JP2001276016A - Magnetic resonance equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To plot a whole blood vessel with high contrast while reducing influence owing to the deviation of an image pickup timing and to selectively plot the image of an artery in contrast MRA measurement. SOLUTION: Measurement points arranged in the respective grid points of a k-space which is stipulated by the number of slice encoding and the number of phase encoding are divided into two groups which share an origin point and which are in complex conjugate relation mutually and successively measured. The measurement of the first group is started at the point of time when the contrast media density of a target blood vessel becomes high, the measurement points are sampling-controlled toward a low frequency component from a high frequency component to permit a distance from the origin point to be gradually close and a part near the origin point is measured at the point of time when the peak of the density is obtained. In the second group, sampling points are sampling-controlled toward the high frequency component from the low frequency component to permit the distance to be gradually separated on the contrary. Then the density of the contrast media becomes its peak when the low frequency component is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus for obtaining a tomographic image of a desired part of a subject by utilizing a nuclear magnetic resonance (hereinafter referred to as "NMR") phenomenon, and particularly to a method for delineating a vascular system. The present invention relates to a magnetic resonance imaging apparatus (hereinafter, referred to as an MRI apparatus) capable of securing a desired rendering range and image quality in a minimum time necessary for the above.

[0002]

2. Description of the Related Art An MRI apparatus uses an NMR phenomenon to measure the density distribution, relaxation time distribution, etc. of nuclear spins (hereinafter simply referred to as spins) at a desired inspection site in a subject, and from the measured data. An image of an arbitrary cross section of the subject is displayed.

One of the imaging functions of this MRI apparatus is MR angiography (hereinafter abbreviated as MRA) for drawing a blood flow.
There are a method using no contrast agent and a method using a contrast agent. As a method using a contrast agent, a method of combining a short T1 contrast agent such as Gd-DTPA with a short TR sequence of a gradient echo system is generally used. In this method, since the blood flow spin including the T1 shortened contrast agent has a T1 shorter than that of the surrounding tissue, saturation is less likely to occur when excitation by the high-frequency magnetic field is performed for a short repetition time TR. By utilizing the fact that a higher signal is emitted from other tissues, blood vessels filled with blood containing a contrast agent are drawn with high contrast to other tissues. By performing measurement of Volume data (specifically, three-dimensional) including blood vessels while the contrast agent stays in the target blood vessels, and performing projection processing by superimposing the obtained three-dimensional images, Draw blood flow. Here, a sequence based on a three-dimensional gradient echo method is generally used to obtain high-resolution information over a wide range.

[0004] In order to obtain a good image in such a three-dimensional contrast MRA, (1) a method of injecting a contrast agent, and (2) imaging time and timing are important. Regarding (1), a contrast agent must be injected into a blood vessel to be imaged so as to stably maintain a high concentration. For this reason, rapid injection using an automatic injector is generally used.

[0005] Regarding (2), for example, in order to separate and selectively image an artery, it is necessary to set the imaging timing so that the concentration of the contrast agent in the artery becomes high during data collection. In particular, it is ideal that the contrast agent concentration reaches a peak in the central portion (low-frequency region) of the k space which controls the contrast of the image, and the timing is set according to the data acquisition method of the pulse sequence to be used.

[0006] The data collection method mainly includes a sequential order in which measurement is performed from one end on the high frequency side of k-space to the other end on the high frequency side through a low-frequency region, and alternately arranged at both ends of the high-frequency region from the low-frequency region of k-space. There is a centric order (Centric Order) that measures toward, and generally a centric order is used. In the centric order of the three-dimensional measurement, one of the phase encode loop and the slice encode loop is set as the outer loop, and the other is set as the inner loop, and one or both of them are controlled in the centric order.

However, the centric order in this case is not a true centric order because the distance from the origin in k-space to the measurement point (sampling point) fluctuates as shown in FIG. Susceptible to
In some cases, arteriovenous separation was insufficient.

As a method for solving such a problem, ky-
Elliptical Centric Ordering has been proposed that takes into account the relative FOV in kz space and controls the distance from the origin in k space to gradually increase as the signal measurement progresses ( Fig. 1 (c)) ("Performance of an Ellipitical Cen"
tric View Order for Signal Enhancement and Motion
Artifact Suppression in Breath-hold Three-Dimensio
nal Gradient Echo Imaging. Alan, et al. Magnetic R
esonance in Medicine 38: 793-802,1997 ").

[0009]

In this data acquisition method, low-frequency data for determining the contrast of an image is measured at the beginning of an imaging time. Therefore, imaging starts when the concentration of a contrast agent in a target blood vessel increases. This makes it possible to selectively obtain arteriovenous images.

However, in the above-described centric order and elliptical centric ordering, the contrast of an image can be determined at an early stage, which is effective for selectively obtaining an arterial image. Since the low-frequency information is acquired only when the agent concentration is low, there is a problem that the image quality is easily deteriorated. In particular, if the measurement is started too early, the data in the low frequency region will be sampled during the time when the signal inside the blood vessel is extremely low, while the data in the high frequency region will be sampled during the time when the signal inside the blood vessel is high. Since sampling is performed, a ringing artifact having no DC component is generated.

On the other hand, in the sequential order, even if the measurement timing is slightly deviated, a remarkable artifact is less likely to appear in the image and a stable image can be obtained. There was a problem that separation was not sufficiently performed.

Accordingly, the present invention provides an MR capable of rendering the entire target blood vessel with high contrast in a short time while reducing the influence on the image quality due to the shift of the optimal imaging timing.
The purpose is to provide I equipment. It is another object of the present invention to provide an MRI apparatus which is hardly affected by body motion and can separate and draw an artery and a vein in MRA. Another object of the present invention is to provide a data collection method suitable for MRA.

[0013]

In order to achieve the above object, according to the present invention, measurement points in a ky-kz space are measured in two groups having a complex conjugate relationship with each other, and measurement is performed first. In the first group, a measurement point at a predetermined distance from the origin is set as a starting point, and measurement is performed toward the origin so that the distance from the origin is gradually reduced. In the second group to be measured thereafter, the distance from the origin to the measurement point is reversed. Adopts a data collection method in which is gradually increased.

That is, the MRI apparatus of the present invention comprises a static magnetic field generating means for generating a static magnetic field in a space where a subject is placed, and a gradient magnetic field for applying a gradient magnetic field in a slice direction, a phase encode direction and a readout direction to the space. Generating means, a transmitting system for irradiating a high-frequency magnetic field to cause nuclear magnetic resonance in atomic nuclei of the living tissue of the subject, a receiving system for detecting an echo signal emitted by the nuclear magnetic resonance, and the gradient magnetic field A control unit for controlling the generation means, the transmission system and the reception system,
A signal processing system for performing an image reconstruction operation using an echo signal detected by a reception system; and a means for displaying an obtained image, wherein the control system performs a three-dimensional sequence for applying slice encoding and phase encoding. Run,
The measurement points in k-space defined by the number of slice encodes and the number of phase encodes are divided into first and second groups that share the origin and have a complex conjugate relationship with each other. In the second group, the gradient magnetic field generating means in the slice direction and the phase encoding direction is controlled so that the distance from the origin to the measurement point gradually increases in the measurement order.

When dividing the measurement points into two groups, it is preferable to divide the adjacent measurement points so that they belong to different groups. In order to satisfy the condition that the measurement points of the two groups have a complex conjugate relationship with each other, it is necessary that the measurement points that are partially adjacent to each other in the vicinity of the origin belong to the same group. Therefore, in this specification, "division of adjacent measurement points so that they belong to different groups" means that the condition that they have a complex conjugate relationship is satisfied, and the condition that adjacent measurement points belong to different groups is the maximum. The state that is being done.

According to the three-dimensional image data acquisition method of the present invention, a step of selecting and exciting a predetermined region of the subject, applying a gradient magnetic field encoding at least in two directions, and measuring an echo signal generated from the region is performed. In a data collection method for repeating a plurality of times while changing the strength of the gradient magnetic field and collecting three-dimensional image data, the measurement points of the measurement space defined by the two-direction encode gradient magnetic field strengths share an origin and are mutually complex. The adjacent measurement points having a conjugate relationship are divided into first and second groups so as to belong to different groups.
And the second group are sequentially measured. At this time, in the first group measured first, the distance from the origin of the measurement space to the measurement point is measured so as to gradually decrease in the order of measurement, and the measurement is performed later. In the second group, the measurement is performed such that the distance from the origin of the measurement space to the measurement point gradually increases in the order of measurement.

According to the data collection method of the present invention, FIG.
As shown in (a), measurement can be performed without distance fluctuation from the origin, and the time when the lowest frequency component is measured coincides with the time when the signal intensity of the target blood vessel peaks due to the contrast agent. Thereby, the target blood vessel can be drawn with high contrast. In addition, even if there is a slight difference between the point in time when the low-frequency component is measured and the peak of the signal intensity, the low-frequency component can be reliably measured, and there is no image deterioration.
1 (b) to 1 (d) show a conventional centric order,
It shows the change in distance from the origin of k-space in elliptical centric order and sequential order.

According to a preferred aspect of the data collection method of the present invention, the first group measures only a part of the measurement points, and the second group measures all the measurement points. It is characterized by the following. Since the two groups have a complex conjugate relationship, one of the groups can estimate the unmeasured data from the measured data of the other group without measuring some of the measurement points.
Thereby, the measurement time of one group can be reduced. In particular, when performing the measurement of the first group before the peak of the contrast agent concentration increases, measurement of unnecessary data having a low signal intensity can be eliminated, and a good image can be obtained.

[0019]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 2 shows an MRI according to the present invention.
It is a block diagram showing the whole composition of a device. This MRI apparatus obtains a tomographic image of a subject using an NMR phenomenon, and includes a static magnetic field generating magnet 2, a magnetic field gradient generating system 3, a sequencer 4, a transmitting system 5, a receiving system 6, and a signal A processing system 7 and a central processing unit (CPU) 8 are provided.

The static magnetic field generating magnet 2 generates a uniform static magnetic field around the subject 1 in the body axis direction or a direction perpendicular to the body axis, and has a certain space around the subject 1. A permanent magnet type, a normal conduction type, or a superconducting type magnetic field generating means is disposed in the apparatus.

The magnetic field gradient generating system 3 comprises a gradient magnetic field coil 9 wound in three directions of X, Y and Z, and a gradient magnetic field power supply 10 for driving each gradient magnetic field coil. By driving the gradient magnetic field power supplies 10 of the respective coils in accordance with the above-mentioned command, gradient magnetic fields Gx, Gy, and Gz in three directions of X, Y, and Z are applied to the subject 1. By applying this gradient magnetic field, a specific slice or slab of the subject 1 can be selectively excited, and the position of a measurement point (sampling point) in a measurement space (k space);
The measurement order can be specified.

The sequencer 4 operates under the control of the CPU 8 and sends various commands necessary for data collection of tomographic images of the subject 1 to the magnetic field gradient generating system 3, the transmitting system 5 and the receiving system 6. I have. The operation timing of the magnetic field gradient generation system 3, the transmission system 5, and the reception system 6 controlled by the sequencer 4 is called a pulse sequence. Here, a sequence for three-dimensional blood flow imaging is adopted as one of the pulse sequences. The control of the sequencer 4 will be described later in detail.

The transmission system 5 irradiates a high-frequency magnetic field to cause nuclear magnetic resonance in the nuclei of the atoms constituting the living tissue of the subject 1 by the high-frequency pulse sent from the sequencer 4. It comprises a device 12, a high-frequency amplifier 13, and a high-frequency coil 14a on the transmission side. The high-frequency pulse output from the high-frequency oscillator 11 is amplitude-modulated by the modulator 12 in accordance with a command from the sequencer 4, and the high-frequency pulse subjected to the amplitude modulation is amplified by the high-frequency amplifier 13, and then the high-frequency pulse placed close to the subject 1 By supplying the electromagnetic wave to the coil 14a, the subject 1 is irradiated with the electromagnetic wave.

The receiving system 6 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of an atomic nucleus of a living tissue of the subject 1. The receiving system 6 includes a high-frequency coil 14b on the receiving side, an amplifier 15, and a quadrature phase detector. 16 and an A / D converter 17. The electromagnetic wave (NMR signal) of the response of the subject 1 due to the electromagnetic wave emitted from the high-frequency coil 14a on the transmitting side is detected by the high-frequency coil 14b arranged close to the subject 1. The detected echo signal is A / D-converted through an amplifier 15 and a quadrature detector 16.
The data is input to the converter 17, converted into a digital amount, further converted into two series of collected data sampled by the quadrature phase detector 16 at a timing according to a command from the sequencer 4, and sent to the signal processing system 7.

The signal processing system 7 includes a CPU 8 and a magnetic disk 18
And a recording device such as a magnetic tape 19, and a display 20 such as a CRT.The CPU 8 performs processing such as Fourier transform and correction coefficient calculation image reconstruction, and performs an appropriate operation on the signal intensity distribution of an arbitrary cross section or a plurality of signals. Is performed, and the obtained distribution is imaged and displayed on the display 20 as a tomographic image. In FIG. 2, the high-frequency coils 14a and 14b on the transmitting side and the receiving side and the gradient magnetic field coil 9 are installed in the magnetic field space of the static magnetic field generating magnet 2 arranged in the space around the subject 1.

Next, the blood flow imaging function of the MRI apparatus of the present invention will be described. Sequence 4 as described above
Is a magnetic field gradient generating system 3, a transmitting system 5 and a receiving system 6 according to a predetermined pulse sequence, here a three-dimensional MRA sequence.
Control of the operation timing. This pulse sequence is
The program is pre-installed as a program in a memory provided in the CPU 8, and can be executed by the user appropriately selecting according to the purpose of photographing, similarly to other pulse sequences. That is, when an MRA using a contrast agent is selected via the input device of the CPU 8, the sequence 4 is controlled by the CPU 8 to execute a three-dimensional MRA sequence.

This pulse sequence is a sequence based on the gradient echo method, as shown in FIG. 3, for example, and is general for a three-dimensional MRA sequence.
That is, the high frequency magnetic field pulse RF is simultaneously generated with the region selection gradient magnetic field Gs.
To excite the region (slab) containing the target blood vessel, apply a gradient magnetic field pulse Ge1 in the slice direction and a gradient magnetic field pulse Ge2 in the phase encode direction, and then apply the readout gradient magnetic field Gr and reverse its polarity. To measure the echo signal. From the high-frequency magnetic field pulse RF to the measurement of the echo signal, the magnetic field strength of the gradient magnetic field Ge1 in the slice direction and the gradient magnetic field Ge2 in the phase encoding direction is changed with a predetermined repetition time TR to obtain three-dimensional data.

The number of encodes in the slice direction and the phase encode direction determines the image resolution in both directions, and is set in advance in consideration of the measurement time and the like. For example, the number of encodes in the phase encode direction is set to 128 or 256, and the slice direction is set to 10 to 30 or the like. The k space (ky-kz) is defined by the number of encodes in the slice direction and the phase encode direction. That is, in the sequence of FIG. 3, a certain value Ge of the gradient magnetic field strength in the slice direction is used.
1 (Gz) and a certain value of the gradient magnetic field intensity in the phase encoding direction Ge2
The signal measured at the time of (Gy) is arranged at the grid point (ky, kz) in the k-space corresponding to Gz and Gy.

For example, the three-dimensional MRA sequence itself shown in FIG. 3 is general in MRA, but in this sequence employed in this embodiment, the data collection method uses the conventional centric order or elliptical centric ordering. And different.

In this method, a ky-kz space (hereinafter simply referred to as k
), Ie, the measurement points are divided into two groups, and these two groups are sequentially measured. When the measurement points are divided into two groups, 1) the two groups share the origin, and the measurement points belonging to the two groups have a complex conjugate relationship with each other;
2) It is necessary that adjacent measurement points in k space belong to different groups.

FIG. 4 shows a k-space of an 8 * 8 matrix in which the number of slice encodes is 8 and the number of phase encodes is 8, as a simplified example of the above data collection method. This matrix has 64 grid points (measurement points), and these grid points are divided into a first group shown on the left and a second group shown on the right in the figure. The lattice points belonging to these two groups have a complex conjugate relationship with each other, and adjacent lattice points belong to different groups. However, in order to satisfy the complex conjugate relationship, adjacent lattice points belong to one group near the origin.

The first of these two groups, the first to be measured,
In the group of, measurement is started from a point at a large distance from the origin 0 in the k space, and then sampling control is performed from the high frequency component to the low frequency component so that the sampling point gradually approaches the origin 0. In the second group, on the other hand, sampling control is performed from the low-frequency component to the high-frequency component such that the distance from the origin 0 gradually increases from or near the origin 0.

In the figure, the circled numbers indicate the data collection order. The measurement points with the same number have no rank, indicating that measurement may be performed from any of them. In the first group where measurement is started first, measurement is started from the grid point (number 1) furthest from the origin (grid point numbered 33), that is, the highest frequency component, and then the grid point of number 2 and number Measurements are sequentially performed up to the origin, such as the grid point of 3. Then the second
The group is measured, and here the grid point (number
34) That is, the measurement is started from the low frequency component, and the measurement is sequentially performed in the order away from the origin.

Next, an embodiment of a contrast-enhanced MRA using the above-described MRI apparatus employing such a data acquisition method will be described with reference to FIG. First, a subject is placed in a measurement space in a static magnetic field magnet, an imaging region including a target blood vessel is determined, and timing imaging is performed. Timing imaging is performed by a test injection method. In this method, a small amount of contrast agent
(Approximately 1 to 2 ml) was injected as a test, and a time-signal curve at the target site was obtained as shown in FIG. 5, and the arrival time of the contrast agent (the time when the signal intensity peaked) t1 was measured therefrom. This is a method of determining the timing for performing the main imaging based on the result. As a method of timing imaging, in addition to this test injection method, ROI is set for a specific part in the monitor area for the arrival of the contrast agent, the signal change of the same part is captured, and when the set threshold is exceeded, automatic There is a method of starting imaging in a short time, a method of short-time imaging called fluoroscopy, a method of observing a target blood vessel in real time by repeating display, and starting imaging when an appropriate signal rise is obtained. Although the test injection method can be adopted, the test injection method is preferable because the timing can be accurately measured by using the contrast agent prior to the main imaging.

After the timing imaging, the main imaging is performed as shown in FIG. The main imaging may be performed only after the injection of the contrast agent, but preferably, images before and after the injection of the contrast agent are taken. The imaging before and after the imaging is performed continuously for the same slice or slab position under the same conditions. The imaging sequence is a sequence based on the short TR three-dimensional gradient echo method as shown in FIG.
In this case, since the blood flow is to be imaged, a gradient magnetic field for rephasing the phase due to the flow, that is, a gradient moment nulling (Gradient Moment Nulli).
ng) may be added, but this is not essential, and it is preferable to use a rather simple gradient echo for shortening TR / TE.

When the pulse sequence repetition time TR, matrix size (number of slice encodes and number of phase encodes), and number of additions are determined, the imaging time T is determined. Therefore, the arrival time of the target blood vessel contrast agent obtained by the timing imaging described above. Based on t1, the imaging start time t2 (from the injection of the contrast agent to the start of imaging, so that data measurement in the low-frequency region of the ky-kz space is performed when the contrast agent reaches the target blood vessel. Time). Imaging is first
The measurement of the group is started, and then the measurement of the second group is performed. In this case, the sequencer 4 controls both the gradient magnetic field pulse in the slice direction and the gradient magnetic field pulse in the phase encoding direction in the first group to be measured first so as to sequentially measure the high frequency component to the low frequency component, and then performs the second measurement. In the second group, control is performed so that measurement is performed in the order of low frequency components to high frequency components. Thus, three-dimensional image data after contrast is obtained.

If three-dimensional image data is obtained before the contrast in the same procedure as above, three-dimensional data of only blood vessels can be obtained by taking the difference between them. The difference processing is performed by, for example, performing a complex difference between slices at the same slice position in three dimensions. The difference may be a difference between absolute values. The method of removing the tissue other than blood vessels by performing difference processing between images before and after contrast in this way is 3D
This is a known technique called MR-DSA (Digital Subtraction Angiography), which is not essential in the present invention, but is particularly suitable for delineating thin blood vessels in which it is difficult to obtain sufficient contrast with tissues other than blood vessels.

Further, the three-dimensional data after the difference processing can be stereoscopically observed by projecting the three-dimensional data in an arbitrary direction such as a coronal section, a sagittal section, or a transverse axis. As a projection method, a known maximum intensity projection method or the like can be employed. It is also possible to perform pseudo three-dimensional display processing such as volume rendering, and it is also possible to perform simple all-slice integration processing because data after the difference is used.

As described above, according to the contrast MRA of the present invention, the low-frequency component in the k-space is measured when the contrast agent reaches the target blood vessel and the signal intensity of the blood flowing through the target blood vessel becomes highest. Thus, an image of the artery can be drawn with high contrast. Moreover, as shown in FIG.
Since there is a time zone for measuring the low-frequency component on both sides across the, even if there is a shift in both contrast agent arrival time t1 due to slight differences in conditions between timing imaging and main imaging, A high-quality image with almost no deterioration in image quality can be obtained.

In the above-described embodiment, the case where all the measurement points belonging to the first group and the second group are measured as the data collection method has been described. However, as shown in FIG. First
The group may adopt a data collection method in which measurement of a predetermined high-frequency component is omitted and low-frequency components are measured in a short time.

FIG. 6 shows an example of such a data collection method. FIG. 6 also illustrates an 8 * 8 matrix k-space in which the number of slice encodes is 8 and the number of phase encodes is 8. In this embodiment, k is set under the same conditions as in the embodiment shown in FIG.
Although the space is divided into two groups, here, the first group to be measured first does not measure a predetermined high-frequency component, but measures only the low-frequency component. In the illustrated embodiment, only the grid points in the 4 * 4 matrix in the low frequency region among the grid points in the k space are measured. First, among these lattice points in the low frequency region, the lattice point having the longest distance from the origin (the lattice point of number 9) is set as the starting point, and the lattice point of number 2 and the lattice point of number 3 are measured up to the origin.

In the second group, as in the embodiment shown in FIG. 4, measurement is performed from the lattice point (number 10) adjacent to the origin, and all the lattice points belonging to the second group are measured up to the highest frequency component in the order away from the origin. I do.

In this case, the data in the high-frequency region that has not been measured in the first group can be estimated based on the complex conjugate of the first group and the second group. As a method of estimating unmeasured data, a method based on a known half Fourier reconstruction method can be adopted. FIG. 7 schematically shows these processes. First, the measurement data is subjected to one-dimensional Fourier transform in the frequency encoding direction (kx direction) to obtain actual measurement data in a three-dimensional hybrid space. Hybrid space data is obtained by obtaining three-dimensional estimation data from the actual measurement data and combining the actual measurement data and the estimation data.
Three-dimensional image data is obtained by subjecting the hybrid spatial data to two-dimensional Fourier transform.

As a result, even if the number of data points is reduced, the spatial resolution does not deteriorate. Also in this embodiment, similarly to the data collection method shown in FIG. 4, when the contrast agent reaches the target blood vessel and the signal intensity of the blood flowing through the target blood vessel becomes the highest, the low-frequency component of the k-space is measured. Thus, an image of the artery can be drawn with high contrast.

Generally, as shown in FIG. 7, after the injection of the contrast agent, the concentration of the contrast agent (signal intensity) sharply rises, so that the point at which the lowest frequency component is measured coincides with the peak of the signal intensity, and the contrast agent reaches In order to avoid the measurement of the unnecessary signal before, the present embodiment in which the measurement before the peak is short is preferable.

FIGS. 8 and 9 show the results of simulation of the difference in arteriovenous separation due to the difference in the imaging method (data collection method). In this simulation, a simulated blood vessel of an artery and a vein was used, and a contrast medium was flowed into the simulated blood vessel at a flow rate of 40 cm / s, an arterial venous return time of 7 seconds, and an injection speed of 2 cc / s, and this was imaged by a different imaging method. . FIG. 8 shows the signal intensities under the above conditions. First, the peak of the signal from the artery is seen, and the peak of the signal from the vein appears later. FIG. 9A is an image obtained by the imaging method of the present invention, and FIG. 9B is an image obtained by an elliptical centric order.

As can be seen from the figure, in the elliptical centric order, the vein as well as the artery is imaged, and the arteriovenous separation is not complete. On the other hand, in the imaging method of the present invention, only the artery is drawn with high contrast. it can.

In the above embodiment, a sequence based on the gradient echo method is exemplified as the three-dimensional MRA sequence. However, an EP for measuring a plurality of echo signals by one excitation is used.
An I (Echo Planer Imaging) method or a split-type EPI can also be adopted.

Further, data collection in k-space is shown in FIG.
In addition to the rectangular matrix shown in FIG.
It is also possible to collect data within a circle (ellipse) centered on the origin as shown at 0. In the first group shown by a solid line in the figure, measurement is started from a point at a large distance from the origin 0 on the k space, and then the sampling points are gradually moved from the high-frequency component to the low-frequency component so as to gradually approach the origin 0. Control sampling. In the second group, on the other hand, sampling control is performed from the low-frequency component to the high-frequency component such that the distance from the origin 0 gradually increases from or near the origin 0.

In this case, the same effect as that of the embodiment shown in FIGS. 4 and 6 can be obtained. Also in this case, the measurement of the first group of high frequency components can be omitted as necessary.

[0051]

As described above, according to the MRI apparatus of the present invention, the measurement points in the ky-kz space are divided into two groups having a complex conjugate relationship with each other, and the first group and the second group are sequentially arranged. Measure,
At that time, in the first group, the sampling point is controlled from the high frequency component to the low frequency component so that the distance from the origin on the k space gradually approaches, and in the second group, the distance gradually increases. The sampling point is controlled from the low-frequency component to the high-frequency component so that the effect of the imaging timing shift is reduced, and artifacts that depend on the contrast timing, which has been a problem in the conventional contrast MRA To prevent the occurrence of arterial and venous overlap,
The ability to visualize blood vessels can be improved. Further, by reducing the number of measurement points of the first group to be measured first, unnecessary signal measurement and image deterioration due to the measurement can be eliminated, and the imaging time can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a data collection method adopted by an MRI apparatus according to the present invention and a conventional data collection method.

FIG. 2 is a block diagram showing an overall configuration of an MRI apparatus to which the present invention is applied;

FIG. 3 is a diagram showing an example of a pulse sequence of a contrast MRA measurement performed by the MRI apparatus of the present invention.

FIG. 4 is a diagram schematically showing an embodiment of a k-space data collection order according to the present invention.

FIG. 5 is a view for explaining MRA imaging by the MRI apparatus of the present invention.

FIG. 6 is a diagram schematically showing another embodiment of the k-space data collection order according to the present invention.

FIG. 7 is a view for explaining an image reconstruction method to which the data collection method of FIG. 6 is applied;

FIG. 8 is a diagram showing a simulation for evaluating MRA imaging by the MRI apparatus of the present invention.

FIG. 9 is a diagram showing simulation results of MRA imaging by the MRI apparatus of the present invention and MRA imaging by a conventional method.

FIG. 10 is a diagram schematically showing another embodiment of the k-space data collection order according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Subject 2 ... Magnetic field generator 3 ... Magnetic field gradient generation system 4 ... Sequencer 5 ... Transmission system 6 ... Receiving system 7 ... Signal processing system 8 ... CPU 9 ... Gradient magnetic field coil 14a, ... High frequency coil 14b on reception side ... Reception High frequency coil on the side

Claims (4)

[Claims] 1. A static magnetic field generating means for generating a static magnetic field in a space in which a subject is placed, a gradient magnetic field generating means for applying a gradient magnetic field in a slice direction, a phase encoding direction, and a readout direction to the space; A transmitting system for irradiating a high-frequency magnetic field to cause nuclear magnetic resonance in an atomic nucleus of a living tissue, a receiving system for detecting an echo signal emitted by the nuclear magnetic resonance, the gradient magnetic field generating means, a transmitting system, and a receiving system A magnetic resonance imaging apparatus comprising: a control system that controls a system; a signal processing system that performs image reconstruction calculation using an echo signal detected by a reception system; and a unit that displays an obtained image. Performs a three-dimensional sequence that provides slice encoding and phase encoding, where k is defined by the number of slice encodings and the number of phase encodings.
A measurement point in space is divided into a first group and a second group that share the origin and are in a complex conjugate relationship with each other. In the first group, the distance from the origin to the measurement point gradually decreases in the order of measurement, and the second group A magnetic resonance imaging apparatus, wherein the gradient magnetic field generating means in the slice direction and the phase encoding direction is controlled so that the distance from the origin to the measurement point in the group gradually increases in the order of measurement. 2. The magnetic resonance imaging apparatus according to claim 1, wherein the measurement points in the k space are divided so that adjacent measurement points belong to different groups. 3. A method according to claim 1, further comprising the steps of selecting and exciting a predetermined region of the subject, applying a gradient magnetic field for encoding in at least two directions, and measuring an echo signal generated from the region while changing the intensity of the gradient magnetic field. Times repeated, in a data collection method of collecting three-dimensional image data, the measurement points in the measurement space defined by the two-direction encoding gradient magnetic field strength, the origin is shared, lattice points adjacent to each other in a complex conjugate relationship and adjacent to each other Is divided into first and second groups so as to belong to different groups, and measurement is sequentially performed on the first and second groups. At this time, the first group measured first has the origin of the measurement space. In the second group, which is measured later, the distance from the origin of the measurement space to the measurement point gradually increases in the measurement order. Data collection methods to be. 4. The data according to claim 3, wherein the first group measures only a part of the measuring points, and the second group measures all the measuring points. Collection method.