Transceiver coil arrangement for a MAS NMR probehead and method for designing a transceiver coil arrangement

Abstract

To provide a transceiver coil for NMR-MAS use in which a uniform region in an axial direction and a radial direction in a visual field is improved.SOLUTION: A first transmitter-receiver coil 1a has at least one solenoid-shaped unit having an electrical conductor with a conductor path width W and N≥3 windings, all windings passing around a longitudinal axis of the transmitter-receiver coil, the electrical conductor having a slope, and each half-winding being inclined at an inclination T with respect to the longitudinal axis. As a result, the transceiver coil can be optimized such that a homogeneity region is improved axially and radially within a field of view and / or strength of a HF magnetic field generated by the transceiver coil increases with given power.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a transceiver coil arrangement for a MAS NMR probehead having a first transceiver coil with a longitudinal axis Z' for generating a first HF magnetic field B1, the first transceiver coil having at least one solenoidal shaped section having an electrical conductor with a conductor path width W and N≧3 turns, all turns passing around the longitudinal axis Z' of the transceiver coil, the electrical conductor having a slope S, each half turn inclined with respect to the longitudinal axis Z' by a tilt T, where T≠0 for at least some of the half turns. The present invention also relates to a method for designing a transceiver coil arrangement. [Background technology]

[0002] A transceiver coil arrangement with tilted windings for a MAS NMR probehead is known from [Sun et al.] and [Barbara et al.].

[0003] In the MAS probehead, the transceiver coil assembly typically stands at a magic angle of 54.7° with respect to the static magnetic field B0 (main field magnet).

[0004] It is known from [Sun et al.] and [Barbara et al.] that solenoid-shaped transceiver coils for NMR-MAS probeheads are designed with a tilt angle relative to the axis of the solenoid coil so that the high-frequency B1 field generated by the solenoid coil is as perpendicular as possible to the static B0 field.

[0005] In [Sun et al.], the tilt angle is ψ=90-φ MAS have attempted to improve the sensitivity of NMR coils using [Sun et al.]. They achieve pulse angles up to 17% shorter at the same transmit power compared to MAS configurations. In [Sun et al.], the generated B1 field is assumed to produce a spatially constant angle, independent of the specific implementation of the coil with an extended conductor cross section. Off-axis effects in the edge regions of the coil are not investigated in [Sun et al.].

[0006] [Barbara et al.] attempts to find a solution for the generated HF field B1 by designing a more complex coil geometry, in which the HF field B1 lies in the XY plane throughout the entire active area of ​​the coil. Therefore, the optimization objective function in [Barbara et al.] is to eliminate the z-component of the generated B1 field in the cylindrical measurement volume. In particular, geometries that deviate from the solenoidal shape, with windings that do not pass around the coil's longitudinal axis, are proposed. The coil geometry presented in [Barbara et al.] should be used in combination with a second coil / resonator, and the HF field generated by the second coil should not have a Bz-component. [Barbara et al.] also assumes that an NMR measurement head with a coil generating an HF field B = Bxy will have maximum sensitivity when used with a measurement head with two or more transceiver coil systems, i.e., for cross-polarization measurements. Shielding effects due to the coil conductors are not taken into account.

[0007] The solutions of [Sun et al.] and [Barbara et al.] start from the disappearance of the conductor path width (for non-extended conductors) and do not represent the best solution for finite conductor paths, especially when the distance between conductor paths is very small.

[0008] In addition to coil geometries based on conductors with circular or elliptical cross sections, it is also known to use strip-shaped conductors in NMR probeheads. In particular, such coil geometries can be structured on cylindrical jacket-shaped conductors (e.g., by structurally applying a metal layer on a substrate with a cylindrical surface or by structuring a uniformly applied conductor using a subtractive manufacturing process) or cut from cylindrical jacket-shaped conductors. These manufacturing methods allow greater freedom in the design of coil geometries, especially variable pitch.

[0009] [Privalov et al.] describe a transceiver coil with strip conductors. To optimize axial uniformity, the conductor path width is reduced toward the axial ends. To minimize radial non-uniformity, the conductor distance between windings is kept as small and constant as possible. However, the efficiency of this transceiver coil is not optimal. Summary of the Invention

[0010] The objective of the present invention is to optimize a transceiver coil for NMR-MAS applications so that the axial and radial homogeneity region in the field of view (the region within the transceiver coil in which the probe to be examined can be positioned and examined by NMR) is improved and / or the strength of the HF magnetic field B1 generated by the transceiver coil is increased for a given power.

[0011] This object is achieved according to the invention by a transceiver coil arrangement as claimed in claim 1 and a method as claimed in claim 8.

[0012] According to the present invention, at least two of the following variables are varied over the course t of the length of the electrical conductor of the transceiver coil: slope S=S(t), tilt T=T(t), and conductor path width W=W(t).

[0013] The change in slope S = S(t) can be achieved by changing the pitch P (slope of the winding), but can also be achieved by changing the local slope S within a winding of constant P.

[0014] The pitch P(n) of the nth winding is

number

[0015] For a constant pitch P, the local slope S can vary within one winding and may even reverse sign. The winding pitch P is called positive if the Z' coordinate of the centerline at tn+1 is greater than the Z' coordinate at tn. This is true even if the Z' coordinate in the interval between tn and tn+1 is smaller than at tn. The winding slope S and the conductor path width W, or the ratio S / W of the slope S to the conductor path width W, affect the axial uniformity.

[0016] The multiple windings of a transceiver coil can also be realized as inductively or capacitively coupled individual windings. The pitch then represents the distance between the centerlines of two adjacent individual windings.

[0017] The winding slope T affects the B1 amplitude (the amplitude of the HF magnetic field B1 generated by the transceiver coil) and its radial uniformity. The slope T is defined as the amplitude of the sinusoidal modulation of the Z' position of the conductor center plane across one winding. For coils with a slope T≠0, the local slope S within the first winding half is different from the local slope S within the second winding half. For a slope T=T(t) that varies over the course t of the length of the electrical conductor, the slope is preferably constant over a portion, particularly for at least one half winding. This allows the slope T to vary from half winding to half winding.

[0018] Coils with slopes where T ≠ 0 can, in principle, also be represented by a variable slope S'(t) = S(t) + T(t) cos(2πt + φ) (general slope). If S'(t) is written as a Fourier series, T represents the (t = 1) periodic part of the slope. For each winding, the slope can be written as:

number

[0019] The conductor path width W is the width of the conductor path perpendicular to the conductor center. If the conductor path width W=W(t) varies over the course of the length t of the electrical conductor, the conductor path width may also vary within a single winding.

[0020] The windings of the transceiver coil according to the invention are windings that pass completely around the longitudinal axis Z' of the transceiver coil, i.e. that describe a circle in a projection perpendicular to the longitudinal axis Z'. Particularly preferably, the transceiver coil is solenoidal or comprises only solenoidal winding sections (e.g. a solenoidal forward winding section and a solenoidal reverse winding section, see below).

[0021] In the transceiver coil according to the invention, the influence of various geometric factors of the transceiver coil on the sensitivity of the transceiver coil is utilized: in order to achieve an optimization of the coil sensitivity of a transceiver coil with extended conductors (perpendicular to the path of the conductors), according to the invention at least two of the above parameters are selected to depend on the execution parameter t along the electrical conductors of the transceiver coil, i.e. along the path of the electrical conductors.

[0022] Preferably, the electrical conductor of the first transceiver coil is designed as a strip conductor, which has a thickness that is small (in particular at least an order of magnitude smaller) than the conductor path width and has a substantially rectangular cross section, and which preferably comprises a substrate with a thin metal plating, in particular an HTS coating.

[0023] Preferably, the conductor thickness d of the conductor (i.e. the extension of the electrical conductor in the radial direction relative to the longitudinal axis Z' of the transceiver coil) is at most 1 mm (preferably at most 200 μm) and / or is at least twice the penetration depth of the RF current into the electrical conductor. Furthermore, it is advantageous if the conductor path thickness d is at least 20 μm, preferably at least 100 μm. The penetration depth should be understood as the depth at which the current density has dropped to 1 / e of its value at the conductor surface (skin effect). This is a function of the material of the electrical conductor and the frequency of the RF magnetic field generated therewith.

[0024] It is known that for conductors with a circular cross section (circular conductors), the optimum quality factor is achieved when the pitch-to-conductor path width ratio P / W is ≈1.5-1.667 (depending on the length / diameter ratio of the solenoid coil). In the context of the present invention, it is recognized that for transceiver coils made of strip conductors, this ratio is significantly smaller. That is, in contrast to circular conductors, when the strip conductor thickness is small, the conductor distance (gap width D) between two windings is significantly smaller than the conductor path width. Furthermore, this gap width D is not uniform over the entire length of the conductor. Due to edge effects in finite solenoid coils, the magnetic field in the edge regions no longer extends parallel to the Z' axis but rotates "outward." As a result, the gap width D between the windings in the edge regions of the transceiver coil should be selected to be larger than in the center; that is, the ratio D / W of the gap width to the conductor path width should be larger at the edges than at the center. In contrast to cylindrical conductors, transceiver coils made from strip-shaped conductors allow significantly greater design flexibility, especially when produced by structuring from tubular metal plating.

[0025] In a preferred embodiment of the transceiver coil according to the invention, the slope S varies over the course t of the length of the electrical conductor and the conductor path width W varies within each winding. In particular, the conductor path width within each winding increases and decreases at least once in each case. Preferably, the conductor path width varies periodically.

[0026] Particularly preferred are embodiments for transceiver coil devices having two maximum and two minimum conductor path widths per winding, in particular for transceiver coils in a cross-coil configuration. Preferably, the regions of the electrical conductors having the minimum conductor path widths are arranged offset by 180° with respect to rotation about the longitudinal axis Z'. The regions of the electrical conductors having the minimum conductor widths are preferably arranged rotated by 90° with respect to rotation about the longitudinal axis Z' with respect to the regions having the maximum conductor widths, i.e., spaced apart by one-quarter of a winding.

[0027] The conductor width W preferably varies between 0.1 mm and 2 mm.

[0028] Furthermore, in the case of a combination of a first transceiver coil with T≠0 generating an HF magnetic field that is substantially present in the measurement sample in the X'Z' plane of a Cartesian X',Y',Z' coordinate system, and a second coil that generates a second HF magnetic field B2 that is substantially present in the Y'Z' plane in the measurement sample, an embodiment of the first transceiver coil advantageously has four maxima and four minima per winding, the minima being in the X' and Y' directions and the maxima being at 45° between X' and Y'.

[0029] In a particular embodiment of the transceiver coil arrangement according to the invention, the slope S and tilt T of the electrical conductor of the first transceiver coil vary along the path of the electrical conductor.

[0030] The tilt T has two effects. First, it generates a magnetic field component in the X' direction. This is particularly advantageous when the transceiver coil is used in a static magnetic field oriented along the Z axis, which is not collinear with the longitudinal axis Z' of the transceiver coil. For a given transceiver coil, the circularly polarized component rotating in the same direction as the nuclei precession is associated with nuclear excitation (excitation field B1+), while the circularly polarized component rotating in the opposite direction to the direction of the nuclei precession is associated with signal reception (excitation field B1-), where B1+ = (B1x + iB1y) / 2 and B1- = (B1x - iB1y) / 2. In other words, only magnetic field components in the X and Y planes, i.e., perpendicular to the direction of the static magnetic field, are relevant for excitation and reception of NMR signals.

[0031] The excitation field B1+ and the excitation field B1- can be maximized by adjusting the tilt T. For transceiver coils with a pitch-to-conductor path width ratio P / W>>1, i.e., for very narrow / thin conductors, the maximum value of the excitation field B1+ is reached when the magnetic field generated by the transceiver coil is located in the X'Z' plane. However, because shielding currents on the conductors reduce the efficiency of the transceiver coil, this maximum value is pushed towards a lower tilt T when wide conductors are used, i.e., when the conductor width W increases.

[0032] As mentioned above, it is recognized within the scope of the present invention that the orientation of the B1 field is not equal to the orientation at the center, such as at the edge regions of a finite transceiver coil. Here, if the longitudinal axis Z' of the transceiver coil is at an angle unequal to 0° or 90° with respect to the Z axis, B1+ above the longitudinal axis Z' (i.e., when X'>0) is not equal to B1+ below the longitudinal axis Z' (i.e., when X'<0). By adapting the tilt T at the edge regions, B1+ can be homogenized throughout the sample volume at the edge regions.

[0033] Varying the gradient T along the length of the conductor can maximize the efficiency of the transceiver coil under conditions of minimum radial uniformity of the B1+ field in the edge regions.

[0034] Preferably, the tilt T of the axial ends of the first transceiver coil is smaller than that of the axial center of the transceiver coil.

[0035] Under the condition that the longitudinal axis Z′ of the transceiver coil is at a magic angle with respect to the Z axis, maximization of efficiency by simultaneously optimizing the radial uniformity at the axial ends of the transceiver coil is achieved by a lower tilt T at the axial ends.

[0036] In a particular embodiment of the transceiver coil device according to the invention, the transceiver coil device comprises at least one further transceiver coil for generating a second HF magnetic field B2 radially outside the first transceiver coil, the first transceiver coil and the further transceiver coil being arranged around a common longitudinal axis Z' such that the HF magnetic fields B1, B2 generated by the first transceiver coil and the further transceiver coil are oriented perpendicular to each other.

[0037] The two transceiver coils are preferably tuned to different frequencies. The fact that the HF magnetic fields B1 and B2 are perpendicular to each other means that the volume integral of the scalar product of vectors B1(x, y, z) and B2(x, y, z) is approximately zero over at least the region of the field of view (FOV) of the two transceiver coils where the measurement sample is located. That is, only the HF magnetic fields B1 and B2 within the measurement sample are considered. In certain embodiments, the orthogonality of the two HF magnetic fields B1 and B2 is achieved by a matching network; that is, the HF magnetic fields B1 and B2 generated directly by the two transceiver coils do not need to be exactly orthogonal to each other.

[0038] In particular, the conductor path width W of the electrical conductors of the first transceiver coil should be minimum in the region where the surface normal of the first transceiver coil is parallel to the second HF magnetic field B2. In other words, in the region of the surface of the first transceiver coil where the HF magnetic field B2 must penetrate to excite the measurement sample within the field of view, the conductor path width W of the electrical conductors of the first transceiver coil is minimum to form a transparent region for B2.

[0039] The further transceiver coil is preferably a saddle coil or a resonator (eg birdcage resonator, Alderman-Grant resonator, ...).

[0040] In yet another particular embodiment of the transceiver coil device according to the invention, the electrical conductor of the first transceiver coil comprises a forward winding section and a reverse winding section, the forward winding section comprises a forward winding that starts from a connection region and leads to an axial end of the transceiver coil with a predetermined winding orientation, the reverse winding section comprises a reverse winding that starts from an axial end of the first transceiver coil and leads to the connection region with a predetermined winding orientation, the windings of the reverse winding section have a pitch P with an opposite sign to the pitch of the forward winding section, and the forward winding and reverse windings of the electrical conductor are arranged on a common cylindrical jacket surface around the longitudinal axis Z′ except for an intersection region where the forward winding and reverse winding intersect (an “intersection geometry”).

[0041] Therefore, the forward and reverse windings are at the same radial distance around the longitudinal axis Z', i.e., have windings that run in opposite directions on a common surface. The connection region is used to connect the electrical coil sections to the matching network and can include connections for multiple electrical coil sections. The forward and reverse winding sections form coil sections that run between two terminals of the terminal section, so that the applied voltage is applied between the start of the forward winding and the end of the reverse winding of each coil section. To arrange the forward and reverse windings on a common cylindrical surface, the forward and reverse windings must cross each other. The crossing is performed in a circumferential section (crossing region) with as little extension as possible. Preferably, the electrical conductor of the forward or reverse winding section remains on the cylindrical surface, while the respective electrical conductor crosses the first electrical conductor in the form of a bridge element.

[0042] This particular embodiment allows the arrangement of windings and connection regions to be selected so that the operational potential of the transceiver coil is equal to or similar in magnitude to that of an equivalent position on an adjacent winding (e.g., the beginning, middle, or end of a winding). The potentials are considered similar if U1 / UN = (N / 2 - 1) / (N / 2), where U1 is the voltage across the first winding and UN is the voltage across the Nth winding. In preferred embodiments in which the coil section includes a reversing winding (established by a so-called balanced network) with a point of zero potential during operation, the forward and reverse windings of the coil section are therefore preferably alternated, except for the reversing winding. In this way, the electric field seen by the conductive sample can be reduced, while other performance losses can be reduced. This embodiment is particularly advantageous for testing conductive measurement samples or measurement samples with high dielectric loss. The geometric arrangement of the conductor sections on a common cylindrical surface according to the present invention significantly minimizes the electric field generated by the coils of the NMR probehead in the measurement sample. Electric fields can lead to performance losses both during transmission and reception, such as heating of the measurement sample, lengthening of the pulse angle at limited transmission power, and reduction of the signal-to-noise ratio.

[0043] There may be multiple coil sections, each having a forward winding section and a reverse winding section.

[0044] Preferably, both the forward and reverse winding sections are designed to have a solenoid shape, and the forward and reverse windings are preferably arranged alternately.

[0045] The present invention also relates to a MAS NMR probehead having the transceiver coil arrangement described above, wherein the NMR probehead is designed to be placed in an elongated bore of an NMR magnet. The elongated bore of the NMR magnet and the static magnetic field B0 generated by the NMR magnet are oriented along the Z direction. The elongated extension of the NMR probehead housing also extends in the Z direction, allowing the NMR probehead to be inserted into the bore of the NMR magnet. The X direction is in the X'Z' plane, where Y=Y'.

[0046] The present invention also relates to a method for designing the aforementioned transceiver coil arrangement, in which an optimization is performed, according to the invention, the signal-to-noise ratio SNR of a given NMR experiment is selected as the objective function for the optimization, or the objective function comprises at least two variables that influence the signal-to-noise ratio (SNR). According to the invention, the optimization is performed by means of optimization parameters, of which at least two selected optimization parameters are varied over the course of the length of the electrical conductor and are selected from the following parameters: slope S, tilt T, conductor path width W.

[0047] The NMR experiment provides, among other things, the type and number of spins to be excited in the sample, as well as the coupling constant between these spins, the angle Θ (Z direction) of the longitudinal axis Z' of the transceiver coil relative to the static magnetic field B0, the excitation pulse sequence (including the transmit power on one or more channels), the relaxation times of the spins, and the rotation speed of the measured sample around the longitudinal axis Z' of the transceiver coil.

[0048] Thus, according to the present invention, the optimization objective function can comprise the SNR itself or several variables that affect the SNR, which can be weighted and incorporated into the objective function, or the objective function can consist of multiple partial functions that are iteratively optimized, e.g., one partial function for each selected variable that affects the SNR.

[0049] As a result of the optimization according to the present invention using various optimization parameters, it is possible to compensate for the shielding effect generated by the electrical conductors of the transceiver coil itself. This leads to an improvement in the quality (uniformity) of the HF magnetic field B1 generated by the transceiver coil and the signal strength (amplitude of the HF magnetic field B1 generated by the transceiver coil), especially for the extension of, for example, strip-shaped conductors. The optimization according to the present invention preferably allows for an HF magnetic field having a component in the direction of the longitudinal axis Z' of the transceiver coil. Therefore, the optimization according to the present invention is not performed with the aim of avoiding the Z' component of the HF magnetic field B1. Therefore, in contrast to [Sun et al.] and [Barbara et al.], the present invention does not assume that the best solution is to position the generated HF magnetic field B1 as completely as possible in the XY plane. In particular, the method according to the present invention takes into account the resistive losses caused by shielding currents in the coil conductors and the reduction of the B1 magnetic field caused by these shielding currents. These losses increase in extended conductors (conductors whose conductor path width does not vanish) as the gradient T increases, and as a result, the best efficiency is generally achieved with an HF magnetic field B1 that is not entirely in the XY plane (the plane perpendicular to the B0 field of the main field magnet).

[0050] The use of strip conductors with a thickness of 3δ to 10δ, δ=penetration depth at a given frequency and for a given coil material, is particularly advantageous.

[0051] The optimization preferably comprises: a) defining the number of windings N, where N≧3; b) in each case determining starting values ​​for the optimization parameters; c) determining an objective function having the determined starting values ​​of the optimization parameters; d) adjusting the optimization parameters, where for at least two selected parameters, a non-constant function is used as a function of the execution parameter t running between 0 and the number of turns N of the transceiver coil arrangement, t∈R″, 0≦t≦N, N∈R″ (R is the set of all real numbers); e) determining an objective function using the adjusted optimization parameters; f) repeating steps d) to e) until the target function is within a predetermined target interval.

[0052] Preferably, the number of windings N is chosen to be an integer or half-integer (N∈N″ or 2N∈N″ (N'': the set of all natural numbers). In principle, N could be ∈R″.

[0053] In a preferred variant of the method according to the invention, one of the at least two variables of the objective function affecting the SNR is the radial homogeneity of the HF magnetic field B1 generated by the transceiver coil during operation within the FOV, and the selected optimization parameters are the slope S and tilt T of the winding.

[0054] Thus, in this variant, the objective function comprises, inter alia, axial and radial uniformity, which is optimized by tilt T and slope S.

[0055] By using radial uniformity as part of the target function, the SNR can be improved, particularly in cross-polarization (CP) and double cross-polarization (DCP) experiments using a cross-coil arrangement with a transceiver coil according to the present invention. While infinitely long solenoidal coils (except in the immediate vicinity of the windings) are characterized by very high radial uniformity, short solenoidal coils have reduced radial uniformity in their end regions (axial ends), even if the axial uniformity is corrected by reducing the slope of the windings in the end regions. When such short solenoidal coils are used in MAS NMR measurement heads, the longitudinal axis Z' of the transceiver coil is tilted by a magic angle about the Y axis with respect to the axis Z of the static magnetic field. Under these conditions, the radial uniformity of the HF magnetic field B1 is significantly reduced in the edge regions. This has a negative impact on the achievable SNR of double cross polarization (CP) and double cross polarization (DCP) experiments, especially when another transceiver coil is provided in addition to the first transceiver coil and the two transceiver coils correspond to different measurement frequencies, especially when the other transceiver coil is designed as a saddle coil and / or resonator and the B2 field points in the Y direction (the longitudinal axis Z' of the first transceiver coil designed as a solenoid coil lies in the YZ plane).

[0056] The optimization of the radial uniformity is performed over a given length L' (plateau region) within the FOV parallel to the longitudinal axis Z' of the transceiver coil. The more similar the B1 intensity values ​​along the plateau region are (i.e., for different radii), the better the radial uniformity.

[0057] Preferably, the tilt T of the windings is adapted over the course of the length of the electrical conductor so that the tilt T at the axial ends of the first transceiver coil is smaller than at the axial centre.

[0058] For each conductor cross section (i.e., specifically for each conductor path width W) and each slope S, there is a slope T at which the B1 field amplitude is maximized. A variable slope T with a maximum value in the central region of the transceiver coil can maximize the efficiency of the transceiver coil while simultaneously correcting radial uniformity. In particular, the outermost one or two windings have a smaller slope T compared to the slope T of windings located more toward the center.

[0059] Preferably, at least one central half-winding of the transceiver coil arrangement is inclined more strongly with respect to the longitudinal axis Z' of the transceiver coil than with respect to the Z-axis defined by the static magnetic field B0 of a given NMR experiment. As a result, for extended conductors, it is possible to achieve a B1 field passing in the XY plane. The solution found here is typically not one with maximum efficiency, but one with maximum generated magnetic field strength per single current, with a reduced coil quality factor. This is particularly advantageous when significant losses occur in other regions of the probe head and, therefore, the coil quality factor is not dominated by conductor losses (but, for example, by dielectric losses).

[0060] The ratio D / W of the gap width D to the conductor path width W to the adjacent winding is preferably set as a function of the winding tilt. The gap width D of a conductor at position t is the distance of the electrical conductor between position t and position t+2π or t−2π.

[0061] If the ratio D / W of the gap width D to the conductor path width W is selected as an optimization parameter in addition to the slope T, then the ratio D / W, i.e., either the conductor path width or the gap width, or both parameters along the length of the conductor, is selected as the optimization parameter, and the ratio D / W is selected as a function of the slope T. That is, the larger the winding slope T, the larger the ratio D / W of the gap width D to the conductor path width W is selected. In particular, D / W also varies over the length of a single winding, and D / W has at least two minima.

[0062] In an advantageous variant of the method according to the invention, one of at least two variables affecting the signal-to-noise ratio SNR is the axial homogeneity of the HF magnetic field B1 generated by the transceiver coil. This is done in particular by varying the slope of the windings. By optimizing the axial homogeneity (homogeneity along the longitudinal axis Z' (axial)), it is possible to improve the SNR, in particular for pulse sequences with several (90° and 180°) pulses, or to increase the usable volume of the active area of ​​the transceiver coil, within which a desired signal quality, in particular a desired signal amplitude, is achieved.

[0063] In the case of a finite transceiver coil, the amplitude of the B1 field drops at the axial ends. By reducing the slope at the axial ends, the windings can be positioned closer to each other. In this way, the missing current density due to the finiteness of the transceiver coil can be compensated for. Therefore, an improvement in uniformity along the longitudinal axis Z' of a short transceiver coil operating away from its natural frequency occurs, especially if the slope at the axial ends of the transceiver coil is selected to be smaller than that at the axial center.

[0064] During operation close to the natural frequency, when connecting the transceiver coil, the current distribution changes, so it must be ensured that the potential is set so that the transceiver coil oscillates symmetrically. Alternatively, the potential distribution can be set by a matching network so that the maximum is not at the center of the solenoid coil, but this leads to a higher electric field and therefore higher losses in the lossy measurement sample.

[0065] A further variation of the method according to the present invention provides that one of the at least two variables affecting the signal-to-noise ratio (SNR) is the amplitude / rating of B1, and the selected optimization parameters are the slope S and the conductor path width W. The optimization of the amplitude / rating of B1 also includes iterative optimization of the B1 amplitude / unit current and the quality factor. The amplitude / rating of B1 improves the efficiency of the transceiver coil.

[0066] In particular, when flat strip conductors are used as electrical conductors (δ = penetration depth, with a conductor path thickness of 3δ to 10δ), the sensitivity of the transceiver coil (B1 amplitude / rated power) can be influenced by varying the ratio D / W of the gap width D to the conductor path width W. In particular, deviations from the values ​​P / W = 1.5...1.667 known from the prior art for solenoid coils in NMR are provided. For very thin metal plating, especially coils with lengths significantly longer than their diameters, the highest efficiency of the solenoid coil is achieved according to the present invention with a ratio P / W < 1.5, especially < 1.25 (i.e., pitch P = 1 mm, conductor path width ≥ 0.8 mm). Therefore, the ratio D / W of the gap width D to the conductor path width is preferably D / W < 0.5, and more preferably D / W = 0.25. Therefore, the gap width D between the windings is preferably less than half the conductor path width W, especially less than one-quarter of the conductor width.

[0067] The tilt T of the windings at the axial center of the transceiver coil is preferably selected so that the B1 amplitude of the HF magnetic field B1 generated by the transceiver coil is nominally maximized for a given ratio of the gap width D to the conductor path width W. Here, the tilt T is the optimization parameter.

[0068] A special variant of the method according to the invention provides that the transceiver coil arrangement comprises a further transceiver coil for generating a further HF magnetic field B2, and one of the at least two variables influencing the signal-to-noise ratio SNR is the amplitude / rated ratio B1 / B2 of the first HF magnetic field B1 and the further HF magnetic field B2.

[0069] To increase the efficiency of the coil, it is advantageous for the electrical conductor to have a conductor thickness d and a rounding radius r, where the conductor thickness d and / or the rounding radius r of the electrical conductor are used as additional optimization parameters that are varied over the course of the length of the electrical conductor, so that the cumulative "blurring" of the current at the corners improves the quality factor and therefore the efficiency of the coil, without significantly affecting other parameters.

[0070] The invention also relates to a method for manufacturing a transceiver coil, the transceiver coil being designed according to the aforementioned method, the geometry of the coil being produced according to the design from a metal tube, in particular by milling, laser or water jet cutting.

[0071] The advantage of this is the small conductor path thickness d that can be achieved. Furthermore, such a transceiver coil can be manufactured without a carrier, especially without a carrier between the conductor and the measurement sample, which results in an improved efficiency of the transceiver coil. To further improve conductivity, methods for rounding the cut edges of the conductor (e.g., trellising) can be used, or the cut edges can be rounded, for example, by milling.

[0072] Alternatively, the designed coil geometry can be realized by a coated carrier, the coating being produced by structuring, for example, etching, milling, laser ablation, etc. The production of the coating on the carrier allows for the production of even thinner layers. The carrier serves to increase mechanical robustness and can be used as a heat conductor, for example, to cool the cryogenic coil by means of a cold finger. The coating is preferably superconducting.

[0073] Further advantages of the present invention will become apparent from the description and drawings. Likewise, the features according to the present invention mentioned above and described below can be used each alone or together in any desired combination. The illustrated and described embodiments should not be understood as an exhaustive list, but are of an exemplary nature for explaining the present invention. [Brief explanation of the drawings]

[0074] [Figure 1]FIG. 1 shows a transceiver coil according to the present invention with a constant slope at the center, a decreasing slope on the two outermost windings, a varying slope with two maxima per winding, and a periodically varying conductor path width for a single coil configuration. [Figure 2] 1 shows a transceiver coil with varying tilt, varying slope, and periodically varying conductor path width with two maxima per winding for a cross coil configuration. [Figure 3a] 3 shows a plan view of a transceiver coil arrangement according to the invention in a cross-coil configuration with a first transceiver coil according to FIG. 2; [Figure 3b] 3b shows a perspective view of the transceiver coil arrangement of FIG. 3a. [Figure 4] 1 shows a transceiver coil according to the present invention having varying tilt, varying slope, and periodically varying conductor path width with four maxima per winding for a cross coil configuration. [Figure 5a] 1 shows a plan view of a transceiver coil arrangement according to the present invention in a cross-coil configuration having a zero-pitch transceiver coil with a periodically varying slope and a periodically varying conductor trace width. [Figure 5b] 5b shows a perspective view of the transceiver coil arrangement of FIG. 5a. [Figure 6] 1 shows a transceiver coil according to the invention for a single coil configuration in which the tilt varies in addition to the slope and conductor path width, and the conductor path width varies periodically with a maximum value at each revolution. [Figure 7] 1 shows a transceiver coil according to the present invention with a varying slope from winding to winding, varying conductor trace width, and a periodically varying conductor trace width with a highly varying slope. [Figure 8] 1 shows a transceiver coil according to the present invention having a constant slope, a varying conductor trace width, and a varying tilt. [Figure 9] 1 shows an NMR probehead according to the present invention. [Figure 10a]10 shows details of a solenoidal coil section to illustrate coil parameters in a coil with tilted windings. [Figure 10b] 10 shows details of a solenoidal coil section to illustrate coil parameters in a coil with non-graded windings. DETAILED DESCRIPTION OF THE INVENTION

[0075] A transceiver coil according to the present invention has coil parameters that vary along the path of the electrical conductor of the transceiver coil. Figures 10a and 10b each show a portion of a solenoid-shaped coil with a strip-shaped conductor 2 (conductor path), with some of the coil parameters first shown. The solenoid-shaped coil of Figures 10a and 10b is oriented along a longitudinal axis Z' (coil axis), which is perpendicular to the X'Y' plane (not shown). The solenoid-shaped coil is parameterized by the conductor path width W of the conductor 2, the gap width D of the gap 10, the local slope S (not shown) and / or pitch P of the windings, the inclination T of the windings, and the radius R of the windings. In the illustrated embodiment, a total of three windings are shown.

[0076] The conductor width W indicates the width of the conductor 2. The conductor path width W is the width of the conductor path perpendicular to the conductor center. In the coil shown in Figures 10a and 10b, the conductor path width W is constant along the longitudinal axis Z' (i.e., W is a constant).

[0077] The gap width D denotes the width of the intermediate spaces 10 between the strip-shaped conductors of adjacent windings of the conductor path 2 .

[0078] The pitch P of the windings indicates the advancement in the Z' direction of the complete winding and is determined through the centerline of the conductor path 2. A constant pitch P does not exclude that the local slope S may vary within one winding.

[0079] The winding tilt T denotes the inclination of the winding with respect to the longitudinal axis Z' and corresponds to the amplitude of the sinusoidal modulation of the Z' position of the conductor center plane across one winding. If the slope and tilt are constant across several windings, it can be easily determined from Max(Z(t)-Z(t+1))-S) / 2, where t varies in the interval tn...tn+1.

[0080] The radius R of the winding indicates the radius at which the conductor 2 exists.

[0081] The solenoid coils shown in Figures 10a and 10b each have a constant conductor path width W, a constant gap width D, a constant slope S, and therefore a constant pitch P, with the coil shown in Figure 10a being a gradient coil (T≠0) and the coil shown in Figure 10b being a non-graded coil (T=0).

[0082] In general, the centerline of the conductor 2 is defined in Cartesian coordinates as follows:

number

[0083] The envelope of the conductor 2 in Cartesian coordinates is defined as follows:

number

[0084] The conductor path width is, in particular, W(t) = W0 + ΣW i (sin(2πt+k)) 2i where the tilt T is constant across each half-winding. Typically, the tilt direction is φ=0 (tilt about the Y' axis) or π / 2 (tilt about the X' axis), and the radius R(t)=R.

[0085] In the following, various variations of the geometry of the transceiver coil according to the invention are described, in which the performance of the NMR coil head according to the invention along the path of the electrical conductor 2 can be optimized by varying the coil parameters.

[0086] 1 and 2 show transceiver coils 1a, 1b according to the present invention, which have a constant tilt T about the x' direction (i.e., the tilt direction φ=π / 2). The pitch P is constant in the central region of the transceiver coils 1a, 1b and decreases toward the two axial ends 4a, 4b of the transceiver coils 1a, 1b. The conductor path width W varies periodically, with two regions of maximum conductor path width per winding and two regions of minimum conductor path contact. Furthermore, W(k) = W(k+0.5) = Wmin and W(k+0.25) = W(k+0.75) = Wmax.

[0087] The parameters of the transceiver coils 1a, 1b that are varied in accordance with the present invention are the conductor path width W, and the pitch P, and therefore the slope S. In these embodiments, the slope S is constant from winding to winding. However, in general, it can also be varied over the length of the winding.

[0088] The two transceiver coils 1a, 1b differ in terms of the placement of the minimum and maximum conductor path widths relative to the tilt direction φ=π / 2 or φ=0 of the transceiver coils 1a, 1b.

[0089] In principle, for gradient windings (T ≠ 0), it is advantageous for the minimum conductor path width in the cross-sectional plane to be perpendicular to the gradient axis. For gradients about the X' axis, the minimum conductor path width lies in the cross-sectional plane of the coil, which is the Y'Z' plane, as shown in Figure 1. The gradient generates a magnetic field component along the Y' axis, i.e., at 90° to the Z' axis. This magnetic field component must "penetrate" the transceiver coil, which is easier when a larger gap width D exists between the conductor sections of the two windings. Shielding currents form in the conductor itself, which increases resistive losses, weakens the magnetic field, and therefore leads to performance losses. By locating the minimum conductor path width W or the maximum gap width D along the Y'Z' plane and the maximum conductor path width W or the minimum gap width D along the X'Z' plane, performance can be improved. This is because the ratio of gap width to conductor path width can be optimized at all spatial positions.

[0090] Due to their good performance, the transceiver coils 1a shown in FIG. 1 are particularly suitable for transceiver coil arrangements 100a, 100b with a single coil configuration.

[0091] If another transceiver coil 11 (see FIGS. 3a and 3b) generating an HF magnetic field B2 oriented in the X' direction (i.e., a saddle coil, resonator, ...) surrounds or is surrounded by the transceiver coil 1b according to the present invention, this magnetic field B2 must penetrate into the first transceiver coil 1b. The conductor paths (windings) of the first transceiver coil 1b are "in the way" and partially shield the magnetic field of the other transceiver coil 11. In this case, as shown in FIG. 2, the performance of the other transceiver coil 11 can be optimized by reducing the conductor path width W in the X' direction of the first transceiver coil 1b. This optimization of the other transceiver coil 11 "detracts" from the performance of the first transceiver coil 1b, but provides better magnetic permeability in the X' direction. Therefore, the transceiver coil 1b shown in FIG. 2 is particularly suitable for a transceiver coil arrangement 100b with a cross-coil configuration.

[0092] 3a and 3b show a transceiver coil arrangement 100b having such a transceiver coil 1b and another transceiver coil 11 in a cross-coil configuration. The transceiver coil arrangement 100b comprises the first transceiver coil 1b shown in FIG. 2 for generating a first HF magnetic field B1 and another transceiver coil 11 for generating a second HF magnetic field B2 for an NMR probehead 23 (see FIG. 9) according to the present invention. Here, the first transceiver coil 1b is arranged coaxially radially inside the other transceiver coil 11 so that the second magnetic field B2 generated by the other transceiver coil 11 is approximately perpendicular to the first magnetic field B1 generated by the first transceiver coil 1b. The other transceiver coil 11 is here formed as an Alderman-Grant resonator consisting of two halves 5 and 5′, radially surrounding the first transceiver coil 1b, and the other transceiver coil 11 is provided with two opposing openings 12 ("windows"). The first transceiver coil 1b and the further transceiver coil 11 are oriented relative to each other such that the region of the first transceiver coil 1b where the conductor path width W of the electrical conductor 2 of the first transceiver coil 1 has a minimum value is within the "window" 12 of the further transceiver coil 11. As a result, the second magnetic field B2 generated by the further transceiver coil 11 passes through the region of the first transceiver coil 1a with the minimum conductor path width W. As a result, the first transceiver coil 1b has high transparency to the second HF magnetic field B2. As an alternative to the embodiment shown in FIGS. 3a and 3b, the further transceiver coil 11 can be disposed within the first transceiver coil 1b (not shown). Similarly, the further transceiver coil can also be designed as a saddle coil, in particular a multi-winding saddle coil, rather than as a resonator (not shown).

[0093] FIG. 4 shows a very specific embodiment of a transceiver coil 1g according to the present invention. The conductor path width W varies periodically for the transceiver coil 1g, with four maximum and four minimum values ​​per winding. The two minimum values ​​along the tilt axis (X' direction) are for generating transparency for the second HF magnetic field B2 of the cross-coil configuration, similar to the transceiver coil 1b of FIG. 2, and the two minimum values ​​perpendicular to the tilt axis (along the Y' direction) are for "uniquely becoming less" for the transceiver coil 1a of FIG. 1. These minimum values ​​generally optimize the performance of the first transceiver coil 1g relative to the transceiver coil with tilted windings, while the transparency-enhancing minimum value optimizes the performance of another transceiver coil (not shown in FIG. 4) at the expense of the first transceiver coil 1g.

[0094] The parameters of the transceiver coil 1g that are varied in accordance with the present invention are the conductor trace width W, and the pitch P and hence the slope S and tilt T.

[0095] 5a and 5b show a further embodiment of a transceiver coil device 100c with a cross-coil geometry and a first transceiver coil 1c. The windings of the transceiver coil 1c have a local slope S(t)=0 over most of their length. Such windings form an unclosed ring, i.e., S(t)=0 for t=t0...t0+1-ε or t=t0+ε / 2...t0+1-ε / 2, where ε>0, which prevents short circuits, and t=t0 is the start of the winding. A solenoid coil 1c designed in this way is known as a "zero-pitch" coil because most of the winding has a local pitch of zero. However, the pitch P of the complete winding has a value that is not equal to zero, and this value is constant in this embodiment (|P|=constant). Therefore, such a transceiver coil 1c can be designed as a combination of an unclosed "ring" with no (local) slope and an electric coil section with a slope S(t)≫0. The ratio W / D of the conductor path width W to the gap width D can be kept constant across the transceiver coil 1c in a simple manner if the conductor path width is designed to be constant. As a result, the quality of the transceiver coil 1c can be maximized and / or the electric field can be minimized in a particularly simple manner. However, the transceiver coil 1c of FIGS. 5a and 5b has a periodically varying conductor path width W, and as a result, the gap width D between the windings also varies periodically. Optimizing the performance of a single transceiver coil 1c and its impact on the performance of a cross-coil arrangement is particularly easy to calculate with this configuration. The transceiver coil 1c also has a constant tilt T.

[0096] The parameters of the transceiver coil 1c that are varied in accordance with the present invention are the conductor trace width W, the slope S or pitch P, and the tilt T.

[0097] The first transceiver coil 1c shown in Figures 5a and 5b is preferably designed in a crossed geometry with forward and reverse windings 14 and 15 preferably arranged alternately.

[0098] Figure 6 shows a transceiver coil 1d according to the invention in which both the local slope S and conductor path width W, as well as the gradient T, are varied. The conductor path width W has exactly one maximum and one minimum value in each winding, and the conductor path width W averaged over the winding decreases towards the axial ends 4a, 4b. The transceiver coil 1d of Figure 6 can be particularly well adapted to multiple cores and is therefore particularly suitable for a one-coil transceiver coil arrangement 100d.

[0099] The parameters of the transceiver coil 1d that are varied according to the invention are the conductor path width W, the inclination T, and the pitch P and therefore the slope S. The inclination T of the axial ends of the coil is T=0. As a result, such a coil can be particularly easily fitted in a defined installation space, for example between the bearings of a MAS stator, and makes particularly good use of the available volume.

[0100] Figure 7 shows a transceiver coil 1e according to the invention, in which both the local slope S and conductor path width W, as well as the tilt T, are varied. In this embodiment, the winding slope S varies discretely, i.e., S(t) = constant within one winding. While this discretization does not provide optimal uniformity, a sufficiently good uniformity level can be achieved. Both the conductor path width W and tilt T, as well as the pitch P, decrease towards the axial ends 4a, 4b.

[0101] The parameters of the transceiver coil 1e that are varied in accordance with the present invention are the conductor trace width W, the tilt, and the pitch P and therefore the slope S.

[0102] The transceiver coil 1e is particularly suitable for a one-coil transceiver coil arrangement 100e.

[0103] The transceiver coil 1f shown in FIG. 8 has a constant pitch P, but the inter-winding tilt T and conductor path width W vary.

[0104] The ratio W / D of the conductor path width W to the gap width D between the windings is constant here. In combination with the tilted windings (T not equal to 0), this results in the maximum conductor path width W being located at the bottom (-Y' direction) in the left half of the transceiver coil 1f, and the maximum conductor path width W being located at the top (+Y' direction) in the right half of the transceiver coil 1f. The transceiver coil 1f shown in FIG. 8 can be used particularly advantageously when the overall length of the transceiver coil arrangement is limited, for example, in a transceiver coil arrangement geometry where the transceiver coil must be inserted between two bearings. The transceiver coil 1f can be used particularly for simple FID experiments where maximizing axial and radial uniformity is not necessary.

[0105] The parameters of the transceiver coil 1f that are varied in accordance with the present invention are the conductor path width W, the gap width D, and the tilt T.

[0106] The transceiver coil 1f is particularly suitable for a one-coil transceiver coil arrangement 100f.

[0107] 9 shows a schematic diagram of an NMR probehead 23 according to the invention. In the example shown, the static magnetic field for performing NMR measurements is aligned parallel to the Z-axis during operation. The NMR probehead 23 comprises transceiver coils 1a-g or transceiver coil arrangements 100a-f according to the invention, which are connected to a matching network 24 and further comprise a spectrometer connection 21. The NMR probehead 23 shown in FIG. 9 is a MAS (Magic Angle Spinning) probehead, in which the longitudinal axis Z' of the transceiver coil 1 is tilted, preferably by the magic angle θ (θ=54.74°), with respect to the Z-axis along which the elongated extension of the NMR probehead 23 extends. [Explanation of symbols]

[0108] 1a-g transceiver coil 2. Electrical conductor 4a,4b Axial end 5,5' Half of another transceiver coil 10 Intermediate spacing between windings 11 Alternate transceiver coil 12 Separate transceiver coil opening / window 21 Spectrometer connection 23 NMR probe head 24 Matching Network 100a-f Transceiver coil device Z' longitudinal axis of the transceiver coil W Conductor path width D Gap width S local slope Pitch T slope R radius

[0109] List of cited references [Sun et al.] YHSun,GEMaciel, J. Magn. Reson., Series A, Vol. 105, pp. 145-150 (1993) Gradient coils for NMR experiments [Barbara et al.] US6359437B1 [Privalov et al.] F. Privalov, SVDvinskikh, H.-M. Vieth J. Magn. Reson., Series A, Vol. 123, pp. 157-160 (1996) Coil design for large volume and high B1 homogeneity for solid-state NMR applications [Mispelter] J. Mispelter et al. NMR Probeheads for Biophysical and Biomedical Experiments. Theoretical Principles and Practical Guidelines (2nd Edition), World Scientific Publishing Company, 2015 ISBN1783268042; 89 pages

Claims

1. A transceiver coil arrangement (100a-f) for a MAS NMR probehead having a first transceiver coil (1a-g) with a longitudinal axis Z' for generating a first HF magnetic field B1, the first transceiver coil (1a-g) has at least one solenoid-shaped portion having an electrical conductor (2) with a conductor path width W and N≧3 windings, all windings passing around the longitudinal axis Z′ of the transceiver coil (1a-g), the electrical conductor (2) having a slope S, each half winding inclined with a tilt T relative to the longitudinal axis Z′, T≠0 for at least a portion of the half windings; ●Slope T=T(t), Slope S = S(t), Conductor path width W = W(t) at least two of the variables vary over a path t of the length of the electrical conductor (2) of the transceiver coil (1a-g), characterized in that Transceiver coil arrangement (100a-f) for a MAS NMR probehead.

2. The transceiver coil arrangement (100a-f) according to claim 1, characterized in that the electrical conductor (2) of the first transceiver coil (1a-g) is a strip conductor.

3. 3. The transceiver coil arrangement (100a-f) according to claim 1, wherein the slope S varies over the path t of the length of the electrical conductor, and wherein the conductor path width W varies within each winding, in particular the conductor path width W increases at least once and decreases at least once within each winding.

4. 3. The transceiver coil device (100d-f) according to claim 1, wherein the slope S and the inclination T of the electrical conductor (2) of the first transceiver coil (1d-f) vary along the path of the electrical conductor (2).

5. The transceiver coil device (100d-f) of claim 4, characterized in that the tilt T at the axial ends (4a, 4b) of the first transceiver coil (1d, 1e, 1f, 1g) is smaller than that at the axial center.

6. the transceiver coil arrangement (100b, 100c) comprises at least one further transceiver coil (11) for generating a second HF magnetic field B2 radially outside the first transceiver coil (1b, 1c); the first transceiver coil (1b, 1c) and the further transceiver coil (11) are arranged around a common longitudinal axis Z' such that the HF magnetic fields B1, B2 generated by the first transceiver coil (1b, 1c) and the further transceiver coil (11) are aligned perpendicular to each other; A transceiver coil arrangement (100b, 100c) according to any one of claims 1 to 2, characterized in that

7. the electrical conductor (2) of the first transceiver coil (1c) comprises a forward winding section and a reverse winding section, the forward winding section comprises a forward winding (14) starting from a connection region and leading to an axial end (4a) of the transceiver coil (1c) with a predetermined winding orientation, the reverse winding section comprises a reverse winding (15) starting from the axial end (4b) of the first transceiver coil (1c) with the predetermined winding orientation and leading to the connection region, the winding of the reverse winding section having a slope S with a sign opposite to that of the forward winding section; the forward winding and the reverse winding of the electrical conductor (2) are arranged on a common cylindrical jacket surface around the longitudinal axis Z', except for an intersection region where the forward winding and the reverse winding cross each other; A transceiver coil arrangement (100c) according to any one of claims 1 to 2, characterized in that

8. A MAS NMR probehead (23) comprising a transceiver coil arrangement (100, 100a-f) according to any one of claims 1 to 2.

9. The optimization is performed wherein either the signal-to-noise ratio SNR of a given NMR experiment is selected as the objective function for optimization, or said objective function comprises at least two variables that affect said signal-to-noise ratio SNR, and, the optimization is performed by optimization parameters, at least two selected optimization parameters of which are varied over the course of the length of the electrical conductor (2); ●Slope S, ●Slope T, Conductor path width W, The parameters are selected from A method (100a-f) for designing a transceiver coil arrangement according to any one of claims 1 to 2, characterized in that

10. The optimization is a) defining the number of windings N, where N≧3; b) in each case determining starting values ​​for said optimization parameters; c) determining the objective function with the determined starting values ​​of the optimization parameters; d) adjusting the optimization parameters, wherein for the at least two selected parameters, a non-constant function is used as a function of a running parameter t running between 0 and the number of turns N of the transceiver coil arrangement (100a-f), t∈R″ (R″: the set of all real numbers) and 0≦t≦N; e) determining the objective function using the adjusted optimization parameters; f) repeating steps d) to e) until the target function is within a predetermined target interval; The method according to claim 9, characterized in that

11. 10. The method of claim 9, wherein one of the at least two variables of the objective function affecting the signal-to-noise ratio SNR is the radial uniformity of the HF magnetic field B1 generated by the transceiver coil (1d, 1e, 1f, 1g) during operation in a field of view, and the selected optimization parameters are the slope S and the tilt T of the winding.

12. 12. The method of claim 11, characterized in that the tilt of the windings is adapted over the course of the length of the electrical conductor (2) such that the tilt T at the axial ends (4a, 4b) of the first transceiver coil (1d, 1e, 1f) is smaller than at the axial center of the first transceiver coil (1d, 1e, 1f, 1g).

13. 10. The method of claim 9, wherein one of the at least two variables of the target function affecting the signal-to-noise ratio SNR is the axial homogeneity of the HF magnetic field B1 generated by the transceiver coil (1a-e, 1g).

14. 10. The method of claim 9, wherein one of the at least two variables of the objective function affecting the signal-to-noise ratio SNR is the amplitude / rating of the B1, and the selected optimization parameters are the slope S and the conductor path width W.

15. 10. The method of claim 9, wherein the tilt T of the winding at the center of the transceiver coil (1a-g) is selected such that the B1 amplitude / rating is maximized for a given ratio S / W of slope S to conductor track width W.

16. 10. The method according to claim 9, wherein the transceiver coil arrangement (100b, 100c) comprises a further transceiver coil (11) for generating a further HF magnetic field B2, and one of the at least two variables of the target function affecting the signal-to-noise ratio SNR is the amplitude / rated ratio B1 / B2 of the first HF magnetic field B1 and the further HF magnetic field B2.

17. 10. The method of claim 9, wherein the electrical conductor (2) has a conductor thickness d and a rounding radius r, and the conductor thickness d and / or the rounding radius r of the electrical conductor (2) are used as additional optimization parameters that are varied over the course of the length of the electrical conductor (2).

18. The transceiver coils (1a-g) are designed according to the method of claim 9, the transceiver coils (1a-g) have a geometry that is manufactured according to the design from a metal tube, or the transceiver coils (1a-g) have a geometry that is realized according to the design by a coated carrier, the coating being manufactured by structuring, A method for manufacturing a transceiver coil (1a-g), characterized in that

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