JPH04282132A - Nuclear magnetic resonance device - Google Patents

Abstract

PURPOSE:To extend the visual field without occurring uneven sensitivity at the time of placing the surface coil of unclear magnetic resonance device of vertical magnetic field system like an array. CONSTITUTION:In the nuclear magnetic resonance device of vertical magnetic field system, each surface coil for constituting a surface coil used therefor is placed like an array by overlapping mutually in its sensitivity uniform direction so as to become the minimum mutual coupling to other unit surface coil being adjacent thereto.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is an NMR system that measures nuclear magnetic resonance (hereinafter referred to as "NMR") signals from hydrogen, phosphorus, etc. in a sample and visualizes the density distribution, relaxation time distribution, etc. of nuclei.
The present invention relates to an NMR apparatus, and particularly to an NMR apparatus with an improved surface coil used therein.

0002

[Prior Art] Conventionally, in an NMR apparatus, an analyte (
For example, various types of head coils, abdominal coils, and surface coils that are less affected by the movement of the heart and the like have been used to examine and image a subject surrounding the body part of interest. By the way, the above-mentioned surface coil has higher sensitivity than the above-mentioned head coil and abdominal coil, but the field of view is limited, so when examining a wide area such as the spine, the above-mentioned surface coil is not used. This poses a problem in that it takes a long time to inspect because it has to be moved along the object and imaged several times. For this, for example, JP-A-2-1343
As disclosed in Publication No. 2, a plurality of surface coils used in an NMR apparatus are arranged with appropriate overlap so that each surface coil does not couple with an adjacent surface coil, and each surface coil receives signals. A method has been proposed in which the field of view is substantially widened by synthesizing the NMR signals obtained.

0003

[Problems to be Solved by the Invention] However, the above-mentioned conventional technology does not take into account the sensitivity distribution peculiar to the surface coil used in an NMR apparatus in which the static magnetic field is a vertical magnetic field, and the direction in which the above-mentioned surface coils are arranged is not considered. In some cases, there is a problem in that sensitivity unevenness occurs. The present invention has been made in view of the above circumstances, and its purpose is to solve the above-mentioned problems in the conventional technology, and to improve the uniform sensitivity direction that the surface coil has in one direction, and to It is an object of the present invention to provide an NMR device that can extend the field of view without causing sensitivity unevenness by aligning the arrangement direction of a "surface coil array" formed by the arrangement.

0004

[Means for Solving the Problems] The above object of the present invention is to form a magnetic field along a first direction in a predetermined space, and to excite the nuclear spins of a subject placed in the space with a high-frequency magnetic field. , in a vertical magnetic field type NMR device that detects high-frequency signals due to nuclear spins, each unit surface coil constituting the surface coil for the NMR device has minimal mutual coupling with other unit surface coils adjacent to it. This is achieved by an NMR device characterized by being arranged so as to overlap each other in the direction of uniform sensitivity.

[0005]

[Operation] In the NMR apparatus according to the present invention, the uniform sensitivity direction of the surface coil used in a vertical magnetic field type NMR apparatus in one direction is made to match the direction in which the surface coils are arranged. , the field of view can be expanded while sensitivity remains uniform. That is, since the sensitivity uniformity is not impaired when forming the surface coil array, sensitivity unevenness does not occur.

[0006]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 6 is a configuration diagram of an NMR apparatus showing an embodiment of the present invention. In the figure, 1A is a surface coil array that will be described later, 2 is a subject, 6 is a control device that controls the entire device, 7 is a high-frequency pulse generator, 8 is a transmission amplifier, 9 is a high-frequency probe that will be described later, and 10 is a A receiving amplifier, 11 a phase sensitive detector, and 12 a signal processing device are shown. Further, 13 to 15 are gradient coils, 16 to 18 are gradient coil drivers, 19 is a static magnetic field coil, 20 is a bed for supporting a subject, and 21 is a bed support stand. coil 19
has a constant strength and constant direction (z-axis direction) in its internal space.
This is a high-frequency coil that generates a static magnetic field. On the other hand, the three sets of gradient coils 13, 14, and 15 are driven by gradient coil drivers 16, 17, and 18, respectively, and respond to the strength of the static magnetic field in the z direction and the x and y directions perpendicular thereto. Create a slope that follows. Inside each of these coils is a high frequency probe 9 formed on a cylindrical bobbin.
is installed. Further, a movable bed 20 is mounted on the support base 21, and the subject 2 and the surface coil array 1A arranged on its back are placed on the bed 20 and inserted into the high frequency probe 9 described above. inserted. The output of the high frequency pulse generator 7 is amplified by a transmitting amplifier 8 and given to the high frequency probe 9, where a high frequency magnetic field is generated. The outline of the operation of this device is as follows. The control device 6 controls the timing of driving each gradient coil and generating a high-frequency magnetic field according to a programmed sequence, and excites the nuclear spins of the subject. N of subject 2
The high frequency signal generated by MR is received by the surface coil array 1A, and guided to the signal processing device 12 via the receiving amplifier 10 and the phase sensitive detector 11. The signal processing device 12 processes the sampled received data and displays an NMR image on a display device (not shown).

FIG. 1 is a diagram showing a specific embodiment of the above-mentioned surface coil array 1A. The surface coil array 1A is
Unit surface coil 1 having lengths L and L' length and width respectively
a, 1b (not limited to two) are arranged in one dimension, and the above-mentioned unit surface coils 1a and 1b are overlapped by a distance D that minimizes mutual coupling (for example, If L=170mm and L'=270mm, D will be approximately 12mm). It goes without saying that the overlap distance varies depending on the length and width ratio L'/L of the unit surface coil. By the way, each of the unit surface coils 1a and 1b described above forms a magnetic field in a first direction (X direction) horizontal to the unit surface coils, as shown in FIG. Note that in the X direction, there is an uneven magnetic field distribution in which the magnetic field strength drops halfway, but in the second direction (Y direction), there is a uniform magnetic field distribution. In addition, Figure 2
The contour lines inside indicate the uniformity distribution of sensitivity. Therefore, in this embodiment, as shown in FIG. 1, the unit surface coils 1a, 1b are arranged in a direction (second direction) of uniform sensitivity that the unit surface coils 1a, 1b have so that the mutual coupling is minimized. They are arranged so as to overlap by a distance D to form a surface coil array 1A. That is, the uniform sensitivity direction of the unit surface coils 1a and 1b is made to match the arrangement direction of the surface coil array 1A. Thereby, the surface coil array 1A does not impair the sensitivity uniformity in the second direction (Y direction), so that it is possible to expand the field of view without causing sensitivity unevenness. FIG. 4 shows how the surface coil array 1A is used. The surface coil array 1A, which is arranged one-dimensionally so that the direction of uniform sensitivity and the arrangement direction coincide with each other and mutual coupling is minimized, is insulated and fixed to a region of the subject 2 to be imaged. For example, if you want to image the spine, there are multiple images (two in the figure) from the cervical vertebrae to the lumbar vertebrae.
unit surface coils are arranged one-dimensionally in the body axis direction. As a result, an enlarged uniform magnetic field region is formed in the body axis direction, making it possible to easily perform spine imaging.

FIG. 5 shows a block diagram of a drive circuit for the surface coil array 1A shown in the above embodiment. A preamplifier 3 having an impedance matching circuit is connected to the signal extraction point of each unit surface coil 1a, 1b of the surface coil array 1A, which is arranged one-dimensionally so that the direction of uniform sensitivity matches the arrangement direction. The output terminal of the preamplifier 3 is led to an adder 5 via a selection circuit 4 which can be arbitrarily selected by the user of the device, and is connected to a phase sensitive detector 11. Note that it is also possible to add a phase shifter to the output of the preamplifier 3 to adjust the phase shift, if necessary. In actual examinations, for example, in the case of examining the spine, a wide imaging field of view is required, so the surface coil array 1A is used to perform imaging with a field of view substantially equivalent to two unit surface coils. In this case, unit surface coils 1a, 1
The NMR signals from the subject received at b are, respectively,
It is amplified by the preamplifier 3, the phase shift is adjusted by a phase shifter as necessary, and the signal is passed through the selection circuit 4, and then added to the adder 5.
are combined and sent to the phase sensitive detector 11 to obtain sagittal and coronal tomographic images. Further, by focusing on a specific region from the sagittal and coronal tomographic images described above, imaging of a limited field of view is performed using only the surface coil (for example, the surface coil 1b) corresponding to that region. In this case, NMR signals from specific parts of the subject 2 are received by the unit surface coils 1a and 1b, respectively amplified by the preamplifier 3, and selected after adjusting the phase shift by a phase shifter as necessary. Leads to circuit 4. Of the NMR signals guided to the selection circuit 4, only those received by the above-mentioned unit surface coil 1b are sent to the subsequent stage, and those received by the unit surface coil 1a are blocked. Through these operations, sagittal and coronal tomographic images of a specific region of the subject 2 are obtained. In other words, the imaging field of view can be set arbitrarily. Thereby, it is possible to prevent the aliasing phenomenon caused by having a sensitivity distribution wider than the field of view determined by phase encoding. Note that the number of unit surface coils is not limited to two, and it is possible to use a plurality of unit surface coils or to combine various unit surface coils.

FIG. 3 is a diagram showing a specific example of the structure of a surface coil array 1A according to another embodiment of the present invention. The surface coil array 1A is a one-dimensional arrangement of unit surface coils 1c and 1d whose lengths are L1 and L2 and whose width is L', and the unit surface coils 1c and 1d have minimum mutual coupling. They are overlapped by a distance D such that As described above, the overlap distance D varies depending on the length and width of the unit surface coil. This embodiment differs from the previous embodiments by changing the vertical lengths of the unit surface coils 1c and 1d to L1 and L2, thereby minimizing the overlap distance D
The advantage is that it is possible to increase the sensitivity and reduce the drop in sensitivity in the overlapping region of the unit surface coils 1c and 1d. Also in this embodiment, the surface coil array 1
Since A does not impair the sensitivity uniformity in the second direction (Y direction), it is possible to expand the field of view without causing sensitivity unevenness. In addition, shown in each of the above-mentioned examples,
In addition to the cross method in which high-frequency magnetic field generation and high-frequency signal reception are performed using separate coils, there is a single method in which high-frequency magnetic field generation and high-frequency signal reception are performed using the same coil. Needless to say, it can be used.

0010

As described in detail above, according to the present invention, in a vertical magnetic field type NMR apparatus, the surface coil has a uniform sensitivity direction in one direction, and the "surface coil" formed by arranging the surface coil By matching the arrangement direction of the "array", it is possible to realize an NMR apparatus that can expand the field of view without causing sensitivity unevenness, which is a remarkable effect.

[0011]

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a specific example of the configuration of a surface coil array used in an NMR apparatus representing an embodiment of the present invention.

FIG. 2 is a diagram showing the magnetic field (sensitivity) distribution of the surface coil according to the example.

FIG. 3 is a diagram showing another embodiment of the present invention.

FIG. 4 is a diagram showing how the surface coil array of the example is used.

FIG. 5 is a block diagram of a circuit using the surface coil array of the example.

FIG. 6 is a configuration diagram of an NMR apparatus showing an embodiment of the present invention.

[Explanation of symbols]

1a to 1d Unit surface coil 1A Surface coil array 2 Subject 3 Preamplifier 4 Selection circuit 5 Adder 6 Control device 7 High frequency pulse generator 8 Transmission amplifier 9 High frequency probe 10 Reception amplifier 11 Phase sensitive detector 12 Signal processing device 13 , 14, 15 Gradient coils 16, 17, 18 Gradient coil driver 19 Static magnetic field coil 20 Bed 21 Support stand

Claims (3)

[Claims] 1. Forming a magnetic field along a first direction in a predetermined space, exciting nuclear spins of a subject placed in the space with a high-frequency magnetic field, and detecting a high-frequency signal due to the nuclear spins. In a vertical magnetic field type nuclear magnetic resonance apparatus,
Each unit surface coil constituting the surface coil for the nuclear magnetic resonance apparatus is arranged so as to overlap each other in the direction of uniform sensitivity so as to minimize mutual coupling with other unit surface coils adjacent thereto. A nuclear magnetic resonance device featuring: 2. The nuclear magnetic resonance apparatus according to claim 1, wherein the surface coil is arranged in a plane perpendicular to the direction of the static magnetic field. 3. The nuclear magnetic resonance apparatus according to claim 1, wherein the arrangement direction of the surface coils and the uniform sensitivity direction are arranged so as to coincide with the body axis direction of the subject.