Dual frequency excitation coil

Abstract

The application relates to the technical field of magnetic resonance imaging, in particular to a dual-frequency excitation coil, which comprises a first birdcage coil, a second birdcage coil, and the resonant frequency of the second birdcage coil is different from that of the first birdcage coil, and the second birdcage coil and the first birdcage coil at least partially overlap in the axial direction.

Description

Technical Field

[0001] This application relates to the field of nuclear magnetic resonance technology, and in particular to a dual-frequency excitation coil. Background Technology

[0002] The human body contains various nuclides, some of which, such as the 1H proton, sodium 23Na, phosphorus 31P, carbon 13C, and fluorine 19F, can generate signals in magnetic resonance imaging (MRI) systems, sometimes even strong enough for imaging. However, in most existing MRI systems, the 1H proton signal is used as the imaging nuclide. This is because the abundance and signal strength of other nuclides (heteronucleates) in the human body are many times lower than those of 1H, resulting in very low signal-to-noise ratios (SNR) in the MRI images, thus limiting their diagnostic and research value.

[0003] However, the signal of nuclides increases with the enhancement of the main magnetic field of the magnetic resonance imaging (MRI). With the promotion and application of ultra-high field strength (7T, 9.4T) MRI systems, imaging of heteronuclei has become possible. Especially from the perspective of human physiological metabolism, protons carry very little physiological information and can provide almost no metabolic information. On the other hand, some non-proton nuclides, such as sodium 23Na and phosphorus 31P, reflect the electrolyte balance concentration inside and outside cells and tissues, and carry richer physiological and metabolic information, making the imaging of heteronuclei highly clinically significant. Based on this, patent document CN118376968 A (referred to as Patent Document 1) discloses a dual-frequency excitation coil, mainly composed of a birdcage coil and an array coil including multiple ring coils. Its advantage is that it is particularly suitable for use in ultra-high field strength (7T, 9.4T) MRI systems. When the coil of Patent Document 1 is applied to relatively low field strength (e.g., 3.0T, 5.0T) MRI systems, its advantages are no longer obvious. Summary of the Invention

[0004] To solve at least one of the above-mentioned technical problems, this application provides a dual-frequency excitation coil.

[0005] The dual-frequency excitation coil proposed in this application includes:

[0006] The first birdcage coil includes two first end rings spaced apart from each other in the axial direction and a plurality of first legs connecting the two first end rings and spaced apart from each other in the circumferential direction around the axial direction;

[0007] The second birdcage coil includes two second end rings spaced apart from each other in the axial direction and a plurality of second legs connecting the two second end rings and spaced apart from each other in the circumferential direction;

[0008] The resonant frequency of the second birdcage coil is different from that of the first birdcage coil, and the second birdcage coil and the first birdcage coil at least partially overlap in the axial direction.

[0009] In some possible implementations, in the axial direction, the two first end rings are located between the two second end rings, and the length of the second leg is longer than that of the first leg.

[0010] In some possible implementations, the first birdcage coil is configured to transmit a radio frequency signal to the target tissue to excite hydrogen nuclei within the target tissue to generate a magnetic resonance signal, and the second birdcage coil is configured to transmit a radio frequency signal to the target tissue to excite heteronuclei within the target tissue to generate a magnetic resonance signal.

[0011] In some possible implementations, the target tissue is the head of the subject.

[0012] In some possible implementations, the axis corresponds to the length direction of the subject;

[0013] Of the two first end rings, the diameter of the first end ring on the side of the subject's head is smaller than the diameter of the first end ring on the side of the subject's feet.

[0014] Of the two second end rings, the diameter of the second end ring on the side of the subject's head is smaller than the diameter of the second end ring on the side of the subject's feet.

[0015] In some possible implementations, it also includes:

[0016] A coil carrier defines a receiving cavity for accommodating the head, the receiving cavity having a first end and a second end disposed opposite to each other in the body length direction, the cross-sectional dimension of the first end being smaller than that of the second end, and the first end being closer to the top of the head than the second end;

[0017] Both the first birdcage coil and the second birdcage coil are mounted on the coil carrier and are arranged around the receiving cavity.

[0018] In some possible implementations, both the first leg and the second leg extend along the shape of the inner wall of the receiving cavity.

[0019] In some possible implementations, the coil carrier includes an inner housing and an outer housing surrounding the inner housing, with both the first birdcage coil and the second birdcage coil disposed between the inner housing and the outer housing.

[0020] In some possible implementations, both the first birdcage coil and the second birdcage coil are attached to and fixed to the outer surface of the inner housing.

[0021] In some possible implementations, the number of the first legs is the same as the number of the second legs, and in the circumferential direction, each of the first legs is positioned between two different adjacent second legs.

[0022] The dual-frequency excitation coil provided in this application includes: a first birdcage coil, comprising two first end rings spaced apart axially, and a plurality of first legs connected between the two first end rings and spaced apart circumferentially around the axial direction; and a second birdcage coil, comprising two second end rings spaced apart axially, and a plurality of second legs connected between the two second end rings and spaced apart circumferentially. The resonant frequency of the second birdcage coil is different from that of the first birdcage coil, and the second birdcage coil and the first birdcage coil at least partially overlap in the axial direction. Therefore, on the one hand, thanks to the advantages of excitation efficiency and uniformity inherent in the birdcage coil itself, this coil has excellent dual-frequency excitation function and can be used for dual-nuclear magnetic resonance imaging of the examined part; on the other hand, the first birdcage coil and the second birdcage coil can be arranged simultaneously in a limited axial space, avoiding the large axial size of the dual-frequency excitation coil, and helping both the first birdcage coil and the second birdcage coil to be as close as possible to the examined part on the inner circumference side, so as to ensure the emission efficiency of both. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of this application, and are not intended to limit this application.

[0024] Figure 1 This is a schematic diagram of the dual-frequency excitation coil provided in the embodiments of this application.

[0025] Figure 2 yes Figure 1 The diagram shows the structure after the coil carrier has been removed.

[0026] Explanation of reference numerals in the attached figures:

[0027] 100-Dual-frequency excitation coil;

[0028] DR1 - Axial direction, DR2 - Circumferential direction;

[0029] 10 - First birdcage coil; 20 - Second birdcage coil; 30 - Coil carrier;

[0030] 1-First end ring;

[0031] 2- First leg;

[0032] 3-Second end ring;

[0033] 4- The second leg;

[0034] 5-Inner shell;

[0035] 6-Receiving cavity, 6a-Opening. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the described embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. It is understood that, without conflict, some technical means of the various embodiments described herein can be substituted for or combined with each other.

[0037] In the description of this application, the terms "first," "second," etc., are used only to distinguish the described objects and have no sequential or technical meaning. Therefore, objects specified with "first," "second," etc., may explicitly or implicitly include one or more of those objects, and, for example, the term "first element" itself does not imply the existence of a "second element," nor does the term "second element" itself imply the existence of a "first element." Furthermore, words such as "a" or "one" do not indicate a quantity limitation, but rather indicate the presence of at least one, while "multiple" indicates not less than two.

[0038] Figure 1 A dual-frequency excitation coil 100 according to an embodiment of this application is shown, which can be used to perform magnetic resonance imaging examination on the head of a subject, and includes a coil carrier 30 and a first birdcage coil 10 and a second birdcage coil 20 placed on the coil carrier 30.

[0039] The coil carrier 30 can be primarily made of plastic, thus possessing a certain degree of rigidity. The coil carrier 30 includes an inner housing 5 and an outer housing (not shown).

[0040] The inner surface of the inner housing 5 defines a receiving cavity 6 that matches the head of the subject. This receiving cavity 6 has a first end and a second end disposed opposite each other along the subject's length direction (also referred to as the axial direction DR1 described later). The first end is closer to the top of the subject's head than the second end, and the cross-sectional dimension of the first end is smaller than that of the second end. Additionally, the receiving cavity 6 has an opening 6a, the first end of which is the end containing the opening 6a, and the opening 6a faces the sole of the subject's feet to allow non-head tissues (e.g., neck tissues) of the subject to protrude from the receiving cavity 6.

[0041] The outer casing, which is not shown in the diagram, has a shape similar to that of the inner casing 5, but the outer casing is slightly larger than the inner casing 5. The outer casing surrounds the inner casing 5 and is detachably fixed to the inner casing 5 by screws or other fasteners. Thus, an annular mounting space, larger at one end and smaller at the other, is formed between the inner casing 5 and the outer casing, within which the first birdcage coil 10 and the second birdcage coil 20 are mounted.

[0042] Please see Figure 2 and combined Figure 1 , Figure 2 for Figure 1 The diagram shown is a schematic of the structure after the coil carrier 30 (more specifically, the inner housing 5 of the coil carrier 30) has been removed, which shows the first birdcage coil 10 and the second birdcage coil 20 in more detail.

[0043] The first birdcage coil 10 includes two first end rings 1 spaced apart from each other in the axial direction DR1 (also the aforementioned length direction), and a plurality of first legs 2 connecting the two first end rings 1 and spaced apart from each other in the circumferential direction DR2 surrounding the axial direction DR1. The second birdcage coil 20 includes two second end rings 3 spaced apart from each other in the axial direction DR1, and a plurality of second legs 4 connecting the two second end rings 3 and spaced apart from each other in the circumferential direction DR2. Furthermore, the first birdcage coil 10 and the second birdcage coil 20 are abutted and fixed to the outer surface of the inner housing 5 in a manner surrounding the receiving cavity 6.

[0044] Furthermore, the second birdcage coil 20 and the first birdcage coil 10 at least partially overlap in the axial direction DR1, so that the first birdcage coil 10 and the second birdcage coil 20 can be arranged simultaneously in the limited axial space of DR1, avoiding the axial size of the dual-frequency excitation coil 100 becoming too large, and helping both the first birdcage coil 10 and the second birdcage coil 20 to be as close as possible to the inner circumference of the tested part (head), so as to ensure that both have excellent emission efficiency. More specifically, in the axial direction DR1, the two second end rings 3 are located between the two first end rings 1, and therefore, the length of the second leg 4 is longer than the length of the first leg 2.

[0045] The resonant frequency of the second birdcage coil 20 differs from that of the first birdcage coil 10. Furthermore, the resonant frequency of the first birdcage coil 10 matches the resonant frequency of hydrogen nuclei, while the resonant frequency of the second birdcage coil 20 matches the resonant frequency of heteronuclei (i.e., non-hydrogen nuclei, such as 23Na nuclei). With this design, in practice, the first birdcage coil 10 can emit a radio frequency signal matching the resonant frequency of hydrogen nuclei towards the subject's head to excite the hydrogen nuclei within the head to generate magnetic resonance signals, and the second birdcage coil 20 can emit a radio frequency signal matching the resonant frequency of heteronuclei towards the subject's head to excite the heteronuclei within the head to generate magnetic resonance signals. Thus, the coils possess dual-frequency excitation capabilities and can be used for dual-nucleus magnetic resonance imaging of target tissues (such as the head) of the subject.

[0046] This dual-frequency excitation coil is particularly suitable for non-ultra-high field magnetic resonance systems, such as 3.0T and 5.0T magnetic resonance systems.

[0047] The different resonant frequencies of the first birdcage coil 10 and the second birdcage coil 20 are achieved by forming the first leg 2 and the second leg 4 with different lengths. Specifically, as described above, the second leg 4 is longer than the first leg 2.

[0048] Corresponding to the shape of the receiving cavity 6, in the two first end rings 1, the diameter of the first end ring 1 on the side closer to the subject's head is smaller than the diameter of the first end ring 1 on the side closer to the subject's feet; in the two second end rings 3, the diameter of the second end ring 3 on the side closer to the subject's head is smaller than the diameter of the second end ring 3 on the side closer to the subject's feet. Furthermore, both the first leg 2 and the second leg 4 extend along the shape of the inner wall of the receiving cavity 6.

[0049] Understandably, by reducing the size of the cavity accommodating the subject's head on the top side, and accordingly reducing the size of the first end ring 1 of the first birdcage coil 10 on the top side and the second end ring 3 of the second birdcage coil 20 on the top side, the size of each of the first and second birdcage coils is reduced. This allows the first and second birdcage coils to be closer to the examination site, which helps improve the emission efficiency of the first and second birdcage coils, especially at the top of the head. Furthermore, since the human head itself has a smaller top side size than the non-top side size, this design does not significantly worsen the adaptability to different head shapes.

[0050] In this embodiment, the number of first legs 2 and the number of second legs 4 are the same, both being eight. Furthermore, on the circumferential DR2, each first leg 2 is positioned between two adjacent second legs 4. Further, the eight first legs 2 are arranged at equal angles on the circumferential DR2, and the nine second legs 4 are arranged at equal angles on the circumferential DR2, with each first leg 2 positioned at the midpoint between two adjacent second legs 4. In other possible embodiments, the number of first legs 2 and the number of second legs 4 are different.

Claims

1. A dual-frequency excitation coil, characterized in that, include: The first birdcage coil includes two first end rings spaced apart from each other in the axial direction and a plurality of first legs connecting the two first end rings and spaced apart from each other in the circumferential direction around the axial direction; The second birdcage coil includes two second end rings spaced apart from each other in the axial direction and a plurality of second legs connecting the two second end rings and spaced apart from each other in the circumferential direction; The resonant frequency of the second birdcage coil is different from that of the first birdcage coil, and the second birdcage coil and the first birdcage coil at least partially overlap in the axial direction.

2. The dual-frequency excitation coil according to claim 1, characterized in that, In the axial direction, the two first end rings are located between the two second end rings, and the length of the second leg is longer than that of the first leg.

3. The dual-frequency excitation coil according to claim 1, characterized in that, The first birdcage coil is configured to transmit a radio frequency signal to the target tissue to excite hydrogen nuclei within the target tissue to generate a magnetic resonance signal, and the second birdcage coil is configured to transmit a radio frequency signal to the target tissue to excite heteronuclei within the target tissue to generate a magnetic resonance signal.

4. The dual-frequency excitation coil according to claim 3, characterized in that, The target tissue is the subject's head.

5. The dual-frequency excitation coil according to claim 4, characterized in that, The axis corresponds to the length direction of the subject; Of the two first end rings, the diameter of the first end ring on the side of the subject's head is smaller than the diameter of the first end ring on the side of the subject's feet. Of the two second end rings, the diameter of the second end ring on the side of the subject's head is smaller than the diameter of the second end ring on the side of the subject's feet.

6. The dual-frequency excitation coil according to claim 5, characterized in that, Also includes: A coil carrier defines a receiving cavity for accommodating the head, the receiving cavity having a first end and a second end disposed opposite to each other in the body length direction, the cross-sectional dimension of the first end being smaller than that of the second end, and the first end being closer to the top of the head than the second end; Both the first birdcage coil and the second birdcage coil are mounted on the coil carrier and are arranged around the receiving cavity.

7. The dual-frequency excitation coil according to claim 6, characterized in that, Both the first leg and the second leg extend along the shape of the inner wall of the receiving cavity.

8. The dual-frequency excitation coil according to claim 7, characterized in that, The coil carrier includes an inner shell and an outer shell surrounding the inner shell, with the first birdcage coil and the second birdcage coil both disposed between the inner shell and the outer shell.

9. The dual-frequency excitation coil according to claim 8, characterized in that, Both the first birdcage coil and the second birdcage coil are attached to and fixed to the outer surface of the inner shell.

10. The dual-frequency excitation coil according to any one of claims 1 to 9, characterized in that, The number of the first legs is the same as the number of the second legs, and in the circumferential direction, each of the first legs is positioned between two adjacent second legs.

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