WO2017121532A1

WO2017121532A1 - Device and method for measuring magnetic resonance signals

Info

Publication number: WO2017121532A1
Application number: PCT/EP2016/078936
Authority: WO
Inventors: Tabea Arndt; Marijn Pieter Oomen
Original assignee: Siemens Aktiengesellschaft
Priority date: 2016-01-14
Filing date: 2016-11-28
Publication date: 2017-07-20
Also published as: DE102016200375A1

Abstract

The invention relates to a device (1) for measuring magnetic resonance signals, having a coil device (3) for generating a magnetic field (B₀) with at least one magnet coil (5, 5a, 5b) with a superconductive coil winding. The coil device (5) has a cooling device (7) for dry cooling the superconductive coil winding. The device (1) has a specified passage direction (x) for sequentially transporting a plurality of measurement objects (9) through the device (1). Furthermore, the coil device (5) has a continuous inner cavity which defines a continuous sample chamber (11) and through which the measurement objects (9) can be transported one behind the other through the device (1) along the passage direction (x). The invention further relates to the use of such a device for security checks, wherein the measurement objects (9) are a plurality of transport goods (9a) and/or persons (9b) which are examined for the presence of defined types of hazardous materials. The invention further relates to a security check method using such a device.

Description

description

Apparatus and method for measuring magnetic resonance signals

The present invention relates to a device for Mes ^¬ solution of magnetic resonance signals, comprising a coil means for generating a magnetic field having at least one magnetic ^¬ coil with a superconducting coil winding, wherein the coil means comprises a cooling device for dry cooling of the superconducting coil winding. Furthermore, the invention relates to a use of such a device as well as to be carried out with such a device method.

According to the state of the art devices for the measurement of magnetic resonance signals are known, which are, for example in the medi ^¬ zinischen imaging or in material analysis, or chemical structure analysis used. The various types of equipment have in common that in each case a strong magnet is required for generating a strong, constant and homogenous magnetic field to align the magnetic ^¬ tables nuclear moments in the center along a preferred direction. The so-aligned magnetic moments of the cores can then be brought into resonant interaction with a high-frequency electromagnetic field (usually in the form of one or more short high-frequency pulses). A magnetic resonance signal is a signal resulting from this resonant interaction, which is mostly measured by a high frequency receiver coil in response to a signal transmitted by a high frequency transmitter coil. The most common form of such a measurement is the Mes ^¬ solution a so-called free induction decay. Based on this basic measuring principle, the prior art describes numerous types of measurements based on different sequences of electromagnetic transmission pulses and reception phases. In nuclear magnetic resonance spectroscopy (short: NMR spectroscopy for English "nuclear magnetic resonance"

Spectroscopy), the electromagnetic signal of the measured free induction decay is typically decomposed by Fourier analysis into its individual frequency components. The plot of the measured intensities to these frequency components is the so-called NMR spectrum, in which for a given type of core (for example, hydrogen or carbon ¹ R ¹³ C) different chemical bond-making environments as different spectral bands, or

Lines are recognizable. This so-called chemical shift Ver ^¬ and through the spin-spin coupling to adjacent cores arising in this way characteristic spektra ^¬ le signatures for the different chemical environments in various compounds. Therefore, the NMR

Spectroscopy can be used both for the structure elucidation of unknown compounds as well as for the detection of already known materials by comparison with existing spectra.

In magnetic resonance imaging (MR imaging), on the other hand, a spatially resolved signal is obtained by superimposing a location-dependent magnetic field B i on the homogeneous magnetic field Bo by one or more additional gradient coils, and then sequentially resonating the cores to be measured. Such an imaging measurement is typically based not on a spectral decomposition as in spectroscopy, but on a spatially resolved determination of the signal intensities and / or the relaxation times of the spins, which affect the decay times of the measured electromagnetic signals. With different types of pulse sequences (for example, so-called spin-echo sequences) may be of different types of Relaxati ^¬ onszeiten be measured. In medical imaging, most often ¹ R-, so proton signals are gemes ^¬ sen, which then the different relaxation times of the hydrogen (mainly in the form of water) in the different types of tissue, as well as the different water- hydrogen content can be mapped. In principle, however, other cores with a suitable nuclear spin can also be measured spatially resolved with regard to their frequency and chemical environment.

Both NMR spectroscopy and MR imaging typically require very strong Bo magnetic fields. For their production permanent magnets, normal ^¬ conducting electromagnets or superconducting solenoids can be used. For magnetic field strengths above 0.5 T predominantly superconducting magnetic coils are used. In a superconducting magnet coil, the direct current required to generate the temporally constant magnetic field can flow virtually loss-free, and high current densities are achieved. The superconducting conductor such sup ^¬ raleitenden solenoid coil must be cooled during operation to a cryogenic temperature below its critical temperature. In order to achieve this, cooling of the superconducting material by flushing with a cryogenic liquid coolant in a bath cryostat is used in many magnetic resonance measuring devices. The coolant most commonly used is liquid helium, can be achieved ^¬ rich of 4 K to the temperatures in the Be. However, helium is limited and is becoming more expensive. A further disadvantage of such cooling is that, in the event of a sudden collapse of the superconducting properties (a so-called "quench"), the entire liquid helium must be vaporized and subsequently replaced, and the cooling and commissioning of such a helium-cooled superconducting coil is altogether very time-consuming - and resource-consuming.

To avoid these disadvantages, it is also mög ^¬ Lich principle to cool magnetic measuring devices dry. This means that the superconducting conductors are not directly surrounded by a liquid coolant. Instead, they may be thermally coupled to a cold head of a chiller. As a result, the consumption of liquid helium is greatly reduced compared to a helium bath cryostat. The chiller can still work with helium, but in this case the helium is present in a closed coolant circuit of the chiller and therefore does not need to be refilled with an evaporate from the cryostat of the coil winding.

So far, no devices have been described for measuring magnetic resonance signals suitable for the routine screening of persons and / or goods in the context of security controls. In addition to the high expenditure on equipment (especially in the case of helium-cooled magnetic coils), the limited sample volume and the limited accessibility of the sample space also play a role in many conventional magnetic resonance apparatus. In most conventional NMR spectrometers, the sample space is defined by a one-sided open cavity inside the magnetic coil (s). A sequential transport of a plurality of measuring objects through the device is not possible with such a spectrometer. Even conventional medical imaging MR tomographs do not operate on the principle of the sequential transport of measurement objects through the device, but patients are driven on a patient couch from one side into an inner cavity and retracted on the same side after completing the tomographic measurements.

Furthermore, in conventional MR measuring devices, it is not readily possible to introduce any measuring objects of unknown material composition into the sample space. The coil means for generating the strong static magnetic fields Bo are generally designed so that the magnetic field strength in a homogeneity region corresponding approximately to the inner cavity is very strong and homogeneous, and that in the adjacent areas outside this cavity with increasing distance from the center of Device drops very quickly to very low values. In the peripheral areas of the sample room and / or in the directly adjacent areas thus occur very high field gradients. If the measurement objects are placed in the vicinity of the device with ferromagnetic material portions and is to be subsequently introduced into the sample compartment can in this case very high magnetic attraction forces occur, so that such metrics are greatly accelerated and can cause high dangerous ^¬ dung potential since they then similar to a bullet act. Also, the introduction of measuring objects with other metallic material fractions can be problematic because high eddy currents are induced by their movement in the region of the strong magnetic field gradients. This effect is based on the same principle as in an eddy current brake, and can restrict a desired movement of the Messob ^¬ jekts strong especially in the peripheral areas of the device.

The object of the invention is therefore to provide a device for measuring magnetic resonance signals, which overcomes the disadvantages mentioned. In particular, such a device should be made available which is suitable for the

Measurement of a variety of samples of unknown composition is suitable. A further object is to ben anzuge- use ei ^¬ ner such a device and a method for the measurement of magnetic resonance signals with such a device.

These objects are achieved by the apparatus described in claim 1, the use described in claim 11 and the method described in claim 12. The inventions dung contemporary apparatus for measuring Magnetresonanzsigna ^¬ len has a coil means for generating a magnetic field. This coil device comprises at least one magnetic coil with a superconducting coil winding. The coil device furthermore has a cooling device for dry cooling of the superconducting coil winding. The device has a predetermined passage direction for the sequential transport of a plurality of measurement objects through the device. The coil device has a NEN continuous internal cavity, which defines a continuous sample space and through which the measurement objects can be transported through ^{¬ ¬ one} behind the other in the direction of passage through the device.

In other words, the device is designed such that it is suitable for the continuous or quasi-continuous passage of successive measurement objects. The interior sample space is therefore accessible not only on one side but on both sides, and the measurement objects can be transported through it se ^¬ quentiell, the measured objects can also follow relatively close to each other, since they are not taken on the same side of the sample space on the they were introduced into the rehearsal room, but on the opposite side. In the context of the present invention, the measured objects may generally be persons and / or transport goods, for example bags, sacks, suitcases or boxes. The sample space is thus dimensioned for the sequential passage of a large number of such measurement objects. In this way, it is ^¬ enables that the device for screening of objects can be used for the purpose of security, for example in the range of airports, buildings or other protected at events. With the aid of the device according to the invention, the test objects to be examined can routinely be examined for the presence of predefined types of hazardous substances, for example of explosives or drugs. The dry cooling of the superconducting coil winding has the advantage that the device for magnetic resonance measurement is much easier to handle and to put into operation, as would be the case with a liquid helium cooled coil winding. In particular, the device can also be much more mobile, so easier to carry out portable, which may be important for applications in security controls. In contrast to a measuring device filled with liquid helium and installed stationary for years Liert, a dry cooled device can also be installed for a short time (eg a few hours or days) at a destination without the equipment cost for commissioning exceeds the economic benefits of the device. In particular, no supply is required for replenishing liquid coolant for dry cooling, since such a cooling device can be operated solely by supplying electrical energy. In the context of the present invention, such a "dry cooling" should generally be understood to mean a cooling in which the superconducting coil winding is not directly surrounded by liquid coolant and is not arranged in a bath cryostat with an open coolant reservoir via a thermal coupling to a solid, low-temperature member such as the cold head of a refrigeration ^¬ machine. This refrigerator can in its operation again using a liquid coolant itself, but which then is present not in an open reservoir, but in a fluidically closed coolant circuit. the thermal coupling of the coil winding to the solid, cryogenic element may for example only a high heat conduction ^¬ SUC gene. Alternatively, or additionally, these thermal coupling can also be effected via a thermosiphon or a heat pump, again with a cooling medium in a closed cycle can be used. In this variant too, the essential difference from cooling in a bath cryostat is that the coolant is present only in a fluidically closed circuit within the device and not an outwardly open reservoir.

A major advantage of dry cooling in the various conceivable embodiments is that a

Transport is possible without emptying and / or filling a helium bath cryostat. Another advantage is that, in the event of breakdown of the superconductivity (for example, in the case of a sudden quench), no evaporation of the liquid coolant into the external environment takes place. Such a quench results in conventional magnetic resonance coils to evaporate a very large amount of helium. It has a high hazard potential, since in this schlagar ^¬ vigen evaporation a high pressure in the cryostat arises, which can even blow up the cryostat in extreme cases. Thus, such devices are not suitable for use

Places with large amounts of people, as is the case with many locations relevant to security controls. This disadvantage is avoided by the described trocke ^¬ ne cooling, and the device of the invention is therefore suitable for use in security controls.

In the use according to the invention, the security control device described above is used, the measured objects being a plurality of persons and / or transport goods, which are examined with regard to the presence of predefined types of hazardous substances.

The inventive method is used for security control with a device according to the invention. In this method, a plurality of measurement objects in the form of persons and / or goods to be transported in succession through the sample space of the device or passes therethrough. Magnetic resonance signals are measured at the respective measurement objects by means of the device, the type of measured magnetic resonance signals being based on the presence or absence of predefined types of hazardous substances. The advantages of the use according to the invention and of the method according to the invention result analogously to the described advantages of the device according to the invention.

Advantageous embodiments and modifications of the invention will become apparent from the dependent claims 1 and 12 claims and the following description. In this case, the described embodiments of the device, the

Use of the method and are advantageous together combinatorial ^¬ defined. The coil device may advantageously be designed to generate a magnetic field Bo, which along the passage ^¬ direction has a field profile, which is characterized in the interior of the hollow ^¬ space by a homogeneity region with substantially homogeneous field course and in the the

Homogeneity area adjacent edge areas is characterized in each case by a sloping outwards and concavely curved field profile with outwardly smaller in absolute terms field gradient. In other words, inside the cavity there is a region of substantially homogeneous magnetic field Bo, which may extend over part of the cavity, for example a major part of the cavity, or substantially the entire cavity. In an area adjacent to this homogeneity range the magnetic falls see field strength initially from relatively strong and takes RESIZE ^¬ SSER becoming intervals steadily becoming further, the slope of this waste always drops further to the outside - that the field profile flattens out gradually towards the outside , Thus ^¬ with results in approximately the shape of a trapezium with concave curved sides.

The advantage of such a shape is that during a transport or a pre-run of the measurement objects along the passage direction, the magnetic field strength gradually increases until it reaches the maximum value Bo for performing the measurement in the sample space. In a further passage along the passing direction, the magnetic field strength decreases then all ^¬ gradually again. This gradual increase and decrease makes it possible to introduce and remove measurement objects of unknown composition, which can also have magnetic and / or electrically conductive material components.

Particularly advantageously, the described field profile of the magnetic field Bo can have a field gradient of not more than 9 T / m in the edge regions which lie next to the homogeneity region in the direction of passage. Particularly advantageously, this field gradient can be below 3 T / m or even below 0.9 T / m. This ensures that the Magnetic attractions on ferromagnetic materials and the deceleration of objects with electrically conductive components are advantageously limited. For example, the maximum field gradient of 9 T / m at a mag- netic flux density of 1.4 T acts locally on a ferromagnetic Whether ^¬ ject with a volume of 1 cm ^3, a magnetic force of a maximum of 10 N. With a correspondingly smaller values for the maxi ^¬ If field gradients (as well as correspondingly smaller volumes and / or magnetic flux densities) are used, the acting forces are advantageously limited to even smaller values.

Additionally or alternatively, the profile of the magnetic field Bo may be formed so that the location at which the magnetic field strength, starting from its maximum value to a

Fraction 1 / e has dropped, at least 50 cm - more preferably at least 2 m or even at least 5 m - is located away from the edge of the homogeneity range. As a result, the magnetic attraction forces and the vortex ^¬ currents are advantageously limited in conductive objects.

The inner cavity of the device forming the sample space can advantageously be at least 0.5 m long in the direction of passage in order to be able to pick up persons or goods to be transported as measuring objects. For this purpose, it can particularly advantageously have a length between 0.5 m and 3 m, in particular between 0.5 and 1.5 m.

The sample space may, for example, have a rectangular cross section or a circular cross section. Regardless of its exact shape, it can have a width and / or height of at least 0.5 m, in particular between 0.6 m and 2.5 m, in order to be able to pick up persons and / or transport goods as measuring objects. In general, the sample space can be arranged centrally within the coil device. This is particularly advantageous when sym ^¬ metric, especially circularly symmetric coil assemblies for generating magnetic fields particularly homogeneous. The apparatus may advantageously comprise at least one ^acid sequence Hochfre coil for transmitting and / or receiving radio frequency signals. This can be a common coil for sending and receiving or else separate transmit and receive coils. The device can be designed to record magnetic resonance spectra. In particular, they can have for this purpose a signal processing unit on ^¬, the Fourier analysis of the frequency components of a (at separate coils by means of the RF coil: the

Receiving coil) measured free induction decay is suitable. By means of such a signal processing unit, magnetic resonance spectra can be determined for the individual measurement objects in which the magnetic resonance signals are present as a function of the individual resonance frequencies, which differ slightly for the different chemical environments of the individual measured cores. These differences are also referred to as chemical shifts. Advantageously, the spectra obtained can then be compared, for example with an analysis unit designed for this purpose, with spectra of known materials. From the comparison of the spectra can then be concluded that the presence or absence of predefined types of hazardous substances, such as certain classes of explosives or drugs. Thus, with this embodiment of the apparatus, a screening of the measuring objects on certain vorzudefinierende ^¬ chemi cal compositions towards possible, whereby the measurement objects in a continuous (or quasi-continuous) flow can be measured. Thus, advantageously, the presence of these predefined substances can be determined very quickly. It is a 100% test allows to investigate ^¬ the objects by the continuous or quasi-continuous flow, as opposed to random investigation of individual selected samples or only the ex actuating drive of the objects to be examined.

The device can be designed particularly advantageously for carrying out double resonance measurements. This is Transfer spin polarization from one core type to another core type. With such a method, for some hazardous substances, detection with a particularly good signal-to-noise ratio is possible, for example for trinitrotoluene, when the transmission of the spin polarization from hydrogen to nitrogen is measured.

Alternatively or in addition to the possibility of the spectral analysis of the magnetic resonance signals, the device for measuring spin-spin relaxation times can be set up.

For example, it may have a transmitting device, by means of which a plurality of high-frequency excitation coils in the form of spin-echo sequences can be emitted. It may further comprise a processing unit with which from the measured via a receiving coil high-frequency

Pulse responses a relaxation time can be determined. In this embodiment, the presence of particular substances can advantageously be determined without having to record a whole magnetic resonance spectrum. Beispielswei- se, the presence of hydrogen peroxide detected ^¬ the by proton with a chemical shift (that is, a resonance frequency) is similar to that of water, the input of the echo time flow in a spin-echo sequence on the measured relaxation time is determined. For example, about determining the ratio of two to different

Echo times measured relaxation times are concluded with a very short measurement time on the presence of hydrogen peroxide. Hydrogen peroxide, however, is a key ingredient in some explosives.

Alternatively, or in addition to the possibility of spectral analysis of the magnetic resonance signals, the device knows ^¬ terhin may include a gradient coil for generating a location-dependent magnetic field within the sample space, so that by means of the device a spatially resolved measurement magneti ^¬ shear resonance is possible. In other words, the device can be designed for magnetic resonance imaging, so that an image of the test objects to be examined is possible. becomes light. Such a mapping may be in the form zweidimensio ^¬ tional sectional images or projections as well as in the form of a three-dimensional tomographic image data set. Through such a possibility of imaging (alternatively or in addition to spectral analysis to certain aufzufindende classes) is a search for auffälli ^¬ gen forms allows to measuring objects, such as ei ^¬ ne search for weapons in the application of the device in the area of security controls. Such a device can be used to replace the x-ray devices customary today, in which case imaging and spectroscopic examination are possible particularly advantageously with the same device. If necessary, particularly conspicuous areas can also be identified in the illustrations, and only then can these be examined in more detail spectroscopically for their composition.

The coil device can be designed so that it can be used to generate a magnetic field Bo, which runs essentially perpendicular to the direction of passage. With others

Words can run within the sample space, a main direction of the magnetic field Bo perpendicular to the direction of passage. For example, the passage direction can generally run substantially parallel to the earth's surface, ie horizontally. The main direction of the magnetic field BO can then be, for example, either vertically in space or it can also be horizontal, but perpendicular to the direction of passage. However, it can also assume other oblique orientations perpendicular to the direction of passage. Regardless of the exact choice of this main direction of Bo is an advantage of a vertical orientation to the passage direction is that the measuring objects are not accelerated by ferromagnetic Mate ^¬ rialkomponenten along the direction of passage (but only perpendicular thereto). In this case, the magnetic field is advantageously oriented downwards. Any ferro ^¬ magnetic components then pull the measurement object in the direction in which it already rests due to gravity anyway. Thus, movements of the DUT are avoided. In the other directions perpendicular to the direction of the measurement objects, however, can be more easily fixed against such magnetic ^¬ table caused movements, since they in these directions in space to run does not have to be mobile.

Alternatively, however, the coil device can also be designed so that it can be used to generate a magnetic field B o which runs essentially parallel to the passage direction. Such parallel magnetic field can be generated with the example of a circular cylindrical magnet coil, which has a circular cylindrical cavity as a sample space in its interior ^¬ example. With such an arrangement, a step kreissymmet ^¬ be ^¬ Sonders homogeneous magnetic field in the interior of the sample chamber can he be generated ^¬ a particularly simple manner.

Regardless of whether the magnetic field B o is perpendicular or paral ^¬ lel to the direction of passage or other, oblique positions relative to the direction of passage assumes the coil device may have either only one or more magnetic coils. This plurality of magnetic coils can be arranged symmetrically around the sample space, or they can also assume an asymmetrical arrangement which generates an approximately homo ^¬ nes magnetic field B o in the interior of the sample chamber. Is Wesent ^¬ Lich that (in ^¬ By running direction) a homogeneity range is present at least over a part of the length of the sample space in which the magnetic field strength is substantially kon ^¬ constant. Particularly in a magnetic field B o, which is pa ^¬ rallel to the passage direction, the coil means may comprise a plurality of circular cylindrical superconducting coils, which are stacked in the axial direction to generate a homogeneous magnetic ^¬ field inside the resulting hollow cylinder. The dimensions of the homogeneity region (both along the passage direction and in the spatial directions perpendicular thereto) should generally correspond at least to the expected dimensions of the objects to be measured. The device can generally advantageously have a conveying device with which the measuring objects can be transported through the cavity of the magnetic coil in succession in a continuous or quasi-continuous process. Such a conveying device may be an automatic conveying device and comprise, for example, a conveyor belt, a roller conveyor, a chain conveyor or a similarly acting conveying means. In addition, the conveying device may also comprise receiving means for receiving the measurement ^¬ objects, such as containers such as plates, Kis ^¬ th or baskets, can also be arranged in groups in which the individual measurement objects or. The various forms of such a conveying device have in common that with it the individual measuring objects can be moved one after the other in the direction of passage at the same time. Thus, while the respective object to be measured is transported through the sample chamber, the foregoing object is transported further through already in ^¬ running direction and the subsequent Messob- ject already engaged in the direction of the sample chamber after. Under ei ^¬ nem continuous process a run is to be understood in the context of the present invention generally, in which a plurality of sequential objects to be measured are simultaneously moved continuously in the region of the device. In contrast, a similar run process is understood to be a quasi-continu ^¬ ous process in which the lead but for the duration of each measurement briefly - for example, for a few seconds - is stopped. This brief pause can either concern only the object to be measured, while the others

Objects in front and behind continue to run. Or, in particular, if the measurement objects follow one another very closely on or in the conveying means, the forward flow can also be measured simultaneously for all objects located in the area of the device for the duration of the measurement

Object to be stopped. Essential for the continuous or quasi-continuous feed is that all at the same time move up the measurement objects in the device.

As an alternative to the automatic conveying devices described, the device can also be designed for the automatic movement of the measuring objects through the sample space. By way of example, the measured objects can be persons who run in a continuous or quasi-continuous sequence in a row one behind the other through the sample space. This is particularly advantageous for the security of per ^¬ sonen, for example, in airports or at events to control many people within a short time. Regardless of whether it is an automatic conveying device or to an automatic cycle, the apparatus may comprise at least one retaining means to me ^¬ mechanically to fix the object to be measured in each case in the region of the sample space. The holding means may be a holding pad, such as a blowable on ^¬ holding pads, for example. One or more holding means can be used, so that the objects can be fixed against movements in different spatial directions for each to be measured Whether ^¬ ject. Special attention should be fixing in direction of the main direction of the magnetic Bo to avoid the risk of possibly occurring defects ^¬ trend (in From ^¬ dependence on the composition of the object) strong accelerations. In addition, the object to be measured in each case can be fixed along the passage path at the position intended for the measurement. Above all, in the case of inanimate measurement objects in which high proportions of ferromagnetic components may possibly also be expected, even a relatively strong fixation can be effected with the holding means (or the holding means) in order to limit deviations from the predetermined pass path as far as possible. For example, the motion ^¬ freedom can be as restricted to a few mm or a few cm ^¬ to. The device can be set up to perform magnetic resonance measurements on measurement objects with a measurement time between 1 second and 1 minute, in particular between 1 second and 30 seconds per sample. For this purpose, the conveyor device can then be set up so that each measurement object remains within the sample space for at least the stated time period. As described, this can be achieved either via a continuous pass through a suitable speed with which the measurement objects arranged one after the other move simultaneously. Or the object to be measured is stopped for this period, as previously described for the quasi-continuous process. The superconducting coil winding of the device can advantageously have a high-temperature oxide superconductor and / or magnesium diboride as conductor material. Such Sup ^¬ raleiter have higher critical temperatures than conventional metallic low-temperature superconductor and may be cooled more easily dry so German lent. Furthermore, with

High-temperature superconductors are also easier particularly high magnetic field strengths can be achieved, since they can be operated at temperatures well below their critical temperature and then the upper critical magnetic field strengths are particularly high. The superconducting

Conductors can be present for example in the form of superconducting wires or in the form of flat strip conductors. Particularly suitable for processing in strip conductors are compounds of the type REBa ₂ Cu30 _x (REBCO for short), where RE stands for a rare earth element or a mixture of such elements. Magnesium diboride has a transition temperature of about 39 K and thus is considered as a high-temperature superconductor, but the transition temperature is rather low compared to other high-temperature superconducting materials. The advantages of this material compared to oxide-ceramic high-temperature superconductors lie in its easy and thus inexpensive manufacturability. The cooling device may comprise a refrigerating machine having a heat conductive ^¬ coupled to the superconducting coil winding cold head, wherein the cooling unit is designed to be operated with a closed coolant circuit. Thus, the device does not completely free of FLÜS ^¬ Sigem coolant, in particular also not be free of liquid helium. However, the liquid coolant is within the refrigerator in a closed circuit and therefore can not evaporate from the device. The refrigerator can be for example a pulse tube cooler or a Kompressi ^¬ onskältemaschine after the Gifford-McMahon principle. It can advantageously be a two-stage or multi-stage refrigerator, with which particularly low temperatures can be achieved without requiring direct cooling of the superconductor with liquid helium.

The coil device can generally be advantageously designed to generate a magnetic field B o with a maximum field strength in the sample space between 0.25 T and 4 T. Such magnetic field strengths are well suited for substance detection by NMR spectroscopy. They are also suitable for optional magnetic resonance imaging on the DUTs. The coil device for generating the magnetic field B o can generally advantageously have a maximum weight of 1000 kg, in particular ^¬ sondere a maximum of 250 kg. The definition of the weight of the coil device should be such that the weight of the cooling device, which is part of the coil device, is included. Advantageously, the entire Spulenein ^¬ direction is so easily executed that it is suitable for mobile appli ^¬ tions. Thus, such a device is also easier to use for security checks, especially if they are not permanently installed as at an airport, but if they are needed for temporary events or even to be moved occasionally between different control points of a logistical transport chain. Especially with a dry cooling instead a cooling with helium bath cryostat such measuring devices can be made much easier to transport. Advantageously, the device has a cryostatic container within which the at least one superconducting coil winding is arranged. This container may for example be a single-walled vacuum container, so that the coil winding (s) can be arranged within this container in an evacuated space. It may in particular be a hollow cylindrical container, wherein the walled inner cylinder wall to the container for the coil winding ^¬ (s) separates from the sample space. In addition to the thermal insulation by the vacuum of the cryostatic container, the at least one coil winding can be thermally insulated by a super insulation against the external environment.

The at least one magnetic coil of the coil device can be operated according to an advantageous embodiment in the so-called continuous short-circuit current mode. In this mode, a continuous current flows through an annular closed superconducting circuit, which almost does not decay over a very long period of time due to the vanishing resistance of the superconducting coil winding. For example, coils can be operated with low temperature superconductors over several years in this short circuit current mode, without the decay of the magnetic field, the magnetic resonance measurement ^¬ substantially impaired. To enable such an operation should form a ringför ^¬-shaped circuit with continuous superconducting properties of the superconducting coil. Any required connections should have a contact resistance of no more than 1 fOhm. In order to enable charging of such a magnetic coil, a superconducting permanent current switch can be advantageously provided within the winding in this embodiment. The superconducting permanent current switch is part of the current ^¬ circle of the coil and is for feeding an external Power from an external power source, for example, by heating in an ohmic conductive state. After switching off the heating and cooling down to the operating temperature, this part of the coil also becomes superconductive again.

A operated in the short circuit current mode coil be ^¬ Sonders advantageous for magnetic applications in which the device is operated at least for several months at a FES th place. The magnetic field generated by such a coil is particularly constant over time, since it is not influenced by the network fluctuations of an additional current source. Alternatively, it is particularly advantageous in mobile applications with shorter operating times between individual transports of the device, when the coil means comprises a current source which is connected in series with the superconducting conductor of the magnetic coil. Such a permanently powered solenoid consumed due to the low electrical losses in the coil winding still little electrical power, and they can be taken relatively quickly and a ^¬ times in operation and / or are turned off again. For example, with such an integrated current source, the operating current of the magnetic coil can be reset daily in order to restart the device for the measurements planned for the respective day.

In the inventive method of frequency components of a means of the device ge ^¬ measured free induction decay, a magnetic resonance spectrum can be determined by Fourier analysis. This magnetic resonance spectrum can then be compared with spectra of known materials, it being concluded from the comparison of the spectra on the presence or absence of predefined types of hazardous substances. In the method, the magnetic resonance signals can be advantageous ^¬ adhesive obtained by a double-resonance measurement.

Alternatively or additionally, can be carried out drive to spectrally resolved measurement principle a spatially resolved measurement of the magnetic resonance signals by the nacheinan ^¬ be brought in magnetic resonance with a stimulating radio frequency field by means of at least one gradient coil different locations within the sample space.

The advantages of these embodiments of the method are analogous to the advantages of the corresponding embodiments of the device. In the following, the invention will be described by means of some preferred embodiments with reference to the appended drawings, in which:

FIG. 1 shows a schematic longitudinal section through a device according to a first exemplary embodiment,

Figure 2 shows a schematic longitudinal section through a device according to a second embodiment and Figure 3 shows a field strength profile of the magnetic field B0 for a

Coil means of such a device shows.

1 shows a device 1 for measuring magnetic resonance signals according to a first exemplary embodiment of the invention in a schematic longitudinal section, cut along the passage direction x through the device. Along this passage direction x measuring objects 9 can be transported through the device one behind the other.

For this purpose, in the example shown, the device 1 has a conveying means, which comprises such measuring objects in the form of

Transport goods and / or persons through a sample chamber 11 of the device can transport therethrough. The conveyor 13 comprises in the example shown a conveyor belt 15, on which individual delivery containers are attached. Within these delivery containers, objects 9 to be measured can be arranged individually and / or bundled together in order to be driven through the sample space 11 in succession in a continuous or quasi-continuous process. 9, magnetic resonance signals are measured within the sample chamber 11 then to the depending position ^¬ weils there measurement objects. The delivery containers 17 may advantageously have a material which contributes comparatively little to this measured signal.

As an alternative to the delivery containers, the measurement objects may also be loose on the conveyor belt or a similar suitable one

Transport be transported. In the arrival order is advantageous in or on a separate conveyor vessel 17, that the measurement objects 9 may be fixed therein against unwanted Relativbewe ^¬ conditions by magnetic attraction forces and / or against braking effects caused by eddy currents. For this purpose, one or more holding means may be provided, in the example shown in FIG. 1 this is for the delivery container 17a shown by way of example on the right side of the illustration an arrangement of a plurality of inflatable holding cushions 21, with which the measurement object 9a within this container 17a fi ^¬ xed is. To fix the measurement object 9a and the holding pad 21 together in the container 9a, as shown in FIG. 1, a lid 19 may be provided for the delivery container 17a. Alternatively or in addition to the holding means shown, such as holding cushions 17a and / or cover 19, however, other holding means may also be used, for example holding straps. The measuring objects 9 generally do not necessarily have to be mechanically fixed, especially if they have a low content of ferromagnetic and / or electrically conductive material components. For measuring the magnetic resonance signals, the device 1 has a coil device 3 for generating a strong, static and within the sample chamber 11 is substantially homo ^¬ gene magnetic field Bo. This coil device 3 has one or more superconducting magnetic coils 5 with windings of superconducting conductor materials. For the first embodiment, in Fig. 1 exemplarily shown two Magnetspu ^¬ len 5a and 5b, one above and one of which is arranged Below the sample compartment 11. With them, a strong magnetic field Bo can be generated, which is perpendicular to the passage direction x. In the example shown, this is the vertical spatial direction with geodesic orientation downwards. In principle, however, the magnetic field BO can also have other orientations.

The superconducting conductor materials of the solenoids 5a and 5b may be advantageous high-temperature superconductor having a transition temperature above 25 K and can therefore be cooled more easily than low temperature superconductor with a refrigerating machine without being immersed himself in a bath of flüssi ^¬ according helium. For example, the superconducting conductors of these coil windings may be formed as a band conductor with a layer of the type REBa ₂ Cu30 _x . Such materials have a particularly high transition temperature.

In order to cool the superconducting coil windings to an operating temperature below the transition temperature of the superconductor, the device 1 has a cooling device 7, which is designed to cool the coil winding dry - ie without direct embedding of the windings in a liquid coolant. Comprises the cooling device 7, a refrigerant ^¬ machine 23 which works in the illustrated example on the basis of a two-step ^¬ Gifford-McMahon cooler compression with a closed helium circuit. This chiller 23 comprises a cold head 25, which is thermally connected to the magnetic coils 5a and 5b here for cooling the windings by high heat conduction materials. In order to insulate these magnet coils 5a and 5b sufficiently thermally against the warm environment that a suitable operating temperature below the transition temperature can be achieved, these coils 5a and 5b are arranged inside a cryostatic vessel 27, which is designed here as a single-walled vacuum vessel. The Coils 5a and 5b are thus arranged within a vacuum space V on ^¬ .

In the example shown in FIG. 1, vacuum space V may be either the hollow cylindrical about a common vacuum chamber, within which are both solenoids 5a and 5b angeord ^¬ net. Alternatively, it may also be separate sub-arrangements with separate vacuum spaces V above and below the sample space 11. Generally and independently of the exact geometry of the embodiment, the sample space 11 is an internal cavity within the device 1, through which the measurement objects 9 can be transported in succession. This cavity may be circular-cylindrical or may have other cross-sectional geometries, for example a rectangular cross-section. It can be arranged centrally or else decentrally within the device. It is only important that it forms a continuous bore in the passage direction x and that it is sufficiently large to receive the objects 9 to be measured.

The magnetic field B0 generated by the coil device 3 has a homogeneity range in which the field strength is substantially constant. The length of this homogeneity region is indicated in FIG. 1 by _h . Advantageously, the length l ^¬ _h at least as large as the to be expected ^¬ tend maximum length l _m of the measuring objects 9. The strength of magnetic field B0, for example, be between 0.25 T and 4 T. Such a static magnetic field is the basis for the magnetic resonance measurements to be carried out with the device 1. In addition, the device 1 can additionally have one or more radiofrequency coils, not shown here for the sake of clarity, with which high-frequency electromagnetic signals (for example pulses) can be transmitted and / or received. Magnetic resonance spectra and / or spin relaxation times can be measured with such a device. Optionally, the device may additionally comprise one or more gradient coils, to enable spatially resolved measurements. The device may have a processing unit, likewise not shown here, in order to amplify and process the measured signals and to determine the desired NMR spectra, relaxation times and / or images.

The thus measured NMR spectra, relaxation times and / or images can be used to perform security checks on the objects 9 to be measured. These objects - regardless of whether they are transported goods or persons - can be examined for example with regard to explosives, drugs or other hazardous substances.

FIG. 2 shows a further apparatus 1 for measuring magnetic resonance signals according to a second exemplary embodiment of the invention. Again, a schematic longitudinal section along the direction of passage x of the device is shown. Instead of the transport goods shown in FIG. 1, persons 9b are examined here with regard to potentially present hazardous substances. These persons each run themselves on a track 22 through the sample space 11 of the device. Alternatively, these persons 9b can also be moved automatically by a conveyor belt similar to the example of FIG. 1 for the transported goods. Incidentally, the device 1 is similar in structure to the device of FIG. 1, the cooling device 7 constructed in a similar way not being shown here for the sake of clarity, and the radio-frequency coils and the processing unit again are not shown.

The coil device 3 for generating the static magnetic field Bo is constructed somewhat in ^¬ DERS in the second embodiment: Namely, here is an arrangement of several ^¬ ren annular magnetic coils 5 in front of which are each disposed in an annular plane perpendicular to the direction x. Each magnetic coil 5 surrounds the inner cavity as ausgebil ^¬ Deten sample chamber 11 so annularly. By way of example, an arrangement of five such axially stacked magnetic coils is shown here. len 5, wherein the exact number can also be larger or smaller. In principle, the measurement also works only with a single annular magnetic coil 5. Overall, a static magnetic field Bo is generated here by the coil device 3, which is parallel to the passage direction x of the objects to be measured.

The magnetic coils 5 of the second embodiment may have a circular cylindrical cross-section and thus surround a circular cylindrical inner cavity 11 symmetrically. Thus, particularly homogeneous magnetic fields BO can be generated. Alternatively, however, other, in particular rectangular cross-sectional geometries are possible. The spatial extent of the sample space may be the same or different in width and height. In the example application with passing persons, it is advantageous if the sample space is significantly higher than it is wide. When measuring Transportgü ^¬ tern, for example suitcases, boxes, bags or other better lying to be transported objects this may be reversed.

The structure of the magnetic coils and the orientation of the magnetic field in Figures 1 and 2 is to be understood only by way of example. In particular, a device for examining persons with a coil device 3 can be equipped similarly as in FIG. 1, and a device for examining transported goods can also be equipped with a coil device 3 similar to that shown in FIG.

FIG. 3 shows an advantageous field profile 31 of the magnetic field Bo generated by the coil devices 3 as a function of the passage direction x, as may be present within the device of the first and / or second exemplary embodiment. The field profile 31 has a homogeneity ^¬ region 33 of length l to _h, which advantageously extends over the largest possible part of the sample room 11, and within which the magnetic field strength Bo at the essential is constant and at a maximum value B _max . This homogeneity region is flanked by two edge areas 35, in which the field strength from the value B _max to we ^¬ sentlich lower values decreases. For example, this waste can be approximately exponential. As the edge region 35 of the area may for example be considered where the field strength of Bmax to a fraction 1 / e of B / max from ^¬ falls. The dots 39 in which this fraction is achieved can be beneficial ge ^¬ separated at least by a distance 41 of at least 2 m from the edges of the homogeneity range 33rd

Such a spatially extended waste of the magnetic field Bo is much more gradual than in the typically used today magnetic resonance imaging apparatus in which the magnet coils to reduce the stray field preferably be so incorporated ^¬ oriented such that a steep drop as possible is achieved. The gradual decay shown has for the dung OF INVENTION ^¬ intended use but the advantage that the lower to the sample chamber 11 passing through the measurement objects 11 are exposed to magnetic attraction forces, since the maximum field gradient 37 are limited to lower values.

Claims

claims

1. Device (1) for measuring magnetic resonance signals (a, 5 b 5, 5a) comprises a coil means (3) for generating a magnetic fields of the (B o) with at least one magnetic coil with egg ^¬ ner superconducting coil winding,

- wherein the coil means (5) comprises a cooling device (7) for dry cooling of the superconducting coil winding,

- wherein the device (1) has a predetermined passage direction (x) for the sequential transport of a plurality of measuring objects (9) through the device (1),

- Wherein the coil means (5) has a continuous inner cavity which defines a continuous sample space (11) and through which the measurement objects (9) can be transported in succession along the passage direction (x) through the device (1).

To he ^¬ testify 2. Device (1) according to claim 1, wherein the Spulenein- device (3) is adapted to generate a magnetic field (B o), which is along the flow direction (x) having a field profile (31) in the Inside of the cavity (11) by a homogeneity region (33) is characterized with substantially homogeneous field profile and in the homogeneity region (33) adjacent edge regions (35) in each case by an outwardly sloping and concavely curved field profile in terms of magnitude decreasing field gradient (37).

3. Device (1) according to claim 2, wherein the field profile (31) of the magnetic field (B o) in the edge regions a field gradient (37) of not more than 9 T / m, in particular not more than 0.9 T / m having.

4. Device (1) according to one of the preceding claims with at least one high-frequency coil for transmitting and / or receiving high-frequency signals, wherein the device is designed for recording magnetic resonance spectra, in particular in particular by Fourier analysis of the frequency components of a measured by ^{¬ means of} the high-frequency coil free induction decay.

5. Device (1) according to one of the preceding claims, which additionally comprises at least one gradient coil for Erzeu ^¬ tion of a location-dependent magnetic field within the sample ^¬ space (11), so that by means of the device, a spatially resolved measurement of magnetic resonances is possible.

6. Device (1) according to any one of the preceding claims, wherein by means of the coil means (3), a magnetic field (Bo) can be generated, which is substantially perpendicular to the passage direction (x).

7. Device (1) according to one of the preceding claims, which has a conveying device (13), with which the measuring objects (9) are successively transported in a continuous or quasi-continuous process through the sample space (11) of the coil means (3) can.

8. Device (1) according to one of the preceding claims, which at least one holding means, in particular a Haltekis ^¬ sen (21), in order to mechanically hold the respectively to be measured object (9) in the region of the sample space (11).

9. Device (1) according to one of the preceding claims, in which the superconducting coil winding contains a high-temperature oxide superconductor and / or magnesium diboride as conductor material.

10. Device (1) according to one of the preceding claims, wherein the cooling device (7) has a chiller (23) with a thermally conductive coupled to the superconducting coil winding cold head (25), wherein the chiller

(23) is designed to be operated with a closed coolant ^¬ circulation.

11. Use of a device (1) according to one of the preceding claims for security control, wherein the Messob ^¬ projects (9) are a plurality of transported goods (9a) and / or persons (9b), in view of the presence of predefined types of Hazardous substances.

12. A security control method with a device (1) according to one of claims 1 to 10,

in which

- Run a plurality of measuring objects (9) in the form of persons (9b) and / or transported goods (9a) in succession through the sample space (11) of the device (1) or transported

- and at the respective measuring objects (9) by means of the device (1) magnetic resonance signals are measured,

- It is concluded from the nature of the measured magnetic resonance signals on the presence or absence of predefined types of hazardous substances.

13. The method according to claim 12,

in which a magnetic resonance spectrum is determined by Fourier analysis of the frequency components of a free induction decay measured by means of the device (1),

- And in which this magnetic resonance spectrum is compared with spectra of known materials, which is concluded from the comparison of the spectra on the presence or absence of predefined types of hazardous substances.

14. The method according to any one of claims 12 or 13, wherein the magnetic resonance signals are obtained by a double resonance measurement.

15. Method according to one of claims 12 to 14, in which a spatially resolved measurement of the magnetic resonance signals takes place, by means of at least one gradient coil, different locations within the sample space successively into magnetic fields Resonance brought with an exciting high-frequency field who ^¬ .