KR20140071856A - Method and apparatus for acquiring b1 information - Google Patents

Abstract

An MRI system including multiple radio frequency (RF) coil elements, in a method for acquiring information related to a magnetic field (B1) formed by RF pulses applied to a target object via at least one coil element among the RF coil elements, acquires initial information on the B1 formed by each of the RF coil elements, and acquires secondary information on the B1 formed by a combination of two or more of the RF coil elements, and acquires a third set of information on the B1 by combining the initial information acquired with the secondary information acquired.

Description

METHOD AND APPARATUS FOR ACQUIRING B1 INFORMATION

The present invention relates to a method and apparatus for obtaining information on a magnetic field (B1) generated by an RF pulse in an MRI system, and more particularly, to a method and an apparatus for obtaining information on a B1 formed by a combination of two or more RF coils And a technique for acquiring a B1 map in consideration of information.

The MRI (Magnetic Resonance Imaging) device is noninvasive, has superior contrast of the tissue as compared with the CT device, and has no advantage of artifact caused by the bone tissue. In addition, the MRI system is widely used because it can capture various cross sections according to a desired direction without changing the position of the object.

The MRI apparatus generates an MR image (Magnetic Resonance image) by using a characteristic difference between tissues of an object. That is, the MRI apparatus reflects a difference in magnetic resonance characteristics between tissues of a subject to the MR image, thereby enabling the examinee to easily distinguish the tissues from the MR image.

The uniformity of the magnetic field B1 generated by an RF (Radio Frequency) pulse in the MRI apparatus affects the uniformity of the MR image. Therefore, a technique called B1 shimming is used to increase the uniformity of the magnetic field B1 formed by the RF pulse. The B1 shimming may include a technique of increasing the uniformity of B1 by driving each coil element included in the RF transmission coil including a plurality of coil elements not in one circuit structure with driving signals having different sizes and phases . In order to perform the B1 shimming, the spatial distribution of B1 must be measured in advance, which is generally referred to as B1 mapping.

On the other hand, the magnetic field B1 generated by the RF pulse can be decomposed into a transmitting RF magnetic field B1 + component rotating clockwise and a receiving RF magnetic field B1- component rotating counterclockwise. Among these two magnetic field components, the B1 + magnetic field causes a nuclear magnetic resonance phenomenon on the magnetization vector, so that the magnetization vector lies on the transverse plane.

When the magnetization vector lies on the transverse plane, the magnetization vector rotates at the Larmor frequency in the transverse plane, and the rotation of the magnetization vector generates the electromotive force at the receiving RF coil by the Faraday's law. At this time, the MR signal received by the receiving RF coil is affected by the B1-magnetic field formed by the receiving RF coil.

That is, in the MRI system, B1 + formed by the transmission RF coil in the RF signal transmission mode and B1- formed by the reception RF coil in the RF signal reception mode contribute to the MR signal formation.

The transmitted RF magnetic field (B1 +) is a magnetic field that substantially causes magnetic resonance by rotating the magnetization vector of at least one kind of nucleus included in the object from the direction of the main magnetic field when the RF pulse is applied to the object through the RF coil in the MRI system .

Therefore, in order to obtain a high-quality MR image in the MRI system, it is required to suppress the formation of B1- as much as possible and to form B1 + firmly. Further, in order to form a uniform B1 +, it is required to accurately measure the spatial distribution of the magnitude and phase of B1 +.

The present invention provides a B1 information acquisition method and apparatus capable of acquiring a phase distribution of B1 + formed in a target object by applying an RF pulse to a target object via an RF coil.

In an MRI system including a plurality of RF (Radio Frequency) coil elements according to an embodiment of the present invention, RF pulses applied to a target object through at least one coil element of the plurality of RF coil elements A method of acquiring information associated with a magnetic field (B1) comprises: acquiring first information on B1 formed by each of the plurality of RF coil elements; Obtaining second information on B1 formed by a combination of two or more of the plurality of RF coil elements; And acquiring third information on the B1 by combining the obtained first information and the obtained second information.

According to an embodiment of the present invention, the step of acquiring the third information may further comprise the step of acquiring, from the first information, the transmission RF magnetic field B1 + from which the phase information of the reception RF magnetic field B1- is removed And acquiring the phase information for the first time. At this time, the transmitted RF magnetic field B1 + may be a magnetic field component that is magnetized by the main magnetic field of the MRI system and rotates in the same direction as the direction of rotation of the magnetization vector of at least one kind of nuclei included in the object.

The method of acquiring B1 information according to an embodiment of the present invention may further include acquiring phase information on the received RF magnetic field B1- by combining the obtained first information and the obtained second information . At this time, the reception RF magnetic field B1- may be a magnetic field component rotating in the direction opposite to B1 +.

The step of acquiring B1 information formed by each of the plurality of RF coil elements comprises the steps of: (a) acquiring first information on B1 formed by each of the plurality of RF coil elements, Selecting a coil element; (b) applying the RF pulse toward the object through a selected RF coil element; And (c) obtaining the first information based on a response signal received from the object, wherein steps (a) through (c) may be performed on each of the plurality of RF coil elements.

The first information according to an embodiment of the present invention may include phase information of a transmission RF magnetic field B1 + formed by each of the plurality of RF coil elements and phase information of a reception RF magnetic field B1- .

The obtaining of the second information on B1 formed by combining two or more of the plurality of RF coil elements according to an embodiment of the present invention may include obtaining RF pulses toward a target object by using two of the plurality of RF coil elements Applying simultaneously through the above combination; And obtaining the second information based on a response signal received from the object.

The step of acquiring second information on B1 formed by combining two or more of the plurality of RF coil elements according to an embodiment of the present invention may include obtaining information on B1 formed by simultaneously driving all of the plurality of RF coil elements And acquiring second information.

The second information according to an embodiment of the present invention may include at least one of phase information of a transmission RF magnetic field (B1 +) formed by combining two or more of the plurality of RF coil elements and a combination of two or more of the plurality of RF coil elements And the phase information of the reception RF magnetic field B1- formed by the RF magnetic field B1-.

The MRI system according to an embodiment of the present invention may be an MRI system using a high magnetic field of 3 Tesla or more.

Meanwhile, in an MRI system including a plurality of RF (Radio Frequency) coil elements according to an embodiment of the present invention, RF pulses applied to a target object through at least one coil element of the plurality of RF coil elements The apparatus for acquiring information related to the magnetic field B1 includes a control unit for controlling the plurality of RF coil elements, A first information obtaining unit obtaining information; A second information obtaining unit for obtaining second information on B1 formed by combining two or more of the plurality of RF coil elements; And a third information obtaining unit that obtains third information on the B1 by combining the obtained first information and the obtained second information.

The third information obtaining unit according to an embodiment of the present invention uses the second information to detect a phase (phase) of a phase of the RF magnetic field B1- from the first information, Information can be obtained.

The control unit according to an embodiment of the present invention may further include a B1-information obtaining unit that obtains phase information on the receiving RF magnetic field B1- by combining the obtained first information and the obtained second information .

A first information obtaining unit according to an embodiment of the present invention includes: a selecting unit for selecting one of the plurality of RF coil elements; An RF pulse applying unit for applying the RF pulse toward the target object through the selected RF coil device; A receiving unit for receiving a response signal from the object; And a processing unit for obtaining the first information based on the response signal received for each of the plurality of RF coil elements.

The first information according to an embodiment of the present invention may include phase information of a transmission RF magnetic field B1 + formed by each of a plurality of RF coil elements and phase information of a reception RF magnetic field B1-.

The second information obtaining unit according to an embodiment of the present invention may include an RF pulse applying unit for simultaneously applying the RF pulse toward the target object through a combination of two or more of the plurality of RF coil elements; A receiving unit for receiving a response signal from the object; And a processing unit for obtaining the second information based on the response signal.

The second information obtaining unit according to an embodiment of the present invention can obtain the second information formed by simultaneously driving all of the plurality of RF coil elements.

The second information according to an embodiment of the present invention includes phase information of a transmission RF magnetic field B1 + formed by combining two or more of the plurality of RF coil elements and phase information of a reception RF magnetic field B1- .

Meanwhile, a computer-readable recording medium according to an embodiment of the present invention may record a program for implementing the above-described B1 information acquisition method.

According to the present invention, it is possible to accurately obtain the B1 map formed on the object in the MRI system including a plurality of RF coil elements.

The present invention may be readily understood by reference to the following detailed description and the accompanying drawings, in which reference numerals refer to structural elements.
1 is a view for explaining an MRI system.
2 is a block diagram of a B1 information acquisition apparatus according to an embodiment of the present invention.
3 is a flowchart of a method of acquiring B1 information according to an embodiment of the present invention.
4 is a flowchart for explaining a step of acquiring first information on B1 in the B1 information acquiring method according to an embodiment of the present invention.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Also, in certain cases, there may be a term selected arbitrarily by the applicant, in which case the meaning thereof will be described in detail in the description of the corresponding invention. Therefore, the term used in the present invention should be defined based on the meaning of the term, not on the name of a simple term, but on the entire contents of the present invention.

When an element is referred to as "including" an element throughout the specification, it is to be understood that the element may include other elements, without departing from the spirit or scope of the present invention. Furthermore, the term "part" or the like described in the specification means a unit for processing at least one function or operation, which may be implemented by hardware or software, or a combination of hardware and software.

Throughout the specification, the term "subject" may be a specific site in various organs, bodies, or animals within the body or animal. In addition, the object may be a phantom, and a phantom means a material having a volume very close to the biological density and the effective atomic number. For example, a phantom can be a sphere-like water phantom with a body-like nature.

Throughout the specification, the term "user" may be a physician, nurse, clinician, medical imaging expert, etc. as a medical professional and may be, but not limited to, a technician repairing a medical device.

Throughout the specification, the term "pulse sequence" means a series of signals repeatedly applied in an MRI system. The pulse sequence may include a time parameter of the RF pulse, for example, a Repetition Time (TR) and a Time to Echo (TE).

Throughout the specification, the "pulse sequence diagram" describes the sequence of events occurring within the MRI system. For example, the pulse sequence schematic diagram may be a schematic diagram showing at least one of an RF pulse, a gradient magnetic field, and an echo RF signal over time.

FIG. 1 is a view for explaining an MRI system 100. FIG.

Referring to FIG. 1, the object 105 is inspected by a cylindrical gantry in a shielded room where an external RF signal is shielded. In the gantry, a main magnetic field 10 is applied to a main magnetic field B0, And a magnetic field gradient pulse is transmitted by a gradient coil 20 to form a magnetic gradient field.

When the main magnetic field B0 is formed outside the object, atomic nuclei in the object undergo car wash motion along the direction of the main magnetic field B0. The frequency of this oscillatory motion, that is, the resonance frequency, is proportional to the intensity of the main magnetic field B0 according to the Lamor equation. At this time, the proportional constant is called a gyromagnetic ratio.

When an electromagnetic wave having the same frequency as that of the resonance frequency is applied to an atomic nucleus performing a car wash motion, the atomic nucleus causes a resonance phenomenon so that the magnetization vector of the atomic nucleus lies in a direction perpendicular to the main magnetic field (B0) . That is, if an RF pulse having the same frequency as the resonance frequency is transmitted toward an atomic nucleus that carries out a kinetic motion at a resonance frequency, and then the transmission of the RF pulse is stopped, the atomic nucleus emits the energy absorbed from the RF pulse to the outside, A voltage signal is induced in the adjacent RF coil. This voltage signal is called a normal magnetic resonance signal.

Since the magnitude of the magnetic resonance signal is proportional to the magnitude of the magnetization vector and the magnitude of the magnetization vector is proportional to the intensity of the main magnetic field B0, the signal-to-noise ratio of the MR image increases as the intensity of the main magnetic field B0 increases. The MRI system 100 can acquire an MR image using an RF signal emitted from an atomic nucleus.

The RF coil 30 may be used to apply an electromagnetic wave to the object 105 to resonate the magnetization vector in the object 105 and to receive a magnetic resonance signal made by the lying magnetization vector in the vertical plane due to the resonance.

One RF coil may perform both transmission and reception of an RF signal, and an RF coil for transmission only and an RF coil for reception may perform transmission and reception of RF signals, respectively.

Since the transmitting coil is generally installed in the gantry of the MRI system 100, it can be made on a cylindrical frame of a size that allows the human body to enter. On the other hand, in many cases, the receiving coil is attached to the object 105 and used. Therefore, when the target object 105 is a human body, it is generally made according to the shape of a human body such as a head coil, a neck coil, and a waist coil.

The RF coil 30 receives an RF signal generated from a predetermined portion of the object 105 and transmits the RF signal to a central control unit 50 of an operating room separate from the shield room. To the MR image. At this time, a weak magnetic field generated by the RF pulse, for example, a magnetic field having an intensity of about 50 mT is referred to as B1.

Three types of magnetic fields are needed to create magnetic resonance imaging. First, the main magnetic field is needed to magnetize atoms such as hydrogen, phosphorus, and sodium, which cause magnetic resonance among the elements distributed in the human body. Secondly, a spatially linear oblique magnetic field is required. Third, an RF magnetic field, B1, is required to lay down the magnetization vector of the atomized nucleus magnetized to produce the MR image signal on the transverse plane. RF coil 30 can be used to make this B1.

The uniformity of B1 in the MRI system affects the uniformity of MR images. Therefore, a technique called B1 shimming is used to increase the uniformity of the magnetic field B1 formed by the RF pulse.

The B1 shimming uses a plurality of independent coil elements to form a phased array structure without making the RF transmission coil into a single circuit structure. Then, by driving each small coil element with a driving signal having its own size and phase, This is a technique for increasing the uniformity of the high-frequency magnetic field. In order to perform B1 shimming, the distribution of the magnetic field formed by the coil element must be measured in advance when a single phased array coil element is driven by a unit current, which is generally referred to as B1 mapping.

In order to measure the spatial distribution of B1, not only the size distribution of B1 but also the phase distribution should be measured. In the B1 shimming, it is necessary to control the phase as well as the magnitude of the high-frequency current for driving the RF coil element. The sum of the magnetic fields produced by the respective coil elements can be spatially uniform as they are added to or subtracted from each other depending on the phase of the high frequency current flowing through each of the coil elements.

On the other hand, the magnetic field B1 formed by the RF pulse can be decomposed into a transmitting RF magnetic field (B1 +) component and a receiving RF magnetic field (B1-) component. B1 + is a magnetic field component that is magnetized by the main magnetic field of the MRI system and rotates in the same direction as the magnetization vector of at least one kind of nuclei (for example, hydrogen, sodium, phosphorus, etc.) . B1- may be a magnetic field component rotating in the opposite direction of B1 +. In other words, if B1 + is a magnetic field that rotates the magnetization vector in the positive direction, B1- is a magnetic field that rotates the magnetization vector in the negative direction opposite to B1 +. For example, if the direction in which the hydrogen atom magnetization vector rotates with respect to the main magnetic field is a positive direction, the opposite direction may be a negative direction.

In a low magnetic field MRI system, the magnitude and phase of B1 + and B1- are almost the same, but in a high magnetic field MRI system of 3T or more, the magnitude and phase of B1 + and B1- may be greatly different from each other.

When an RF pulse is applied to the object through the RF coil, not only B1 + but also B1- is formed in the object. At this time, since B1- does not play a role in causing magnetic resonance phenomenon, it is required to suppress the formation of B1- as much as possible and to form B1 + firmly.

As a method for suppressing the formation of B1- and maximizing B1 +, there is a quadrature driving method in which two RF transmission coils are driven with a phase difference of 90 degrees. For example, one RF transmit coil may be driven with a current waveform of cos? T, and the other RF transmit coil may be driven with a current waveform of sin? T.

In the case of quadrature driving, theoretically B1 + can be formed, and the transmission power to the RF coil can be reduced to 1/2. However, in high-field MRI systems of 3T or more, the result of quadrature drive differs from the theoretical value.

On the other hand, according to the B1 shimming, the magnitude and the phase of the current applied to the respective coil elements can be freely controlled to form B1 + which is more uniform than the quadrature drive.

When the RF pulse is applied to the human body, the wavelength of the RF pulse is very short due to the high permittivity of water molecules. Therefore, the phase of B1 + magnetic field can be greatly changed depending on the position on the object. Therefore, in order to achieve effective B1 shimming, the size of B1 + as well as the distribution of phase must be accurately measured.

If the phase distribution of B1 + is known, the distribution of electrical conductivity in the human body can be calculated. B1 causes magnetic resonance in the human body, but at the same time causes heat to accumulate in the human body. The heat accumulated in the body by B1 can destroy the cells thermally, which is very harmful to the patient.

Heat accumulation in the human body by B1 is greatly influenced not only by B1 but also by the electrical conductivity of the human body. Therefore, in order to predict the accumulation of heat in the body by B1, it is very important to know the electric conductivity distribution in the human body. Knowing the electrical conductivity distribution in the body from the phase distribution information of B1 + can predict the heat distribution accumulated in the patient's body during MR imaging.

When phase preserving image reconstruction is performed from the MR image signal, the phase φ of B1 corresponding to one pixel in the MR image is the sum of the phase φ B1 + of B1 + and the phase φ B1- of B1- . That is, the phase? Of B1 satisfies the following formula (1).

At this time, assuming that the phase of B1 + is the same as the phase of B1 -, the phase of B1 + ( _{B1 B1 +} ) can be derived from the phase of B1 as shown in the following equation (2).

In the low-field MRI system of 1.5 T or less, since it can be assumed that the phase of B1 + and the phase of B1- are almost the same, there is no large error even when [Equation 2] is applied. However, in the case of a high-field MRI system of 3T or more, when [Equation 2] is applied, a large error occurs. In particular, when imaging the abdomen or chest having a size larger than that of the head, a large error may occur when the phase distribution of B1 + is obtained through the expression (2).

Therefore, the B1 + phase information obtained by the B1 information acquiring method according to an embodiment of the present invention includes the B1 shimming for improving the spatial uniformity of B1 + and the EPT (Electrical Property Tomography) for obtaining the electric conductivity distribution in the human body as an image Can be used.

RF transmit coils can form both B1 + and B1-, but only B1 + causes nuclear magnetic resonance to the RF nucleus applied from the RF transmit coil, causing the magnetization vector of the nucleus to lie on the transverse plane. When the magnetization vector lies on the transverse plane, the magnetization vector rotates at the resonance frequency in the transverse plane, and the rotation of the magnetization vector generates the electromotive force at the RF receiving coil by the Faraday's law.

At this time, the MR signal received at the RF receiving coil is affected by B1- formed by the RF receiving coil. That is, in the transmission mode in which the RF pulse is applied to the object, the B1 + component of the RF transmission coil and in the reception mode in which the response signal is received from the object, the B1 component of the RF reception coil contributes to the formation of the MR signal. The signal received by the RF receiving coil is amplified by an RF amplifier and then demodulated with a sinusoidal wave of a Lamor frequency to obtain a baseband MR signal. A computer receiving the baseband MR signal processes the MR signal to obtain an MR image.

The spatial uniformity of B1 + formed by the RF transmit coil is important because it directly affects the uniformity of the MR image. That is, the brightness of a specific pixel in the MR image is affected by a declination angle of the magnetization vector at a position on the object corresponding to the pixel, and the declination angle of the magnetization vector is proportional to the magnitude of B1 +.

In order to form a uniform B1 +, it is important to design the shape of the RF coil. For example, birdcage RF coils, which are widely used as RF transmit coils, are created such that several wires making up a high frequency magnetic field are arranged at an equal angle on a cylindrical frame and these wires are coupled to a capacitor. Cage-type RF coils can produce very uniform B1. However, in a high magnetic field of 3T or more, the uniformity of B1 may be deteriorated by the object to be imaged of the MR image. Therefore, in a high-field MRI system of 3T or more, the B1 shimming can be performed using a phased array coil composed of a plurality of coil elements to increase the uniformity of B1.

The phased array coil is composed of a plurality of coil elements. Each coil element can take various forms. For example, the coil element may have a micro-strip line shape or a planar loop shape. Each coil element is designed to be capable of independent driving and is designed to minimize the electrical and magnetic coupling between the coil elements. If there is an electrical or magnetic coupling between the coil elements, adjacent coil elements are also driven when one of the coil elements is driven. The current driving each coil element oscillates at a ramore frequency and can be independently controlled to have different magnitudes and phases. The magnitude and phase of the current applied to the coil element can be controlled using a numerically controlled oscillator.

For an effective B1 shimming, a spatial distribution of the magnitude and phase of B1 + formed by each transmitting coil element is required. Therefore, there is a need for a method for accurately obtaining not only the size of B1 + but also the phase distribution. However, conventionally, the phase of B1 + and the phase of B1- can not be discriminated from the phase of the MR signal which is the sum of the phase of B1 + and the phase of B1-. According to the present invention, the phase distribution of B1 + can be obtained.

2 is a block diagram of a B1 information acquisition apparatus according to an embodiment of the present invention.

The B1 information acquisition apparatus 200 according to an embodiment of the present invention may be a device physically separated from the MRI system 100 capable of providing an MR image for a target object by using nuclear magnetic resonance, have.

2, the B1 information obtaining apparatus 200 according to an embodiment of the present invention may include a plurality of RF coil elements 210 and a controller 220. [ However, the B1 information obtaining apparatus 200 may be implemented by a larger number of components than the illustrated components, and the B1 information obtaining apparatus 200 may be implemented by fewer components.

A plurality of RF coil elements 210 may apply an RF pulse to a target object. At this time, the RF pulse applied to the object may be generated based on the input of the user or based on the RF pulse information stored in the memory (not shown) or on the basis of the command of the control unit 220 and applied to the object. In addition, the plurality of RF coil elements 210 can receive a response signal corresponding to the RF pulse from the object. The plurality of RF coil elements 210 may include a transmitting coil element and / or a receiving coil element and / or a transmitting / receiving coil element.

The control unit 220 can control the overall operation of the B1 information obtaining apparatus 200. [ For example, the control unit 220 can individually control a plurality of RF coil elements 210 by executing programs stored in a memory (not shown). Furthermore, the control unit 220 can control the overall operation of the MRI system 100.

The control unit 220 may include a first information obtaining unit 222, a second information obtaining unit 224, and a third information obtaining unit 226. The first information obtaining unit 222 may obtain first information on B1 formed by driving each of the plurality of RF coil elements 210. [

The second information obtaining unit 224 may obtain second information on B1 formed by combining two or more of the plurality of RF coil elements 210. [

The third information obtaining unit 226 combines the first information obtained by the first information obtaining unit 222 and the second information obtained by the second information obtaining unit 224 to obtain a plurality of RF coil elements 210). ≪ / RTI > The third information acquiring unit 226 may acquire, as the third information, phase information on a transmission RF magnetic field formed by at least one of the plurality of RF coil elements 210. For example, the third information obtaining unit may obtain phase information on the transmission RF magnetic field (B1 +) from which the phase information on the reception RF magnetic field B1- is removed from the first information using the second information as the third information Can be obtained.

The control unit 220 according to an embodiment of the present invention may generate and provide a B1 map indicating the spatial distribution of B1 with respect to the object based on the obtained B1 information. The B1 map may include an image in which the magnitude or phase distribution of the magnetic field formed in the object by the RF pulse is expressed in hue or contrast.

Hereinafter, a method of acquiring B1 information using the above-described configuration of the B1 information acquiring apparatus 200 shown in FIG. 2 will be described in detail with reference to FIG.

3 is a flowchart of a method of acquiring B1 information according to an embodiment of the present invention.

According to an embodiment of the present invention, information related to the magnetic field B1 formed by the RF pulse in the MRI system 100 including a plurality of RF coil elements can be obtained. At this time, the MRI system 100 may be an MRI system using a high magnetic field of 3T or more.

The plurality of RF coil elements 210 included in the B1 information obtaining apparatus 200 according to an exemplary embodiment of the present invention can be designed to be independently driven.

For example, the magnitude and phase of the current driving the i-th RF coil element among the plurality of RF coil elements 210 may be defined as (ai, φi). When a current of cos ω o t is generated in a current source oscillating at a ramore frequency ωo, the i th RF coil element is driven by a control unit 220 whose magnitude and phase are controlled by the current ai cos (ω o t + φ i) .

First, in step S310, the B1 information obtaining apparatus 200 may obtain first information on B1 formed by each of the plurality of RF coil elements 210. [ At this time, the first information may be information related to the magnetic field formed by driving any one of the plurality of RF coil elements 210. [ For example, the first information acquired by the B1 information acquisition apparatus 200 may be generated by applying a predetermined RF pulse to a target object through one of the plurality of RF coil elements 210, May be information obtained based on the response signal. A method of driving any one of the plurality of RF coil elements 210 will be described below with reference to FIG.

4 is a flowchart for explaining a step of acquiring first information on B1 in the B1 information acquiring method according to an embodiment of the present invention.

In step S410, the B1 information obtaining apparatus 200 can select any RF coil element among the plurality of RF coil elements 210. [

In step S420, the B1 information obtaining apparatus 200 may apply a predetermined RF pulse toward the target object through the RF coil element selected in step S410.

In step S430, the B1 information obtaining apparatus 200 can obtain the first information on B1 based on the response signal received from the object.

Steps S410 to S430 are repeated for each RF coil included in the plurality of RF coil elements with respect to the RF coil. For example, steps S410 to S430 are performed for the first RF coil element of the N RF coil elements, and steps S410 to S430 are performed for the second RF coil element, respectively, for each of the N RF coil elements Steps S410 to S430 may be performed.

As a result, the B1 information obtaining apparatus 200 can obtain information on a plurality of magnetic fields formed by driving each of the plurality of RF coil elements as first information.

The response signal received for the applied RF pulse in step S310 may be received via at least one of the plurality of RF coil elements 210 or by a separate receiving coil. The first information may include phase information of a transmission RF magnetic field B1 + formed by each of the plurality of RF coil elements 210 and phase information of the reception RF magnetic field B1-.

For example, the B1 information obtaining apparatus 200 may include N RF coil elements. The B1 information acquisition apparatus 200 drives the i-th RF coil element among the N RF coil elements with a current of cos ω _o t and applies a zero-magnitude input to the remaining RF coil elements to generate a response signal generated from the object .

The B1 information acquisition apparatus 200 can generate the MR signal Si by amplifying the received response signal with a low noise amplifier (LNA). The B1 information obtaining apparatus 200 can obtain the MR image information Ii (x, y) from the generated Si by using the phase preservation image reconstruction method. At this time, the phase? _I (x, y) of the MR image information Ii (x, y) can be expressed by the following equation (3).

In Equation (3),? _{TX , i} (x, y) represents the phase distribution of B1 + formed by the i-th RF coil element, and? _RX (x, y) can represent the phase distribution of B1- produced by the receiving coil. At this time, φ _RX (x, y) is a phase value that is commonly included when the receiving coil receives the MR image signal regardless of which coil element of the plurality of RF coil elements 210 is driven.

The N phase distributions measured for each of the N RF coil elements can be represented by N [Equation 3]. For example, φ ₁ (x, y) is _{φ TX, 1 (x, y} ) + φ RX (x, y) is represented by, φ ₂ (x, y) is _{φ TX, 2 (x, y} ) + φ _RX (x, y) N-number of the phase distribution (φ ₁ (x, y) through φ _N (x, y)), as represented by a may be represented as the [equation 3].

One equation may be needed to obtain the phase component (e.g., N _{TX , i} (x, y) components and one? _RX (x, y) component) for each of the RF coil elements. (For example, N _{TX , i} (x, y) components and one? _RX (x, y) component) included in the total of N [Math Figure 3].

In other words, additional information is required to obtain each phase component (e.g., N _{TX , i} (x, y) components and one φ _RX (x, y) component). This additional information may be obtained at step 320.

In step S320, the B1 information obtaining apparatus 200 may obtain second information on Bl formed by combining two or more of the plurality of RF coil elements 210. [

For example, the second information may be information obtained based on an MR signal received for a predetermined pulse applied to a target object through two or more coil elements selected from a plurality of RF coil elements 210. For example, the second information may be information related to the magnetic field formed by simultaneously driving all of the plurality of RF coil elements 210. [ The second information may include phase information of a transmitting RF magnetic field B1 + formed by combining two or more of the plurality of RF coil elements 210 and phase information of a receiving RF magnetic field B1-.

를 동시에 인가할 수 있다. B1 정보 획득 장치 (200)는 수신된 응답 신호를 저잡음 증폭기로 증폭하여 MR 신호 S_total 을 생성하고, S_total 로부터 위상 보존 영상 재구성법을 이용하여 MR 영상 정보 I_total (x, y) 를 획득할 수 있다. 이 때, MR 영상 정보 I_total (x, y) 의 위상 φ_total (x, y) 는 다음의 [수학식 4] 로 표현될 수 있다.For example, in step S310, corresponding to the driving of the i-th RF coil element by the current of cos ω _o t,

Can be simultaneously applied. The B1 information acquisition apparatus 200 amplifies the received response signal with a low noise amplifier to generate an MR signal S _total and acquires the MR image information I _total (x, y) from the phase _total image reconstruction method from S _total . At this time, the phase? _Total (x, y) of the MR image information I _total (x, y) can be expressed by the following equation (4).

The formula _{4] φ TX, total (x} , y) in denotes the phase distribution of B1 + is formed by driving an N-number of RF coil elements at the same time, φ _RX (x, y) is the B1- making the receiving coil Phase distribution.

In step S330, the B1 information obtaining apparatus 200 may obtain the third information related to B1 using the first information and the second information obtained in step S310 and step S320. For example, the third information may include phase information for a transmitted RF magnetic field (B1 +) formed by at least one coil element of the plurality of RF coil elements 210. Step S330 may include combining the first information and the second information obtained in steps S310 and S320 and obtaining the phase information of B1 + and the phase information of B1- according to the combined result. At this time, "combination of information" may include a mathematical operation or the like.

The information obtained in step S330 may include phase information of B1 + formed by each of the plurality of RF coil elements 210. [ Further, the B1 information acquiring apparatus 200 can acquire more phase information for B1- by combining the first information and the second information obtained in steps S310 and S320. For example, the B1 information acquiring device 200 acquires the phase information on the transmission RF magnetic field B1 + from which the phase information on the reception RF magnetic field B1- is removed from the first information, using the second information 3 information.

For example, the following equation (5) can be derived from the magnitude-phase relationship of the measured B1 maps.

는 i 번째 RF 코일 소자만 cos ω_o t 로 구동했을 때 형성되는 B1+ 의 크기 분포를 나타낸다.

는 N 개의 RF 코일 소자를 모두

로 구동했을 때 형성되는 B1+ 의 크기 분포를 나타낸다.In the above equation (5)

Denotes the size distribution of B1 + formed when driven by the i-th RF coil element only cos ω _o t.

RTI ID = 0.0 > RF < / RTI &

≪ + >

(X, y), phi _{TX , N} (x, y) and phi _{TX , 1} (x, y) _RX (x, y) can be obtained. That is, the phase distribution of B1 + produced by the N transmission coil elements and the phase distribution of B1- produced by the reception coil can be obtained. In the above-described example, the B1 information obtaining apparatus 200 can obtain the phase distribution of B1 + produced by the N transmitting coil elements as the third information.

As described above, according to the B1 information acquisition method according to an embodiment of the present invention, B1 + phase information can be obtained. The obtained B1 + phase information can be used for B1 shimming for improving the spatial uniformity of B1 +, and Electrical Property Tomography (EPT) for obtaining an electric conductivity distribution in the human body as an image.

Further, the MRI system according to another embodiment of the present invention can obtain the B1 + map by the above-described methods, and perform the B1 shimming based on the obtained B1 + map. By controlling the high-frequency current driving the RF coil element based on the obtained B1 + map, the amplitude or phase of the high-frequency current can be adjusted until the desired B1 + map is obtained. For example, an MRI system can perform a B1 shimming such that B1 + is uniformly distributed on a subject. The method according to an embodiment of the present invention can be implemented in the form of a program command which can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the present invention or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

Claims (21)

In an MRI system including a plurality of RF (Radio Frequency) coil elements, information relating to a magnetic field (B1) formed by RF pulses applied to a target object through at least one coil element of the plurality of RF coil elements In the method,
Obtaining first information on B1 formed by each of the plurality of RF coil elements;
Obtaining second information on B1 formed by a combination of two or more of the plurality of RF coil elements; And
And acquiring third information on the B1 by combining the obtained first information and the obtained second information. The method according to claim 1,
Wherein the acquiring of the third information comprises:
Obtaining phase information on a transmission RF magnetic field (B1 +) from which phase information on a reception RF magnetic field (B1-) has been removed from the first information using the second information; Acquisition method. 3. The method of claim 2,
Wherein the transmission RF magnetic field B1 + is a magnetic field component magnetized by the main magnetic field of the MRI system and rotating in the same direction as the direction of rotation of the magnetization vector of at least one kind of nuclei included in the object How to obtain B1 information. The method of claim 3,
Further comprising obtaining phase information for the received RF magnetic field (B1-) by combining the obtained first information and the obtained second information,
Wherein the reception RF magnetic field (B1-) is a magnetic field component rotating in the direction opposite to B1 +. The method according to claim 1,
Wherein obtaining the first information on B1 formed by each of the plurality of RF coil elements comprises:
(a) selecting any RF coil element among the plurality of RF coil elements;
(b) applying the RF pulse toward the object through the selected RF coil element; And
(c) acquiring the first information based on a response signal received from the object,
Wherein the steps (a) to (c) are performed for each of the plurality of RF coil elements. The method according to claim 1,
Wherein the first information includes phase information of a transmission RF magnetic field (B1 +) formed by each of the plurality of RF coil elements and phase information of a reception RF magnetic field (B1-). The method according to claim 1,
Wherein acquiring second information on B1 formed by combining two or more of the plurality of RF coil elements comprises:
Simultaneously applying the RF pulse toward the target object through a combination of two or more of the plurality of RF coil elements; And
And acquiring the second information based on a response signal received from the object. The method according to claim 1,
Wherein acquiring second information on B1 formed by combining two or more of the plurality of RF coil elements comprises:
And acquiring second information on B1 formed by simultaneously driving all of the plurality of RF coil elements. The method according to claim 1,
Wherein the second information includes phase information of a transmitting RF magnetic field (B1 +) formed by combining two or more of the plurality of RF coil elements and phase information of a receiving RF magnetic field (B1-) Information acquisition method. The method according to claim 1,
Wherein the MRI system is an MRI system using a high magnetic field of 3 tesla or more. In an MRI system including a plurality of RF (Radio Frequency) coil elements, information relating to a magnetic field (B1) formed by RF pulses applied to a target object through at least one coil element of the plurality of RF coil elements The apparatus comprising:
And a controller for controlling the plurality of RF coil elements,
Wherein,
A first information obtaining unit obtaining first information on B1 formed by driving each of the plurality of RF coil elements;
A second information obtaining unit for obtaining second information on B1 formed by combining two or more of the plurality of RF coil elements; And
And a third information obtaining unit that obtains third information on the B1 by combining the obtained first information and the obtained second information. 12. The method of claim 11,
Wherein the third information obtaining unit comprises:
And obtains phase information on a transmitted RF magnetic field (B1 +) from which the phase information of the RF magnetic field (B1-) is removed from the first information using the second information. 13. The method of claim 12,
Wherein the transmission RF magnetic field B1 + is a magnetic field component magnetized by the main magnetic field of the MRI system and rotating in the same direction as the direction of rotation of the magnetization vector of at least one kind of nuclei included in the object B1 information acquisition device. 14. The method of claim 13,
Wherein,
Further comprising a B1-information obtaining section for obtaining phase information about the received RF magnetic field (B1-) by combining the obtained first information and the obtained second information,
Wherein the reception RF magnetic field (B1-) is a magnetic field component rotating in the direction opposite to B1 +. 12. The method of claim 11,
Wherein the first information obtaining unit comprises:
A selector for selecting one of the plurality of RF coil elements;
An RF pulse applying unit for applying the RF pulse toward the target object through the selected RF coil device;
A receiving unit for receiving a response signal from the object; And
And a processing unit for obtaining the first information based on the response signal received for each of the plurality of RF coil elements. 12. The method of claim 11,
Wherein the first information includes phase information of a transmission RF magnetic field (B1 +) formed by each of the plurality of RF coil elements and phase information of a reception RF magnetic field (B1-). 12. The method of claim 11,
Wherein the second information obtaining unit comprises:
An RF pulse applying unit for simultaneously applying the RF pulse toward the target object through a combination of two or more of the plurality of RF coil elements;
A receiving unit for receiving a response signal from the object; And
And a processing unit for acquiring the second information based on the response signal. 12. The method of claim 11,
Wherein the second information obtaining unit comprises:
And obtains second information on B1 formed by simultaneously driving all of the plurality of RF coil elements. 12. The method of claim 11,
Wherein the second information includes phase information of a transmitting RF magnetic field (B1 +) formed by combining two or more of the plurality of RF coil elements and phase information of a receiving RF magnetic field (B1-) Information acquisition device. 12. The method of claim 11,
Wherein the MRI system is an MRI system using a high magnetic field of 3 tesla or more. A computer-readable recording medium on which a program for implementing the B1 information obtaining method of claim 1 is recorded.

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