Wireless coil array structure for human head magnetic resonance imaging and imaging method

Abstract

The invention discloses a wireless coil array structure for human head magnetic resonance imaging and an imaging method. The wireless coil array structure is composed of a plurality of passive deformable single coils, and each single coil unit in the wireless coil array is decoupled at a set overlapping decoupling distance. In the using state, the wired coil is used for being attached to the head of a target, when the coil is worn by a human body, namely under the condition that a load exists, the working frequency of the coil is basically not changed due to stretching of the coil, namely, the coupling effect of a coil array is basically not affected, and the adaptable change is crucial to brain imaging. The stretchable coil array designed by the invention can be attached to various head forms, is suitable for various body positions, and can be combined with a wired coil, so that the SNR (Signal to Noise Ratio) of a central area and a surface area is simultaneously improved, and more imaging details, higher resolution and better acceleration capability are obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of radio frequency coils, and more particularly to a wireless coil array structure and an imaging method for magnetic resonance imaging of a human head. Background Art

[0002] In the field of magnetic resonance imaging (MRI), high-resolution imaging is crucial for studying brain structure. MRI can provide high-resolution images of brain structure, helping researchers and doctors observe the anatomical structure of the brain, including gray matter, white matter, ventricles, and sulci, which is of great significance for studying brain development, aging, and brain diseases (such as tumors, stroke, neurodegenerative diseases, etc.). However, due to the constraints of signal-to-noise ratio (SNR), existing commercial head coils cannot meet the imaging requirements of some MRI brain function studies and are difficult to support imaging with appropriate resolution.

[0003] Generally speaking, the signal-to-noise ratio of a coil is proportional to the number of units in the coil. However, as the number of units increases, the design and manufacture of the coil becomes more difficult, and the coil becomes smaller accordingly, making the imaging depth shallower. After reaching the theoretical upper limit of SNR, it is difficult to improve the SNR in the center, and only the SNR in the surface area is improved. If you want to further improve the central SNR, you have to provide a new structure and use new materials, which is an unknown challenge. Therefore, some researchers have adopted the combined use of wireless coils and wired coils to further improve the SNR and imaging quality. The existing technical solutions for improving SNR mainly include: using printed flexible circuit boards to make wireless coils, which are used in places that need to bend during scanning, such as the knees; passive enhancement coils based on new structures, whose structure is to imitate birdcage coils; supersurface coils based on metamaterials; and wired coils made of cables to achieve flexible bending functions.

[0004] After analysis, it was found that the wireless coil imitating the birdcage coil structure is relatively large. During the use of the head coil, some patients cannot stay in it for a long time due to the narrow space on its inner wall. Although flexible circuit boards and wireless structures based on metamaterials can enhance SNR, they cannot completely fit the imaging object, which will significantly reduce the degree of SNR improvement, especially the metamaterial structure, which cannot be bent and fitted. For wired flexible coils, although they are close to the imaging object and can adapt to various body positions, the SNR improvement is limited. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a flexible wireless coil array structure for magnetic resonance imaging of the human head to improve the signal-to-noise ratio (SNR) and imaging quality. It can fit the heads of different patients and meet the scanning requirements of different body positions, such as lying on the side, which is very meaningful for patients with cervical spondylosis or head trauma.

[0006] According to a first aspect of the present invention, there is provided a wireless coil array structure for magnetic resonance imaging of a human head, comprising a plurality of deformable flexible single-loop coil units, wherein each flexible single-loop coil unit in the wireless coil array structure fixes a different position of a wired coil at a set overlapping decoupling distance, and the wired coil is used to fit the head area of ​​a target when in use.

[0007] In one embodiment, the circuit of the flexible single-turn coil unit includes a first diode, a second diode, an inductor, a first capacitor, a second capacitor and a third capacitor, wherein the first capacitor, the second capacitor and the third capacitor are connected in series, and the cathode of the first diode and the anode of the second diode are connected between the first capacitor and the third capacitor, the anode of the first diode and the cathode of the second diode are connected to one end of the inductor, and the other end of the inductor is connected between the first capacitor and the second capacitor.

[0008] In one embodiment, the circuit of the flexible single-turn coil unit further includes a fourth capacitor arranged between the conductors.

[0009] In one embodiment, the flexible single-turn coil unit is made of a flexible bendable and deformable material, and its conductor is made of a 50-ohm coaxial line.

[0010] In one embodiment, with the goal of covering the head area of ​​the target, the number of single-turn coil units included in the flexible wireless coil array structure is set within a range of 10-24.

[0011] In one embodiment, the flexible wireless coil array includes 10 single-turn coil units, and the overlapping decoupling distance between each single-turn coil unit is preset.

[0012] In one embodiment, the wired coil is configured as an elastic headgear.

[0013] In one embodiment, in use, the wireless coil array is fixed to the headband and the model.

[0014] According to a second aspect of the present invention, there is provided an imaging method, comprising:

[0015] Wearing the provided wireless coil array structure for magnetic resonance imaging of the human head on the target head;

[0016] The target head is scanned using a set magnetic resonance scanning sequence to obtain imaging results.

[0017] According to a third aspect of the present invention, there is provided a computer-readable storage medium having a computer program stored thereon, wherein the computer program implements the steps of the provided imaging method when executed by a processor.

[0018] Compared with the prior art, the advantage of the present invention is that a new type of passive stretchable coil array is designed, which can fit various head shapes and is suitable for various body positions, and can be combined with a wireless head coil of a wired coil, thereby improving the SNR of the center and surface areas at the same time, obtaining more imaging details, higher resolution and better acceleration capability.

[0019] Further features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments of the present invention with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0021] Figure 1 is a schematic diagram of a coil circuit and frequency change caused by coil deformation according to an embodiment of the present invention;

[0022] Figure 2 is a schematic diagram of a coil example according to an embodiment of the present invention;

[0023] Figure 3 is a schematic diagram of the overall structural layout of a wireless coil array according to an embodiment of the present invention;

[0024] Figure 4 is a schematic diagram of the overlapping distance between single-turn coils according to an embodiment of the present invention;

[0025] Figure 5 is a schematic diagram of imaging results according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

[0027] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0028] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

[0029] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0030] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0031] The present invention provides a wireless coil array structure for magnetic resonance imaging of the human head, which is used for imaging the human brain under the MRI magnetic field. The coil array formed by the combination of single coils of different shapes can adapt to different head shapes and does not affect the remaining space of the head coil, that is, it does not reduce the activity space of the subject. The wireless coil array can simultaneously achieve SNR improvement in the center and surface areas, and can achieve higher resolution and provide more detailed information when imaging the human brain. Due to the passive structural characteristics, the provided wireless coil array can be used in combination with a variety of wired head coils, which enhances the signal strength and is safe and reliable. The wired coil is used to fit the target's head and is suitable for examinations of various patient positions.

[0032] Figure 1 This is a schematic diagram of the circuit of the wireless coil array and the frequency change caused by coil deformation. Figure 1 In the coil unit circuit shown in (a), D1 and D2 are a pair of bidirectional diodes, which form a detuning loop of the coil with the inductor L and the capacitor C1. When the sequence pulses are transmitted at the resonant frequency of the magnetic resonance system, the detuning effect of the wireless coil is achieved to avoid coil damage. Capacitors C1, C2, and C3 are the tuning part of the coil. When the wired receiving coil is working, its wireless coil is also working, which can produce an enhancement effect on it. This is because, in the MRI system, the radio frequency coil (RF coils) has two main functions: 1) generating a B1 field to rotate the magnetization vector in the pulse sequence, and detecting the transverse magnetization vector signal of the precession in the XY plane. This means that the RF coil is not only responsible for exciting magnetic resonance signals, but also for receiving these signals; 2) Transmission and reception: RF coils can be divided into transmitting and receiving coils, receiving coils only, and transmitting coils only. The transmitting and receiving coils are used to both excite the B1 field and receive RF energy from the imaged object. The transmitting coil is used to generate the B1 field, while the receiving coil works in conjunction with the transmitting coil to detect or receive signals emitted by the spin of the imaged object. The working principle of the wireless coil designed in the present invention is to use the near-field coupling effect to transmit the signal emitted by the spin of the imaged object to the receiving coil to enhance the strength of its received signal. Near-field coupling refers to the coupling effect caused by the interaction of electromagnetic fields when the distance between two objects or structures is very close (usually less than half the wavelength). This coupling effect can enable information or energy to be transmitted between objects without direct contact. Unlike far-field propagation, near-field coupling mainly realizes information transmission and energy exchange through electromagnetic induction and electrostatic interaction.

[0033] C2 and C3 are used to achieve uniform current distribution when the coil is working. If the coil size is too large, a capacitor C4 needs to be added between the conductors. For example, the coil is divided into three equal points with the detuning module, and then C3 or C4 is added at the other two equal points of its circumference, and the design is placed according to the requirements of uniform current distribution. The distribution of each capacitor can be set as needed. The main function is to make the current distribution more uniform when the coil is working to meet the tuning frequency requirements.

[0034] In one embodiment, the stretchable coil array includes welding inner and outer conductors using a coaxial cable as a single conductor, using a 50-ohm coaxial line with a stretchable property, which basically does not cause frequency deviation when stretched. The coaxial line has two layers of conductors, and the inner conductor is also called the core wire, which is a strand of wire and serves as a signal transmission line in the communication system. The outer conductor (or skin wire) is outside the core wire and is separated from the core wire by an insulating layer. Generally speaking, the outer conductor is mainly grounded as a ground wire in the communication system. The outer conductor is a plurality of thin wires that are evenly distributed and wrap around the inner conductor.

[0035] Figure 1 (b) is a schematic diagram of the coil before stretching. Figure 1 (c) is a schematic diagram of the coil after stretching. Figure 1 (d) is the S21 curve on the vector network analyzer, which is used to evaluate whether the operating frequency of the coil is offset before and after stretching. After analysis, the frequency change caused by a large deformation stretch of the coil can be basically ignored. For MRI systems, the difference in operating frequency between 3T and 5T systems is the Larmor frequency of atoms. In order to receive the signal emitted after the atoms relax and form an image, the resonant frequency of the coil must be consistent with its Larmor frequency. Figure 1 In (d), the horizontal axis is the Larmor frequency of the H atom at a frequency of 5 T, which is also the operating frequency of the coil, and the unit is Hertz (Hz). Figure 1 (d) After the coil is stretched, there will be a certain frequency offset, that is, the change in the coil's operating frequency. If the operating frequency offset is too large, the received signal will be very small, and imaging will not be possible or the imaging quality will be very poor. The operating frequency of the traditional copper coil is very sensitive to the deformation and bending of the coil, so they are all attached to the outer casing. The frequency offset of the wireless coil designed in the present invention is relatively small before and after stretching. In addition, generally speaking, there will not be such a large deformation when the patient wears it, and the impact is even smaller when tested under a large load (such as a human brain model, a hydrocephalus model), which meets the need to adapt to human heads of different sizes. The coil array designed in the present invention can be tightly mounted on a stretchable head cap and adjusted on a phantom in the shape of a human head, such as Figure 2 shown.

[0036] Figure 3It is a schematic diagram of the overall structural layout of the wireless coil array. The coil elements adopt an overlapping decoupling method. According to the corresponding different areas of the head, each single-loop coil can be stretched into different shapes. For example, it contains 10 single-loop coil units, of which 1 to 8 are roughly square and measure 8cm×8cm, and 9 and 10 are ovals with a size of 10cm×13cm.

[0037] Figure 4 is a schematic diagram of the overlap distance between single-turn coils, where Figure 4 (a) Schematic diagram of the overlapping decoupling distance of single loops 1 and 5 set in the top area of ​​the head, Figure 4 (b) is a schematic diagram of the overlapping decoupling distance of the single loops 4 and 8 set in the back of the head area. Figure 4 (c) is a schematic diagram of the dimensions of coils 9 and 10.

[0038] By setting a suitable decoupling distance, the signal transmission loss can be reduced while ensuring the imaging quality. The basic principle of decoupling is to adjust the overlapping area between adjacent coils so that the magnetic flux generated by one coil inside the coil just offsets the magnetic flux in the overlapping area, thereby achieving decoupling. The overlapping area adjustment can change the overlapping area between adjacent surface coils by adjusting the position between them to achieve decoupling. In addition, the distance between the metal conductors of the secondary adjacent coils along the direction perpendicular to the bonding surface can also be adjusted to change their overlapping area to achieve decoupling between secondary adjacent coils. For the adjustment of the overlapping distance, in some embodiments, the overlapping area can be changed by adjusting the distance between the two overlapping metal conductors along the direction perpendicular to the bonding surface to achieve decoupling. This method does not change the position of the surface coil, thereby avoiding secondary decoupling between adjacent coils.

[0039] The wireless coil used in the present invention has negligible frequency changes caused by slight deformation of the coil when worn by the patient due to the selection of the conductor. The use of a combined elastic headgear makes it more suitable for patients and various body positions compared to other head coils or head and neck combined coils, which is of great significance for clinical applications. In addition, the coil has very few components as a whole, and the hollow in the center can also be cut out to provide a better experience for patients or to be used in conjunction with an ultrasound probe for multimodal imaging. During use, the coil needs to achieve an ideal effect, which requires a very good coupling effect, but the decoupling distance of the present invention has been set, and it shows a good decoupling effect both on the hydrocephalus model and when worn by volunteers.

[0040] In summary, the present invention designs and manufactures a wireless coil array, which is flexible and bendable. As the patient wears the elastic headgear, the coil always fits the patient's scalp and does not cause a significant shift in the target frequency of the coil. For example, the conductor of the coil is made of a 50-ohm coaxial cable, and the coil itself has elastic characteristics that are easy to bend and recover, and the frequency of the coil prepared by it is not affected by deformation. The improvement of the SNR by the coil is mainly related to the size of the coil. In order to make the improvement effect cover the entire brain, the central SNR of the human brain can also be significantly improved, so the coil array is mainly composed of 8cm×8cm coils. For the entire head, for example, in order to observe the hypothalamus and the area below the brainstem, it is necessary to increase the number of channels to 10-24 (i.e., the number of single-turn coils) channels. This design can achieve simultaneous improvement of the central SNR and the surface area SNR.

[0041] To further verify the effect of the present invention, an experimental simulation was conducted. In a 5T MRI system, the wireless coil array of the present invention was used in combination with a 48-channel head coil. The coil array and the test method are as follows: Figure 5 As shown, Figure 5 (a) Corresponding layout of wired head coil combined with wireless coil array, Figure 5 (b) Corresponding to the wired head coil, Figure 5 (c) Yes Figure 5 (a) and Figure 5 (b) The corresponding SNR in the scene. The SNR was calculated by 2D GRE sequence, and the results showed that the surface SNR increased by 1.3 times and the center increased by 23% in the hydrocephalus model imaging.

[0042] It should be understood that since the present invention is a signal-enhancing coil, the use of receiving coils is not limited, and conventional coils can be used. The present invention is not limited to the size, dimensions, and type of wireless coils. If the deformation of single-channel coils of other designs during use by patients does not cause a frequency deviation of more than 1Mhz, they all belong to the flexible coil design proposed by the present invention.

[0043] In summary, compared with the prior art, the present invention has the following advantages:

[0044] 1) By using a wireless coil array, the central and surface area SNR of human brain imaging is significantly improved, thereby enhancing the clarity of imaging.

[0045] 2) The coil array is designed to be stretchable and can adapt to heads of different shapes and sizes, including adapting to hydrocephalus models and human brain models.

[0046] 3) The enhanced SNR enables the present invention to provide high-resolution imaging results, such as 0.3x0.2x3 mm and 0.9x0.9x3 mm resolution, which is crucial for observing subtle brain structures.

[0047] 4) The coil array is compatible with a variety of MRI sequences, including 2D GRE, T2-FSE, epi_dwi_msh, and 3D TOF sequences, and can be used for a variety of imaging purposes.

[0048] 5) Because the coil array is stretchable, it can better fit the patient's head, improving patient comfort.

[0049] 6) The coil array can be directly adhered or otherwise fixed to the headband and model to facilitate adjustment and reuse, ensuring the repeatability of the experiment.

[0050] 7) The present invention not only improves the imaging quality, but also has clinical feasibility and can be used in actual medical environments.

[0051] 8) It has been verified that the coil array designed by the present invention is applicable to multimodal imaging, which provides new possibilities for future research and clinical applications. For example, the overall flexibility of the coil can be applied to multimodal imaging of CT and MRI.

[0052] The present invention may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present invention.

[0053] Computer readable storage medium can be a tangible device that can hold and store instructions used by an instruction execution device. Computer readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination thereof. More specific examples (non-exhaustive list) of computer readable storage medium include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, for example, a punch card or a convex structure in a groove on which instructions are stored, and any suitable combination thereof. The computer readable storage medium used here is not interpreted as a transient signal itself, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagated by a waveguide or other transmission medium (for example, a light pulse by an optical fiber cable), or an electrical signal transmitted by a wire.

[0054] Embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the marketplace, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein. The scope of the present invention is defined by the appended claims.

Claims

1. A wireless coil array structure for magnetic resonance imaging of the human head, comprising a plurality of deformable flexible single-loop coil units, wherein each single-loop coil unit in the wireless coil array structure fixes a different position of a wired coil at a set overlapping decoupling distance, and the wired coil is used to fit the head area of ​​the target when in use.

2. The wireless coil array structure for magnetic resonance imaging of the human head according to claim 1, characterized in that: The circuit of the flexible single-turn coil unit includes a first diode, a second diode, an inductor, a first capacitor, a second capacitor and a third capacitor, wherein the first capacitor, the second capacitor and the third capacitor are connected in series, and the cathode of the first diode and the anode of the second diode are connected between the first capacitor and the third capacitor, the anode of the first diode and the cathode of the second diode are connected to one end of the inductor, and the other end of the inductor is connected between the first capacitor and the second capacitor.

3. The wireless coil array structure for magnetic resonance imaging of the human head according to claim 1, characterized in that: The circuit of the flexible single-turn coil unit further includes a fourth capacitor arranged between the conductors.

4. The wireless coil array structure for magnetic resonance imaging of the human head according to claim 1, characterized in that: The flexible single-turn coil unit is made of a flexible bendable and deformable material, and its conductor is made of a 50-ohm coaxial line.

5. The wireless coil array structure for magnetic resonance imaging of the human head according to claim 1, characterized in that: With the goal of covering the head area of ​​the target, the number of flexible single-loop coil units included in the wireless coil array structure is set within the range of 10-24.

6. The wireless coil array structure for magnetic resonance imaging of the human head according to claim 5, characterized in that: The wireless coil array includes 10 flexible single-loop coil units, and the overlapping decoupling distance between each flexible single-loop coil unit is preset.

7. The wireless coil array structure for magnetic resonance imaging of the human head according to claim 1, characterized in that: The wired coil is configured as an elastic headgear.

8. The wireless coil array structure for magnetic resonance imaging of the human head according to claim 1, characterized in that: In use, the wireless coil array is fixed to the headband and the model.

9. An imaging method comprising: Wearing the wireless coil array structure for magnetic resonance imaging of the human head according to any one of claims 1 to 8 on the target head; The target head is scanned using a set magnetic resonance scanning sequence to obtain imaging results.

10. A computer-readable storage medium having a computer program stored thereon, wherein: When the computer program is executed by a processor, the steps of the imaging method according to claim 9 are implemented.

Images