JP2000325327A - Mri apparatus and mr imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set a pulse sequence quickly, with small operational labor and with good accuracy by setting a pulse sequence for generating plural echo signals per one time application of RF excitation pulses to set the data collection time, and determining the number of echos and the number of RF excitation pulse shots. SOLUTION: A host computer 6 receives information instructed by an operator according to a stored software procedure, and gives a command of sequential information to a sequencer 5. A user can arbitrarily set the number of slices to be done during the repeat time TR and the scan time corresponding to a variable length echo train according to a matrix size and the number of shots of a photographed image. The sequencer 5 stores pulse sequence information sent from the host computer 6, controls a series of operation of a inclined magnetic field power supply 4, a transmitter 8T, and a receiver 8R, once inputs digital data of an MR signal from the receiver 8R, and transfers the data to an arithmetic unit 10 for conducting reconfiguration processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MRI (Magnetic Resonance Imaging) apparatus and an MR imaging method for obtaining an image in a subject by utilizing a magnetic resonance phenomenon of a nuclear spin existing in the subject. In particular, an EPI (echo planar imaging) method capable of generating a plurality of echo signals in response to one excitation pulse applied to generate a magnetic resonance phenomenon and collecting data in a short time,
The present invention relates to magnetic resonance imaging which performs FSE (Fast Spin Echo) methods or pulse sequences based on them.

[0002]

2. Description of the Related Art In magnetic resonance imaging, nuclear spins of a subject placed in a static magnetic field are magnetically excited by a high frequency signal of a Larmor frequency, and FI generated by the excitation is excited.
This is a technique for obtaining an image inside the subject from a D (free induction attenuation) signal or an echo signal.

[0003] This magnetic resonance imaging is extremely effective as a technique for noninvasively obtaining an anatomical tomographic image of a subject. For this reason, for example, it is also used for diagnosis of the central nervous system of the brain covered with bone.

[0004] In the field of such magnetic resonance imaging, when performing T2 weighted imaging with high clinical effectiveness, it is necessary to use a pulse sequence in which the echo time TE and the repetition time TR are set long. For this reason, the entire photographing time becomes as long as about 10 minutes, and the burden on the patient is large.

[0005] In order to shorten the imaging time, EPI is used to collect data a plurality of times for a single excitation pulse.
Law and FSE method (also called RARE method) are proposed,
It is used.

The EPI method is a method proposed by "Mansfield" and uses a process of continuously generating a field echo while switching the polarity of a gradient magnetic field in a readout direction (see "Mansfield, P.M.
“NMR Imaging in Biomedicin
e ", Advances in Magnetic
Resonance, Academic Pres
s, New York, 1982 ").
By using the method, single shot shooting became possible. In the case of single shot imaging, however, the influence of magnetic field inhomogeneity, image blur due to T2 relaxation, and the like become apparent. In order to suppress this, imaging using a multi-shot type EPI method is often used in practice.

On the other hand, the FSE method is a method proposed by "Hennig" and employs a process of generating a multi-echo signal by continuously applying a refocusing pulse to a single excitation pulse (""). Hennig,
J. , “RARE Imaging: Fast I
Managing Method Clinical M
R ", Magn. Reson. Med 3, 82
3-33 (1986) "). This FSE method is described in EP
Compared with the method I, there is an advantage that the imaging time is longer, but there is no influence of the non-uniformity of the magnetic field. Also in the case of the FSE method, since it is used in a multi-shot manner, its clinical effectiveness is increased due to shortening of the effective echo time and reduction of image blurring, and has been widely used.

[0008] As described above, the imaging speed of the T2-weighted image (T2 contrast image) is increased by the EPI method or the FSE method. As the number of echo trains corresponding to one excitation pulse application increases, the degree of the acceleration increases. Increase. The data acquisition time for one excitation in these high-speed imaging is about 100 to 150 ms in the case of the EPI method, and about 200 to 400 ms in the case of the FSE method.

On the other hand, in the imaging of a T1-weighted image compared to a T2-weighted image, when a multi-shot type FSE method is used to obtain a multi-echo signal, MT (mag) accompanying the application of an RF refocusing pulse is used.
network transfer) is not suitable for use as a T1-weighted image because changes in contrast occur in the image. In addition, the EPI method cannot be used due to image distortion, and it has been difficult to obtain the effect of shortening the photographing time by echo train.

For this reason, the T1-weighted image has the SE
A method of shortening the photographing time by using a method such as repeating the method or the FE method with a shortened repetition time TR is used. However, also in this case, the problem that the image density is deteriorated due to factors such as the MT effect is inevitable as the application density of the RF pulse is increased for the purpose of speeding up, as in the case of the FSE method. Further, even if the repetition time TR is shortened with the conventional FE method, it is difficult to obtain a desired T1 contrast, and almost only a proton contrast is obtained.

To overcome this situation, an imaging method using a multi-shot FE type EPI method has been proposed (for example, “Slavin S. and R”).
iederer SJ. , Magn. Reson.
Med. 38 368-377; 1997 "," E.
pstein FH. , Et al. , 6thAn
neutral meeting ISMRM 801; 19
98 ", and" Slavin S. et a
l. , 6th Annual meeting ISM
RM 320; 1998 "). The sequence based on this imaging method has been developed mainly for imaging the heart, and its characteristic is the ETL of the sequence.
(Echo Train Length) to reduce the influence of magnetic field inhomogeneity. This makes it possible to capture an oblique image of the heart or the like, which has been difficult to capture using the conventional single-shot type EPI method.

[0012]

However, multi-shot FE in T1-weighted imaging described above.
When the type EPI method is used, the number of parameters to be controlled increases, so that there are many restrictions in determining the values of parameters that affect image quality, such as the echo train length (ETL) of the pulse sequence and the number of shots. Become.

For example, if the pulse sequence is set so as to increase the echo train length, the speed of the imaging itself can be increased, but on the other hand, the data collection time increases as is particularly noticeable in the EPI method. As a result, the amount of occurrence of chemical shift artifacts and the image distortion due to the non-uniformity of the magnetic field increase. As described above, since there are many restrictions on parameters that affect image quality and complexity, a method of operating a one-dimensional slide bar of each parameter installed on a conventional operation panel while calculating with a calculator to set shooting conditions. In such a case, it is extremely difficult to set the photographing conditions optimally.

In particular, since the weighting of each parameter is different depending on the evaluation function, even if a skilled operator operates a one-dimensional slide bar, it is quite difficult to set the optimum photographing conditions. Is inevitable.

If the setting accuracy of the photographing conditions is low, the pulse sequence may not be executed in actual photographing,
This means that only images with poor image quality can be obtained. As a result, situations such as forced re-imaging occur frequently, and thus there is a problem in that operation labor is increased and patient throughput is reduced. Such a situation also puts a considerable physical and mental burden on the patient.

The present invention has been made in view of the above-mentioned problems of the prior art, and a first object of the present invention is to provide a plurality of echo signals (eg, multi-shot type FSE method and EPI method) for each shot. When performing magnetic resonance imaging to obtain an echo train, a pulse sequence that satisfies the optimum imaging conditions according to the imaging purpose is set quickly, with less operation labor, and set with high accuracy to obtain high-quality MR.
The ability to provide images.

A second object of the present invention is to provide a multi-shot type FSE method, an EPI method, etc., for performing magnetic resonance imaging for obtaining a plurality of echo signals (echo train) for each shot. An object of the present invention is to provide an interface that can quickly and accurately set a pulse sequence satisfying an optimum imaging condition according to a purpose with a small operation effort.

[0018]

According to the present invention, there is provided a method for improving the speed, for example, in the above-mentioned EPI method, that is, improving the relationship between the extension of data acquisition time and the increase in image distortion due to chemical shift artifacts and magnetic field inhomogeneities. Focuses on the fact that the constraint on the echo train length is effective. When fat suppression is further added, it is not necessary to consider the occurrence of chemical shift artifacts, so that the data collection time can be extended to such an extent that image distortion due to the influence of magnetic field non-uniformity does not occur. Further, if the echo train is lengthened, the data collection efficiency does not decrease even if the repetition time TR is extended, so that the SNR per unit time can be improved.

To achieve the above object, the following configuration is adopted.

According to the first aspect, an MRI for applying a pulse sequence to a subject placed in a uniform static magnetic field to collect echo signals and generate an image inside the subject.
In the apparatus, one RF pulse is used as the pulse sequence.
A pulse sequence for generating a plurality of echo signals per application of the excitation pulse is set, a data collection time for collecting the plurality of echo signals is set to a desired value, and the plurality of echo signals are set from the desired time. Pulse sequence setting means for determining the number of echoes of the echo signal and the number of shots of the RF excitation pulse; and pulse sequence executing means for executing the pulse sequence set by the pulse sequence setting means and collecting the echo signal. It is characterized by.

Preferably, the type of the pulse sequence set by the pulse sequence setting means is a pulse train for applying a plurality of refocusing RF pulses to generate the plurality of echo signals or a gradient magnetic field pulse in a reading direction. , A pulse train for inverting the polarity of a plurality of times. For example, the pulse sequence is a pulse sequence for obtaining a T1-weighted image, and its repetition time TR is 600 m
s or less.

Also, for example, the pulse sequence includes a pulse train for inverting the polarity of the readout gradient pulse a plurality of times, and applies a fat suppression pulse before applying the pulse train. Preferably, the data collection time for collecting the plurality of echo signals is set to a value of 30 ms or less.

As an example, the data collection time for collecting the plurality of echo signals can be set to a value of 10 ms or less. Further, the pulse sequence may be a pulse sequence that does not use a fat saturation pulse.

On the other hand, the pulse sequence setting means comprises:
Preferably, an interactive user interface with a planar graph display for constraining the data acquisition time of the pulse sequence to an optimal value is provided.

This user interface is, for example, an interactive user interface for displaying a planar graph using two variables. These two variables are the number of shots and the number of phase encodes of the RF pulse. For example,
The user interface is an interface for designating a prohibited area for a combination of an echo train length (ETL) and the number of shots on the two-dimensional graph, and performing parameter selection within a range excluding the prohibited area. Further, for example, the user interface is an interface that displays a recommended range on the two-dimensional graph with respect to a combination of an echo train length (ETL) and the number of shots on the two-dimensional graph. As an example,
In this user interface, at least one of the invalid range and the recommended range is displayed with a pattern or color.

Further, the user interface includes:
The operator may have means for inputting a straight line having an arbitrary inclination on the graph, and means for allowing a photographing parameter to be selected only on the straight line.

Further, the user interface may be an interactive user interface for displaying a two-dimensional graph using three variables. These three variables are
For example, the number of shots, the number of phase encodes, and the number of segments of the RF pulse.

As another aspect of the first invention, a reception processing means for receiving the plurality of echo signals each time the RF excitation pulse is applied, and processing the echo signals into echo data of a digital amount; Reconstructing means for arranging the echo data in a frequency space of a predetermined matrix size and performing image reconstruction processing on the echo data in the frequency space, the reconstructing means comprising: When generating the echo data exceeding the number of data necessary for the arrangement, a part of the echo data may be discarded and the remaining echo data may be arranged in the frequency space.

Preferably, when the application of the RF excitation pulse generates the echo data exceeding the number of data necessary for the arrangement of the frequency space, the reconstructing means preferably selects the first one of the echo data trains. A part of the data generated at the end and a part of the data generated at the end are discarded, and the remaining echo data is arranged in the frequency space.

With this configuration, the T1 contrast image, which has conventionally been difficult to reduce the photographing time, can be converted into an EPI image.
When speeding up using a pulse sequence such as a method, it is possible to determine an optimum imaging parameter by a variable function of the ETL and a graphic interface for inputting those parameters. The photographing parameters can be set while intuitively understanding the possible values of the photographing parameters according to the desired image quality and the current setting status in relation to other parameters.

On the other hand, according to the second aspect of the present invention, an echo signal is collected by applying a pulse sequence to a subject placed in a uniform static magnetic field, and an image of the inside of the subject is generated. In the MR imaging method, a pulse sequence for generating a plurality of echo signals per application of one RF excitation pulse is set as the pulse sequence, and a data acquisition time for acquiring the plurality of echo signals is desired. The number of echoes of the plurality of echo signals and the number of shots of the RF excitation pulse are determined from the desired time, and the set pulse sequence is executed to collect the echo signals. .

[0032]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) A first embodiment will be described with reference to FIGS.

The MRI (Magnetic Resonance Imaging) apparatus according to this embodiment can generate a plurality of echo signals for one application of an excitation pulse to collect data in a short time, EPI (Echo Planar Imaging), FSE (Echo Planar Imaging). An apparatus for executing a pulse sequence based on a fast spin echo method or a pulse sequence based on the method, which is characterized in that data acquisition time by the pulse sequence is restricted. This constraint uses the graphical interface
Interactively with the operator. With this constraint,
Image degradation factors such as chemical shift artifacts, image distortion due to magnetic field inhomogeneity, and image blurring due to T2 attenuation can be eliminated or suppressed, and image quality can be improved.

FIG. 1 shows a schematic configuration of the MRI apparatus.
The MRI apparatus includes a bed on which the subject P is placed, a static magnetic field generator for generating a static magnetic field, a gradient magnetic field generator for adding positional information to the static magnetic field, and a transmitter / receiver for transmitting and receiving a high-frequency signal; A control / arithmetic unit for controlling the entire system and reconstructing an image is provided.

The static magnetic field generator includes, for example, a superconducting magnet 1 and a static magnetic field power supply 2 for supplying a current to the magnet 1, and has a cylindrical opening (diagnostic space) into which the subject P is loosely inserted. the axial direction (Z axis direction) to generate a static magnetic field H _0.
Note that a shim coil 14 is provided in this magnet portion. The shim coil 14 is supplied with a current for homogenizing a static magnetic field from a shim coil power supply 15 under the control of a controller described later. The couch part can retreatably insert the top plate on which the subject P is placed into the opening of the magnet 1.

The gradient magnetic field generator has a gradient magnetic field coil unit 3 incorporated in the magnet 1. The gradient magnetic field coil unit 3 includes three sets (types) of x, y, and z coils 3x to 3z for generating gradient magnetic fields in X, Y, and Z axis directions orthogonal to each other. The gradient magnetic field further includes x,
A gradient magnetic field power supply 4 for supplying a current to the y, z coils 3x to 3z is provided. The gradient magnetic field power supply 4 supplies a pulse current for generating a gradient magnetic field to the x, y, and z coils 3x to 3z under the control of a sequencer 5 described later.

An x, y, z coil 3x from the gradient magnetic field power supply 4
By controlling the pulse current supplied to ~ 3z,
The gradient magnetic fields in the X, Y, and Z directions, which are three axes as physical axes, are synthesized, and the slice-direction gradient magnetic fields G _S as logical axes are synthesized.
It can be arbitrarily set and changed each direction of the phase-encoding direction gradient magnetic field G _E, and readout direction (frequency encode direction) gradient magnetic field G _R. Slice direction, phase encoding direction, and gradient magnetic fields in the readout direction are superimposed on the static magnetic field H _0.

The transmitting and receiving unit includes an RF coil 7 disposed near the subject P in the imaging space in the magnet 1,
And a transmitter 8T and a receiver 8R, which are connected to each other. The transmitter 8T and the receiver 8R are connected to a sequencer 5 described later.
Supplies RF current pulses of a Larmor frequency for causing a magnetic resonance (MR) phenomenon to the RF coil 7 under the control of the RF coil 7, and receives a high-frequency MR signal received by the RF coil 7 to generate various signals. Processing is performed to form a corresponding digital signal.

The control / arithmetic unit includes a sequencer (also called a sequence controller) 5, a host computer 6, an arithmetic unit 10, a storage unit 11, and a display unit 1.
2 and an input device 13.

The host computer 6 includes the sequencer 5
, The arithmetic unit 10 and the storage unit 1
1 and a function of controlling the operation of the entire apparatus including the display unit 12, and also functions as a user interface at the time of scan planning. That is, the host computer 6
Provides, along with the display 12 and the input unit 13, an interactive user interface for receiving information instructed by the operator based on the stored software procedure, and instructing the sequencer 5 with scan sequence information based on this information. It has become. Through this user interface, the user can freely set the number of slices and the scan time possible during the repetition time TR corresponding to the variable length echo train corresponding to the matrix size of the image to be captured and the number of shots (the number of excitations). It can be set to.

The sequencer 5 has a CPU and a memory, stores pulse sequence information sent from the host computer 6, and operates the gradient magnetic field power supply 4, the transmitter 8T, and the receiver 8R in accordance with the information. Control. In addition, the sequencer 5 temporarily inputs the digital data of the MR signal from the receiver 8R, and transfers the data to the arithmetic unit 10 that performs the reconstruction processing.

Here, the pulse sequence information is all information necessary to operate the gradient magnetic field power supply 4, the transmitter 8R and the receiver 8T in accordance with a series of pulse sequences, for example, x, y, z coils. Information about the intensity of the pulse current applied to 3x to 3z, application time, application timing, and the like are included.

The pulse sequence that can be employed in the present embodiment includes the FE type EPI method, the SE type EPI method,
SE method, FASE (High-speed Asymmetric SE)
Law.

The arithmetic unit 10 reads the input raw data, arranges the raw data in the Fourier space (also called k-space or frequency space) of the image, averages the data, and reconstructs the raw data into real space data (For example, two-dimensional or three-dimensional Fourier transform processing), MIP (maximum intensity projection) processing and the like are performed in an appropriate order to generate two-dimensional image data from three-dimensional image data. .

In particular, in the present embodiment, in order to improve the degree of freedom in setting the effective echo time TE _eff , the data can be arranged by shifting the center of the Fourier space in the phase encoding direction. As the reconstruction processing, a reconstruction processing to which the half Fourier method is applied can be performed.

The storage unit 11 can temporarily store not only raw data and reconstructed image data but also various data generated in the course of arithmetic processing. The display 12 displays an image. In addition, the operator can input necessary information for specifying imaging conditions such as a desired scan condition, scan sequence, and image processing method to the host computer 6 via the input device 13.

As elements of the control / arithmetic unit, a sound generator 16, an ECG sensor 17, and an ECG unit 1
8 are provided. The sound generator 16 includes the sequencer 5
Alternatively, in response to an instruction from the host computer 6, a voice message for breath holding is generated for the patient (subject). Further, the ECG sensor 17 and the ECG unit 18 detect an electrocardiogram signal of the patient and output it to the sequencer 5, so that an electrocardiographic synchronized imaging can be performed.

The MRI apparatus according to the present embodiment is characterized in that optimum imaging conditions can be easily set. The core of the setting is easy selection and setting of a pulse sequence used for imaging. Here, the relationship between various parameters of the pulse sequence that affects the image quality will be examined in relation to the pulse sequence selection method.

Now, description will be made assuming that a pulse sequence of the EPI method is used. Echo interval (ETS: Echo Train Spacin) determines the capability of the gradient magnetic field, that is, the resolution and the sampling pitch (bandwidth).
g), it is assumed that this echo interval is a shooting condition (parameter) that is first input by the user. Existing M
According to one of the RI devices, this echo interval is
For example, 0.6 ms, 0.8 ms, 1.2 ms, 1.6 m
About seven types of values such as s, 2.4 ms, 3.2 ms, and 4.8 ms can be selected.

Next, the echo time TE is determined. In the case of the pulse sequence based on the FE type EPI method, when the method of fat suppression is not used together, In with the nuclear spin of fat is used.
Phase and Out Phase are important in determining image contrast. When the order of the echo signal to collect the data of the echo time TE is determined, that is, E
TL _contrast (Echo Train Len
gth), the echo signal responsible for data collection in the center of k-space is internally set by its ETL _contrast . Actually ETL _contrast >
1 so that the echo time TE is equal to the echo interval ET
Constrained by S. That is,

(Equation 1) Becomes the relationship.

Next, an ETL _eff for determining the amount of image distortion and chemical shift artifacts generated at the time of image reconstruction, and an ETL for defining the minimum repetition time TR.
_{The total} will be described. As an example, the phase encoding direction matrix size PE = 128, ETL
_{If contrast} = 4, the number of applied RF pulses,
That the following 3 modes depending on the number of shots Sh can be calculated _{ETL eff} and _{ETL-to tal.}

[0053]

(Equation 2) It is.

[0054] Further, in order to consider the echo spacing ETS, to classify the shooting EPI method in terms of data collection time T ₀ as follows.

[0055]

(Equation 3) When the data acquisition time _{T 0} is defined such, _{ETL eff} when the above number of shots Sh = small (FIG. 2 (a))
= At 32 conditions, ETS to satisfy the data acquisition time _{T 0} of the above (C) is not present. This is the basis for the fact that fat suppression is essential in the single shot EPI method. Under the condition of ETL _eff = 32, the above (B)
Just satisfying the data collection time T ₀ of
It must be 0.8 ms. Furthermore, in order to satisfy the data acquisition time _{T 0} of the above (A) is, ETS <2.4
ms is the limit.

On the other hand, the number of shots Sh = large (FIG. 2
Under the condition of ETL _eff = 4 in (c)),
Data acquisition time _{T 0} of the above (B) is ETS = 4.8 m
s can also be satisfied. The data collection time T ₀ of (C) is E
TS = 2.4 ms is sufficient.

That is, when the matrix size PE in the phase encoding direction is given, if the number of shots is changed,
ETL _eff (ie, the number of echoes per RF excitation that determines the amount of image distortion and chemical shift artifacts) can be controlled.

Although shortening the ETL _eff is very effective in reducing image distortion and chemical shift artifacts, the performance as EPI, that is, the advantage of high-speed photographing, is reduced. On the contrary, if the ETL _eff is extended, it is possible to improve the data collection efficiency by covering the RF pulse, the time required for winding / rewinding the amount of phase encoding, and the overhead such as the echo time shift. it can. Therefore, it is desired to set the ETL _eff in consideration of the balance between suppression of image distortion and chemical shift artifacts and data collection efficiency.

Normally, in order to obtain T1 contrast, a repetition time TR of about 500 ms or less is desired. TR> 100
The SNR can be increased by increasing the flip angle to about 70 ° in ms or more. Further, overhead occurs outside the pulse sequence for the main photographing, such as the empty shot of the RF pulse and the scan for collecting the phase correction data, but the overhead is relatively increased by increasing the number of shots and shortening the TR. Can be reduced.

That is, the data collection time T ₀ is

(Equation 4) It is represented by

As described above, various photographing parameters which influence the image quality have been examined. However, since the weighting of the parameters differs depending on the evaluation function, as in the prior art, one parameter on the console is used.
In the case of setting the shooting conditions using the dimensional slide bar,
It is quite difficult for a skilled operator to set the optimal shooting conditions.

An interface that significantly reduces this difficulty is provided by an embodiment of the present MRI apparatus as follows.

This interface is a visual and interactive graphic interface provided by the host computer 6, the display unit 12, and the input unit 13 in cooperation with each other when the operator makes a shooting plan.

By the way, there are more than 300 various hardware and software parameters at the time of the radiographing plan handled by the MRI apparatus. However, in actuality, due to the processing (not shown) of the host computer 6 of the apparatus, 50 parameters are required. About parameters are open to the user as parameters that can be changed by the user. When the photographing plan process is started, about 250 device-side parameters invisible to the user are automatically set by the host computer 6 according to a predetermined procedure. Therefore, when the processing of the photographing plan is started, the main scan can be executed as it is, and the operator is urged to set parameters for opening the user. The host computer 5 according to the value of the user-open parameter set by the operator.
Immediately corrects about 250 parameter values left to the apparatus within an allowable range. The result of this fix is
This is reflected in urging the user to open the parameters as necessary. That is, the processing of the photographing plan interactive with the apparatus side is advanced. Therefore, no matter what value the operator sets the parameter for user opening,
The executable state of the main scan is always maintained. That is, it is possible to avoid a situation in which it is determined that the main scan is not started for the first time when the image is actually taken depending on the setting of the parameters.

The visual and interactive graphic interface of the present embodiment is provided for setting the above-mentioned user-open parameters. The user open type parameters include the type of imaging target, type of sequence, repetition time TR, echo time TE, ETS, E
TL, number of shots, flip angle, matrix size in phase encoding direction, number of segments, scan time, FO
Main parameters such as V, the presence or absence of a gate, the type of gate, and the presence or absence of fat suppression are included.

As an image of the graphic interface, the display 12 displays a two-dimensional graph shown in FIG. As shown in the figure, the horizontal axis represents the number of shots Sh on the horizontal axis, and the matrix size PE on the vertical axis represents the phase encoding direction matrix size, and the evaluation function described above in the case of the EPI method (A) to (A). C) taking data acquisition time T ₀ shown in section.

The relationship between the two variables Sh and PE is

## EQU5 ## This is expressed by a linear equation of PE = ETL × Sh (see the straight line S in FIG. 3), and the slope of the straight line S is ETL. The prohibited area in which the straight line S is prohibited from entering is shown in FIG.

## EQU6 ## This is represented by a region R where PE> T ₀ / ETS × Sh (see the hatched region in FIG. 3). As described above, T ₀ is the data collection time. In the case of the EPI method, for example, values of T ₀ = 100, 30, and 10 ms are selectively taken (see the above-mentioned condition items (A) to (C)). ).

That is, an area partitioned by a straight line T0 (A) determined by the data collection time T ₀ = 100 ms corresponding to the condition (A): PE> T ₀ / ETS × Sh forms a prohibited area R. This region is drawn in red on the graph, for example. On the other hand, a straight line T determined by the data collection time T ₀ = 30 ms and 10 ms corresponding to the conditions (B) and (C).
The areas partitioned by 0 (B) and T0 (C) are respectively drawn in yellow and blue, for example. In this embodiment, the yellow and blue areas are set as recommended areas for setting the number of shots.

In this two-variable graphic interface, rectangular bars B0 to B0 on the horizontal axis X and the vertical axis Y
B2 indicates a range that can be set by the user for the number of shots Sh and the matrix size PE by automatically calculating on the device side. For the number of shots Sh, the rectangular bars B0, B
A range R1 on the horizontal axis defined by 1 is a range of possible values. Regarding the matrix size PE, a range R2 on the horizontal axis defined by the rectangular bars B0 and B2 is a range of possible values. The positions of the rectangular bars B0 to B2, that is, the range of possible values R1 and R2 of the variables are changed in real time by calculation on the device side according to the values of the parameters of the user opening operated by the operator.

The operator operates the input device 13 while looking at this graph, and handles X1 for the number of shots Sh, X2 for the matrix size PE, and straight line S: PE = ET.
The optimum photographing conditions are determined while operating the L × Sh handle Y1. As an example of the handle operation, the following modes can be adopted.

For example, when the handle X2 of the matrix size PE is fixed and the handle X1 of the shot number Sh is moved (see the arrow a in FIG. 3), a straight line S:
The slope of PE = ETL × Sh changes (see arrow a ′ in FIG. 3). With the movement of the handle X1, the prohibited area R: PE> T ₀ / ETS × Sh, which is determined by substituting the numerical value of the condition (A) for the data collection time T ₀ , changes in real time in conjunction with it (arrow a). see). in this case, the straight line S is in accordance with the movement of which is controlled its inclination that turning prohibited region R. handle X1, data acquisition time T ₀
Each of the areas determined by substituting the numerical values of the above conditions (B) and (C) respectively changes in real time (see a).

Further, as another mode, the range of the prohibited area R may be changed in consideration of or changing other imaging conditions such as application of a fat suppression pulse.

In the MRI apparatus of this embodiment, the pulse sequence is set as a part of the scan plan according to the above principle. FIG. 4 shows an outline of the setting procedure, and FIG. 5 shows an example of a pulse sequence set through such a procedure.

The operator activates an interactive user interface realized by the cooperation of the display unit 12 and the input unit 13 by the software processing of the host computer 6 in the processing for preparing the scan plan.

When the interface is activated, first, the type of the pulse sequence and the echo interval ETS are selectively input (step S1). Now, it is assumed that the multi-shot FE type EPI method is selected as the pulse sequence. The echo time TE is determined according to the ETS value (step S2). With this determination, the echo that collects data at the center of the k-space in the phase encoding direction is E
Internally set by TL _contrast (step S3).

Next, the operator, depending on the purpose of photographing,
Inputting the data acquisition time T ₀ for depends pulse sequence selected EPI method as an evaluation function (Step S
4). This is performed, for example, by inputting time values classified as in the above-described conditions (A) to (C).

Next, the host computer 6 (which also functions as a user interface) creates data for graphic display from the data received so far and the calculated data, displays the data on the display 12 and displays the data on the display 12. (User) (step S5). While referring to the presented graphic interface, the operator appropriately moves the handle of the graphic interface screen via the input device 13. This allows intuitive (visual) capture of shooting parameters such as the number of shots for maintaining image quality (suppression of image distortion and chemical shift artifact) when the matrix size PE in the phase encoding direction is increased or for achieving a desired state. While you can set.

The photographing parameters determined through the graphic user interface of the interactive input method are stored as control data for the main scan (step S7).

As a result, in the main scan, a pulse sequence based on the FE type EPI method according to the multi-shot method is executed as shown in FIG. 5, for example. In FIG.
Gradient G _S phase encoding indicates only that the phase encoding for each echo signal is subjected. There are various modes of applying this phase encoding.

When this main scan is executed, for example, with the number of shots = small (see the state of FIG. 2A), the arithmetic unit 10 performs image reconstruction by the half Fourier method. On the other hand, when the processing is executed with the number of shots = large (see the state of FIG. 2C), all or a part of the echoes at the beginning and end of the echo train are processed by the operation unit 10.
And are subjected to reconstruction processing without being arranged in the k-space.

When the multi-shot FE type EPI method in T1-weighted imaging is used, the number of parameters that need to be controlled increases, and parameters that affect image quality, such as the echo train length (ETL) of the pulse sequence and the number of shots, are increased. Although there are more restrictions on the determination, according to the MRI apparatus of the present embodiment, a pulse sequence that satisfies the optimum imaging conditions according to the imaging purpose is set quickly, with less operation labor, and with high accuracy. Photographing can be performed to provide a high-quality MR image.

In particular, since a graphic user interface of an interactive input method is used, such a pulse sequence can be set more quickly, with less operation labor, and more accurately than in a conventional one-dimensional slide bar type interface. . In addition, the pulse sequence is always executed reliably in actual photographing, and a high-quality image can be provided.

Therefore, the number of re-photographs is reduced, the operation effort is reduced, and the patient throughput is increased. This significantly reduces the physical and mental burden on the patient.

The pulse sequence based on the EPI method described above does not apply a fat suppression pulse. However, as shown in FIG.
It may be set to apply the fat suppression pulse P _fat . As the fat suppression pulse, a binomial pulse, a sink function, a Gaussian function, or the like may be used in a slice-selective or non-slice-selective manner.

In the graphic user interface of the first embodiment described above, the display method of the prohibited area and the other areas is not necessarily limited to coloring the area. It is only necessary to visually classify.

Further, the recommended area may be displayed over the area other than the prohibited area. Further, the recommended condition may be separately displayed by a numerical value or the like.

Further, in this graphic user interface, the aforementioned straight line S: PE = ETL × S
Instead of h, the operator may input a straight line having an arbitrary inclination, and the photographing condition may be selected only on the straight line.

[0088] Further, the graphical user interface of the first embodiment has been described data acquisition time T ₀ when the EPI method as the evaluation function, when using the FASE method as pulse sequence, as an example,

(Equation 7) May be used.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIGS. Note that the hardware configuration of the MRI apparatus of this embodiment is the same as or equivalent to that of the first embodiment.

In the present embodiment, the scan planning and the execution of the main scan using the graphic user interface according to the present invention are applied to an example in which the heart and the like are imaged by a synchronous imaging method. FIG. 7 shows a multi-shot segment EP.
FIG. 3 shows a schematic diagram of a sequence structure of the I method (FE type).

When this synchronous photographing method is performed, in addition to the first embodiment described above, restrictions such as the RR interval of the ECG signal are further added, and setting of photographing conditions (parameters) becomes more complicated. That is, when using the EPI method,
The above-mentioned constraints in terms of data collection time _{T 0 (A) ~ (C} ), for example, any of the following conditions is applied.

(D) One heartbeat imaging: An imaging method for observing changes over time such as arrhythmia and perfusion. The heartbeat is collected with a time width of 200 to 300 ms excluding the cardiac contractor. Since the number of segments Se is 1, the repetition time TR is made as long as possible within the range of the amount of image distortion and chemical shift to increase the data collection efficiency.

(E) Dynamic observation (I): The patient is held for about 5 to 8 seconds with less burden on the patient,
An image is taken at a resolution of a cardiac phase of about ms.

(F) Dynamic observation (II): In order to precisely observe the movement of the heart valve and the like, this is an imaging in which the breath is held for about 30 seconds or intermittently for about 5 to 8 seconds. ,
The data collection is stopped for about 10 to 30 ms before shooting. In this case, the number of shots Sh may become 1.

In the imaging of the heart, the imaging is repeated in synchronization with the RR interval of the ECG signal. Therefore, the setting of the photographing condition is further complicated, and in order to solve the problem, a graphic user interface of an interactive input method is provided.

FIG. 8 shows a graph display state of this interface. As variables, three values are taken: the number of shots Sh, the number of phase encodings PE (= matrix size in the phase encoding direction), and the number of segments Se. The vertical axis represents the phase encoding number PE, and the horizontal axis on the first quadrant side represents the shot number Sh.
To form a two-dimensional graph in which the horizontal axis in the second quadrant indicates the number of segments Se.

In the three-variable graphic interface, rectangular bars B0 to B0 on the horizontal axis X and the vertical axis Y
B3 indicates a range that can be set by the user for the number of shots Sh, the matrix size PE, and the number of segments Se automatically calculated by the apparatus. Regarding the number of shots Sh, the range on the horizontal axis defined by the rectangular bars B0 and B1 is the range of possible values at present. Regarding the matrix size PE, the range on the horizontal axis defined by the rectangular bars B0 and B2 is the range of possible values at present. Regarding the segment number Se, the range on the horizontal axis defined by the rectangular bars B0 and B3 is the range of possible values at present. Rectangular bar B0
The position of B3, that is, the range of values that the variable can take, is changed in real time by a calculation on the device side in accordance with the value of the user-opened parameter operated by the operator.

The relationship between each variable is

(Equation 8) The slope of the straight line S1 is “ETL × Se”, and the slope of the straight line S2 is “ETL × Sh”. Straight lines S1, S
2 prohibited areas R1 and R2 respectively

(Equation 9) It is.

The graph of this interface includes:
As in the case of the first embodiment, the conditions (A) to (A)
Data acquisition time _{T 0} represented by (C) is used as the evaluation function, linear T0 (A), T0 (B ) and T0
(C): PE> T ₀ / ETS × Se or PE> T ₀
Areas divided by / ETS × Sh are displayed by color for each quadrant as an example. This color-coded area dynamically fluctuates on the image with the fluctuation of the variable.

While looking at the screen of the graphic user interface, the operator operates the handle, for example, as follows.

For example, if the handle X2 of the number PE of phase encodes is fixed, and the handle X1 of the number of shots Sh is moved, the straight line S1: PE = ETL × Se ×
The slope of Sh changes. The slope of the straight line S1 is the number of segments S
Since it is a function of e, the hand X3 of the number of segments Se is also linked in real time. This handle X1, X
With the movement of 3, the prohibited areas R1 and R2 also change in real time. At this time, the inclination of the straight lines S1 and S2 is controlled so as not to enter the prohibited areas R1 and R2.
Conversely, the same applies when the handle X3 on the segment number Se side is moved.

By using this interface in an interactive manner, the number of shots and the number of segments for maintaining the image quality when the matrix size PE in the phase encoding direction is increased are set while grasping the photographing conditions visually (intuitively). can do. Therefore, the same effects as in the first embodiment can be obtained even in cardiac imaging based on the ECG gate.

Although the imaging in the first and second embodiments has been described as a two-dimensional imaging method, the same interface input can be applied to a three-dimensional imaging method.

The pulse sequence is not limited to the EPI method, but may be the FSE method (RARE method).
In the case of the SE method, instead of the image distortion due to T2 ^* , T
A similar interface can be applied by taking into account image blurring due to 2 mitigation.

Further, in the graphic user interface according to the present invention, the variables that the user adjusts while viewing the graph screen are not limited to the two or three variables described above, but are open to the user as shooting parameters that affect the image quality. Any parameters that have been set can be adopted. For example, in the graph screen of FIG. 8, FOV may be set as another variable instead of the phase encoding number PE forming the vertical axis. On the other hand, the number of variables per se may be four or more. For example, in the graph screen of FIG. 8, the number of shots Sh and the number of segments Se may be taken on the horizontal axis, and the number of phase encodings PE or FOV and the breath-hold scan time may be taken on the vertical axis.

Accordingly, the characteristics of the graphic user interface to which the present invention is applied are summarized as follows. First, a plurality of shooting parameters can be set simultaneously. Secondly, the possible values of the plurality of photographing parameters can be simultaneously and visually expressed to give the operator an intuitive image of the setting range, thereby facilitating the setting of the photographing parameters. Third, a combination of a plurality of parameters can be changed as appropriate. Fourth, when the handle position of the photographing parameter is changed, the forbidden area is also dynamically linked, so that the operator always has an intuitive image of an accurate setting range.

Further, the user interface includes:
The operator may have means for inputting a straight line having an arbitrary inclination on the graph, and means for allowing a photographing parameter to be selected only on the straight line.

Note that the present invention is not limited to the above-described exemplary embodiments, and those skilled in the art can understand, based on the contents of the appended claims, within the spirit and scope of the invention. Can be modified and changed into various modes, which also belong to the scope of the present invention.

[0109]

As described above, the MR according to the present invention is used.
According to the I device and the MR imaging method, for example,
When the echo time TE and the repetition time TR of the EPI method are limited to form a multi-shot, a graphic user interface used in the preparation for the shooting makes it easy to visually understand the optimum shooting parameters for each shooting target while easily understanding. The imaging parameters can be set without changing the image quality significantly even when the matrix size in the phase encoding direction is changed, and stable MR imaging based on the imaging parameters can be executed. Therefore, it is possible to reliably provide a high-accuracy and high-quality MR image with less burden on the patient and the operator.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an MRI apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram schematically illustrating the relationship among the number of shots, ETL, and data arrangement.

FIG. 3 is a screen view of a graphic user interface for explaining a restriction on the number of shots in the first embodiment.

FIG. 4 is a flowchart showing an outline of an operation performed by an operator on a graphic user interface.

FIG. 5 is a multi-shot EPI used in the first embodiment.
7 is a timing chart illustrating a pulse sequence of the FE type (FE type).

FIG. 6 is a timing chart illustrating a pulse sequence of a multi-shot EPI method (FE type) to which a fat suppression pulse is added, as a modified example.

FIG. 7 is a timing chart illustrating a pulse sequence of the multi-shot segment EPI method (FE type) according to the second embodiment of the present invention.

FIG. 8 is a screen diagram of a graphic user interface for explaining restrictions on the number of shots and the number of segments in the second embodiment.

[Explanation of symbols]

 Reference Signs List 1 magnet 2 static magnetic field power supply 3 gradient magnetic field coil unit 4 gradient magnetic field power supply 5 sequencer 6 host computer (user interface) 7 RF coil 8T transmitter 8R receiver 10 operation unit 11 storage unit 12 display (user interface) 13 input device ( User interface) 17 ECG sensor 18 ECG unit

Continued on the front page F term (reference) 4C096 AA03 AA06 AB14 AB18 AB25 AB37 AD06 AD15 AD27 BA07 BA12 BA13 BA41 BA42 BB05 BB28 BB31 DD07 DD14 DD16 5E501 AA25 AC17 BA09 EB05 EB06 FA14 FB28

Claims (19)

[Claims] 1. An MRI apparatus for applying a pulse sequence to a subject placed in a uniform static magnetic field to collect an echo signal and generate an image inside the subject, wherein the pulse sequence is 1 A pulse sequence for generating a plurality of echo signals per application of the RF excitation pulse is set, and a data collection time for collecting the plurality of echo signals is set to a desired value, and from the desired time, Pulse sequence setting means for determining the number of echoes of a plurality of echo signals and the number of shots of the RF excitation pulse; and pulse sequence executing means for executing the pulse sequence set by the pulse sequence setting means and collecting the echo signals. An MRI apparatus comprising: 2. The MRI apparatus according to claim 1, wherein a type of the pulse sequence set by the pulse sequence setting means is to apply a plurality of refocus RF pulses to generate the plurality of echo signals. MRI which is a pulse sequence including a pulse train to be inverted or a pulse train for inverting the polarity of the readout direction gradient magnetic field pulse plural times
apparatus. 3. The MRI apparatus according to claim 2, wherein the pulse sequence is a pulse sequence for obtaining a T1-weighted image, and has a repetition time TR of 600 ms or less. 4. The MRI apparatus according to claim 2, wherein the pulse sequence includes a pulse train for inverting the polarity of the readout gradient pulse a plurality of times, and applies a fat saturation pulse before applying the pulse train. An MRI apparatus that is a pulse sequence. 5. The MRI apparatus according to claim 4, wherein the data collection time for collecting the plurality of echo signals is set to a value of 30 ms or less. 6. The MRI apparatus according to claim 3, wherein the data collection time for collecting the plurality of echo signals is set to a value of 10 ms or less. 7. The MRI apparatus according to claim 6, wherein the pulse sequence is a pulse sequence that does not use a fat saturation pulse. 8. The MRI apparatus according to claim 1, wherein the pulse sequence setting means has an interactive user interface of a planar graph display for limiting data acquisition time of the pulse sequence to an optimum value.
I device. 9. The MRI apparatus according to claim 8, wherein the user interface is an interactive user interface for displaying a planar graph using two variables.
RI equipment. 10. The MRI apparatus according to claim 9, wherein the two variables are a shot number and a phase encoding number of the RF pulse. 11. The MRI apparatus according to claim 10, wherein the user interface specifies a prohibited area for a combination of an echo train length (ETL) and the number of shots on the two-dimensional graph. An MRI apparatus that is an interface that allows the user to select parameters in a range excluding the above. 12. The MRI apparatus according to claim 11, wherein the user interface sets a recommended range on the two-dimensional graph for a combination of an echo train length (ETL) and the number of shots on the two-dimensional graph. An MRI device that is an interface to display. 13. The MRI apparatus according to claim 12, wherein the user interface is an interface that displays at least one of the invalid area and the recommended area by patterning or coloring. 14. The MRI apparatus according to claim 8, wherein the user interface allows the operator to input a straight line having an arbitrary inclination on the graph, and enables an operator to select an imaging parameter only on the straight line. M with means
RI equipment. 15. The MRI apparatus according to claim 8, wherein the user interface is an interactive user interface for displaying a two-dimensional graph using three variables. 16. The MRI apparatus according to claim 15, wherein the three variables are a shot number, a phase encoding number, and a segment number of the RF pulse. 17. The MRI apparatus according to claim 1, wherein each time the RF excitation pulse is applied, the plurality of echo signals are received, and the echo signals are processed into digital echo data. Reconstructing means for arranging the echo data in a frequency space of a predetermined matrix size and performing image reconstruction processing on the echo data in the frequency space, the reconstructing means comprising: MRI apparatus characterized in that when generating the echo data exceeding the number of data required for the arrangement, a part of the echo data is discarded and the remaining echo data is arranged in the frequency space. . 18. The MRI apparatus according to claim 17, wherein the reconstructing unit is configured to generate the echo data when the application of the RF excitation pulse generates the number of data that exceeds the number of data required for the arrangement of the frequency space. In the echo data sequence,
An MRI apparatus in which a part of data generated at the beginning and a part of data generated at the end are discarded and the remaining echo data is arranged in the frequency space. 19. An MR imaging method for applying a pulse sequence to a subject placed in a uniform static magnetic field to collect an echo signal and generate an image inside the subject, wherein the pulse sequence is A pulse sequence for generating a plurality of echo signals per application of one RF excitation pulse is set, and a data collection time for collecting the plurality of echo signals is set to a desired value. An MR imaging method, wherein the number of echoes of a plurality of echo signals and the number of shots of the RF excitation pulse are determined, and the set pulse sequence is executed to collect the echo signals.