High frequency RF transmit coil for magnetic resonance imaging system

Abstract

A high frequency RF transmit coil for transmitting an RF field to a magnetic resonance examination zone of a magnetic resonance imaging system having a carrier structure for separating the examination zone from the RF transmit coil, the carrier structure being surrounded by an RF transmit antenna of the RF transmit coil, the carrier structure being made of a first material having a first dielectric constant, at least one recess being formed in the carrier structure between the layered capacitor structure of the RF transmit antenna and a patient (8) in the examination zone, the recess extending completely circumferentially along the carrier structure, the recess being filled with at least a second material, such that the second material surrounds the carrier structure as an additional layer, the second material having a second dielectric constant, the second dielectric constant of the second material being higher than the first dielectric constant of the first material of the carrier structure.

Description

[Technical field]

[0001] The present invention relates to the field of high frequency RF transmit coils for magnetic resonance imaging systems, in particular to an improved carrier structure for an RF transmit coil. [Background technology]

[0002] The magnetic resonance imaging system 1, as shown in FIG. 1, consists of three cylindrical concentric subsystems, namely, a static magnet 2, a gradient coil 4, and a quadrature body coil 5, which surround a carrier structure 7 or patient bore.

[0003] The gradient coils 4 generate gradients in the static magnetic field that are used to localize image signals and pulses at frequencies in the kHz range. Between the gradient coils 4 and the carrier structure 7 is a quadrature body coil 5 which transmits and receives RF field pulses in the MHz range that are used for image acquisition.

[0004] A typical body coil 5 design is a birdcage, which consists of a number of conductive rods, also known as rungs 12, along the central axis of the patient bore, connected to each other at both ends by two large rings 9, 10. The body coil 5 typically has the conductive rings 9, 10 and rungs 12 printed out on a large PCB. This PCB is folded into a cylindrical shape and connected at the edges to form the birdcage. The overlapping portions of the printed rungs 12 and rings 9, 10 form the capacitor structure 13 of the antenna body coil 6. The size of these capacitors is adjusted to ensure that the birdcage coil 5 achieves electrical resonance at a given frequency and optimizes the electromagnetic power delivery.

[0005] FIG. 1 shows a schematic of an MRI system 1 showing the location of a gradient coil 4, a body coil 5, and a carrier structure 7 according to the prior art. FIG. 1(a) shows a cross-sectional side view of the MRI system 1, and FIG. 1(b) shows a front view of the MRI system 1. A patient 8 is placed inside the patient bore or body coil carrier structure 7. The region of interest for the MRI scan should typically be at the geometric center of the body coil 5. In this region, a homogenous H or B1+ field is generated for the MR scan. Due to the nature of the antenna PCB design with integrated capacitors, some locally significant electric fields can also be directed into the bore and into the patient. These magnetic fields can expose the patient to high RF power coupling and potentially harmful increases in tissue temperature. The ring portions 9, 10 have some of the strongest electric fields of the body coil, especially at the edges of the overlapping capacitors 13 on the patient side 16.

[0006] Figure 2(a) shows an example of a patient 8 position for an abdominal scan. For this scan, the patient's shoulders and wrists are closest to the ring capacitor 13 and experience the highest SAR values. Figure 2(b) shows a cross-sectional view along the stack-up of the body coil antenna 6 and carrier structure 7. A typical distance of the patient 8 from the support structure 7 closest to the ring capacitor may be only a few centimeters or less.

[0007] FIG. 3 shows a schematic diagram of a body coil antenna 6 having a standard carrier structure 7 stackup according to the prior art, where FIG. 3A) shows a front view of the body coil antenna 6, FIG. 3B) shows a cross-sectional view along the body coil antenna 6 and carrier structure 7 stackup, and FIG. 3C) shows an isometric view of the carrier structure 7.

[0008] As shown in FIG. 2, the time-varying electric field 16 from the layered capacitors 13 of the ring portions 9, 10 of the body coil 5 couples with the patient tissue 8 when in close proximity. This changing magnetic field 18 can induce a significant temperature rise in the patient tissue and in the surface of the carrier structure 7 itself. In electromagnetic analysis, the amount of absorbed RF energy is normalized to the weight of the tissue and parameterized as the Specific Absorption Rate (SAR). The maximum value of SAR to which the patient 8 can potentially be exposed by any medical device is subject to strict regulations. The resulting heat can pose a risk to both the patient 8 and the components. Furthermore, the unwanted electric field coupling 18 negatively impacts the overall performance of the quadrature body coil and therefore reduces the quality of the resulting MR images. This effect is well understood and many methods are used today to improve the situation. One possibility is that immersions 19 can be formed in the body coil carrier structure 7 between the edges of the antenna capacitors 13 and the patient 8 to modify the local electric field distribution to reduce patient coupling. A commonly used method, especially for 1.5T systems, is to use a recess 19, i.e. a small hole or recess in the body coil carrier structure 7 below the edge of the capacitor on the patient side of the antenna PCB, as shown in FIG.

[0009] FIG. 4 shows a schematic representation of a body coil antenna 6 and a standard carrier structure 7 stacked at the position of the immersion 19 according to the prior art, where FIG. 4A) shows a front view of the body coil antenna 6, FIG. 4B) shows a cross-sectional view along the body coil antenna 6 and the carrier structure 7, and FIG. 4C) shows an isometric view on the carrier structure 7. The immersion 19 shown in FIG. 4 forms an additional layer of air with a thickness half the thickness of the carrier structure 7 (4 mm) whose dielectric permittivity is approximately equal to 1. A typical carrier structure is made of glass-reinforced epoxy with a dielectric constant of 4.4 with a thickness of 8 mm. In this case, the immersion 19 acts as an electric field scatterer that results in a reduction of the local electric field density towards the inside of the bore. However, this method has a fundamental limitation, since there are no materials with a dielectric constant less than 1, and as a result the scattering process is limited as well. Moreover, a quadrature body coil 5 with two capacitors between the rungs 12 requires two immersions (a total of 64 immersions for a 16 rung body coil). This leads to structural weaknesses in the carrier structure 7 as well as insufficient contact surfaces to support the antenna PCB.

[0010] From US 2008 / 0054901 A1 a partition made of at least one first wall material is known for defining a patient positioning region from an antenna structure of a magnetic resonance imaging apparatus, the partition having at least one region in which certain substructures of the antenna structure are located on a side of the partition opposite the patient positioning region, the partition having a wall portion made of a second wall material having a dielectric constant lower than the dielectric constant of the first wall material.

[0011] Chinese patent application CN 11 2162 224 discloses an RF probe for MR animal scanning. This known RF probe has a birdcage setup and comprises a cylindrical housing switch end ring in the form of an arc-shaped copper strip and an axial copper strip connected by a non-magnetic capacitor. A dielectric ceramic unit is provided inside the inner wall substrate of the housing over the axial length of the cylindrical housing.

[0012] Direct coupling of the electric field between the body coil ring and patient tissue and the associated SAR effects are significant patient safety and regulatory concerns. Existing methods for SAR reduction through the use of immersions are limited and introduce potential reliability issues. Summary of the Invention [Problem to be solved by the invention]

[0013] An object of the present invention is to improve the SAR reduction in the patient associated with the direct coupling of the electric field from the laminar capacitor inside the body coil to the patient. [Means for solving the problem]

[0014] According to the invention, this object is addressed by the subject matter of the independent claims. Preferred embodiments of the invention are set forth in the dependent claims.

[0015] Thus, according to the invention, there is provided a high frequency RF transmit coil for transmitting an RF field into a magnetic resonance examination zone of a magnetic resonance imaging system, the RF transmit coil comprising: an RF transmit antenna, the RF transmit antenna being formed by a number of rungs arranged along a central axis of the examination zone around a volume; a first end ring connected to first ends of the plurality of rungs; a second end ring connected to second ends of the plurality of rungs; and having a layered capacitor structure is formed by overlapping portions of the rungs, the first end ring, and the second end ring; a carrier structure for separating the examination zone from the RF transmit coil, the carrier structure being surrounded by the RF transmit antenna, the carrier structure being made from a first material having a first dielectric constant; at least one recess is formed in a carrier structure between the layered capacitor structure and the test zone, the recess extending completely circumferentially and partially axially along the carrier structure over an axial extension of at least one of the first and second end rings; A high frequency RF transmission coil is provided, in which the recess is filled with at least one second material such that the second material surrounds the carrier structure as an additional layer, the second material having a second dielectric constant, the second dielectric constant of the second material being higher than the first dielectric constant of the first material of the carrier structure. The recess further extends partially axially along the carrier structure over an axial extension of at least one of the first and second end rings. In one embodiment of the invention, a recess is provided which extends partially axially along the carrier structure and covers the first and second end rings respectively. That is to say, according to the invention, the coverage of the recess is limited to the axial extension of the end rings, optionally with some additional margin extending axially beyond the axial extension of the end rings. Typically the axial extension of the recess is in the range of 2 to 15 cm, typically around 7 cm, which is at least one or two orders of magnitude smaller than the total axial extension of the carrier structure, i.e. the axial length of the RF transmission coil. These recesses may be filled with a dielectric material that forms a gasket that underlies the ring section of the body coil antenna that reduces electric field coupling with the patient's body, particularly at the end rings.

[0016] The recess located under the ring section of the body coil antenna filled with a material having a higher dielectric constant than the material of the support structure ensures less coupling of the electric field with the patient, especially in the area closest to the surface of the support structure. Thus, a means is provided for reducing the electric field induced specific absorption rate (SAR) of the patient, thus improving patient safety and comfort or alternatively allowing more RF power to be applied and scan times to be reduced. Unwanted system interactions between the body coil and the patient or the receive coil, e.g. changes in tuning and matching of the body coil, can be mitigated. The risk of inner bore heating is reduced. As a result of less undesired system interactions, image quality is improved. With reduced SAR values, it may be more free to apply more RF power and reduce scan times. An advantage of the present invention is the reduction of electric field coupling from the body coil antenna to the patient. As a result, harmful patient exposure due to electric fields or patient SAR is reduced and patient safety and comfort is improved. Furthermore, unwanted system interactions between the body coil and the patient or the receive coil, e.g. changes in tuning and matching of the body coil, can be mitigated. This improves image quality. The risk of inner bore heating is reduced. Another advantage is that when the SAR value is reduced, it may be more free to apply more RF power and reduce the scan time. The material-filled recess can be considered as a gasket that extends completely circumferentially along the carrier structure. Thus, the SAR can be reduced and patient safety and comfort are improved as well as image quality. As dielectric material, a material with a dielectric constant different from air or the carrier structure material is used. Thus, instead of the scattered electric field being coupled to the patient, the electric field is contained and blocked within the dielectric material. When using a material with a significantly higher dielectric constant than the carrier structure material, the effect of wavelength shortening is advantageous. This effect allows more of the electric field to be compressed and contained inside the material. In addition, this increases the intraboundary reflectivity and reduces the field transmission.This is similar to Bragg's law, i.e. 2dsinθ=nλ (n is a positive integer, λ is the wavelength of the incident wave, d is the gasket thickness, and θ is the wave incidence angle), which describes the diffraction maximum and allows to estimate the possible reflected field attenuation. The gasket placed under the ring section of the body coil antenna ensures that these effects result in less electric field coupling with the patient, especially in the areas closest to the carrier structure surface. This reduces the SAR and improves patient safety and comfort as well as image quality.

[0017] In an advantageous embodiment of the invention, the width of each recess along the rung corresponds at least to the size of the overlap between the rung and the first and second end rings.

[0018] In an advantageous embodiment of the invention, the thickness of the carrier structure is between 8 mm and 12 mm and the depth of the recess is between 2 mm and 6 mm.

[0019] In an advantageous embodiment of the invention, the dielectric material in the recess has a dielectric constant of 50-100.

[0020] In an advantageous embodiment of the invention, the recess is filled with at least two different materials forming an outer layer on the system side and an inner layer between the carrier structure and the outer layer on the patient side, the dielectric constant of the outer layer being different from that of the inner layer. The SAR can be further improved by applying the effect multiple times between the body coil antenna and the patient. This can be done by introducing a multi-layer carrier structure gasket instead of a single layer.

[0021] In an advantageous embodiment of the invention, the outer layer has a higher dielectric constant than the inner layer, which in turn has a higher dielectric constant than the material of the carrier structure.

[0022] In a preferred embodiment of the invention, the outer layer has a dielectric constant of 50-100 and the inner layer has a dielectric constant of 5-10.

[0023] In an advantageous embodiment of the invention, the thickness of the inner layer and the thickness of the outer layer are each half the depth of the recess.

[0024] In an advantageous embodiment of the invention, the recess is filled with three or more layers of different materials.

[0025] In an advantageous embodiment of the invention, the RF transmit coil is a quadrature body coil of a birdcage coil.

[0026] The invention further relates to a magnetic resonance imaging system comprising an RF transmit coil as described above.

[0027] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter, but such embodiments do not necessarily represent the full scope of the invention, and therefore reference should be made to the claims and this specification for interpreting the scope of the invention. [Brief description of the drawings]

[0028] [Figure 1] 1 shows a schematic representation of an MRI system showing the location of gradient coils, body coils and carrier structures according to the prior art, FIG. 1a) showing a cross-sectional side view of the MRI system and FIG. 1b) showing a front view of the MRI system. [Diagram 2] Figure 2b) shows a schematic diagram of a patient position on a carrier structure facing a body coil antenna for abdominal scanning with the antenna and carrier structure stackup at the topmost electric field coupling position to the patient according to the prior art, Figure 2a) shows a front view of the patient position on the carrier structure and Figure 2b) shows a cross-sectional view along the body coil antenna and carrier structure stackup. [Diagram 3] FIG. 3a) shows a schematic of a body coil antenna and a standard carrier structure stackup according to the prior art, FIG. 3b) shows a front view of the body coil antenna, and FIG. 3c) shows an isometric view on the carrier structure. [Figure 4]The body coil antenna and standard carrier structure stackup are shown diagrammatically, with Figure 4a) showing a front view of the body coil antenna, Figure 4b) showing a cross-sectional view along the body coil antenna and carrier structure stackup, and Figure 4c) showing a schematic isometric view on the carrier structure. [Diagram 5] Figure 5a) shows a front view of the body coil antenna, Figure 5b) shows a cross-sectional view along the body coil antenna and carrier structure stackup, and Figure 5c) shows an isometric view on the carrier structure. [Figure 6] 6A) shows a schematic cross-sectional view along the body coil antenna and carrier structure stackup, FIG. 6B) shows a cross-sectional view along the body coil antenna and carrier structure stackup, and FIG. 6C) shows a schematic isometric view on the carrier structure, in accordance with an embodiment of the present invention, of a body coil antenna and carrier structure stackup at the position of a recess filled with two layers of different materials. [Figure 7] 2 illustrates a schematic diagram of a body coil antenna and carrier structure stackup according to an embodiment of the present invention. [Figure 8] 1 shows diagrams of electric field coupling from the open part of the ring capacitor to patient tissue for different types of carrier structures according to the state of the art and different embodiments of the present invention. [Figure 9] 1 shows diagrams of electric field coupling from the open part of the ring capacitor to patient tissue for different types of carrier structures according to the state of the art and different embodiments. [Figure 10] 1 shows different electric field distributions on a patient surface for different types of carrier structures according to the state of the art and according to different embodiments of the present invention when the patient is in contact with the carrier structure. [Figure 11] 1 shows different electric field distributions for different types of carrier structures according to the state of the art and according to different embodiments of the present invention on a patient surface when the patient is in contact with the carrier structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] 1 to 4 show prior art embodiments and have already been explained in the introductory part of the description.

[0030] FIG. 5 shows a schematic of a body coil antenna 5 and a carrier structure 7 stacked at the location of a material-filled recess according to an embodiment of the present invention. FIG. 5(a) shows a front view of the body coil antenna 5, FIG. 5(b) shows a cross-sectional view along the stack-up of the body coil antenna 5 and the carrier structure 7, and FIG. 5(c) shows an isometric view of the carrier structure 7. The RF transmit antenna 5 is formed around a volume forming a rung section 11 by a plurality of rungs 12 arranged along the central axis of the examination zone 3. A first end ring 9 is connected to a first end of the plurality of rungs 12, and a second end ring 10 is connected to a second end of the plurality of rungs 12. The overlapping portions of the rungs 12 and the first end ring 9 and the second end ring 10 form a layered capacitor structure 13. Furthermore, FIG. 5 shows a carrier structure 7 for isolating the examination zone 3 from the RF transmit coil 5. The carrier structure 7 is surrounded by the RF transmit antenna 6. The RF transmit antenna consists of a system side antenna 14, an antenna dielectric 15 and a patient side antenna 16. Also, an open portion 17 of the capacitor 13 can be seen on the ring portion 9, 10 of the carrier structure 7. The carrier structure 7 is made of a first material having a first dielectric constant, and at least one recess 20 is formed in the carrier structure 7 between the layered capacitor structure 13 and the patient 8 in the examination zone 3, the recess 20 extending completely circumferentially along the carrier structure 7. The recess 20 is filled with at least a second material, so that the second material surrounds the carrier as an additional layer, the second material having a second dielectric constant, the second dielectric constant of the second material being higher than the first dielectric constant of the first material of the carrier structure 7. This concept achieves its objective without significant redesign of existing systems. It uses standard layered dielectrics and can be applied as a redesign for most of the existing systems using this type of carrier structure and layered PCB structure to improve their current SAR performance.

[0031] Using advanced computational analysis methods, a layered carrier structure gasket structure was designed, which has numerous advantages compared to the standard immersion section 19. In a first embodiment, the local immersion section 20 is filled with a solid material that surrounds the support structure like an additional layer. This not only supports the PCB during antenna bonding, but also provides additional mechanical stability to the carrier structure 7 and prevents structural damage. In a second embodiment, the filler used is a material with a dielectric constant different from that of the air or fiberglass reinforced epoxy resin of the support structure 7. Thus, instead of scattered electric fields being coupled to the patient 8, the electric fields are contained and blocked within the filling material. By using a material with a much higher dielectric constant than the material of the carrier structure 7, the wavelength is shortened. This effect allows more of the electric field to be compressed and contained inside the material. In addition, this increases the boundary reflectivity and reduces the field transmission. This is similar to Bragg's law, namely 2dsinθ=nλ (n is a positive integer, λ is the wavelength of the incident wave, d is the gasket thickness and θ is the wave incidence angle), which describes the diffraction maximum and allows to estimate the possibility of reflected field attenuation. The gasket 20 placed under the ring sections 9, 10 of the body coil antenna 6 ensures that these effects result in less electric field coupling with the patient 8, especially in the areas closest to the surface of the carrier structure 7. Thus, the SAR can be reduced and the safety and comfort of the patient is improved as well as the image quality. The proposed idea can be further enhanced by applying the effect multiple times between the body coil antenna 6 and the patient 8. This can be done by introducing a multi-layer carrier structure 7 gasket 21, 22 instead of the single layer 20 shown in Figure 6. For example, instead of a single layer carrier structure gasket 20 with the same thickness as the commonly used immersion depth of 4 mm, as shown in Figure 5, a multi-layer gasket can be composed of two layers 21, 22, each 2 mm thick, as shown in Figure 6.

[0032] FIG. 6 shows a schematic of a body coil antenna 6 and a carrier structure 7 stacked at the location of the recess 20 filled with two layers 21, 22 of different materials according to an embodiment of the present invention. FIG. 6(a) shows a front view of the body coil antenna 6, FIG. 6(b) shows a cross-sectional view along the stack-up of the body coil antenna 6 and the carrier structure 7, and FIG. 6(c) shows an isometric view of the carrier structure 7. In an embodiment of the present invention, the dielectric permittivity of the outer layer carrier structure gasket 21 (system side) is higher than that of the inner layer carrier structure gasket 22 (layer between the carrier structure 7 and the outer gasket layer 21, patient side), which in turn is higher than that of the carrier structure 7. This forms a gradient transmission of permittivity from the body coil antenna 6 to the carrier structure 7. This transmission creates an extra boundary and applies the above-mentioned field blocking mechanism several times in a row. Within the scope of Bragg's law, varying the thickness of the material can be compensated by the difference in permittivity between the layers. As a result, an even better electric field coupling reduction could be achieved with the multi-layer gasket design.

[0033] Numerous RF simulations were performed to prove the concept. The modeled system was based on a 3T system Ingenia Elition Rx. This is a 60 cm narrow bore system, which could potentially be more critical for SAR issues. All simulations were performed with a detailed 90 kg typical patient model as the load. The model defined the patient with 32 different types of tissue with at least 315 different blocks including separately segmented muscle-fat-skin structures. Power sensitivity and system power calculations were derived for a normalized B1+ field of 23 μT at the ISO center of the body coil. Field magnitude, SAR for body parts, local SAR and average 1g SAR calculations were derived for a normalized B1+ field of 2.29 μT. This value corresponds to a B1+ of 13.5 μT for a duty cycle of 2.88%. RF shimming was applied to all models. Two use cases were investigated: a patient with the abdomen at the body coil center and the same load, but with the patient moving away from the center and touching the body coil carrier structure. The model with recesses has 64 of them at the location of the open part of the capacitor in the ring section of the carrier structure. The size of each recess is 5 cm x 7 cm and the depth is 4 mm. The single layer gasket model shown in Figure 5 has a layer of material with a high dielectric constant (εr = 80). The gasket surrounded the carrier structure with an additional layer of thickness 4 mm. The height of the layer along the bore carrier structure is 7 cm and is below the body coil ring section of 8.4 cm. The multilayer gasket model shown in Figure 6 included two layers 21, 22 of material with a high dielectric constant. There is a layer attached to the antenna outer layer carrier structure gasket 21 (εr = 80) and the inner layer carrier structure gasket 22 (εr = 7). Each layer has a thickness of 2 mm and forms a hoop with a height of 7 cm below the body coil ring section 9, 10. It is important to note that the use of a dielectric material with a dielectric constant lower than 80 is still worthwhile as long as it is still higher than the dielectric constant of the carrier structure material, but the overall effect is reduced.

[0034] One of the most important loading conditions for the electric field coupling 18 towards the patient 8 is the situation when the patient 8 comes into contact with the carrier structure 7. This use case shown in Figure 7 demonstrates the full potential of the proposed invention.

[0035] Figure 7 shows a schematic of the stack-up of the body coil antenna 6 and the carrier structure 7. In the two image sections on the right side of Figure 7, the upper image shows the shoulder of the patient 8 and the area of ​​the carrier structure 7 in front of the open portion 17 of the ring capacitor 13, while the lower image shows the patient touching the carrier structure with his hand. The difference when the patient 8 touches the carrier structure 7 can be seen in Figures 8 and 9 and Figures 10 and 11.

[0036] Fig. 8 shows a diagram of the electric field coupling 18 from the open part 17 of the ring capacitor 13 towards the tissue of the patient 8 for different types of carrier structures 7 according to the state of the art and according to different embodiments of the invention. In Fig. 8 the electric field coupling is shown for a standard carrier structure 7, a carrier structure 7 with a recessed part 19, a carrier structure 7 with a single layer gasket 20 according to an embodiment of the invention and a carrier structure 7 with a multilayer gasket according to another embodiment of the invention. On the right side the electric field coupling in the area of ​​the carrier structure 7 is shown in an enlarged manner. On the left side of Fig. 8 the electric field coupling 18 in the area of ​​the carrier structure 7, in the area of ​​the space between the carrier structure 7 and the patient 8 and in the area of ​​the patient 8. It can be seen that the value of the magnitude of the electric field with a carrier structure 7 with a single layer gasket 20 according to an embodiment is reduced compared to a carrier structure 7 according to the state of the art. With a carrier structure 7 with a multilayer gasket according to another embodiment of the invention the value can be further reduced.

[0037] Figure 9 shows a diagram of the electric field coupling 18 from the open part 17 of the ring capacitor 13 towards the tissue of the patient 8 for different types of carrier structures 7 according to different embodiments of the invention and according to the prior art, when the patient is in contact with the carrier structure 7. It can also be seen that in this case the value of the magnitude of the electric field with a carrier structure 7 with a single layer gasket 20 according to an embodiment is reduced compared to a carrier structure 7 according to the state of the art. With a carrier structure 7 with a multilayer gasket according to another embodiment of the invention the value can be further reduced.

[0038] Figure 10 shows the different electric field distributions on the patient surface for different types of carrier structures according to the state of the art and according to different embodiments of the invention. It can be seen that the electric field magnitude values ​​are reduced compared to the carrier structure 7 known in the prior art.

[0039] Figure 11 shows the different electric field distributions on a patient for different types of carrier structures according to the state of the art and according to different embodiments of the invention, when the patient is in contact with the carrier structure surface. It can also be seen that in this case the value of the electric field magnitude is reduced compared to the carrier structure 7 known in the prior art.

[0040] While the present invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered as illustrative or exemplary and not restrictive, and the present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be interpreted as limiting the scope. Moreover, for the sake of clarity, not all elements in the drawings have been labeled with reference signs.

[0041] Embodiments of the present invention can be summarized as follows. Embodiment 1: A high frequency RF transmit coil (5) for transmitting an RF field in a magnetic resonance examination zone of a magnetic resonance imaging system (1), the RF transmit coil (5) comprising: an RF transmit antenna, the RF transmit antenna being formed by a number of rungs arranged along a central axis of the examination zone around a volume; a first end ring connected to first ends of the plurality of rungs; a second end ring connected to second ends of the plurality of rungs; having a layered capacitor structure is formed by overlapping portions of the rungs, the first end ring, and the second end ring; a carrier structure for separating the examination zone from the RF transmit coil, the carrier structure being surrounded by the RF transmit antenna, the carrier structure being made from a first material having a first dielectric constant; at least one recess is formed in a carrier structure between the layered capacitor structure and the test zone, the recess extending completely circumferentially and partially axially along the carrier structure over an axial extension of at least one of the first and second end rings; 1. A high frequency RF transmit coil, wherein the recess is filled with at least one second material such that the second material surrounds the carrier structure as an additional layer, the second material having a second dielectric constant, the second dielectric constant of the second material being higher than a first dielectric constant of a first material of the carrier structure. Embodiment 2: A high frequency RF transmit coil (5) as described in embodiment 1, wherein the width of each recess along the rung corresponds at least to the size of the overlap between the rung, the first end ring, and the second end ring. Embodiment 3: A high frequency RF transmit coil (5) according to any one of embodiments 1 to 2, wherein the thickness of the carrier structure is between 8 mm and 12 mm and the depth of the recess is between 2 mm and 6 mm. Embodiment 4: A high frequency RF transmit coil (5) according to any one of embodiments 1 to 3, wherein the dielectric material in the immersed portion has a dielectric constant between 50 and 100. Embodiment 5: A high frequency RF transmit coil (5) as described in any one of embodiments 1 to 4, wherein the recess is filled with at least two different materials forming an outer layer on the system side and an inner layer between the outer layer and the carrier structure on the patient side, the dielectric constant of the outer layer being different from that of the inner layer. Embodiment 6: A high frequency RF transmit coil (5) as described in embodiment 5, wherein the dielectric constant of the outer layer is higher than the dielectric constant of the inner layer, and the dielectric constant of the inner layer is higher than the dielectric constant of the material of the carrier structure. Embodiment 7: A high frequency RF transmit coil as described in embodiment 6, wherein the outer layer has a dielectric constant between 50 and 100 and the inner layer has a dielectric constant between 5 and 10. Embodiment 8: A high frequency RF transmit coil according to any one of embodiments 5 to 7, wherein the thickness of the inner layer and the thickness of the outer layer are each half the depth of the recess. Embodiment 9: A high frequency RF transmit coil (5) according to any one of the preceding embodiments, wherein the recess is filled with more than two layers of different materials. Embodiment 10: A high frequency RF transmit coil (5) according to any one of embodiments 1 to 9, wherein the RF transmit coil is a quadrature body coil of a birdcage coil. Embodiment 11: A magnetic resonance imaging system comprising a high-frequency RF transmission coil according to any one of embodiments 1 to 10. [Explanation of symbols]

[0042] Magnetic resonance imaging diagnostic equipment 1 Magnetic Resonance Imaging Magnet 2 Inspection Zone 3 Gradient coil 4 Body Coil 5 RF Transmitting Antenna 6 Career Structure 7 patient 8 First End Ring 9 Second End Ring 10 Lang Section 11 Lang 12 Region where multilayer capacitor is formed in the ring section 13 RF transmit antenna system side 14 RF Transmitting Antenna Dielectric 15 RF Transmitting Antenna Patient Side 16 Open area 17 Electric Field Coupling to Patients 18 Immersion Part 19 Carrier structure gasket / immersion part filled with second material 20 Outer layer carrier gasket 21 Inner layer carrier gasket 22

Claims

1. A high-frequency RF transmitting coil for transmitting an RF field into the magnetic resonance inspection zone of a magnetic resonance imaging system, wherein the RF transmitting coil is An RF transmitting antenna, wherein the RF transmitting antenna is formed by a plurality of lungs arranged along the central axis of the magnetic resonance inspection zone around a volume, A first end ring connected to the first end of the plurality of lungs, A second end ring connected to the second end of the plurality of lungs and It has, The layered capacitor structure is formed by the overlapping portion of the lung, the first end ring, and the second end ring. A carrier structure for separating the magnetic resonance inspection zone from the RF transmitting coil, wherein the carrier structure is surrounded by the RF transmitting antenna, and the carrier structure is made of a first material having a first dielectric constant. At least one immersion portion is formed in the carrier structure between the layered capacitor structure and the magnetic resonance testing zone, the immersion portion extends fully circumferentially and partially axially along the carrier structure over at least one axially extending portion of the first and second end rings, The immersion portion is filled with at least one second material such that the second material surrounds the carrier structure as an additional layer, the second material having a second dielectric constant, the second dielectric constant of the second material being higher than the first dielectric constant of the first material of the carrier structure, the high-frequency RF transmitting coil.

2. The high-frequency RF transmitting coil according to claim 1, wherein the width of each recessed portion along the lung corresponds at least to the size of the overlapping portion between the lung, the first end ring, and the second end ring.

3. The high-frequency RF transmitting coil according to claim 1 or 2, wherein the thickness of the carrier structure is 8 mm to 12 mm, and the depth of the immersion portion is 2 mm to 6 mm.

4. The high-frequency RF transmitting coil according to claim 1 or 2, wherein the dielectric material in the immersed portion has a dielectric constant between 50 and 100.

5. The immersion portion is filled with at least two different materials forming an outer layer on the system side and an inner layer between the outer layer and the carrier structure on the patient side, wherein the dielectric constant of the outer layer is different from that of the inner layer, as described in claim 1.

6. The high-frequency RF transmitting coil according to claim 5, wherein the dielectric constant of the outer layer is higher than that of the inner layer, and the dielectric constant of the inner layer is higher than that of the material of the carrier structure.

7. The high-frequency RF transmitting coil according to claim 6, wherein the outer layer has a dielectric constant between 50 and 100, and the inner layer has a dielectric constant between 5 and 10.

8. The high-frequency RF transmitting coil according to claim 6, wherein the thickness of the inner layer and the thickness of the outer layer are each half the depth of the immersion portion.

9. The high-frequency RF transmitting coil according to claim 1 or 2, wherein the immersion portion is filled with two or more layers of different materials.

10. The high-frequency RF transmitting coil according to claim 1 or 2, wherein the RF transmitting coil is an orthogonal body coil of a birdcage coil.

11. A magnetic resonance imaging system comprising a high-frequency RF transmitting coil according to claim 1 or 2.

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