JPH067528B2 - Magnet device for magnetic resonance imaging - Google Patents

Description

The present invention relates to a magnetic device for a magnetic resonance imaging device (MRI device), and more particularly to a magnet device suitable for use in an imaging device using electron spin resonance.

[Prior Art] In an MRI apparatus, it is necessary to apply a static magnetic field and a gradient magnetic field to a measurement target, and a magnetic field gradient coil is arranged in the static magnetic field generated by an iron core magnet or an air core magnet.

[Problems to be Solved by the Invention] When the gradient coil is arranged in the static magnetic field in this way, the space in which the measurement object is arranged is limited, and it becomes difficult to insert a large measurement object. I will end up.

The present invention has been made in view of the above points, and an object of the present invention is to provide a magnet device that can secure a large measurement space with a small coil.

[Means for Solving the Problems] In order to achieve this object, the magnet device of the present invention includes a first Helmholtz coil arranged in the same space as the first Helmholtz coil arranged in a space in which a measurement target is arranged. A second Helmholtz coil arranged orthogonal to the first Helmholtz coil, and four power sources for supplying independent currents to the four coils forming the first and second Helmholtz coils. It has a feature.

[Operation] In the present invention, since the static magnetic field and the gradient magnetic field are simultaneously generated by independently setting the currents supplied to the four coils forming the first and second Helmholtz coils arranged orthogonally, It is possible to secure a large measurement space with a small coil.

An embodiment of the present invention will be described in detail below with reference to the drawings.

[Embodiment] FIG. 1 is a configuration diagram showing an embodiment of the present invention, in which 1 is a measurement space in which a measurement target is placed. 2a,
Reference numeral 2b is a Helmholtz coil that is opposed to each other with the measurement space 1 in between, and generates a magnetic field in the z-axis direction. Helmholtz coils 3a and 3b are arranged orthogonal to the Helmholtz coils 2a and 2d with the measurement space 1 in between, and generate a magnetic field in the y-axis direction. Reference numerals 4 to 7 are power supplies for supplying current to the coils 2a, 2b, 3a, 3b. Reference numeral 8 denotes a microwave resonator arranged in the measurement space, in which a measurement target is housed, the measurement target is irradiated with a microwave magnetic field to cause electron spin resonance, and a resonance signal accompanying the electron spin resonance is illustrated. Not for taking out via a spectrometer.

In the above configuration, when the same current I1 is passed through the coils 2a and 2b in the same direction, a uniform magnetic field in the z-axis direction is formed in the space 1. FIG. 2 (a) shows the intensity distribution of this magnetic field along the z-axis.

From this state, if the exciting current of the coil 2a is slightly decreased to I1−Δa, and the exciting current of the coil 2b is slightly increased to I1 + Δa, the intensity distribution along the z axis becomes the second value.
As shown in FIG. 6B, a gradient magnetic field in the z-axis direction is formed around the center 0 of the space 1.

On the other hand, when an exciting current (-Δb) is applied to the coil 3a and an exciting current (+ Δb) is applied to the coil 3b, the intensity distribution along the y-axis becomes as shown in FIG. A gradient magnetic field is formed in the y-axis direction centered at. Since the gradient magnetic field actually generated is a gradient magnetic field obtained by vector-synthesizing the gradient magnetic field in the z-axis direction and the gradient magnetic field in the y-axis direction, Δa,
By changing the magnitude and polarity of Δb, a magnetic field gradient can be generated in any direction within the yz plane.

When the magnetic field strength is swept by maintaining the gradient by sweeping I1 in the state where the magnetic field gradient is generated in the desired direction in the yz plane, the projected ESR spectrum in the direction perpendicular to the gradient is obtained. Obtained from the spectrometer. Then, by repeating the measurement by systematically changing the direction of the magnetic field gradient (for example, by rotating each by a predetermined angle), projection spectra in multiple directions are obtained, and for a large number of the obtained projection spectra,
Back projection using the same algorithm as X-ray CT,
A two-dimensional image can be obtained by reconstructing the image.

In order to systematically change the direction of the magnetic field gradient with respect to the measurement target, the measurement target may be rotated around the x axis by a predetermined angle. In this case, the magnetic field gradient should be fixed in one direction. Good.

In order to generate a magnetic field gradient in the x-axis direction, if Helmholtz coils 2a, 2b and 3a, 3b are arranged orthogonal to each other across the measurement space 1,
A magnetic field gradient can be generated in the three-axis directions, and three-dimensional imaging becomes possible.

By the way, although the direction of the static magnetic field is fixed to the z-axis direction in the above description, the direction of the static magnetic field can be rotated about the x-axis by the configuration of FIG. That is, if the exciting current I2 is passed in the same direction not only in the coils 2a and 2b but also in the coils 3a and 3b, a static magnetic field is generated also in the y direction, and as a result, a static magnetic field in the z-axis direction is generated by the coils 2a and 2b. By synthesizing, the synthetic static magnetic field can be generated in all directions. The exciting current for the gradient magnetic field may be superimposed on the exciting current for the static magnetic field.

Although the Helmholtz coil having the two-coil structure is used in the above embodiment, it goes without saying that the Helmholtz coil having the four-coil structure may be used.

[Effect] As described in detail above, according to the present invention, since the static magnetic field and the gradient magnetic field are generated by the Helmholtz coil, a larger measurement can be performed as compared with the conventional case in which the dedicated gradient generating coil is arranged in the static magnetic field. It becomes possible to secure a space.

[Brief description of drawings]

FIG. 1 is a block diagram showing the construction of an embodiment of the present invention, and FIG. 2 is a diagram showing a magnetic field strength distribution. 1: Measurement space 2a, 2b, 3a, 3b: Helmholtz coil 4-7: Power supply 8: Microwave resonator

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Claims (2)

[Claims] 1. A first Helmholtz coil arranged across a space in which a measurement target is arranged, a second Helmholtz coil arranged across the same space and orthogonal to the first Helmholtz coil, and the first Helmholtz coil. And a four power source for supplying independent currents to the four coils forming the second Helmholtz coil, a magnet device for a magnetic resonance imaging apparatus. 2. A magnet device for a magnetic resonance imaging apparatus according to claim 1, further comprising a third Helmholtz coil which is orthogonal to each of the first and second Helmholtz coils.