Magnetic particle imaging device

Abstract

A static magnetic field generator (2) generates a region without a magnetic field. An alternating magnetic field applicator (3) applies an alternating magnetic field to the region without a magnetic field. A detection coil (1) has an axis parallel to the direction of the alternating magnetic field for detecting the magnetization signal. A measuring device (4) is connected to the detection coil (1). A resonant frequency variable device (5) includes a capacitor connected in parallel with the detection coil (1) to adjust the resonant frequency of the detection coil (1) and the measuring device (4). The capacitance of the capacitor is adjusted in such a way that the resonant frequency of the closed circuit including the detection coil (1), the measuring device (4), and the resonant frequency variable device (5) containing the capacitor is consistent with the frequency of the higher harmonic signal.

Description

Technical Field

[0001] This disclosure relates to a magnetic particle imaging apparatus. Background Technology

[0002] A method is known that uses a living organism as the object and images the distribution of magnetic particles (e.g., superparamagnetic iron oxide) injected into the body being examined (see, for example, Patent Document 1). This method is called "magnetic particle imaging (MPI)".

[0003] The magnetic particle imaging device generates a zero-magnetic-field region by producing magnetic fields facing opposite directions. An alternating magnetic field is applied using a solenoid coil large enough to contain both the object being examined and the receiving coil. Outside this zero-magnetic-field region, if the magnetic flux density of the magnetic particles saturates even with an applied alternating magnetic field, the magnetic flux density remains unchanged. Conversely, within the zero-magnetic-field region, the magnetization effect caused by the static magnetic field is small, resulting in magnetization variations when an alternating magnetic field is applied to the magnetic particles.

[0004] The magnetization variation of magnetic particles in the zero magnetic field region generates a change in the magnetic flux that links the detection coil. This change in magnetic flux depends on the amount of magnetic particles in the zero magnetic field region. The change in the magnetic flux that links the detection coil can be detected as a change in the induced electromotive force generated in the detection coil.

[0005] Using this principle, if the subject is moved within a zero-magnetic-field region or a region within a zero-magnetic-field region while the signal generated in the detection coil is measured, an image reflecting the distribution of magnetic particles can be generated. Furthermore, the device used to achieve the above-mentioned magnetic particle imaging is called a magnetic particle imaging device.

[0006] Regarding the subject being examined for magnetic particle imaging, the amount of magnetic particles contained is often minute. When the amount of magnetic particles is minute, the measured magnetic signal becomes weak. Therefore, a method is known to obtain the odd-order high harmonics of the applied alternating magnetic field by synchronous detection based on the characteristics of the magnetic susceptibility curve of the magnetic particles, and to distinguish them from external noise (see, for example, Patent Document 2).

[0007] Existing technical documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2003-199767

[0009] Patent Document 2: Japanese Patent Application Publication No. 2014-224741 Summary of the Invention

[0010] However, in the method of Patent Document 2, it is necessary to detect the signal associated with the magnetization change of the magnetic particles with a sensitivity sufficiently high than that generated in the same frequency band in the measurement circuit, etc. As the amount of magnetic particles becomes small, the magnitude of the signal associated with the magnetization change of the magnetic particles decreases.

[0011] The purpose of this disclosure is to provide a magnetic particle imaging device that can detect signals associated with magnetization changes of magnetic particles with high sensitivity, even when the amount of magnetic particles in the body being examined is extremely small.

[0012] The magnetic particle imaging apparatus disclosed herein, which images the distribution of magnetic particles within an examined body, comprises: a static magnetic field generator that generates a magnetic field-free region; an alternating magnetic field applicator that applies an alternating magnetic field to the magnetic field-free region; and a magnetization distribution measuring device that measures high-order harmonic signals generated from magnetic particles within the magnetic field-free region. The magnetization distribution measuring device includes: a detection coil having an axis parallel to the direction of the alternating magnetic field for detecting the magnetization signal; a measuring device connected to the detection coil; and a resonant frequency variable, comprising a capacitor connected in parallel with the detection coil for adjusting the resonant frequency of the detection coil and the measuring device. The capacitance is adjusted such that the resonant frequency of the closed circuit including the detection coil, the measuring device, and the resonant frequency variable is consistent with the frequency of the high-order harmonic signal.

[0013] According to this disclosure, the capacitance is adjusted such that the resonant frequency of the closed circuit, including the detection coil, the measuring instrument, and the resonant frequency variable, is consistent with the frequency of the higher harmonic signal. Therefore, even if the amount of magnetic particles in the tested body is extremely small, the signal accompanying the magnetization change of the magnetic particles can be detected with high sensitivity. Attached Figure Description

[0014] Figure 1 This is a diagram showing the structure of the magnetic particle imaging device according to Embodiment 1.

[0015] Figure 2 This is a diagram showing the equivalent circuit of the magnetic particle imaging apparatus of Embodiment 1.

[0016] Figure 3 It is shown in Figure 2 A schematic diagram of the frequency characteristics of the signal voltage detected by measuring device 4 in the equivalent circuit of the magnetic particle imaging device shown.

[0017] Figure 4 This is a diagram showing the structure of a magnetic particle imaging apparatus according to a modified example of Embodiment 1.

[0018] Figure 5 This is a diagram showing the structure of the magnetic particle imaging device according to Embodiment 2.

[0019] Figure 6This is a diagram showing the equivalent circuit of the magnetic particle imaging device according to Embodiment 2.

[0020] Figure 7 It is shown by using Figure 6 The diagram shows the frequency characteristics of the current flowing through the inductance L4 of the transmission coil 41, obtained by analyzing the equivalent circuit shown.

[0021] Figure 8 This is a cross-sectional view of the coil of the magnetic particle imaging device according to Embodiment 3.

[0022] Figure 9 This is a schematic diagram showing the frequency characteristics obtained by the magnetic particle imaging apparatus of Embodiment 3.

[0023] Figure 10 This is a cross-sectional view of the coil of the magnetic particle imaging device according to Embodiment 4.

[0024] Figure 11 This is a schematic diagram showing the frequency characteristics obtained by the magnetic particle imaging apparatus of Embodiment 4.

[0025] (Symbol Explanation)

[0026] 1: Detection coil; 2: Static magnetic field generator; 3: AC magnetic field applicator; 5, 5A: Resonant frequency variable; 6: Subject under inspection; 7: Superconducting coil; 8: Superconductor; 9: Cooler; 10: AC power supply; 11: First detection coil; 12: Second detection coil; 41: Transmission coil; 42: Magnetic measuring instrument; 70: Normal conducting cable; 81: Heater; 90: Magnetization distribution measuring instrument; Ca, Cb, Cc: Capacitor; L: Coil; SW: Switching circuit. Detailed Implementation

[0027] Hereinafter, the embodiments will be described with reference to the accompanying drawings.

[0028] Implementation method 1.

[0029] Figure 1 This is a diagram showing the structure of the magnetic particle imaging apparatus according to Embodiment 1. Figure 1 As shown, the magnetic particle imaging device includes a static magnetic field generator 2, an alternating magnetic field applicator 3, and a magnetization distribution measuring device 90.

[0030] The magnetization distribution measuring device 90 includes a detection coil 1 consisting of a first detection coil 11 and a second detection coil 12, a measuring device 4, and a resonant frequency variable device 5.

[0031] The static magnetic field generator 2 forms a zero magnetic field region in the imaging area where the subject 6 is placed. Specifically, the static magnetic field generator 2 includes two permanent magnets arranged facing each other in such a way that the magnetization directions are opposite. In this embodiment, the case where two opposing permanent magnets are used as the static magnetic field generator 2 is described, but instead of two opposing permanent magnets, two permanent magnets with yokes that are magnetized facing each other, or electromagnets, may also be used.

[0032] In the case of magnetic particle imaging, the measurement position is scanned by changing the relative position of the zero magnetic field region formed by the static magnetic field generator 2 with respect to the subject 6. Among the methods of changing the relative position are methods of moving the zero magnetic field region by applying a static magnetic field from the outside, methods of mechanically moving the static magnetic field generator, or methods of mechanically moving the subject 6.

[0033] An alternating current magnetic field applicator 3 applies an alternating current magnetic field to an imaging area on which the subject 6 is placed. Specifically, the alternating current magnetic field applicator 3 consists of an alternating current power supply 10 and a coil L connected to the alternating current power supply 10. Here, in the drawing, the detection coil 1, which consists of a first detection coil 11 and a second detection coil 12, and the coil L constituting the alternating current magnetic field applicator 3 are depicted unfolded, but the detection coil 1, which consists of the first detection coil 11 and the second detection coil 12, and the coil L constituting the alternating current magnetic field applicator 3 are arranged to overlap coaxially. The direction of the axis of the detection coil 1 is parallel to the direction of the alternating current magnetic field generated by the alternating current magnetic field applicator 3.

[0034] In this embodiment, the detection coil 1 is composed of a first-order differential coil, which is coaxially configured with a first detection coil 11 and a second detection coil 12 with opposite winding directions. By using the first-order differential coil, the induced electromotive force generated by the alternating magnetic field applied by the alternating magnetic field applicator 3 and the magnetic noise of the environment can be removed.

[0035] The object under test 6 is disposed inside the first detection coil 11, and an alternating magnetic field is applied by the alternating magnetic field applicator 3. Based on the alternating magnetic field applied by the applicator 3, the object under test 6 generates a magnetic signal of fundamental frequency f0 and its higher harmonic signals (n×f0) according to its magnetic susceptibility curve. These magnetic signals are measured as voltages by the measuring device 4. In this embodiment, the object under test 6 is a superparamagnetic particle composed of iron oxide magnetic microparticles, so its magnetic susceptibility curve is an odd function. Therefore, among the higher harmonic signals in the object under test 6, the intensity of the odd-order components (n=2m+1; m=0, 1, 2, …) is high. The higher harmonic components, which do not contain the influence of the fundamental frequency f0, have the characteristics of low noise and a high signal-to-noise ratio (SN ratio).

[0036] The resonant frequency variable 5 is composed of a capacitor with electrostatic capacitance. The detection coil 1, consisting of the first detection coil 11 and the second detection coil 12, the measuring device 4, and the resonant frequency variable 5 composed of the capacitor form a closed circuit for measuring the high-order harmonic signals generated from the object under inspection 6. Here, a closed circuit refers to a circuit in an electrical circuit where a switch or similar device is closed, establishing a path for current flow.

[0037] Therefore, when the resonant frequency variable 5 and the detection coil 1 are connected in parallel, the resonant circuit is formed by the combined inductance and combined capacitance of the closed circuit. The resonant frequency of the resonant circuit is determined by the inductance and capacitance of the resonant circuit. For example, when the third harmonic 3f0 is used as the detection signal for magnetic particle imaging, by measuring the inductance and capacitance in the detection coil 1 and the measuring device 4 in the closed circuit, the electrostatic capacitance C of the resonant frequency variable 5 is selected, thereby allowing the third harmonic 3f0 to be adjusted to become the resonant frequency of the closed circuit. As a result, the signal strength of the target high-harmonic signal can be maximized.

[0038] Figure 2 This is a diagram showing the equivalent circuit of the magnetic particle imaging apparatus of Embodiment 1. Figure 2 The equivalent circuit shown is a circuit consisting of a detection coil 1 composed of a first detection coil 11 and a second detection coil 12, an AC magnetic field applicator 3, a measuring device 4, and a resonant frequency variable 5.

[0039] To improve detection sensitivity, the winding density of detection coil 1 needs to be increased. For example, the winding density of detection coil 1 is several hundred turns / mm. Therefore, the parasitic capacitance generated between the windings of detection coil 1 significantly affects the resonant frequency.

[0040] In the first detection coil 11, the parasitic capacitance C1 generated between the windings of the first detection coil 11 is connected in parallel to the resistive component R1 and the inductor L1 of the first detection coil 11, which are connected in series. In the second detection coil 12, the parasitic capacitance C2 generated between the windings of the second detection coil 12 is connected in parallel to the resistive component R2 and the inductor L2 of the second detection coil 12, which are connected in series. The detection coil 1 is configured as a first-order differentiating coil and does not generate a signal from the AC magnetic field applied by the AC magnetic field applicator 3.

[0041] The AC magnetic field applicator 3 (coil L and AC power supply 10) is combined with inductors L1 and L2. Due to the effect of the differential coil, the signals between the AC magnetic field applicator 3 and inductor L1, and between the AC magnetic field applicator 3 and inductor L2, are eliminated. Therefore, the AC magnetic field applicator 3 (coil L and AC power supply 10) is not visible from the detection system. Only the signal of the magnetic particles in inductor L1 is energized, and this signal is obtained.

[0042] Assuming that the magnetization signal from the object under inspection 6 is combined with the inductance L1 of the first detection coil 11 to generate an induced electromotive force, it is explained that... Figure 2 The result obtained by analyzing the equivalent circuit shown.

[0043] Figure 3 It is shown in Figure 2 A schematic diagram of the frequency characteristics of the signal voltage detected by measuring device 4 in the equivalent circuit of the magnetic particle imaging device shown.

[0044] The results are shown by analyzing the frequency characteristics of the voltage applied to the internal resistor R5 of the measuring device 4.

[0045] Figure 3 The dashed line represents the frequency characteristics in the circuit without the resonant frequency variable 5 electrically connected. In the circuit without the resonant frequency variable 5 electrically connected, the resonant frequency exists in the high-frequency band above the 20th harmonic, resulting in low sensitivity in the frequency band of the 3rd harmonic level, which is the target of magnetic particle imaging.

[0046] Figure 3 The solid line represents the analytical result of selecting the electrostatic capacitance C of the resonant frequency variable 5 with a resonant frequency having the third harmonic 3f0. Through the resonant frequency variable 5, the voltage applied to the internal resistance R5 of the measuring device 4 is maximized near the third harmonic 3f0.

[0047] In this way, by selecting the electrostatic capacitance C of the resonant frequency variable 5, the frequency of the high-order harmonic signal required for magnetic particle imaging can be made to match the resonant frequency of the closed circuit including the detection coil 1, the measuring device 4, and the resonant frequency variable 5. This increases the amplitude of the signal detected by the measuring device 4. As a result, even if the amount of magnetic particles in the subject being examined is extremely small, the signal accompanying the magnetization change of the magnetic particles can be detected with high sensitivity.

[0048] Variation 1 of Implementation Method 1.

[0049] When reconstructing an image, obtaining multiple higher harmonic components increases the amount of information available for obtaining spatial resolution and density dependence compared to obtaining only one higher harmonic component. Consider setting up multiple resonant frequency variable circuits 5 selected to resonate with higher harmonics such as the 3rd and 5th.

[0050] Figure 4This is a diagram showing the structure of a magnetic particle imaging apparatus according to a modified embodiment 1. The resonant frequency variable 5A of the magnetic particle imaging apparatus of this modified embodiment includes a plurality of capacitors Ca, Cb, and Cc connected in parallel, and a switching circuit SW that switches the capacitor among the plurality of capacitors Ca, Cb, and Cc connected to the detection coil 1.

[0051] The capacitances of the multiple capacitors Ca, Cb, and Cc are adjusted in such a way that the resonant frequency of the closed circuit, which includes the detection coil 1, the measuring device 4, and one of the multiple capacitors Ca, Cb, and Cc, is consistent with the frequency of one of the multiple higher harmonic signals.

[0052] For example, the capacitance of capacitor Ca is adjusted so that the resonant frequency of the closed circuit including detection coil 1, measuring device 4, and capacitor Ca is consistent with the frequency of the 3rd higher harmonic 3f0. The capacitance of capacitor Cb is adjusted so that the resonant frequency of the closed circuit including detection coil 1, measuring device 4, and capacitor Cb is consistent with the frequency of the 5th higher harmonic 5f0. The capacitance of capacitor Cc is adjusted so that the resonant frequency of the closed circuit including detection coil 1, measuring device 4, and capacitor Cc is consistent with the frequency of the 7th higher harmonic 7f0.

[0053] Implementation method 2.

[0054] Figure 5 This is a diagram showing the structure of the magnetic particle imaging device according to Embodiment 2.

[0055] In this embodiment, the measuring device 4a consists of a transmission coil 41 and a magnetic measuring device 42. In Embodiment 1, the magnetic signal from the object under inspection 6 detected by the first detection coil 11 is transmitted to the measuring device 4 as a voltage signal. On the other hand, in this embodiment, by connecting the transmission coil 41, a closed circuit is formed only by the detection coil 1, the transmission coil 41, and the resonant frequency variable device 5. The magnetic signal generated from the object under inspection 6 propagates within the closed circuit as a current. The transmission coil 41 is energized based on the current of the magnetic signal generated from the object under inspection 6, and the transmission coil 41 excites the magnetic field according to the energizing current.

[0056] The magnetic measuring device 42 detects the magnetic signal generated from the object under inspection 6 by measuring the magnetic field energized by the transmission coil 41. This allows for magnetic particle imaging. The magnetic measuring device 42 can be a SQUID magnetic detection device, a fluxgate sensor, or a MI-effect element.

[0057] In this embodiment, a closed circuit is formed including a detection coil 1, a transmission coil 41, and a resonant frequency variable 5. By selecting the electrostatic capacitance C of the resonant frequency variable 5, the frequency of the high-order harmonic signal required for magnetic particle imaging can be made to match the resonant frequency of the closed circuit including the detection coil 1, the transmission coil 41, and the resonant frequency variable 5.

[0058] Figure 6 This is a diagram showing the equivalent circuit of the magnetic particle imaging device according to Embodiment 2.

[0059] The equivalent circuit includes a detection coil 1 consisting of a first detection coil 11 and a second detection coil 12, a transmission coil 41, and a resonant frequency variable 5.

[0060] Figure 7 It is shown by using Figure 6 The diagram shows the frequency characteristics of the current flowing through the inductance L4 of the transmission coil 41, obtained by analyzing the equivalent circuit shown.

[0061] exist Figure 7 In the diagram, dashed lines represent the frequency characteristics of the results analyzed by the magnetic particle imaging device of Embodiment 1, and solid lines represent the results analyzed by the magnetic particle imaging device of Embodiment 2.

[0062] As in Embodiment 1, in a typical voltage measuring instrument, a high internal resistance (e.g., 10 MΩ used in this analysis) results in a wider half-value width of the resonant peak and a lower peak intensity. On the other hand, in this embodiment, since each peak intensity is dimensionless (1), it is impossible to compare the intensities. However, in this embodiment, by reducing the resistive component on the resonant circuit through the transmission coil 41, it is possible to confirm that the half-value width of the resonant peak is narrower.

[0063] As described above, according to this embodiment, by using the transmission coil 41, the resistive component on the resonant circuit can be reduced, thus narrowing the half-width of the resonant peak. This reduces the frequency band sensitivity around the target higher harmonics, thereby improving the signal-to-noise ratio (S / N) of the signal detected by the magnetic measuring instrument 42.

[0064] Implementation method 3.

[0065] Figure 8This is a cross-sectional view of the superconducting coil 7, which includes the detection coil 1 and the transmission coil 41, constituting the magnetic particle imaging apparatus of Embodiment 3. As explained in Embodiment 2, if the resistance component in the closed circuit comprising the detection coil 1 (composed of the first detection coil 11 and the second detection coil 12), the measuring device 4, and the resonant frequency variable 5 constituting the magnetic particle imaging apparatus can be reduced, the Q value, expressed as resonant peak intensity / peak width, can be improved. Therefore, in this embodiment, the resistance component is reduced by using the superconducting coil 7 as the detection coil 1 and the transmission coil 41, which are the main causes of the resistance component in the closed circuit.

[0066] The superconducting coil 7 has a superconductor 8 and a cooler 9.

[0067] The superconductor 8 is preferably an oxide-based high-temperature superconductor that exhibits superconductivity at liquid nitrogen temperatures above 77 K. The cooler 9 is made of a low-temperature material, such as stainless steel. The superconductor 8 is cooled by immersion in liquid nitrogen within the cooler 9.

[0068] By electrically connecting the inside and outside of the cooler 9 with a normal conductive cable 70, only the winding portions of the detection coil 1 and the transmission coil 41 can be treated as superconductors. As a result, for example, the detection coil 1, the transmission coil 41, and the resonant frequency variable 5 can be connected using a normal conductive cable 70.

[0069] Figure 9 This is a schematic diagram showing the frequency characteristics obtained by the magnetic particle imaging apparatus of Embodiment 3. Figure 9 The solid line represents the way through Figure 6 The analysis results are shown when the inductors L1, L2, and L4 in the equivalent circuit are set as superconducting coil 7, reducing the resistance component to approximately 1 / 300. The analysis results are shown with dashed lines indicating the case where inductors L1, L2, and L4 are normal conductors. In this analysis, it can be confirmed that reducing the resistance component increases the Q (Quality factor) value by more than 30 times.

[0070] In this embodiment, by using a superconducting coil 7 to construct the detection coil 1 and the transmission coil 41, the resistive components of these coils with a large number of turns can be reduced. This reduces the half-width of the resonant peak and increases the peak intensity. As a result, the detection sensitivity of the magnetic particle imaging device is improved.

[0071] In the above embodiment, both the detection coil 1 and the transmission coil 41 are designated as superconducting coils 7, but this is not a limitation. Either the detection coil 1 or the transmission coil 41 can be designated as a superconducting coil 7. Therefore, compared to the case where both the detection coil 1 and the transmission coil 41 are designated as normal conductive coils, the resistance components of these coils can be reduced.

[0072] Implementation method 4.

[0073] Figure 10 This is a cross-sectional view of the superconducting coil 7, which includes the detection coil 1 and the transmission coil 41, in the magnetic particle imaging apparatus of Embodiment 4. Figure 10 As shown, a heater 81 that is thermally connected to the superconducting coil 7 is provided near the superconductor 8 that constitutes the superconducting coil 7.

[0074] Heater 81 converts only the specified portion of the superconducting coil 7 into a normal conductive band by heating only the specified portion.

[0075] For example, heater 81 is composed of multiple systems of nickel-chromium wire, thus allowing the heating area to be controlled by dividing the heating zone. Furthermore, the area where normal conductivity transition is to occur can be controlled by adjusting the heat output of heater 81. By controlling the heating area energized by heater 81, only the heated portion of the superconductor 8 can undergo a normal conductivity transition.

[0076] Therefore, the resistance component of the closed circuit comprising the detection coil 1 (composed of the first detection coil 11 and the second detection coil 12), the measuring device 4, and the resonant frequency variable 5, which constitutes the magnetic particle imaging device, can be varied. As a result, the Q value of the resonant circuit can be adjusted without embedding new components in the circuit.

[0077] Figure 11 This is a schematic diagram showing the frequency characteristics obtained by the magnetic particle imaging apparatus of Embodiment 4.

[0078] Figure 11 The dashed lines and Figure 9 The solid lines in the text are the same. Figure 11 The solid line in the diagram represents the analytical result of the normal conductivity transition occurring in approximately one-third of the superconductor 8 of the superconducting coil 7. By causing a portion of the superconductor 8 to undergo a normal conductivity transition via the heater 81, the resistance in the circuit can be varied. As a result, the sensitivity of the resonant peak and the half-width can be adjusted to accommodate changes in electrical characteristics caused by the insertion of the object under test.

[0079] It should be understood that the embodiments disclosed herein are merely illustrative and not restrictive in all respects. The scope of this disclosure is not limited to the foregoing description but is set forth in the claims and is intended to include all modifications of the same meaning and scope as the claims.

Claims

1. A magnetic particle imaging device, which images the distribution of magnetic particles in the body to be examined, comprising: A static magnetic field generator produces a region without a magnetic field. An alternating magnetic field applicator applies an alternating magnetic field to the region without a magnetic field; as well as A magnetization distribution measuring instrument measures high-order harmonic signals generated by magnetic particles from the magnetic field-free region. The magnetization distribution measuring device includes: The detection coil has an axis parallel to the direction of the alternating magnetic field in order to detect the magnetization signal; The measuring device is connected to the detection coil; and A resonant frequency converter, for adjusting the resonant frequency of the detection coil and the measuring instrument, includes a capacitor connected in parallel with the detection coil. The capacitance of the capacitor is adjusted so that the resonant frequency of the closed circuit, including the detection coil, the measuring device, and the resonant frequency variable, matches the frequency of the higher harmonic signal generated from the magnetic particles in the magnetic field-free region. The measuring device includes: A transmission coil, energized by a current based on a magnetic signal generated from the object being inspected, excites a magnetic field according to the energizing current; and A magnetic measuring instrument measures the magnetic field energized by the transmission coil. The closed circuit includes the detection coil, the transmission coil, and the resonant frequency variable.

2. The magnetic particle imaging device according to claim 1, wherein, The resonant frequency variable includes: The plurality of said capacitors connected in parallel; and A switching circuit switches the capacitor connected to the detection coil among the plurality of capacitors. The capacitance of the plurality of capacitors is adjusted such that the resonant frequency of the closed circuit comprising the detection coil, the measuring device, and one of the plurality of capacitors is consistent with the frequency of one of the plurality of higher harmonic signals.

3. The magnetic particle imaging device according to claim 1, wherein, The detection coil and the transmission coil, or either one of them, are superconducting coils.

4. The magnetic particle imaging device according to claim 3, wherein, The superconducting coil includes a superconductor and a cooler. The detection coil, the transmission coil, and the resonant frequency variable are connected by a normal conductive cable.

5. The magnetic particle imaging device according to claim 3 or 4, wherein, The superconducting coil includes a heater, which is thermally connected to the superconducting coil. The heater converts only a specified portion of the superconducting coil into a normal conductive band by heating only that specified portion.

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