KR101541821B1 - Birdcage RF Coil for Small Animal NMR Imaging at MRI System - Google Patents

Abstract

The present invention relates to a cage-type receiving stage RF coil for a small animal MRI system, comprising: a housing of a hollow cylindrical translucent flockstick material; A flexible printed circuit board (FPCB) having a rectangular shape and being attached to the housing in a cylindrical shape; a horizontal end ring formed at upper and lower ends of the flexible printed circuit board; Wherein the end portions of the end rings of the coil legs have a serration-like structure composed of a vertical oblique portion extending in a diagonal direction and a horizontal end portion connected in a horizontal direction at an end of each of the vertically oblique portions, A coil sheet patterned in a strip shape on the flexible printed circuit board by forming a gap at the center of the horizontal end; A capacitor mounted in the gap; And a detuning circuit which is installed in at least one gap of the end ring and detuning the impedance.
An RF coil for an MRI system capable of forming a uniform and strong internal magnetic field with a simple structure and configuration, capable of enhancing resonance frequency generation and reception sensitivity of high quality, and enhancing signal detection performance deep in a sample.

Description

{Birdcage RF Coil for Small Animal NMR Imaging at MRI System}

The present invention relates to an RF coil for an MRI system, and more particularly to a bird-type RF coil for a small animal MRI system.

The RF coil is considered to be the most important part of the MRI system because of its direct relevance in accepting NMR signals emitted by the excited nuclei of the body to reestablish steady state. This weak NMR signal is produced during very small span intervals. There is a very sensitive meter that is required for its measurement. In many studies, the development of NMR detectors, known as RF coils, has continued until recently. However, the invention of the cage coil has provided a new dimension in the design of RF coils. This has proven to be the most static candidate for NMR imaging of humans and animals in diagnostic MRI systems. To bring further improvements in the design-based cage coil acceptance mechanism, researchers are still working on other forms of research for other MRI applications.

In NMR (Magnetic Resonance Imaging) systems, NMR (Nuclear Magnetic Resonance) imaging is very closely dependent on the design of RF coils. An RF coil is an RF meter capable of measuring very weak RF signals formed in the current state of an object (human or animal) in an MRI system based on nuclear magnetic resonance phenomena. The most substantial and important consideration in the design of RF coils 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 due to their ability to form very strong magnetic fields and homogenous magnetic fields in their regions. 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 resonant capabilities. They can measure NMR signals from the nuclei of ¹ H nuclei and other atoms, but such RF coils are limited in operation with specific magnetic field strengths.

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.

In addition, the magnetic resonator includes an interchangeable capacitor or a variable capacitor, and the resonance frequency can be adjusted by exchanging the interchangeable 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 which is totally harmless to human body compared with X-ray, it is possible to perform advanced non-destructive and non-radioactive examination with high contrast and resolution without being harmful to human body for long time shooting or many times of photographing .

However, in the related art, by using a method of manufacturing and attaching a coil in the form of a wire, not only the manufacturing is complicated and the precision is low, but also the output stability of the electromagnetic device and the generation of the accurate resonance frequency are difficult. There is a problem in the receiver RF coil that the circuit configuration for enhancing the tuning characteristics is complicated and the operation for impedance matching is difficult and the signal detection performance for the portion where the signal absorption rate (SAR) is deep is inferior There is a problem.

Korean Public Release No. 10-2011-0104807 (public date: September 23, 2011)

An object of the present invention which intends to solve the above-described problems is to provide a magnetic sensor capable of forming a uniform and strong internal magnetic field with a simple structure and configuration, capable of increasing resonance frequency generation and reception sensitivity of good quality, And to provide an RF coil for an MRI system.

According to an aspect of the present invention, there is provided a method of manufacturing a light emitting device, comprising: a housing of a hollow cylindrical translucent flocked material; A flexible printed circuit board (FPCB) having a rectangular shape and being attached to the housing in a cylindrical shape; a horizontal end ring formed at upper and lower ends of the flexible printed circuit board; Wherein the end portions of the end rings of the coil legs have a serration-like structure composed of a vertical oblique portion extending in a diagonal direction and a horizontal end portion connected in a horizontal direction at an end of each of the vertically oblique portions, A coil sheet patterned in a strip shape on the flexible printed circuit board by forming a gap at the center of the horizontal end; A capacitor mounted in the gap; And a detuning circuit which is installed in at least one gap of the end ring and detuning the impedance.

Preferably, the receiving end RF coil is for a 1.5T MRI system, and the gap between the upper and lower end rings is located at the center between the coil legs, And the gap of the lower end ring is positioned at a center between the coil legs so that the end ring upper end gap and the lower end gap coincide with each other on a vertical line.

Preferably, the width of the horizontal end of the coil leg may be smaller than the width and size of the remaining end rings and coil legs, and the detuning circuit may include a PIN diode and a switching diode in parallel And a capacitor and an inductor connected in series with the PIN diode and the switching diode.

In addition, it is preferable that the capacitor of the resonance circuit is a non-magnetic variable capacitor, the transparent plastic material is preferably an acrylic resin, and the end ring and the coil leg are made of copper desirable.

It is preferable that the power supply line extending from any one of the end rings further includes an impedance matching capacitor for serial and parallel impedance matching.

As described above, the present invention provides a high performance RF coil for an MRI system capable of improving uniformity and strong internal magnetic field with a simple structure and configuration and improving quality of NMR imaging by increasing resonance frequency generation and reception sensitivity of high quality.

Also provided is a receiving end RF coil applied to an MRI system capable of enhancing output stability and structural stability and precision of an electromagnetic device of an electromagnetic device.

In addition, it provides an RF coil having a high detection performance for weak NMR signals from an inner region where the number of coil legs can be reduced, which is easy to manufacture and has a very low signal absorption rate (SAR).

1 is a perspective view showing a conventional 8-section high-pass RF coil,
2 is a perspective view showing the configuration of a receiving-end RF coil for a small animal MRI system according to an embodiment of the present invention,
3 is a view showing Embodiment 1 of a coil sheet structure of a receiving end RF coil for a small animal MRI system according to an embodiment of the present invention,
4 is a view showing Embodiment 2 of a coil sheet structure of a receiving end RF coil for a small animal MRI system according to an embodiment of the present invention,
5 is a view showing a three-dimensional model of a cage-type receiving end RF coil for an MRI system having a serrated coil leg according to an embodiment of the present invention
FIG. 6 is a graph illustrating a return loss through simulation of a cage-type receiving end RF coil for an MRI system according to an embodiment of the present invention,
FIG. 7 shows a magnetic field distribution in a coil through a simulation of a cage-type receiver RF coil for an MRI system according to an embodiment of the present invention,
8 is a signal absorption ratio (SAR) distribution in a coil through a simulation of a cage-type receiver RF coil for an MRI system according to an 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 of the present invention will be described in detail with reference to the drawings.

2 is a perspective view showing a configuration of a receiving end RF coil for a small animal MRI system according to an embodiment of the present invention. As shown in FIG. 2, the RF coil according to the embodiment of the present invention includes: a housing 100 of a hollow cylindrical translucent flocked material; A flexible printed circuit board 210 (FPCB) having a rectangular shape and being attached to the housing 100 in a cylindrical shape, and a horizontal end ring 230 formed at the upper and lower ends of the flexible printed circuit board 210, And a horizontal end 257 connected in the horizontal direction at the end of each of the vertical slanting parts 253, the vertical slanting part 253 extending in the vertical slanting direction in the upper and lower end rings 230, Wherein a gap is formed between a certain portion of the end ring (230) between the coil legs (250) and the center of the horizontal end portion (257) A coil sheet 200 patterned in a strip form on a substrate 210; A capacitor 300 mounted in the gap; And a detuning circuit (400) installed in at least one gap of the end ring (230) and detuning the impedance.

As described above, the present invention proposes a cage-type RF coil having a broadband characteristic for a small animal MRI system, and unlike an RF coil having a general straight leg or a modified crossed or helical pattern coil leg 250 structure, The present invention proposes an RF coil having a four-coil bridge (250) structure that resembles a saw tooth shape based on a leg 250 pattern. Such an RF coil system can be applied to small animal NMR imaging to detect NMR signals generated by the excitation of H protons when the resonance frequency is 63.85 MHz in a 1.5T MRI system. That is, in the embodiment of the present invention, the coil leg 250 and the end ring 230 are etched in the FPCB board to form one coil sheet 200, and the coil sheet 200 is mounted on the bottom of the cylindrical transparent plastic material Thereby forming an RF coil system. In the embodiment of the present invention, the coil is a receiving end RF coil having an output signal through a feed line provided with a pair of capacitors 300 for impedance matching.

That is, the present invention proposes a structure or design of a modified cage-type RF coil for small animal NMR imaging and a new method for the process. An RF coil according to an embodiment of the present invention is a broadband type birdcage coil that is substantially and specifically designed to perform full body NMR imaging of a small animal in a 1.5T MRI system. The designed coil includes a sawtooth pattern with a coil leg 250 conductor. A magnetic field generated at a resonance frequency of 63.85 MHz by an RF coil having a sawtooth coil leg 250 pattern according to the embodiment of the present invention is generated by a general straight legged broadband cage coil designed with the same dimensions Which is much stronger than the magnetic field.

The embodiment of the present invention simulates two slightly different designs as RF coils with serrated coil legs 250. The design difference is in the position of the capacitor 300 at the end ring 230. FIG. 3 is a view of Embodiment 1 of a coil sheet 200 structure of a receiving end RF coil for a small animal MRI system according to an embodiment of the present invention. FIG. 4 is a cross- 2 is a view of Embodiment 2 of the structure of the coil sheet 200 of the RF coil.

The RF coil according to the embodiment of the present invention includes a coil leg 250 (cylindrical surface) formed in parallel with the axis of the coil and having a sawtooth shape, and the coil axis 250 connecting the coil leg 250 at both ends And a copper conductor known as an end ring 230 formed vertically. The four coil legs 250 of the RF coil have the same gap to ensure a homogeneity issue.

The coil sheet 200 of the RF coil according to the embodiment of the present invention shown in Figs. 3 and 4 shows two embodiments of RF coils with small structural differences. The capacitors 300 are connected to the end ring 230 between the coil legs 250 as well as the coil leg 250 when the RF coil having the serrated coil leg 250 according to an embodiment of the present invention exhibits a wide band characteristic. The mounting is also required in the part. In the case of the embodiment 1 shown in FIG. 3, the capacitors of both end rings 230 are vertically and vertically aligned with each other, whereas in the embodiment 2 shown in FIG. 4, End ring 230 segment.

In the case of Embodiment 1, as shown in Fig. 3, symmetry exists between the capacitors 300 of each end ring 230. The capacitors 300 of the lower end ring 230 located in the center of the segment are equidistantly spaced from both coil legs 250 while the capacitors 300 of the upper end ring 230 are spaced apart from the coil legs 250 250) to the right of the coil leg (250). However, in the case of design 2, there is a diagonal symmetry between both capacitors 300, as shown in Fig. The capacitors 300 of both endrings 230 are located at the center of their respective end ring 230 segments.

These two embodiments are based on the cross direction of the leg in the RF coil pattern. That is, the shape of the connection of each coil leg 250 extending from the lower and upper end rings 230 is not aligned on a vertical line. Thus, the legs are each in a diagonal symmetry to each other, and each leg is joined in such a way as to form two horizontal ends 257 perpendicular to the nose axis extending from its end and joining together. And these horizontal end 257 conductors are smaller in width than the vertically oblique coil leg 250 conductors.

In other words, the coil legs 250 according to the embodiment of the present invention may include a vertically oblique portion 253 extending in the vertical oblique direction at the upper end and an end ring 230 at the lower end, And a horizontal end portion 257 connected in the horizontal direction. The width of the horizontal end portion 257 is smaller than the width of the vertical slanting portion 253.

Since the RF coils of the first and second embodiments are the receiving end RF coils, the detuning circuits 400 are added to both end rings 230 of the RF coils, as shown in FIGS. The position of the capacitor 300 in the segment of the end ring 230 becomes important when the oscillator circuit 400 is connected in parallel to the end ring 230 capacitors 300. The conductor lines for the diodes 400 diodes may cause impedance mismatches that may interfere with the field uniformity of the RF coil. This is the main reason for suggesting an embodiment of two different structures as shown in Figs. 3 and 4. Fig.

The switching circuit 400 includes a PIN diode connected in series with an inductor, and a limiter circuit including four switching diodes and a capacitor 300 connected in parallel with the PIN diode. The tuning circuit 400 is connected in parallel with the end ring 230 capacitors 300, and the switching and PIN diodes are non-magnetic. The switching and PIN diodes are surface mounting type. In order to mount such a device and configure a circuit, conductor strips of 1 mm as solder paste for each of the diodes are formed extending from each end ring 230.

As described above, in the cradle-type RF coil for the MRI system according to the embodiment of the present invention, all the capacitors 300 located at the respective coils are non-magnetic type and the RF coil is a broadband receiver cradle type coil, Is required. This is to neutralize and neutralize the effect of the induction current due to the RF transmission coil in the RF receiver coil during that interval when the ¹ H and ³¹ P nuclei are excited at the frequency of the rammer. Detuning refers to changing the capacitance inductance of the tuning circuit, or both, to deviate from 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 decalpling is realized by a diode controlled by the biasing 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, an electric field is not required in the RF coil, which requires the use of the above-mentioned modulation circuit 400 because it is necessary to supply a high impedance in the coil loop for deriving the RF current from the induced electric field.

As described above, the cage-type receiving stage RF coil for the MRI system according to the embodiment of the present invention forms the coil sheet 200 described above, and the coil sheet 200 is formed of a capacitor 300, an inductor, a PIN diode and a switching diode The structure of the tuning circuit 400 can be easily installed and a structure capable of easily changing the impedance for increasing the decoupling at the resonance frequency as the characteristic of the receiving end coil is proposed. The impedance can be changed by changing the capacitance value and changing the total impedance by using the non-magnetic variable capacitor 300 with ease.

RF  Simulation of coil structure

In the embodiment of the present invention, it is designed to be optimized at a resonance frequency of 63.85 MHz for obtaining NMR signals in a 1.5T MRI system. And the measured values of the birdcage RF coils of the newly constructed structure. All result graphs were simulated by placing a water phantom inside the coil. The reason for this is that small animals and bodies have diverse dielectric constants in them, and the most similar materials are seawater with various dielectric constants in them, including many minerals.

5 is a view showing a three-dimensional model of a cage-type receiving end RF coil for an MRI system having a serrated coil leg 250 according to an embodiment of the present invention. As shown in Fig. 5, was made using HFSS, a radio wave three-dimensional electromagnetic simulation software. The simulations of Examples 1 and 2 of the cage-shaped cage-type RF coil were carried out independently. For simulation, the relay circuit 400 housing 100 is not included in the simulation design as shown in Figs. 5 (a) and 5 (b).

The simulation model is shown in Fig. 5, so that a hollow acrylic cylinder having a thickness of 5 mm, an inner diameter of 40 mm and a length of 212.5 mm supporting the RF coil conductor pattern is etched in the FPCB, so that a 0.2 mm thick FR4 epoxy dielectric FPCB Layer is included in the simulation structure. The copper conductor pattern of the RF coil is drawn on the outer surface of the FPCB layer in the simulation.

The length of the feed line was set at 40mm and the port was placed at the end to transmit the NMR signal from the small animal to the MRI system to make the image. In addition, series and parallel capacitors are placed on the feed line to provide impedance matching. The spacing of all capacitors was set to 2 mm for use with non-magnetic (SMT) type capacitors.

The main purpose of the simulation model generation is to obtain the highest value of the RF coil which can form a strong magnetic field inside the RF coil at the desired resonant frequency of 63.85MHz for the detection of ¹ H NMR signal through the whole body of small animal in the 1.5T MRI system . And since the broadband pendant coil is an LC resonator, the second objective of the simulation is to find the best capacitor 300 values that will enable the desired resonance at the desired frequency.

It was confirmed that the conductor width optimized by performing the three-dimensional simulation of the RF coil according to the embodiment of the present invention was 5 mm in the end ring 230, the vertical oblique portion 253, the coil leg 250, and the feed line , While the horizontal end portion 257 of the coil leg 250 is 2 mm. The total length of the legs was determined to be 182.8 mm, and the diagonal and horizontal lengths of the legs were determined to be 81.5 mm and 19.8 mm, respectively. The total length of the end ring 230 was determined by the 2? R relation. Where r is the radius of the RF coil taking into account the acrylic cylinder and FPCB thickness. The gap in which the capacitors 300 are installed is fixed at 2 mm through coils coinciding with the actual non-magnetic (SMT) capacitors 300. Although the values of the end ring 230 and the coil leg 250 capacitor 300 optimized for the simulation of the structure according to both embodiments and the corresponding preferred resonant frequency are found to be the same, the values of the matching capacitor 300 are slightly There was a difference.

The values of all the capacitors 300 are as shown in Table 1. The simulation of the RF coil is used not only for dimension optimization of the coil conductor, but also for checking the performance of the coil at the desired frequency. The coil performance is determined by the return loss graph (FIG. 6), the magnetic field distribution along the coil center axis (FIG. 7), and the signal absorption rate (SAR) distribution 8). ≪ / RTI > The results for the two embodiments (Example 1 and Example 2) are shown in Figures 6-8.

It can be seen that the return loss curve for the structures of both embodiments is close to 63.85 MHz, which is a very desirable resonance frequency due to the coil leg 250 current, as shown in FIG. The SARs (Signal Absorption Ratio) images have a signal absorption rate (SAR) as shown in FIG. 8, while the magnetic field patterns for the structures of both embodiments show strong and uniform magnetic field distributions within the RF coil, This is at a very low level. All the results shown in FIGS. 6 to 8 show that the RF coil according to the embodiment of the present invention has a good performance for detecting weak NMR signals from an inner region having a low SAR.

Thus, the present invention proposes a new structure for a broadband cage-type RF coil that performs small animal NMR imaging in a 1.5T MRI system. This is a simple cage-shaped RF coil based on four coil legs 250 and an end ring 230, the shape of the coil leg 250 being similar to the sawtooth shape. The cross diagonal direction of the coil leg 250 can very effectively detect the NMR signal through the entire volume of the sample inside the RF coil, and the three-dimensional electromagnetic simulation sufficiently demonstrates the effectiveness of the features and structures described above.

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: flexible printed circuit board, 230: end ring,
250: coil leg, 300: capacitor, 400:

Claims (10)

A housing of hollow cylindrical translucent flocked material;
A flexible printed circuit board (FPCB) having a rectangular shape and being attached to the housing in a cylindrical shape; a horizontal end ring formed at upper and lower ends of the flexible printed circuit board; Wherein the end portions of the end rings of the coil legs have a serration-like structure composed of a vertical oblique portion extending in a diagonal direction and a horizontal end portion connected in a horizontal direction at an end of each of the vertically oblique portions, A coil sheet patterned in a strip shape on the flexible printed circuit board by forming a gap at the center of the horizontal end;
A capacitor mounted in the gap; And
And a detuning circuit installed at a gap of at least one of the end rings for detuning an impedance,
Wherein the width of the horizontal end of the coil leg is smaller than the width and size of the remaining end rings and coil legs but smaller.
The method according to claim 1,
Wherein the receiving end RF coil is for a 1.5T MRI system.
The method according to claim 1,
And a gap between the upper and lower end rings is located at a center between the coil legs.
The method according to claim 1,
Characterized in that the gap of the upper end ring is located close to any one of the coil legs and the gap of the lower end ring is located at the center between the coil legs so that the end ring upper end gap and the lower end gap coincide with a vertical line. Receiver RF coil for animal MRI system.
delete 5. The method according to any one of claims 1 to 4,
The detuning circuit comprises:
And a capacitor and an inductor connected in parallel to the PIN diode and the switching diode, wherein the PIN diode and the switching diode are connected in parallel, and the PIN diode and the switching diode are connected in series.
The method according to claim 6,
Wherein the capacitor of the tuning circuit is a non-magnetic variable capacitor.
The method according to claim 6,
And the translucent plastic material is an acrylic resin.
The method according to claim 6,
Wherein the end ring and the coil leg are made of copper. The cradle type MRI receiving stage RF coil according to claim 1, wherein the end ring and the coil leg are made of copper.
The method according to claim 6,
Further comprising an impedance matching capacitor for series and parallel impedance matching on a feed line extending from any one of the end rings.

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