JP3144044B2 - Magnetic field measurement material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field measuring material for measuring the uniformity of a magnetic field.

[0002]

2. Description of the Related Art In recent medical institutions, an image diagnostic apparatus generally called a magnetic resonance image diagnostic apparatus (MRI for short) has been widely used.

[0003] This magnetic resonance imaging diagnostic apparatus utilizes nuclear magnetic resonance (so-called NMR) as a nuclear physics phenomenon, and irradiates an atomic nucleus of a human cell with an electromagnetic wave of a predetermined frequency, and uses a computer to analyze the resonance phenomenon. Atomic level pathological states of cells of the human body can be visually diagnosed by imaging using the image processing system used. The majority of the atoms that constitute human cells are a hydrogen atom (H), a Part nucleus ⁽¹ H) is the same as the very small magnet say clarity, rotating and swinging in the normal state I keep exercising. However, when this is placed in a strong magnetic field, all the nuclei ( ¹ H) are oriented in the direction of the magnetic field.

When an electromagnetic wave (radio wave) is irradiated from the direction perpendicular to the direction of the magnetic field in each state, each of the above nuclei outputs a voltage signal of a specific frequency to notify its position. Therefore, the mechanism is such that an image is formed by catching the voltage signal and a disease is diagnosed.

That is, in the magnetic resonance imaging diagnostic apparatus, since the difference between abnormal cells and normal cells can be grasped at the nuclear level, a portion where a lesion exists can be grasped very clearly. For example, hydrogen nuclei in cancer cells of the human body are generally denser than in normal cells. In addition, the movement of water molecules in the cancer cells is completely different from the movement of water molecules in normal cells. Furthermore, the time required for the hydrogen nuclei to return to the original state after magnetic resonance is different.

Therefore, if such a difference is tracked by the reaction of the nucleus, a clue for diagnosing the disease accurately can be obtained even at a stage where the disease has not yet specifically appeared as a lesion.

[0007]

When a highly uniform magnetic field uniformity is required in a wide space as in the magnetic resonance imaging diagnostic apparatus, the magnetic field uniformity in the target space is reduced by at least 1 /. It is necessary to suppress the deviation amount to 10 ⁶ (1 ppm) or less. To improve the uniformity of the magnetic field, it is necessary to measure a small magnetic field strength or a magnetic field gradient and adjust the current value of the shim coil.For measuring the small magnetic field strength or the magnetic field gradient, an NMR (nuclear magnetic resonance) apparatus is conventionally separately provided. Had to be prepared. The NMR apparatus has a problem that it is heavy and difficult to move, is expensive, and requires calibration for each movement, which is troublesome. Therefore, development of a measuring means that can easily measure a magnetic field strength or a magnetic field gradient is particularly desired.

[0008]

Means for Solving the Problems Claims 1 and 2 of the present application
The described inventions have been made for the purpose of solving the above problems, and have the following configurations.

(1) Constitution of the invention according to claim 1 The magnetic field measuring material according to the invention according to claim 1 is based on a temperature indicating material that changes color at a specific temperature as a base material, and generates magnetic resonance on the surface of the base material. A resonance material layer is provided to measure the magnetic field uniformity from the distribution of the magnetic field strength.

(2) Constitution of the invention according to claim 2 The magnetic field measuring material according to the invention according to claim 2 uses a temperature-indicating material that changes color at a specific temperature as a base material, and generates a magnetic field that causes magnetic resonance on the surface of the base material. Two or more magnetic resonance material layers having different intensities are provided, and the magnetic field uniformity is measured from a magnetic field gradient.

[0011]

The magnetic field measuring materials according to the first and second aspects of the present invention are configured as described above and, as a result, exhibit the following operations corresponding to the respective configurations.

(1) Operation of the magnetic field measuring material according to the first aspect of the invention In the magnetic field measuring material according to the first aspect, a temperature indicating material that changes color at a specific temperature is used as a base material, and the surface of the base material has a magnetic property. A magnetic resonance material layer that generates resonance is provided, and the magnetic field uniformity is measured from the distribution of the magnetic field strength. The base material made of the above-described temperature indicating material generates heat in the magnetic resonance material layer due to absorption of electromagnetic energy accompanying magnetic resonance. Changes color at the corresponding resonance point. Therefore, when the measurement material is placed at the place where uniformity is to be measured and the target magnetic field strength is applied with electromagnetic waves of a frequency at which nuclei and unpaired electrons are resonantly absorbed, only the region having the target magnetic field strength changes color. In addition, it is possible to easily measure a region where the magnetic field is constant. As a result, the magnetic field uniformity can be easily evaluated.

(2) Operation of the magnetic field measuring material according to the second aspect of the invention In the magnetic field measuring material according to the second aspect of the present invention, a temperature indicating material that changes color at a specific temperature is used as a base material, and the surface of the base material has magnetic properties. Providing two or more magnetic resonance material layers having different magnetic field strengths for causing resonance,
The uniformity of the magnetic field is measured from the magnetic field gradient, and when heat is generated due to the absorption of electromagnetic energy accompanying magnetic resonance, the portions corresponding to the resonance magnetic field of each magnetic field resonance material layer are separately colored and shown . Therefore, place the measurement material in the place where you want to check the magnetic field gradient and irradiate it with a specific electromagnetic wave,
The magnetic field gradient can be measured by detecting the magnetic field strength regions of the two types of resonance material layers. As a result, the magnetic field uniformity can be evaluated.

[0014]

Therefore, according to the magnetic field measuring material of the present invention, it is possible to easily evaluate the magnetic field uniformity without using expensive and inconvenient equipment such as NMR.

[0015]

【Example】

(1) First Embodiment FIGS. 1 to 6 show the structure and operation of a magnetic field measuring material according to a first embodiment of the present invention.

First, FIG. 1 shows the structure of the magnetic field measuring material 3A, and reference numeral 1 in the figure denotes a mount-shaped temperature indicating material that changes color to a predetermined color when a specific temperature T.degree. In addition, 2 is mainly composed of a material having a large number of nuclei or unpaired electrons that generate magnetic resonance (nuclear magnetic resonance or electron spin resonance) such as water or fat applied to the surface of the temperature indicator 1 as a base material. The magnetic field measuring material 3A is formed in a thermo emblem structure in which the temperature indicating material 1 and the magnetic resonance material 2 are integrated.

Therefore, the magnetic field measuring material 3A having the above structure
Is placed in a place where the magnetic field uniformity of the tissue selective heating device is to be examined as shown in FIG. 2, for example, and is measured by irradiating an electromagnetic wave of a predetermined frequency as follows.

Incidentally, the tissue selective heating apparatus shown in FIG. 2 employs a heating system based on nuclear magnetic resonance absorption as a heating system.

Therefore, the principle of heating by nuclear magnetic resonance absorption will be described first.

Nuclear magnetic resonance absorption is generally known as a method of analyzing and measuring nuclear magnetic resonance phenomena (NMR). In short, the energy loss accompanying nuclear magnetic resonance, that is, the energy loss that occurs at resonance It means the absorption of electromagnetic waves.

Many atomic nuclei have a spin angular momentum, and this spin angular momentum is also quantized, and the spin angular momentum where the nuclear spin quantum number is I becomes √ {I (I + 1)} · (h / 2π). . Here, the hydrogen nucleus ( ¹ H) is mainly taken up. In this case, the nuclear spin quantum number I is I = １ ／.
Spin angular momentum in a certain direction in space is also quantized.

When no magnetic field is applied, approximately the same number of +1
There are nuclei in the states of / 2 and -1/2, and their energy levels are the same as shown in FIG. However, when the hydrogen nucleus ( ¹ H) is placed in a magnetic field B ₀ having a predetermined strength, the above +1/2 and −1/2 are proportional to the strength of the magnetic field as shown in FIG.
The nucleus in the two states (clockwise and counterclockwise) is ± 1
An energy level difference of 2 μB ₀ is formed between energy levels of / 2 (where μ is a magnetic moment caused by the influence of a magnetic field). Hydrogen nuclei ( ¹ H) when the magnetic field is applied
The spin angular motion component in the magnetic field direction is + ／ (h / 2
π) or-／ (h / 2π).

That is, since the nucleus has a spin angular momentum of ± 1/2 (h / 2π) and therefore has a magnetic moment, it has two different energy levels as described above when a magnetic field is applied. become.

After a certain time has elapsed after the application of the magnetic field as described above, each spin nucleus (nucleus having spin angular momentum) has a low energy level according to the Boltzmann distribution determined based on the following equation. +1/2 spin nuclei (open circles) increase and thermal equilibrium state as shown in Fig. 5
(A state where the speed distribution is constant regardless of time).

Ne / Nb = eXP (−ΔE / KT) N: Number of nuclei ΔE: Energy level difference [J] K: Bolman constant (1,380 / 10 ²³ [J / K]) T: Absolute temperature [K] Next, in the thermal equilibrium state, for example, an electromagnetic wave (radio wave of about several tens of MH) having a frequency ν ₀ corresponding to the energy of 2 μB ₀ is irradiated.

At this time, if the following condition is satisfied, a transition of the energy level surface + 1/2 → −1 / 2 occurs as shown in FIG.

Hν ₀ = 2 μB ₀ where h: Planck's constant (6.626176 / 10 ³⁴ J) ν ₀ : frequency (frequency) of electromagnetic wave This phenomenon is called nuclear magnetic resonance absorption. First, the kinetic energy of the lattice is converted to thermal energy of the molecular system constituting the lattice, and heat is generated. Therefore, the tissue portion constituted by the atoms can be heated by this heat.

In addition, since the nuclear magnetic resonance frequency at this time varies depending on the environment (for example, molecular structure) surrounding the atomic nucleus even for the same nuclide, it is possible to selectively heat a molecule having an arbitrary structure. For example, hydrogen atom ^{1 of} fat
Since the resonance frequency ν ₀ differs by about 3 ppm between H and water hydrogen atom ¹ H, they can be selectively heated.

Here, the calorific value due to the nuclear magnetic resonance absorption will be roughly estimated.

(1) Target example: Target nuclide ... proton ( ¹ H) (2) Target condition: magnetic field strength Bo = 8T Ambient temperature = 37 ° C. First, assuming that the absorption energy per nucleus is ΔE, Δ
E is given by ΔE = 2 μBo = 2.260258 / 10 ²⁵ [J] (where μ = 1.141661 / 10 ²⁶ [JT-1]).

Next, the ground state in 1 mole of hydrogen atom ( ¹ H)
Assuming that the number of nuclei at (+1/2 energy level) is Nb, Nb is Nb = Na / {1+ (Ne + Nb)} = 3.011103 × 10 ²³ (where Na = 6.022045 × 10 ²³ ).

Then, the absorption energy E ₁ per mole of proton is given by E ₁ = ΔE × Nb = 0.0680587 [J].

Therefore, the calorific value Q ₁ per unit time is Q ₁ = E ₁ × Nb / Na / T _1. For example, if T ₁ = 0.5 sec, Q ₁ = 0.0680605 [W] and T ₁ Assuming = 1/10 ⁶ seconds, the calorific value is Q ₁ = 34.0303 [KW].

The above-mentioned T ₁ is called a spin-lattice relaxation time, and is a time constant when energy of electromagnetic waves due to nuclear magnetic resonance absorption is converted into heat energy, and varies depending on an environmental structure surrounding an atomic nucleus. Generally, it is set to about 0.5 seconds, but it can be reduced to about 1/10 ⁶ seconds.

Further, the calorific value Q per kg is as follows: Q = 1000 × Q ₁ × (α / M) [J] α: Number of target nuclei per molecule M: Molecular weight

Next, the tissue selective heating apparatus of FIG. 2 which employs such a principle of nuclear magnetic resonance absorption is configured as follows, for example.

That is, in FIG. 2, reference numeral 6 denotes an electromagnet which can form a magnetic field of an arbitrary magnitude by changing the value i of the applied current. Is used. The electromagnet 6 is incorporated in a sleeve shape in the apparatus main body after performing a sufficient shielding technique.

An electromagnetic wave transmitting antenna 7 for transmitting an electromagnetic wave (radio wave) in a frequency band of, for example, about several tens of MHz toward the center OO 'is provided inside the sleeve-shaped electromagnet 6. ing.

On the other hand, reference numeral 8 denotes an electromagnetic wave generator (oscillator) for generating an electromagnetic wave in the above-mentioned frequency band, and its output terminal is connected to the electromagnetic wave transmitting antenna 7 via an amplifier 9.

On the other hand, reference numeral 3 denotes the above-described magnetic field measuring material, and the magnetic field measuring material 3 is held in a state where the magnetic field measuring material 3 is inserted into the center of the electromagnet 6 and the transmitting antenna 7.

In the above configuration, as described above, the electromagnet 6 is applied to the magnetic field measuring material 3 by, for example, 6 Tesla.
When a magnetic field of about (60 KG) to 8 Tesla (80 KG) is applied, and an electromagnetic wave of, for example, about several tens of MHz is emitted from the electromagnetic wave transmitting antenna 7 and radiated to the magnetic field measuring material 3A in this state, as described above, hνo = 2μBo, the transition between the energy levels of ± 1/2 occurs in the magnetic resonance material 2 by nuclear magnetic resonance absorption, and the energy of the absorbed electromagnetic wave forms the lattice via the energy of the lattice. It is converted into the energy of the molecular system and generates heat. Then, the base material-side temperature indicating material 1 is heated to a predetermined temperature by the heat to change the color.

The degree of discoloration is proportional to the strength of the magnetic field. Therefore, the uniformity of the magnetic field strength can be easily determined and evaluated by looking at the distribution of the degree of discoloration of the entire temperature indicating material 1.

(2) Second Embodiment FIG. 7 shows the structure of a magnetic field measuring material according to a second embodiment of the present invention.

Reference numeral 1 in the drawing denotes a mount-shaped temperature indicating material that changes color to a predetermined color when the temperature reaches a specific temperature T ° C. similar to that of the first embodiment. On the other hand, reference numeral 4 denotes a first magnetic resonance material containing water (H ₂ O) containing a large amount of nuclei and unpaired electrons applied as a first layer on the surface side of the temperature indicator 1 as a base material, 5 is further provided on the surface side of the first magnetic resonance material 4 with a second
The magnetic field measuring material 3B is a second magnetic resonance material mainly composed of fat applied as a layer, and the thermomagnetic material 3B is formed by integrating the temperature indicating material 1 and the first and second magnetic resonance materials 4 and 5 with each other. The structure is formed.

Therefore, the magnetic field measuring material 3B having the above structure
Is placed in a place where the uniformity of the magnetic field is to be checked, such as the tissue selective heating device shown in FIG. 2 described above, and an electromagnetic wave having a predetermined frequency is irradiated similarly to the case of the first embodiment.

Then, as in the case of the first embodiment, due to the magnetic field resonance absorption generated in the first and second magnetic resonance members 4 and 5, the portions where magnetic resonance occurs due to the temperature rise in each of these portions. The color of the magnetic resonance materials 4 and 5 is changed separately due to a difference in the amount of electromagnetic wave absorption.

Therefore, the magnetic field gradient becomes apparent by looking at the two types of discolored areas in the temperature indicator 1, and the uniformity of the magnetic field intensity can be easily evaluated based on the gradient.

In each of the embodiments described above, the heating method of the tissue selective heating apparatus shown in FIG. 2 is of the nuclear magnetic resonance absorption type, but the heating system employs an electron spin resonance absorption type heating system. Needless to say, it may be the one that did.

Electron spin resonance (ESR) absorption means
In general, it is known as an analytical measurement method of electron spin resonance. In short, it means energy loss accompanying electron spin resonance, that is, absorption of electromagnetic waves at resonance.

Electron spin resonance (ESR) is generally classified into (a) paramagnetic resonance, (b) ferromagnetic resonance, and (c) antiferromagnetic resonance according to the magnetism of a sample. When an unpaired electron (an unpaired electron is an electron that does not form an electron pair and is also called an odd electron) in a molecule or ion of a substance, the interaction between the magnetic moment β of the electron and the external magnetic field Bo is caused. By the action, two kinds of energy levels of + βBo and −βBo are generated, and the same NMR spectrum as in the case of nuclear magnetic resonance described above can be obtained. This is called electron spin resonance (ESR). Since the magnetic moment β of the electrons is much larger than the magnetic moment μ of the nucleus in the above-described nuclear magnetic resonance, the absorption wavelength due to the resonance is in the microwave region.

In this method, the energy of the irradiated electromagnetic wave is first converted into the kinetic energy of the lattice and then converted into the thermal energy of the molecular system constituting the lattice, thereby generating heat. Therefore, the tissue portion composed of the molecule can be heated by this heat.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a magnetic field measuring material according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a configuration of a tissue selective heating device used in the first embodiment of the present invention.

FIG. 3 is a spin nucleus arrangement diagram illustrating a heating principle of the tissue selective heating device in a state where a static magnetic field is not applied.

FIG. 4 is an explanatory diagram showing a change in energy level of a spin nucleus and a level difference when a static magnetic field is applied by the tissue selective heating device.

FIG. 5 is an explanatory diagram of a spin nuclear thermal equilibrium state of the tissue selective heating device in a state where the static magnetic field is applied.

FIG. 6 is an explanatory view showing transition of spin nuclei when the heating device is irradiated with electromagnetic waves.

FIG. 7 is a cross-sectional view showing a configuration of a magnetic field measuring material according to a second embodiment of the present invention.

[Explanation of symbols]

1 is a temperature indicating material, 2 is a magnetic resonance material, 3A and 3B are magnetic field measuring materials, 4 is a first magnetic resonance material, and 5 is a second magnetic resonance material.

Claims (2)

(57) [Claims] 1. A magnetic field in which a temperature indicating material that changes color at a specific temperature is used as a base material, a magnetic resonance material layer that generates magnetic resonance is provided on the surface of the base material, and the magnetic field uniformity is measured from a magnetic field intensity distribution. Measurement material. 2. A temperature indicator which changes color at a specific temperature is used as a base material, and two or more magnetic resonance material layers having different magnetic field strengths for generating magnetic resonance are provided on the surface of the base material, and the magnetic field uniformity is determined from the magnetic field gradient. Magnetic field measurement material to be measured.