JP2010233665A - Coil, coil device, and magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decrease coil sensitivity at a position relatively near the coil and to increase coil sensitivity at a position away from the coil. <P>SOLUTION: A coil 11 having an outside coil element 21 and an inside coil element 22 is configured. The inside coil element 22 is located inside the outside coil element 22. An end part 21a of the outside coil element 21 and an end part of the inside coil element 22 are connected by a connection part 23. An end part 21b of the outside coil element 21 and an end part of the inside coil element 22 are connected by a connection part 24. The outside coil element 21 and the inside coil element 22 are configured so as to flow current in the opposite direction to each other. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a coil, a coil device, and a magnetic resonance imaging apparatus for collecting magnetic resonance signals from a subject.

  When imaging arterial blood of a subject with a magnetic resonance imaging apparatus, if the fat is rendered with high contrast together with the arterial blood, it may hinder the visual recognition of the blood flow state of the arterial blood. Then, the technique which suppresses fat is known (refer patent document 1).

JP 2008-264501 A

  In Patent Document 1, a fat signal is suppressed using a fat suppression pulse. However, in a region where the magnetic field is not uniform, the fat signal may not be made sufficiently small. In particular, the fat on the body surface of the subject is present at a position closer to the coil than the tissue existing under the fat, so there is a problem that the fat on the body surface of the subject tends to be a high signal. As a method for solving this problem, it is conceivable to lower the coil sensitivity at a position relatively close to the coil and increase the coil sensitivity at a position away from the coil. If such coil sensitivity can be realized, it becomes possible to make fat present at a position close to the coil into a low signal.

  Accordingly, an object of the present invention is to provide a coil having the above coil sensitivity, a coil device having the coil, and a magnetic resonance imaging apparatus.

The coil of the present invention that solves the above problems
An outer coil element;
An inner coil element disposed inside the outer coil element;
A coil having
The outer coil element and the inner coil element are configured such that currents in opposite directions flow.

  In this invention, it has an outer coil element and the inner coil element distribute | arranged inside the outer coil element, and the outer coil element and the inner coil element are comprised so that the electric current of the mutually opposite direction may flow. . By providing the outer coil element and the inner coil element configured as described above, the magnetic flux density generated by the outer coil element cancels most of the magnetic flux density generated by the inner coil element at a position relatively close to the coil. Can do. Therefore, the coil sensitivity can be lowered at a position relatively close to the coil. On the other hand, the magnetic flux density generated by the inner coil element is considerably small at a position relatively far from the coil, but the magnetic flux density generated by the outer coil element remains to some extent, so that the coil sensitivity is increased at a position relatively far from the coil. be able to.

1 is a schematic diagram of a magnetic resonance imaging apparatus 1 of a first embodiment. FIG. 3 is a diagram showing a positional relationship between a subject 7 and a coil device 10. It is a perspective view of the coil apparatus of 1st Embodiment. 2 is a perspective view of a coil 11. FIG. It is the top view and sectional drawing of a coil 11. FIG. 3 is a diagram illustrating the structure of an outer coil element 21. FIG. 4 is a diagram illustrating the structure of an inner coil element 22. It is a figure explaining the structure of the coil element connection parts 23 and 24. FIG. It is explanatory drawing of the direction of the electric current which flows into the coil. It is a figure which shows a simulation result. It is a figure explaining how the coil sensitivity distribution which the coil 11 produces overlaps with the subject 7. FIG. It is a figure which shows the coil 111 of 2nd Embodiment. 3 is a plan view of a coil 111. FIG. It is a figure which shows the coil 112 of 3rd Embodiment. It is a top view of the coil 112 of 3rd Embodiment. It is a figure which shows the coil 113 of a triangular structure. It is the schematic of the magnetic resonance imaging apparatus 100 of 5th Embodiment. FIG. 3 is a diagram showing a positional relationship between a subject 7 and a coil device 30. It is a perspective view of the coil apparatus 30 of 5th Embodiment. 3 is a perspective view showing two coils 11 and 31 housed in a coil housing 12. FIG. It is the perspective view which divided and showed the two coils 11 and 31. FIG. 3 is a plan view of coils 11 and 31. FIG. It is a figure which shows the simulation result of the coil sensitivity of the loop coil 31. FIG. It is a figure explaining how the coil sensitivity distribution which the coils 11 and 31 produce overlaps with respect to the subject. It is a figure which shows the simulation result of the relationship between the space | interval Sx and Sz and the mutual inductance M.

  Hereinafter, although an embodiment of the present invention is described, the present invention is not limited to the following embodiment.

(1) First Embodiment FIG. 1 is a schematic diagram of a magnetic resonance imaging apparatus 1 according to a first embodiment.

Magnetic Resonance Imaging (MRI)
Resonance Imaging) 1) includes a coil assembly 2, a table 3, a coil device 10, a control device 4, an input device 5, and a display device 6.

  The coil assembly 2 includes a bore 2a in which the subject 7 is accommodated, a superconducting coil 2b, a gradient coil 2c, and a transmission coil 2d. The superconducting coil 2b applies a static magnetic field B0, the gradient coil 2c applies a gradient pulse, and the transmission coil 2d transmits an RF pulse.

  The table 3 has a cradle 3a. The cradle 3a is configured to move in the z direction and the -z direction. As the cradle 3a moves in the z direction, the subject 7 is transported to the bore 2a. When the cradle 3a moves in the −z direction, the subject 7 transported to the bore 2a is unloaded from the bore 2a.

  The coil device 10 is attached to the subject 7. An MR (Magnetic Resonance) signal received by the coil device 10 is transmitted to the control device 4.

  The control device 4 has a coil control means 41 and a signal processing means 42.

  The coil control unit 41 controls the gradient coil 2c and the transmission coil 2d so that the pulse sequence is repeatedly executed based on the imaging command input from the input device 5. The signal processing means 42 processes the MR signal from the coil device 10 and reconstructs an image.

  The input device 5 transmits various commands to the control device 4 by the operation of the operator 8.

  The display device 6 displays an image or the like.

  FIG. 2 is a diagram illustrating a positional relationship between the subject 7 and the coil device 10.

  A pad 9 is sandwiched between the subject 7 and the coil device 10. The pad 9 is for adjusting the distance between the subject 7 and the coil device 10. In the first embodiment, by using the coil device 10, the liver 7a of the subject 7 is collected with a high signal, while the subcutaneous fat 7b existing closer to the coil device 10 than the liver 7a is collected with a low signal. Can be collected. In order to explain the reason, first, the structure of the coil device 10 will be described.

  FIG. 3 is a perspective view of the coil device according to the first embodiment.

  The coil device 10 includes a coil 11 and a coil housing 12 that houses the coil 11.

  4 is a perspective view of the coil 11, FIG. 5A is a plan view of the coil 11, and FIG. 5B is a cross-sectional view of the coil 11 in the XY plane of FIG. 5A.

  The coil 11 includes an outer coil element 21, an inner coil element 22, and coil element connection portions 23 and 24. Below, the structure of the outer side coil element 21, the inner side coil element 22, and the coil element connection parts 23 and 24 is demonstrated in order.

  FIG. 6 is a view for explaining the structure of the outer coil element 21.

  6A is a plan view of the coil 11, and FIG. 6B is a cross-sectional view taken along line AA of FIG. 6A. In FIG. 6A, the outer coil element 21 of the coil 11 is indicated by a solid line, and the inner coil element 22 and the coil element connection portions 23 and 24 are indicated by a broken line.

  The outer coil element 21 has two end portions 21a and 21b and element pieces 21c to 21g.

  A predetermined gap length G is provided between the end portions 21a and 21b.

  The element pieces 21c to 21g are connected in a square shape and are formed so as to connect the two end portions 21a and 21b. The width of each element piece 21c-21g is Wo. The element pieces 21c to 21g are configured by a combination of an electronic component such as a capacitor and a conductive wire. However, for convenience of explanation, the element pieces 21c to 21g are shown in a simplified manner in FIG.

  Next, the inner coil element 22 will be described.

  FIG. 7 is a diagram illustrating the structure of the inner coil element 22.

  Fig.7 (a) is a top view of the coil 11, FIG.7 (b) is BB sectional drawing of Fig.7 (a). 7A, the inner coil element 22 of the coil 11 is indicated by a solid line, and the outer coil element 21 and the coil element connection portions 23 and 24 are indicated by broken lines.

  The inner coil element 22 is disposed inside the outer coil element 21. The inner coil element 22 has two end portions 22a and 22b and element pieces 22c to 22g.

  A predetermined gap length G is provided between the end portions 22a and 22b.

  The element pieces 22c to 22g are connected in a square shape and are formed so as to connect the two end portions 22a and 22b. The width of each element piece 22c to 22g is Wi. The element pieces 22c to 22g are configured by a combination of an electronic component such as a capacitor and a conducting wire. However, in FIG. 7, the element pieces 22c to 22g are shown in a simplified manner for convenience of explanation.

  Next, the coil element connection portions 23 and 24 will be described.

  FIG. 8 is a diagram for explaining the structure of the coil element connecting portions 23 and 24.

  In FIG. 8, the coil element connecting portions 23 and 24 of the coil 11 are indicated by solid lines, and the outer coil element 21 and the inner coil element 22 are indicated by broken lines.

  The coil element connection portion 23 extends linearly along the X axis, and connects the end 21 a of the outer coil element 21 and the end 22 a of the inner coil element 22. The coil element connecting portion 24 extends linearly along the X axis, and connects the end 21 b of the outer coil element 21 and the end 22 b of the inner coil element 22. The outer coil element 21 and the inner coil element 22 are electrically connected to each other by coil element connecting portions 23 and 24.

  The coil 11 is configured as described above.

  Next, the direction of the current flowing through the coil 11 configured as described above will be described.

  FIG. 9 is an explanatory diagram of the direction of the current flowing through the coil 11. 9A is a plan view of the coil 11, and FIG. 9B is a cross-sectional view of the coil 11 in FIG. 9A in the XY plane.

  In FIG. 9A, currents flowing through the coil 11 are indicated by currents I1 to I12. The current flowing through the coil 11 flows from the outer coil element 21 into the inner coil element 22 via the coil element connection portion 23, and follows a loop returning from the inner coil element 22 to the outer coil element 21 via the coil element connection portion 24. (Note that currents I1 to I12 are also schematically shown in FIG. 9B). FIG. 9A shows an example in which current flows through the outer coil element 21 counterclockwise. In this case, a current flows clockwise through the inner coil element 22. When a current flows clockwise through the outer coil element 21 (not shown), a current flows counterclockwise through the inner coil element 22. Therefore, it can be seen that the current flowing through the outer coil element 21 and the current flowing through the inner coil element 22 are opposite to each other.

Next, in order to investigate the coil sensitivity of the coil 11, a simulation was performed. The simulation conditions are as follows.
(1) The length of one side of the outer coil element 21 is 200 mm.
(2) Gap length G between end portions 21a and 21b of outer coil element 21 = 10 mm
(3) The length of one side of the inner coil element 22 is 100 mm.
(4) Gap length G = 10 mm between the end portions 22a and 22b of the inner coil element 22
(5) The width Wo (see FIG. 6) of the outer coil element 21 and the width Wi (see FIG. 7) of the inner coil element 22 are infinitely small.

  FIG. 10 is a diagram showing a simulation result.

  FIG. 10 shows a sensitivity map of the coil 11 in the XY plane (see FIG. 10). At a position relatively close to the coil 11, the magnetic flux density generated by the outer coil element 21 cancels the magnetic flux density generated by the inner coil element 22, and as a result, the coil sensitivity is lowered. On the other hand, at a position away from the coil 11, the magnetic flux density generated by the outer coil element 21 becomes a relatively larger value than the magnetic flux density generated by the inner coil element 22, and as a result, the coil sensitivity increases. Referring to FIG. 10, the coil sensitivity is low at a position relatively close to the coil 11 (position about ± 60 mm away from the coil 11), but a position away from the coil 11 (position about ± 120 mm away from the coil 11). ) Shows that the coil sensitivity is high. Further, FIG. 10 also shows that when the sensitivity distribution on the right side of the Y axis of the sensitivity map is compared with the sensitivity distribution on the left side, the sensitivity distribution is almost the same.

  Next, see FIG. 11 for how the coil sensitivity distribution created by the coil 11 overlaps the subject 7 when the coil device 10 of the first embodiment is arranged as shown in FIG. While explaining.

  FIG. 11 is a diagram for explaining how the coil sensitivity distribution created by the coil 11 overlaps the subject 7.

  In FIG. 11, the level of the coil sensitivity distribution created by the coil 11 is schematically represented by broken lines. Referring to FIG. 11, the coil sensitivity distribution of the coil 11 is low for the subcutaneous fat 7b that is relatively close to the coil device 10 and high for the liver 7a that is relatively far from the coil device 10 in the AP direction of the subject 7. ing. Therefore, the MR signal of the liver 7a can be collected with a high signal, while the MR signal of the subcutaneous fat 7b can be collected with a low signal. In the first embodiment, a pad 9 is provided between the coil device 10 and the subject 7. By providing this pad 9, an appropriate interval is maintained between the coil device 10 and the subcutaneous fat 7b, so that a portion with low coil sensitivity can be overlapped with the subcutaneous fat 7b. However, the pad 9 is not necessarily provided depending on the photographing conditions.

  In the coil 11, since the sensitivity distribution on the right side of the Y axis of the sensitivity map and the sensitivity distribution on the left side are substantially the same, the symmetry of the sensitivity distribution can be enhanced, and the coil 11 can be moved with respect to the imaging region. Can be easily aligned to the optimum position.

  The gap length G of the outer coil element 21 may be the same length as the gap length G of the inner coil element 22 or may be a different length.

(2) Second Embodiment Since the magnetic resonance imaging apparatus of the second embodiment has the same configuration as that of the first embodiment except for the coil, in the following description, the coil in the second embodiment is mainly described. Explained.

  FIG. 12 is a diagram illustrating the coil 111 according to the second embodiment. FIG. 12 shows (a) a plan view of the coil 111, (b) a cross-sectional view in the XY plane, (c) a cross-sectional view along AA, and (d) a cross-sectional view along BB.

  The coil 111 according to the second embodiment includes an outer coil element 21, an inner coil element 22, coil element connection portions 23 and 24, and an insulating sheet 25. When the coil 111 of the second embodiment and the coil 11 of the first embodiment are compared, the shape of the outer coil element 21 is different, and the shape of the inner coil element 22 is also different. Hereinafter, the structure of the coil 111 of the second embodiment will be specifically described with reference to FIG. 13 together with FIG.

  FIG. 13 is a plan view of the coil 111. However, in FIG. 13, for convenience of explanation, the insulating sheet 25, a part of the outer coil element 21, a part of the inner coil element 22, and the coil element connection portion 24 are not shown.

  In the coil 111, the element piece 21c of the outer coil element 21 is provided so as to cross the X axis, and the element piece 22c of the inner coil element 22 is also provided so as to cross the X axis.

  The coil element connection portion 23 extends along the X axis, and connects the end portion 21 a of the outer coil element 21 and the end portion 22 a of the inner coil element 22.

Returning to FIG. 12, the description will be continued.
The insulating sheet 25 is provided so as to cover the end 21a of the outer coil element 21 and a part of the element piece 21c (see FIG. 12C). The insulating sheet 25 also covers the end 22a of the inner coil element 22 and a part of the element piece 22c (see FIG. 12D). Furthermore, the insulating sheet 25 also covers the coil element connecting portion 23 (see FIG. 12B).

  On the insulating sheet 25, the other end portion 21b of the outer coil element 21 and a part of the element piece 21g are present (see FIG. 12C). Further, the other end 22b of the inner coil element 22 and a part of the element piece 22g are present on the insulating sheet 25 (see FIG. 12D). Furthermore, the coil element connection part 24 exists on the insulating sheet 25 (refer Fig.12 (a)).

  The coil 111 of the second embodiment is configured as described above.

  In the coil 111 of the second embodiment, a part of the element piece 21g of the outer coil element 21 overlaps the element piece 21c via the insulating sheet 25 (see FIG. 12C), and the inner coil element 22 is overlapped. A part of the element piece 22g overlaps the element piece 22c via the insulating sheet 25 (see FIG. 12D). Even with such a coil 111, a coil sensitivity distribution almost the same as that of the coil 11 of the first embodiment can be obtained, so that MR signals of the liver 7a (see FIG. 11) are collected as high signals, while fat The MR signal 7b (see FIG. 11) can be collected as a low signal.

(3) Third Embodiment Since the magnetic resonance imaging apparatus of the third embodiment has the same configuration as that of the first embodiment except for the coil, in the following description, the coil in the third embodiment is mainly described. Explained.

  FIG. 14 is a diagram illustrating the coil 112 according to the third embodiment. FIG. 14 shows (a) a plan view of the coil 111, (b) a cross-sectional view in the XY plane, (c) a cross-sectional view along AA, and (d) a cross-sectional view along BB.

  The coil 112 according to the third embodiment includes an outer coil element 21, an inner coil element 22, coil element connection portions 23 and 24, and an insulating sheet 25. When the coil 112 of the third embodiment and the coil 11 of the first embodiment are compared, the shape of the outer coil element 21 is different, and the shape of the inner coil element 22 is also different. Hereinafter, the structure of the coil 112 according to the third embodiment will be specifically described with reference to FIG. 15 together with FIG.

  FIG. 15 is a plan view of the coil 112 according to the third embodiment. However, in FIG. 15, for convenience of explanation, the insulating sheet 25, a part of the outer coil element 21, a part of the inner coil element 22, and the coil element connection portion 24 are not shown.

  In the coil 112 of the third embodiment, the end 21a of the outer coil element 21 is located on the X axis, and the end 22a of the inner coil element 22 is also located on the X axis. Moreover, the coil element connection part 23 is also located on the X-axis. The coil element connection portion 23 extends in the X-axis direction, and connects the end portion 21 a of the outer coil element 21 and the end portion 22 a of the inner coil element 22.

Returning to FIG. 14, the description will be continued.
The insulating sheet 25 is provided so as to cover the end portion 21a of the outer coil element 21, the end portion 22a of the inner coil element 22, and the coil element connection portion 23 (see FIG. 14B).

  On the insulating sheet 25, the other end 21b of the outer coil element 21 is present (see FIG. 14C). Further, the other end 22b of the inner coil element 22 is present on the insulating sheet 25 (see FIG. 14D). Further, a coil element connecting portion 24 also exists on the insulating sheet 25 (see FIG. 14A). The two coil element connecting portions 23 and 24 overlap in the Y-axis direction with the insulating sheet 25 interposed therebetween.

  The coil 112 of the third embodiment is configured as described above.

  In the coil 112 of the third embodiment, the end 21b of the outer coil element 21 overlaps the other end 21a via the insulating sheet 25 (see FIG. 14C), and the inner coil element 22 is overlapped. The end 22b of the second end overlaps the other end 22a via the insulating sheet 25 (see FIG. 14D). Even with such a coil 112, the same coil sensitivity as that of the coil 11 of the first embodiment can be obtained. Therefore, even if the coil 112 of the third embodiment is used, the MR of the liver 7a (see FIG. 11) is obtained. The signal can be collected with a high signal, while the MR signal of fat 7b (see FIG. 11) can be collected with a low signal.

(4) Fourth Embodiment In the first to third embodiments, the outer coil element 21 and the inner coil element 22 have a quadrangular structure. However, it does not necessarily have to be a quadrangular structure, and may be a structure having another shape. In the fourth embodiment, a coil having a structure other than a quadrangle will be described.

  FIG. 16 is a diagram showing a coil 113 having a triangular structure.

  The coil 113 includes an outer coil element 21, an inner coil element 22, and coil element connection portions 23 and 24. The outer coil element 21 has two end portions 21a and 21b and three element pieces 21c, 21d and 21e, and the inner coil element 22 has two end portions 22a and 22b and three pieces. Element pieces 22c, 22d, and 22e. In the fourth embodiment, the outer coil element 21 has a triangular structure, and the inner coil element 22 also has a triangular structure. Even with such a coil 113, a coil sensitivity distribution as shown in FIG. 10 is obtained, so that MR signals of the liver 7a (see FIG. 11) are collected as high signals, while fat 7b (see FIG. 11). MR signals can be collected with a low signal.

  In addition to a coil having a triangular structure, a coil having a polygonal structure such as a pentagon or a hexagon, or a coil having a structure such as a circle or an ellipse can be used.

(5) Fifth Embodiment FIG. 17 is a schematic diagram of a magnetic resonance imaging apparatus 100 according to a fifth embodiment.
The magnetic resonance imaging apparatus 100 according to the fifth embodiment includes a coil apparatus 30 having a structure different from that of the coil apparatus 10 according to the first embodiment. The structure other than the coil apparatus 30 is the same as that in the first embodiment. This is the same as the magnetic resonance imaging apparatus 1 of FIG. Therefore, in describing the fifth embodiment, the coil device 30 will be mainly described.

  The coil device 30 is attached to the back of the subject 7.

  FIG. 18 is a diagram illustrating a positional relationship between the subject 7 and the coil device 30.

  A pad 9 is sandwiched between the subject 7 and the coil device 30. The pad 9 is for adjusting the distance between the subject 7 and the coil device 30. In the fifth embodiment, an area including the spinal cord 7d of the subject 7 is imaged using a parallel imaging method that performs phase encoding in the AP direction (front-rear direction). The coil device 30 is a coil suitable for imaging the subject 7 using the parallel imaging method. In order to explain the reason, first, the structure of the coil device 30 will be described.

  FIG. 19 is a perspective view of the coil device 30 according to the fifth embodiment.

  The coil device 30 includes a coil 11, a coil 31, an insulating sheet 26, and a coil housing 12.

  20 is a perspective view showing the two coils 11 and 31 housed in the coil housing 12, and FIG. 21 is a perspective view showing the two coils 11 and 31 separately.

  In FIG. 20 and FIG. 21, the coil 31 is indicated by hatching in order to easily distinguish the coils 11 and 31.

  Since the coil 11 in the fifth embodiment has the same structure as the coil 11 in the first embodiment, the description of the coil 11 is omitted.

  The coil 31 is a square loop coil. An insulating sheet 26 is provided between the coil 31 and the coil 11.

  FIG. 22 is a plan view of the coils 11 and 31.

  The loop coil 31 is located between the outer coil element 21 and the inner coil element 22 of the coil 11. The loop coil 31 has four element pieces 31a, 31b, 31c, and 31d. The four element pieces 31 a to 31 d are provided along the inner coil element 22 of the coil 11. The width of each element piece 31a to 31d is WL. The element pieces 31a to 31d are configured by a combination of an electronic component such as a capacitor and a conductive wire. However, in FIG. 22, the element pieces 31a to 31d are shown in a simplified manner for convenience of explanation.

  The loop coil 31 is configured as described above.

  A predetermined interval Sx is provided in the X-axis direction and a predetermined interval Sz is provided in the Z-axis direction between the loop coil 31 and the inner coil element 22 of the coil 11.

Next, in order to investigate the coil sensitivity of the loop coil 31, a simulation was performed. The simulation conditions are as follows.
(A) The length of one side of the loop coil 31 is 120 mm.
(B) The width WL of the loop coil 31 is infinitely small.

  FIG. 23 is a diagram illustrating a simulation result of the coil sensitivity of the loop coil 31.

  FIG. 23 shows a sensitivity map of the coil 11 in the XY plane (see FIG. 22). FIG. 23 shows that the coil sensitivity is high at a position about ± 60 mm away from the loop coil 31, but the coil sensitivity is low at a position about ± 120 mm away from the loop coil 31.

  Comparing FIG. 23 and FIG. 10, it can be seen that the loop coil 31 has a coil sensitivity characteristic opposite to that of the coil 11 in the Y-axis direction. Accordingly, the two coils 11 and 31 of the coil device 30 of the fifth embodiment have coil sensitivity characteristics opposite to each other with respect to the Y-axis direction. Next, how the coil sensitivity distribution created by the coils 11 and 31 overlaps the subject 7 when the coil device 30 is arranged as shown in FIG. 18 will be described with reference to FIG. .

  FIG. 24 is a diagram for explaining how the coil sensitivity distribution created by the coils 11 and 31 overlaps the subject 7.

  FIG. 24 schematically shows a coil sensitivity distribution created by the coil 11 and a coil sensitivity distribution created by the loop coil 31. The coil sensitivity (high and low) represented by a solid line is a coil sensitivity distribution created by the coil 11, and the coil sensitivity (high and low) represented by a broken line is a coil sensitivity distribution created by the loop coil 31. . Referring to FIG. 24, the coil sensitivity distribution of the coil 11 is low in a region relatively close to the coil device 30 and high in a region relatively distant from the coil device 30 with respect to the AP direction of the subject 7. On the other hand, the coil sensitivity distribution of the loop coil 31 is high in a region relatively close to the coil device 30 and low in a region relatively distant from the coil device 30 in the AP direction. Therefore, the region relatively close to the coil device 30 can be collected with a high signal by the loop coil 31, while the region relatively distant from the coil device 30 is collected with a high signal by the coil 11. be able to. For this reason, when imaging the spinal cord 7d of the subject 7, it is possible to perform imaging by parallel imaging in which phase encoding is performed in the AP direction (Y-axis direction), so that the entire region from the back to the abdomen of the subject 7 can be captured at high speed. You can shoot with

As shown in FIG. 22, predetermined intervals Sx and Sz are provided between the loop coil 31 and the inner coil element 22 of the coil 11 in the X-axis direction and the Z-axis direction. Since the value of the mutual inductance M between the loop coil 31 and the coil 1 differs depending on the values of the distances Sx and Sz, it is necessary to set the values of the distances Sx and Sz so that the mutual inductance M is as close to zero as possible. There is. Therefore, in order to investigate how much the intervals Sx and Sz are set to make the mutual inductance M close to zero, the relationship between the intervals Sx and Sz and the mutual inductance M was examined by simulation. The simulation conditions are as follows.
(1) The length of one side of the outer coil element 21 of the coil 11 is 200 mm.
(2) Gap length G = 10 mm between the end portions 21a and 21b of the outer coil element 21 of the coil 11
(3) The length of one side of the inner coil element 22 of the coil 11 is 100 mm.
(4) Gap length G = 10 mm between the end portions 22a and 22b of the inner coil element 22 of the coil 11
(5) The width Wo of the outer coil element 21 and the width Wi of the inner coil element 22 of the coil 11 are infinitely small. (6) The width WL of the loop coil 31 is infinitely small. (7) The interval Sx in the X-axis direction and the Z-axis The interval Sz in the direction is Sx = Sz

  FIG. 25 is a diagram illustrating a simulation result of the relationship between the intervals Sx and Sz and the mutual inductance M.

  FIG. 25 shows that the mutual inductance M can be made substantially zero by setting the interval Sx = Sz = 15 mm in the simulation conditions (1) to (8). In the above simulation, the interval Sx in the X-axis direction and the interval Sz in the Z-axis direction are Sx = Sz (simulation condition (7)), but the intervals Sx and Sz are not necessarily Sx = Sz. There is no.

  In the fifth embodiment, the coil 11 is used, but other coils such as the coils 112, 112, or 113 of the second to fourth embodiments may be used instead of the coil 11. In the fifth embodiment, the substantially square loop coil 31 is used, but a loop coil of another shape may be used.

  Furthermore, in the fifth embodiment, two coils 11 and 31 are used, but three or more coils may be used.

  In the first to fifth embodiments, the end portions 22a and 22b of the inner coil element 22 are arranged in the Z-axis direction, but are not necessarily arranged in the Z-axis direction and intersect with the Z-axis. You may comprise so that it may rank in a direction. Similarly, the end portions 21a and 21b of the outer coil element 21 may be arranged in a direction intersecting the Z axis.

DESCRIPTION OF SYMBOLS 1,100 MRI apparatus 2 Coil assembly 2a Bore 2b Superconducting coil 2c Gradient coil 2d Transmitting coil 3 Table 4 Control apparatus 5 Input apparatus 6 Display apparatus 7 Subject 7a Liver 7b Fat 7c Spinal cord 8 Operator 9 Pad 10, 30 Coil apparatus 11 , 111, 112, 113 Coil 21 Outer coil elements 21a, 21b, 22a, 22b End portions 21c-21g, 22c-22g, 31a-31d Element piece 22 Inner coil elements 23, 24 Coil element connecting portion 31 Cradle 41 Coil control means 42 Signal processing means

Claims (13)

An outer coil element;
An inner coil element disposed inside the outer coil element;
A coil having
The outer coil element and the inner coil element are configured such that currents that are opposite to each other flow. A first coil element connecting portion for connecting the outer coil element and the inner coil element;
A second coil element connecting portion for connecting the outer coil element and the inner coil element;
The coil according to claim 1, comprising: The outer coil element has a first end and a second end;
The inner coil element has a third end and a fourth end;
The first coil element connection portion connects a first end portion of the outer coil element and a third end portion of the inner coil element,
The coil according to claim 2, wherein the first coil element connection portion connects a second end portion of the outer coil element and a fourth end portion of the inner coil element.   The coil according to claim 3, wherein the first end portion of the outer coil element overlaps the second end portion of the outer coil element via an insulating sheet.   The coil according to claim 3 or 4, wherein the third end portion of the inner coil element overlaps the fourth end portion of the inner coil element via an insulating sheet.   The coil according to any one of claims 3 to 5, wherein the first coil element connection portion overlaps the second coil element connection portion via an insulating sheet. The outer coil element has a first element piece and a second element piece,
The coil according to any one of claims 1 to 6, wherein the first element piece overlaps the second element piece via an insulating sheet. The inner coil element has a third element piece and a fourth element piece,
The coil according to any one of claims 1 to 7, wherein the third element piece overlaps the fourth element piece via an insulating sheet.   The coil apparatus which has a coil as described in any one of Claims 1-8. A coil device having a plurality of coils,
The coil device according to claim 1, wherein a first coil of the plurality of coils is a coil according to claim 1.   The coil device according to claim 10, wherein a second coil of the plurality of coils has a coil sensitivity characteristic different from that of the first coil. The first coil has a low coil sensitivity at a first position, and has a higher coil sensitivity at a second position farther from the first coil than the first position;
The coil device according to claim 11, wherein the second coil has high coil sensitivity at the first position and low coil sensitivity at the second position.   A magnetic resonance imaging apparatus comprising the coil device according to claim 9.