Patent Application
20190018097
The present disclosure relates to a magnetic resonance imaging (MRI) apparatus and a magnetic resonance (MR) image acquisition method thereof, and more particularly, to an MRI apparatus for acquiring MR images by simultaneously acquiring MR signals of a plurality of slices.
Magnetic resonance imaging (MRI) refers to a process of producing an image by using information that is obtained through resonance after an atomic nucleus is exposed to a magnetic field. Resonance of an atomic nucleus refers to a phenomenon whereby, when a specific high-frequency wave enters an atomic nucleus magnetized by an external magnetic field, the atomic nucleus in a low energy state absorbs high-frequency energy and is excited to a high energy state. Atomic nuclei have different resonance frequencies depending on their types, and resonance is affected by the intensity of an external magnetic field. There are innumerous atomic nuclei in a human body, and hydrogen atomic nuclei are generally used for MRI.
When magnetic resonance (MR) images are acquired, there is a demand for technologies of processing MR images in a short time.
When information about a three-dimensional (3D) volume of an object is to be obtained in a short time, a method of acquiring a plurality of two-dimensional (2D) slice images in a direction of slices constituting the 3D volume is used. In this case, it is common to capture as many 2D slice images as the number of the slices.
In a multi-slice method, when each 2D slice image is acquired in a plurality of repetition time (TR) periods, an imaging time is reduced by alternately acquiring data about each 2D slice in the same TR period. That is, there exists a dead time when a TR period is much longer than an active time required for slice selection, phase encoding, and frequency encoding. In order to obtain information about another slice, the dead time may be used.
In parallel imaging, in order to reduce a scan time, a plurality of 2D slices are simultaneously excited to simultaneously acquire MR signals, through a plurality of coils, from the plurality of 2D slices, and the MR signals for the 2D slices are separated by using a difference in coil sensitivity information between the 2D slices. A 2D encoding method was used in conventional parallel imaging. The parallel imaging may correspond to a simultaneous multi-slice method. Representative examples of the parallel imaging include a sensitivity encoding (SENSE) method and a generalized autocalibrating partially parallel acquisition (GRAPPA) method.
Provided are a magnetic resonance imaging (MRI) apparatus and a magnetic resonance (MR) image acquisition method thereof that acquire MR images having a plurality of contrasts by simultaneously exciting a plurality of slices.
An MRI apparatus according to an embodiment includes: a controller configured to determine a first slice and a second slice so that a difference between a slice number of the first slice of an object and a slice number of the second slice is a predetermined interval value; and a radio frequency (RF) coil configured to transmit a preparation pulse signal including a frequency component enabling the first slice to be excited and transmit an RF signal including a plurality of frequency components so that both the first slice and the second slice are excited.
A magnetic resonance imaging (MRI) apparatus according to an embodiment includes: a controller configured to determine a first slice and a second slice so that a difference between a slice number of the first slice of an object and a slice number of the second slice of the object is a predetermined interval value; and a radio frequency (RF) coil configured to transmit a preparation pulse signal including a frequency component enabling the first slice to be excited and transmit an RF signal including a plurality of frequency components so that both the first slice and the second slice are excited.
Also, the controller may be further configured to determine the first slice and the second slice so that when the first slice is an even-numbered slice, the second slice is an odd-numbered slice, and when the first slice is an odd-numbered slice, the second slice is an even-numbered slice.
Also, the controller may be further configured to determine the first slice and the second slice so that the difference between the slice number of the first slice and the slice number of the second slice is half a total number of slices constituting the object.
Also, the RF coil may be further configured to receive magnetic resonance (MR) signals of the first slice and the second slice, wherein the MRI apparatus further includes an image processor configured to acquire an MR image having a first contrast for the first slice and an MR image having a second contrast for the second slice.
Also, the RF coil may be further configured to transmit an inverted RF pulse signal including a frequency component enabling the first slice to be excited.
Also, the image processor may be further configured to acquire a fluid-attenuated inversion recovery (FLAIR) image for the first slice and acquire at least one image from among a T1-weighted image and a T2-weighted image for the second slice.
Also, the image processor may be further configured to sequentially acquire images having the first contrast for a plurality of slices including the first slice, and simultaneously acquire images having the second contrast for slices respectively corresponding to the plurality of slices in a state where the images having the second contrast overlap the images having the first contrast, wherein a difference between a slice number of each of the corresponding slices and a slice number of each of the plurality of slices is the predetermined interval value.
Also, each of the images having the first contrast may be a FLAIR image, and each of the images having the second contrast may be a T1-weighted image or a T2-weighted image.
Also, the predetermined interval value may be a value obtained by dividing a total number of slices constituting the object by a multi-band acceleration factor.
A magnetic resonance imaging (MRI) method according to an embodiment includes: determining a first slice and a second slice of an object; transmitting a preparation pulse signal including a frequency component enabling the first slice to be excited; and transmitting a radio frequency (RF) signal including a plurality of frequency components so that both the first slice and the second slice are excited, wherein the determining includes determining the first slice and the second slice so that a difference between a slice number of the first slice and a slice number of the second slice is a predetermined interval value.
Also, the determining may include determining the first slice and the second slice so that when the first slice is an even-numbered slice, the second slice is an odd-numbered slice, and when the first slice is an odd-numbered slice, the second slice is an even-numbered slice.
Also, the determining may include determining the first slice and the second slice so that the difference between the slice number of the first slice and the slice number of the second slice is half a total number of slices constituting the object.
Also, the MRI method of claim 10 may further include: receiving magnetic resonance (MR) signals of the first slice and the second slice; and acquiring an MR image having a first contrast for the first slice and an MR image having a second contrast for the second slice.
Also, the transmitting of the preparation pulse signal may include transmitting an inverted RF pulse signal including a frequency component enabling the first slice to be excited.
Also, the acquiring may include: acquiring a fluid-attenuated inversion recovery (FLAIR) image for the first slice; and acquiring at least one image from among a T1-weighted image and a T2-weighted image for the second slice.
Also, the MRI method may further include sequentially acquiring images having the first contrast for a plurality of slices including the first slice, wherein the sequentially acquiring includes simultaneously acquiring images having the second contrast for slices respectively corresponding to the plurality of slices in a state where the images having the second contrast overlap the images having the first contrast, wherein a difference between a slice number of each of the corresponding slices and a slice number of each of the plurality of slices is the predetermined interval value.
Also, each of the images having the first contrast may be a FLAIR image, and each of the images having the second contrast may be a T1-weighted image or a T2-weighted image.
Also, the predetermined interval value may be a value obtained by dividing a total number of slices constituting the object by a multi-band acceleration factor.
There is provided a computer-readable recording medium having embodied thereon a program for executing the MRI method according to an embodiment.
Advantages and features of the present disclosure and methods of accomplishing the same may be understood more readily by reference to the following detailed description of embodiments and the accompanying drawings. However, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the present embodiments to one of ordinary skill in the art, and the present disclosure will only be defined by the appended claims.
Terms used herein will now be briefly described and then one or more embodiments will be described in detail.
The terms used in the present disclosure are selected from among common terms that are currently widely used in consideration of their functions in the present disclosure. However, the terms may vary according to the intention of one of ordinary skill in the art, a precedent, or the advent of new technology. Also, in particular cases, some terms are discretionally selected by the applicant, and in this case, the meaning of the selected terms will be described in detail in the detailed description of the disclosure. Thus, the terms used herein have to be defined based on the meaning of the terms together with the description throughout the specification.
When a part “includes” or “comprises” an element, unless there is a particular description contrary thereto, the part may further include other elements, not excluding the other elements. Also, the term “unit” in the embodiments of the present disclosure means a software component or hardware component such as a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), and performs a specific function. However, the term “unit” is not limited to software or hardware. The “unit” may be formed so as to be in an addressable storage medium, or may be formed so as to operate one or more processors. Thus, for example, the term “unit” may include any one or more of components such as software components, object-oriented software components, class components, and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, micro codes, circuits, data, a database, data structures, tables, arrays, and variables. Functions provided by the components and “units” may be combined into a smaller number of components and “units”, or may be divided into additional components and “units”.
Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings in order to enable one of ordinary skill in the art to easily embody and practice the present disclosure. Also, parts in the drawings unrelated to the detailed description are omitted to ensure clarity of the present disclosure.
In the present specification, an “image” may refer to multi-dimensional data composed of discrete image elements (e.g., pixels in a two-dimensional (2D) image and voxels in a three-dimensional (3D) image). For example, the image may include a medical image of an object captured by an X-ray apparatus, a computed tomography (CT) apparatus, a magnetic resonance imaging (MRI) apparatus, an ultrasound diagnosis apparatus, or another medical imaging apparatus.
Furthermore, in the present specification, an “object” may be a human, an animal, or a part of a human or an animal. For example, the object may include an organ (e.g., the liver, heart, womb, brain, breast, or abdomen), or a blood vessel. Furthermore, the “object” may be a phantom. The phantom means a material having a density, an effective atomic number, and a volume that are approximately the same as those of an organism. For example, the phantom may be a spherical phantom having properties similar to a physical body.
Furthermore, in the present specification, a “user” may be, but is not limited to, a medical expert such as a medical doctor, a nurse, a medical laboratory technologist, a medical imaging specialist, or a technician who repairs a medical apparatus.
Furthermore, in the present specification, an “MR image” refers to an image of an object acquired by using the nuclear magnetic resonance principle.
Furthermore, in the present specification, a “pulse sequence” refers to continuity of signals repeatedly applied by an MRI apparatus. The pulse sequence may include a time parameter of a radio frequency (RF) pulse, for example, repetition time (TR) or echo time (TE).
Furthermore, in the present specification, a “pulse sequence schematic diagram” shows an order of events that occur in an MRI apparatus. For example, the pulse sequence schematic diagram may be a diagram showing an RF pulse, a gradient magnetic field, an MR signal, or the like according to time.
Also, a “multi-band acceleration factor” may refer to the number of images to be simultaneously acquired in a single sequence. For example, when the multi-band acceleration factor is 2, a pulse sequence may include two frequency components. Accordingly, when the multi-band acceleration factor is 2, two MR images may be simultaneously acquired in an overlapping state.
An MRI system is an apparatus for acquiring a sectional image of a part of an object by expressing, in a contrast comparison, a strength of an MR signal with respect to an RF signal generated in a magnetic field having a specific strength. For example, if an RF signal that only resonates a specific atomic nucleus (for example, a hydrogen atomic nucleus) is emitted for an instant toward the object placed in a strong magnetic field and then such emission stops, an MR signal is emitted from the specific atomic nucleus, and thus the MRI system may receive the MR signal and acquire an MR image. The MR signal denotes an RF signal emitted from the object. An intensity of the MR signal may be determined according to a density of a predetermined atom (for example, hydrogen) of the object, a relaxation time T1, a relaxation time T2, and a flow of blood or the like.
MRI systems include characteristics different from those of other imaging apparatuses. Unlike imaging apparatuses such as CT apparatuses that acquire images according to a direction of detection hardware, MRI systems may acquire 2D images or 3D volume images that are oriented toward an optional point. MRI systems do not expose objects or examiners to radiation, unlike CT apparatuses, X-ray apparatuses, position emission tomography (PET) apparatuses, and single photon emission CT (SPECT) apparatuses, may acquire images having a high soft tissue contrast, and may acquire neurological images, intravascular images, musculoskeletal images, and oncologic images that are required to precisely capture abnormal tissues.
The gantry 20 prevents external emission of electromagnetic waves generated by a main magnet 22, a gradient coil 24, and an RF coil 26. A magnetostatic field and a gradient magnetic field are formed in a bore in the gantry 20, and an RF signal is emitted toward an object 10.
The main magnet 22, the gradient coil 24, and the RF coil 26 may be arranged in a predetermined direction of the gantry 20. The predetermined direction may be a coaxial cylinder direction. The object 10 may be disposed on a table 28 that is capable of being inserted into a cylinder along a horizontal axis of the cylinder.
The main magnet 22 generates a magnetostatic field or a static magnetic field for aligning magnetic dipole moments of atomic nuclei of the object 10 in a constant direction. A more precise and accurate MR image of the object 10 may be acquired as a magnetic field generated by the main magnet 22 is stronger and more uniform.
The gradient coil 24 includes X, Y, and Z coils for generating gradient magnetic fields in X-, Y-, and Z-axis directions crossing each other at right angles. The gradient coil 24 may provide location information of each region of the object 10 by differently inducing resonance frequencies according to the regions of the object 10.
The RF coil 26 may emit an RF signal toward a patient and receive an MR signal emitted from the patient. In detail, the RF coil 26 may transmit, toward atomic nuclei included in the patient and having precessional motion, an RF signal having the same frequency as that of the precessional motion, stop transmitting the RF signal, and then receive an MR signal emitted from the atomic nuclei included in the patient.
For example, in order to transit an atomic nucleus from a low energy state to a high energy state, the RF coil 26 may generate and apply an electromagnetic wave signal having an RF corresponding to a type of the atomic nucleus, for example, an RF signal, to the object 10. When the electromagnetic wave signal generated by the RF coil 26 is applied to the atomic nucleus, the atomic nucleus may transit from the low energy state to the high energy state. Then, when electromagnetic waves generated by the RF coil 26 disappear, the atomic nucleus to which the electromagnetic waves were applied transits from the high energy state to the low energy state, thereby emitting electromagnetic waves having a Lamor frequency. In other words, when the applying of the electromagnetic wave signal to the atomic nucleus is stopped, an energy level of the atomic nucleus is changed from a high energy level to a low energy level, and thus the atomic nucleus may emit electromagnetic waves having a Lamor frequency. The RF coil 26 may receive electromagnetic wave signals from atomic nuclei included in the object 10.
The RF coil 26 may be realized as one RF transmitting and receiving coil having both a function of generating electromagnetic waves having an RF corresponding to a type of an atomic nucleus and a function of receiving electromagnetic waves emitted from an atomic nucleus. Alternatively, the RF coil 26 may be realized as a transmission RF coil having a function of generating electromagnetic waves having an RF corresponding to a type of an atomic nucleus, and a reception RF coil having a function of receiving electromagnetic waves emitted from an atomic nucleus.
Also, the RF coil 26 may be fixed to the gantry 20 or may be detachable. When the RF coil 26 is detachable, the RF coil 26 may be an RF coil for a part of the object 10, such as a head RF coil, a chest RF coil, a leg RF coil, a neck RF coil, a shoulder RF coil, a wrist RF coil, or an ankle RF coil.
The RF coil 26 may communicate with an external apparatus via wires and/or wirelessly, and may also perform dual tune communication according to a communication frequency band.
Also, the RF coil 26 may be a birdcage coil, a surface coil, or a transverse electromagnetic (TEM) coil according to coil structures.
Also, the RF coil 26 may be a transmission exclusive coil, a reception exclusive coil, or a transmission and reception coil according to methods of transmitting and receiving an RF signal.
Also, the RF coil 26 may be an RF coil having various numbers of channels, such as 16 channels, 32 channels, 72 channels, or 144 channels.
The gantry 20 may further include a display 29 disposed outside the gantry 20 and a display (not shown) disposed inside the gantry 20. The gantry 20 may provide predetermined information to a user or the object 10 through the display 29 and the display respectively disposed outside and inside the gantry 20.
The signal transceiver 30 may control the gradient magnetic field formed inside the gantry 20, i.e., in the bore, according to a predetermined MR sequence, and control transmission and reception of an RF signal and an MR signal.
The signal transceiver 30 may include a gradient amplifier 32, a transmission and reception switch 34, an RF transmitter 36, and an RF receiver 38.
The gradient amplifier 32 drives the gradient coil 24 included in the gantry 20, and may supply a pulse signal for generating a gradient magnetic field to the gradient coil 24 under the control of a gradient magnetic field controller 54. By controlling the pulse signal supplied from the gradient amplifier 32 to the gradient coil 24, gradient magnetic fields in X-, Y-, and Z-axis directions may be synthesized.
The RF transmitter 36 and the RF receiver 38 may drive the RF coil 26. The RF transmitter 36 may supply an RF pulse in a Lamor frequency to the RF coil 26, and the RF receiver 38 may receive an MR signal received by the RF coil 26.
The transmission and reception switch 34 may adjust transmitting and receiving directions of the RF signal and the MR signal. For example, the transmission and reception switch 34 may emit the RF signal toward the object 10 through the RF coil 26 during a transmission mode, and receive the MR signal from the object 10 through the RF coil 26 during a reception mode. The transmission and reception switch 34 may be controlled by a control signal output by an RF controller 56.
The monitoring unit 40 may monitor or control the gantry 20 or devices mounted on the gantry 20. The monitoring unit 40 may include a system monitoring unit 42, an object monitoring unit 44, a table controller 46, and a display controller 48.
The system monitoring unit 42 may monitor and control a state of the magnetostatic field, a state of the gradient magnetic field, a state of the RF signal, a state of the RF coil 26, a state of the table 28, a state of a device for measuring body information of the object 10, a power supply state, a state of a thermal exchanger, and a state of a compressor.
The object monitoring unit 44 monitors a state of the object 10. In detail, the object monitoring unit 44 may include a camera for observing a movement or position of the object 10, a respiration measurer for measuring the respiration of the object 10, an electrocardiogram (ECG) measurer for measuring the electrical activity of the object 10, or a temperature measurer for measuring a temperature of the object 10.
The table controller 46 controls a movement of the table 28 where the object 10 is positioned. The table controller 46 may control the movement of the table 28 according to a sequence control of a sequence controller 52 comprised in the sequence control unit 50. For example, during moving imaging of the object 10, the table controller 46 may continuously or discontinuously move the table 28 according to the sequence control of the system control unit 50, and thus the object 10 may be imaged in a field of view (FOV) larger than that of the gantry 20.
The display controller 48 controls the display 29 disposed outside the gantry 20 and the display disposed inside the gantry 20. In detail, the display controller 48 may control the display 29 and the display to be on or off, and may control a screen image to be output on the display 29 and the display. Also, when a speaker is located inside or outside the gantry 20, the display controller 48 may control the speaker to be on or off, or may control sound to be output via the speaker.
The system control unit 50 may include a sequence controller 52 for controlling a sequence of signals formed in the gantry 20, and a gantry controller 58 for controlling the gantry 20 and the devices mounted on the gantry 20.
The sequence controller 52 may include the gradient magnetic field controller 54 for controlling the gradient amplifier 32, and the RF controller 56 for controlling the RF transmitter 36, the RF receiver 38, and the transmission and reception switch 34. The sequence controller 52 may control the gradient amplifier 32, the RF transmitter 36, the RF receiver 38, and the transmission and reception switch 34 according to a pulse sequence received from the operating unit 60. Here, the pulse sequence includes all information required to control the gradient amplifier 32, the RF transmitter 36, the RF receiver 38, and the transmission and reception switch 34. For example, the pulse sequence may include information about a strength, an application time, and application timing of a pulse signal applied to the gradient coil 24.
The operating unit 60 may request the system control unit 50 to transmit pulse sequence information while controlling an overall operation of the MRI system.
The operating unit 60 may include an image processor 62 for receiving and processing the MR signal received by the RF receiver 38, an output unit 64, and an input unit 66.
The image processor 62 may process the MR signal received from the RF receiver 38 so as to generate MR image data of the object 10.
The image processor 62 receives the MR signal received by the RF receiver 38 and performs any one of various signal processes, such as amplification, frequency transformation, phase detection, low frequency amplification, and filtering, on the received MR signal.
The image processor 62 may arrange digital data in a k-space (for example, also referred to as a Fourier space or a frequency space) of a memory, and rearrange the digital data into image data via 2D or 3D Fourier transformation.
Also, the image processor 62 may perform a composition process or a difference calculation process on the image data if required. The composition process may be an addition process performed on a pixel or a maximum intensity projection (MIP) process. The image processor 62 may store not only the rearranged image data but also image data on which a composition process or a difference calculation process is performed, in a memory (not shown) or an external server.
The image processor 62 may perform any of the signal processes on the MR signal in parallel. For example, the image processor 62 may perform a signal process on a plurality of MR signals received by a multi-channel RF coil in parallel so as to rearrange the plurality of MR signals into image data.
The output unit 64 may output image data generated or rearranged by the image processor 62 to the user. The output unit 64 may also output information required for the user to manipulate the MRI system, such as a user interface (UI), user information, or object information. The output unit 64 may be a speaker, a printer, a cathode-ray tube (CRT) display, a liquid crystal display (LCD), a plasma display panel (PDP) display, an organic light-emitting device (OLED) display, a field emission display (FED), a light-emitting diode (LED) display, a vacuum fluorescent display (VFD), a digital light processing (DLP) display, a flat panel display (FPD), a 3D display, a transparent display, or any one of other various output devices that are well known to one of ordinary skill in the art.
The user may input object information, parameter information, a scan condition, a pulse sequence, or information about image composition or difference calculation by using the input unit 66. The input unit 66 may be a keyboard, a mouse, a track ball, a voice recognizer, a gesture recognizer, a touch screen, or any one of other various input devices that are well known to one of ordinary skill in the art.
The signal transceiver 30, the monitoring unit 40, the system control unit 50, and the operating unit 60 are separate components in
The gantry 20, the RF coil 26, the signal transceiver 30, the monitoring unit 40, the system control unit 50, and the operating unit 60 may be connected to each other by wire or wirelessly, and when they are connected wirelessly, the MRI system may further include an apparatus (not shown) for synchronizing clock signals therebetween. Communication between the gantry 20, the RF coil 26, the signal transceiver 30, the monitoring unit 40, the system control unit 50, and the operating unit 60 may be performed by using a high-speed digital interface such as low voltage differential signaling (LVDS), asynchronous serial communication such as a universal asynchronous receiver transmitter (UART), a low-delay network protocol such as error synchronous serial communication or a controller area network (CAN), optical communication, or any of other various communication methods that are well known to one of ordinary skill in the art.
The communication unit 70 may transmit and receive data to and from a hospital server or another medical apparatus in a hospital, which is connected through a picture archiving and communication system (PACS), and perform data communication according to the digital imaging and communications in medicine (DICOM) standard.
As shown in
In detail, the communication unit 70 may transmit and receive data related to the diagnosis of an object through the network 80, and may also transmit and receive a medical image captured by the medical apparatus 94, such as a CT apparatus, an MRI apparatus, or an X-ray apparatus. In addition, the communication unit 70 may receive a diagnosis history or a treatment schedule of the object from the server 92 and use the same to diagnose the object. The communication unit 70 may perform data communication not only with the server 92 or the medical apparatus 94 in a hospital, but also with the portable device 96, such as a mobile phone, a personal digital assistant (PDA), or a laptop of a doctor or patient.
Also, the communication unit 70 may transmit information about a malfunction of the MRI system or about medical image quality to a user through the network 80, and receive a feedback regarding the information from the user.
The communication unit 70 may include at least one component enabling communication with an external apparatus. For example, the communication unit 70 may include a local area communication module 72, a wired communication module 74, and a wireless communication module 76.
The local area communication module 72 refers to a module for performing local area communication with an apparatus within a predetermined distance. Examples of local area communication technology according to an embodiment include, but are not limited to, a wireless local area network (LAN), Wi-Fi, Bluetooth, ZigBee, Wi-Fi direct (WFD), ultra wideband (UWB), infrared data association (IrDA), Bluetooth low energy (BLE), and near field communication (NFC).
The wired communication module 74 refers to a module for performing communication by using an electric signal or an optical signal. Examples of wired communication technology according to an embodiment include wired communication techniques using a twisted pair cable, a coaxial cable, and an optical fiber cable, and other well known wired communication techniques.
The wireless communication module 76 transmits and receives a wireless signal to and from at least one selected from a base station, an external apparatus, and a server in a mobile communication network. Here, the wireless signal may be a voice call signal, a video call signal, or data in any one of various formats according to transmission and reception of a text/multimedia message.
The controller 110 of
The controller 110 determines a first slice and a second slice so that a difference between a slice number of the first slice of an object and a slice number of the second slice of the object is a predetermined interval value.
In an embodiment, the first slice and the second slice are included in a plurality of slices of the object. The plurality of slices of the object may refer to two or more slices from among 2D slices constituting a volume of the object.
The predetermined interval value may be a value set to maintain constant an interval between the first slice and the second slice. In detail, the predetermined interval value may be a value set to maintain the interval between the first slice and the second slice at a predetermined distance or more.
For example, the predetermined interval value may be a value obtained by dividing a total number of slices constituting the object by a multi-band acceleration factor. For example, when the multi-band acceleration factor is 2, the predetermined interval value may be half the total number of the slices constituting the object.
The controller 110 may reduce the influence of a preparation pulse for the first slice on the second slice by maintaining the interval between the first slice and the second slice at the predetermined distance or more.
In an embodiment, when the first slice is an even-numbered slice, the second slice may be an odd-numbered slice, and when the first slice is an odd-numbered slice, the second slice may be an even-numbered slice.
The RF coil 120 transmits a preparation pulse signal including a frequency component that enables the first slice to be excited.
Also, the RF coil 120 transmits an RF signal including a plurality of frequency components so that both the first slice and the second slice are excited.
Excitation may refer to the transition to a high energy state of magnetized atomic nuclei by absorbing high-frequency energy when an RF signal is transmitted to the magnetized nuclei. Excitation of a slice may refer to the transition from a low energy state to a high energy state of atomic nuclei included in the slice when an electromagnetic wave signal is applied to the atomic nuclei.
Excitation of a plurality of slices together may include simultaneous excitation of the plurality of slices.
The plurality of frequency components may respectively correspond to the plurality of slices. In detail, when the RF signal includes an A frequency component and a B frequency component, the A frequency component may excite the first slice from among the plurality of slices, and the B frequency component may excite the second slice from among the plurality of slices.
The preparation pulse signal may be a signal that is previously transmitted to adjust a contrast of an image to be acquired. For example, the preparation pulse signal may be an inverted pulse signal that is previously transmitted to acquire a fluid-attenuated inversion recovery (FLAIR) image.
The controller 110 of
In an embodiment, the RF coil 120 may receive MR signals of a first slice and a second slice.
The first slice and the second slice of an object may emit the MR signals as an RF signal and a gradient magnetic field are applied. The gradient magnetic field may be applied by the gradient amplifier 32 of
The RF coil 120 may receive the MR signals emitted by the first slice and the second slice. The RF coil 120 may acquire the MR signals emitted by the first slice and the second slice in an overlapping state during the same repetition time (TR) period.
The RF coil 120 may include a plurality of coils, and each of the plurality of coils may receive an MR signal. For example, the plurality of coils may include RF coils having various numbers of channels such as 16 channels, 32 channels, 72 channels, or 144 channels. The MR signals in the overlapping state may be distinguished based on a sensitivity difference between the plurality of coils.
The image processor 140 may acquire an MR image having a first contrast for the first slice, and an MR image having a second contrast for the second slice.
In an embodiment, the MR image having the first contrast may be a FLAIR image. Also, the MR image having the second contrast may be a T1-weighted image or a T2-weighted image.
In detail, the image processor 140 may receive the MR signals from the RF coil 120. The image processor 140 may generate 3D k-space data based on the received MR signals.
Also, the image processor 140 may acquire the MR images of the first slice and the second slice of the object based on the generated 3D k-space data. In detail, the image processor 140 may generate the 3D k-space data by performing 3D spatial encoding and performing 3D Fourier transform on the MR signals.
Also, the image processor 140 may acquire the MR images of the first slice and the second slice from the MR signals in the overlapping state by using at least one of parallel imaging and compressed sensing (CS).
For example, the image processor 140 may simultaneously acquire the MR signals from the first slice and the second slice through the plurality of coils by simultaneously exciting the first slice and the second slice according to the parallel imaging.
Also, the image processor 140 may separate the MR signals of the first slice and the second slice by using a difference in coil sensitivity information between the first slice and the second slice.
The parallel imaging may include a SENSE method and a GRAPPA method. The CS may refer to a method of reconstructing an MR image after acquiring signals only for subsets instead of acquiring signals for all grids of a k-space.
When the 3D spatial encoding is performed on the MR signals, it may mean that digital data of the MR signals is arranged in a k-space of a memory. That is, the k-space may refer to a set of raw data of the MR signals and may include location information and contrast information.
Also, the k-space may refer to 2D or 3D Fourier transform of the measured MR signals. The image processor 140 may acquire the MR images by performing inverse 3D Fourier transform on the 3D k-space data.
The controller 110 may sequentially transmit RF signals to a plurality of slices of the object. Also, the controller 110 may transmit an RF signal including a frequency component that enables a slice corresponding to each of the plurality of slices to be excited.
For example, the controller 110 may control the RF coil 120 to sequentially transmit RF signals to odd-numbered slices of the object. In this case, the controller 110 may determine an even-numbered slice separated by a predetermined interval from each of the odd-numbered slices.
The RF coil 120 may transmit an RF signal including a frequency component that enables each odd-numbered slice to be excited and a frequency component that enables the even-numbered slice separated by the predetermined interval from the odd-numbered slice to be excited.
The RF coil 120 may receive MR signals in an overlapping state from each odd-numbered slice and the even-numbered slice separated by the predetermined interval from the odd-numbered slice.
The image processor 140 may receive the MR signals from the RF coil 120. The image processor 140 may acquire MR images in an overlapping state for each odd-numbered slice and the even-numbered slice separated by the predetermined interval from the odd-numbered slice, from the MR signals received from the RF coil 120.
The image processor 140 may acquire the MR image of each slice by separating the overlapping signals or the overlapping images.
In an embodiment, each MR image may include at least one from among a T1-weighted image, a T2-weighted image, a T2*-weighted image, a proton density (PD) image, and a FLAIR image.
In operation 502, the MRI apparatus 100 determines a first slice and a second slice of an object. In an embodiment, the MRI apparatus 100 determines the first slice and the second slice so that a difference between a slice number of the first slice and a slice number of the second slice is a predetermined interval value.
In an embodiment, when the first slice is an even-numbered slice, the second slice may be an odd-numbered slice, and when the first slice is an odd-numbered slice, the second slice may be an even-numbered slice.
In an embodiment, the predetermined interval value may be a value obtained by dividing a total number of slices constituting the object by a multi-band acceleration factor. For example, when the multi-band acceleration factor is 2, the predetermined interval value may be half the total number of the slices constituting the object.
In another embodiment, the multi-band acceleration factor may be N. In this case, the MRI apparatus 100 may simultaneously acquire MR images for N (N>2) slices.
For example, the MRI apparatus 100 may transmit an RF signal including a frequency component that enables the N slices including the first slice and the second slice to be simultaneously excited. In this case, the predetermined interval value may be a value obtained by dividing the total number of the slices constituting the object by N.
In an embodiment, the MRI apparatus 100 may determine a plurality of slices including the first slice and the second slice of the object.
In operation 504, the MRI apparatus 100 transmits a preparation pulse signal including a frequency component that enables the first slice to be excited. The preparation pulse signal may be a signal that is previously transmitted to adjust a contrast of an image to be acquired. For example, the preparation pulse signal may be an inverted pulse signal that is previously transmitted to acquire a FLAIR image.
In operation 506, the MRI apparatus 100 transmits an RF signal including a plurality of frequency components so that both the first slice and the second slice are excited. In an embodiment, the MRI apparatus 100 may transmit the RF signal including the plurality of frequency components so that the plurality of slices including the first slice and the second slice are excited.
The MRI apparatus 100 may determine the first slice and the second slice so that a difference between a slice number of the first slice and a slice number of the second slice is a predetermined interval value. In an embodiment, the predetermined interval value may be a value obtained by dividing a total number of slices constituting an object by a multi-band acceleration factor. For example, when the multi-band acceleration factor is 2, the predetermined interval value may be half the total number of the slices constituting the object.
For example, the slice number of the first slice may be 1, and the total number of the slices may be 22. In this case, the predetermined interval value may be 11 that is half of 22. Accordingly, the MRI apparatus 100 may determine a slice whose slice number is 12 as the second slice.
In another embodiment, the multi-band acceleration factor may be N. In this case, the MRI apparatus 100 may simultaneously acquire MR images for N (N>2) slices.
For example, the MRI apparatus 100 may transmit an RF signal including a frequency component that enables the N slices including the first slice and the second slice to be simultaneously excited. In this case, the predetermined interval value may be a value obtained by dividing the total number of the slices constituting the object by N.
In operation 604, the MRI apparatus 100 may transmit a preparation pulse signal for the first slice. Also, the MRI apparatus 100 may transmit an RF signal including a plurality of frequency components so that both the first slice and the second slice are excited.
In an embodiment, the MRI apparatus 100 may transmit an inverted pulse signal for the first slice.
In operation 606, the MRI apparatus 100 may receive MR signals of the first slice and the second slice. The MRI apparatus 100 may acquire the MR signals emitted from the first slice and the second slice in an overlapping state.
In operation 608, the MRI apparatus 100 may acquire MR images for the first slice and the second slice. In an embodiment, the MRI apparatus 100 may acquire a FLAIR image for the first slice. Also, the MRI apparatus 100 may acquire a T1-weighted image or a T2-weighted image for the second slice.
In an embodiment, the MRI apparatus 100 may acquire the MR image for the first slice and the MR image for the second slice in an overlapping state. The MRI apparatus 100 may acquire the MR image for each slice by separating the overlapping images.
The MRI apparatus 100 may transmit a preparation pulse signal 710. In an embodiment, the preparation pulse signal 710 may include a frequency component that enables a first slice to be excited.
In an embodiment, the preparation pulse signal 710 may be an inverted pulse signal used to acquire a FLAIR image.
The MRI apparatus 100 may transmit an RF signal including a plurality of frequency components so that both the first slice and a second slice are excited. Referring to
In an embodiment, an RF signal may include a 90° pulse signal 720 including a frequency component that enables the first slice to be excited, and a 90° pulse signal 730 including a frequency component that enables the second slice to be excited.
Also, the RF signal may include a 180° pulse signal 740 including a frequency component that enables the first slice to be excited, and a 180° pulse signal 750 including a frequency component that enables the second slice to be excited.
The MRI apparatus 100 may receive MR signals 760 of the first slice and the second slice. The MRI apparatus 100 may acquire the MR signals 760 emitted from the first slice and the second slice in an overlapping state.
In an embodiment, the number of the plurality of slices of the object may be 22. Also, the slices may sequentially have slice numbers from 1 to 22. Referring to
In the specification, a slice whose slice number is an odd number is an odd-numbered slice, and a slice whose slice number is an even number is an even-numbered slice.
In an embodiment, the MRI apparatus 100 may simultaneously acquire MR images having a plurality of contrasts for the plurality of slices.
In an embodiment, when a preparation pulse signal for the first slice is applied, slices around the first slice may be affected by the preparation pulse signal.
For example, when an inverted pulse signal for the slice 820 whose slice number is 2 is applied, phases of atomic nuclei included in the slice 820 whose slice number is 2 may be inverted. Also, due to the inverted pulse signal for the slice 820 whose slice number is 2, phases of atomic nuclei included in the slice 810 whose slice number is 1 and the slice 830 whose slice number is 3 may be changed.
Accordingly, when MR images having different contrasts for the first slice and a second slice are simultaneously acquired, the second slice that may be least effected by the preparation pulse signal for the first slice may be determined.
In an embodiment, a slice separated by half a total number of slices constituting the object from the first slice may be determined as the second slice. In detail, the second slice may be determined so that a difference between a slice number of the first slice and a slice number of the second slice is half the total number of the slices.
For example, when the first slice is the slice 810 whose slice number is 1, the second slice may be the slice 840 whose slice number is 12. Also, when the first slice is the slice 850 whose slice number is 13, the second slice may be the slice 820 whose slice number is 2.
Table 1 900 is a table showing a case where a first slice is an odd-numbered slice. Table 2 910 is a table showing a case where a first slice is an even-numbered slice.
In an embodiment, the MRI apparatus 100 may acquire MR images having a plurality of contrasts for all slices constituting an object. For example, the MRI apparatus 100 may acquire a FLAIR image and a T2-weighted image.
In an embodiment, the MRI apparatus 100 may acquire a FLAIR image for an odd-numbered slice, and then may sequentially acquire a FLAIR image for an even-numbered slice. In another embodiment, the MRI apparatus 100 may acquire a FLAIR image for an even-numbered slice, and then may sequentially acquire a FLAIR image for an odd-numbered slice.
In an embodiment, when the MRI apparatus 100 acquires a FLAIR image for an odd-numbered slice, the MRI apparatus 100 may simultaneously acquire a T2-weighted image for an even-numbered slice.
In an embodiment, the MRI apparatus 100 may acquire a FLAIR image for a first slice that is an odd-numbered slice. In this case, the MRI apparatus 100 may simultaneously acquire a T2-weighted image for a second slice that is an even-numbered slice that may be least affected by an inverted pulse signal.
In an embodiment, the MRI apparatus 100 may determine a second slice by using Equation 1.
In Equation 1, a multi-band factor may be the number of slices to be simultaneously excited by using an RF signal. In detail, the multi-band factor may refer to the number of frequencies included in the RF signal.
For example, when a FLAIR image for a first slice and a T2 image for a second slice are to be simultaneously acquired, the multi-band factor is 2.
In another embodiment, the MRI apparatus 100 may simultaneously acquire MR images for N (N>2) slices. In this case, the MRI apparatus 100 may transmit an RF signal including a frequency component that enables the N slices including a first slice and a second slice to be simultaneously excited. In this case, the multi-band factor is N.
Referring to
slice number of second slice=(slice number of first slice+11)%22 (2)
For example, when a slice number of a first slice is 1, a slice number of a second slice may be 12. Also, when a slice number of the first slice is 17, a slice number of the second slice may be 6.
Referring to
The embodiments may be written as computer programs and may be implemented in general-use digital computers that execute the programs using a computer-readable recording medium.
Examples of the computer-readable recording medium include magnetic storage media (e.g., read-on memories (ROMs), floppy disks, hard disks, etc.), optical recording media (e.g., compact disk (CD)-ROMs or digital versatile disks (DVDs)), and carrier waves (such as data transmission through the Internet).
While the present disclosure has been particularly shown and described with reference to embodiments thereof, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2016-0011840 | Jan 2016 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2016/010811 | 9/27/2016 | WO | 00 |
