JP2006043473A - Rf pulse tuning device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device which performs RF (radio frequency) pulse tuning so that the ability of an RF transmitter can be effectively utilized. <P>SOLUTION: The device tunes an RF pulse for excitation so that the flip angle of a spin agrees with a target value. It is provided with a pulse width adjusting means which gradually increases the pulse width of the RF pulse from a predetermined initial value until the flip angle of the spin agrees with an intermediate target value, and a calculating means which calculates conditions of the RF pulse which makes the flip angle of the spin agree with a final target value smaller than the above intermediate target value from the conditions of the RF pulse which makes the flip angle of the spin agree with the intermediate target value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an RF pulse tuning method and apparatus, and more particularly, to a method for adjusting an RF pulse for excitation such that a spin flip angle matches a target value, and an apparatus for adjusting the RF pulse for excitation. Relates to the device.

  In a magnetic resonance imaging (MRI) apparatus, an object to be imaged is carried into an internal space of a magnet system (namely, an imaging space in which a static magnetic field is formed), and a gradient magnetic field and a high-frequency magnetic field are applied to the object. The spin inside is excited to generate a magnetic resonance signal, and an image is reconstructed based on the received signal.

  The application of the high frequency magnetic field is performed in the form of RF pulse transmission. In order to appropriately perform spin excitation, RF pulses are adjusted prior to imaging. The adjustment of the RF pulse is also called RF pulse tuning.

  In RF pulse tuning, transmission of RF pulses is tried while sequentially changing the transmission gain (gain) of the RF transmitter, that is, the amplitude of the RF pulse. Then, the reach of the spin flip angle is examined based on the magnetic resonance signal obtained each time, and the optimum transmission gain is obtained.

  The optimum transmission gain is a transmission gain that can match the flip angle with a target value. Since the optimum transmission gain differs for each object to be imaged, RF pulse tuning is performed for each object. Hereinafter, RF pulse tuning is also simply referred to as tuning.

  The RF pulse can be switched to a large pulse width so that tuning can be properly performed on a subject having a large physique. The switching of the pulse width is performed according to the weight of the subject. Weight data (data) is input in advance by the user of the magnetic resonance imaging apparatus.

  The larger pulse width is set to be quite large so that it can always be tuned for a subject with a large physique. In other words, the RF transmitter is configured so that such output is possible.

  Such an RF transmitter has a considerable capacity in view of the output that is really necessary in actual photographing. For this reason, when the pulse width is increased, the RF pulse is often transmitted with a gain that is considerably lower than the maximum gain. This means that the capability of the RF transmitter is not effectively utilized.

  Therefore, an object of the present invention is to provide an apparatus that performs RF pulse tuning so that the capability of the RF transmission apparatus can be used effectively.

  In a first aspect, the present invention is an apparatus for tuning an RF pulse for excitation so that a spin flip angle matches a target value, and the RF pulse is adjusted until the spin flip angle matches an intermediate target value. A pulse width adjusting means for sequentially increasing the pulse width of the spin pulse from a predetermined initial value, an RF pulse condition for matching the spin flip angle to a final target value smaller than the intermediate target value, and the spin flip angle An RF pulse tuning apparatus comprising: a calculating means for calculating from a condition of an RF pulse that matches an intermediate target value.

  According to a second aspect, the present invention is characterized in that, in the RF pulse tuning apparatus according to the first aspect, the calculation means obtains a pulse width when the amplitude of the RF pulse is set to a maximum value that can be adjusted.

  In a third aspect, the present invention provides the RF pulse tuning device according to the first aspect or the second aspect, wherein the pulse width adjustment means sets the RF pulse amplitude to a maximum adjustable value, and the flip angle is the intermediate value. When the target value is not reached, the amount of increase in the next pulse width is determined according to the degree of the target attempt.

  In a fourth aspect, the present invention is the RF pulse tuning device according to any one of the first to third aspects, wherein the intermediate target value is 90 °. .

  In a fifth aspect, the present invention is the RF pulse tuning device according to any one of the first to third aspects, wherein the intermediate target value is 180 °. .

  According to the present invention, an RF pulse tuning device can be provided so that the capability of the RF transmitter can be effectively used.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the embodiment. FIG. 1 shows a block diagram of the magnetic resonance imaging apparatus. RF pulse tuning is performed in this apparatus. This apparatus is an example of an embodiment of the present invention. An example of an embodiment relating to the apparatus of the present invention is shown by the configuration of the apparatus. An example of an embodiment related to the method of the present invention is shown by the operation of the apparatus.

  As shown in the figure, the apparatus has a magnet system 100. The magnet system 100 is installed in the scan room. The magnet system 100 includes a main magnetic field coil unit 102, a gradient coil unit 106, and an RF coil unit 108. Each of these coil portions has a substantially cylindrical shape and is arranged coaxially with each other. A subject 1 to be imaged is mounted on a cradle 500 in a generally cylindrical inner space (bore) of the magnet system 100 and is carried in and out by a conveying means (not shown).

  The main magnetic field coil unit 102 forms a static magnetic field in the internal space of the magnet system 100. The direction of the static magnetic field is generally parallel to the direction of the body axis of the object 1. That is, a so-called horizontal magnetic field is formed. The main magnetic field coil unit 102 is configured using, for example, a superconducting coil. Of course, it is possible to use not only superconducting coils but also normal conducting coils.

  The gradient coil section 106 generates three gradient magnetic fields for giving gradients to the static magnetic field strength in the directions of three axes perpendicular to each other, that is, the slice axis, the phase axis, and the frequency axis.

  When the coordinate axes perpendicular to each other in the static magnetic field space are x, y, and z, any of the axes can be a slice axis. In that case, one of the remaining two axes is a phase axis, and the other is a frequency axis. In addition, the slice axis, the phase axis, and the frequency axis can have arbitrary inclinations with respect to the x, y, and z axes while maintaining the perpendicularity therebetween. In this apparatus, the direction of the body axis of the target 1 is the z-axis direction.

  The gradient magnetic field in the slice axis direction is also called a slice gradient magnetic field. The gradient magnetic field in the phase axis direction is also referred to as a phase encode gradient magnetic field or a phase encode gradient magnetic field. The gradient magnetic field in the frequency axis direction is also referred to as a read out gradient magnetic field. In order to make it possible to generate such a gradient magnetic field, the gradient coil unit 106 has three gradient coils (not shown). Hereinafter, the gradient magnetic field is also simply referred to as a gradient.

  The RF coil unit 108 forms a high-frequency magnetic field for exciting spins in the body of the target 1 in the static magnetic field space. Hereinafter, the formation of a high-frequency magnetic field is also referred to as transmission of an RF excitation signal. The RF excitation signal is also referred to as an RF pulse. The RF coil unit 108 also receives an electromagnetic wave generated by excited spin, that is, a magnetic resonance signal.

  The RF coil unit 108 includes a transmission coil and a reception coil (not shown). As the transmission coil and the reception coil, the same coil is used or a dedicated coil is used.

  A gradient driving unit 130 is connected to the gradient coil unit 106. The gradient driving unit 130 gives a driving signal to the gradient coil unit 106 to generate a gradient magnetic field. The gradient drive unit 130 has three systems of drive circuits (not shown) corresponding to the three systems of gradient coils in the gradient coil unit 106.

  An RF drive unit 140 is connected to the RF coil unit 108. The RF drive unit 140 gives a drive signal to the RF coil unit 108 and transmits an RF pulse to excite spins in the body of the subject 1.

  A data collection unit 150 is connected to the RF coil unit 108. The data collecting unit 150 takes in the received signal received by the RF coil unit 108 by sampling and collects it as digital data.

  A control unit 160 is connected to the gradient driving unit 130, the RF driving unit 140, and the data collection unit 150. The controller 160 controls the gradient driving unit 130 or the data collecting unit 150 to collect magnetic resonance signals.

  The control unit 160 is configured using, for example, a computer. The controller 160 has a memory (not shown). The memory stores a program for the control unit 160 and various data. The function of the control unit 160 is realized by the computer executing a program stored in the memory.

  The output side of the data collection unit 150 is connected to the data processing unit 170. Data collected by the data collection unit 150 is input to the data processing unit 170. The data processing unit 170 is configured using, for example, a computer. The data processing unit 170 has a memory (not shown). The memory stores a program for the data processing unit 170 and various data.

  The data processing unit 170 is connected to the control unit 160. The data processing unit 170 is above the control unit 160 and controls it. The function of this apparatus is realized by the data processing unit 170 executing a program stored in the memory.

  The data processing unit 170 stores the data collected by the data collection unit 150 in a memory. A data space is formed in the memory. This data space constitutes a two-dimensional Fourier space. Hereinafter, the two-dimensional Fourier space is also referred to as k-space. The data processing unit 170 reconstructs the image of the target 1 by performing two-dimensional inverse Fourier transform on the k-space data.

  A display unit 180 and an operation unit 190 are connected to the data processing unit 170. The display unit 180 is configured by a graphic display or the like. The operation unit 190 includes a keyboard having a pointing device.

  The display unit 180 displays the reconstructed image and various information output from the data processing unit 170. The operation unit 190 is operated by the user and inputs various commands and information to the data processing unit 170. The user operates the apparatus interactively through the display unit 180 and the operation unit 190.

  FIG. 2 shows a block diagram of another type of magnetic resonance imaging apparatus. RF pulse tuning is also performed in this apparatus. The magnetic resonance imaging apparatus shown in the figure is an example of an embodiment of the present invention. An example of an embodiment relating to the apparatus of the present invention is shown by the configuration of the apparatus. An example of an embodiment related to the method of the present invention is shown by the operation of the apparatus.

  This apparatus has a magnet system 100 ′ that is different from the apparatus shown in FIG. 1. The magnet system 100 'is installed in the scan room. Except for the magnet system 100 ′, the configuration is the same as that of the apparatus shown in FIG. 1.

  The magnet system 100 'includes a main magnetic field magnet section 102', a gradient coil section 106 ', and an RF coil section 108'. Each of the main magnetic field magnet section 102 'and each coil section is composed of a pair facing each other across a space. Moreover, all have a substantially disk shape and are arranged sharing the central axis. The object 1 is mounted on the cradle 500 and carried into and out of the internal space (bore) of the magnet system 100 ′ by a conveying means (not shown).

  The main magnetic field magnet unit 102 'generates a static magnetic field in the internal space of the magnet system 100'. The direction of the static magnetic field is substantially orthogonal to the body axis direction of the target 1. That is, a so-called vertical magnetic field is formed. The main magnetic field magnet unit 102 'is configured using, for example, a permanent magnet. Of course, not only permanent magnets but also superconducting electromagnets or normal conducting electromagnets may be used.

  The gradient coil section 106 'generates three gradient magnetic fields for giving a gradient to the static magnetic field strength in the directions of three axes perpendicular to each other, that is, the slice axis, the phase axis, and the frequency axis.

  When the coordinate axes perpendicular to each other in the static magnetic field space are x, y, and z, any of the axes can be a slice axis. In that case, one of the remaining two axes is a phase axis, and the other is a frequency axis. In addition, the slice axis, the phase axis, and the frequency axis can have arbitrary inclinations with respect to the x, y, and z axes while maintaining the perpendicularity therebetween. Also in this apparatus, the direction of the body axis of the target 1 is the z-axis direction.

  The gradient magnetic field in the slice axis direction is also called a slice gradient magnetic field. The gradient magnetic field in the phase axis direction is also called a phase encode gradient magnetic field or a phase encode gradient magnetic field. The gradient magnetic field in the frequency axis direction is also called a readout gradient magnetic field. In order to make it possible to generate such a gradient magnetic field, the gradient coil section 106 'has three gradient coils (not shown).

  The RF coil unit 108 ′ transmits an RF pulse for exciting spins in the body of the subject 1 to the static magnetic field space. The RF coil unit 108 'also receives a magnetic resonance signal in which excited spin occurs.

  The RF coil section 108 'has a transmission coil and a reception coil (not shown). As the transmission coil and the reception coil, the same coil is used or a dedicated coil is used.

  FIG. 3 shows an example of a pulse sequence used for magnetic resonance imaging. This pulse sequence is a pulse sequence of a spin echo (SE: Spin Echo) method.

  That is, (1) is a sequence of 90 ° pulses and 180 ° pulses for RF excitation in the SE method, and (2), (3), (4) and (5) are respectively the slice gradient Gs and the lead. This is a sequence of an out gradient Gr, a phase encode gradient Gp, and a spin echo MR. The 90 ° pulse and the 180 ° pulse are represented by center signals. The pulse sequence proceeds from left to right along the time axis t.

  As shown in the figure, 90 ° excitation of spin is performed by a 90 ° pulse. At this time, the slice gradient Gs is applied, and selective excitation for a predetermined slice is performed. After a predetermined time from the 90 ° excitation, 180 ° excitation by a 180 ° pulse, that is, spin inversion is performed. At this time, the slice gradient Gs is applied, and selective inversion is performed for the same slice.

  In the period between 90 ° excitation and spin reversal, a readout gradient Gr and a phase encode gradient Gp are applied. Spin dephase is performed by the lead-out gradient Gr. Spin phase encoding is performed by the phase encoding gradient Gp.

  After the spin inversion, the spin is rephased at the readout gradient Gr to generate the spin echo MR. The spin echo MR is an example of an embodiment of the magnetic resonance signal in the present invention. The spin echo MR is an RF signal having a symmetrical waveform with respect to the echo center. The central echo occurs after TE (echo time) from 90 ° excitation. TE is also called echo time. The spin echo MR is collected as view data by the data collecting unit 150.

  Such a pulse sequence is repeated 64 to 512 times with a period TR (repetition time). The phase encoding gradient Gp is changed every time it is repeated, and a different phase encoding is performed each time. Thereby, view data of 64 to 512 views with different phase encoding amounts are obtained.

  Another example of a pulse sequence for magnetic resonance imaging is shown in FIG. This pulse sequence is a pulse sequence of a gradient echo (GRE) method.

  That is, (1) is a sequence of α ° pulses for RF excitation in the GRE method, and (2), (3), (4) and (5) are respectively slice gradient Gs, readout gradient Gr, It is a sequence of a phase encoding gradient Gp and a spin echo MR. The α ° pulse is represented by a center signal. The pulse sequence proceeds from left to right along the time axis t.

  As shown in the figure, the α ° excitation of the spin is performed by the α ° pulse. α is 90 or less. At this time, the slice gradient Gs is applied, and selective excitation for a predetermined slice is performed.

  After the α ° excitation, spin phase encoding is performed by the phase encoding gradient Gp. Next, the spin is first dephased by the readout gradient Gr, and then the spin is rephased to generate a gradient echo MR. The gradient echo MR is an example of an embodiment of a magnetic resonance signal in the present invention. The gradient echo MR is an RF signal having a symmetrical waveform with respect to the echo center. The central echo occurs after TE from α ° excitation. The gradient echo MR is collected as view data by the data collection unit 150.

  Such a pulse sequence is repeated 64 to 512 times with a period TR. The phase encoding gradient Gp is changed every time it is repeated, and a different phase encoding is performed each time. Thereby, view data of 64 to 512 views with different phase encoding amounts are obtained.

  View data obtained by the pulse sequence of FIG. 3 or 4 is collected in the memory of the data processing unit 170. Note that the pulse sequence is not limited to the SE method or the GRE method, and may be of any other appropriate technique such as the Fast Spin Echo (FSE) method or Echo Planar Imaging (EPI). Needless to say.

  FIG. 5 shows a conceptual diagram of the k space. In k space, the horizontal axis kx is the frequency axis, and the vertical axis ky is the phase axis. In the figure, each of a plurality of horizontally long rectangles represents view data. Hereinafter, the view data is also referred to as MR data. The number written in the rectangle represents the amount of phase encoding. The amount of phase encoding is normalized by π / N. N is 64 to 512. The phase encoding amount is 0 at the center of the phase axis ky. The phase encoding amount gradually increases from the center to both ends. The polarities of the increase are opposite to each other. The data processing unit 170 reconstructs a tomographic image of the object 1 by performing two-dimensional inverse Fourier transform on such view data. The reconstructed image is stored in the memory.

  FIG. 6 shows a flow chart of the photographing operation of this apparatus. As shown in the figure, in step 602, shooting conditions are set. The photographing condition setting is performed by the user through the operation unit 190. As a result, desired shooting conditions including a scan parameter are set. RF pulse tuning is performed as part of imaging condition setting. The RF pulse tuning will be described later.

  At step 604, a scan is performed. The scan is performed by executing the above-described pulse sequence under the control of the control unit 160, and MR data is sequentially acquired for each view.

  After acquiring MR data of all views, image reconstruction is performed by the data processing unit 170 in step 606. The reconstructed image is displayed on the display unit 180 in step 608 and stored in the memory.

  FIG. 7 shows a functional block diagram of this apparatus focusing on RF pulse tuning. This functional block diagram shows the configuration of the RF pulse tuning device. As shown in the figure, this apparatus has a pulse generator 702 and a transmitter 704. The RF pulse generated by the pulse generation unit 702 is supplied to the RF coil unit 108 through the transmission unit 704 to excite the spin in the target 1.

  The RF pulse supplied to the RF coil unit 108 has a waveform as shown in FIG. 8, for example. The amplitude of the RF pulse is a, and the pulse width is τ. The transmission unit 704 has a variable output gain. The amplitude a of the RF pulse changes according to the gain. The gain is controlled by the gain control unit 706. Accordingly, the amplitude a of the RF pulse is controlled by the gain control unit 706.

  The function of the part composed of the pulse generation unit 702, the transmission part 704, and the gain control part 706 corresponds to the function of the part composed of the RF drive part 140 and the control part 160 in the apparatus shown in FIG.

  Excited spins within object 1 produce a magnetic resonance signal. The magnetic resonance signal is, for example, FID (free induction decay). The magnetic resonance signal is received by the receiving unit 708 through the RF coil unit 108. The function of the reception unit 708 corresponds to the function of the data collection unit 150.

  A reception signal of the magnetic resonance signal is input to the flip angle determination unit 710. The flip angle determination unit 710 determines whether the spin flip angle matches the target value based on the received signal. The determination of the flip angle by the flip angle determination unit 710 will be described later.

  The determination signal of the flip angle determination unit 710 is input to the pulse width adjustment unit 712. The pulse width adjustment unit 712 generates a pulse width adjustment signal based on the determination signal. The pulse width adjustment signal is input to the pulse generator 702 and adjusts the pulse width of the RF pulse generated by the pulse generator 702.

  The function of the part composed of the flip angle determination unit 710 and the pulse width adjustment unit 712 corresponds to the function of the data processing unit 170. A portion including the flip angle determination unit 710 and the pulse width adjustment unit 712 is an example of an embodiment of the pulse width adjustment unit in the present invention.

  FIG. 9 shows a flowchart of the operation of this apparatus. As shown in the figure, in step 902, the pulse width is set. The pulse width setting is performed by the pulse width adjustment unit 712. As a result, the pulse width τ0 is set.

  Next, in step 904, an optimal pulse amplitude search is performed. The optimum pulse amplitude search is an operation for searching for the optimum value of the amplitude of the RF pulse. The optimum value of the amplitude of the RF pulse is an amplitude capable of exciting the spin so that the flip angle matches the target value.

  The flip angle is proportional to the amplitude of the RF pulse. Therefore, it is possible to know whether or not the flip angle matches the target value by trying transmission of the RF pulse while sequentially changing the amplitude of the RF pulse and examining the obtained magnetic resonance signal (FID). As the target value of the flip angle, 90 ° or 180 ° is selected.

  The relationship between the flip angle and the signal strength of the FID is as shown in FIG. That is, the signal strength of the FID is maximum when the flip angle is 90 °, and is minimum when the flip angle is 0 ° and 180 °. Using such a relationship, the amplitude of the RF pulse for exciting the spin can be obtained so that the flip angle is 90 ° or 180 °.

  The sequential transmission of RF pulses is performed by the operations of the pulse generator 702 and the transmitter 704. For each transmission, the gain controller 706 sequentially increases the amplitude of the RF pulse. The determination of the target achievement degree of the flip angle based on the FID is performed by the flip angle determination unit 710. The determination is made based on the relationship between the flip angle and the FID as shown in FIG.

When the pulse amplitude that matches the flip angle with the target is obtained, the search is successful. In that case, the RF pulse tuning ends based on the determination in step 906.
If the target is not reached even when the amplitude of the RF pulse is maximized, the search is unsuccessful. In that case, based on the determination in step 906, the pulse width is set to τ + Δτ in step 910. That is, the pulse width is increased by Δτ. The pulse width is increased by the pulse width adjustment unit 712. As a result, the pulse width of the RF pulse generated by the pulse generator 702 is updated.

  Next, in step 912, it is determined whether τ> T. T is the upper limit of the normal value of the pulse width of the RF pulse. The upper limit T is appropriately determined in consideration of the performance of the transmission unit 704 and the like. If τ> T, it is processed as an error, but if not, the process returns to step 904. Then, the optimum pulse amplitude search is performed in accordance with the above under a new pulse width.

  Since the flip angle is also proportional to the pulse width of the RF pulse, increasing the pulse width increases the flip angle even if the pulse amplitude is the same. Therefore, even if the optimum pulse amplitude is not obtained in the previous search, there is a possibility that it will be obtained this time. Hereinafter, if the optimum pulse amplitude search is unsuccessful in this manner, the search is repeated while increasing the pulse width by Δτ in step 910.

  By setting the initial value τ0 and the increase Δτ of the pulse width to relatively small values, the amplitude of the RF pulse that makes the flip angle coincide with the target value is set to the maximum value that can be output by the transmission unit 704 or a value in the vicinity thereof. be able to. Such a pulse amplitude is output using 100% or almost 100% of the capability of the transmitter 704. Therefore, it is possible to obtain a pulse amplitude that can effectively use the capability of the transmission unit 704.

  Further, since the pulse amplitude is such a value, the pulse width becomes a minimum necessary value. Since the pulse width is small, it is possible to shorten the time of the pulse sequence, thereby shortening the photographing time or improving the image quality.

  The increment Δτ of the pulse width may be dynamically changed by calculation instead of a fixed value as described above. In that case, as shown in FIG. 11, in step 908, the pulse width increase amount Δτ is calculated. The calculation of Δτ is performed by the pulse width adjustment unit 712. The calculation of Δτ is performed as follows.

  The fact that the search for the optimum pulse amplitude has been unsuccessful means that the flip angle has not yet reached the target even if the pulse amplitude is set to the maximum value that can be output by the transmission unit 704. In this case, the degree of failure to achieve the target indicates an insufficient amount of excitation. Therefore, if the pulse width is increased so as to compensate for this lack of excitation, the flip angle can be matched with the target value.

  For example, if the flip angle of the spin excited at the maximum output of the transmission unit 704 with respect to the target value of 180 ° is 170 °, the target can be achieved by multiplying the excitation amount by the RF pulse by 180 ° / 170 °. is there. In order to do so, the pulse width τ may be multiplied by 180 ° / 170 °. Therefore, the increment Δτ of the pulse width is calculated by the following equation.

  If this is generalized, the calculation formula of Δτ is given by the following formula. By using such Δτ, the tuning time can be shortened.

here,
θT: target flip angle θ max: ultimate flip angle When the target value of the flip angle is smaller than 90 °, such as 20 °, for example, based on the optimum pulse amplitude and pulse width obtained as described above, Calculate the final optimum pulse amplitude and pulse width that match the target values.

  FIG. 12 shows a functional block diagram of this apparatus when performing such RF pulse tuning. In the figure, the same components as those shown in FIG.

  As shown in the figure, this apparatus has a pulse width calculator 714. The function of the pulse width calculation unit 714 corresponds to the function of the data processing unit 170. The pulse width calculation unit 714 performs calculation using input signals from the flip angle determination unit 710 and the pulse width adjustment unit 712. An input signal from the flip angle determination unit 710 has an optimum pulse amplitude. The input signal from the pulse width adjustment unit 712 is a pulse width setting value. The pulse width calculation unit 714 is an example of an embodiment of calculation means in the present invention.

  13 and 14 are flowcharts showing the operation of the present apparatus. These flowcharts are obtained by adding step 914 to the flowcharts shown in FIGS. In step 914, the pulse width is calculated according to the flip angle. This calculation is performed by the pulse width calculator 714. The pulse width calculator 714 calculates the pulse width τ by the following formula.

here,
θT1: Intermediate target flip angle θT2: Final target flip angle aT1: Optimal pulse amplitude amax: Maximum RF pulse amplitude τT1 that can be output by the transmission unit 704: Pulse width setting value The intermediate target flip angle θT1 is, for example, 90 ° or 180 ° It is. The final target flip angle θT2 is, for example, 30 °. The optimum pulse amplitude aT1 is an input signal from the flip angle determination unit 710. This is the optimum pulse amplitude that matches the flip angle to the intermediate target value. The pulse width setting value τT1 is an input signal from the pulse width adjustment unit 712. This is a pulse width setting value for matching the flip angle with the intermediate target value.

  Expression (3) is an expression for obtaining a pulse width for making the flip angle coincide with the final target value θT2 when the pulse amplitude is set to the maximum amplitude amax of the RF pulse that can be output by the transmission unit 704. Since the pulse amplitude is set to the maximum amplitude amax, the pulse width becomes a smaller value than when it is 90 ° or 180 °. As a result, the photographing time can be further shortened.

  The present invention has been described above based on the preferred embodiments. However, those skilled in the art to which the present invention pertains have the technical scope of the present invention with respect to the above embodiments. Various changes and substitutions can be made without departing. Therefore, the technical scope of the present invention includes not only the above-described embodiments but also all the embodiments belonging to the claims.

It is a block diagram of an example of an apparatus of an embodiment of the invention. It is a block diagram of an example of an apparatus of an embodiment of the invention. It is a figure which shows an example of the pulse sequence which the apparatus of an example of embodiment of this invention performs. It is a figure which shows an example of the pulse sequence which the apparatus of an example of embodiment of this invention performs. It is a conceptual diagram of k space. It is a flowchart of operation | movement of the apparatus of an example of embodiment of this invention. It is a functional block diagram of the apparatus of an example of embodiment of this invention. It is a wave form diagram of RF pulse. It is a flowchart of operation | movement of the apparatus of an example of embodiment of this invention. It is a graph which shows the relationship between a flip angle and FID signal strength. It is a flowchart of operation | movement of the apparatus of an example of embodiment of this invention. It is a functional block diagram of the apparatus of an example of embodiment of this invention. It is a flowchart of operation | movement of the apparatus of an example of embodiment of this invention. It is a flowchart of operation | movement of the apparatus of an example of embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Object 100, 100 'Magnet system 102 Main magnetic field coil part 102' Main magnetic field magnet part 106, 106 'Gradient coil part 108, 108' RF coil part 130 Gradient drive part 140 RF drive part 150 Data collection part 160 Control part 170 Data Processing unit 180 Display unit 190 Operation unit 500 Cradle 702 Pulse generation unit 704 Transmission unit 706 Gain control unit 708 Reception unit 710 Flip angle determination unit 712 Pulse width setting unit 714 Pulse width calculation unit

Claims (5)

An apparatus for tuning an RF pulse for excitation so that a flip angle of a spin matches a target value,
Pulse width adjusting means for sequentially increasing the pulse width of the RF pulse from a predetermined initial value until the spin flip angle matches the intermediate target value;
And a calculation means for calculating an RF pulse condition that matches a spin flip angle to a final target value smaller than the intermediate target value from an RF pulse condition that matches a spin flip angle to the intermediate target value. An RF pulse tuning device.   2. The RF pulse tuning apparatus according to claim 1, wherein the calculating means obtains a pulse width when the amplitude of the RF pulse is set to a maximum adjustable value.   The pulse width adjusting means determines an increase amount of the next pulse width according to the degree of the attempted target when the flip angle does not reach the intermediate target value even if the RF pulse amplitude is a maximum adjustable value. The RF pulse tuning device according to claim 1 or 2, wherein   The RF pulse tuning device according to any one of claims 1 to 3, wherein the intermediate target value is 90 °.   The RF pulse tuning device according to any one of claims 1 to 3, wherein the intermediate target value is 180 °.

Images