Traveling wave antenna unit, array and method of improving high-field magnetic resonance radio frequency field homogeneity

Abstract

The application discloses a traveling wave antenna unit, an array and a method for improving high-field magnetic resonance radio frequency field uniformity, relates to the field of magnetic resonance imaging, and aims to improve high-field magnetic resonance radio frequency field uniformity. The application increases the component of the wave number of the traveling wave antenna unit in the traveling wave transmission line direction in the traveling wave antenna array through physical or chemical means to relieve the radial standing wave effect. The traveling wave antenna unit comprises a layer-by-layer designed metal microstrip, a first bearing substrate, a filling layer substrate, a slotted metal floor, a second bearing substrate and a spacing layer substrate. A feeding port is connected between the first end of the metal microstrip and the slotted metal floor, and a load is connected between the second end of the metal microstrip and the slotted metal floor. The filling layer substrate is a fillable structure. The component in the traveling wave transmission line direction is increased by increasing the relative dielectric constant of the filling medium or changing the slotted structure. The application is simple in design, convenient in operation and does not need additional hardware.

Description

Technical Field

[0001] This invention relates to the field of magnetic resonance imaging, and in particular to a traveling wave antenna element, array, and method for improving the uniformity of high-field magnetic resonance radio frequency fields. Background Technology

[0002] Magnetic resonance imaging (MRI) is one of the most promising medical imaging technologies. Higher field strength MRI equipment can better improve the signal-to-noise ratio of imaging, thereby obtaining clearer image quality.

[0003] Magnetic resonance imaging (MRI) technology faces several challenges under high field strength. Because the wavelength of the RF field in high-field MRI is relatively short, traditional birdcage antenna designs with orthogonal excitation methods struggle to meet the requirement of uniform magnetic field transmission within the human body area. Furthermore, in high-field MRI systems, the operating state of the RF transmitting coil is inevitably affected by the metal cavity and spatial loading objects. This effect is particularly pronounced for ordinary resonant coils (birdcage coils, dipoles, TEM coils, etc.) with narrow operating bandwidths.

[0004] Currently, there are RF shimming techniques for multi-channel parallel transmission arrays to improve RF field uniformity (such as the method proposed in the paper "Evolution of UHF Body Imaging in the Human Torso at 7T" (Erturk MA et al.)). These include static shimming techniques and the later-proposed dynamic shimming techniques. These techniques primarily calibrate and adjust the relative phase and amplitude of each independent transmission unit to maximize RF field uniformity. However, this method is closely related to the subject, requiring recalibration for different subjects and necessitating more hardware, leading to increased operational difficulty and cost. Furthermore, this RF field uniformity optimization technique is mainly based on the array perspective, rather than antenna design. Other RF schemes based on resonant design to improve RF field uniformity also exist, but due to the influence of standing wave effects, the improvement in field uniformity is relatively limited, generally only achieving a uniform field distribution within a small field of view. Summary of the Invention

[0005] The purpose of this invention is to address all or part of the problems mentioned above by providing a traveling wave antenna element, array, and method for improving the uniformity of the high-field magnetic resonance radio frequency field. This method improves the uniformity of the high-field magnetic resonance radio frequency field from the perspective of traveling wave antenna design, thereby improving the imaging quality of high-field magnetic resonance.

[0006] The technical solution adopted in this invention is as follows:

[0007] A traveling wave antenna element includes a layered metal microstrip, a first carrier substrate, a filler substrate, a slotted metal ground plane, a second carrier substrate, and a spacer substrate; a feed port is connected between the first end of the metal microstrip and the slotted metal ground plane, and a load is connected between the second end of the metal microstrip and the slotted metal ground plane; at least the filler substrate is a fillable structure.

[0008] Furthermore, the metal microstrip is elongated, with its length direction aligned with the length direction of the traveling wave antenna element.

[0009] Furthermore, the slotted metal floor has multiple slots periodically cut along the length of the traveling wave antenna unit.

[0010] Furthermore, the slot is I-shaped.

[0011] Furthermore, the substrate material used to fill the filling layer substrate is distilled water.

[0012] The present invention also provides a traveling wave antenna array comprising at least one pair of the aforementioned traveling wave antenna elements, the pair of traveling wave antenna elements surrounding the imaging object in a paired manner, the feeding phases of the pair of traveling wave antenna elements being 180 degrees out of phase.

[0013] The present invention also provides a method for improving the uniformity of high-field magnetic resonance radio frequency field by modifying the above-mentioned traveling wave antenna array, the method comprising: increasing the wave number component of the traveling wave antenna element in the direction of the traveling wave transmission line.

[0014] Furthermore, the wavenumber component of the traveling wave antenna element in the direction of the traveling wave transmission line can be increased by changing the structural parameters of the traveling wave antenna element.

[0015] Furthermore, the structural parameters of the traveling wave antenna element can be changed by increasing the relative permittivity of the first carrier substrate and / or the filling layer substrate material.

[0016] Furthermore, the structural parameters of the traveling wave antenna unit can be changed by altering the slotted structure features of the slotted metal floor.

[0017] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0018] This invention starts from the perspective of traveling wave antenna structure design. By designing a traveling wave antenna unit with a specific structure, it provides a basis for conveniently modifying the structure of the traveling wave antenna unit. This allows for a quick increase in the wave number of the traveling wave antenna unit in the direction of the traveling wave transmission line without the need for additional hardware or operations. Furthermore, it does not require additional calibration for different imaging objects, making it highly versatile. Attached Figure Description

[0019] The present invention will be described by way of example and with reference to the accompanying drawings, wherein:

[0020] Figure 1 This is a schematic diagram of the wave number and its components of the traveling wave antenna array in the medium before modification in the embodiments of this application.

[0021] Figure 2 It is to utilize Figure 1 A schematic diagram of the standing wave effect in high-field magnetic resonance imaging using a traveling wave antenna array, as described in the embodiment.

[0022] Figure 3 This is a distribution diagram of the traveling wave antenna array provided in the embodiments of this application.

[0023] Figure 4 This is a hierarchical structure diagram of the traveling wave antenna unit provided in the embodiments of this application.

[0024] Figure 5 This is a cross-sectional view of the traveling wave antenna element provided in the embodiments of this application.

[0025] Figure 6 This is a structural diagram of a magnetic resonance imaging system using a traveling wave antenna array according to an embodiment of this application.

[0026] Figure 7 This is a schematic diagram of the wave number and its components of the modified traveling wave antenna array in the medium in the embodiments of this application.

[0027] In the figure, 1 is the traveling wave antenna element, 2 is the imaging object, 3 is the traveling wave antenna array, 4 is the high field magnetic resonance spectrometer, 11 is the metal microstrip, 12 is the first carrier substrate, 13 is the filler layer substrate, 14 is the slotted metal ground plane, 15 is the second carrier substrate, 16 is the spacer layer substrate, 17 is the feed port, and 18 is the load. Detailed Implementation

[0028] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0029] Any feature disclosed in this specification (including any appended claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0030] To address the issue of poor radio frequency field uniformity in high-field magnetic resonance imaging, and the fact that existing technologies for improving radio frequency field uniformity are either difficult and costly to implement or have poor improvement effects, this application proposes a method for improving radio frequency field uniformity from the perspective of traveling wave antenna array 3. The aim is to provide a traveling wave antenna element 1 with a specific structure, and improve the radio frequency field uniformity quickly and efficiently by simply modifying the structural design of the traveling wave antenna element 1.

[0031] In the field of magnetic resonance imaging, B1 + Radio frequency field (abbreviated as B1) + The magnetic field is a crucial parameter for measuring image quality, and it is related to the two transverse components H of the magnetic field. x and H y Relevant, defined as:

[0032]

[0033] Radio frequency field uniformity requirement B1 + The amplitude of the field is as uniform as possible in the spatial domain because B1 + The field amplitude determines the flip angle of the spin proton excitation in magnetic resonance imaging (MRI), which in turn determines the image contrast. Non-uniform radio frequency (RF) emission fields can introduce RF artifacts into MRI images, interfering with doctors' diagnoses, and therefore need to be avoided as much as possible.

[0034] Traveling wave antennas exhibit non-resonant radiation characteristics. When placed close to a high-dielectric material (such as the human body), they can easily radiate energy into the dielectric space as fast waves, exhibiting a large operating bandwidth. Traveling wave antennas can be analyzed using transmission line theory. When a traveling wave antenna radiates towards a dielectric space (such as the human body), the wave number k in the dielectric space satisfies:

[0035]

[0036] Where ω is the angular velocity of the electromagnetic wave, μ0 and ε0 are the permeability and permittivity in vacuum, and ε r Let β be the relative permittivity of the medium. Ideally, the wave number k is equal to the phase constant β. The wave number k can be decomposed into two orthogonal components k in the radiation direction. z and k r k z The wavenumber component of a traveling wave antenna element along the traveling wave transmission line, k r The radial component of the wavenumber of a traveling-wave antenna element, such as... Figure 1 As shown.

[0037] For a traveling wave transmission line, we have:

[0038] k z =β z -jα z

[0039] Where β z Let α be the phase constant in the traveling wave transmission line. z This is the attenuation factor caused by energy radiation. Since the traveling wave antenna exhibits beam pointing in spatial energy radiation, it generates a radiation angle θ, the value of which can be approximated by the following formula:

[0040]

[0041] Along the Z-direction of the traveling wave transmission line, the guided wave is a traveling wave, with no standing wave problem and good uniformity. However, in the radial plane perpendicular to the Z-direction, due to the opposing radiation of the traveling wave antenna array 3, the two opposing traveling wave components will generate significant standing waves within the imaging object 2, the mathematical expression of which is:

[0042] f SW (r,t)=sin(ω·t)·cos(|k r |·r)

[0043] Where r is a spatial coordinate quantity, and k r =2π / λ r , λ r It is the equivalent radial wavelength of electromagnetic waves.

[0044] This means that the higher the radio frequency operating frequency, the larger the imaging object 2 appears in terms of electrical size compared to the electromagnetic wavelength, resulting in a shorter standing wave wavelength, more pronounced standing wave amplitude fluctuations, and a significant standing wave effect. This leads to non-uniformity of the radio frequency field in high-field magnetic resonance imaging, such as... Figure 2 As shown.

[0045] For traveling wave transmission lines, their electromagnetic propagation characteristics are closely related to their dielectric properties. Their phase constant β... z With relative permittivity ε eff The relationship is as follows:

[0046]

[0047] Where k0 is the wave number of the electromagnetic wave in a vacuum. This means that as long as k0 is increased... This allows for an increase in the wavenumber component k of traveling wave antenna element 1 along the traveling wave transmission line direction. z Thus utilizing k z k r The relative relationship with k is used to reduce k. r This increases the equivalent radial wavelength λ of the electromagnetic wave. r As a result, the radial standing wave effect is mitigated, and the uniformity of the radio frequency field is effectively improved.

[0048] Based on this principle, the embodiments of this application improve the structural design of the traveling wave antenna array 3 to increase the wavenumber component k of the traveling wave antenna element 1 in the direction of the traveling wave transmission line. z When applied to magnetic resonance imaging, the traveling wave antenna array 3 surrounds the imaging object 2, thereby improving the uniformity of the radio frequency field and enhancing the quality of high-field magnetic resonance imaging.

[0049] Traveling wave antenna array 3 includes at least two traveling wave antenna elements 1, such as Figure 3 The illustration shows an embodiment comprising two pairs of traveling wave antenna elements 1. Therefore, this application also proposes a traveling wave antenna element 1 with a specific structure to facilitate structural design adjustments, thereby achieving rapid improvement in radio frequency field uniformity.

[0050] like Figure 4 As shown, in some embodiments, the traveling-wave antenna element 1 includes a layered design of a metal microstrip 11, a first carrier substrate 12, a filler substrate 13, a slotted metal ground plane 14, a second carrier substrate 15, and a spacer substrate 16. A feed port 17 is connected between the first end of the metal microstrip 11 and the slotted metal ground plane, through which the traveling-wave antenna element 1 is fed. A load 18 is connected between the second end of the metal microstrip 11 and the slotted metal ground plane to absorb residual power and suppress standing waves. The so-called first end and second end refer to the two ends along the length of the traveling-wave antenna element 1.

[0051] To facilitate increasing the relative permittivity of the traveling wave antenna element 1, the filling layer substrate 13 is designed as a fillable structure. The relative permittivity of the traveling wave antenna element 1 can be changed by altering the relative permittivity of the filling substrate material.

[0052] In some feasible implementations, such as Figure 5 As shown, the metal microstrip 11 is elongated, with its length aligned with the length of the traveling wave antenna element 1. Multiple slots are periodically formed on the slotted metal ground plane 14 along the length of the traveling wave antenna element 1 to better facilitate space radiation in conjunction with the metal microstrip 11. Figure 5 As shown, as a possible implementation, the slots on the slotted metal floor 14 can be I-shaped slots, the number of which is adapted to the length of the traveling wave antenna element 1.

[0053] In some feasible implementations, the spacer substrate 16 is also designed as a fillable structure, which can also change the relative permittivity of the filler substrate material.

[0054] In a preferred embodiment, the traveling wave antenna element 1 is designed with a length of 350mm to 400mm, a width of 50mm to 100mm, and a height of 10mm to 40mm. Both the first carrier substrate 12 and the second carrier substrate 15 are made of Rogers RO4003C (relative permittivity 3.55) with a thickness of 0.5mm to 1.5mm, serving to support the printed metal microstrip 11 and the slotted metal ground plane 14. The filler material of the filling layer substrate 13 is distilled water (relative permittivity 78.4) as a high-dielectric-constant material, aiming to ensure a large phase constant for the electromagnetic wave in the traveling wave transmission line direction. The spacer layer substrate 16 uses the same distilled water as the filler material as the filling layer substrate 13, maintaining a certain thickness, to prevent direct contact between the traveling wave antenna element 1 and the imaging object 2, ensuring safety. Two traveling wave antenna elements 1 are arranged in an array facing each other and placed around the imaging object 2 for imaging. The feed phases are 0° and 180° respectively, or they can be designed to have other feed phases that are 180 degrees apart.

[0055] Therefore, it can be seen that the traveling wave antenna unit 1 proposed in the embodiments of this application can easily increase the relative permittivity of the filling layer substrate 13 material, thereby reducing the radial component, thereby alleviating the radial standing wave effect and improving the uniformity of the radio frequency field.

[0056] Based on the traveling wave antenna element 1 proposed in the above embodiments, this application also proposes a traveling wave antenna array 3, which includes at least two of the above-mentioned traveling wave antenna elements 1, and each traveling wave antenna element 1 surrounds the imaging object 2.

[0057] In some embodiments, the traveling-wave antenna array 3 includes pairs of traveling-wave antenna elements 1, each pair of traveling-wave antenna elements 1 surrounding the imaging object 2. For example... Figure 3 The diagram shows the structure of the traveling wave antenna array 3, which includes two pairs of traveling wave antenna elements 1.

[0058] This application also proposes a method to improve the uniformity of high-field magnetic resonance radio frequency field by modifying the traveling wave antenna array 3.

[0059] like Figure 6 As shown, placing the traveling wave antenna array 3 in the high-field magnetic resonance imaging system 4 can improve the uniformity of the radio frequency field in high-field magnetic resonance imaging, thereby improving the imaging quality.

[0060] In some embodiments, the wavenumber component k in the traveling wave transmission line direction of the traveling wave antenna element 1 is increased by physical or chemical means. z This is to improve the uniformity of the radio frequency field in high-field magnetic resonance imaging.

[0061] As a feasible implementation method, the physical or chemical means employed all involve increasing the wavenumber component k of the traveling wave antenna element 1 in the traveling wave transmission line direction by changing the structural parameters of the traveling wave antenna element 1. z This improves the uniformity of the radio frequency field in high-field magnetic resonance imaging.

[0062] In some possible implementations, the structural parameters of the traveling wave antenna element 1 are changed by increasing the relative permittivity of the material of at least one of the first carrier substrate 12 and the filling layer substrate 13.

[0063] In this type of implementation, the traveling-wave antenna array 3 includes at least one pair of traveling-wave antenna elements 1. For example... Figure 3 As shown, the traveling wave antenna array 3 is placed around the imaging object 2, and kept close to (or at a certain distance from) the imaging object 2. A suitable feed phase and amplitude are set for the traveling wave antenna array 3 (same as in the prior art). For example, during the design process, the wavenumber component k in the traveling wave antenna element 1 in the traveling wave transmission line direction is increased by increasing the relative permittivity of the material filling the filling layer substrate 13 in the traveling wave antenna element 1 (or by replacing the first carrier substrate 12 with a higher relative permittivity). z This reduces the standing wave effect of the opposing electromagnetic energy radiated in the traveling wave antenna array 3, thereby improving the uniformity of the radio frequency field in high-field magnetic resonance imaging.

[0064] In some other possible implementations, the structural parameters of the traveling wave antenna element 1 can be changed by altering the slotted structural features of the slotted metal floor 14.

[0065] In this type of implementation, the traveling-wave antenna array 3 includes at least one pair of traveling-wave antenna elements 1. For example... Figure 3 As shown, the traveling wave antenna array 3 is placed around the imaging object 2 and kept close to it. A suitable feed phase and amplitude are set for the traveling wave antenna array 3. During the design process, the wavenumber component k of the traveling wave antenna element 1 in the traveling wave transmission line direction is increased by changing the structural features of the slotted metal ground plane 14, such as its shape and size (e.g., extending the length of the slotted structure, or while extending the length of the slotted structure, reducing the width of the metal microstrip 11). z This reduces the standing wave effect of the opposing electromagnetic energy radiated in the traveling wave antenna array 3, thereby improving the uniformity of the radio frequency field in high-field magnetic resonance imaging.

[0066] Furthermore, in other possible implementations, the component k of the wavenumber of the traveling wave antenna element 1 in the traveling wave transmission line direction can also be changed. z Other structural parameters that have an impact can be used to increase the wavenumber component k of traveling wave antenna element 1 in the traveling wave transmission line direction. z .

[0067] It should be noted that the various implementation methods described above for changing the structural parameters of the traveling wave antenna element 1 can be implemented individually or together, except that they cannot coexist in principle.

[0068] like Figure 7 The figure shows the component k of the wavenumber of the increased traveling wave antenna element 1 in the traveling wave transmission line direction. z A schematic diagram showing the wavenumber and components of the traveling wave antenna array 3 in the medium when it is placed in the magnetic resonance imager 4. Figure 7 It can be seen that, compared to Figure 1 For the same imaging object 2, the wavenumber component k in the traveling wave transmission line direction of the traveling wave antenna element 1 is increased. z Then, the radial component k r As the radiation angle θ increases, the standing wave wavelength becomes longer, the amplitude fluctuations become less pronounced, and the radial standing wave effect is alleviated, thus effectively improving the uniformity of the radio frequency field.

[0069] This application innovatively improves the uniformity of the high-field magnetic resonance radio frequency field by using the correlation between the electromagnetic characteristics of the traveling wave antenna element 1 and the equivalent radio frequency wavelength of the imaging region. This is an innovative work that uses the structure of the traveling wave antenna element 1 to achieve this effect. It does not require additional hardware or additional operations for different imaging objects 2. Existing standing wave resonant radio frequency coils do not have this effect.

[0070] This invention is not limited to the specific embodiments described above. The invention extends to any new feature or combination disclosed in this specification, as well as any new method or process step or combination disclosed herein.

Claims

1. A traveling-wave antenna element, characterized in that, It includes a layered metal microstrip, a first carrier substrate, a filler substrate, a slotted metal ground plane, a second carrier substrate, and a spacer substrate; a power supply port is connected between the first end of the metal microstrip and the first end of the slotted metal ground plane, and a load is connected between the second end of the metal microstrip and the second end of the slotted metal ground plane; at least the filler substrate is a fillable structure.

2. The traveling wave antenna element as described in claim 1, characterized in that, The metal microstrip is elongated, with its length direction aligned with that of the traveling wave antenna element.

3. The traveling wave antenna element as described in claim 1, characterized in that, The slotted metal floor has multiple slots periodically cut along the length of the traveling wave antenna element.

4. The traveling wave antenna element as described in claim 3, characterized in that, The slot is I-shaped.

5. The traveling wave antenna element as described in claim 1, characterized in that, The substrate material used to fill the filling layer substrate is distilled water.

6. A traveling-wave antenna array, characterized in that, It includes at least one pair of traveling wave antenna elements as described in any one of claims 1-5, the pair of traveling wave antenna elements surrounding the imaging object in a paired manner, the feed phases of the pair of traveling wave antenna elements being 180 degrees out of phase.

7. A method for improving the uniformity of high-field magnetic resonance radio frequency fields by modifying the traveling-wave antenna array as described in claim 6, characterized in that, include: Increase the wavenumber component of the traveling wave antenna element in the direction of the traveling wave transmission line.

8. The method for improving the uniformity of high-field magnetic resonance radio frequency fields as described in claim 7, characterized in that, The wavenumber component of the traveling wave antenna element in the direction of the traveling wave transmission line can be increased by changing the structural parameters of the traveling wave antenna element.

9. The method for improving the uniformity of high-field magnetic resonance radio frequency fields as described in claim 8, characterized in that, The structural parameters of the traveling wave antenna element are changed by increasing the relative permittivity of the first carrier substrate and / or the filler substrate material.

10. The method for improving the uniformity of high-field magnetic resonance radio frequency fields as described in claim 8, characterized in that, The structural parameters of the traveling wave antenna unit can be changed by altering the slotted structure features of the slotted metal floor.

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