KR20040017030A - New Reference Scan Method for Diffusion Imaging - Google Patents

Abstract

PURPOSE: A phase correction method is provided to achieve improved quality of diffusion image and accuracy of phase correction by obtaining reference scan data at the state where the diffusion gradient is turned off. CONSTITUTION: A phase correction method is characterized in that the same pulse sequence is not used in the reference scan and the actual image scan, and positions and phases between echoes are corrected by performing a one-dimensional Fourier transform and a linear phase correction on the time domain signal of the reference scan data at the state where the diffusion gradient is turned off.

Description

Phase correction method in diffusion imaging technique {New Reference Scan Method for Diffusion Imaging}

The present invention relates to phase correction of magnetic resonance imaging (MRI). More specifically, the time domain signal of the reference scan data is linearly compensated after 1D FT. The present invention relates to a phase correction method in a diffusion imaging technique capable of achieving phase correction of a diffusion image by correcting a position and a phase.

In general, phase plays a very important role in the imaging of Magnetic Resonance Imaging (MRI). If the phase is not properly obtained, the reconstructed image will have severe distortion and may shift from where it was.

In the conventional imaging method, the phase may be initialized every time the image data is received, thereby obtaining an accurate phase. However, imaging methods like EPI do not accumulate the phase as the phases continue to accumulate.

Therefore, a correct phase is obtained by using a method such as a reference scan or a navigator echo, and the phase of the image data actually experimented with the phase is corrected.

In order to receive image data from the MRI, a program called a pulse sequence is performed. This pulse sequence contains time-dependent information on three axes of gradient. Based on this, the spectrometer is driven to output an accurate pulse sequence. The three axes consist of a selection gradient, a phase encoding gradient, and a frequency coded readout gradient. The combination of these three axes provides an image.

However, in the conventional phase correction, since the diffusion gradient magnetic field is applied during the reference scan, accurate phase information cannot be obtained in the reference scan.

Therefore, in the present invention, more accurate phase information can be obtained by receiving the diffusion gradient magnetic field without applying it.

The present invention has been made to solve such a conventional problem, and the phase correction (Phase Correction) of the magnetic resonance imaging diagnostic apparatus is the time domain of the reference scan (reference scan) signal after the 1D FT linear echo between the echo It is to provide a phase correction method in the diffusion imaging technique that can improve the effect of the phase correction of the diffusion image and ultimately increase the performance of the diffusion image by adjusting the position and phase.

1 is a flowchart for image reconstruction according to the present invention;

2 is a pulse sequence for obtaining a diffusion image,

3 is a pulse sequence used in the reference scan of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flowchart for reconstructing an image according to the present invention, and FIGS. 2 and 3 illustrate pulse sequences for obtaining a diffusion image. FIG. 2 is used in a scan for obtaining a real image, and the reference stand of FIG. Was used to obtain the data for phase correction.

As shown in FIGS. 1 to 3, the phase correction method in the diffusion imaging method of the present invention is applied with a phase correction method using a reference scan to obtain a diffusion image.

First, in order to perform phase correction, only the phase encoding gradient is turned off and data is received. The description of the phase correction is as follows.

First, the reference scan data (ie, phase encoding gradient) is turned off to obtain the received data, and the data is calculated as shown in Equation 1-1.

(1-1)

In this part, if the denominator is smaller than a certain number, P (r) and P (i) are treated as zero.

The second step is to turn on phase encoding gradient field in the first step, receive the actual experimental data, and apply the result to equation (1-2).

(1-2)

Here, P (r) and P (i) are the result values of Formula (1-1), and R and I represent actual experimental data.

In two steps, phase correction is completed, and the reconstructed image can be obtained by vertically performing one-dimensional fft of the data.

1 is a diagram illustrating a reconstruction step.

Reconstructing the image can be divided into four stages.

In the first step, a pulse sequence is driven to receive original MRI data, and in this case, actual test data and reference scan data for phase correction are respectively received. Reference scan data is experimented with only a phase encoding gradient zero in the real image scan.

Step 2 is a step of obtaining P (r) and P (i) using reference scan data from the transmitted original MRI data. In this process, phase information is obtained from reference scan data. Here, in order to prevent the phase correction from being correct due to the reference scan data, a one-step process is performed through a conditional expression as shown in FIG. 1 according to the denominator value.

Step 3 takes the phase result and multiplies the actual experimental data to perform phase correction.

Step 4 is to reconstruct the image if the data is vertically one-dimensional fft.

Since the reference scan is almost similar to the real image scan, it has an echo position and phase almost similar to the experiment when the phase encoding gradient field is turned on. Therefore, if linear phase correction is performed on the time domain signal of reference scan data after 1D FT, the position and phase between echoes can be corrected. As described above, the same pulse sequence should be used between the reference scan and the real image scan.

The technique applied in the present description will be described in detail as follows.

To obtain the reference scan data required for phase correction, turn off the phase encoding gradient and obtain the data (conventional method), in addition to the diffusion gradient Turn off the gradient to get the data.

Referring to the drawings, the conventional method turns off only the phase coded gradient field in FIG. 2 and receives data, but the present invention turns off the gradient gradient field as shown in FIG.

In other words, in the case of a pulse sequence that generally receives reference scan data, in the conventional method, a phase encoding gradient is performed in exactly the same pulse sequence. Turning off and receiving only, in the present invention, turning off and receiving a diffusion gradient is different from the conventional method.

The actual scan is performed, and a phase correction technique is performed with reference scan data in the same manner as the conventional method.

In order to perform phase correction, reference scan data must be obtained before the actual scan. In this case, the reference scan turns off the phase encoding gradient and obtains data. In the present invention, the data is turned off to the diffusion gradient and the data is applied to the diffusion gradient application. By reducing the distortion of the echo signal, it is possible to obtain accurate phase information to improve the quality of the diffusion image.

Since diffusion gradients are generally used to spread water signals, echo signals are inevitably reduced, and thus the desired information cannot be obtained. Therefore, accurate correction cannot be performed with the phase information obtained here.

Therefore, the pulse sequence is the same and only by turning off the diffusion gradient, it is possible to obtain more accurate phase information than the conventional method.

As described above, according to the diffusion imaging method according to the present invention, when obtaining reference scan data for phase correction, the diffusion is turned off and obtained by turning off the diffusion gradient. The image quality can be improved and the phase correction can be made more accurate than the conventional method.

Claims (1)

In the method of obtaining a diffusion image of a magnetic resonance imaging diagnostic apparatus (MRI), The same pulse sequence is not used between the reference scan and the real image scan, and linear phase correction is performed after 1D FT of the time domain signal of the reference scan data without applying a diffusion gradient magnetic field. And correcting the position and phase between the echoes.