Embodiment. It is a flowchart showing a part of process which the computer system according to 2nd Embodiment performs.

  Embodiments according to the present invention will be described below with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated. Each embodiment or modification described below may be selectively combined as appropriate.

<New reference materials>
As described above, there is a demand for a substance (that is, a reference substance) in place of NAA in which the resonance frequency hardly changes due to a temperature change and the resonance frequency changes due to a magnetic field change. The inventors have discovered that phosphorus compounds can be new reference materials.

  With reference to FIG. 1 to FIG. 5, the basis on which a phosphorus compound can become a new reference substance will be described. FIG. 1 is a diagram showing the appearance of the MRI 100. The inventors conducted experiments on the possibility that phosphorus compounds can serve as reference substances using MRI100. In this experiment, MAGENTOM 7T manufactured by Siemens (registered trademark) was used as MRI100.

  As a result, the inventors newly discovered that the resonance frequency of the phosphorus compound is almost constant regardless of the temperature change. Furthermore, the inventors have newly discovered that the change in the resonance frequency of the phosphorus compound due to the change in the magnetic field is similar to the change in the resonance frequency of the NAA.

The experimental results are shown in FIGS. FIG. 2 shows a temporal change in resonance frequencies of water (typically proton ( ¹ H)), NAA, and organophosphate when the temperature is changed and the magnetic field is kept constant (hereinafter, “ It is also referred to as “chemical shift”. In the experiment of FIG. 2, a mixed aqueous solution of NAA and phosphocreatine (PCr), which is a kind of organic phosphoric acid, was used as a phantom.

  The horizontal axis of the graph 51 in FIG. The vertical axis of the graph 51 indicates the chemical shift. In the graph 51, the chemical shift of each substance with reference to time “0” is shown as an experimental result. As shown in graph 51, the chemical shift of NAA and organophosphoric acid is smaller than the chemical shift of water. Further, the chemical shift of organic phosphoric acid is almost constant regardless of the temperature change, similar to the chemical shift of NAA.

  FIG. 3 is a diagram showing temporal changes (that is, chemical shifts) of chemical shifts of water, NAA, and inorganic phosphoric acid when the temperature is changed and the magnetic field is kept constant. In the experiment of FIG. 3, a mixed aqueous solution of NAA and sodium dihydrogen phosphate dihydrate, which is a kind of inorganic phosphoric acid, was used as a phantom.

  The horizontal axis of the graph 53 in FIG. The vertical axis of the graph 53 indicates the chemical shift. In the graph 53, the chemical shift of each substance with respect to time “0” is shown as an experimental result. As shown in graph 53, the chemical shift of NAA and inorganic phosphoric acid is smaller than the chemical shift of water. In addition, the chemical shift of inorganic phosphoric acid is almost constant regardless of the temperature change, similar to the chemical shift of NAA.

  From the experimental results of FIG. 2 and FIG. 3, it was confirmed that the resonance frequency of phosphorus compounds such as organic phosphoric acid and inorganic phosphoric acid was almost constant without depending on temperature.

  FIG. 4 is a diagram showing temporal changes in the resonance frequency of organic phosphoric acid and NAA when the temperature is constant and the magnetic field is naturally drifted. The horizontal axis of the graphs 55 and 57 in FIG. 4 indicates time. The vertical axis of the graph 55 indicates chemical shift. The vertical axis of the graph 57 indicates the difference between the chemical shift of organophosphoric acid and the chemical shift of NAA.

  As shown in the graph 55, organic phosphoric acid and NAA have similar chemical shift changes in an environment where a magnetic field naturally drifts. Further, as shown in the graph 57, the difference between the chemical shift of organic phosphoric acid and the chemical shift of NAA is within ± 0.002 ppm. From this, it can be confirmed that the tendency of the chemical shift change is almost the same between the organic phosphoric acid and NAA.

  FIG. 5 is a diagram showing temporal changes in the resonance frequencies of inorganic phosphoric acid and NAA when the temperature is kept constant and the magnetic field is naturally drifted. The horizontal axis of the graphs 59 and 61 in FIG. 5 indicates time. The vertical axis of the graph 59 indicates the chemical shift. The vertical axis of the graph 61 indicates the difference between the chemical shift of organophosphoric acid and the chemical shift of NAA.

  As shown in graph 59, inorganic phosphoric acid and NAA have similar chemical shift changes in an environment where the magnetic field naturally drifts. Moreover, as shown in the graph 61, the difference between the chemical shift of inorganic phosphoric acid and the chemical shift of NAA is within ± 0.0007 ppm. This also confirms that the tendency of change in chemical shift is almost the same between inorganic phosphoric acid and NAA.

  From the experimental results of FIGS. 4 and 5, it was confirmed that the resonance frequency of phosphorus compounds such as organic phosphoric acid and inorganic phosphoric acid changes in the same manner as NAA in an environment where the magnetic field changes.

  From the above experimental results, it was shown that the resonance frequency of the phosphorus compound has temperature invariance and magnetic field variability, similar to NAA. This indicates that phosphorus compounds can be a new reference material to replace NAA.

  As far as the inventors know, there is no prior art document showing the above properties of phosphorus compounds. This is thought to be due to the following circumstances.

  The magnetic resonance signal of the phosphorus compound is very weak, and it has been difficult to accurately capture the magnetic resonance signal. However, in this experiment, MRI capable of generating an extremely high magnetic field strength of 7T (terrace) was used, and the magnetic resonance signal of the phosphorus compound could be captured with high accuracy. The world's most advanced MRI has hardly been used in Japan because the device itself is expensive. The fact that the above properties of the phosphorus compound could not be confirmed without using ultra-high performance MRI is considered to be one of the reasons that the properties were not found.

  The newly discovered properties in phosphorus compounds can be applied in various ways. For example, the characteristic can be applied to a temperature measurement method and a magnetic field measurement method inside the subject. Hereinafter, the MRI 100 according to the first embodiment using the temperature measurement method and the MRI 100 according to the second embodiment using the magnetic field measurement method will be described in order.

<First Embodiment>
[MRI100]
With reference to FIG. 6 and FIG. 7, an outline of the apparatus of MRI 100 according to the first embodiment will be described. FIG. 6 is a diagram showing the main configuration of the MRI 100. FIG. 7 is a diagram illustrating the timing of the high-frequency magnetic field applied to the subject S.

  As shown in FIG. 6, the MRI 100 includes a static magnetic field magnet 1, a gradient magnetic field coil 2, a transmission unit 3, a transmission coil 4, a reception coil 5, a reception unit 6, a power supply 10, and a sequence control unit. 13, a bed 20, a top board 21, and a computer system 200.

  The static magnetic field magnet 1 is a magnet formed in a hollow cylindrical shape, and generates a uniform static magnetic field in an internal space. As the static magnetic field magnet 1, for example, a permanent magnet or a superconducting magnet is used. Preferably, a magnet that generates a static magnetic field strength of about 7T is used as the static magnetic field magnet 1. The static magnetic field strength of the static magnetic field magnet 1 is not limited to about 7T. The static magnetic field strength may be 7T or less (for example, about 1.5T, about 3T) if the conditions and environment are optimized. Alternatively, the static magnetic field strength may be 7T or more.

  The gradient magnetic field coil 2 is a coil formed in a hollow cylindrical shape, and is disposed inside the static magnetic field magnet 1. The gradient magnetic field coil 2 is formed by combining three coils respectively corresponding to the X, Y, and Z axes orthogonal to each other. These three coils are individually supplied with current from the power supply 10 and generate gradient magnetic fields whose magnetic field strengths change along the X, Y, and Z axes, respectively. The Z-axis direction is the same direction as the static magnetic field.

  The gradient magnetic fields of the X, Y, and Z axes generated by the gradient magnetic field coil 2 correspond to, for example, the slice selection gradient magnetic field Gs, the phase encoding gradient magnetic field Ge, and the readout gradient magnetic field Gr, respectively. The slice selection gradient magnetic field Gs is used to arbitrarily determine an imaging section. The phase encoding gradient magnetic field Ge is used to change the phase of the magnetic resonance signal in accordance with the spatial position. The readout gradient magnetic field Gr is used for changing the frequency of the magnetic resonance signal in accordance with the spatial position.

  The transmission unit 3 transmits a high-frequency signal corresponding to the Larmor frequency to the transmission coil 4 under the control of the sequence control unit 13. The transmission coil 4 is disposed inside the gradient magnetic field coil 2, receives a high-frequency signal (RF (Radio Frequency) signal) from the transmission unit 3, and applies a high-frequency magnetic field to the subject S.

  In the present embodiment, the transmission unit 3 includes a high-frequency magnetic field including a resonance frequency of water (hereinafter also referred to as “water high-frequency magnetic field”) and a high-frequency magnetic field including a resonance frequency of a phosphorus compound (hereinafter referred to as “phosphorus-use magnetic field”). Are also generated in the transmission coil 4 alternately.

  Preferably, when applying the high frequency magnetic field for water, the transmission coil 4 applies the high frequency magnetic field for water with a predetermined bandwidth (for example, ± 2000 Hz) based on the resonance frequency of water. Thereby, magnetic resonance signals radiated from substances other than water are eliminated, and the receiving coil 5 described later can receive the magnetic resonance signals of water with high accuracy. Further, when the high frequency magnetic field for phosphorus is applied, the transmission coil 4 applies the high frequency magnetic field for water with a predetermined bandwidth (for example, ± 3000 Hz or ± 4000 Hz) centering on the resonance frequency of the phosphorus compound. Thereby, magnetic resonance signals radiated from substances other than the phosphorus compound are eliminated, and the receiving coil 5 described later can accurately receive the magnetic resonance signals of the phosphorus compound.

  Preferably, as shown in FIG. 7, the transmission unit 3 applies the high frequency magnetic field for phosphorus continuously after the application of the high frequency magnetic field for water is stopped. Thereby, the receiving coil 5 to be described later can acquire magnetic resonance signals of water and the phosphorus compound at substantially the same timing and in substantially the same environment. For example, the transmission coil 4 alternately applies a high-frequency magnetic field for water and a high-frequency magnetic field for phosphorus every 5 seconds. Since the magnetic resonance signal may be weak depending on the type of phosphorus compound, the high frequency magnetic field for phosphorus may be applied multiple times. Alternatively, the application time of the high frequency magnetic field for phosphorus may be longer than the application time of the high frequency magnetic field for water.

  The receiving coil 5 is capable of receiving magnetic resonance signals of a plurality of channels. In the present embodiment, the receiving coil 5 includes at least a magnetic resonance signal emitted from the subject S by application of the high frequency magnetic field for water and a magnetic resonance signal emitted from the subject S by application of the high frequency magnetic field for phosphorus. Two magnetic resonance signals are received. The receiving coil 5 outputs the received magnetic resonance signal to the receiving unit 6. As an example, the receiving coil 5 is a Multi-Nuclear Loop Coil manufactured by QED.

  The receiving unit 6 generates time-domain signal data by performing A / D (Analog-to-Digital) conversion on the magnetic resonance signal output from the receiving coil 5 under the control of the sequence control unit 13. The signal data generated by the receiving unit 6 includes the above-described slice selection gradient magnetic field Gs, phase encoding gradient magnetic field Ge, and readout gradient magnetic field Gr, and the PE (Phase Encode) direction in the k space, RO (Read A component indicating a position in the Out) direction and SE (Slice Encode) direction is encoded.

  The sequence control unit 13 collects data for generating an image of the subject S by driving the transmission unit 3, the reception unit 6, and the power supply 10 according to the sequence execution data transmitted from the computer system 200. The sequence execution data is information that defines a pulse sequence for collecting raw data from the subject S. More specifically, the sequence execution data includes the strength of the power supplied to the gradient magnetic field coil 2 by the power supply 10 and the timing of supplying power, the level of the high-frequency signal transmitted from the transmission unit 3 to the transmission coil 4, and the high-frequency signal. This is information defining a procedure for collecting data such as a transmission timing and a timing at which the receiving unit 6 detects a magnetic resonance signal.

  When the raw data is transmitted from the reception unit 6 as a result of scanning the subject S by driving the power source 10, the transmission unit 3, and the reception unit 6, the sequence control unit 13 transfers the raw data to the computer system 200. .

  A couchtop 21 on which the subject S is placed is attached to the bed 20. The top plate 21 is inserted into the cavity (imaging port) of the gradient magnetic field coil 2 with the subject S placed thereon. Normally, the bed 20 is installed so that the longitudinal direction is parallel to the central axis of the static magnetic field magnet 1.

  The computer system 200 performs overall control of the MRI 100. For example, the computer system 200 performs data collection, image reconstruction, and the like by driving the above-described units. The computer system 200 performs temperature measurement and magnetic field measurement of the subject based on the collected data.

[Temperature measurement method]
With reference to FIG. 8, a temperature measurement method using the above characteristics of the phosphorus compound will be described. FIG. 8 is a conceptual diagram schematically showing a temperature measurement method by the computer system 200. The computer system 200 includes, as functional configurations, FFT (Fast Fourier Transform) units 251 and 252, extraction units 253 and 254, calculation units 255 and 256, a difference unit 257, a detection unit 258, and a specification unit 260. Including.

The FFT unit 251 converts the magnetic resonance signal f _H (t) detected from the subject by the application of the high frequency magnetic field for water into a frequency spectrum F _H (ω) indicating the signal intensity for each frequency. That is, the FFT unit 251 converts the time-domain magnetic resonance signal f _H (t) into a frequency spectrum F _H (ω) in the frequency domain. As an example, fast Fourier transform is used for the conversion process.

The FFT unit 252 converts the magnetic resonance signal f _P (t) detected from the subject by applying the high frequency magnetic field for phosphorus into the frequency spectrum F _P (ω). That is, the FFT unit 252 converts the magnetic resonance signal f _P (t) in the time domain into a frequency spectrum F _P (ω) in the frequency domain. As an example, fast Fourier transform is used for the conversion process.

The extraction unit 253 extracts a frequency f _1H having a relatively high signal intensity from the frequency spectrum F _H (ω) and corresponding to the resonance frequency of water. More specifically, the extraction unit 253 selects the maximum signal intensity from a predetermined range of spectrum centered on the resonance frequency of water, and sets the frequency corresponding to the selected signal intensity as the resonance frequency of water. Extracted as the corresponding frequency f _1H .

The extraction unit 254 extracts the frequency f _1P having a relatively high signal intensity from the frequency spectrum F _P (ω) and corresponding to the resonance frequency of the phosphorus compound. More specifically, the extraction unit 254 selects the maximum signal intensity from a spectrum in a predetermined range centered on the resonance frequency of the phosphorus compound, and sets the frequency corresponding to the selected signal intensity to the resonance of the phosphorus compound. Extracted as a frequency f _1P corresponding to the frequency.

The calculation unit 255 calculates the temporal change amount Δf _H (that is, chemical shift) of the resonance frequency of water. For example, calculator 255 calculates the amount of change Delta] f _H by subtracting the frequency f _0H a resonance frequency of the obtained water before the frequency f _IH from the frequency f _IH.

The calculation unit 256 calculates the temporal change amount Δf _P (that is, chemical shift) of the phosphorus compound. For example, calculator 256 calculates the amount of change Delta] f _P by subtracting the frequency f _0P is a resonance frequency of the phosphorus compound obtained before the frequency f _1P from the frequency f _1P.

The frequency f _0H and the frequency f _0P are detected at the same timing or almost the same timing. Alternatively, the frequency f _0H and the frequency f _0P may be set in advance. The frequency f _1H and the frequency f _1P are detected at the same timing or almost the same timing.

Here, the calculation process by the calculation unit 256 will be described in more detail with reference to FIG. FIG. 9 is a diagram showing the frequency spectrum F _P (ω) as a graph 64. The horizontal axis of the graph 64 indicates chemical shift. The vertical axis of the graph 64 indicates the intensity of the magnetic resonance signal.

The horizontal axis of the graph 64 indicates a chemical shift based on the resonance frequency of the phosphorus compound at a predetermined timing in the past. That is, the deviation from 0 ppm corresponds to the chemical shift of the phosphorus compound. The calculation unit 256 selects the maximum signal intensity from a spectrum in a predetermined range (for example, ± 5 ppm) centered at 0 ppm. In the example of FIG. 9, the maximum spectrum 64A is selected. Calculating unit 256, the value of chemical shift corresponding to the maximum spectral 64A and variation Delta] f _P.

Referring to FIG. 8 again, the difference unit 257 calculates a change amount Δf _{H−P as} a difference between Δf _H calculated by the calculation unit 255 and Δf _P calculated by the calculation unit 256. As described above, the resonance frequency of water depends on both temperature and magnetic field. As shown in the above experimental results, the resonance frequency of the phosphorus compound does not depend on the temperature but depends on the magnetic field. Therefore, if the amount of change in the resonance frequency of water is focused on the basis of the amount of change in the resonance frequency of the phosphorus compound, the influence of the magnetic field change can be excluded. That is, the change amount Δf _H−P indicates the change amount of the resonance frequency caused only by the temperature change.

The detection unit 258 detects a temperature change according to the change amount Δf _H−P using a correlation between the change amount of the resonance frequency of water and the temperature. It is known that the resonance frequency of water changes by about 0.01 ppm (more specifically, 0.0104 ppm) with a change of 1 ° C. Detector 258, a variation Delta] f _H-P divided by the correlation value "0.01 ppm / ° C." and detects the division result as a change in temperature of the object.

The specifying unit 260 specifies the position of the subject from which the resonance frequency f _H (t) has been emitted. More specifically, the gradient magnetic field coil 2 (see FIG. 6) generates the slice selection gradient magnetic field Gs, the phase encoding gradient magnetic field Ge, and the readout gradient magnetic field Gr, as described above. The specifying unit 260 encodes components indicating positions in the PE direction, the RO direction, and the SE direction in the k space by the slice selection gradient magnetic field Gs, the phase encoding gradient magnetic field Ge, and the readout gradient magnetic field Gr. The specifying unit 260 specifies the position of the subject from which the resonance frequency f _H (t) is emitted based on the encoding result. The position information is indicated by, for example, three-dimensional coordinates (x, y, z).

  The identifying unit 260 can identify the resonance frequency of water and the phosphorus compound for each unit region in the subject (for example, in the brain). Thereby, the detection unit 258 can detect a temperature change for each unit region in the subject.

[Experimental result]
With reference to FIG. 10, the temperature measurement result by the temperature measurement method according to the present embodiment will be described. FIG. 10 is a diagram illustrating a temperature measurement result obtained by this temperature measurement method.

  FIG. 10 (A) shows a comparison result between the temperature measurement result by this temperature measurement method and the temperature measurement result by the optical fiber thermometer. The horizontal axis of the graph 63 represents a change with time. The vertical axis of the graph 63 indicates the temperature change of the inorganic phosphoric acid aqueous solution with respect to the time “0”. The temperature change 65 is a result of measuring the temperature of the inorganic phosphoric acid aqueous solution with an optical fiber thermometer. The temperature change 67 is a result of measuring the temperature of the inorganic phosphoric acid aqueous solution by this temperature measurement method.

  As shown in the graph 63, the temperature change 65 detected by the optical fiber thermometer and the temperature change 67 detected by this temperature measurement method show the same tendency. Although there is a slight difference between the temperature changes 65 and 67, it can be detected that at least a relative temperature change has occurred by using this temperature measurement method. If the correlation value (“0.01 ppm / ° C.” described above) used at the time of temperature calculation is optimized for this temperature measurement process, the temperature detection accuracy can be further improved. The result of graph 63 indicates that the above-described characteristics of the phosphorus compound can be applied to the temperature measurement process.

  FIG. 10B shows a temperature measurement method using organophosphoric acid as a reference material and a temperature measurement method using NAA as a reference material. The horizontal axis of the graph 71 indicates a change with time. The vertical axis of the graph 71 indicates the temperature change of the aqueous solution with respect to time “0”. The aqueous solution contains organic phosphoric acid and NAA. The temperature change 73 is a temperature measurement result using organophosphoric acid as a reference substance. The temperature change 75 is a temperature measurement result using NAA as a reference material.

  As shown in the graph 71, the temperature change 73 and the temperature change 75 show the same tendency. The results in graph 71 show that organophosphoric acid can serve as a reference material instead of NAA.

[Output mode of temperature measurement result]
With reference to FIG. 11, an example of the output mode of the temperature measurement result by this temperature measurement process is demonstrated. FIG. 11 is a diagram showing the temperature distribution in the brain detected by this temperature measurement method.

  The temperature measurement result is displayed on, for example, the display unit 205 provided in the computer system 200 (see FIG. 6). As an example, the display 205 displays temperature distributions 220A and 220B in the brain measured at different timings.

  For example, the temperature distributions 220A and 220B are indicated by colors associated with each temperature. For example, a warm color (for example, red) is used as the temperature is high, and a cold color (for example, blue) is used as the temperature is low. By displaying the temperature distributions 220A and 220B side by side, temporal temperature changes in the brain can be understood at a glance.

  In addition, an index image 222 is displayed on the display unit 205. The index image 222 shows the correspondence between temperature and color. The diagnostician can understand the temperature in the brain at a glance by comparing the color shown in the index image 222 with the temperature distributions 220A and 220B.

  Although FIG. 11 shows an example in which the temperature distributions 220A and 220B are displayed side by side, only one of the temperature distributions 220A and 220B may be displayed. In this case, the diagnostician can understand the spatial temperature change in the brain at a glance.

  In FIG. 11, the temperature distributions 220A and 220B obtained at different timings are displayed side by side, but the temperature distributions of different regions in the brain may be displayed side by side. This makes it easier for the diagnostician to compare the temperature distribution for each location in the brain.

  Further, in FIG. 11, the absolute temperature in the brain is displayed as the detection result, but the relative temperature in the brain may be displayed as the detection result. For example, the diagnostician instructs a specific position on the temperature distributions 220A and 220B by a touch operation or the like. The computer system 200 calculates the relative temperature in the brain with reference to the designated position, and updates the display of the temperature distributions 220A and 220B according to the calculation result. As an example, a warm color (for example, red) is displayed for a portion whose temperature is higher than the designated position. For a portion whose temperature is lower than the designated position, a cool color (for example, blue) is displayed. At this time, the correspondence between the temperature and the color shown in the index image 222 is also updated.

[Control structure of computer system 200]
A control structure of computer system 200 according to the first embodiment will be described with reference to FIG. FIG. 12 is a flowchart showing a part of processing executed by computer system 200 according to the first embodiment. The processing in FIG. 12 is realized by a CPU (Central Processing Unit) 202 of the computer system 200 executing a temperature measurement program. In other aspects, some or all of the processing may be performed by circuit elements or other hardware.

  In step S20, the CPU 202 sends a control signal for applying a high-frequency magnetic field including the resonance frequency of the phosphorus compound (that is, a high-frequency magnetic field for phosphorus) to the subject to the transmission unit 3 (see FIG. 6). Thereby, the high frequency magnetic field for phosphorus is applied to the subject.

  In step S <b> 22, the CPU 202 receives a magnetic resonance signal emitted from the subject due to application of the high frequency magnetic field for phosphorus. As the above-described FFT unit 252 (see FIG. 8), the CPU 202 converts the received magnetic resonance signal in the time domain into a frequency spectrum in the frequency domain.

  In step S24, the CPU 202 extracts a frequency corresponding to the resonance frequency of the phosphorous compound from the frequency spectrum as the above-described extraction unit 254 (see FIG. 8). The CPU 202 calculates the difference between the resonance frequency of the phosphorus compound obtained in the past and the current resonance frequency of the phosphorus compound as the calculation unit 256 (see FIG. 8). This difference corresponds to the chemical shift of the resonance frequency of the phosphorus compound.

  In step S30, the CPU 202 sends a control signal for applying a high-frequency magnetic field including the resonance frequency of water (that is, a high-frequency magnetic field for water) to the subject to the transmission unit 3 (see FIG. 6). Thereby, the high frequency magnetic field for water is applied to the subject.

  In step S <b> 32, the CPU 202 receives a magnetic resonance signal emitted from the subject by applying the high frequency magnetic field for water. As the above-described FFT unit 251 (see FIG. 8), the CPU 202 converts the received time-domain magnetic resonance signal into a frequency spectrum in the frequency domain.

  In step S <b> 34, the CPU 202 extracts a frequency corresponding to the resonance frequency of water from the frequency spectrum as the above-described extraction unit 253 (see FIG. 8). CPU202 calculates the difference between the resonance frequency of the water obtained in the past, and the resonance frequency of the present water as the above-mentioned calculation part 255 (refer FIG. 8). This difference corresponds to a chemical shift in the resonance frequency of water.

  In step S40, the CPU 202 calculates the chemical shift of the phosphorus compound calculated in step S24 from the chemical shift of water calculated in step S34 as the above-described difference unit 257 (see FIG. 8).

  In step S50, the CPU 202 uses a correlation (for example, “0.01 ppm / ° C.”) between the amount of change in the resonance frequency of water and the temperature as the above-described detection unit 258 (see FIG. 8). A temperature change corresponding to the difference calculated in step S40 is detected. Typically, the CPU 202 divides the difference by the correlation coefficient “0.01 ppm / ° C.”.

  In step S60, CPU 202 determines whether or not to end the temperature measurement process according to the present embodiment. For example, the CPU 202 ends the temperature measurement process when the temperature measurement process for all the areas to be inspected is completed. When CPU 202 determines that the temperature measurement process for all the areas to be inspected has been completed (YES in step S60), CPU 202 determines to end this temperature measurement process. If not (NO in step S60), CPU 202 returns control to step S20.

  The order of applying the high frequency magnetic field for water and the high frequency magnetic field for phosphorus is arbitrary. That is, as shown in FIG. 12, the high frequency magnetic field for phosphorus may be applied after the high frequency magnetic field for phosphorus is applied, or after the high frequency magnetic field for water is applied as shown in FIG. A high frequency magnetic field for phosphorus may be applied.

[Hardware Configuration of Computer System 200]
An example of the hardware configuration of computer system 200 according to the first embodiment will be described with reference to FIG. FIG. 13 is a block diagram illustrating a main hardware configuration of the computer system 200. As shown in FIG. 13, the computer system 200 includes a ROM (Read Only Memory) 201, a CPU 202, a RAM (Random Access Memory) 203, a network I / F (interface) 204, a display unit 205, and a storage. Device 210.

  The ROM 201 stores an operating system (OS), a control program executed by the computer system 200, and the like. The CPU 202 controls the operation of the computer system 200 by executing various programs such as an operating system and a control program for the computer system 200. The RAM 203 functions as a working memory and temporarily stores various data necessary for program execution.

  The network I / F 204 transmits / receives data to / from other communication devices via an antenna (not shown). Other communication devices include, for example, a server and other devices having communication functions. The computer system 200 may be configured to download a program for realizing various processes according to the present embodiment via an antenna.

  The display unit 205 includes, for example, a liquid crystal display, an organic EL (Electro Luminescence) display, or other display devices. The display unit 205 may be configured as a touch panel in combination with a touch sensor (not shown). As a result, the diagnostician can perform operations on the MRI 100 on the touch panel.

  The storage device 210 is a storage medium such as a hard disk or an external storage device. As an example, the storage device 210 holds a temperature measurement program 212 for realizing various processes according to the present embodiment.

  The temperature measurement program 212 may be provided by being incorporated in a part of an arbitrary program, not as a single program. In this case, temperature measurement processing according to the present embodiment is realized in cooperation with an arbitrary program. Even such a program that does not include some modules does not depart from the spirit of the computer system 200 according to the present embodiment. Furthermore, part or all of the functions provided by temperature measurement program 212 according to the present embodiment may be realized by dedicated hardware. Furthermore, the computer system 200 and the server may cooperate to realize the temperature measurement process according to the present embodiment. Furthermore, the computer system 200 may be configured in a so-called cloud service form in which at least one server realizes the temperature measurement process according to the present embodiment.

[Brief Summary]
Through the above-described experiment, the inventors have found that the resonance frequency of the phosphorus compound is almost constant in an environment where the temperature changes. The inventors have also found that the resonance frequency of a phosphorus compound changes in the same manner as NAA in an environment where the magnetic field changes. On the other hand, the resonance frequency of water is susceptible to both temperature and magnetic field changes. Therefore, if the amount of change in the resonance frequency of water is focused on the basis of the amount of change in the resonance frequency of the phosphorus compound, the influence of the magnetic field change can be excluded.

  Based on such a principle, the temperature measurement method according to the present embodiment calculates the difference between the amount of change in the resonance frequency of water and the amount of change in the resonance frequency of the phosphorus compound. And the said temperature measurement method detects the temperature change according to the said difference using the correlation between the variation | change_quantity of the resonance frequency of water, and temperature. Accordingly, even if the NAA is not present in the subject, the temperature can be accurately measured if the phosphorus compound is present.

<Second Embodiment>
[Overview]
In the first embodiment, the newly discovered characteristics of the phosphorus compound are applied to the temperature measurement process. On the other hand, in the second embodiment, the characteristic of the phosphorus compound is applied to the magnetic field measurement process.

  As described above, the resonance frequency of the phosphorus compound changes according to the change of the magnetic field. On the other hand, the resonance frequency of the phosphorus compound is almost constant without depending on the temperature. Therefore, the amount of change in the resonance frequency of the phosphorus compound can be an index indicating the strength of the magnetic field. In particular, in an environment where the temperature changes, the amount of change in the resonance frequency of the phosphorus compound can be an effective index. The magnetic field measurement method according to the second embodiment measures the amount of change in the magnetic field using temperature invariance and magnetic field variability at the resonance frequency of the phosphorus compound.

  This magnetic field measurement method applies the experimental results of FIGS. 4 and 5 and can be applied to a magnetic field measurement apparatus or the like. The magnetic field measurement device is used when checking a magnetic field generation device such as the MRI 100, for example. As an example, the static magnetic field magnet 1 (see FIG. 6) of the MRI 100 is an inspection target. As described above, a superconducting magnet or a permanent magnet is used as the static magnetic field magnet 1. A static magnetic field applied by a superconducting magnet or a permanent magnet deteriorates with time. The magnetic field measurement apparatus can check such deterioration, and can determine whether or not the magnetic field generator is operating normally based on the check result. In the inspection, for example, an aqueous solution containing a phosphorus compound or a phosphorus compound existing in the human body is used. When an aqueous solution containing a phosphorus compound is used, the stability of the static magnetic field magnet 1 can be checked. When a phosphorus compound existing in the human body is used, the performance of the MRI 100 during operation can be evaluated.

  Further, the magnetic field measurement device can be applied to detect that an abnormality has occurred when the magnetic field generation device is used. As a result, it is possible to detect at an early stage that an abnormality has occurred in the magnetic field generation device, and it is possible to quickly take measures such as stopping the magnetic field measurement device.

[Magnetic field measurement method]
With reference to FIG. 14, the magnetic field measurement method using the said characteristic of a phosphorus compound is demonstrated. FIG. 14 is a conceptual diagram schematically showing a magnetic field measurement method by computer system 200 according to the second embodiment. The computer system 200 includes an FFT unit 282, an extraction unit 284, a calculation unit 286, a detection unit 288, and a specifying unit 290 as functional configurations.

The FFT unit 282 converts the magnetic resonance signal f _P (t) detected from the subject by applying the high frequency magnetic field for phosphorus into the frequency spectrum F _P (ω). That is, the FFT unit 282 converts the magnetic resonance signal f _P (t) in the time domain into a frequency spectrum F _P (ω) in the frequency domain. As an example, fast Fourier transform is used for the conversion process.

The extraction unit 284 extracts the frequency f _1P having a relatively high signal intensity from the frequency spectrum F _P (ω) and corresponding to the resonance frequency of the phosphorus compound. More specifically, the extraction unit 284 selects the maximum signal intensity from a spectrum in a predetermined range centering on the resonance frequency of the phosphorus compound, and the frequency corresponding to the selected signal intensity is selected from the phosphorus compound. Extracted as a frequency f _1P corresponding to the resonance frequency.

The calculation unit 286 calculates the temporal change amount Δf _P (that is, chemical shift) of the phosphorus compound. For example, calculator 286 difference frequency _{f 0P} is a resonance frequency of the phosphorus compound obtained before the frequency _{f 1P} from the frequency _{f 1P.}

Detector 288 uses the correlation between the change amount and the magnetic field strength of the resonant frequency of the phosphorus compounds, for detecting the magnetic field change in accordance with the amount of change Delta] f _P.

The specifying unit 290 specifies the position of the subject from which the resonance frequency f _P (t) has been emitted. More specifically, the gradient magnetic field coil 2 (see FIG. 6) generates the slice selection gradient magnetic field Gs, the phase encoding gradient magnetic field Ge, and the readout gradient magnetic field Gr, as described above. The specifying unit 290 encodes components indicating positions in the PE direction, the RO direction, and the SE direction in the k space by the slice selection gradient magnetic field Gs, the phase encoding gradient magnetic field Ge, and the readout gradient magnetic field Gr. The specifying unit 290 specifies the position of the subject from which the resonance frequency f _P (t) is emitted based on the encoding result. The position information is indicated by, for example, three-dimensional coordinates (x, y, z).

  The identifying unit 290 can identify the resonance frequency of the phosphorus compound for each unit region of the subject. Accordingly, the detection unit 288 can detect a magnetic field change for each unit region of the subject.

[Control structure of computer system 200]
With reference to FIG. 15, the control structure of computer system 200 according to the second embodiment will be described. FIG. 15 is a flowchart showing a part of processing executed by computer system 200 according to the second embodiment. The processing in FIG. 15 is realized by the CPU 202 of the computer system 200 executing a temperature measurement program. In other aspects, some or all of the processing may be performed by circuit elements or other hardware.

  In step S70, the CPU 202 sends a control signal for applying a high-frequency magnetic field including the resonance frequency of the phosphorus compound (that is, a high-frequency magnetic field for phosphorus) to the subject to the transmission unit 3 (see FIG. 6). Thereby, the high frequency magnetic field for phosphorus is applied to the subject.

  In step S72, the CPU 202 receives a magnetic resonance signal emitted from the subject due to application of the high-frequency magnetic field for phosphorus. As the above-described FFT unit 282 (see FIG. 14), the CPU 202 converts the received time-domain magnetic resonance signal into a frequency spectrum in the frequency domain.

  In step S74, the CPU 202 extracts a frequency corresponding to the resonance frequency of the phosphorous compound from the frequency spectrum as the above-described extraction unit 284 (see FIG. 14). The CPU 202 calculates a difference between the resonance frequency of the phosphorus compound obtained in the past and the current resonance frequency of the phosphorus compound as the calculation unit 286 (see FIG. 14). This difference corresponds to the chemical shift of the resonance frequency of the phosphorus compound.

  In step S80, the CPU 202 uses the correlation between the change amount of the resonance frequency of the phosphorus compound and the magnetic field intensity as the detection unit 288 (see FIG. 14), and changes the magnetic field according to the change amount of the frequency. Is detected.

  In step S90, CPU 202 determines whether or not to end the magnetic field measurement process according to the present embodiment. For example, the CPU 202 ends the magnetic field measurement process when the magnetic field measurement process for all the areas to be inspected is completed. If the CPU 202 determines that the magnetic field measurement processing has been completed for all the areas to be inspected (YES in step S80), the CPU 202 determines to end the magnetic field measurement processing. If not (NO in step S80), CPU 202 returns control to step S70.

[Brief Summary]
As described above, in the second embodiment, the amount of change in the magnetic field is measured using temperature invariance and magnetic field variability at the resonance frequency of the phosphorus compound. Since the magnetic field measurement method in the second embodiment is not affected by temperature change, it is possible to accurately measure the magnetic field.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Static magnetic field magnet, 2 Gradient magnetic field coil, 3 Transmission part, 4 Transmission coil, 5 Reception coil, 6 Reception part, 10 Power supply, 13 Sequence control part, 20 Bed, 21 Top plate, 51,53,55,57,59 , 61, 63, 64, 71 graph, 64A maximum spectrum, 65, 67, 73, 75 temperature change, 100 MRI, 200 computer system, 201 ROM, 202 CPU, 203 RAM, 204 network I / F, 205 display unit, 210 storage device, 212 temperature measurement program, 220A, 220B temperature distribution, 222 index image, 251, 252, 282 FFT unit, 253, 254, 284 extraction unit, 255, 256, 286 calculation unit, 257 difference unit, 258, 288 Detection unit, 260, 290 identification unit.

Claims (5)

A step of applying a first high frequency magnetic field including a resonance frequency of water to a subject existing in a static magnetic field, and applying a second high frequency magnetic field including a resonance frequency of a phosphorus compound after the application of the first high frequency magnetic field. When,
A magnetic resonance signal detected from the subject by application of the first high-frequency magnetic field is converted into a first frequency spectrum indicating a signal intensity for each frequency, and detected from the subject by application of the second high-frequency magnetic field. Converting the magnetic resonance signal to a second frequency spectrum;
The signal intensity is relatively high from the first frequency spectrum and a first frequency corresponding to the resonance frequency of water is acquired, and the signal intensity is relatively high from the second frequency spectrum. Obtaining a second frequency corresponding to the resonant frequency;
Detecting a temperature change according to a difference between the change amount of the first frequency and the change amount of the second frequency using a correlation between the change amount of the resonance frequency of water and the temperature; A temperature measurement method provided.   The temperature measurement method according to claim 1, wherein the applying step applies the second high-frequency magnetic field continuously after the application of the first high-frequency magnetic field is stopped.   3. The temperature measurement method according to claim 1, wherein the detecting step includes subtracting a change amount of the second frequency from a change amount of the first frequency and detecting a temperature change according to a result of the difference.   The temperature measurement method according to claim 1, wherein the phosphorus compound includes phosphocreatine. Applying a high-frequency magnetic field including a resonance frequency of a phosphorus compound to a subject existing in a static magnetic field;
Converting a magnetic resonance signal detected from the subject by application of the high-frequency magnetic field into a frequency spectrum indicating a signal intensity for each frequency;
Obtaining a frequency corresponding to the resonance frequency of the phosphorus compound, the signal intensity of which is relatively high from the frequency spectrum;
A magnetic field measurement method comprising: detecting a magnetic field change corresponding to the change amount of the frequency using a correlation between the change amount of the resonance frequency of the phosphorus compound and the magnetic field intensity.