MAGNETIC RESONANCE IMAGING RADIO-FREQUENCY COIL ASSEMBLY WITH HIGH TIME-DOMAIN SIGNAL STABILITY

Abstract

Disclosed is a magnetic resonance imaging radio-frequency coil assembly with high time-domain signal stability, mainly including a radio-frequency transmitting coil unit, a plurality of radio-frequency receiving coil units, and a housing structure. A plane area of the radio-frequency transmitting coil unit is larger than a sum of layout plane areas of all of the plurality of radio-frequency receiving coil units. The plurality of radio-frequency receiving coil units are arranged at an internal side of the radio-frequency transmitting coil unit. An overall size of an array formed by the plurality of radio-frequency receiving coil units is larger than a size of an imaging region. A circumference of each radio-frequency receiving coil unit is less than one tenth of a wavelength of a vacuum electromagnetic wave. Thermal noise from the load accounts for a small proportion in the radio-frequency receiving coil units.

Claims

1. A magnetic resonance imaging radio-frequency coil assembly with high time-domain signal stability, comprising: a radio-frequency transmitting coil unit and a plurality of radio-frequency receiving coil units, wherein a plane area of the radio-frequency transmitting coil unit is larger than a sum of layout plane areas of all of the plurality of radio-frequency receiving coil units, the plurality of radio-frequency receiving coil units are arranged at an internal side of the radio-frequency transmitting coil unit, an overall size of an array formed by the plurality of radio-frequency receiving coil units is larger than a size of an imaging region, a circumference of each of the plurality of radio-frequency receiving coil units is less than one tenth of a wavelength of a vacuum electromagnetic wave, and a quality factor of the plurality of radio-frequency receiving coil units in a no-load state is more than 2 times a quality factor of the plurality of radio-frequency receiving coil units in a load state.

2. The magnetic resonance imaging radio-frequency coil assembly with high time-domain signal stability according to claim 1, wherein the radio-frequency transmitting coil unit and the plurality of radio-frequency receiving units are directly placed inside a housing and are fixed relative to each other.

3. The magnetic resonance imaging radio-frequency coil assembly with high time-domain signal stability according to claim 2, wherein a fixed device interface is provided at an external side of the housing, such that the housing has no relative displacement with respect to a to-be-imaged object.

4. The magnetic resonance imaging radio-frequency coil assembly with high time-domain signal stability according to claim 1, wherein the radio-frequency transmitting coil unit and the plurality of radio-frequency receiving coil units are metal conductors.

5. The magnetic resonance imaging radio-frequency coil assembly with high time-domain signal stability according to claim 4, wherein the radio-frequency transmitting coil unit and the plurality of radio-frequency receiving coil units are copper wires with insulation coating.

6. The magnetic resonance imaging radio-frequency coil assembly with high time-domain signal stability according to claim 1, wherein the radio-frequency transmitting coil unit and the plurality of radio-frequency receiving coil units comprise a diode circuit for ensuring that the radio-frequency transmitting coil unit and the plurality of radio-frequency receiving coil units are not in an operating state simultaneously.

7. The magnetic resonance imaging radio-frequency coil assembly with high time-domain signal stability according to claim 6, wherein the plurality of radio-frequency receiving coil units are connected in series with a parallel LC resonance circuit with a diode, and an operating frequency of the resonance circuit is the same as an operating frequency of the plurality of radio-frequency receiving coil units; and when the diode is forward-biased, the parallel LC resonance circuit connected in series with the plurality of radio-frequency receiving coil units is in a resonance state, and the radio-frequency transmitting coil unit is in an off-resonance state and does not operate; when the diode is backward-biased, the radio-frequency transmitting coil unit operates.

8. The magnetic resonance imaging radio-frequency coil assembly with high time-domain signal stability according to claim 6, wherein the radio-frequency transmitting coil unit is connected in series with a circuit with a diode, when the diode is forward-biased, the radio-frequency transmitting coil unit is in a resonance state and operates; when the diode is backward-biased, the radio-frequency transmitting coil unit does not operate.

9. The magnetic resonance imaging radio-frequency coil assembly with high time-domain signal stability according to claim 1, wherein signal isolation among the plurality of radio-frequency receiving coil units is achieved by geometric overlap; and the plurality of radio-frequency receiving coil units are directly connected to a pre-amplifier to reduce a coaxial-cable loss, and the plurality of radio-frequency receiving coil units and the pre-amplifier are encapsulated together at an internal side of a housing structure.

10. The magnetic resonance imaging radio-frequency coil assembly with high time-domain signal stability according to claim 1, wherein the radio-frequency transmitting coil unit and the plurality of radio-frequency receiving coil units operate at a frequency of 297.2 MHz, the radio-frequency transmitting coil unit is of an annular structure, a diameter of the radio-frequency transmitting coil unit is 7 cm, and a diameter of each of the plurality of radio-frequency receiving coil units is 1.5 cm.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate technical solutions described in the embodiments of the present disclosure, the accompanying drawings used in the embodiments are briefly introduced as follows. It should be noted that the drawings described as follows are merely part of the embodiments of the present disclosure, and other drawings can also be acquired by those skilled in the art according to the drawings without paying creative efforts.

[0019] FIG. 1 is a schematic diagram of layout of an array of radio-frequency receiving coils in a magnetic resonance imaging radio-frequency coil assembly with high time-domain signal stability according to an embodiment of the present disclosure, in which 1 denotes the radio-frequency receiving coil;

[0020] FIG. 2 is a schematic diagram of a connection between a radio-frequency receiving coil array and a radio-frequency pre-amplifier, in which 1 denotes the radio-frequency receiving coil and 2 denotes the radio-frequency pre-amplifier;

[0021] FIG. 3 is a schematic diagram of the layout of an array of radio-frequency receiving coils and a radio-frequency transmitting coil, in which 1 denotes the radio-frequency receiving coil, 2 denotes a radio-frequency pre-amplifier, and 3 denotes a radio-frequency transmitting coil unit;

[0022] FIG. 4 is a structural diagram of a housing of a radio-frequency coil assembly, in which 4 denotes a device interface and 5 denotes the housing;

[0023] FIG. 5 is a schematic diagram of an overall structure according to an embodiment of the present disclosure, in which 1 denotes a radio-frequency receiving coil, 2 denotes a radio-frequency pre-amplifier, 3 denotes a radio-frequency transmitting coil unit, 4 denotes a fixed device interface, and 5 denotes a housing;

[0024] FIG. 6 is a schematic diagram of a magnetic resonance imaging experiment design for studying the influence of the displacement of a load object on a radio-frequency receiving coil signal and thermal noise, in which 6 denotes a radio-frequency coil assembly including a radio-frequency transmitting coil unit and radio-frequency receiving coil units, 7 denotes a Teflon pad, and 8 denotes a cylindrical liquid model (whose conductivity and dielectric constant close to those of human tissue);

[0025] FIG. 7 shows comparison results of the influence of the displacement of a load object on a thermal noise level of different types of radio-frequency receiving coils;

[0026] FIG. 8 shows comparison results of time-domain fluctuation of thermal noise levels of radio-frequency receiving coils with different quality factor ratios under no load/load in the presence of the displacement of a load object; and

[0027] FIG. 9 is a diagram of comparison results of signal time-domain fluctuation amplitudes of radio-frequency receiving coils with different diameters in the presence of the displacement of a load object.

DESCRIPTION OF EMBODIMENTS

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the following clearly and completely describes the technical solutions of this application with reference to specific embodiments of this application and the corresponding accompanying drawings. Apparently, the described embodiments are merely part of rather than all of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of this application are within the protection scope of this application.

[0029] The quality factor ratio under no load/load mentioned in the specification refers specifically to a ratio of a quality factor of a radio-frequency receiving coil unit in a no-load state to a quality factor of the radio-frequency receiving coil unit in a load state.

[0030] As shown in FIG. 1 to FIG. 5, an embodiment of the present disclosure provides a magnetic resonance imaging radio-frequency coil assembly with high time-domain signal stability, mainly including a single-channel radio-frequency transmitting coil unit 3 and a plurality of radio-frequency receiving coil units 1. All the radio-frequency receiving coil units 1 are arranged into an array on a circular plane (i.e., the plurality of radio-frequency receiving coil units 1 are arranged in the form of a circular array). The receiving coil units 1 overlap each other, and signal isolation between the radio-frequency receiving coils is enhanced by mutual inductance. A central axis of the radio-frequency transmitting coil 3 is coincident with a central axis of a circular plane where the array of the radio-frequency receiving coils 1 is located, with a coverage range greater than a sum of coverage ranges of all the radio-frequency receiving coils 1. The array of the radio-frequency receiving coils is compatible with a parallel imaging function of a magnetic resonance imaging system, which helps to shorten the scanning time and improve the image quality. The radio-frequency receiving coils are connected in series with a capacitor and then is connected to respective pre-amplifiers 2. The capacitor is used for impedance matching and enhancement of the decoupling performance between radio-frequency coil channels.

[0031] The single-channel radio-frequency transmitting coil 3 is used to match the electromagnetic load of the to-be-imaged object, so as to achieve high transmission efficiency and uniform excitation of a brain range.

[0032] A further technical solution is to obtain a ratio of a quality factor of the radio-frequency receiving coil unit in a no-load state to a quality factor of the radio-frequency receiving coil unit in a load state through a radio-frequency network analyzer test. The quality factor of the radio-frequency receiving coil unit in the no-load state is more than 2 times that of the radio-frequency receiving coil unit in the load state. In an embodiment, each radio-frequency receiving coil 1 is a circular structure with an effective diameter of 1.5 cm, and the array of the plurality of radio-frequency receiving coils 1 is arranged with an effective coverage diameter of 7 cm.

[0033] A further technical solution is that a resonant frequency of the radio-frequency coil shown in the embodiment is equal to 297.2 MHz, which can be used in a magnetic resonance system with the field intensity of the main magnetic field greater than or equal to 7 tesla and in a magnetic resonance system without a body transmitting coil.

[0034] The pre-amplifiers 2 are directly connected to the radio-frequency receiving coils 1, which reduces the space occupied by the coil through integrated design to facilitate the fixation with the to-be-imaged object, that is, to maintain no relative displacement, while avoiding a coaxial-cable loss and improving an imaging SNR.

[0035] An overlap range of geometric overlap of the radio-frequency receiving coils 1 is determined by an overlap range measured by a network analyzer when a forward transmission coefficient S21 between channels is less than −15 dB. The radio-frequency transmitting coil unit 3 and the radio-frequency receiving coil units 1 may be copper wires with insulation coating.

[0036] Three fixed device interfaces 4 are mounted to a radio-frequency coil housing 5, which can facilitate the fixation with an external fixed device, so as to be used for mechanical fixing in the process of magnetic resonance imaging, to ensure that there is no relative displacement between the radio-frequency transmitting coil, the radio-frequency receiving coils, and the to-be-imaged object.

[0037] The working principle of the magnetic resonance imaging radio-frequency coil assembly with high time-domain signal stability according to the present disclosure is as follows:

[0038] Based on experimental measurement data, a larger effective coverage range of a radio-frequency coil indicates that a signal is less affected by the object-coil displacement. A smaller size of a single radio-frequency receiving unit indicates a smaller ratio of a quality factor under no load to a quality factor under load. That is, a smaller ratio of thermal noise from the load to an overall thermal noise level indicates that the thermal noise level is less affected by the object-coil displacement. A large-scale high-density radio-frequency receiving coil array composed of small-sized radio-frequency receiving coil units is proposed, which has a large signal coverage range. The object-coil displacement during magnetic resonance imaging can be further minimized from the source through the design of a housing that can interface with an external fixed device. Thus, an overall effect can achieve high time-domain signal stability.

[0039] FIG. 6 is a schematic diagram of a magnetic resonance imaging experiment design for studying the influence of the displacement of a load object on a radio-frequency receiving coil signal and thermal noise. In the experimental design, a cylindrical liquid model 8, which has conductivity and dielectric constant close to those of human tissue, is used as the load object. In an experiment, a Teflon pad 7 with different thicknesses (3 mm, 6 mm, 8 mm) is placed between a radio-frequency coil and the load object to simulate the influence of the displacement of the load object on the radio-frequency coil signal and thermal noise characteristics. A dielectric constant of the Teflon pad 7 is close to a vacuum dielectric constant. In a case that the Teflon pad 7 with each thickness is used, 60 imaging samples are taken in 2 minutes for a signal level and a thermal noise level of a radio-frequency coil 6, so as to acquire time-domain fluctuation data and variance of the radio-frequency receiving coil signal and thermal noise in the absence of the displacement of the load object. When a Teflon pad 7 with different thicknesses is used, acquired signal and thermal noise time-domain fluctuation data is randomly mixed to obtain simulated data under the displacement of the load object. Four types of radio-frequency coils 6 with different sizes and quality factor ratios under no load/load are used in the experiment, including: the radio-frequency coil according to the embodiment of the present disclosure, an annular radio-frequency coil with a diameter of 2 cm having both receiving and transmitting functions, an annular radio-frequency coil with a diameter of 3.5 cm having both receiving and transmitting functions, and an annular radio-frequency coil with a diameter of 5 cm having both receiving and transmitting functions. The radio-frequency coil according to the embodiment of the present disclosure used in the experiment and three other annular radio-frequency coils having both receiving and transmitting functions are equipped with different types of pre-amplifiers. All experiments are carried out on a 7-T ultra-high field large-aperture human magnetic resonance system.

[0040] FIG. 7 shows comparison results of thermal noise fluctuation amplitudes of radio-frequency receiving coils. Data is from a 7-T ultra-high field magnetic resonance water model imaging experiment, and thermal noise is obtained by turning off radio-frequency excitation energy acquisition. The figure shows that the radio-frequency coil array according to the embodiment of the present disclosure has a minimum thermal noise fluctuation, embodied in the minimum inter-group variance, followed by the annular radio-frequency coil with a diameter of 2 cm having both receiving and transmitting functions, and finally the annular radio-frequency coil with a diameter of 5 cm having both receiving and transmitting functions. At the same time, the size of the radio-frequency receiving unit of the radio-frequency coil array according to the embodiment of the present disclosure is the smallest, followed by the annular radio-frequency coil with a diameter of 2 cm having both receiving and transmitting functions, and finally the annular radio-frequency coil with a diameter of 5 cm having both receiving and transmitting functions. According to the consensus in the field of magnetic resonance radio-frequency coils, the smaller a physical size of a radio-frequency receiving coil unit is, the smaller the contribution made by the thermal noise from the load is, that is, the smaller a quality factor ratio of the radio-frequency receiving unit under no load/load is. Therefore, a conclusion can be reached that the contribution made by the thermal noise from the load is smaller, that is, the thermal noise level of the radio-frequency receiving coil unit with a smaller quality factor ratio under no load/load is insensitive to the load displacement.

[0041] FIG. 8 shows results of time-domain thermal noise variance of various radio-frequency receiving coils and ratios of quality factors of the radio-frequency receiving units under no load/load. It can be seen that the time-domain noise variance of the radio-frequency receiving coils is correlated with the ratios of the quality factors of the radio-frequency receiving units under no load/load. Therefore, a conclusion can be reached that the contribution made by the thermal noise from the load is smaller, that is, the thermal noise level of the radio-frequency receiving coil unit with a smaller quality factor ratio under no load/load is insensitive to the load displacement. Finally, differences in types of radio-frequency pre-amplifiers used in various radio-frequency receiving coils need to be discussed, that is, the use of different radio-frequency pre-amplifiers between the radio-frequency coil according to the present embodiment and other radio-frequency coils may potentially lead to deviations in data correlation.

[0042] FIG. 9 shows comparison results of quality factors of radio-frequency receiving units when various radio-frequency receiving coil signal time-domain fluctuations are under no load/load. The radio-frequency receiving coil array according to the embodiment of the present disclosure has a maximum coverage range, followed by the annular radio-frequency coil with a diameter of 5 cm having both receiving and transmitting functions and the annular radio-frequency coil with a diameter of 3.5 cm having both receiving and transmitting functions, and finally the annular radio-frequency coil with a diameter of 2 cm having both receiving and transmitting functions. It can be seen from the results in the figure that the radio-frequency coil with a larger radio-frequency receiving coil coverage range has a smaller signal time-domain fluctuation. Although the radio-frequency receiving coil array according to the embodiment of the present disclosure is formed by radio-frequency receiving coil units of the smallest size, an overall radio-frequency receiving coil formed by a plurality of radio-frequency receiving coil unit arrays has a maximum effective coverage range, which still shows the smallest signal time-domain fluctuation. Thus, a conclusion can be reached that a signal level of the radio-frequency receiving coil with a smaller radio-frequency receiving coil coverage range is less sensitive to the load displacement.

[0043] The above are merely preferred embodiments of the present disclosure, but are not intended to limit the patent scope of the present disclosure. Any equivalent structure transformation made by using the specification and the content of the drawings of the present disclosure, or direct or indirect applications to other related technical field should be included in the patent protection scope of the present disclosure.