CN117518049A - Low inductance planar multilayer coil - Google Patents

Abstract

The invention discloses a novel coil structure with low inductance, which is used for magnetic resonance imaging of joint parts and is formed by densely arranging concentric annularly arranged coils, wherein an outer coil is a reverse winding coil of an inner coil between two adjacent coils, and the current directions between the two adjacent coils are opposite, wherein the coil size is determined according to the size of the part to be inspected, the size of a single coil is determined according to the number of channels, and the number of turns is determined according to the imaging depth requirement. The invention can change the inductance of the coil and adjust the mutual coupling between a plurality of coil channels by adjusting the number of turns and the inner diameter and the outer diameter of the reverse coil without using a decoupling circuit. Finally, the improvement of the signal-to-noise ratio and the uniformity is realized.

Description

Low inductance planar multilayer coil

Technical Field

The invention belongs to the technical field of magnetic resonance imaging, relates to a radio frequency coil structure capable of weakening electric field intensity while improving joint imaging signal-to-noise ratio, and particularly relates to a planar multilayer coil with low inductance.

Background

Magnetic Resonance Imaging (MRI) is a non-invasive painless green diagnostic technique that is widely used in modern hospitals. A magnetic resonance imaging system generally comprises: a main magnet generating a static uniform magnetic field; the radio frequency system comprises a radio frequency power amplifier, a transmitting coil and a receiving coil; a gradient system; and a computer system.

In the nuclear magnetic resonance imaging technology, a receiving coil is used for collecting radio frequency signals stimulated by a sample, and the collected radio frequency signals are amplified and then used for reconstructing an image of the sample. The electric structure of the receiving coil mainly comprises a coil body made of conductive materials, and circuit components such as an inductor, a capacitor and the like which are connected in the coil body. In the working state, the receiving coil surrounds the inspected part of the patient, the magnetic resonance signals output by the receiving coil carry the inspected human tissue information, and the obtained images are used for diagnosis by doctors.

Up to now, the prior art method of using overlap or decoupling capacitance to achieve the maximum number of channels in a certain area is limited by the nature of the traditional conductive material, and further increasing the number of channels becomes very difficult, since there is an optimal value for the overlap area theoretically. That is, too large and too small an overlap area may cause the magnetic flux between the channels to be unable to cancel, and the isolation becomes poor in terms of S parameter. Thus failing to densely lay out the multiple channels, resulting in too low a receive coil field uniformity and SNR.

The decoupling circuit not only increases the complexity of the system, is time-consuming and labor-consuming to debug, but also indirectly increases the manufacturing cost. Some coils based on special conductive materials can realize low inductance. However, this material is relatively expensive to manufacture and is relatively difficult to obtain.

In order to improve SNR and uniformity and solve the cost and efficiency problem caused by multi-channel decoupling, the invention provides a novel coil structure based on a traditional conductive material.

Disclosure of Invention

The invention aims to provide a planar multi-layer coil with low inductance, which realizes low inductance by a method of reversing adjacent loop currents, thereby reducing mutual coupling among multi-channel coils. The field distribution with higher uniformity and the maximization of the channel number are realized.

Therefore, the invention provides a novel coil structure with low inductance, which is formed by densely arranging a plurality of coils which are concentrically and annularly arranged, wherein the outer coils between two adjacent coils are reverse winding coils of the inner coils, the current directions between the two adjacent coils are opposite, the coil size is determined according to the size of a part to be inspected, the size of a single coil is determined according to the number of channels, and the number of turns is determined according to the imaging depth requirement.

The current of each coil in the planar multilayer coil is opposite to the current of the adjacent coil, so that the inductance of the whole coil can be effectively reduced. The coil has the advantages that the coil turns and the inner diameter and the outer diameter can be adjusted on the premise that a decoupling circuit is not used, so that the inductance of the coil can be changed, and the size of mutual coupling among a plurality of coil channels can be adjusted. Finally, the improvement of the signal-to-noise ratio and the uniformity is realized.

In addition to the objects, features and advantages described above, the present invention has other objects, features and advantages. The present invention will be described in further detail with reference to the drawings.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:

FIG. 1 is a schematic structural view of a planar multilayer coil of low inductance of the present invention;

fig. 2 is a flow chart of determining the dimensional parameters of the planar multilayer coil of low inductance of the present invention.

Detailed Description

The invention will be described in detail below with reference to the drawings in connection with embodiments.

As shown in fig. 1, the planar multi-layer coil of the present invention is composed of a multi-turn circular coil with variable turns, height and inner and outer diameters, which is placed over the wrist. The current of the first circular coil 1 of the coil is clockwise, and the current of the second circular coil 2 is anticlockwise. The current of the third round coil 3 is clockwise, and the current of the fourth round coil 4 is anticlockwise. And so on, namely, the current direction of each two adjacent circular coils of the planar multilayer coil always keeps opposite directions. So that the coupling to adjacent channels is very small. In another aspect, the inductance of the coil is reduced.

As shown in fig. 2, the inner and outer radii of the coil and the number of turns of the coil are designed according to the size of the portion to be inspected. The number of channels is determined according to the magnetic resonance system; the impedance matching circuit adjusts the resonant frequency of the coil to the operating frequency of the MRI system; the whole coil can be manufactured through flexible circuit boards, such as FPC processing, and is integrally formed. Therefore, the surface of the coil is provided with the minimum bulge, and the comfort is ensured.

Existing magnetic resonance receive coils typically employ a phased array design, where each array element is a loop coil. The coil loops are typically made of copper foil or wire and the array of loop coils may be mounted on a carrier made using a rigid or flexible printed circuit board. In order to form resonance, a lumped capacitor needs to be connected in series with the coil, however, in the resonance state, a local electric field exists at two ends of the capacitor, and the electric field is coupled with a scanned load, so that dielectric loss and frequency deviation are caused, and finally, the signal to noise ratio of a received image is affected.

The design of the planar multilayer coil avoids the above disadvantages of conventional receiver coils: 1. the overlapping area of the annular coils is large, so that the uniformity of the field is fully improved; 2. the matching and tuning elements are concentrated at port 5. The series-parallel capacitance is not distributed on the coil, so that when the series-parallel capacitance is used, dielectric loss and frequency deviation caused by coupling of local electric fields at two ends of the distributed capacitance and a scanned load can not be caused, and finally the signal-to-noise ratio of a received image is influenced.

Compared with the traditional receiving coil, the planar multilayer coil has the following technical characteristics/advantages:

1. the reverse winding realizes the reverse direction of adjacent loop current, thereby reducing the inductance of the whole coil. Finally, in the multichannel magnetic resonance coil, dense arrangement is realized, the maximization of the channel number is achieved, and the uniformity of the field is high.

2. The flexible receiving coil is flexibly wound on an FR4 rigid or FPC flexible board, so that the traditional receiving coil with relatively fixed space position of the inspected part is realized, or the flexible receiving coil is convenient for pediatric or facet joint inspection and diagnosis.

3. The inductance of the coil can be changed by adjusting the number of turns of the coil, namely, the distance between adjacent current loops, so that the intensity of the normal field of the whole coil is indirectly improved, and the design requirement of convenient adjustment is met according to the imaging depth requirement.

4. Because the inductance of a single coil is small, the magnetic field strength within the coverage area of such a multi-turn reversing coil can be made more uniform than with a conventional small loop.

The planar multilayer coil of the present invention may be designed in other shapes, such as oval, square, arch, etc., depending on the site of detection.

The coil is a multi-channel phased array coil and is composed of a plurality of coil sub-units (elements) which can simultaneously and independently receive radio frequency signals of a main magnetic field. The main advantage of phased array coils is that they can improve the signal-to-noise ratio and shorten the scan time. Under the condition that the imaging areas are the same, the more coil subunits of the phased array coil are, the smaller the area to be imaged of each coil subunit of each surface coil is, the less noise is acquired by the coil under the same signal acquisition time, but the signal intensity of the total imaging area is the same, the noise of the received image is reduced, so that the signal-to-noise ratio of the image is high, and if the required signal-to-noise ratio is unchanged, the scanning time of the multi-channel phased array coil can be correspondingly shortened. Determining inner and outer radii, selecting turns, and determining an impedance matching element and a detuning circuit; of these, the most important is the determination of the number of turns. Since the inductance of the coil is determined by the number of turns with the outer diameter of the coil fixed. Here, the design may be aided by electromagnetic simulation software.

The above embodiments of the present invention are only examples, and are not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (6)

1. The planar multilayer coil with low inductance is characterized by comprising a plurality of coils which are concentrically and annularly arranged in a dense manner, wherein an outer coil is a reverse winding coil of an inner coil between two adjacent coils, the current directions between the two adjacent coils are opposite, the coil size is determined according to the size of a part to be inspected, the size of a single coil is determined according to the number of channels, and the number of turns is determined according to the imaging depth requirement.

2. The low inductance planar multilayer coil of claim 1, wherein the ports of the multi-turn circular coil are located at the same radial position.

3. The low inductance planar multilayer coil of claim 2, wherein the matching and tuning elements are centrally disposed at the ports.

4. The low inductance planar multilayer coil of claim 1, wherein the multilayer planar coil is fabricated on FPC flexible board or FR4 rigid board.

5. The low inductance planar multilayer coil of claim 1, wherein said planar multilayer coil is circular, elliptical or square.

6. The low inductance planar multi-layer coil of claim 1, wherein the site to be examined is a joint, the planar multi-layer coil being used for joint imaging.