JPWO2020244689A5 - - Google Patents

Description

The present invention relates to a dipole antenna array for a hybrid MR-PET and MR-SPECT tomography device, the use of the dipole antenna array, and an MR-PET or MR-SPECT tomography device having a dipole antenna array.

For nuclear magnetic resonance imaging with hybrid MR-PET or MR-SPECT devices, a radio-frequency antenna is used, which is arranged in the magnet bore and thus in the PET or SPECT measurement range. In combined methods, where MR imaging is performed simultaneously with PET or SPECT imaging, the measurement components resulting from the PET or SPECT ratios must be kept as interference-free as possible.

MRT coils are used to transmit and/or receive high frequency electromagnetic radiation. Typically, they work in the near field of the antenna and also in the transition region between the near field and the far field for high field MRT. As a result, the conductive structure, i.e. the antenna, must be placed close to the examination volume.

The combination of an MRT system with a PET or SPECT system offers the advantage of making it possible to measure two or more modalities simultaneously. Technically, these systems are implemented by integrating the scintillation crystal and possibly the evaluation electronics in the magnet bore of the MRT system. In order to keep the sensitivity losses of the MRT measurements to a minimum, a combined MR-PET or MR-SPECT system needs to place the MRT antenna, often also called the MRT coil, in the PET/SPECT detector ring. On the one hand, this leads to a strong coupling of the magnetic field used in the MRT with the PET/SPECT detector unit, and on the other hand, an absorption of the gamma quanta of the PET/SPECT measurements by the inserted antenna.

PET and SPECT derive their PET and SPECT signals from annihilation quanta (German: Annihilationsquanten), or gamma quanta, which typically have an energy of 511 keV. Along the path these signals travel, they are absorbed or scattered by materials in their propagation path. For this reason, the introduction of MRT coils into a PET/SPECT system adversely affects the sensitivity of the PET/SPECT measurements.

In prior art MRTs operating at up to 7T, or 1.5T and 3T in clinically approved devices, for wavelengths corresponding to the resonant frequencies of protons of approximately 300 MHz (7T), 128 MHz (3T), or 64 MHz (1.5T), a straight dipole is too long to ensure efficient coupling into the examination volume. Therefore, as described in non-patent document 1, components, such as inductors, are inserted into the dipole antennas used to shorten them. Usually, such shortened dipole antennas are also connected in the middle of the dipole. However, all these measures result in additional absorption or scattering of the PET/SPECT gamma quanta by highly absorbing materials such as electronic components and additional conductive structures in the PET/SPECT measurement volume. The central connection of the dipole elements adds further components such as coaxial lines and concentrated components to the PET/SPECT sensitive region. In MRT, the use of long dipole elements has negative effects in two respects. On the one hand, they limit the measurement volume; for example, a cylindrical arrangement of dipoles with a small diameter, as desired for head imaging, may be geometrically restricted by the extended anatomical structure in the shoulder region. Furthermore, straight dipole antennas result in a large sensitivity region along the magnetic axis, which often exceeds the homogeneous region of the switchable gradient field and can therefore result in signal folding in the MRT images.

The MRT antenna must have as little gamma quantum absorption as possible for the quanta in the PET and/or SPECT energy range so as not to reduce the sensitivity of the nuclear medicine modality.

German patent JP 2003-133663 A discloses a dipole antenna that is folded and has a connection at the folded part.

Therefore, when measuring with an MR-PET or MR-SPECT device, it is necessary to introduce as little material as possible into the examination volume or spatial measurement range. There is a need to improve the quality of MRT-PET/SPECT measurements, and to obtain with combined MR-PET/SPECT devices a quality nearly identical to that of the separate component MRT, PET, and SPECT measurements.

German Patent No. 000010322186

"Kurze Antennen: Entwurf und Berechnung verkuerzter Sende- und Empfangsantennen" Publisher: Franckh, 1986, Number of pages: 408 pages, ISBN 344005469 1

The object of the present invention is therefore to enable acquisition of MR-PET or MR-SPECT data in a combined system, in particular without interference or with as little loss of sensitivity as possible, in comparison with devices for one modality. With regard to the PET or SPECT portion of the MR-PET or MR-SPECT measurement, acquisition with increased sensitivity should be possible in comparison with devices for combined MR-PET or MR-SPECT measurements according to the prior art, with as few artifacts as possible, in particular no aliasing, occurring in the MRT images. The technical solution to this problem should be inexpensive and easy to implement. Attenuation and/or scattering of gamma rays or other photons that must be detected should be minimized. Higher B 0 magnetic fields, such as for example 7 Tesla or ultra-high magnetic fields greater than 7 Tesla as well as high magnetic fields of ₃ Tesla and above, should be easier to use. Magnetic fields of 9.4 Tesla, 10.5 Tesla, 11.7 Tesla, 14 Tesla and even 20 Tesla can be mentioned by way of example. Backscattering and absorption of the gamma quanta must be reduced or avoided.

Based on the preamble of claim 1 and the claims arranged in parallel, this problem is solved according to the invention by the features specified in the characterizing parts of these claims.

The dipole antenna array and the dipole antenna arrangement according to the invention make it possible to generate interference-free MRT-PET/SPECT images, in particular without aliasing or artifacts in the MRT images. The combined components of the MR-PET/SPECT tomography device according to the invention have approximately the same quality as the individual components of MR, PET and SPECT have. The attenuation or scattering of gamma rays is reduced. The use of higher B 0 magnetic fields, for example 7 Tesla or ultra-high magnetic fields greater than 7 Tesla, such as 9.4 Tesla, 10.5 Tesla, 11.7 Tesla, 14 Tesla but also ₂₀ Tesla, as well as high magnetic fields of 3 Tesla and above, becomes more accessible. With regard to the PET or SPECT fraction of the MR-PET or MR-SPECT measurements, imaging that increases the sensitivity of the measurements to these components in the MR-PET or MR-SPECT devices according to the prior art becomes possible. The physical size of the dipole antenna is reduced.The solution to the problem according to the invention is cheap and technically easy to implement.

The term MRT-PET/SPECT is used hereinafter to indicate that it can refer to both MRT-PET and MRT-SPECT embodiments.

Advantageous embodiments of the invention are described in the dependent claims.

In the following, the dipole antenna array according to the present invention will be described in its general form without being interpreted in a limiting manner.

The present invention provides a dipole antenna array in which at least two dipole antenna elements, folded on at least one side, are coupled to each other to at least partially enclose a cavity.

In one embodiment, the dipole antenna elements of the dipole antenna array according to the invention are folded at one end, preferably at an angle of more than 90° and up to 180°. In this case, the connections and components to which the dipole antenna array is connected are located at the folded part outside the measurement range of the PET-SPECT sensor given by the area along the rotation axis in which the PET or SPECT sensor of the PET/SPECT ring is located. In a further embodiment, one dipole antenna element is also folded at both ends.

The connections of the connections and components outside the PET-SPECT measurement range, especially at the fold of the dipole antenna element, result in no interference of the measurements within the PET/SPECT measurement range. Advantageously, in this case, outside the PET/SPECT measurement range, further electronic components, such as matching circuits, transmit/receive switches or preamplifiers, can also be arranged close to the antenna feed point without affecting the PET/SPECT measurement. The gamma quanta are no longer absorbed by device components located within the PET/SPECT measurement range, preventing scattering of the gamma quanta at these components. Typically, the gamma quanta have an energy of 511 keV.

The folding of the dipole antenna array results in a shortened spatial scale of the dipole antenna array, which is advantageous in the limited free volume of the hybrid MR-PET/SPECT device. At the same time, the functional folding, for example in the form of a "J", results in a reduction of the electromagnetic field emitted by the dipole antenna array in this region by the geometrically anti-parallel flowing currents. This reduces the coupling of the dipoles to the components in the vicinity of the feed point and reduces the excitation of nuclear magnetic resonance in this region, which should be prevented. In particular, by preventing the excitation of nuclear magnetic resonance in the folded region of the dipole antenna, artifacts in the MRT images due to, for example, folding can be prevented.

The folded portions of the dipole antenna elements of the dipole antenna array, located outside the PET/SPECT measurement range, allow for power-matched electrical connections of the dipoles formed by the dipole antenna array. This allows for power-matched connections using capacitors by properly selecting the electrical connection points. The appropriate selection of the connection points is based on the knowledge of a person skilled in the art.

When the connection is spatially close to the PET/SPECT measurement range, backscattering of gamma quanta into the PET/SPECT measurement range can be reduced by using fewer components.

The folded region of the dipole antenna element includes the bend, the region of the folded length, and the perpendicular projection of the folded region onto the long side of the dipole antenna element.

The curved portion may be a radius in the form of an arch, an ellipse, or other geometric curvature. Knick-knocks of the dipole antenna array including angles according to the invention are also possible. The curved portion may be assembled from at least two partial curved portions.

The folded portion is a portion that is folded back in the longitudinal direction of the dipole antenna at an angle of 90° or more and 180° following the curved portion .

The vertical projection of the folded region onto the longer side of the dipole antenna element is the portion of the dipole antenna element that is in front of the bend in the longitudinal direction, and is the projection of the folded region that is perpendicular to the longitudinal direction of the dipole antenna element.

The two ends of the dipole antenna element are the end points, i.e., the end of the straight section and the end of the folded region, and, in the embodiment where there are folds at both ends of the dipole antenna element, the end points of the two folds.

The measurement range of the dipole antenna array or dipole antenna element according to the invention may be in a range along the length of the dipole antenna array between the end point that does not have a bend and the point resulting from the projection of the end points of the curved portion in the longitudinal direction. In one embodiment where both ends of the dipole antenna element are folded, the measurement range can be located between the points resulting from the projection of the end points of the respective curved portions in the longitudinal direction. This measurement range may be at least a partial area of the aforementioned longitudinal portion of the dipole antenna array or dipole antenna element, and also depends on the design of the MR-PET or ME-SPECT device or external factors such as magnetic fields. In this case, it is the longitudinal portion that is available as a transmitter and receiver. Furthermore, the measurement range of the dipole antenna element or dipole antenna array is at least a partial area of the portion without the fold in the folded dipole antenna element or dipole antenna array.

In particular, in the PET or SPECT measurement range of the dipole antenna element or dipole antenna array, there are no connections such as inductors, capacitors, connecting wires, coaxial cables, or preamplifiers.

Preferably, the connection or component is at least partially located in the folded portion of the dipole antenna element or dipole antenna array.

Preferably, all connections and components are at the dipole antenna array or dipole antenna element folds. As a result, better image quality is achieved in PET or SPECT imaging.

For example, in one preferred embodiment, the coaxial cables can be connected such that their ends are assigned to the folded area of the fold and to the area of the perpendicular projection of the folded area onto the length of the dipole antenna element, thereby allowing a power matching connection using a simple capacitor by precise selection of the electrical connection points.

The angle at which the dipole antenna array or dipole antenna elements are folded may have any desired value between 90° and 180°. For example, it may be 95°, 100°, 115°, 120°... 165°, 170°, 175°, or 179°.

A dipole antenna element of a dipole antenna array has a length between its end points that corresponds to λ/2 of the wavelength at the resonant frequency. The physical length for λ/2 may vary to a lower or higher value as long as the operating mode is maintained in which a dipole-shaped current distribution on the dipole antenna array or dipole antenna element is maintained.

Preferably, the dipole antenna elements have a cross section that does not cause a sudden change in the absorption coefficient for gamma rays, for example a circular or elliptical cross section. This makes it possible to prevent artifacts in PET/SPECT image reconstruction.

Preferably, the dipole antenna elements of the dipole antenna array according to the invention are formed thin. Thin in the sense of the present invention means a thickness of the dipole antenna element that corresponds to a penetration depth of 1 to 5 of the high frequency field into the dipole antenna element.

Preferably, the dipole antenna array or dipole antenna elements are made of an electrically conductive material, preferably a metal with a low atomic number such as aluminum. Using a dipole antenna element material with a low atomic number, as in the case of aluminum, also results in preventing or reducing interference in the PET/SPECT measurements and artifacts in the recorded images. The material selection of the conductor material for the dipole antenna array is a compromise between electrical conductivity and low atomic number.

Advantageously, the dipole antenna array according to the invention can be combined with a multi-channel MRT coil, for example to extend the MRT measurement range.

According to the invention, at least two dipole antenna elements are grouped in an array via a support to define a cavity. In practical use, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 or more dipole antenna elements may surround a cavity that is preferably cylindrical, the dipole antenna elements being radially spaced apart on an imaginary surrounding cylinder. The above-mentioned number of dipole antenna elements so arranged is limited only by practical considerations.

The number of dipole antenna elements used may depend on the strength of the magnetic field or the dimensions of the object to be examined. For example, 8 dipole antenna elements may be advantageous when imaging the head at 9.4 Tesla. When examining the entire body, 16 dipole antenna elements may be advantageous. The higher the _B0 magnetic field used, the greater the interfering coupling between the dipole antenna elements, and therefore preferably fewer dipole antenna elements are interconnected in the dipole antenna array. However, the interfering coupling between the dipole antenna elements can also be reduced by technical measures. These are known to those skilled in the art.

In this case, the folded parts of the dipole antenna elements of the dipole antenna array can also be assigned to opposite longitudinal ends, but it is preferred that the dipole antenna elements are arranged on the support such that all curved ends are arranged on the same longitudinal side. In this way, all connections or components are at the same end of the dipole antenna array. As a result, all cables can be pulled out of the carrier housing in the same direction.

In the case of the support as a means for holding the dipole antenna elements together, in one simple embodiment it may be two rings connected with the dipole antenna elements on the inside or outside, or the dipole antenna elements may extend through a bore in the rings so that they are fixed.

It is advantageous if the support ring does not protrude within the measurement range of the PET-SPECT measurement range.

The cylinder to which the dipole antenna elements are attached by fixing means can also function as a support.

Preferably, the support is made of a non-magnetic material whose μ corresponds approximately to air, preferably of plastic.

A portion or the entire area of the dipole antenna array or dipole antenna elements bounded by the support can be used for MRT measurements. As a result, the measurement range for MRT may be greater than, equal to, or less than the measurement range of the PET/SPECT system.

Various device elements can be connected to the folded portion of the dipole antenna element.

For example, the feed line may be connected via a matching network. In this case, the symmetrical network may be connected either directly together with the matching circuit or via a matching network. Along with the adaptation circuit, a detuning circuit may also be installed.

The present invention further relates to a magnetic resonance imaging system, in particular a high-field/ultra-high-field magnetic resonance imaging system, a magnetic resonance spectroscopy system or a nuclear magnetic resonance spectroscopy system, having an integrated PET or SPECT system with the above-mentioned coil arrangement according to the present invention, which solves the above-mentioned problems.

Furthermore, the present invention relates to the use of the above-described dipole antenna array according to the present invention as a radio-frequency transmitter and/or receiver coil in magnetic resonance tomography, in particular high-field/ultra-high-field magnetic resonance tomography, magnetic resonance spectroscopy or nuclear magnetic resonance spectroscopy, with an integrated PET or SPECT system.

Further features and advantages of the present invention will become apparent from the following description of one embodiment of a coil arrangement according to the present invention, taken in conjunction with the accompanying drawings.

The invention is illustrated in the figures.

1 shows a dipole antenna array with several regions or sections depicted. 1 shows a dipole antenna array with connections shown. 1 shows a dipole antenna array in which six dipole antennas are arranged according to the present invention. 1 shows a plan view of a dipole antenna array in the longitudinal direction. 1 shows a plan view of a dipole antenna array in the longitudinal direction. An enlarged view of the spherical phantom is shown. An image of the head is shown. 1 shows a patient and a measuring device for measuring the head.

1 shows a dipole antenna element 1 having a fold 2 with a curved portion 3, a folded region 4 and a projection of the folded region 5. The end points of the folded region have reference number 6 and the long end points of the dipole antenna array have reference number 7.

2 shows a dipole antenna element 1 in which a coaxial cable 8 is connected by an inner cable 9 to a capacitor 10 (connected to a portion of the dipole antenna element 1 that is the projection 5 of the folded area). An outer cable 11 of the coaxial cable 8 is connected to the folded area 4.

Figure 3 shows a longitudinal view of a dipole antenna array 10 having strip-shaped dipole antenna elements 1a-1f arranged cylindrically relative to one another.

FIG. 4 shows a longitudinal plan view of the dipole antenna array 10 in which the folded regions 4a, 4b, . . . , 4f and the projections 5a, 5b, . . . , 5f of the folded regions can be seen.

In FIG. 5, the dipole antenna array 10 is depicted in a cross-sectional view with the folded regions 4a, 4b, . . . 4f and the projections of the folded regions disposed along the cylindrical circumference of the support.

Figure 6 shows the magnetic field in the axial and sagittal directions in a spherical phantom using a dipole antenna array 10 according to the present invention compared to a linear antenna.

Figure 7 shows the distribution of magnetic fields in the head in the axial and sagittal directions when using a dipole antenna array 10 according to the present invention.

8 shows an MR-PET or MR-SPECT device in which a patient's head is to be measured. In the figure, magnets 11, 11a equipped with gradient coils 12, 12a are shown. A PET module in the case of the MR-PET device and a SPECT module in the case of the MR-SPECT device are indicated with reference numerals 13, 13a. Dipole antenna elements which are components of a dipole antenna array are indicated with reference numerals 1, 1a.
This application relates to the invention described in the claims, but also includes the following as other aspects.
1.
In a dipole antenna array having at least two dipole antenna elements, the dipole antenna element (1) has a folded portion (2) at one end,
The folding portion comprises a curved portion (3), a folded region (4), and a projection (5) of the folded region of the dipole antenna element (1) in the longitudinal direction of the dipole antenna element (1),
The dipole antenna element (1) at least partially surrounds the cavity.
1. A dipole antenna array comprising:
2.
2. The dipole antenna array according to claim 1, characterized in that the folded portion (2) is formed to allow for at least one connection of another component.
3.
3. The dipole antenna array according to claim 1 or 2, characterized in that the connection part is suitable for connection to a capacitor, an electrical connection line, a coaxial cable, an inductor, a preamplifier, a matching circuit, a transmit/receive switch, a symmetrical network, a matching network, or a detuning circuit.
4.
4. A dipole antenna array as described in any one of 1 to 3 above, characterized in that there are no connections on the outside of the folded portion (2).
5.
5. A dipole antenna array according to any one of claims 1 to 4, characterized in that the ends of the dipole antenna elements (1) are folded at the ends at an angle of more than 90° and up to 180°.
6.
6. A dipole antenna array according to any one of claims 1 to 5, characterized in that the folded portion (2) is formed by at least one curved portion (3) which is realized by a radius or a bend.
7.
7. The dipole antenna array according to any one of claims 1 to 6, characterized in that connection areas for electrical components are assigned to the folded area of the fold (2) and to the projection (5) of the folded area onto the dipole antenna element (1).
8.
8. A dipole antenna array according to any one of claims 1 to 7, characterized in that the dipole antenna elements (1) are made of a metal with a low atomic number.
9.
9. A dipole antenna array according to claim 1, characterized in that the cross section perpendicular to the longitudinal direction of the dipole antenna elements (1) is shaped in such a way that there is no abrupt change in the absorption coefficient for gamma quanta.
10.
10. A dipole antenna array according to any one of claims 1 to 9, characterized in that the dipole antenna element (1) has a thickness corresponding to 1 to 5 times the penetration depth of the high frequency electric field.
11.
11. A dipole antenna array according to any one of claims 1 to 10, comprising 3 to 16 dipole antenna elements (1).
12.
12. A dipole antenna array according to any one of claims 1 to 11, characterized in that at least one dipole antenna element (1) is folded at both ends.
13.
10. A dipole antenna array as claimed in any one of claims 1 to 9, characterised in that all the folds (2) are at the same end of the dipole antenna array.
14.
14. Use of a dipole antenna array according to any one of claims 1 to 13 as an antenna in an MR-PET or MR-SPECT tomography apparatus, in which the folded parts (2) of the dipole antenna elements with their connections are located outside the PET or SPECT measurement range.
15.
13. An MR-PET or MR-SPECT tomography apparatus having a dipole antenna array according to any one of claims 1 to 12, as an antenna in which a folded portion (2) of a dipole antenna element having a connection portion is located outside a PET or SPECT measurement range.

Claims (12)

A dipole antenna array for hybrid MR-PET or MR-SPECT tomography, comprising at least two dipole antenna elements (1),
The dipole antenna element (1) has a folded portion (2) at one end,
the folding portion (2) comprises a U-shaped curved portion (3), a folded region (4) extending from one leg of the curved portion (3), and a projection (5) of the folded region (4) extending from the other leg of the curved portion (3) onto the longitudinal direction of the dipole antenna element (1); the at least two dipole antenna elements (1) are arranged in an array via a cylindrical support so as to at least partially surround a cylindrical cavity;
the folded portions (2) of the at least two dipole antenna elements (1) are at the one end on the same side of the dipole antenna array and comprise at least one connection for an electronic component;
The at least one connection is located outside the PET or SPECT measurement range.
1. A dipole antenna array comprising: The dipole antenna array of claim 1, characterized in that the at least one connection is suitable for connection to a capacitor, an electrical connection line, a coaxial cable, an inductor, a preamplifier, a matching circuit, a transmit/receive switch, a symmetrical network, a matching network, or a detuning circuit. A dipole antenna array as described in claim 1 or 2, characterized in that there are no connections on the outside of the folded portion (2). A dipole antenna array as claimed in any one of claims 1 to 3, characterized in that the ends of the dipole antenna elements (1) are folded at the ends at an angle of more than 90° and up to 180°. A dipole antenna array according to any one of claims 1 to 4, characterized in that the folded portion (2) is formed by at least one curved portion (3) which is realized by a radius or a bend. 6. The dipole antenna array according to claim 1, characterized in that connections for electrical components are assigned to the folded areas (4) of the folds (2) and to the projections (5) of the folded areas onto the dipole antenna elements (1). A dipole antenna array as claimed in any one of claims 1 to 6, characterized in that the dipole antenna elements (1) are made of a metal with a low atomic number. A dipole antenna array as claimed in any one of claims 1 to 7, characterized in that the cross section perpendicular to the longitudinal direction of the dipole antenna element (1) is formed so as not to cause an abrupt change in the absorption coefficient for gamma quanta. A dipole antenna array as claimed in any one of claims 1 to 8, characterized in that the dipole antenna element (1) has a thickness corresponding to 1 to 5 times the penetration depth of the high frequency electric field. A dipole antenna array as claimed in any one of claims 1 to 9, characterized in that it has 3 to 16 dipole antenna elements (1). Use of a dipole antenna array according to any one of claims 1 to 10 as an antenna in an MR-PET or MR-SPECT tomography device in which the folded portion (2) of the dipole antenna element with the connection portion is located outside the PET or SPECT measurement range. An MR-PET or MR-SPECT tomography device having a dipole antenna array according to any one of claims 1 to 10 as an antenna in which the folded portion (2) of the dipole antenna element having a connection portion is located outside the PET or SPECT measurement range.