Portable magnetic resonance imaging system based on magnet rotation and radio frequency phase encoding

Abstract

The application relates to a portable magnetic resonance imaging system based on magnet rotation and radio frequency phase coding, and belongs to the technical field of medical imaging detection. The system comprises a Halbach magnet, a radio frequency phase coding coil, a receiving coil array and a magnet rotation and support system. The Halbach magnet, the radio frequency phase coding coil and the receiving coil array are sequentially nested. The magnet rotation and support system is used for bearing the Halbach magnet and driving the Halbach magnet to rotate; the Halbach magnet is used for generating an imaging magnetic field, the radio frequency phase coding coil is used for coding a magnetic resonance image, and the receiving coil array is used for receiving a magnetic resonance signal. The magnet rotation and support system comprises a box body, a guide rail, a motor and a pulley. The motor is used for driving the guide rail to rotate and driving the Halbach magnet 1 placed above the guide rail to rotate. The application has low equipment cost, is convenient to carry, can realize noninvasive continuous monitoring, is light in weight and reliable in performance.

Description

Technical Field

[0001] This invention belongs to the field of medical imaging detection technology and relates to a portable magnetic resonance imaging system based on magnet rotation and radio frequency phase encoding. Background Technology

[0002] Traditional high-field magnetic resonance imaging (MRI) scanners are widely used in brain diagnostic imaging related to headaches, tumors, strokes, and epilepsy. However, the use of MRI scanners is severely limited by specific site requirements, large size, and high cost. Currently, stroke detection mainly relies on imaging equipment such as CT and MRI, but these cannot meet the needs of continuous monitoring, emergency transport, and community healthcare. Traumatic brain injuries caused by natural disasters such as earthquakes, traffic accidents, and war also lack on-site diagnostic equipment.

[0003] The increasing prevalence of portable computed tomography (CT) scanners underscores the need for low-cost, portable imaging diagnostics. Compared to CT imaging, magnetic resonance imaging (MRI) offers the advantage of no ionizing radiation exposure. Low-cost portable MRI scanners can facilitate the early diagnosis of stroke, immediately determining whether there is cerebral hemorrhage after a stroke; if no hemorrhage is found, thrombolytic drugs are used to break down the blood clot. Low-cost portable MRI scanners can also be used for image monitoring of patients in intensive care units (ICUs), imaging traumatic brain injury (TBI), and conducting health checkups in remote areas.

[0004] Currently, traditional MRI equipment mainly uses C-type or H-type magnets, employing yokes to form the magnetic circuit. Therefore, their weight often exceeds one ton, significantly impacting the cost and portability of the MRI system. Furthermore, traditional MRI systems utilize gradient coil subsystems, requiring three high-precision gradient current sources, resulting in high operating costs. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a low-cost, lightweight, non-invasive, and continuously monitorable portable magnetic resonance imaging system based on magnet rotation and radio frequency phase encoding.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A portable magnetic resonance imaging system based on magnet rotation and radio frequency phase encoding includes a Halbach magnet 1, a radio frequency phase encoding coil 2, a receiving coil array 3, and a magnet rotation and support system 4. The Halbach magnet 1, the radio frequency phase encoding coil 2, and the receiving coil array 3 are nested sequentially. The magnet rotation and support system 4 supports the Halbach magnet 1 and drives its rotation; the Halbach magnet 1 generates a main magnetic field to magnetize hydrogen protons in the analyte; the radio frequency phase encoding coil 2 generates a radio frequency magnetic field to encode the magnetic resonance image; and the receiving coil array 3 receives the magnetic resonance signal.

[0008] Optionally, the Halbach magnet is composed of stacked single magnetic rings. Specifically, the Halbach magnet consists of a ring group composed of 12 stacked single magnetic rings, and also includes two single magnetic rings located at both ends of the ring group along its axial direction to eliminate edge effects due to the finite length of the ring group. The radii of the 12 single magnetic rings constituting the ring group are optimized using a genetic algorithm.

[0009] Optionally, the radio frequency phase encoding coil 2 includes a birdcage coil and a Maxwell coil, with the Maxwell coil sleeved at both ends of the birdcage coil along its axial direction.

[0010] Optionally, the receiving coil array 3 can be a rectangular saddle-shaped coil array or a circular saddle-shaped coil array. The coil array is composed of two pairs of coils placed opposite each other. Relative placement means that the two coils in a pair are placed symmetrically about the axis of the receiving coil array 3.

[0011] When the coil array consists of a pair of coils placed opposite each other, the receiving coil array 3 needs to rotate together with the Halbach magnet 1 to achieve magnetic resonance imaging; when the coil array consists of no fewer than two pairs of coils placed opposite each other, the receiving coil array 3 can achieve magnetic resonance imaging without rotating together with the Halbach magnet 1.

[0012] Optionally, the magnet rotation and support system 4 includes a housing, a guide rail disposed on the top of the housing, a motor disposed inside the housing, and pulleys disposed at the bottom of the housing. The motor drives the guide rail to rotate, thereby causing the Halbach magnet 1 placed above the guide rail to rotate. The guide rail drives the Halbach magnet 1 to rotate via gears.

[0013] The beneficial effects of this invention are as follows: This invention uses a guide rail to rotate the magnet, utilizing the gradient generated by the non-uniformity of the main magnetic field. It employs a rotating spatially encoded magnetic field method and a filtered back-projection algorithm to achieve two-dimensional imaging (Y and Z directions). Therefore, it eliminates the need for the gradient coils and gradient power amplifier systems required in conventional magnetic resonance imaging. Simultaneously, a radio frequency magnetic field is formed by a receiving coil array to achieve one-dimensional imaging in the X direction. Ultimately, three-dimensional imaging of the magnetic resonance imaging system can be realized, reducing the size of the imaging system and lowering costs. Furthermore, this invention uses a pulley box to hold the magnet, achieving portability of the magnetic resonance imaging system.

[0014] The low-cost portable MRI system provided by this invention is suitable for brain stroke detection, image monitoring of patients in intensive care units, and imaging of traumatic brain injury. It can be used for health checkups in remote areas, achieving lightweight, reliable, non-invasive continuous monitoring, and has broad application prospects.

[0015] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0016] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0017] Figure 1 This is a schematic diagram of the portable magnetic resonance imaging system of the present invention;

[0018] Figure 2 A schematic diagram of the Halbach magnet structure;

[0019] Figure 3 This is a schematic diagram of the radio frequency phase encoding coil structure;

[0020] Figure 4 This is a schematic diagram of radio frequency phase encoding;

[0021] Figure 5 The diagram shows a receiving coil array, (a) a rectangular saddle-shaped coil and (b) a circular saddle-shaped coil.

[0022] Figure 6 This is a schematic diagram of a rotating magnet.

[0023] Reference numerals: 1-Halbach magnet; 2-RF phase encoding coil; 3-Receiver coil array; 4-Magnet rotation and support system. Detailed Implementation

[0024] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0025] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0026] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0027] like Figure 1 The diagram shows a portable magnetic resonance imaging system based on magnet rotation and radio frequency phase encoding, which includes a Halbach magnet 1, a radio frequency phase encoding coil 2, a receiving coil array 3, and a magnet rotation and support system 4. The Halbach magnet 1, the radio frequency phase encoding coil 2, and the receiving coil array 3 are nested sequentially.

[0028] When the axial length to inner diameter (length-to-diameter ratio) of a conventionally designed Halbach magnet ring assembly is 4:1, the magnetic field uniformity in the target region within the magnet can reach 1000 ppm. However, such long magnets are very heavy and can induce claustrophobia, limiting their clinical application. A conventionally designed shorter magnet (axial length to inner diameter ratio of 2:1) produces a magnetic field non-uniformity of 10000 ppm, requiring complex design methods and sophisticated shimming techniques. Therefore, to eliminate the edge effect of a finite-length Halbach magnet ring assembly, this invention uses a genetic algorithm to optimize the magnetic field uniformity within the target region (ROI) of the Halbach magnet 1, and employs a high-coercivity Rubidium Iron Boron (NdFeB) magnet and magnetic ring stacking assembly method to reduce the weight and length-to-diameter ratio of the Halbach magnet. This embodiment utilizes a genetic algorithm for optimization, ultimately achieving a magnetic field uniformity within 10,000 ppm (parts per million) in a spherical target region with a diameter of 24 cm, a length-to-diameter ratio reduced to 1:1, a main magnetic field strength of 50 mT to 70 mT, and a magnet weight within 50 kg. The entire Halbach magnet consists of 14 magnetic rings, all using magnets of the same specification to reduce costs. This embodiment employs high-coercivity NdFeB magnets of grade N42, with small cubic magnetic blocks measuring 2.54 cm × 2.54 cm × 2.54 cm. Each ring contains 20 small magnetic blocks, which are rotated sequentially by 36° to form a single Halbach magnet ring, creating a uniform magnetic field at the center of the ring. The basic framework of the Halbach magnet ring assembly consists of 12 single magnetic rings. Two additional single magnetic rings are located at either end of the axial direction of the Halbach magnet ring assembly to eliminate edge effects due to the finite length of the assembly. Figure 2 As shown.

[0029] In magnetic resonance imaging (MRI), the conventional main magnetic field B0 is uniform. Imaging in the YOZ plane requires two gradient coils to generate two orthogonal gradient magnetic fields in the Y and Z directions, respectively. y (y)=G y *y, B y (z)=G z *z (assuming the main magnetic field B0 is along the Y direction). Since the main magnetic field B0 generated by the Halbach magnet used in this invention is a non-uniform magnetic field, a gradient is naturally formed. Therefore, this naturally formed gradient can be used to allow the magnet to rotate in the YOZ plane, eliminating the need for two gradient coils and a gradient power amplifier, thus reducing costs.

[0030] Magnet rotation can only achieve two-dimensional imaging. Three-dimensional magnetic resonance imaging requires three gradient coils and a power amplifier to generate a three-dimensional gradient magnetic field superimposed on a uniform main magnetic field. This invention has already achieved two-dimensional imaging based on magnet rotation; therefore, to achieve three-dimensional imaging, radio frequency (RF) phase encoding needs to be added in the X-direction. Thus, an RF phase encoding coil 2 is designed to generate an RF magnetic field B1 to encode the magnetic resonance image. The RF phase encoding coil 2 is a combination coil using a birdcage coil and a Maxwell coil, such as... Figure 3 As shown, the software is used to implement Transmit Array Spatial Encoding (TRASE), such as... Figure 4 As shown, a linear phase gradient is used in the transmitted radio frequency magnetic field B1 to encode a one-dimensional (X-direction) magnetic resonance image, eliminating the need for traditional main magnetic field B0 gradient switching, thus reducing cost and weight.

[0031] The receiving coil array 3 can be a receiving coil array composed of multiple saddle-shaped coils, and can be a rectangular saddle-shaped coil array or a circular saddle-shaped coil array. For example, two rectangular or circular saddle-shaped coils placed 180° opposite each other can be used, which need to rotate with the magnet during magnetic resonance imaging; or multiple pairs of rectangular or circular coils placed in a circle on a cylindrical surface can be used, where each pair of coils needs to be placed opposite each other, such as... Figure 5 As shown in (a) and (b), when the magnet is working, it does not need to rotate with the magnet, but the number of coils increases, and there is mutual inductive coupling between the coils. Therefore, the coils need to be decoupled. Decoupling can be achieved using a decoupling circuit, or by overlapping a portion of adjacent coils.

[0032] The magnet rotation and support system 4 includes an aluminum housing, guide rails on the top of the housing, a motor inside the housing, and casters at the bottom of the housing. The guide rails are double rails, driven by the motor to rotate. The double rails, through gears, drive the Halbach magnet 1 placed above them to rotate. Figure 6 As shown. The magnet rotation and support system 4 can achieve two-dimensional imaging (Y and Z directions) by utilizing the non-uniformity of the main magnetic field and employing the rotating spatial coding magnetic field method and the filtered back projection algorithm. Therefore, it does not require the gradient coil and gradient power amplifier system of conventional magnetic resonance imaging. At the same time, radio frequency phase coding and regularized least squares method are used along the axial direction (X direction) of the rotating magnet to finally achieve three-dimensional imaging.

[0033] The mounting and fixing housing of the Halbach magnet can be 3D printed. The magnet support housing is made of non-magnetic aluminum, and the magnet rotation bearing is made of copper. There is a magnet fixing device when the magnet is transported and moved, and a safety protection device when the magnet is working and rotating.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A portable magnetic resonance imaging system based on magnet rotation and radio frequency phase encoding, characterized in that: The system includes a Halbach magnet (1), an RF phase encoding coil (2), a receiving coil array (3), and a magnet rotation and support system (4); the Halbach magnet (1), the RF phase encoding coil (2), and the receiving coil array (3) are nested in sequence; the magnet rotation and support system (4) is used to support the Halbach magnet (1) and drive it to rotate; The Halbach magnet (1) is used to generate a main magnetic field to magnetize hydrogen protons in the test object; the radio frequency phase encoding coil (2) generates a radio frequency magnetic field to encode magnetic resonance images; the receiving coil array (3) is used to receive magnetic resonance signals. The Halbach magnet (1) is composed of stacked single magnetic rings. Specifically, the Halbach magnet (1) is composed of 12 stacked single magnetic rings, and also includes 2 single magnetic rings located at both ends of the axial direction of the ring group to eliminate the edge effect of the finite length of the ring group. The radio frequency phase encoding coil (2) includes a birdcage coil and a Maxwell coil, with the Maxwell coil sleeved at both ends of the birdcage coil along its axial direction. The receiving coil array (3) is a rectangular saddle-shaped coil array or a circular saddle-shaped coil array. The coil array is composed of two pairs of coils placed opposite each other. When the coil array is a pair of coils placed opposite each other, the receiving coil array (3) needs to rotate together with the Halbach magnet (1) to achieve magnetic resonance imaging. When the coil array consists of at least two pairs of coils placed opposite each other, the receiving coil array (3) does not rotate together with the Halbach magnet (1); The magnet rotation and support system (4) includes a housing, a guide rail on the top of the housing, a motor inside the housing, and a pulley on the bottom of the housing; the motor drives the guide rail to rotate and drives the Halbach magnet (1) placed above the guide rail to rotate.

2. The portable magnetic resonance imaging system according to claim 1, characterized in that: The guide rail drives the Halbach magnet (1) to rotate via gears.

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