JPH10286246A - Mr real-time image pickup method and mri device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make such an improvement to prevent unevenness of variation in contrast of images which are successively reconstituted by MR real-time image pickup. SOLUTION: MR data are collected on a plurality of spiral loci which fill up a k-space through a pulse sequence in a spiral scan process (Q1) so as to reconstitute an image (Q2). Subsequently, only MR data on a single or a small number of spiral loci are collected in order to update the corresponding part of the MR data (Q3), and an image is reconstituted from MR data in the updated k-shaped. With the repetition of the above steps, the images can successively be obtained in real time. In this phase, unevenness of variation in contrast of images which are successively reconstructed is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an MR (Magnetic R)
esonance) real-time imaging method and MRI (Magnet)
ic Resonance Imaging) device. More specifically, M which continuously performs acquisition of MR data and image reconstruction
An R real-time imaging method, which relates to an MR real-time imaging method capable of preventing a change in contrast of an image reconstructed one after another from occurring, and an MRI apparatus implementing the method.

[0002]

2. Description of the Related Art FIG. 7 shows an example of a pulse sequence of the spin echo method. In this pulse sequence RS, 9
An RF pulse R1 of 0 ° is applied and a slice gradient S1 is applied to a slice axis. Next, a phase encode gradient PE (m) is applied to the phase axis. Next, 180 ° RF
A pulse R2 is applied and a slice gradient S2 is applied to the slice axis. Next, the echo echo is sampled while applying the read gradient RD to the frequency axis to collect MR data dm. As shown in FIG. 8, the pulse sequence RS is represented by m = 1 to M (M is, for example, 256,
For the sake of illustration, M = 4) is repeated while changing the magnitude of the phase encoding gradient PE (m), and as shown in FIG. 9, MR data d1 to d4 filling the k-space KS are collected. This is repeated cyclically for m = 1 to 4, and M
The R data d1 to d4 are continuously updated in order. First, the image I is obtained from the MR data d1 to d4 that fill the k-space KS.
After that, every time one MR data is updated, a new image I is obtained from the MR data in the k-space KS at that time.
2, I3,... For example, as shown in FIG. 10, when the MR data d1 is updated with d1 ', k at that time is updated.
A new image I2 is reconstructed from the MR data in the space KS. Thus, a new image I2, I
3, ... will be obtained. The time Tr is, for example, 50
ms, and an image can be obtained substantially in real time.

[0003]

In the conventional MR real-time imaging method described above, MR data on a linear trajectory parallel to the frequency axis of the k-space KS is collected from one echo. Then, repeating the acquisition of MR data while changing the position of the linear trajectory in the phase axis direction is cyclically repeated. For this reason, as shown in FIG.
The MR data d1 at a position distant from the phase axis center of the space KS is updated to d1 'to reconstruct an image. Also, as shown in FIG. The data d2 is updated to d2 ', and the image is reconstructed. However, the contrast of the image is determined by the MR near the center of the phase axis of the k-space KS.
Since the data is almost dominant, there is almost no change in contrast in the image when the MR data at a position away from the center of the phase axis of the k-space KS is updated compared to the previous image, and the phase axis of the k-space KS is not changed. The contrast of the image at the time when the MR data at the position near the center is updated is greatly changed as compared with the previous image. In other words, there is a problem that the contrast of an image reconstructed one after another is uneven. Therefore, an object of the present invention is to
It is an object of the present invention to provide an MR real-time imaging method and an MRI apparatus which are improved so as not to cause a change in contrast of images successively reconstructed by MR real-time imaging.

[0004]

According to a first aspect of the present invention, there is provided an MR data acquisition step of acquiring MR data on a spiral trajectory spirally extending from a center point of a space to an end from one echo. , While changing the position of the spiral trajectory,
1st to Mth to fill the k-space by repeating the data collection step
A collection iterative update step of cyclically collecting MR data on the spiral trajectory and updating the MR data on the spiral trajectory;
Reconstructing a new image from the current k-space MR data each time the MR data on one or a few spiral trajectories is updated.
An R real-time imaging method is provided. In the MR real-time imaging method according to the first aspect, the image is reconstructed every time the MR data on one or a small number of spiral trajectories filling the k-space is updated. Similarly, a new image can be obtained substantially in real time. On the other hand, unlike the conventional case, MR data on a spiral trajectory is collected, so that in each of the phase axis direction and the frequency axis direction, MR data near the center to MR data at a position away from the center are included every time. Therefore, the change in the contrast of the image compared to the previous image is the same every time, and no unevenness occurs.

According to a second aspect, the present invention provides an MR data acquisition means for acquiring MR data on a spiral trajectory spirally extending from a center point of k-space to an end from one echo, and a position of the spiral trajectory. The above MR data acquisition step is repeated while changing k to fill the k-space.
Acquisition iterative updating means for cyclically collecting data and updating the MR data on the helical trajectory, and each time the MR data on one or a small number of helical trajectories is updated, the k-space MR at that time
An image reconstructing means for reconstructing a new image from data. The MRI apparatus according to the second aspect can suitably implement the MR real-time imaging method according to the first aspect.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the drawings. Note that the present invention is not limited by this. FIG. 1 is a block diagram of an MRI apparatus according to one embodiment of the present invention. This MRI
In the device 100, the magnet assembly 1 has a space (hole) for inserting a subject therein, and a main magnetic field coil that applies a constant main magnetic field to the subject so as to surround the space. And a gradient magnetic field coil for generating a gradient magnetic field (the gradient magnetic field coil has respective coils of x-axis, y-axis, and z-axis, and a combination of these coils determines a slice axis, a phase axis, and a frequency axis). A transmission coil for transmitting an RF pulse for exciting nuclear spins in the specimen, a receiving coil for receiving an NMR signal from the subject, and the like are arranged. The main magnetic field coil, gradient magnetic field coil, transmitting coil and receiving coil are connected to a main magnetic field power supply 2, a gradient magnetic field driving circuit 3, an RF power amplifier 4 and a preamplifier 5, respectively.

The computer 7 creates a pulse sequence,
It is passed to the sequence storage circuit 8. Sequence storage circuit 8
Stores a pulse sequence, operates the gradient magnetic field drive circuit 3 based on the pulse sequence, generates a gradient magnetic field from the gradient magnetic field coil of the magnet assembly 1, operates the gate modulation circuit 9, and operates the RF oscillation circuit 10
Is modulated into a pulse signal having a predetermined timing and a predetermined envelope shape, which is applied as an RF pulse to the RF power amplifier 4 and power-amplified by the RF power amplifier 4 and then transmitted to the transmission coil of the magnet assembly 1. Apply.

The preamplifier 5 includes a magnet assembly 1
, And amplifies the NMR signal received by the receiving coil, and inputs the amplified signal to the phase detector 12. The phase detector 12 is an RF oscillation circuit 1
The carrier signal of 0 is used as a reference signal, the NMR signal is subjected to phase detection, and given to the A / D converter 11. A / D converter 1
1 is a method for converting an analog NMR signal into a digital signal M signal.
The data is converted into R data and input to the computer 7.

The computer 7 reads the MR data from the A / D converter 11, performs an image reconstruction operation, and creates an image. This image is displayed on the display device 6. Further, the computer 7 is responsible for overall control such as receiving information input from the console 13.

FIG. 2 is a diagram showing the M
It is a flowchart of R real-time imaging processing. In step Q1, MR data D1 to D4 filling the k-space KS shown in FIG. 5 are collected by the pulse sequence SS of the spiral scan method shown in FIG. That is, in the pulse sequence SS shown in FIG. 3, the 90 ° RF pulse R1 is applied and the slice gradient S1 is applied to the slice axis. Next, a 180 ° RF pulse R2 is applied and a slice gradient S2 is applied to the slice axis. Next, FIG.
And a phase encoding gradient PE (m) so as to form a spiral trajectory (spiral trajectory) extending spirally from the center point (intersection of the phase axis center and the frequency axis center) of the k-space KS to the end as shown in FIG. Lead gradient FE
While applying (m), the echo echo is sampled to collect MR data Dm. As shown in FIGS. 4 and 5, this pulse sequence SS is subjected to a phase encode gradient PE (m) and a phase encode gradient PE (m) for m = 1 to M (M is, for example, 32, but for convenience of illustration, M = 4). Lead gradient F
By repeatedly changing the size of E (m), MR data D1 to D4 filling the k-space KS are collected as shown in FIG. Then, the MR data is set as fixed data.

Returning to FIG. 2, in step Q2, the k space K
An image is reconstructed from MR data that fills S. As shown in FIG. 4, at the time when the acquisition of the MR data D1 to D4 filling the k-space KS is completed, the image I1 is reconstructed.

Returning to FIG. 2, in step Q3, only MR data on one spiral locus is newly collected, and only the corresponding MR data of the fixed data (see step Q1) is updated. For example, as shown in FIG.
Only 1 'is newly collected and updated. Then, the process returns to step Q2.

After all, as shown in FIG. 4, every time MR data on one spiral trajectory is collected, that is, every time TR, new images I2, I3,. Become. The time TR is, for example, 50 ms to 100 ms.
Thus, an image can be obtained substantially in real time. And since the MR data on the spiral trajectory is collected,
In both the phase axis direction and the frequency axis direction, the data from the MR data near the center to the MR data at a position distant from the center is included every time, and the change in the contrast of the image compared to the previous image becomes the same every time. That is,
There is no unevenness in the change in the contrast of the image.

The order in which the positions of the spiral trajectories are changed is arbitrary. As shown in FIG. 4, the spiral trajectories may be changed in the order in which the spiral trajectories are adjacent to each other. The change may be performed in a step-by-step manner, or may be performed in a completely random manner.

[0015]

According to the MR real-time imaging method and MRI apparatus of the present invention, the change in the contrast of the images reconstructed one after another in MR real-time imaging becomes the same every time. That is, there is no unevenness in the change in the contrast of the image.

[Brief description of the drawings]

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

FIG. 2 is a flowchart of an MR real-time imaging process in the MRI apparatus of FIG. 1;

FIG. 3 is an explanatory diagram of a pulse sequence of the spiral scan method.

FIG. 4 is a diagram illustrating the relationship between updating of MR data and a reconstructed image.

FIG. 5 is an explanatory diagram showing a spiral trajectory of MR data filling a k-space.

FIG. 6 is an explanatory diagram showing updating of MR data on one spiral trajectory.

FIG. 7 is an explanatory diagram of a pulse sequence of the spin echo method.

FIG. 8 is an explanatory diagram illustrating a relationship between updating of MR data and a reconstructed image.

FIG. 9 is an explanatory diagram showing a linear trajectory of MR data filling a k-space.

FIG. 10 is an explanatory diagram showing updating of MR data on one linear locus at a position distant from the phase axis center.

FIG. 11 is an explanatory diagram showing an update of MR data on one linear locus near a phase axis center.

[Explanation of symbols]

Reference Signs List 100 MRI apparatus 1 Magnet assembly 3 Gradient magnetic field drive circuit 7 Computer 8 Sequence storage circuit SS Pulse sequence of spiral scan method

Claims (2)

[Claims] An MR data acquisition step of acquiring MR data on a spiral trajectory spirally extending from a center point of k-space to an end from one echo, and an MR data acquisition step while changing the position of the spiral trajectory. And an acquisition iterative update step of cyclically collecting MR data on the first to Mth spiral trajectories filling the k-space and updating the MR data on the spiral trajectory; An image reconstructing step of reconstructing a new image from the current k-space MR data each time the MR data is updated. 2. An MR data acquisition means for acquiring MR data on a spiral trajectory spirally extending from a center point to an end of k-space from one echo, and said MR data acquisition step while changing the position of the spiral trajectory. Is repeated to collect the MR data on the first to Mth spiral trajectories that fills the k-space and updates the MR data on the spiral trajectory; and one or a small number of spiral trajectories on the spiral trajectory. Image reconstruction means for reconstructing a new image from the current k-space MR data each time the MR data is updated.
RI equipment.