KR101388574B1 - Birdcage type rf receive coil with single leg capacitor, and thereof method - Google Patents

Abstract

The present invention relates to a birdcage type MRI reception end RF coil having a single leg capacitor and a method for manufacturing the same. The birdcage type MRI reception end RF coil having a single leg capacitor comprises a housing which is made of a hollowed cylindrical transparent plastic material; a coil sheet which is attached to the circumference of the side surface of the housing in a cylindrical shape, includes end coils formed in the upper end and the lower end in the horizontal direction and a plurality of coil legs (250) vertically connected to the end coil, and is patterned in a strip type on a flexible printed circuit board by forming gaps in the center of the coil legs and the end coils located among the coil legs; a capacitor which is mounted on the gaps formed in the coil legs and the end coils; and a detuning circuit which is installed in at least one end coil and changes impedance to be detuned. With the above simple structure and constitutions, the present invention is able to form a uniform internal magnetic field, generate a resonant frequency of a good quality and increase the receiving sensibility to provide the RF coil for an MRI system having high performance of improving an NMR imaging quality. Furthermore, the present invention provides a method for manufacturing the RF coil which is capable of improving the output stability of an electromagnetic element and is easy for a mass production.

Description

Bird type MRI receiver RF coil with single leg capacitor and its manufacturing method {birdcage type RF receive coil with single leg capacitor, and description method}

The present invention relates to an RF coil, and more particularly to a cage-type MRI receiver RF coil having a single leg capacitor formed of FPCB coil sheet and a method of manufacturing the same.

In Magnetic Resonance Imaging (MRI) systems, NMR (Nuclear Magnetic Resonance) imaging depends very closely on the design of the RF coil. RF coils are RF meters that have the ability to measure very weak RF signals formed in the current appearance of an object (human or animal) in an MRI system based on nuclear magnetic resonance. The most practical and important consideration in the design of an RF coil is the strong magnetic field that the RF coil must generate in that area. This magnetic field must produce the same resonance frequency as the nuclear magnetic resonance signal.

Many other techniques have been proposed for designing RF coils. Most are cage-shaped RF coils. Cage-shaped RF coils are widely used in NMR imaging because of their ability to form very strong and homogenous magnetic fields in the area. RF coils are usually designed to perform H nuclear NMR imaging at specific magnetic field strengths. Therefore, RF coils are limited to use in MRI systems designed for specific magnetic field strengths. Some RF coils are designed to have multiple resonance capabilities. Although they can measure NMR signals from H nuclei and nuclei of other atoms, such RF coils are limited in operation by their specific magnetic field strength.

The NMR RF coil is introduced in the conventional patent document 10-2011-0104807. 1 is a perspective view showing a conventional eight-section high-pass RF coil. As shown in Fig. 1, a ring-shaped metal pattern is formed on a cylindrical PCB (Printed Circuit Board) substrate up and down, and a capacitor is arranged therebetween as described above.

The magnetic resonator may include a replaceable capacitor or a variable capacitor, and is configured to control the resonance frequency by exchanging the replaceable capacitor or adjusting the capacitance of the variable capacitor.

In this manner, resonance is generated by the time-varying magnetic field in the coil-shaped magnetic resonator inductively coupled to the loop antenna. Thus, it is possible to provide a magnetic resonator in which a large number of capacitors are arranged so as to form a magnetic resonator in the upper and lower loop antenna type metal strips 23 and 25, .

In a small object such as a small animal, a magnetic resonance imaging (MRI) apparatus detects a magnetic field of a specific frequency emitted by the hydrogen nuclei contained in the human body and converts the magnetic field into a two-dimensional or three-dimensional image, An apparatus for inspecting an internal tissue type includes a CT (Computed Tomography)

By using a magnetic field that is completely harmless to the human body compared to Tomography or X-ray, it is possible to perform advanced non-destructive and non-radioactive tests with excellent contrast and resolution without harming the human body even for a long time or a large number of shots. .

However, conventionally, by using a method of manufacturing and attaching a coil in the form of a wire, manufacturing is not only complicated and inferior in precision, but also has difficulty in generating output stability and accurate resonant frequency of an electromagnetic device. In the receiving RF coil, there is a problem in that a circuit configuration for enhancing the duplex characteristic is complicated, and an operation for impedance matching is difficult.

An object of the present invention to solve the above problems is to provide a high performance MRI system capable of improving the image quality of NMR imaging by forming a uniform internal magnetic field with a simple structure and configuration, The present invention aims to provide an easy manufacturing method for mass production of RF coils which not only provides RF coils but also can improve the output stability of electromagnetic devices.

A first aspect of the present invention to solve the above problems is a housing of a hollow cylindrical translucent plastic material; It is cylindrically attached around the side of the housing, and comprises a horizontal end coil formed in the upper and lower ends, and a plurality of coil legs vertically connected to the end coil, between the center of the plurality of coil legs and the coil legs A coil sheet patterned in the form of a strip on a flexible printed circuit board by forming a gap in the end coil located in the flexible printed circuit board; A capacitor mounted in a gap formed in the coil leg and the end coil; It is installed in one of the end coils, and includes a detuning circuit for detuning by varying the impedance.

Preferably, the detuning circuit includes a PIN diode and a switching diode connected in parallel, and a capacitor and an inductor connected in series with the PIN diode and the switching diode, It is preferable that the capacitor is a non-magnetic variable capacitor.

In addition, preferably the transparent plastic material may be an acrylic resin, the flexible printed circuit board may be a FR4 epoxy resin FPCB, the coil may be made of copper (Copper) material.

In addition, it is preferable to further include an impedance matching capacitor for series and parallel impedance matching in the feed line extending from the one end coil, wherein the housing is a coaxial structure, the coil sheet is attached to the side of the inner cylinder It is desirable to be.

The second aspect of the present invention provides a method of manufacturing the RF coil, which includes: (a) a plurality of coils vertically connecting the end coils in a horizontal direction to the upper and lower ends of the substrate and the end coils in a flexible printed circuit board process; Patterning the coil structure in the form of a strip, the bridge having end portions between the coil legs and a gap formed at the center of the coil legs; (b) attaching a capacitor to the gap and detaching the impedance by changing a detuning circuit, the method comprising: forming at least one RF coil sheet by mounting at least one end coil on the end coil; And (c) attaching the RF coil sheet to a side surface of an inner cylinder of a cylindrical light transmitting housing of a hollow coaxial structure to form the cage coil.

The detuning circuit may include a capacitor and an inductor, in which a PIN diode and a switching diode are connected in parallel, and connected in series with the PIN diode and the switching diode.

As described above, the present invention provides a high-performance RF coil for an MRI system that can form a uniform internal magnetic field with a simple structure and configuration, and improve the image quality of NMR imaging by generating a high quality resonance frequency and receiving sensitivity.

In addition, the present invention provides a method of manufacturing a receiver RF coil that is easy to manufacture and is applied to an MRI system that can increase the stability and precision of the output stability and structure of an electromagnetic device.

1 is a perspective view showing a conventional 8-section high-pass RF coil,
2 is a photograph showing the configuration of a caged MRI receiver RF coil having a single leg capacitor according to an embodiment of the present invention,
3 is a photograph showing a coil sheet in the configuration of the cage-shaped MRI receiver RF coil having a single leg capacitor,
4 is a diagram illustrating a detuning circuit in the configuration of a caged MRI receiver RF coil having a single leg capacitor according to an embodiment of the present invention;
FIG. 5 is a diagram illustrating a model simulation of a caged MRI receiver RF coil having a single leg capacitor according to an embodiment of the present invention; FIG.
6 is a graph showing the return loss and Smith chart given by SEMCAD X 3D to see the impedance matching of the RF coil according to an embodiment of the present invention,
FIG. 7 shows the reflection loss (FIG. 7A) and Smith chart for a caged MRI receiver RF coil with a dual tune single leg capacitor according to an embodiment of the present invention of 4.7T for small animals. (B) is a graph showing
8 is a flowchart illustrating a method of manufacturing a cage-type MRI receiver RF coil having a single leg capacitor according to another embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and how to accomplish it, will be described with reference to the embodiments described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. The embodiments are provided so that those skilled in the art can easily carry out the technical idea of the present invention to those skilled in the art.

In the drawings, embodiments of the present invention are not limited to the specific forms shown and are exaggerated for clarity. Also, the same reference numerals denote the same components throughout the specification.

The expression "and / or" is used herein to mean including at least one of the elements listed before and after. Also, singular forms include plural forms unless the context clearly dictates otherwise. Also, components, steps, operations and elements referred to in the specification as " comprises "or" comprising " refer to the presence or addition of one or more other components, steps, operations, elements, and / or devices.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the drawings.

2 is a photograph showing the configuration of a caged MRI receiver RF coil having a single leg capacitor according to an embodiment of the present invention, Figure 3 is a coil sheet of the configuration of a caged MRI receiver RF coil having a single leg capacitor It is a photograph. As shown in Fig. 2, a housing 100 of silver hollow cylindrical translucent plastic material; The cylindrical shape is attached around the side of the housing 100, consisting of a horizontal end coil 230 formed in the upper and lower ends, and a plurality of coil legs 250 are vertically connected to the end coil 230, A coil sheet 200 patterned in a strip shape on a flexible printed circuit board 210 by forming a gap in an end coil 230 positioned between the centers of the plurality of coil legs 250 and the coil legs 250; A capacitor mounted in a gap 255 formed in the coil leg 250 and the end coil 230; And a detuning circuit (400) installed in one of the end coils (230) for detuning the impedance.

The cage-type MRI receiver RF coil having a single leg capacitor according to an embodiment of the present invention is a coil leg connecting upper and lower ring-shaped end coils and the end coils 230 to a conventional cylindrical housing 100 with a wire of conductive material. Instead of the configuration consisting of 250, the horizontal end coil 230 and the coil leg 250 vertically connecting the end coil 230 to the cylindrical housing 100 are formed in the form of a strip on the flexible printed circuit board 210. By proposing a structure for attaching the patterned coil sheet 200, it is easy to manufacture, and the system precision is not only increased, but also contributes greatly to the output stability of the electromagnetic element and the generation of accurate resonance frequency.

According to the embodiment of the present invention, a detuning circuit for detuning the impedance of any one of the end coils 230 is included so that the characteristics of the receiving end coil applied to the MRI system So that the resonance characteristic and the reception characteristic can be enhanced.

More specifically, as shown in Figure 3, looking at the manufacturing process of the cage-type MRI receiver RF coil having a single-leg capacitor according to an embodiment of the present invention, the coil sheet 200 is copper etched in a flexible epoxy dielectric material It is made of a conductor, which forms a pattern of conductive material having a line structure in the form of horizontal and vertical strips using the flexible printed circuit board 210 process, thereby facilitating the manufacturing process and increasing the stability and precision of the coil structure. Will be.

The caged MRI receiving RF coil with a single leg capacitor according to an embodiment of the present invention is composed of eight coil legs 250 and two end coils 230 (end rings), which are consistent with a simulation model made in advance. Here, the end coil 230 forms two strip lines in the horizontal direction at the top and bottom of the flexible printed circuit 400 substrate 210, and the coil leg 250 includes two end coils (the top and bottom). 230 is formed into eight strip lines connecting vertically.

A plurality of constant gaps 255 are formed in the end coil 230 and the coil leg 250, which is a structure for mounting the capacitor. The gaps 255 are formed at positions of the end coils 230 between the coil legs 250, and the gaps 255 are formed at the centers of the coil legs 250 to install capacitors. By forming a coil pattern on a flexible printed circuit 400 substrate 210 formed of a flexible epoxy material having a thickness of 0.23 mm, the coil sheet 200 is formed in a sheet form, thereby increasing the stability of the electromagnetic device and using an acrylic resin. We propose a structure that can be easily attached to the light-transmissive cylindrical housing 100 made.

In addition, as shown in FIG. 3, two feed lines are formed in one of the end coils 230, and a gap 255 is provided in each line so as to be composed of series and parallel capacitors for impedance matching. A line for configuring the detuning circuit 400 is formed at a position adjacent to the power supply line 270.

4 illustrates a detuning circuit 400 of a caged MRI receiver RF coil having a single leg capacitor according to an embodiment of the present invention. 4, the detuning circuit 400 is composed of an inductor, a PIN diode, a switching diode, and a capacitor, and four passive circuits 400, each of which is provided with two end coils, Lt; RTI ID = 0.0 > RF < / RTI >

The switching circuit 400 is composed of a PIN diode connected in series with an inductor, and a limiter circuit 400 including four switching diodes and capacitors connected in parallel with the PIN diode. This ripple circuit 400 is connected in parallel with the end coil 230 capacitors, and the switching and PIN diodes are non-magnetic. Switching and PIN diodes are surface-mounted, with 1 mm of conductor strips extending to each end coil 230 as solder paste for each of the diodes for mounting devices such as Io and configuring circuit 400. .

As such, in a caged MRI receiver RF coil having a single leg capacitor according to an embodiment of the present invention, all capacitors located in each coil are non-magnetic, and the RF coil is a broadband receiver cage coil, so that the double circuit 400 is Required. This is to neutralize and detun the effect of induced current due to the RF transmitting coil in the RF receiver coil during the period when the nuclei of ¹ H and ³¹ P are excited at the frequency of the rammer. Here, detuning refers to a change in the capacitance inductance of the tuning circuit 400 or both to deviate the tuning.

That is, the receiving and transmitting end coils operate at the same frequency, and they are required to decouple each other in receive and transmit modes. This decoupling is realized by a diode controlled by the dual element. The receiving coil operates in the transmitting magnetic field B1, which changes the magnetic field and induces an electric field in the coil loop. Strictly no electric field is required in the RF coil, since the duplex element needs to supply a high impedance in the coil loop to derive the RF current from the induced electric field, so the use of the duplex circuit 400 is necessary.

As described above, the cage-type MRI receiver RF coil having a single leg capacitor according to an embodiment of the present invention forms the coil sheet 200 described above, and the coil sheet 200 includes a capacitor, an inductor, a PIN diode, and a switching diode. The structure of the dual circuit 400 of the structure can be easily installed, and a structure capable of easily changing the impedance for increasing the decoupling at the resonance frequency as a characteristic of the receiving end coil is proposed. The change in impedance can be easily manipulated using a nonmagnetic variable capacitor to change the capacitance value and the overall impedance.

FIG. 5 is a diagram illustrating a model simulation of a caged MRI receiver RF coil having a single leg capacitor according to an embodiment of the present invention.

The cage MRI receiver RF coil with a single leg capacitor according to an embodiment of the present invention is a receiver wideband cage coil for whole body NMR imaging for small animals. The RF coil was simulated by SEMCAD X 3D, a 3D electromagnetic simulation software. Simulation software helps to optimize the peak values of the coil and capacitor so that the RF coil can resonate simultaneously at 81 MHz and 200 MHz. The RF coil was simulated without rat phantoms, and the RF coil is a wideband LC resonator. While the lumped capacitors in the end coil 230 and the coil leg 250 supply the capacitance, the inductance of the end coil 230 and the coil legs 250 is due to the copper conductor material.

As shown in FIG. 5, the simulation model of the RF receiver coil is shown by the coil legs 250, the end coils 230 and the feed line 270 as yellow copper strips, and the end coils 230 and the capacitors of the coil legs 250. Are indicated by blue arrows. On the other hand, flexible printed circuit board 210 (FPCB) is represented by a green sheet wound and attached to a hollow acrylic cylinder shown in gray. The optimized dimensions were used in the simulation model for the RF coils shown in Table 1 below.

Looking at the simulation results performed under the same model and conditions, the reflection loss and Smith chart given by SEMCAD X 3D to see the impedance matching of the RF coil according to the embodiment of the present invention are shown in FIG.

As shown in FIG. 6, the return loss graph shows the presence of multiple resonant frequencies in the simulated FPCB RF coil. Lower resonant frequencies are due to the coil leg 250. One of the leg current resonant frequencies enhances the ³¹ P measurement in the animal body. The higher resonant frequency is due to the end coil 230 current and represents a ¹ H measurement for the 4.7T magnetic field. The Smith chart graph shows that impedance matching is required for the RF coil. The main purpose of the RF coil is to form a magnetic field inside the RF coil. The state of the magnetic field traveling direction of the simulation structure obtained by SEMCAD X 3D at the center of the RF coil is shown in FIG. 5.

FIG. 7 shows the reflection loss (FIG. 7A) and Smith chart for a caged MRI receiver RF coil with a dual tune single leg capacitor according to an embodiment of the present invention of 4.7T for small animals. It is a graph which shows (b of FIG. 7).

As shown in FIG. 7, the return loss of the RF coil and the results of the Smith chart are obtained from an Agilent network analyzer. For dual modulation operation in a 4.7T MRI system, the resonant frequencies should be 81 MHz for ³¹ P and 200 MHz for H. It can be clearly seen in FIG. 7 that the RF coil has the ability to resonate at 81.81 MHz and 200.28 MHz at -19.64 dB and 24.27 dB, respectively.

The return loss values are somewhat different from the return loss simulation results shown in FIG. 6, but these return loss values are more desirable. This is due to the impedance matching performed through nonmagnetic impedance matching capacitors connected in series and in parallel with the feed line 270. These capacitors do not include a simulation model only to reduce simulation time. After performing impedance matching, an appropriate resonant dynamic of the RF coil was obtained, and the variable capacitors were replaced with fixed-value nonmagnetic chip capacitors before performing NMR imaging.

As described above, the present invention forms a sheet-shaped coil having a single leg capacitor in an FPCB manufacturing process and easily attaches it to the housing 100, and decoupling impedance matching and transmission and receiving end resonance frequencies through a detuning circuit 400. By suggesting a coil structure and a system that can easily form (decoupling) and easily operate, it is easy to manufacture, and the stability of the output of the electromagnetic element of the electromagnetic element and the stability of the receiver RF coil structure applied to the MRI system. Precision can be increased.

8 is a flowchart illustrating a method of manufacturing a cage-type MRI receiver RF coil having a single leg capacitor according to another embodiment of the present invention. As shown in FIG. 8, a method of manufacturing a dual resonant RF coil according to an exemplary embodiment of the present invention includes (a) a straight end coil in a horizontal direction at the top and bottom of the substrate 210 in a flexible printed circuit board 210 process. 230 and a plurality of coil legs 250 that vertically connect the end coils 230, and a gap in the center of the end coils 230 and the coil legs 250 between the coil legs 250. Patterning the coil structure in the form of a strip in which 255 is formed; (b) attaching a capacitor to the gap 255, and attaching at least one detuning circuit 400 to the end coil 230 for detuning by varying the impedance to the RF coil sheet ( 200); And (c) attaching the RF coil sheet 200 to the side of the inner cylinder of the hollow coaxial cylindrical translucent housing 100 to form a cage coil. do.

Unlike the conventional method in which a copper wire-type conductor is directly attached as a hollow cylindrical supporting structure of an acrylic material, in the embodiment of the present invention, a flexible dielectric material By using a method of forming a coil sheet 200 by patterning the copper in a strip shape by etching copper and attaching the coil sheet 200 to the hollow cylindrical support structure 100 as the housing 100 The present invention proposes a manufacturing method which is not only capable of improving the output stability of an electromagnetic device, but also facilitating mass production.

It has also been found that the preferred resonance modes are improved by etching the copper conductor to a flexible dielectric material and undesired resonance modes are inhibited. In SAR water phantoms found in simulations of RF coils, the SAR is below the safe limit.

While the invention has been shown and described with respect to the specific embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Anyone with it will know easily.

100: housing, 200: coil sheet, 210: FPCB, 230: end coil,
250: coil leg, 255: gap, 270: feed line, 300: capacitor,
400:

Claims (10)

A housing of hollow cylindrical translucent plastic material;
It is cylindrically attached around the side of the housing, and comprises a horizontal end coil formed in the upper and lower ends, and a plurality of coil legs vertically connected to the end coil, between the center of the plurality of coil legs and the coil legs A coil sheet patterned in the form of a strip on a flexible printed circuit board by forming a gap in the end coil located in the flexible printed circuit board;
A capacitor mounted in a gap formed in the coil leg and the end coil; And
A PIN diode and a switching diode are connected in parallel, and include a capacitor and an inductor connected in series with the PIN diode and the switching diode. The PIN diode and the switching diode are installed in one of the end coils to change and detun the impedance. A caged MRI receiver RF coil with a single leg capacitor, characterized in that it comprises a detuning circuit.
delete The method of claim 1,
The caged MRI receiver RF coil having a single-leg capacitor, characterized in that the capacitor of the two-circuit circuit is a non-magnetic variable capacitor.
The method of claim 1,
The cage-shaped MRI receiver RF coil having a single leg capacitor, characterized in that the transparent plastic material is an acrylic resin.
The method of claim 1,
The caged MRI receiver RF coil having a single bridge capacitor, characterized in that the flexible printed circuit board is FR4 epoxy resin FPCB.
The method of claim 1,
The coil is a cage type MRI receiver RF coil having a single bridge capacitor, characterized in that the copper (Copper) material.
The method of claim 1,
The cage type MRI receiver RF coil having a single leg capacitor, characterized in that it further comprises an impedance matching capacitor for series and parallel impedance matching in the feed line extending from any one end coil.
The method of claim 1,
The housing includes:
A coaxial structure, wherein the caged MRI receiver RF coil having a single-leg capacitor, characterized in that the coil sheet is attached to the side of the inner cylinder.
(a) In a flexible printed circuit board process, a straight end coil in a horizontal direction and a plurality of coil legs for vertically connecting the end coils are formed at upper and lower ends of the substrate, and end coils and coil legs between the coil legs. Patterning the coil structure in the form of a strip with a gap formed in the center;
(b) a capacitor is mounted in the gap, a PIN diode and a switching diode are connected in parallel, and are installed in one of the end coils including a capacitor and an inductor connected in series with the PIN diode and the switching diode. Attaching at least one detuning circuit to said end coil for detuning by varying impedance to form an RF coil sheet; And
(c) attaching the RF coil sheet to a side of an inner cylinder of a hollow coaxial cylindrical translucent housing to form a cage coil, wherein the cage has a single leg capacitor. Method of manufacturing MRI receiver RF coil.









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