KR100260508B1 - Quadrature breast coil for mri system - Google Patents

Abstract

PURPOSE: A quadrature breast coil for a MRI(magnetic resonance imaging) system is provided to improve signal-to-noise ratio by uniformly forming X-axis and Y-axis magnetic fields by adjusting a tuning condenser. CONSTITUTION: A quadrature breast coil for a MRI consists of a rod(1,2,3,4,5,6,7,8) equally arranged to form an orthogonal field such as an X-axis magnetic field and a Y-axis magnetic field. Four rods among eight rods are connected to have same polarity, and the others are connected to have opposite polarity, thereby signals generated from an inspection object are detected after being separated into the X-axis magnetic field and the Y-axis magnetic field. The breast coil has tuning condensers for tuning a center frequency. Two condensers among three condensers serve to adjust the center frequency of the X-axis magnetic field, and the other condenser serves to adjust the Y-axis magnetic field.

Description

Spherical Chest Coil for Magnetic Resonance Imaging

The present invention relates to a coil used in magnetic resonance imaging (MRI) imaging, and more particularly, to a breast coil for obtaining a breast image of a human body.

In general, magnetic resonance imaging (MRI) is an image diagnosis device that diagnoses the inside of the human body by converting this energy into a signal, which causes resonance by releasing an atomic nucleus in an electromagnetic field and applying a constant frequency and energy. Unlike energy-emitting imaging devices such as computed tomography (CT) and X-ray imaging devices, this MRI device uses physical methods, so there is no risk of radiation exposure. It is a trend.

The breast coil used in the conventional MRI apparatus generally used a birdcage coil. Since the cage coil is made of a cylindrical frame, the magnetic field is uniformly formed. To convert these cage coils into chest coils, they must be designed in a hemispherical shape to fit the shape of the chest. Therefore, it has a structure in which one side is opened. For this reason, when a capacitor is connected to each of the rods constituting a cage coil (hereinafter, referred to as a "rod") to the same value as a conventional cage coil, the same circuit is manufactured. (quadrature field) could not be formed.

When the chest coil is formed in a symmetrical structure by modifying the conventional cage coil, the side which makes the X-axis magnetic field can be theoretically formed by current feeding. However, the conventional cage-shaped structure does not form a Y-axis magnetic field. According to the theory, a chest coil consisting of eight rods must have the same polarity in the current direction formed by the four rods, and four must be opposite in polarity to the preceding rod. In practice, however, the current directions of the first and eighth rods showed opposite polarities. As a result, when scanning due to this error in the current direction, part of the image was crushed or streaked. Therefore, the formation of this current direction in theory is one of the very important factors in manufacturing the chest coil.

Therefore, an object of the present invention is to produce a chest coil in a hemispherical shape with one side open of a cage coil forming a Y-axis magnetic field, using the same amount of capacitors used in each rod. The resulting tuning point, or change in center frequency, is to provide a quadrature chest coil for adjustment with a tuning capacitor.

1 is a view showing a circuit configuration of a spherical chest coil of the present invention,

2 is a view showing the strength and direction of the current to make the X-axis and Y-axis magnetic field according to the current supply in the circuit configuration of FIG.

3 conceptually illustrates forming an X, Y axis magnetic field in accordance with the present invention in a phantom;

※ Explanation of codes for main parts of drawing

C _H , 2C _H : Condenser ~ C _H : Tuning Capacitor

12, 14: earth circuit breaker 16: coupler

A feature of the present invention for achieving the above object is to open one side of the cage coil so that the X, Y axis magnetic field is uniformly formed in a breast coil for magnetic resonance imaging (MRI) imaging, respectively. Rods are arranged in a hemispherical shape, and the spherical chest coils are characterized in that the signals generated from the inspection object are separated and detected by the X and Y axis magnetic fields, respectively.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing the circuit configuration of a spherical chest coil of the present invention. In the present invention, in order to form a quadrature field (quadrature field), the general cage coil is modified into a hemispherical shape to form the X, Y axis magnetic field according to the current supply direction. In an embodiment of the invention, the chest coil consists of eight rods in total. In order to make the Y-axis magnetic field uniform, four should be of the same polarity and the other four should be opposite to the previous rod. To do this, the upper part of the chest coil was connected to open the rod 1 and the rod 8 differently from the lower part. The capacitors C _H connected at equal intervals between the rods are positioned. In order to create a uniform spherical X- and Y-axis magnetic field, the center frequencies must be tuned independently of each other, so the tuning points must be different. The spherical chest coil of the present invention includes tuning capacitors capable of adjusting the center frequency at different tuning points to adjust the center frequency to the X and Y axis magnetic fields, respectively. The tuning capacitor (˜C _H ) uses a variable capacitor that adjusts the center frequency independently of each other in the fields of the x and y axes. This tuning capacitor is located in three places, as shown in FIG. One of the three capacitors is a variable capacitor for adjusting the center frequency of the Y-axis magnetic field, and the other two are variable capacitors for adjusting the center frequency of the X-axis terminal. A tuning capacitor (~ C _H ) was connected between rod 3 and rod 6 of the upper coil to adjust the center frequency of the Y-axis magnetic field. This point has little effect on the X-axis magnetic field, while the y-axis magnetic field shows a large frequency change even with a very small change. This point was obtained through experiments, and it is more desirable to find a point where the frequency of the Y-axis magnetic field can be adjusted without affecting the X-axis magnetic field at all. In an embodiment, the value of the tuning capacitor (˜C _H ) used is 1-10 kHz, which can find a change in the center frequency of 7-8 MHz. In contrast, two tuning capacitors (~ C _H ) for adjusting the change in the center frequency of the X-axis magnetic field are connected between the rod 1 and the rod 8 without affecting the Y-axis magnetic field. The at least two tuning capacitors for adjusting the center frequency of the X-axis magnetic field are positioned between the rod 2 and the rod 3 of the lower part, and the rod 6 and the lower part of the lower part to adjust the center frequency of the X-axis magnetic field. The second tuning capacitor is located between the rods 7. The capacitors C _H used for each rod are all the same value. In addition, the spherical chest coil of the present invention is provided with ground breakers (12, 14) to eliminate the signal interference caused by the ground loop (ground loop). The signals detected by the X-axis magnetic field and the Y-axis magnetic field whose center frequency is adjusted are input to ground breakers 12 and 14, respectively. The ground breakers 12 and 14 are for preventing ground loops that may be caused by the length of the coaxial cable used to receive a signal. The ground circuit breakers 12 and 14 eliminate the signal interference caused by the ground loop by causing a resonance value by giving a capacitor value according to the inductance value generated by winding the coaxial cable. Coupler 16 synthesizes two signals applied from ground breakers 12 and 14. That is, since the signal generated in the X-axis and Y-axis magnetic field has a phase difference of 90 °, the coupler 16 synthesizes this and outputs the synthesized RF signal. In addition, the detuning circuits 21 to 28 connected to the upper portion of the coil of the present invention are a kind of switching circuit that operates as a reception-only mode circuit. This detuning circuit consists of an inductor (L) and a diode.

As shown in FIG. 1, when the current is simultaneously supplied to both terminals of X and Y, the direction and intensity of the current as shown in FIGS. 2A and 2B are formed. As a result, the X-axis magnetic field and the Y-axis magnetic field are formed, so that a spherical magnetic field is formed at the center of the coil. According to Lenz's law, a magnetic field is formed in the direction perpendicular to the current direction. In the figure, the direction indicated by the arrow indicates the direction of the current, and the length indicates the strength of the magnetic field. Figure 2a shows the shape to create the X-axis magnetic field. In general, the horizontal plane is called the X-axis, so the middle four rods have the same direction of current in order to create a magnetic field along the horizontal axis, and the remaining two first, seventh, and eighth rods have four centers (3, 4, 5). 6 rod), and the current must be supplied with the opposite polarity. Figure 2b is a shape to create a Y-axis magnetic field. If the vertical axis is referred to as the Y axis, the first, second, third, and fourth rods and the fifth, sixth, seventh, and eighth rods may have opposite polarities to create a magnetic field. Such a current supply can form a desired Y-axis magnetic field.

FIG. 3 conceptually illustrates forming X and Y magnetic fields in a phantom. In the case of using the phantom manufactured to have a structure similar to the chest of the human body before the actual clinical experiment, the horizontal plane becomes X and the vertical plane becomes Y axis, and magnetic fields of X and Y axes are independently formed as shown in the drawing.

As described above, the present invention relates to a coil for chest imaging of an MRI apparatus, and constitutes a ladder-shaped coil in which a cage coil is modified among RF coils commonly used in an MRI apparatus. Chest imaging coil of the present invention is deformed in the hemispherical shape of one side of the cage coil so that the X, Y axis magnetic field is formed uniformly, so that the rods and condensers are arranged, all the capacitors at equal intervals It is arranged and equipped with a tuning capacitor that can adjust the center frequency of the X, Y axis magnetic field. The apparatus of the present invention has the effect of improving the signal-to-noise ratio (SNR) by constructing the chest capturing coil configured as described above, and adjusting the tuning capacitor to uniformly form the X and Y axis magnetic fields.

Claims (7)

In a breast coil for magnetic resonance imaging (MRI) imaging, It is composed of 8 rods in a hemispherical shape with one side of the cage coil open so that the X- and Y-axis magnetic fields are uniformly formed. A spherical chest coil, characterized in that for connecting and detecting the signals generated from the inspection object separated by the X, Y axis magnetic field, respectively. The spherical chest coil of claim 1, wherein the rod is a winding disposed at equal intervals to create an orthogonal field. The spherical chest coil according to claim 1, wherein the chest coil has a ladder shape connected to open the first rod and the eighth rod of the upper portion. The spherical chest coil of claim 1, wherein the values of the capacitors used in each of the rods are the same. According to claim 3, wherein the chest coil has at least three tuning capacitors for tuning the center frequency, of which at least two are for adjusting the center frequency of the X-axis magnetic field, at least one of the Y-axis magnetic field Spherical chest coil, characterized in that for adjusting the center frequency. 6. The method of claim 5, wherein at least one tuning capacitor (˜C _H ) is positioned between the third and sixth rods of the upper coil portion for adjusting the center frequency of the Y axis magnetic field, and for adjusting the center frequency of the X axis magnetic field. A spherical chest coil, characterized in that at least two tuning capacitors (˜C _H ) are connected between the first and eighth rods in the lower coil portion. 7. The apparatus of claim 6, wherein the at least two tuning capacitors for adjusting the center frequency of the X-axis magnetic field are positioned between the second and third rods of the lower portion to adjust the center frequency of the X-axis magnetic field. And a second tuning capacitor located between the sixth and seventh rods of the lower portion.