RU192958U1 - Multi-frequency transceiver coil for magnetic resonance imaging - Google Patents

Abstract

The utility model relates to medical equipment. The essence of the utility model lies in the fact that the multi-frequency transceiver coil for magnetic resonance imaging additionally contains a butterfly type radio frequency surface coil located under the scan object parallel to the plane formed by the system of periodically arranged elements, and one of the structural elements of the distributed resonator capacitance , consisting of a system of periodically located non-magnetic elements, is implemented as a system of metal tracks on an insulating nth substrate and is fixedly mounted, and the second structural element of variable distributed capacitance is formed by dielectric plates metallized on one side on both sides of the first structural element and mounted to move relative to metal tracks on an insulating substrate along the main axis of the device. The technical result is the expansion of the frequency range of the tuning of the resonator. 2 ill.

Description

The utility model relates to medical equipment, namely, it represents a set of transmitting and receiving antennas with a special type of tuning of the operating frequency for a clinical or preclinical tomograph with a constant magnetic field level of 7 Tesla and higher and is intended to provide the possibility of transmitting radio frequency excitation pulses in tomography and spectroscopy nuclear magnetic resonance and receiving radio frequency response signals of nuclei at Larmor precession frequencies of a set of three or more different nuclei.

A well-known universal multilayer multifrequency RF sensor for MRI and MRS (US Patent 6081120A, IPC G01R 33/3635, priority date 05/20/1998, publication date 06/27/2000), in which the construction of the nuclear magnetic resonance signal of multiple nuclei is used two loop antennas made in the form of conductive sections on two sides of a thin printed circuit board, a set of fixed concentrated capacitances connected to them and a high-speed switching circuit. In this device, the presence of a switching circuit allows you to change the order of connection of the loop antennas, which changes the inductance of the resonant circuit of the device, as well as the value of the capacitance connected to one or two loop antennas, which allows you to vary the capacitance of the resonant circuit. The disadvantage of this device is primarily the use of all its structural elements to adjust the operating frequency of the sensor to one Larmor frequency of the selected core. Thus, at each instant of time, this sensor makes it possible to excite and record the nuclear magnetic resonance signal of one isotope. On the other hand, high-speed switching does not allow fine tuning to several resonant frequencies and independently control the stability of this setting. Another disadvantage is the use in the device under consideration of expensive high-speed switching circuits and a lowered signal-to-noise ratio of concentrated capacitance. As a result of this, on the basis of this technical solution, it is impossible to build a transmitting and receiving device for exciting and registering a nuclear magnetic resonance signal of two or more nuclei.

Also known is a two-frequency system of RF coils for MRI (Patent US 8193811 B2, IPC G01R 33/3415, priority date 05/29/2009, publication date 5/06/2012), consisting of a number of unrelated components, where each of the elements is two concentric frame antennas tuned each to the Larmor frequency of nuclei of a certain type (for example, an external antenna - at a frequency of ¹³ C nuclei, internal - at a frequency of ¹ N nuclei), united in a single structure by isolation and switching circuits. The presence of unrelated structural elements makes it possible to construct a large-sized transmitting and receiving device for recording the nuclear magnetic resonance signal of the isotopes of two nuclei by the indicated method. The disadvantage of this device is the fixed tuning of the loop antennas to a specific Larmor frequency, as a result of which it is possible to register a nuclear magnetic resonance signal from only two isotopes in a single volume of space. Moreover, despite the possibility of using the design, both as a receiving and as a transmitting antenna, the possibility of tuning the operating frequency of each antenna element in this device is not provided. Another disadvantage is the use of expensive switching and isolation circuits, low-quality loop antennas and a lowered signal-to-noise ratio of concentrated capacitance in the device under consideration. As a result of this, on the basis of this technical solution, it is impossible to construct a transmitting and receiving device for exciting and registering a nuclear magnetic resonance signal of more than two nuclei in one region of space.

The closest technical solution adopted for the prototype is a radio frequency coil of a magnetic resonance imager (Patent RU 183997 U1, IPC AB 5/055, priority date 12/13/2017, publication date 10/11/2018), including at least: a resonator radiofrequency coil, consisting of a system of periodically arranged non-magnetic elements of the same length and a means of communication of the radiofrequency coil with the transceiver of a magnetic resonance imager in the form of radio frequency cables, while periodically located non-magnet The elements are made in the form of extended metal conductors with a length of not more than five wavelengths of an RF signal in air and a cross-sectional diameter of not less than four skin-layer widths at the Larmor frequency of a magnetic resonance imager and not exceeding the distance between conductors located on several coaxial cylindrical surfaces on a distance of not more than a quarter of the wavelength of the radio frequency signal at the Larmor frequency of the magnetic resonance imager in air from each other, the ends of the adjacent conductor on the one hand are connected to each other by a system of insulated metal tracks placed in at least one layer of the printed circuit board on an insulating substrate, while on the other hand, the ends of adjacent conductors are electrically connected, and the means of communication of the radio frequency coil with the transceiver is made by RF cables through loop antennas. However, the use of a constant distributed capacitance in the indicated technical solution significantly limits the tuning range of the operating frequency of the proposed device, fixing it about two Larmor frequencies of two pre-selected cores. Thus, a significant drawback of this solution is the impossibility of using a device of a similar design to excite and register nuclear magnetic resonance signals from more than two different nuclei.

The problem to which the claimed technical solution is directed is the ability to use a set of coils as a transceiver for exciting and observing a nuclear magnetic resonance signal of the following cores: ¹ N, ² N, ¹³ C, ²³ Na, ³¹ R. For permanent magnetic fields, for example, 11.7 T, this corresponds to a frequency of 500 MHz for a ¹ N core and a Larmor frequency range from 76 to 203 MHz for the remaining cores.

The technical result consists in expanding the frequency range of the tuning of the resonator based on a periodic structure of a number of metal conductors connected by constructive capacitive loads of variable capacitance and the inclusion in the set of transmitting and receiving antennas of an independent butterfly frame coil for excitation and registration of a nuclear magnetic resonance signal of nuclei

The essence lies in the fact that the multi-frequency transmitter-receiver coil for magnetic resonance imaging includes at least a resonator of a radio frequency coil, consisting of a system of periodically arranged non-magnetic elements of the same length, a radio frequency feed coil for a resonator of periodically arranged non-magnetic elements, a butterfly-type radio-frequency surface coil and a radio-frequency coil coupling means with a magnetic resonance volume transceiver graph in the form of radio frequency cables, while one of the structural elements of the distributed capacitance of the resonator, consisting of a system of periodically arranged non-magnetic elements, is implemented as a system of metal tracks on an insulating substrate and it is stationary, and the second structural element of variable distributed capacitance is formed located on both sides of of the first structural element with dielectric plates metallized on one side, which are mounted with the possibility of movement relative to Lines on an insulating substrate along the main axis of the device.

This technical result is achieved on the one hand by the fact that in addition to the distributed capacitance implemented as a system of metal tracks on an insulating substrate, to which the ends of the conductors are connected on both sides, the distributed capacitance is formed by metallized dielectric plates on one side located on top and bottom of substrates with metal tracks. The plates are mounted to move relative to the substrate with metal tracks. On the other hand, the achievement of this result is the use of nuclei to excite and register a signal of nuclear magnetic resonance ^! A butterfly-type coil, which generates a radio-frequency alternating field perpendicular to the coil field to excite and record the nuclear magnetic resonance of the nuclei of the other isotopes.

The essence of the claimed utility model is illustrated by figures, where:

FIG. 1 shows a General view of the proposed device;

FIG. 2 shows the reverse surface of the butterfly bottom coil.

The composition of the proposed device includes two RF coils, one of which is located above the object to be scanned, and the second one below it, parallel to the plane formed by the structure of the metal conductors 1. The upper coil is a nonmagnetic multimode resonator based on the periodic structure of the metal conductors 1 and serves to its power supply to the frame coil 2. The frame coil 2 is mounted above a plane formed by a plurality of conductors 1 in its central part. An RF cable 3 connects the frame coil 2 to a tomograph transceiver (not shown in FIG.). The ends of the conductors 1 on both sides are connected to a distributed capacitance, one of the structural elements of which is implemented as a system of metal tracks on an insulating substrate 4. The second structural element of a variable distributed capacitance is formed by metallized plates on one side of a dielectric 5 located above and below the substrates with metal tracks 4.

The bottom coil is a butterfly frame coil. The coil is implemented in the form of metal tracks on a dielectric plate 6 and is tuned to the operating frequency (Larmor frequency of the selected core) using constant and variable capacitors 7. An RF cable 8 connects a butterfly coil to a tomograph transceiver.

The proposed set of transceiver coils works as follows.

Upon receipt of a high-power RF signal from the transmission system of the tomograph over the RF cable 3, the signal reaches the frame coil 2, which through being inductively coupled to the structure of the conductors 1, excites one of the eigenmodes of the periodic structure from the plurality of conductors 1. Various eigenmodes are formed by different distribution of electric currents flowing across a plurality of conductors 1. Due to the formation in the structure of the conductors of the distribution of currents corresponding to the excited m A resonator ode in the scanning area immediately below the plurality of conductors 1 where the scanning object is located creates a radio frequency magnetic field that excites spins in the scanning object. The most effective for the needs of magnetic resonance imaging is the first eigenmode of the periodic structure. It has the most uniform distribution of the magnetic field and the maximum depth of its penetration into the scanned object. In the magnetic field created by the first mode of the periodic structure in the scanning region, the vertical component predominates. To tune the resonator to the operating frequency of the first mode, the plates 5 are shifted along the main axis of the device. In this case, the overlap area of the plates 5 and metal tracks on the insulating substrate 4 changes, thereby changing the capacitance. Fine tuning in frequency can be done by changing the inductance of conductors 1. For this, they are made in the form of telescopic non-magnetic metal tubes of variable length. When a radio frequency signal is transmitted by a tomograph transmitter via a radio frequency cable 8 connected to metal tracks on a dielectric plate 6, the signal reaches a butterfly coil, and it creates an alternating magnetic field in the scanning area at a frequency different from the frequency of the magnetic field generated top coil 2. In the magnetic field generated by the butterfly coil in the scanning area, the horizontal component prevails. The operating frequency of the coil is tuned by changing the capacitance of the capacitors 7. Due to the orthogonality of the magnetic field distributions in the object when the first eigenmode of the periodic structure and the butterfly coil are excited, it is possible to independently adjust two corresponding resonant frequencies to two Larmor frequencies determined by the types of nuclei.

As an example of the practical implementation of the proposed technical solution, the following are the geometric parameters of the RF coil for MRI of small animals in a constant magnetic field of 11 T with a Larmor frequency of 500 MHz for a core of ¹ N.

RF coil geometrical parameters:

Length of metal conductors 1: varies from 78 mm to 138 mm

Overlapping the system of metal tracks on the insulating substrate 4 with plates of dielectric 5 metallized on one side: varies from 3 mm to 33 mm.

The distance between the frame coil 2 and the plane formed by many conductors 1:10 mm

The distance between the plane formed by the plurality of conductors 1 and the dielectric plate is 6:50 mm.

The number of metal conductors forming a periodic structure 1: 5

As the dielectric for the system of metal tracks 4 and plates 5 metallized on one side, Arlon AD1000 grade material with a dielectric constant of 10 and a loss tangent of 0.0023 and a thickness of 0.508 mm is used. The plate with metal tracks 6 is implemented in the form of a printed circuit board on a FR-4 substrate with a dielectric constant of 4.4, a loss tangent of 0.02, and a thickness of 1.5 mm.

Thus, the claimed utility model can be used as a transceiver for exciting and observing a nuclear magnetic resonance signal of the following nuclei: ¹ H, ² H, ¹³ C, ²³ Na, ³¹ R. For a constant magnetic field, for example, 11.7 T this corresponds to a frequency of 500 MHz for a ¹ H core and a Larmor frequency range from 76 to 203 MHz for the remaining cores.

Claims (1)

A multi-frequency transceiver coil for magnetic resonance imaging, including at least a resonator of a radio frequency coil, consisting of a system of periodically arranged non-magnetic elements of the same length, a radio frequency power coil for a resonator of periodically arranged non-magnetic elements and a means for communicating radio frequency coils with transceiver of a magnetic resonance imager in the form of radio frequency cables, characterized in that the introduced radio frequency surface a clear butterfly-type coil located under the scan object parallel to the plane formed by a system of periodically arranged elements, and one of the structural elements of the distributed cavity capacitance, consisting of a system of periodically arranged non-magnetic elements, is implemented as a system of metal tracks on an insulating substrate and is mounted motionless and the second structural element of variable distributed capacity is formed located on both sides of the first structural element m metalized from one side dielectric plates that are mounted with the possibility of movement relative to metal tracks on an insulating substrate along the main axis of the device.

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