Birdcage-type resonance chamber for high-resolution NMR applications

Abstract

A birdcage-type or birdcage-derived resonator 1 for use in irradiation and detection in NMR experiments comprises two conductive circular rings 2 at their axial ends, joined and fastened with a plurality of mutually isolated parallel conductive rods 3 distributed over the circumference of the rings 2, the axial outer faces 16 of the rings 2 being axially spaced apart to a birdcage height BCh, at least one capacitor being provided between each of the rods 3 and each of the rings 2, or at least one capacitor being provided in each of the rings 2 between adjacent conductive rods 3 in each of the ring segments. The resonator takes the form of an axial capacitor bar 19, the capacitors extending beyond their outer faces 16 between the rings 2 and forming protruding portions 24 on both axial sides, the length SPl of the protruding portions 24 on each side being at least 25% of the birdcage height BCh.

Description

Technical Field

[0001] The present invention relates to a novel resonance apparatus design, particularly for high-resolution NMR applications, especially for liquid NMR spectroscopy. Further, the present invention relates to a method of using such a resonance apparatus design and a method of fabricating such a resonance apparatus design.

Background Art

[0002] In a typical nuclear magnetic resonance experiment, a static magnetic field Bo is provided within the bore of a magnet, a sample is placed at the magnetic center of this magnet, the nuclei in the sample having nuclear spins are irradiated, and then or simultaneously, they are detected by a frequency corresponding to the Larmor frequency of the nuclei, that is, the so-called magnetic resonance frequency of the nuclei in the corresponding magnetic field. The irradiation / detection frequencies typical of currently available static magnetic field strengths are frequencies in the range of megahertz to low gigahertz.

[0003] For irradiation and detection, highly efficient coils in the form of resonance apparatuses are used, and the resonance frequencies thereof are adapted to the corresponding frequencies of the nuclei detected in the corresponding fields. The goal of these resonance apparatuses is to provide the highest possible uniform irradiation field for a given irradiation power and to function as a receiver with the highest possible sensitivity for detection.

[0004] For high-resolution applications, so-called saddle coils are typically used, and their natural resonance frequencies are adjusted for optimization, for example, by additional external capacitors. In particular, in the field of magnetic resonance imaging, so-called birdcage resonators are also used, which essentially consist of two end-axial rings connected by a pair of axial bars (usually 8 to 32 metal rods) distributed circumferentially around the circumference of the rings and connecting the two rings. When capacitors are introduced between each end of the rings and bars, these birdcage resonators exhibit low-pass behavior; when capacitors are introduced between adjacent bars in the rings, these birdcage resonators exhibit high-pass behavior. In the case of 8 metal rods, 16 capacitors are used. Hybrid birdcage resonators with capacitors in both the rings and bars are also possible.

[0005] This type of birdcage-type resonant device exhibits high sensitivity, resulting in high irradiation field (B1) uniformity and high efficiency, thus combining many advantages that are important for high radio frequency (RF) performance.

[0006] Patent Document 1 discloses an NMR high-frequency coil made of a plurality of conductive segments that are evenly spaced around a periphery and interconnect a pair of conductive loop elements. Each conductive segment comprises at least one reactive element which may include a variable capacitance or inductive element.

[0007] Patent Document 2 discloses a birdcage coil comprising multiple birdcage-shaped elements, wherein the element density is such that the contribution of the mutual inductance of its legs to the total inductance exceeds 45% according to conventional model calculations. To accommodate the desired element density, the required capacitance can be obtained from a compact structure such as interconnected patterns that can be directed axially or between elements, or from the arrangement of element portions on both sides of a cylindrical substrate.

[0008] Patent Document 3 discloses a superconducting birdcage coil having low-pass and high-pass coil configurations, formed using strips, each having elongated sapphire substrates on which layers of high-temperature superconductor (HTS) material are grown in a full-length wavy pattern on one of the main surfaces. The low-pass coil is formed by a pair of ring elements made of a conductive metal and a plurality of such strips that are arranged parallel to each other and interconnect these ring elements at junctions that are spaced apart peripherally along each of the rings. At each junction, the ring elements and the HTS layer form a capacitance. The high-pass coil is similarly formed by a plurality of such strips, each having electrodes of HTS material grown at two separate end positions on the other main surface of the sapphire substrate. These strips are arranged parallel to each other and continuously around a central axis, and each lies in a plane containing the central axis. The electrodes and the HTS layers in pairs of adjacent strips are in close proximity in a face-to-face relationship and thereby function as a ring portion of a birdcage configuration including a capacitor.

[0009] Patent document 4 and the corresponding patent document 5 disclose an NMR probe head comprising a birdcage-type resonator having two conductive rings and a plurality of bar-shaped connectors between them. The connectors are provided with reactance elements that can be individually adjusted to compensate for asymmetry in the birdcage-type resonator.

[0010] Patent Document 6 relates to a high-dielectric-constant ultra-high-field animal magnetic resonance (HRF) probe equipped with a coil unit, the coil unit comprising a cylindrical coil circuit board and a cylindrical inner wall board, the inner wall board being placed on the coil circuit board. The two ends of the HRF ceramic unit are fixed between the coil circuit board and the coil inner wall board via a ceramic unit support. All units are independent of each other and can be assembled flexibly, and the sensitivity of the HRF probe can be effectively improved. Multiple HRF ceramic blocks can significantly improve the B1 field radiation efficiency in the central region and avoid the adverse effects of increased coil modes and disorder caused by a perfectly cylindrical barium titanate ceramic.

[0011] Patent Document 7 proposes an NMR probe head having a substantially cylindrical casing extending along the probe head axis. The NMR probe head can be inserted into the room-temperature bore of an NMR spectrometer magnet that provides a uniform static magnetic field along the probe head axis in the measurement area. The NMR probe head is equipped with a cylindrical radio frequency (RF) resonator that is oriented along the resonator axis and generates an RF magnetic field that is essentially uniform transverse to the resonator axis. According to this invention, the angle between the probe head axis and the resonator axis is other than 0 degrees. Thus, the tilt of the resonator does not affect the useful RF magnetic field, and the signal-to-noise ratio of the received NMR signal does not depend on the tilt angle. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] U.S. Patent No. 4,694,255 [Patent Document 2] U.S. Patent No. 6,285,189 [Patent Document 3] U.S. Patent No. 6,735,851 [Patent Document 4] International Publication No. 2019 / 041053 [Patent Document 5] European Patent No. 3655790 [Patent Document 6] Chinese Patent Publication No. 112162224 [Patent Document 7] U.S. Patent No. 6118274 [Overview of the project]

[0013] Despite the significant advantages mentioned above, conventional birdcage resonance spectrometers are rarely used in high-resolution NMR spectroscopy. One reason for this is that conventional birdcage resonance spectrometers exhibit very pronounced susceptibility inhomogeneities due to the need to assemble various different components. Compensating for susceptibility, especially with respect to capacitive elements, is not easily possible.

[0014] Therefore, an object of the present invention is to provide a novel birdcage-type resonant apparatus that generally offers the above-mentioned advantages of a birdcage-type resonant apparatus, but at the same time does not suffer from the introduction of non-uniformity of magnetic susceptibility and the corresponding expansion of the detected linewidth.

[0015] In fact, magnetic compensation for high-resolution NMR resonance apparatus is essential to achieve the required irradiation and detection characteristics. Compensation of metal components is achievable if a suitable alloy is found, in which case near-ideal compensation can be achieved. A thin, highly conductive layer (also compensated) can restore high conductivity. RF capacitors are widely available and used, but not all of these materials are magnetically compensated. In contrast to metals, magnetic compensation for dielectric materials is relatively complex.

[0016] Unfortunately, meeting the requirements of high-resolution NMR (e.g., the resonator can be used over a wide frequency range: 300 MHz to over 1200 MHz) requires two or more dielectric materials. While birdcage-type resonators guarantee excellent RF characteristics on the one hand, each individual design is narrowband on the other hand (e.g., 600 MHz ± 30 MHz). This results in numerous resonator designs, requiring one special design for each NMR principal frequency, which typically increases in 100 MHz steps. Furthermore, the diameter and length of the resonator need to be adapted depending on the application. Consequently, the capacitance of the capacitor needs to vary over a wide range, and ceramic materials with dielectric constants of 10 to over 100 are required to shape the capacitor to achieve the desired frequency and mechanically conform to the design.

[0017] Here, it was found that magnetic compensation can be achieved, in a sense, without the need for magnetic compensation, by extending the axial range along the Z-axis of the dielectric material of the capacitor element, without adding any further magnetic compensation material.

[0018] Magnetic compensation of dielectric materials in capacitors requires shaping the dielectric material for optimal relative permittivity, mechanical stability, and dielectric loss, while simultaneously optimizing its magnetic susceptibility. This strategy is extremely time-consuming and costly when the dielectric material is created using a mixture of ceramic powders.

[0019] Using the strategies proposed herein, the susceptibility optimization step is not mandatory, thus providing a simple and reliable method to mitigate the previous disadvantages of birdcage resonators, particularly for high-resolution applications, while maintaining the advantages of birdcage resonators.

[0020] According to a first aspect of the present invention, the present invention relates to a birdcage type resonance apparatus for use in irradiation and detection in NMR experiments, which includes two conductive circular rings at both axial ends (the rings may be open or closed over the circumference, but are preferably closed except for intervening capacitors for high-pass resonance apparatuses, for example), and the conductive circular rings are joined and fastened to a plurality (at least two, preferably at least four) of mutually isolated parallel conductive rods distributed (preferably evenly) over the circumference of the ring. (Here, resonance apparatuses derived from birdcages are included, and thus the angle is not 2π / (number of bars) here).

[0021] The outer axial surfaces of the rings are axially separated by the birdcage height.

[0022] (In the case of a low-pass design), at least one capacitor is provided between each of the rods and each of the rings (that is, for each rod, in the capacitor regions of the upper ring and the lower ring contact region). In this case, it is preferable that at least one capacitor is provided between each rod and the inner circumferential surface of the ring, or between each rod and the outer circumferential surface of the ring, or between each rod and the inner surfaces facing axially of the ring (that is, the surfaces facing each other of the rings).

[0023] Or, (in the case of a high-pass design), in each of the rings, at least one capacitor is provided between adjacent conductive rods in at least two ring segments, or between adjacent conductive rods in each of the ring segments.

[0024] The capacitors in both cases are elements separated from the parallel conductive rods. Also, the capacitors do not form part of the parallel conductive rods or are integrated with the parallel conductive rods.

[0025] Capacitors are fixed elements in that their capacitance cannot be adjusted during assembly and / or by the end user. Therefore, it is preferable that capacitors are not part of, or do not form, a reactance element that can be individually and / or collectively adjusted, for example, by mutually movable electrodes, to compensate for asymmetry in a birdcage-type resonant device.

[0026] According to the present invention, the design is further characterized in that the dielectric material (which also provides the required capacitance through the corresponding electrodes) extends beyond the axial outer surface between the rings, forming protruding portions of the dielectric material on both axial sides of the rings, in the form of an axial capacitor bar or dielectric material bar. Furthermore, the design is characterized in that the length of the protruding portions on each axial side of the rings is at least 15%, or at least 20%, or at least 25% of the birdcage height. It is preferable that all capacitors take the form of such an axial capacitor bar.

[0027] Such birdcage-type resonators are not adjustable because the rings and rods are fixedly mounted to each other. Therefore, the desired degenerate resonant mode of such a resonator cannot be changed; however, in practice, fine-tuning is done by the corresponding inductances and capacitors in the wiring to and from such a resonator. For example, a birdcage-type resonator with 16 bars has 16 resonances, two end-ring resonances, and seven resonances in degenerate pairs, while a birdcage-type resonator with 8 bars has eight resonances, two end-ring resonances, and three resonances in degenerate pairs. In the case of a low-pass birdcage-type resonator, the first two non-zero frequency modes are usually the desired modes. In the case of a high-pass birdcage-type resonator, the second highest frequency mode is usually the desired mode.

[0028] Since capacitors having dielectric extensions in the form of the aforementioned protruding portions are formed as long axial capacitor partners, the effect in a static magnetic field is the same along the entire length of these bars of dielectric material. This means that magnetic inhomogeneity is not introduced by the capacitor element of the resonant apparatus in the relevant spatial volume for irradiation and / or detection, which also means that further susceptibility matching is usually not required due to the presence of the capacitor element in such a birdcage-type resonant apparatus.

[0029] Preferably, all condenser bars have the same length, width, and thickness. Also, the condenser bars typically have the same cross-sectional shape. Furthermore, it is preferable that all condenser bars are located in the same axial position relative to the magnetic center. The condenser bars are preferably distributed regularly and / or mirror-symmetrically or point-symmetrically around the circumference of the magnetic center.

[0030] According to a first preferred embodiment of such a birdcage-type resonator, the length of the protruding portion is at least 30%, preferably at least 40%, or at least 50% of the birdcage height.

[0031] Typically, the birdcage height BCh is in the range of 15 mm to 35 mm, preferably 20 mm to 27 mm, and the condenser bar length Bl is in the range of 35 mm to 60 mm, preferably 40 mm to 50 mm. These are values ​​for a typical high-resolution NMR configuration for liquid spectroscopy using sample tube diameters of 3 mm, 5 mm, or 10 mm.

[0032] Each capacitor server typically has a thickness Bt in the range of 0.05 mm to 1 mm, preferably in the range of 0.1 mm to 0.5 mm, and a width Bw in the range of 0.5 mm to 3 mm, preferably in the range of 1 mm to 2 mm. The thickness is usually selected to achieve the corresponding desired capacitance of each capacitor.

[0033] The cross-sectional shape of the condenser server is preferably rectangular, with rounded edges as needed, but it may also have another desired cross-section (e.g., U-shaped).

[0034] Typically, each ring has a thickness Rt in the range of 0.5 mm to 3 mm, preferably in the range of 0.75 mm to 1.5 mm, and / or a width in the range of 0.5 mm to 3 mm, preferably in the range of 1 mm to 2 mm.

[0035] The cross-sectional shape of the ring is preferably rectangular, but other shapes are also possible.

[0036] Each ring preferably has an inner diameter Rd in the range of 1 mm to 12 mm, or 2 mm to 12 mm, more preferably in the range of 3 mm to 10 mm.

[0037] It is preferable that both rings have exactly the same dimensions.

[0038] Regarding the metal bars, it is preferable that they have a circular or rectangular, preferably square, cross-sectional shape with a diameter / diagonal in the range of 0.2 mm to 2 mm, preferably in the range of 0.5 mm to 1.25 mm. It is preferable that all bars have the same shape, material, and dimensions.

[0039] In yet another preferred embodiment, the protruding portion is at least partially embedded in a material that shields from high frequencies on both sides, and preferably, at both ends, a block (ring) of RF shielding material is provided having blind receiving holes or radial slots into which the protruding portion is at least partially penetrated.

[0040] The axial height of each of these blocks is preferably at least equal to the length of the protruding portion, preferably at least 1.5 times that length, and more preferably at least 2 times the length of the protruding portion.

[0041] In a preferred embodiment, the ring and / or rod are made of metal, or include a coating of at least one of metal, preferably copper and silver.

[0042] Typically, the capacitor bar described above contains or consists of a material having a relative permittivity in the range of 10 to 1000 or 10 to 100, and / or a dielectric loss less than tanΔ < 0.001.

[0043] The condenser server preferably contains or consists of a sapphire or ceramic material selected from the group consisting of aluminum oxide, zirconium oxide, titanium oxide, or mixtures thereof, and / or alkaline earth metal oxides.

[0044] The condenser server may also be provided with a U-shaped cross-section to increase capacitance and resistance to arc discharge.

[0045] The condenser server may also be provided in the form of a laminate to increase resistance to arc discharge. Such a laminate preferably includes a central polymer layer, which is preferably a perhalogenated polymer, selected from polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxy polymer (PFA), ethylene fluoride-propylene (FEP), polyethylene tetrafluoroethylene (ETFE), polyethylene chlorotrifluoroethylene (ECTFE), perfluoroelastomer (FFPM / FFKM), fluorocarbon [chlorotrifluoroethylene vinylidene fluoride] (FPM / FKM), fluoroelastomer [tetrafluoroethylene-propylene] (FEPM), or chlorinated analogs or formulations thereof. Such a central polymer layer preferably has a thickness of less than 50 μm, or in the range of 10 μm to 40 μm.

[0046] Such a laminate preferably further comprises at least two ceramic outer layers comprising or consisting of a sapphire or ceramic material selected from the group consisting of aluminum oxide, zirconium oxide, titanium oxide, or mixtures thereof, and / or alkaline earth metal oxides or alloys thereof. At least one or both of the ceramic layers preferably have a thickness in the range of 50 μm to 500 μm, more preferably in the range of 150 μm to 350 μm.

[0047] Typically, such resonant devices have an equal number of rods and condenser bars, but designs with, for example, twice the number of bars as the condenser bars can also be realized.

[0048] Furthermore, such a resonant apparatus typically comprises 2 to 12, preferably 6 to 10, and most preferably 8 rods and / or condenser bars.

[0049] In yet another preferred embodiment, in the case of a low-pass birdcage type resonant device, at least one condenser bar is provided between each end of the rod and each of the rings, the condenser bar is provided on the radial inner surface of each of the rings, and each of the rods is provided on the radial inner side of each of the condenser bars.

[0050] It is preferable that the condenser server and rod are separated by a gap in most of the region between the rings.

[0051] A conductive or dielectric, preferably conductive, intermediate layer can be provided between each condenser server and the corresponding radially adjacent rod, and / or between each condenser server and the radially inner surface of each ring.

[0052] In another preferred embodiment, in a high-pass birdcage type resonant apparatus, at least one condenser bar is provided in each ring between adjacent conductive rods in each ring segment, and the condenser bars and rods are preferably evenly distributed along the circumference of the ring (e.g., point symmetry or mirror symmetry). It is preferable that there is a free intermediate space (gap) between the rods and the condenser bars.

[0053] Here too, a conductive or dielectric intermediate layer, preferably a conductive one, can be provided between each of the condenser servers and the corresponding ring segments.

[0054] The condenser server preferably takes the form of slats arranged radially or tangentially, having a rectangular cross-section with a circumferential thickness Bt in the range of 0.1 mm to 0.5 mm and a radial width Bw in the range of 1 mm to 3 mm, preferably in the range of 1.2 mm to 2.5 mm.

[0055] The desired mode(s) having the desired resonant frequency of such a birdcage-type resonant apparatus can be adapted by selecting the dimensions and materials of the capacitor, in particular, so that it is in the range of 300 MHz to 1200 MHz, preferably in the range of 600 MHz to 1000 MHz.

[0056] According to yet another aspect of the present invention, the present invention relates to a nuclear magnetic resonance probe equipped with the birdcage type resonance apparatus described in detail above.

[0057] The present invention also relates to the use of the birdcage-type resonator described above for measuring a liquid sample using nuclear magnetic resonance, preferably in a static magnetic field of at least 1 Tesla. The axial length (H) of the liquid in the sample is greater than the axial length (Bl) of the condenser server, and preferably the resonator has a resonance frequency in the range of 300 MHz to 1200 MHz, more preferably in the range of 600 MHz to 1000 MHz.

[0058] Furthermore, the present invention relates to a method for fabricating the birdcage-type resonance device described above.

[0059] In the case of a low-pass resonant device design, preferably in this method, a ring is provided, and condenser bars are connected to the inner surface in a specified, preferably circumferentially distributed manner, preferably soldered, and rods are connected to the radially inward side of each condenser bar, preferably soldered, preferably so that a free gap exists between each condenser bar and each rod, at least in the central portion between the two rings.

[0060] In the case of a high-pass resonant device design, preferably, ring segments are soldered to the ends of the bars, and the segments are joined, preferably by soldering, by placing condenser bars between adjacent segments (the set of condenser bars can first be attached to the RF shielding block described above at both ends via protruding portions), and preferably, a free gap exists between the condenser bars and the rods, at least in the central portion between the two rings.

[0061] Further embodiments of the present invention are described in the dependent claims.

[0062] Preferred embodiments of the present invention are described below with reference to the drawings, which are intended to illustrate preferred embodiments of the present invention and are not intended to limit the present invention. [Brief explanation of the drawing]

[0063] [Figure 1] Figure 1 shows a typical RF coil configuration in an NMR probe. [Figure 2] Figure 2 shows a conventional low-pass birdcage type resonant apparatus, where a) is a schematic side view and b) is a view of the inner surface of one of the rings as seen from the center. [Figure 3]Figure 3 shows a conventional high-pass birdcage type resonant apparatus, where a) is a schematic side view and b) is a view of the inner surface of one of the rings as seen from the center. [Figure 4] Figure 4 shows a low-pass birdcage type resonant apparatus according to the present invention, where a) shows an axial cross-section and b) shows a radial cross-section passing through one of the end rings. [Figure 5] Figure 5 shows a high-pass birdcage type resonant apparatus according to the present invention, where a) is a schematic side view and b) is a view of the inner surface of one of the rings as seen from the center. [Figure 6] Figure 6 is a schematic side view showing the evolution from a high-pass birdcage type resonant device representing the current state of technology (left) to an embodiment (right) of the high-pass birdcage type resonant device according to the present invention (center) and an RF shielding section for the protruding portion of the condenser server. [Figure 7] Figure 7 shows a high-pass birdcage type resonant apparatus according to the present invention, which includes an RF shielding block for the protruding portion of the condenser server. [Figure 8] Figure 8 shows two further resonance devices according to the present invention, where a) and b) show the upper and lower rings of the first embodiment, respectively, and c) and d) show the upper and lower rings of the second embodiment, respectively. [Modes for carrying out the invention]

[0064] Figure 1 shows a typical surrounding mechanism of a resonance apparatus according to the present invention in a high-resolution NMR spectroscopy device, particularly for the analysis of liquid samples. A strong static magnetic field is generated by a superconducting magnet (not shown) having a central vertical bore 14 that generates a strong magnetic field along the Z axis. In the region of the magnetic center 12 along the Z axis, there are shim coils 10 that affect the uniformity of the static magnetic field, and these shim coils 10 are mounted on a shim tube 11 located at the bottom of the bore 14.

[0065] In the central bore of the shim unit, the actual NMR probe head, typically shown as the NMR probe 13, is inserted, usually from below. The NMR probe 13 in the region of the magnetic center 12 is equipped with a pair of gradient shield coils 9 running radially from the outside to the inside, followed by a pair of gradient coils 8 that provide a transient gradient of the measurement as needed. The actual (liquid) NMR sample 5, a glass tube typically having a diameter of 3 mm, 5 mm, or 10 mm (outer diameter), is inserted into the bore from above and positioned within the NMR coil 7. Above and below the NMR coil 7 along the Z-axis are radio frequency (RF) shields 6.

[0066] The NMR coil 7 is an actual resonance device that, on the one hand, irradiates the sample with a high frequency corresponding to the Larmor frequency of the nucleus being measured over the irradiation period of the corresponding measurement sequence, and on the other hand, receives the signal emitted from the nucleus during the detection period of the corresponding measurement sequence. For both of these functions, particularly during the detection period, the uniformity of the static magnetic field is crucial to obtain the narrowest possible linewidth. Therefore, it is important that the corresponding coil design does not compromise the uniformity of the static magnetic field, while simultaneously providing the irradiation magnetic field B1 that is desirable for the measurement and as controllable as possible.

[0067] Typically, for liquid measurements, these resonant devices take the form of so-called saddle coils. A saddle coil system can be constructed by bending two equal rectangular coils on a cylindrical surface. The same current flows through each coil, and the direction of the current flow can be set to a Helmholtz configuration or an anti-Helmholtz configuration. It is known that a uniform magnetic field in a given direction can be generated using the former configuration, and a linear magnetic field gradient can be generated using the second configuration. Helical designs or resonant cavities are also possible.

[0068] Birdcage resonators offer a different type of resonator. Birdcage resonators are particularly well known in MRI applications. Birdcage coils differ fundamentally from structures such as saddle coils and helices in that phase shifts are employed between constituent current loops to produce a suitable current distribution. In the case of birdcage resonators, the phase shifts are discretely distributed around the circumference of the coil from zero to 2π. The phase shift of each element is rather frequency-dependent, and birdcage resonators are tuned to discrete frequencies to achieve the desired phase shift constraints. A further goal is to obtain a birdcage coil driven by perpendicular phase to maximize power efficiency during transmission and the signal-to-noise ratio during signal reception.

[0069] This type of resonant device combines many advantages that are important for high RF performance, such as high sensitivity, high B1 field uniformity, and high efficiency.

[0070] Figures 2 and 3 show two basic types of birdcage-type resonators. Figure 2 typically shows a low-pass resonator with frequencies from 300 MHz to 1200 MHz, while Figure 3 shows a high-pass resonator with frequencies at least 600 MHz.

[0071] As shown in these figures, a birdcage-type resonant apparatus typically comprises two metal rings 2 offset symmetrically around the magnetic center 12 of a magnet along the Z-axis. These rings 2 are joined by an integer, usually eight, metal rods 3 that are electrically connected to the rings and are arranged parallel to each other and parallel to the Z-axis.

[0072] In the low-pass resonant apparatus shown in Figure 2, capacitors 4 are provided between each ring 2 and each rod 3 to form a resonant apparatus on the inner surface 15 of each ring 2 at each position where the corresponding rod 3 is located. Electrically, such a birdcage-type resonant apparatus is represented by a series of capacitors, inductances, capacitors in each vertical structure, and inductances between each of these rods with capacitors.

[0073] In the case of the high-pass resonant device shown in Figure 3, capacitors 4 are provided so that the circumference of the ring is separated into individual segments joined by capacitors in order to form a resonant device between each of the metal rods in the ring. In this case, electrically, the birdcage resonant device is represented as the inductance of the bars, and there is a series of inductances and capacitors between two bars along the circumference of the ring.

[0074] There is an intermediate space 18 between the metal rods 3, and the axial height BCh of such a birdcage-type resonator is typically in the range of 20 mm to 27 mm, the inner diameter Rd of the ring is typically in the range of 5.5 mm to 10 mm, the radial width Rw of the ring is typically in the range of 1 mm to 2 mm, and the axial thickness Rt of the ring is typically in the range of 0.5 mm to 2 mm, usually in the range of 1 mm. The metal rods 3 typically have a circular cross-section and a diameter in the range of 0.5 mm to 1.5 mm, usually in the range of 1 mm. The rings and rods are made from metal.

[0075] Preferably, all metal components are made from highly conductive materials optimized for 300 MHz to 1200 MHz, with Cu and Ag being preferred. Due to the typical skin depth at high frequencies (300 MHz to 1200 MHz), only 20 μm of the surface metal layer is accessible for conductivity (skin effect). Therefore, it is important to have a large skin depth region (wire circumference × skin depth) that is large enough to reduce resistance.

[0076] Capacitor 4 is typically a low dielectric loss material with a relative permittivity of e = 10 to 1000. Capacitors are usually made from ceramic materials for their low dielectric loss, high dielectric constant, temperature stability, and to allow for a very well defined metal-to-ceramic interface via soldering.

[0077] The capacitance of a capacitor is given by the following equation C = ε × ε0 × A / d, where, in the case of 400MHz to 800MHz (low-pass), A is typically 1mm. 2 ~3mm 2 And d is in the range of 0.1mm to 0.5mm. Capacitor 4 can also be installed in an alternating configuration (only 8 instead of 16).

[0078] As mentioned above, one of the main problems hindering the widespread use of birdcage-type resonators is the difficulty in matching the susceptibility of individual construction blocks. This means that it is difficult to achieve the desired magnetic field uniformity required for narrow linewidths in birdcage-type resonators.

[0079] According to the present invention, in order to realize a birdcage-type resonance spectrometer for high-resolution NMR, one important feature is added: magnetic compensation for ceramic components, which is essential for obtaining the required fine-line shape (resolution).

[0080] The gist of the present invention is best illustrated by the figures provided in Figure 6.

[0081] As mentioned above, the main challenge in matching susceptibility in birdcage-type resonant devices is matching the susceptibility of the capacitor element 4. Matching the susceptibility of these capacitor elements is difficult, if not impossible. The concept of the present invention is to ensure that the capacitor element 4 extends along the Z-axis where the sample volume relevant to the measurement is located, and therefore the capacitor element 4 extends across the entire extension range relevant to the measurement along the Z-axis, thus eliminating the need for additional susceptibility matching due to the presence of the capacitor element.

[0082] As a starting point, we will begin with the high-pass configuration shown in Figure 3. Please refer to the high-pass design on the left side of Figure 6.

[0083] In the first step, according to the present invention, all capacitors are extended along the Z-axis so that they are much longer than the birdcage coil, typically 40 mm or more (see center of Figure 6). This adaptation eliminates the need for material compensation to achieve a uniform magnetic field along the Z-axis. What were originally 16 small capacitors 4 dividing the ring into individual segments are replaced by 8 long ceramic strips 19.

[0084] In a second optional but highly desirable step, means 25 are provided to mechanically stabilize the entire ceramic stripe, or rather, its protruding portions 24 that extend beyond the outer surface 16 of each ring, such as RF shielding blocks, for example, in the form of fixings in the top and bottom RF shields (see the right side of Figure 6).

[0085] Typically, this step is followed by metallizing the surface (both sides) of the ceramic stripe with pads 20, and then soldering the ceramic stripe to create a metal design.

[0086] The frequency of the desired mode in such a resonant apparatus can be easily changed by replacing the dielectric material. Low-loss ceramic materials with relative permittivity of 10 to over 100 are commercially available.

[0087] The method for actually implementing this concept is shown in the low-pass birdcage type resonator design in Figure 4. The ring 2 is the same as described above, but in this case, the ring 2 is connected to the condenser bar 19 via a radial inner surface 21, rather than being joined to the condenser 4 via a corresponding inner surface 15. On the radial inner side, these condenser bars 19 are followed by a metal rod 3, which is twice as long as the metal rod in the conventional design shown in Figure 2, by the thickness Rt of the ring. Similarly, the rod 3 is positioned as close as possible to the sample for irradiation and detection, which leads to high power input and high sensitivity. The axial length Bl of the condenser server 19 is approximately equal to the height H of the liquid in the sample tube. There is only a small gap d between the outer surface of the sample tube and the bar 3, preferably an air gap 23 between the rod 3 and each associated condenser bar 19. The condenser server 19 has a thickness Bt in the same range as described above for conventional condenser designs and is made of ceramic material. The width Bw of the condenser server is as detailed above. The condenser server 19 can also have a layered structure, particularly to avoid arc discharge. This can be achieved by having a sandwich structure with an outer layer of ceramic or another dielectric material and a middle layer of a plastic material, preferably PTA or PTFE, which has a much higher arc voltage in the range of about 50,000 V than typical ceramic dielectric materials, when the arc voltage at the frequency in this application is in the range of about 10,000 V. In such a configuration, the thickness of the plastic layer is usually less than 50 μm, and the thickness of the ceramic dielectric outer layer is adapted to the corresponding desired capacitance, which is usually in the range of about 250 μm.

[0088] Intermediate layer patches 20, which may be metal pads or simply layers of soldering material, are provided to mount the capacitor server 19 on both sides. The dimensions and materials of the ring, bar, and capacitor can be selected as described above with respect to conventional designs.

[0089] Figure 5 shows how this concept is actually implemented in a high-pass birdcage type resonant device design. In this case, the condenser bar 19 is located between the segments 27 of each ring 2. The condenser bar 19 extends beyond the outer surface 16 of the corresponding ring in the form of a protruding portion 24. As mentioned above, this also applies to a low-pass birdcage type resonant device design, where the protruding portion is contained within an RF shielding block 25 (see further description and examples in Figure 7 below). The dimensions of the condenser bar 19 are the same as those of the low-pass resonant device detailed above. In this case, the condenser bar 19 is oriented radially with respect to its long axis in a cross-sectional view and intersects the corresponding ring at regular intervals.

[0090] As mentioned above, the protruding portion 24 of the condenser bar 19 is held within an RF shielding block 25 for shielding purposes as well as for stability, as shown in Figure 7 for a high-pass birdcage type resonant device design. These RF shielding blocks 25 take the form of a ring with a series of blind receiving holes 26 or slots (where the radial width of the shielding block ring 25 is approximately the same as the width Bw of the condenser bar 19).

[0091] As described above, different designs of the birdcage type resonator are also possible. Figure 8 shows two further embodiments of the high-pass resonator. In a) and b), the upper and lower rings of the first embodiment are schematically shown. In this embodiment, the upper and lower rings are separated by condenser bars 19, in which case the condenser bars are oriented tangentially rather than radially. These condenser bars 19 also have protruding portions 24 that extend beyond the upper and lower surfaces of the resonator. In this case, the upper ring is provided with two additional gaps.

[0092] The upper and lower rings of the second embodiment are schematically shown in c) and d), respectively, but the condenser bar 19 can also simply obstruct the conductivity of the lower ring. These condenser bars 19 also include protruding portions 24 that extend beyond the upper and lower surfaces of the resonant device. In this case, the upper ring is provided with two additional gaps. [Explanation of symbols]

[0093] 1. Birdcage-type resonator 2 metal rings 3 Metal rods 4 Capacitors 5 NMR samples 6RF Shield 7. NMR coil, resonance device 8 gradient coils 9. Gradient Shield Coil 10 Shim Coils 11 Shim tube 12 Magnetic Center 13 NMR probes 14 High-temperature magnet bore 15 Inner surface facing the axial direction, inner surface of 2 16 2 outer surface 17 Outer surface, radial outer surface of 2 18 3 intermediate space 19 Condenser Servers 20 Intermediate layer between 3 and 19, metal pad 21 Inner circumferential surface, radial inner surface of 2 22 1 internal space 23 Gap between 3 and 19 24 19 protruding parts that extend beyond 16 25 RF Shielding Block Blind receiving hole in 26 25 27 Ring Segments 28 Gap in the ring Axial length of Bl 19 Bt 19 thickness Bw 19 width BCh Birdcage Height Ct Capacitor Thickness d. Gap between the sample and the coil Liquid height in 1H NMR samples MRd Metal Rod Diameter Rd Ring Inner Diameter Rt ring thickness Rw Ring width SPl protruding portion length ZZ axis

Claims

1. A birdcage-type resonance apparatus (1) used for irradiation and detection in NMR experiments, comprising two conductive circular rings (2) at both axial ends, wherein the conductive circular rings (2) are joined and fastened to at least two mutually isolated parallel conductive rods (3) distributed around the circumference of the rings (2), The axial outer surface (16) of the ring (2) is spaced axially apart by the birdcage height (BCh), At least one capacitor is provided between each of the rods (3) and each of the rings (2), preferably between each of the rods (3) and the inner circumferential surface (21) of the ring (2), or between each of the rods (3) and the outer circumferential surface (17) of the ring (2), and / or at least one capacitor is provided between adjacent conductive rods (3) in one or both of the rings (2). The capacitor, preferably all capacitors, take the form of an axial capacitor bar (19) that provides capacitance between at least two electrodes, the capacitor bar (19) extends beyond its outer surface (16) between the rings (2) and forms protruding portions (24) on both sides of the rings (2) in the axial direction. The length (SPl) of the protruding portion (24) on each side in the axial direction is at least 15% of the birdcage height (BCh). The birdcage-type resonator characterized by the above.

2. The length (SPl) of the protruding portion is at least 20%, 25%, or 30%, preferably at least 40%, or at least 50%, of the birdcage height (BCh), and / or The birdcage type resonator according to claim 1, wherein the birdcage height (BCh) is in the range of 15 mm to 35 mm, preferably in the range of 20 mm to 27 mm, and the length (Bl) of the condenser bar (19) is in the range of 35 mm to 60 mm, preferably in the range of 40 mm to 50 mm.

3. Each of the condenser bars (19) has a thickness (Bt) in the range of 0.05 mm to 1 mm, preferably in the range of 0.1 mm to 0.5 mm, and a width (Bw) in the range of 0.5 mm to 3 mm, preferably in the range of 1 mm to 2 mm, and preferably the cross-sectional shape of the condenser bar is rectangular or U-shaped, and / or Each of the rings (2) has a thickness (Rt) in the range of 0.5 mm to 3 mm, preferably in the range of 0.75 mm to 1.5 mm, and a width in the range of 0.5 mm to 3 mm, preferably in the range of 1 mm to 2 mm, and preferably the cross-sectional shape of the ring is rectangular and / or Each of the rings (2) has an inner diameter in the range of 2 mm to 12 mm, preferably in the range of 3 mm to 10 mm, and / or The birdcage type resonator according to claim 1 or 2, wherein at least one or each of the bars (2) has a circular or rectangular, preferably square, cross-sectional shape with a diameter or diagonal in the range of 0.2 mm to 2 mm, preferably in the range of 0.5 mm to 1.25 mm.

4. The protruding portion (24) is at least partially embedded in a material that shields from high frequencies on both sides, and preferably, at both ends, a block (25) of RF shielding material is provided having a blind receiving hole (26) into which the protruding portion (24) at least partially penetrates. Preferably, the axial height of each of these blocks (25) is at least equal to the length (SPl) of the protruding portion (24), preferably at least 1.5 times the length, and more preferably at least 2 times the length of the protruding portion (24), the birdcage type resonator according to claim 1 or 2.

5. The ring (2) and the rod (3) are made of metal, or include a coating of at least one of metal, preferably copper or silver, and / or The capacitor bar (19) includes or is made of a material having a relative permittivity in the range of 10 to 1000 or 10 to 100, and / or a dielectric loss lower than tanΔ < 0.001, and / or The condenser bar (19) preferably contains or consists of a sapphire or ceramic material selected from the group consisting of aluminum oxide, zirconium oxide, titanium oxide, or mixtures thereof, and / or alkaline earth metal oxides, The birdcage type resonant apparatus according to claim 1 or 2, wherein in each of the rings (2), at least one capacitor is provided in at least two or each of the ring segments (27) between adjacent conductive rods (3).

6. The capacitor bar (19) is preferably, In particular, a central polymer layer is preferably a perhalogenated polymer selected from polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxy polymer (PFA), fluoroethylene-propylene (FEP), polyethylene tetrafluoroethylene (ETFE), polyethylene chlorotrifluoroethylene (ECTFE), perfluoroelastomer (FFPM / FFKM), fluorocarbon [chlorotrifluoroethylene vinylidene fluoride] (FPM / FKM), fluoroelastomer [tetrafluoroethylene-propylene] (FEPM), or chlorinated analogs or formulations thereof, preferably having a thickness of less than 50 μm, more preferably in the range of 10 μm to 40 μm. Preferably, at least two ceramic outer layers comprising or consisting of a sapphire or ceramic material selected from the group consisting of aluminum oxide, zirconium oxide, titanium oxide, or mixtures thereof, and / or alkaline earth metal oxides, wherein at least one or both ceramic layers have a thickness in the range of 50 microns to 500 microns, preferably in the range of 150 microns to 350 microns, A birdcage-type resonant device according to claim 1 or 2, provided in the form of a laminate including the above.

7. The birdcage-type resonator has the shape of a high-pass resonator, a low-pass resonator, or a hybrid of both, and the condenser and metal bar are distributed point-symmetrically or mirror-symmetrically in the XY plane defined by the ring, and / or The birdcage-type resonator according to claim 1 or 2, comprising the same number of rods (3) and condenser bars (19).

8. The birdcage-type resonator according to claim 1 or 2, comprising 2 to 12, preferably 6 to 10, most preferably 8 rods (3) and / or condenser bars (19).

9. At least one condenser bar (19) is provided between each end of the rod (3) and each of the rings (2), the condenser bar (19) is provided on the radial inner surface (21) of each of the rings (2), and each of the rods (3) is provided on the radial inner side of each of the condenser bars (19), Preferably, the condenser bar (19) and rod (3) are spaced apart in most of the region between the rings (2), and / or The birdcage type resonant apparatus according to claim 1 or 2, wherein a conductive intermediate layer for forming the electrode (20) is provided between each of the condenser bars (19) and the corresponding radially adjacent rod (3), and / or between each of the condenser bars (19) and the radial inner surface (21) of each of the rings (2).

10. The birdcage resonant apparatus according to claim 1 or 2, wherein in each of the rings (2), at least one condenser bar (19) is provided between adjacent conductive rods (3) in at least two or each of the ring segments (27), preferably the condenser bar (19) and the rods (3) are evenly distributed over the circumference of the ring (2), and preferably a free intermediate space (23) exists between the rods (3) and the condenser bar (19).

11. The birdcage type resonant apparatus according to claim 10, wherein the condenser bar (19) takes the form of a slat arranged radially or tangentially, having a rectangular cross-section with a circumferential thickness (Bt) in the range of 0.1 mm to 0.5 mm and a radial width (Bw) in the range of 1 mm to 3 mm, preferably in the range of 1.2 mm to 2.5 mm.

12. The birdcage-type resonant apparatus according to claim 1 or 2, wherein the resonant frequency is in the range of 300 MHz to 1200 MHz, preferably in the range of 600 MHz to 1000 MHz.

13. A nuclear magnetic resonance probe (13), comprising a birdcage-type resonance apparatus as described in claim 1 or 2.

14. Use of a birdcage-type resonator according to claim 1 or 2 for measuring a liquid sample using nuclear magnetic resonance in a static magnetic field of at least 1 Tesla, wherein the axial length (H) of the liquid in the sample is greater than the axial length (Bl) of the condenser bar (19), and preferably the resonator has a resonant frequency in the range of 300 MHz to 1200 MHz, preferably 600 MHz to 1000 MHz.

15. The ring (2) is provided, and the capacitor bars (19) are connected to it, preferably soldered, so as to be evenly distributed around the circumference of the inner circumferential surface (21). The rods (19) are connected to the radially inward side of each of the capacitor bars (19), preferably soldered. Preferably, at least in the central portion between the two rings (2), there is a free gap (23) between each capacitor bar (19) and each of the rods (3), or A method for manufacturing a birdcage-type resonant apparatus according to claim 1 or 2, wherein ring segments are soldered to the ends of rods (3), the segments are joined by placing condenser bars (19) between adjacent segments, preferably by soldering, and preferably a free gap (23) exists between the condenser bars (19) and the rods (3) in the central portion between at least two of the rings.

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