JP4803768B2 - Biomagnetic field measurement method, biomagnetic field enhanced image creation method, and magnetic resonance imaging apparatus - Google Patents

Description

  The present invention relates to a biomagnetic field measurement method, a biomagnetic field emphasized image creation method, and a magnetic resonance imaging apparatus. More specifically, the present invention directly measures a nerve activity of a living body and uses a current source flowing in a direction perpendicular to the surface of the living body. The present invention relates to a biomagnetic field measurement method capable of measuring a biomagnetic field, a biomagnetic field enhanced image creation method using the biomagnetic field measurement method, and a magnetic resonance imaging apparatus.

Conventionally, a brain function detection method using a magnetic resonance imaging method is known (for example, see Patent Document 1).
Also, MEG (Magnetoencephalography) measurement using SQUID is known (for example, see Non-Patent Document 1).
In addition, low magnetic field magnetic resonance imaging apparatuses using SQUIDs are known (see, for example, Non-Patent Documents 1 to 4).

JP 2005-137411 A

Vadim S Zotev et al, “Multi-Channel SQUID System for MEG and Ultra-Low-Field MRI”, Internet <URL: http://arxiv.org/ftp/physics/papers/0611/0611290.pdf> AN Matlashov et al, “SQUIDs for Magnetic Resonance Imaging at Ultra-low Magnetic Field”, PIERS ONLINE, Vol. 5, No. 5, 2009, Internet <URL: http://piers.mit.edu/piersonline/download. php? file = MDkwMzEwMTQwMjEzfFZvbDVObzVQYWdlNDY2dG80NzAucGRm> Michelle Espy et al, “Ultra-low-field MRI for Detection of Liquid Explosives Using SQUIDs”, IEEE / CSC & ESAS EUROPEAN SUPERCONDUCTIVITY NEWS FORUM (ESNF), No.8, April 2009, Internet <URL: http: // ewh .ieee.org / tc / csc / europe / newsforum / pdf / ST114-EspyMetal_MagViz_Final_042009.pdf> Vadim S Zotev et al, “SQUID-based instrumentation for ultra-low-field MRI”, Internet <URL: http://arxiv.org/ftp/arxiv/papers/0705/0705.0661.pdf>

A conventional brain function detection method using magnetic resonance imaging measures changes in blood flow distribution and does not directly measure cranial nerve activity.
On the other hand, the conventional MEG measurement using the SQUID detects the brain magnetic field generated by the current source flowing in the direction along the brain surface, and directly measures the cranial nerve activity. Met. However, the brain magnetic field generated by a current source flowing in a direction perpendicular to the brain surface (radial direction) does not come out in the outer peripheral space of the head, and thus cannot be detected.
In addition, the conventional low-field magnetic resonance imaging apparatus using SQUID has a problem that an image including biomagnetic field information cannot be obtained.

  Accordingly, an object of the present invention is to directly measure a nerve activity of a living body, and uses a biomagnetic field measuring method and a biomagnetic field measuring method capable of measuring a biomagnetic field by a current source flowing in a direction perpendicular to the surface of the living body. An object of the present invention is to provide a biomagnetic field enhanced image creation method and a magnetic resonance imaging apparatus.

In a first aspect, the present invention relates to a first process in which a polarization magnetic field is applied to a living body and the magnetization direction is aligned in the polarization magnetic field direction, and a magnetization field is applied to the living body to change the magnetization direction in the measurement magnetic field direction. A biomagnetic field measuring method comprising two steps and a third step of collecting magnetic resonance data from echo signals generated from the magnetization by performing at least one reversal of the magnetization direction by reversing the polarity of the measurement magnetic field The measurement magnetic field in the second process is set to a low magnetic field that does not prevent the biomagnetic field from affecting the magnetization, and the measurement magnetic field in the third process is set to a size required for observation by the echo signal. A biomagnetic field measurement method characterized by using a high magnetic field is provided.
In the biomagnetic field measurement method according to the first aspect, the measurement magnetic field in the second process is set to a low magnetic field that does not prevent the biomagnetic field from affecting the magnetization. Thereby, in a 2nd process, a Larmor frequency changes according to the strength of a biomagnetic field. And since magnetization exists in a living body, it is also influenced by a biomagnetic field by a current source flowing in a direction perpendicular to the surface of the living body. Next, the measurement magnetic field in the third process is set to a high magnetic field such that the echo signal has a magnitude necessary for observation. Thereby, magnetic resonance data including the influence of the biomagnetic field can be suitably collected. That is, it directly measures the nerve activity of a living body, and can also measure a biomagnetic field by a current source flowing in a direction perpendicular to the surface of the living body.

In a second aspect, the present invention provides the biomagnetic field measurement method according to the first aspect, wherein the measurement magnetic field in the second process is 0.5 μT or less and the measurement magnetic field in the third process is 2 μT or more. A biomagnetic field measurement method is provided.
In the biomagnetic field measurement method according to the second aspect, since the measurement magnetic field in the second process is 0.5 μT or less, it does not prevent the biomagnetic field from affecting the magnetization. Further, since the measurement magnetic field in the third process is set to 2 μT or more, the echo signal has a size necessary for observation.

In a third aspect, the present invention provides the living body magnetic field measuring method according to the first or second aspect, wherein the living body is stimulated so that the living body magnetic field is generated in the second process. A magnetic field measurement method is provided.
In the biomagnetic field measurement method according to the third aspect, the biomagnetic field can be generated in the second process by adjusting the timing of applying the stimulus to the living body and the start timing of the second process.

In a fourth aspect, the present invention provides the biomagnetic field measurement method according to any one of the first to third aspects, wherein a gradient magnetic field is applied in the second process or the third process. A magnetic field measurement method is provided.
In the biomagnetic field measurement method according to the fourth aspect, since position information is given to the echo signal, an image can be created.

In a fifth aspect, the present invention provides the biomagnetic field measurement method according to the fourth aspect, wherein the polarity of the gradient magnetic field is reversed without reversing the polarity of the measurement magnetic field in the third step. A biomagnetic field measurement method is provided.
In the biomagnetic field measurement method according to the fifth aspect, a gradient echo signal can be observed. In the biomagnetic field measurement method according to the first aspect, a spin echo signal can be observed.

In a sixth aspect, the present invention reconstructs a biomagnetic field magnetic image from magnetic resonance data collected by the biomagnetic field measurement method according to the fourth or fifth aspect, and the fourth or fifth aspect. The biomagnetic field image is reconstructed from the magnetic resonance data collected in a state where the biomagnetic field does not affect the magnetization in the second process in the biomagnetic field measurement method using the biomagnetic field, and the biomagnetic field magnetic image and the nonbiological magnetic field magnetic image are Provided is a biomagnetic field enhanced image creating method characterized by creating a differential image, processing the differential image, and synthesizing the processed differential image and a non-biological magnetic field magnetic image to create a biomagnetic field enhanced image.
In the biomagnetic field enhanced image creation method according to the sixth aspect, an image in which the biomagnetic field generation position is clarified can be created.

In a seventh aspect, the present invention provides a polarization magnetic field coil that generates a polarization magnetic field, a measurement magnetic field coil that generates a measurement magnetic field orthogonal to the polarization magnetic field, a gradient magnetic field coil that generates a gradient magnetic field, and magnetic resonance data. A SQUID to be collected, a first process in which the polarization magnetic field is applied to the living body to align the magnetization direction in the polarization magnetic field direction, and a second process in which the measurement magnetic field is applied to the living body and the magnetization direction is changed in the measurement magnetic field direction And a control device for controlling the third process of collecting the magnetic resonance data from the echo signal generated from the magnetization by reversing the direction of the magnetization by reversing the polarity of the measurement magnetic field one or more times. In the low magnetic field magnetic resonance imaging apparatus, the control device sets the measurement magnetic field in the second process to a low magnetic field that does not prevent the biomagnetic field from affecting the magnetization, and the measurement magnetic field in the third process. The provides a magnetic resonance imaging apparatus, characterized in that the echo signal is a high magnetic field such that the size required for the observation.
In the magnetic resonance imaging apparatus according to the seventh aspect, the biomagnetic field measurement method according to the first aspect can be suitably implemented.

In an eighth aspect, the present invention provides the magnetic resonance imaging apparatus according to the seventh aspect, wherein the measurement magnetic field in the second process is 0.5 μT or less and the measurement magnetic field in the third process is 2 μT or more. A magnetic resonance imaging apparatus is provided.
In the magnetic resonance imaging apparatus according to the eighth aspect, the biomagnetic field measurement method according to the second aspect can be suitably implemented.

In a ninth aspect, the present invention provides the magnetic resonance imaging apparatus according to the seventh or the eighth aspect, wherein the control device does not reverse the polarity of the measurement magnetic field in the third process, and the gradient magnetic field is reversed. The magnetic resonance imaging apparatus is characterized by reversing the polarity of the magnetic resonance imaging apparatus.
In the magnetic resonance imaging apparatus according to the ninth aspect, the biomagnetic field measurement method according to the fourth aspect can be suitably implemented.

According to the biomagnetic field measurement method of the present invention, the nerve activity of a living body is directly measured, and the biomagnetic field by a current source flowing in a direction perpendicular to the living body surface can also be measured.
According to the biomagnetic field enhanced image creation method of the present invention, an image in which the biomagnetic field generation position is clarified can be created.
According to the magnetic resonance imaging apparatus of the present invention, the biomagnetic field measurement method of the present invention can be suitably implemented.

1 is a schematic diagram illustrating a magnetic resonance imaging apparatus according to a first embodiment. FIG. 3 is a pulse sequence diagram according to the first embodiment. It is a schematic diagram of a living body magnetic field image, a non-biological magnetic field image, and a difference image. It is a schematic diagram of a biomagnetic field emphasis image. 6 is a pulse sequence diagram according to Embodiment 2. FIG. FIG. 9 is a pulse sequence diagram according to the third embodiment.

  Hereinafter, the present invention will be described in more detail with reference to embodiments shown in the drawings. Note that the present invention is not limited thereby.

Example 1
FIG. 1 is a configuration explanatory diagram illustrating a magnetic resonance imaging apparatus 10 according to the first embodiment.
The magnetic resonance imaging apparatus 10 includes a polarization magnetic field coil 1p that generates a polarization magnetic field Bp, a measurement magnetic field coil 2m that generates a measurement magnetic field Bm orthogonal to the polarization magnetic field Bp, and a gradient magnetic field that generates gradient magnetic fields Gx, Gy, and Gz. The coil 3x, 3y, 3z, SQUID4 which collects magnetic resonance data, the control apparatus 5, and the irritation | stimulation apparatus 6 which gives irritation | stimulation, such as light, a sound, and a tactile sensation, are provided.

  A space between the polarization magnetic field coil 1p and the SQUID 4 is a measurement space, and a living body that generates a biomagnetic field to be measured is placed in the measurement space.

  In the following, it is assumed that cerebral magnetism is the biomagnetic field to be measured. In this case, the head of the living body is placed in the measurement space.

FIG. 2 is a pulse sequence diagram according to the first embodiment.
[First step]
The control device 5 drives the polarization magnetic field coil 1p, applies the polarization magnetic field Bp to the living body, and aligns the direction of magnetization of the living body in the polarization magnetic field direction. The strength of the polarization magnetic field Bp is, for example, 30 mT.
The control device 5 gives a stimulus to the living body from the stimulation device 6 only before the delay time from the stimulation to the generation of the brain magnetic field so that the brain magnetic field is generated during the next second process.

[Second process]
The control device 5 stops driving the polarization magnetic field coil 1p, drives the measurement magnetic field coil 2m, applies the measurement magnetic field Bm to the living body, and changes the magnetization direction of the living body in the direction of the measurement magnetic field. The strength of the measurement magnetic field Bm in the second process is set to a low magnetic field that does not prevent the biomagnetic field from affecting the magnetization, for example, 0.5 μT or less.

[Third process]
The control device 5 drives the measurement magnetic field coil 2m, reverses the polarity of the measurement magnetic field Bm, and reverses the magnetization direction. Further, the gradient magnetic field coils 3x, 3y, 3z are driven for imaging, and gradient magnetic fields Gx, Gy, Gz are applied.
The control device 5 repeatedly reverses the polarity of the measurement magnetic field Bm. As a result, spin echo signals e1, e2, e3,... Are generated.
The intensity of the measurement magnetic field Bm in the third process is set to a high magnetic field such that the echo signals e1, e2, e3,...

  The control device 5 collects magnetic resonance data from the echo signals e1, e2, e3,.

The first echo signal e1 is difficult to observe because it overlaps with the gradient magnetic fields Gy and Gz. For this reason, the collection of magnetic resonance data may be started from the second echo signal e2.
Therefore, it is preferable to reverse the polarity of the measurement magnetic field Bm twice or more, and it is preferable that the measurement magnetic field in the third process is a high magnetic field so that the echo signal e2 has a magnitude necessary for observation.

  The control device 5 repeats the collection of magnetic resonance data by changing the magnitudes of the gradient magnetic fields Gy and Gz.

When the control device 5 has collected magnetic resonance data necessary for image creation, it creates a biological magnetic field image.
FIG. 3A illustrates an example of a magnetic field magnetic field image.

Next, the control device 5 collects magnetic resonance data necessary for image creation with the same pulse sequence as in FIG. 2 except for stopping applying a stimulus to the living body, and creates a non-biological magnetic field image.
FIG. 3B illustrates an in-vivo magnetic field image.

Next, the control device 5 creates a difference image between the living body magnetic field image and the non-biological magnetic field image.
FIG. 3C illustrates a difference image.

Next, the control device 5 performs processing such as coloring on the difference image, and then combines the difference image with the non-biological magnetic field image to create a biomagnetic field emphasized image.
FIG. 4 illustrates a biomagnetic field enhanced image.

According to the magnetic resonance imaging apparatus 10 of the first embodiment, the following effects can be obtained.
(1) The influence of a biomagnetic field can be given to magnetization.
(2) The influence of a biomagnetic field by a current source flowing in a direction perpendicular to the living body surface can also be given to magnetization.
(3) The echo signal can be made as large as necessary for observation.
(4) Neural activity in the living body can be directly measured.
(5) A biomagnetic field enhanced image can be created.

-Example 2-
FIG. 5 is a pulse sequence diagram according to the second embodiment.
[First step]
The control device 5 drives the polarization magnetic field coil 1p, applies the polarization magnetic field Bp to the living body, and aligns the direction of magnetization of the living body in the polarization magnetic field direction.
The control device 5 gives a stimulus to the living body from the stimulation device 6 only before the delay time from the stimulation to the generation of the brain magnetic field so that the brain magnetic field is generated during the next second process.

[Second process]
The control device 5 stops driving the polarization magnetic field coil 1p, drives the measurement magnetic field coil 2m, applies the measurement magnetic field Bm to the living body, and changes the magnetization direction of the living body in the direction of the measurement magnetic field. The strength of the measurement magnetic field Bm in the second process is set to a low magnetic field that does not prevent the biomagnetic field from affecting the magnetization.
The control device 5 drives the gradient magnetic field coils 3x, 3y, 3z for imaging after the generation and termination of the cerebral magnetic field, and applies the gradient magnetic fields Gx, Gy, Gz.

[Third process]
The control device 5 drives the measurement magnetic field coil 2m, reverses the polarity of the measurement magnetic field Bm, and reverses the magnetization direction.
The control device 5 repeatedly reverses the polarity of the measurement magnetic field Bm. As a result, spin echo signals e1, e2, e3,... Are generated.
The strength of the measurement magnetic field Bm in the third process is set to a high magnetic field such that the echo signals e1, e2, e3,...

  The control device 5 collects magnetic resonance data from the echo signals e1, e2, e3,.

  The control device 5 repeats the collection of magnetic resonance data by changing the magnitudes of the gradient magnetic fields Gy and Gz.

  When the control device 5 has collected magnetic resonance data necessary for image creation, it creates a biological magnetic field image.

  Next, the control device 5 collects magnetic resonance data necessary for image creation with the same pulse sequence as in FIG. 5 except for stopping applying the stimulus to the living body, and creates a non-biological magnetic field image.

  Next, the control device 5 creates a difference image between the living body magnetic field image and the non-biological magnetic field image.

  Next, the control device 5 performs processing such as coloring on the difference image, and then combines the difference image with the non-biological magnetic field image to create a biomagnetic field emphasized image.

  According to the magnetic resonance imaging apparatus of the second embodiment, the same effect as the magnetic resonance imaging apparatus 10 of the first embodiment can be obtained.

-Example 3-
FIG. 6 is a pulse sequence diagram according to the third embodiment.
[First step]
The control device 5 drives the polarization magnetic field coil 1p, applies the polarization magnetic field Bp to the living body, and aligns the direction of magnetization of the living body in the polarization magnetic field direction.
The control device 5 gives a stimulus to the living body from the stimulation device 6 only before the delay time from the stimulation to the generation of the brain magnetic field so that the brain magnetic field is generated during the next second process.

[Second process]
The control device 5 stops driving the polarization magnetic field coil 1p, drives the measurement magnetic field coil 2m, applies the measurement magnetic field Bm to the living body, and changes the magnetization direction of the living body in the direction of the measurement magnetic field. The strength of the measurement magnetic field Bm in the second process is set to a low magnetic field that does not prevent the biomagnetic field from affecting the magnetization.

[Third process]
The control device 5 drives the measurement magnetic field coil 2m, reverses the polarity of the measurement magnetic field Bm, and reverses the magnetization direction. Further, the gradient magnetic field coils 3x, 3y, 3z are driven for imaging, and gradient magnetic fields Gx, Gy, Gz are applied.
The control device 5 repeatedly reverses the gradient magnetic field Gx without changing the polarity of the measurement magnetic field Bm. As a result, gradient echo signals e1, e2, e3,... Are generated.
The strength of the measurement magnetic field Bm in the third process is set to a high magnetic field such that the echo signals e1, e2, e3,...

The control device 5 collects magnetic resonance data from the echo signals e1, e2, e3,.
Since the first echo signal e1 is difficult to observe because it overlaps with the gradient magnetic fields Gy and Gz, collection of magnetic resonance data may be started from the second echo signal e2.

  The control device 5 repeats the collection of magnetic resonance data by changing the magnitudes of the gradient magnetic fields Gy and Gz.

  When the control device 5 has collected magnetic resonance data necessary for image creation, it creates a biological magnetic field image.

  Next, the control device 5 collects magnetic resonance data necessary for image creation with the same pulse sequence as in FIG. 6 except for stopping applying a stimulus to the living body, and creates a non-biological magnetic field image.

  Next, the control device 5 creates a difference image between the living body magnetic field image and the non-biological magnetic field image.

  Next, the control device 5 performs processing such as coloring on the difference image, and then combines the difference image with the non-biological magnetic field image to create a biomagnetic field emphasized image.

  According to the magnetic resonance imaging apparatus of the third embodiment, the same effect as the magnetic resonance imaging apparatus 10 of the first embodiment can be obtained.

  The biomagnetic field measurement method, biomagnetic field weighted image creation method, and magnetic resonance imaging apparatus of the present invention can be used, for example, for brain function testing and research.

1p polarization magnetic field coil 2m measurement magnetic field coil 3x, 3y, 3z gradient coil 4 SQUID
5 Control Device 6 Stimulation Device 10 Magnetic Resonance Imaging Device

Claims (9)

A first process of applying a polarization magnetic field to a living body to align the magnetization direction in the polarization magnetic field direction, a second process of applying a measurement magnetic field to the living body and changing the magnetization direction in the measurement magnetic field direction, and the polarity of the measurement magnetic field A biomagnetic field measurement method comprising: a third step of reversing and reversing the direction of the magnetization one or more times and collecting magnetic resonance data from an echo signal generated from the magnetization, wherein the measurement magnetic field in the second step Is a low magnetic field that does not prevent the biomagnetic field from affecting the magnetization, and the measurement magnetic field in the third process is a high magnetic field such that the echo signal has a size required for observation. A biomagnetic field measurement method. The biomagnetic field measurement method according to claim 1, wherein the measurement magnetic field in the second process is 0.5 μT or less, and the measurement magnetic field in the third process is 2 μT or more. The biomagnetic field measurement method according to claim 1 or 2, wherein a stimulus is given to the living body so that the biomagnetic field is generated in the second process. The biomagnetic field measurement method according to any one of claims 1 to 3, wherein a gradient magnetic field is applied in the second process or the third process. 5. The biomagnetic field measurement method according to claim 4, wherein the polarity of the gradient magnetic field is reversed without reversing the polarity of the measurement magnetic field in the third step. The second step in the biomagnetic field measurement method according to the fourth or fifth aspect by reconstructing a biomagnetic field magnetic image from magnetic resonance data collected by the biomagnetic field measurement method according to the fourth or fifth aspect, To reconstruct a non-biological magnetic field image from magnetic resonance data collected in a state where the biomagnetic field does not affect the magnetization, create a difference image between the magnetic field magnetic image and the non-biological magnetic field image, and process the difference image Then, a biomagnetic field enhanced image creation method comprising creating a biomagnetic field enhanced image by synthesizing the processed difference image and the non-biological magnetic field magnetic image. A polarization magnetic field coil for generating a polarization magnetic field, a measurement magnetic field coil for generating a measurement magnetic field orthogonal to the polarization magnetic field, a gradient magnetic field coil for generating a gradient magnetic field, a SQUID for collecting magnetic resonance data, and the polarization magnetic field on a living body To reverse the polarity of the measurement magnetic field, the first process of applying the measurement magnetic field to the living body and changing the magnetization direction to the measurement magnetic field direction by applying the measurement magnetic field to the living body. A low-field magnetic resonance imaging apparatus comprising: a control device that controls a third process of collecting magnetic resonance data from echo signals generated from the magnetization by performing reversal of the magnetization direction at least once; The control device sets the measurement magnetic field in the second process to a low magnetic field that does not prevent the biomagnetic field from affecting the magnetization, and the echo signal is used to observe the measurement magnetic field in the third process. Magnetic resonance imaging apparatus characterized by a high magnetic field such that the main size. The magnetic resonance imaging apparatus according to claim 7, wherein a measurement magnetic field in the second process is 0.5 μT or less and a measurement magnetic field in the third process is 2 μT or more. 9. The magnetic resonance imaging apparatus according to claim 7, wherein the control device reverses the polarity of the gradient magnetic field without reversing the polarity of the measurement magnetic field in the third process. Magnetic resonance imaging apparatus.

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