NMR probe head with temperature control device made of thermally conductive material

Abstract

An NMR probe head (10'), designed for insertion into an MR apparatus (101), comprising a probe head housing (4) for receiving a cylindrical temperature control tube (2) made of thermally conductive material surrounding a sample (5), a heat exchanger (1) being mounted at the axial end of which is in thermal contact with the temperature control tube and projecting radially from the latter onto the inner wall of the probe head housing, and a first insulation element (3) made of poorly thermally conductive material surrounding the temperature control tube at an axial distance from the heat exchanger and comprising an RF coil (6), is characterized in that at least one temperature control element (7) made of thermally conductive material is positioned radially between the first insulation element and the inner wall of the probe head housing for heat distribution along the z-axis.which completely surrounds the first insulation element azimuthally and extends axially along the z-axis at least over the full axial length of the first insulation element. This minimizes the temperature gradient across the sample in both axial and radial directions.

Description

[0001] The invention relates to an NMR probe head, designed for insertion into a magnetic resonance apparatus for performing an MR measurement on a sample, comprising a probe head housing for receiving a temperature control tube cylindrical about a z-axis, which surrounds the sample with a sample substance in a sample volume during NMR measurement operation, made of thermally conductive material with a thermal conductivity of at least 20 W / mK for temperature control of the sample during NMR measurement operation, wherein a heat exchanger is attached to at least one axial end of the temperature control tube, which is in thermal contact with the temperature control tube, a first insulation element made of poorly thermally conductive material with a thermal conductivity of at most 1 W / mK and surrounding the temperature control tube azimuthally at an axial distance in the direction of the z-axis from the at least one heat exchanger, and an RF coil.

[0002] An NMR probe head with these features is known per se from US 2007 / 0257673 A1 = Reference [1]. Background of the invention

[0003] The present invention relates generally to the field of magnetic resonance, in particular nuclear magnetic resonance (NMR), and to probe heads for MR instruments.

[0004] NMR spectroscopy is a commercially widespread and highly efficient instrumental analytical method used to characterize the chemical composition of substances or to determine the structure of materials in samples. The sample substance, typically in solid or liquid form, is placed in a cylindrical sample tube. For measurement, it is positioned within the measuring region of a probe head of an MRI apparatus. There, the sample substance is exposed to a strong, static magnetic field with flux density B0, homogeneous in the z-direction, which aligns the nuclear spins. High-frequency electromagnetic pulses are then injected into the sample. This, in turn, generates an electromagnetic response in the sample in the form of high-frequency electromagnetic fields, which are detected by the NMR apparatus. Information about the properties of the sample can be obtained from the detected RF fields.In particular, the position and intensity of NMR lines can be used to infer the chemical composition and chemical bonding in the sample.

[0005] The temperature of the sample fundamentally influences the results of NMR measurements. The spatial temperature gradient across the active measurement volume and the temporal stability of the sample temperature have a significant impact on the quality of NMR measurements.

[0006] For particularly high-quality measurements, the temperature is typically set using a temperature control unit and kept as constant as possible spatially and temporally across the active measurement volume.

[0007] NMR measurements can be performed with both heated and cooled samples. If, for example, the sample is to be cooled below room temperature, a sufficiently cold temperature control fluid stream is passed through the inlet tube and heated to the target temperature by a heater.

[0008] For example, temperature control units for minimizing the temperature gradient in the active measurement volume are already known from the old publication DE 40 18 734 C2 =Reference [2] or also from DE 10 2010 029 080 B4 =Reference [3].

[0009] A cooled NMR probe head with uniform temperature control of the sample is described in DE 100 06 323 C2 = reference [4].

[0010] A similarly cooled NMR probe head with thermal insulation of the sample is known from DE 100 06 317 C2 = reference [5].

[0011] A cooled NMR probe head in a vacuum container is disclosed in DE 10 2006 046 888 B4 = reference [6].

[0012] In DE 10 2016 218 772 A1 =Reference [7] an improved temperature control of an NMR-MAS probe head is described.

[0013] Reference US 5 530 353 A [8] shows a variable-temperature sample head for NMR spectrometers. To control the temperature of the sample tube, an outer wall is fitted with a temperature-controlled water jacket with its own inlet and outlet. The water jacket is made of stainless steel for electromagnetic shielding. Coaxially within the water jacket is a ceramic tube forming a coil former. The space between the RF coil and the water jacket is filled with an electrical insulator with relatively high thermal conductivity.

[0014] Thermal insulation is not described in reference [8]. It is possible that a heat exchanger is present in the water supply system of the temperature-controlled water jacket in the known apparatus. However, this is definitely not located inside the sample head.

[0015] The reference already cited at the beginning [1] discloses an NMR probe head with all the generic feature sets of the preamble of claim 1.

[0016] Reference [1] describes an NMR probe for performing high-temperature NMR measurements. To maintain the temperature of the sample tube, it is positioned inside thermally conductive transfer tubes. The transfer tubes are connected to a heating device, while the external environment of the sample is thermally insulated by four layers of heat-insulating tubes.

[0017] The heating device comprises a heat exchanger at both axial ends of the temperature control tube, above and below the sample tube, radially outward, which is in thermal contact with the temperature control tube and projects radially away from the temperature control tube towards the inner wall of the sample head housing.

[0018] However, this device known from reference [1] is expressly designed to be able to generate a significant and steep temperature gradient in the sample during NMR measurement operation, which is certainly advantageous or even necessary for the type of NMR measurements intended there. Previously unresolved specific problems in the state of the art

[0019] In contrast, for other types of NMR measurements, such as relaxometry, it is often desirable or even essential to minimize or completely avoid a temperature gradient across the sample, because NMR measurements are temperature-dependent. The goal in such cases is therefore to achieve thermal insulation that significantly reduces the temperature gradient of the sample in the z-direction.

[0020] Here too, the sample should be temperature-controlled within the probe head. However, the temperature distribution should now be as homogeneous as possible, especially with a minimal temperature gradient across the sample. Metallic components that generate magnetic fields must not be used.

[0021] For NMR instruments based on permanent magnets, good thermal insulation of the magnets, which are typically heated above room temperature (>30°C), is necessary to generate a uniformly homogeneous magnetic field. Simultaneously, temperature control of the sample, typically ranging from -10°C to +70°C, is required. This necessitates effective shielding of the sample temperature control system from the permanent magnet.

[0022] Since the geometry within the magnet bore is limited, a temperature control and insulation concept is necessary that works efficiently even in confined spaces.

[0023] A conventional temperature control system located inside the magnet bore, as used in the "MINISPEC" benchtop system. R “The system, which has been manufactured by the applicant since the 1970s, works in principle as follows: The sample chamber, into which the sample or sample tube is inserted, is located radially at the innermost point of the assembly. The sample tube is surrounded by an AIN tube, which is in thermally conductive contact with the heat exchanger. AIN is a typical non-electrically conductive material that, with a thermal conductivity of 100-200 W / mK, is an excellent heat conductor. The heat exchanger is heated to the desired temperature by pre-tempered water. The AIN tube is attached to this heat exchanger. Due to its high thermal conductivity, the RF coil and the sample tube are thus heated in the area of ​​the sample.

[0024] Outside the AIN tube, the RF coil is mounted on a coil former, typically made of PTFE. The probe head housing, made of a suitable plastic, is located in an air-filled spacer volume outside the coil. Radially outside this spacer are usually gradient coils, also mounted on coil formers.

[0025] Since the heat exchanger can only be mounted on one side and there is a thermal load from the outside, e.g. due to the gradient, but also due to the temperature of the magnet, a temperature gradient of approximately 2 K forms above the measurement sample.

[0026] For the MINISPEC mentioned above R -System or generally in time-domain NMR, this temperature difference of 2 K is actually too large: With the MINISPEC RRelaxation measurements are performed using this system. Relaxometry is highly temperature-dependent. The relaxation times measured in relaxometry can be influenced by temperature. In particular, the spin-lattice relaxation time T1 and the spin-spin relaxation time T2 are temperature-dependent because molecular motion and interactions between molecules are temperature-dependent. Therefore, the aforementioned temperature gradient along the sample is actually too large and significantly limits the quality of the measurement results. Typically, relaxometry is limited to 1H measurements.

[0027] Furthermore, the thermal insulation to the outside in the direction of the housing is inadequate because the moving air between the RF coil and the housing causes a relatively strong heat convection. Object of the invention

[0028] The present invention is therefore based on the relatively complex problem of providing a probe head, using conventional components such as those commonly used for an MR apparatus with the features defined above, with which there is as little or no temperature gradient as possible across the sample during NMR measurement operation.

[0029] The invention aims to provide a temperature control device for MRI apparatus, particularly for benchtop instruments with permanent magnets, that tempers a sample located within the NMR measurement volume along its entire length in the z-direction without creating a significant, and especially not a strong, temperature gradient along the z-direction. Furthermore, no temperature loss should occur radially outside the sample, i.e., in the x- and y-directions where the permanent magnet is located. The objective is therefore anisotropic heat conduction in the z-direction with simultaneous thermal insulation in the radial direction.

[0030] Preferably, a space-saving solution should be presented that can also be easily retrofitted to existing, commercially available MR systems. Brief description of the invention

[0031] This complex problem is solved by the present invention in a surprisingly simple yet effective manner by means of an NMR probe head with the generic features described above, in that at least one temperature control element made of thermally conductive material is positioned in the radial direction between the coil carrier and the inner wall of the probe head housing for heat distribution along the z-axis, which completely surrounds the coil carrier azimuthally and extends in the axial direction along the z-axis at least over the full axial length of the coil carrier.

[0032] Preferably, only a single heat exchanger is present, which is mounted axially above or below the temperature control tube, usually radially outside, with thermal contact to the temperature control tube and projects radially away from it towards the inner wall of the sample head housing.

[0033] The basic idea of ​​the present invention is to fill the air space around the coil with at least one tube made of a material with good thermal conductivity in order to reduce the temperature gradient in the z-direction. This measure prevents air convection and thus heat transfer in the radial direction, while simultaneously reducing the temperature gradient in the z-direction.

[0034] The solution according to the invention is particularly advantageous for typical benchtop applications.

[0035] The present invention opens up previously unimagined possibilities, for example in commercial relaxometry.

[0036] The present invention thus provides an NMR probe head that elegantly and simply solves all the technical problems mentioned above. Preferred embodiments of the invention

[0037] A preferred group of embodiments of the NMR probe head according to the invention is characterized in that the RF coil is attached to the temperature control tube, which is thus designed as a coil carrier.

[0038] Since the temperature control tube is usually made of stainless steel, it has a relatively low coefficient of thermal expansion. Therefore, the geometry and consequently the set frequency of the RF coil remain unchanged even with temperature fluctuations.

[0039] In an alternative embodiment of the NMR probe head according to the invention, the RF coil - as in the next prior art - is attached to the first insulating element designed as a coil carrier.

[0040] In a particularly preferred class of embodiments of the NMR probe head according to the invention, at least one further insulation element is arranged in the radial direction between the inner wall of the probe head housing and the at least one temperature control element, which completely surrounds the first insulation element azimuthally and extends in the axial direction along the z-axis at least over the full axial length of the first insulation element.

[0041] This also further reduces the air space between the sample head housing and the temperature control element, thereby further reducing convection.

[0042] In preferred further developments of this class of embodiments, the NMR probe head according to the invention has at least one further temperature control element arranged coaxially to the first temperature control element in the radial direction between the inner wall of the probe head housing and the at least one further insulation element, which completely surrounds the first insulation element azimuthally and extends in the axial direction along the z-axis at least over the full axial length of the first insulation element.

[0043] This further reduces the temperature gradient in the z-direction, as also shown in the graph of Fig. 5 can be seen.

[0044] Preferably, the temperature control elements and the insulation elements form a lamellar structure extending radially away from the z-axis.

[0045] In this arrangement, preferably two coaxial AIN tubes are arranged outside the first insulation element, separated by a layer of a material with low thermal conductivity.

[0046] Further developments of this class of embodiments are advantageous in that the temperature control elements and the insulation elements are arranged in a tightly packed manner, in particular with as little as possible, preferably no, remaining air space in the area between the inner wall of the sample head housing and the first insulation element.

[0047] In previous NMR probe designs, the space between the coil and the housing was filled with air. Now, preferably, three tubes are inserted into this space, in particular two made of AlN and one of PTFE, the choice of material being based on the significantly different thermal conductivities of the two materials. However, air causes convection, which increases thermal conductivity. The idea is to maintain low thermal conductivity in the z-axis direction while significantly increasing it in the perpendicular direction. This achieves temperature equalization.

[0048] In practice, embodiments of the NMR probe head according to the invention have proven effective in which the temperature control elements and the insulation elements each have a radial thickness of 0.5 mm to 2 mm.

[0049] The thickness of the individual layers, i.e., the AIN layer and the insulating layer in between, should be as thin as possible to save installation space; however, the pipe should be sufficiently stable so that the half-shells are inherently rigid. A layer thickness of 0.5 mm to 2 mm has proven effective in this regard, even with the arrangement using half-shells.

[0050] Further advantageous embodiments of the NMR probe head according to the invention are characterized in that the temperature control elements are not in thermal contact with the heat exchanger.

[0051] This also simplifies assembly with the two half-shells.

[0052] In particularly preferred embodiments of the NMR probe head according to the invention, the temperature control elements, preferably also the temperature control tube, are made of thermally conductive material with a conductivity of 20 to 200 W / m*K, in particular of AIN or of sapphire = Al2O3 or of stainless steel.

[0053] Basically, instead of AIN, another material with good thermal conductivity in the range of 20-200 W / m*K that is not magnetic can be used.

[0054] AIN is particularly well suited alongside sapphire in an NMR probe head because it is neither electrically conductive nor magnetic.

[0055] An advantageous embodiment of the invention is characterized in that the insulating elements, preferably also the first insulating element, are made of a poorly thermally conductive material with a conductivity < 20 W / m*K, in particular of plastic, preferably of PTFE (=polytetrafluoroethylene) or PEEK (=polyetheretherketone).

[0056] With a thermal conductivity of 0.25 W / m*K, PEEK or PTFE are well-suited materials for the insulation elements according to the invention.

[0057] The present invention also encompasses a magnetic resonance apparatus with an NMR probe head of the type described above according to the invention, which is characterized in that the magnet system of the MR apparatus for generating a homogeneous B0 field comprises at least one permanent magnet, and in particular is composed exclusively of one or more permanent magnets.

[0058] Permanent magnets are more robust and require less maintenance than electromagnets. They are therefore commonly used in benchtop NMR instruments. However, the magnetic field B0 is highly temperature-dependent, which is why magnet temperature control must be accurate to > 0.1 K. Accordingly, the sample itself and the sample temperature control equipment must be thermally isolated from the permanent magnet.

[0059] In preferred embodiments, this MR apparatus can be designed as a particularly compact NMR benchtop device.

[0060] Further developments of these embodiments are advantageous, in which the MR apparatus is designed to perform relaxometric MR measurements in time-domain NMR.

[0061] The improvement in sample temperature control according to the invention is particularly important for relaxometric measurements to prevent temperature gradients from forming within the sample tube. This is because the relaxation of the nuclei is temperature-dependent. Since the measurement is averaged over the entire sample, temperature gradients within the sample lead to less accurate results.

[0062] Finally, the present invention also includes a method for manufacturing an NMR probe head of the type described above according to the invention, which is characterized in that the temperature control elements, optionally the further insulation elements and optionally the first insulation element, if the RF coil is arranged on the temperature control tube, are first produced in the form of coaxial cylindrical half-shells, which are joined together azimuthally around the coil-carrying component for installation in the NMR probe head.

[0063] In manufacturing, the AIN tubes are not slid over the coil; instead, two half-shells are provided that are placed around the RF coil. This method is advantageous in production because it is easier to place half-shells around the coil-supporting structure than to slide the entire insulating tube over it.

[0064] Further advantages of the invention will become apparent from the description and the drawing. Likewise, the features mentioned above and those described in more detail below can each be used individually or in any combination according to the invention. The embodiments shown and described are not to be understood as an exhaustive list, but rather serve as examples for illustrating the invention. Detailed description of the invention and drawing

[0065] The invention is illustrated in the drawing and is explained in more detail using exemplary embodiments.

[0066] They show: Fig. 1 a schematic vertical section view of an embodiment of a magnetic resonance apparatus equipped with an NMR probe head according to the invention, in which the temperature control tube is designed directly as a coil support; Fig. 2 a vertical section view of an embodiment of the magnetic resonance apparatus, wherein the NMR probe head according to the invention is equipped with a first insulation element designed as a coil carrier; Fig. 3 a schematic vertical section view of one embodiment of Fig. 2 similar MR apparatus; Fig. 4 a schematic vertical section view of a further embodiment of the NMR probe head according to the invention; and Fig. 5 a graphical representation of the results of simulation calculations of the temperature gradient along the z-axis along the measurement sample, namely - solid line with a state-of-the-art NMR probe head with air gap, - dashed line with an NMR probe head according to the invention with only one temperature control element, - dotted line with an NMR probe head according to the invention with two temperature control elements and an insulation element each between the RF coil and the probe head housing.

[0067] The present invention relates primarily to an NMR probe head 10; 10'; 10", which is configured for insertion into a magnetic resonance apparatus 101; 102 for carrying out an MR measurement on an NMR sample 5.

[0068] The NMR probe head 10; 10'; 10" comprises a probe head housing 4 for receiving a temperature control tube 2, cylindrical about a z-axis and surrounding the sample 5 with a sample substance in a sample volume during NMR measurement operation, made of thermally conductive material for temperature control of the sample 5 during NMR measurement operation, wherein a heat exchanger 1 is attached radially outside at at least one axial end of the temperature control tube 2, which is in thermal contact with the temperature control tube 2 and, in the embodiments shown in the drawing, projects radially away from the temperature control tube 2 towards the inner wall of the probe head housing 4, a first insulation element 3 made of poorly thermally conductive material and surrounding the temperature control tube 2 azimuthally at an axial distance in the direction of the z-axis from the heat exchanger 1, and an RF coil 6.

[0069] Compared to conventional NMR probe heads according to the prior art, the present invention is characterized in that the probe head housing 4 contains only exactly one heat exchanger 1 in the axial direction either above or below the insulation element 3, and that in the radial direction between the insulation element 3 and the inner wall of the probe head housing 4 at least one temperature control element 7, 7' made of thermally conductive material is positioned for heat distribution along the z-axis, which completely surrounds the insulation element 3 azimuthally and extends in the axial direction along the z-axis at least over the full axial length of the insulation element 3.

[0070] The MR apparatus 101; 102, equipped with an NMR probe head 10; 10'; 10" according to the invention, includes as an essential element an NMR magnet system 9 for generating a static homogeneous B0 field. The NMR magnet system 9 can comprise at least one permanent magnet, and in particular may be composed exclusively of one or more permanent magnets. Such an MR apparatus 101; 102 is particularly suitable for design as a particularly compact NMR benchtop instrument and is preferably configured for performing relaxometric MR measurements in time-domain NMR.

[0071] Fig. Figure 1 shows a schematic cross-sectional view of an MR apparatus 101 with a preferred embodiment of the NMR probe head 10' according to the invention, in which the RF coil 6 is attached directly to the radial outer wall of the temperature control tube 2, which thus serves as a coil carrier. The temperature control element 7 and the insulation elements 8 form a lamellar structure 11' extending radially away from the z-axis in the form of a multi-part insulating tube.

[0072] In Fig. Figure 2 shows an embodiment of the MR apparatus 102 equipped with an NMR probe head 10" according to the invention, in which an insulating element 8 and a further cooling element 7' are additionally arranged coaxially to the first cooling element 7 in the NMR probe head 10" in the radial direction between the inner wall of the probe head housing 4 and the first cooling element 7. Both the insulating element 8 and the further cooling element 7' completely surround the coil carrier 3 azimuthally and each extend axially along the z-axis at least over the full axial length of the coil carrier 3. Together, the cooling elements 7, 7' and the insulating elements 8 form a lamellar structure 11" extending radially away from the z-axis in the form of a multi-part insulating tube.

[0073] As a rule, the temperature control elements 7, 7' and the insulation element(s) 8 will be arranged close together to minimize or avoid heat convection.

[0074] While in the Fig. In the embodiment of the NMR probe head 10" shown in Figure 2, a small remaining air space can still be seen in the area between the inner wall of the probe head housing 4 and the insulating element 3, which facilitates the insertion of the insulating tube, constructed in a lamellar structure 11", during the assembly of the probe head. Fig. In the embodiment shown in Figure 3, the insulating tube is directly attached to the inner wall of the sample head housing 4 and the outer wall of the coil carrier 3. As a result, in this embodiment, there is no remaining air space and convection in this area is prevented.

[0075] The in Fig. The NMR probe head 10 shown in Figure 4 has a similar internal structure to the one in Figure 4. Fig. 3 sample heads shown.

[0076] In none of the embodiments of the NMR probe head 10 according to the invention Fig. The temperature control elements 7, 7' are in good thermal contact with the heat exchanger 1, as is the insulation element 8.

[0077] In the graphic of Fig. Finally, the simulated temperature profile along the inner temperature control tube 2, which is directly adjacent to the sample tube, is plotted against the distance in the z-direction, with the zero point being the center of the sample tube containing the measurement sample 5. For the calculation, it was assumed that the temperature control tube 2 is made of AIN.

[0078] The curve with the solid line represents the state of the art, in which no further material is arranged radially outside the RF coil 6 up to the probe head housing 4. Typically, the space between the RF coil 6 and the probe head housing 4 is filled with air.

[0079] The dashed line represents the case where a first temperature control element 7 in the form of an AIN tube is present radially around the RF coil 6. It can be seen that in this variant of the present invention, there is already a significantly lower temperature gradient of approximately 1.1 K along the z-direction.

[0080] Finally, the dotted line represents the result for the preferred embodiment of the NMR probe head 10; 10'; 10" according to the invention, in which the HF coil 6 is separated by two temperature control elements 7, 7' in the form of AIN tubes, which are separated in a lamellar structure 11 by an insulating element 8 made of insulating material, such as PTFE or PEEK.

[0081] The temperature difference is then only 0.6 K instead of the 2 K without these pipes. Reference symbol list: 1 heat exchanger 2 temperature control tubes 3 first insulation element 4 probe head housings 5 Sample 6 HF coil 7; 7' Tempering element 8 additional insulation elements 9 NMR magnetic system 10; 10'; 10" NMR probe head 11'; 11" louver structure 101; 102 MR apparatus Reference list:

[0082] Publications considered for the assessment of patentability: [1] US 2007 / 0257673 A1 [2] DE 40 18 734 C2 [3] DE 10 2010 029 080 B4 ≈ US 8,847,595 B2 ≈ EP 2 388 609 B1 ≈ JP 5432211 B [4] DE 100 06 323 C2 ≈ US 6,437,570 A ≈ EP 1 126 284 B1 ≈ JP 4027341 B [5] DE 100 06 317 C2 ≈ US 6,441,617 A ≈ EP 1 124 138 B1 ≈ JP 3573449 B [6] DE 10 2006 046 888 B4 ≈ US 7,514,922 A ≈ EP 1 909 111 B1 ≈ JP 4839292 B [7] DE 10 2016 218 772 A1 ≈ US 10,459,044 B2 ≈ EP 3 301 467 B1 ≈ JP 6517896 B ≈ CN 107870309 B [8] US 5 530 353 A

Claims

[1] NMR probe head (10; 10'; 10"), designed for insertion into a magnetic resonance apparatus (101; 102) for performing an MR measurement on a sample (5), comprising a probe head housing (4) for receiving a temperature control tube (2) made of thermally conductive material with a thermal conductivity of at least 20 W / mK, which is cylindrical about a z-axis and surrounds the sample (5) containing a sample substance in a sample volume during NMR measurement operation, for temperature control of the sample (5) during NMR measurement operation, wherein a heat exchanger (1) is attached to at least one axial end of the temperature control tube (2), which is in thermal contact with the temperature control tube (2), a first insulation element (3) made of poorly thermally conductive material with a thermal conductivity of at most 1 W / mK, which surrounds the temperature control tube (2) azimuthally at an axial distance in the direction of the z-axis from at least one heat exchanger (1), as well as an RF coil (6), characterized by , that in the radial direction between the first insulation element (3) and the inner wall of the sample head housing (4) at least one temperature control element (7, 7') made of thermally conductive material with a thermal conductivity of at least 20 W / mK is positioned for heat distribution along the z-axis, which completely surrounds the first insulation element (3) azimuthally and extends in the axial direction along the z-axis at least over the full axial length of the first insulation element (3). [2] NMR probe head (10') according to claim 1, characterized by , that the RF coil (6) is attached to the temperature control tube (2) designed as a coil support. [3] NMR probe head (10") according to claim 1, characterized by , that the RF coil (6) is attached to the first insulating element (3) designed as a coil support. [4] NMR probe head (10; 10'; 10") according to any one of the preceding claims, characterized by, that in the radial direction between the inner wall of the sample head housing (4) and the at least one temperature control element (7) at least one further insulation element (8) is arranged, which azimuthally completely surrounds the first insulation element (3) and extends in the axial direction along the z-axis at least over the full axial length of the first insulation element (3). [5] NMR probe head according to claim 4, characterized by , that in the radial direction between the inner wall of the sample head housing (4) and the at least one further insulation element (8) at least one further temperature control element (7') is arranged coaxially to the first temperature control element (7), which completely surrounds the first insulation element (3) azimuthally and extends in the axial direction along the z-axis at least over the full axial length of the first insulation element (3). [6] NMR probe head according to claim 5, characterized by, that the temperature control elements (7, 7') and the other insulation elements (8) form a lamellar structure extending radially away from the z-axis. [7] NMR probe head according to one of claims 4 to 6, characterized by , that the temperature control elements (7, 7') and the further insulation elements (8) are arranged in a tightly packed manner, in particular with as little as possible, preferably no, remaining air space in the area between the inner wall of the sample head housing (4) and the first insulation element (3). [8] NMR probe head according to any of the preceding claims, characterized by , that the temperature control elements (7, 7') and the other insulation elements (8) each have a radial thickness of 0.5 mm to 2 mm. [9] NMR probe head according to any of the preceding claims, characterized by , that the temperature control elements (7, 7') are not in thermal contact with the heat exchanger (1). [10] NMR probe head according to any of the preceding claims, characterized by , that the temperature control elements (7, 7'), preferably also the temperature control tube (2), are made of thermally conductive material with a conductivity of 20 to 200 W / m*K, in particular of AIN or of sapphire (= Al2O3) or of stainless steel. [11] NMR probe head according to any of the preceding claims, characterized by , that the further insulation elements (8), preferably also the insulation element (3), are made of poorly thermally conductive material with a conductivity < 1 W / m*K, in particular of plastic, preferably of PTFE or PEEK. [12] Magnetic resonance apparatus (101; 102) with an NMR probe head (10; 10'; 10") according to one of claims 1 to 11, characterized by, that the magnet system (9) of the MR apparatus (101; 102) for generating a static B0 field comprises at least one permanent magnet, in particular is composed exclusively of one or more permanent magnets. [13] Magnetic resonance apparatus according to claim 12, characterized by , that the MR apparatus (101; 102) is designed as an NMR benchtop device. [14] Magnetic resonance apparatus according to claim 13, characterized by , that the MR apparatus (101; 102) is designed to perform relaxometric MR measurements in time-domain NMR. [15] Method for producing an NMR probe head (10; 10'; 10") according to any one of claims 1 to 11, characterized by, that the temperature control elements (7, 7'), optionally the further insulation elements (8) and optionally the first insulation element (3) when the RF coil (6) is arranged on the temperature control tube (2), are first produced in the form of coaxial cylindrical half-shells, which are joined azimuthally around the coil-carrying component for installation in the NMR probe head (10; 10'; 10").

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