Patent Application
20090118607
1. Field of the Invention
The present invention relates to an MRI apparatus for generating a MRI (magnetic resonance imaging) image using a binomial pulse for exciting a same nuclide.
2. Description of the Related Art
An MRI apparatus is a unit with an imaging process for reconstructing the MRI image of a cross section in an object based on an MR signal generated by magnetically exciting a nucleus spin of the object in the static magnetic field with a high frequency signal at Larmor frequency.
When generating the MRI image based on the MR signal received by water (free water) excitation with the MRI apparatus, a fat suppression technology to prevent collection of the MR signal from the fat is necessary to avoid the chemical shift artifact caused by the fat (bound water) in the cross section. Meanwhile, when generating the MRI image based on the MR signal received by the fat excitation, the water suppression technology to prevent collection of the MR signal from water is necessary to avoid the chemical shift artifact caused by the water in the cross section. Generally, the process using various types of pulse sequence has been well known to perform the aforementioned fat suppression and the water suppression.
For examples the signal from fat or water may be suppressed using a frequency selective excitation pulse. The process employs an RF wave (binomial pulse) with a flip angle ratio of 1-2-1 series or 1-3-3-1 series of water or fat as the frequency selective excitation pulse.
However, in order to improve properties of water excitation and fat excitation with the generally employed technology, both an echo time (TE) and a repetition time (TR) are prolonged, and accordingly, the entire imaging time becomes long, which may exert the stress to the object.
In the generally employed art, the segregation property between water and fat cannot be improved owing to weakened susceptibility as the case may be. The longer the pulse length becomes, the lower the S/N ratio becomes.
The present invention has taken into consideration the above-described problems, and it is a purpose of the present invention to provide a MRI apparatus of the present invention which is capable of alleviating the stress to the object (patient) during the imaging operation.
Further, the present invention has taken into consideration the above-described problems, and it is a purpose of the present invention to provide a MRI apparatus of the present invention which is capable of providing an MRI image optimum for the image diagnosis.
To solve the above-described problems, the present invention provides the MRI apparatus comprising: a waveform setting unit configured to set an asymmetric RF pulse waveform; an applying control unit configured to control an application of a pulse in accordance with the RF pulse waveform; a reconstructing unit configured to reconstruct an image based on a signal received by the application; and a display control unit configured to control a display of the image.
To solve the above-described problems, the present invention provides the MRI apparatus for generating an MRI image using a binomial pulse for a same nuclide excitation, comprising: a waveform setting unit configured to generate and set a deformed binomial pulse waveform by deleting a portion of the binomial pulse waveform and adding an flip angle calculated based on the deleted waveform to a rest of the waveform if a number of waves of the binomial pulse waveform is 3 or more; and an applying control unit configured to control application of a pulse in accordance with the deformed binomial pulse waveform set by the waveform setting unit.
To solve the above-described problems, the present invention provides the MRI apparatus for generating an MARI image using a binomial pulse for a same nuclide excitation, comprising: a waveform setting unit configured to generate and set a deformed binomial pulse waveform by admeasuring an intensity or a flip angle which should be used for one waveform included in the binomial pulse waveform to the other waveform; and an applying control unit configured to control application of a pulse in accordance with the deformed binomial pulse waveform set by the waveform setting unit.
In the accompanying drawings:
An embodiment of an MRI apparatus according to the present invention will be described referring to the drawings.
The imaging system 11 of the MRI apparatus 10 includes a gantry (not shown) which stores a static field magnet 21, a cylindrical shim coil 22 provided inside the static field magnet 21 coaxially therewith, and a cylindrical gradient coil unit 23 formed inside the static field magnet 21. The imaging system 11 includes an RF coil 24 and a bed mechanism 25 which retractably moves a patient P with respect to the gantry.
The control system 12 of the MRI apparatus 10 includes a static magnetic field power supply 31, a gradient magnetic field power supply 33, a shim coil power supply 32, a transmitter 34, a receiver 35, a sequence controller (sequencer) 36, and a computer 37.
The static field magnet 21 is connected to the static magnetic field power supply 31 for supplying electric current to generate the static magnetic field at an imaging region (FOV: Field of view).
The shim coil 22 is connected to the shim coil power supply 32 for supplying electric current to the shim coil 22 to uniformize the static magnetic field.
The gradient coil unit 23 is formed of an X-axis gradient coil 23x, a Y-axis gradient coil 23y, and a Z-axis gradient coil 23z. A tabletop (bed) 26 on the bed mechanism 25 is formed inside the gradient coil unit 23 to accommodate the patient P to lie down and moved by the bed mechanism 25.
The gradient coil unit 23 is connected to the gradient magnetic field power supply 33. The X-axis gradient coil 23x, the Y-axis gradient coil 23y, and the Z-axis gradient coil 23z of the gradient coil unit 23 are connected to the X-axis gradient magnetic field power supply 33x, the Y-axis gradient magnetic field power supply 33y, and the Z-axis gradient magnetic field power supply 33z of the gradient magnetic field power supply 33, respectively.
Further, electric current supplied to the K-axis gradient coil 23x from the X-axis gradient magnetic field power supply 33x, the Y-axis gradient coil 23y from the Y-axis gradient magnetic field power supply 33y, and the Z-axis gradient coil 23z from the Z-axis gradient magnetic field power supply 33z generates a gradient magnetic field Gx in the X-axis direction, a gradient magnetic field Gy in the Y-axis direction and a gradient magnetic field Gz in the Z-axis direction in the imaging region.
The RF coil 24 is formed of a multi coil, and connected to the transmitter 34 and the receiver 35. The RF coil 24 functions in sending a high frequency signal (RF: radio frequency) at Larmor frequency to an imaging site of the patient (object) P upon reception of the high frequency signal from the transmitter 34, and functions in receiving a nuclear magnetic resonance (NMR) signal generated by excitation with the high frequency signal of the nucleus spin inside the imaging site, and sending the signal to the receiver 35. Note that, the signal may be sent to/received from the RF coil 24 with a single coil serving as the transmission coil and the reception coil, or with the transmission coil and the reception coil separately. The MRI apparatus 10 in
Meanwhile, the sequence controller 36 of the control system 12 is connected to the bed mechanism 25, the gradient magnetic field power supply 33, the transmitter 34 and the receiver 35. The sequence controller 36 includes a not shown processor, for example, a CPU (central processing unit) and a memory structured to store control information required to drive the bed mechanism 25, the gradient magnetic field power supply 33, the transmitter 34 and the receiver 35, for example, intensity of the pulse current applied to the gradient magnetic field power supply 33, the time period for application of the pulse current, and sequence control which contains the operation control information such as the application timing.
The sequence controller 36 drives the bed mechanism 25 in accordance with the stored predetermined sequence to move the table-top 26 retractably in the Z-axis direction with respect to the gantry. Further, the sequence controller 36 drives the gradient magnetic field power supply 33, the transmitter 34, and the receiver 35 in accordance with the stored predetermined sequence to generate the X-axis gradient magnetic field Gx, the Y-axis gradient magnetic field Gy, the Z-axis gradient magnetic field Gz, and the RF signal in the gantry.
The transmitter 34 sends the RF signal to the IP coil 24 based on the control information from the sequence controller 36. Meanwhile, the receiver 35 subjects the NMR signal received from the RF coil 24 to a predetermined signal processing and an analog to digital (A/D) conversion to generate raw data as digitized NMR signal from the receiver 35. The generated raw data are transmitted to the sequence controller 36 so as to be sent to the computer 37.
The computer 37 has a basic hardware structure including a CPU 51 as a processor, a memory 52, a hard disk (HD) 53, an interface (IF) 54, a display device 55, and an input device 56. The CPU 51 is connected to the hardware components 52, 53, 54, 55 and 56 which constitute the computer 37 mutually via a bus B as a common signal transmission path. The computer 37 is connected to the network N such as a local area network (LAN) of the infrastructure built in a hospital so as to be mutually communicated via the IF 54 such that the past image (to be described later) is derived from a not shown image control device (server) on the network N.
Note that, the computer 37 may be provided with a drive for reading various application programs and data from the medium which stores the application programs and data.
The CPU 51 runs the program stored in the memory 52. Alternatively, the CPU 51 runs the program stored in the HD 53, and the program transferred from the network N, received by the IF 54, and installed in the HD 53, which are loaded into the memory 52.
The memory 52 is a storage device that has a read only memory (ROM) and a random access memory (RAM). The memory 52 stores a basic input/output system (BIOS), an initial program loading (IPL), and the image, and is used as a work memory of the CPU 51 and a temporarily storage of data.
The HD 53 is a storage device formed by a metal disk to which the magnetic material is applied or deposited, and built in a data reader (not shown) so as not to be detached. The HD 53 is a data storage unit for storing the program installed in the computer 37 (including an operation system (OS) in addition to the application program) and image data such as MRI image. The OS may be provided with a graphical user interface (GUI) through which the basic operation is performed by the graphics laden input device 56 for displaying the information for the user.
The IF 54 is a communication control unit for executing the communication control in accordance with the respective standards, and allows the computer 37 to be connected to the network N.
The display device 55 includes a digital to analog-(D/A) conversion circuit and a monitor for displaying the MRI image.
A keyboard and a mouse operated by an operator as an engineer may be employed as the input device 56 for sending the input signal corresponding to the operation to the CPU 51.
The MRI apparatus 10 has a function as an asymmetric pulse waveform setting unit 61, a pulse application control unit 62, and a signal reception/Image reconstructing unit 63 shown in
The asymmetric pulse waveform setting unit 61 has a function to set an RF pulse (described with “asymmetric pulse” as follows) waveform of an anterior-posterior asymmetric. The asymmetric pulse waveform setting unit 61 sets the asymmetric pulse waveform such that a decrease ratio of the flip angle after an excitation center is different from an increase ratio of the flip angle to the excitation center. The asymmetric pulse waveform setting unit 61, for example, has a binomial pulse waveform setting unit 61a, a deformed binomial pulse waveform generating unit 61b, and a deformed binomial pulse waveform setting unit 61c to set the asymmetric pulse waveform.
The binomial pulse waveform setting unit 61a has a function to set the desired binomial pulse waveform by operation of the operator via the input device 56.
The deformed binomial pulse waveform generating unit 61b shown in
Note that, the deformed binomial pulse waveform generating unit 61b forms the added waveform by using waves from a beginning to the excitation center in the binomial pulse waveform when the number of waves for forming the binomial pulse waveform is an odd number. Meanwhile, the deformed binomial pulse waveform generating unit 61b forms the added waveform by using waves from a beginning to shortly after the excitation center in the binomial pulse waveform when the number of waves for forming the binomial pulse waveform is an even number. Note that, the deformed binomial pulse waveform generating unit 61b may form the waveform by using half of the waves in the binomial pulse waveform when the number of waves for forming the binomial pulse waveform is an even number.
The number of the waves in a 1-3-3-1 series binomial pulse waveform showing in
Further, the deformed binomial pulse waveform generating unit 61b generates a deformed binomial pulse waveform (shown in
In addition, the number of the waves in a 1-4-6-4-1 series binomial pulse waveform showing in
Further, the deformed binomial pulse waveform setting unit 61c showed in
The pulse application control unit 62 has a function to control the transmitter 34 via the sequence controller 36 so as to control application of the frequency selective excitation pulse in accordance with the asymmetric pulse waveform set by the asymmetric pulse waveform setting unit 61.
The MRI image based on the pulse sequence in accordance with the binomial pulse waveform with the flip angle ratio of 1-1 series shown in the left side of
Referring to
Further, the signal reception/image reconstructing unit 63 shown in
Referring to
Note that, the effect of the operation of the MRI apparatus 10 upon water excitation with the pulse sequence shown in
In the MRI apparatus 10, the RF, coil 24 is formed of the multi coil, which allows the user to perform the parallel imaging process where the multi coil is disposed in the interest site of the patient P, and reconstruct the MRI image for receiving and processing the NMR signal from the multi coil for the imaging operation. The use of the PI process allows the number of phase encodes required for reconstructing the MRI image to be decreased by an amount corresponding to the number of the surface coils, thus reducing the imaging time.
Further, in the MRI apparatus 10, the RF coil 24 is formed of the multi coil, which allows the user to perform the transmit sense process where the multi coil is disposed in the interest site of the patient P, and the RF pulse is transmitted from the multi coil for the imaging operation.
With the MRI apparatus 10 at the imaging timing, the binomial pulse is set by the binomial pulse waveform setting unit 61a shown in
The use of the MRI apparatus 10 according to the embodiment may reduce the pulse length to decrease both TE and TR, and accordingly, the imaging time is reduced. This may alleviate the stress to the patient P during the imaging operation.
Furthers the use of the MRI apparatus 10 is capable of providing the MRI image optimum for the image diagnosis.
| Number | Date | Country | Kind |
|---|---|---|---|
| 285888/2007 | Nov 2007 | JP | national |
