KR19990024812A - Line Projection Eco Planner Magnetic Resonance Image Generation Method - Google Patents

Abstract

The present invention relates to a line projection echo planner image generating method, wherein a two-dimensional image screen on which a magnetic resonance signal is discrete Fourier transformed and then scanned is converted to k-space. Applying a predetermined gradient magnetic field when performing the eco-planner image generating method, and scanning the scan line generated by the gradient magnetic field to rotate the k-space by a predetermined angle; And generating a magnetic resonance image by scanning the scan line generated in the scanning step so as to pass a zero point of the k-space at every scan.

According to the present invention, a high-speed echo planner imaging method is used to obtain line projection image data for a motile part, and the interlaced scan reduces signal loss due to the difference in susceptibility, and has a high signal-to-noise ratio, high resolution, and high mobility. When taking images of the part continuously, no artifacts are generated to ensure continuity.

Description

Line Projection Eco Planner Magnetic Resonance Image Generation Method

The present invention relates to a method for generating a magnetic resonance image, and more particularly, to a method for generating a line projection echo planner magnetic resonance image.

The magnetic resonance imaging apparatus inserts an image object (patient) into a magnetic field of a strong magnet, excites the nuclear magnetic resonance spin of the image object with a high frequency magnetic field emitted at a high frequency for transmission, and then receives a magnetic resonance signal from the image object. The image information is obtained by receiving the coil. At this time, the gradient magnetic field generated by the gradient magnetic coil is appropriately applied to the x and y axes to obtain stereoscopic image information about the image object. Here, when the direction of drawing the image object, that is, the patient's lying tray, is called the z axis, the x axis is opposite to the direction in which the lying patient faces the front, and the y axis is 90 ° to the right of the z axis.

There is an echo planar image generating method (EPI), which is a method for obtaining an image at high speed in the magnetic resonance imaging apparatus. This method is performed by using one radio frequency (weak RF) pulse. Excitation of the nucleus of an atom, and having an amplitude smaller than the amplitude of the x-axis gradient magnetic field and the x-axis gradient magnetic field in which the positive and negative pulses are alternated, the y-axis gradient composed of positive or negative pulses Magnetic pulse trains are applied to produce a two-dimensional image from the magnetic resonance signal from the excited nucleus. However, in the above-described EPI image generation method, high resolution images are often not obtained due to the limitation of the gradient magnetic field or the deterioration of the signal-to-noise ratio (hereinafter referred to as SNR). In addition, due to the difference in susceptibility between the tissues or their components, the susceptibility is changed locally, and the signal is likely to be lost.

In order to solve the above problem, an interlaced scan EPI method has been used as a method of synthesizing several times of EPI data to obtain an image having a high resolution. The interlaced scan EPI method is particularly difficult to obtain high resolution images due to the limitation of the gradient magnetic field. When several interlaced scan EPI methods are used as shown in FIG. Can be improved. FIG. 1A shows the interlaced echo planner scanning method in k-space and FIG. 1B is a pulse train that is walked to obtain the image of FIG. 1A.

However, the interlaced scan EPI method can generate a high resolution and high SNR image by receiving data several times with the interlaced scan method when the object is stationary. As a result, artifacts appear in the reconstructed image by synthesizing the past and present data of different parts, and there is a problem in that the discontinuity of the reconstructed image of the object does not appear as a continuous movement but suddenly changes.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a line projection echo planner magnetic resonance image generation method for ensuring continuity of an image when capturing a moving part by incorporating a line projection method into an EPI image generation method. The purpose is.

FIG. 1A illustrates a k-space scanning method of the interlaced-echo planner image generating method, and FIG. 1B is a pulse train of the interlaced-echo eco-planner image generating method.

FIG. 2A illustrates a first scanning method in k-space of the method of generating a line projection echo planner image according to the present invention, and FIG. 2B is a pulse train for forming FIG. 2A.

FIG. 3A illustrates a second scanning method in k-space of the line projection echo planner image generating method for interlaced scanning of FIG. 2A, and FIG. 3B is a pulse train for forming FIG. 3A.

4 is a k-space scanning method of the interlaced scanning line projection echo planner image generating method of FIG. 2A and FIG. 3A.

According to the present invention for achieving the above object, the interlaced scanning line projection echo planner magnetic resonance image generating method is a k-space when the magnetic resonance signal is discrete Fourier transform, and then the converted signal is scanned is k-space And applying a predetermined gradient magnetic field when performing the eco-planner image generating method, which is a high-speed magnetic resonance image generating method, and scanning the scan line generated by the gradient magnetic field to rotate the k-space by a predetermined angle; And generating a magnetic resonance image by scanning such that the scan line generated in the scanning step passes a zero point of the k-space at every scan.

Hereinafter, with reference to the accompanying drawings will be described in more detail. 2A and 3A show the first and second k-space scanning methods of the line projection echo planner image generating method according to the present invention, and FIGS. 2B and 3B show the k-spaces shown in FIGS. 2A and 3A, respectively. It shows the RF pulse for scanning and the gradient magnetic field to walk in each direction. Here, the k-space refers to a frequency-phase space in which the magnetic resonance signal is Discrete Fourier Transformed and then the transformed signal is scanned as in the image.

In the present invention, a well-known line projection image generation method (hereinafter referred to as LPI) is applied to an EPI to obtain an image. The LPI method obtains one line of data by one RF pulse and is thus made at low speed. In order to speed up, the EPI method is used, and the above-mentioned LP-EPI is interlaced again to obtain a clearer image. In addition, data near kx = 0 (or ky = 0) with low spatial frequency in k-space affects the contrast of the image, and since most of the energy is concentrated, the data of the low frequency portion If collected at the time of injection, it is possible to maintain continuous motility in a continuous image of a moving object.

The LPI described above is an image generating method used for X-ray computed tomography. When the X-ray tube rotates 180 ° by 1 ° around the subject and emits X-rays, the X-ray absorption rate of the human body, that is, penetrates the human body A method of reconstructing an image by calculating a computer attenuation constant of an X-ray.

In the case of MRI, the same data as X-ray Citi can be obtained. In this case, the same data is obtained by creating a rotating magnetic field, and the result is reconstructed to produce an image.

Pulse trains for obtaining the above-described LP-EPI image are shown in FIGS. 2B and 3B. RF pulses and selective gradient magnetic fields are pulses for selecting slices when the human body is divided into slices, and when the x and y axis gradient fields are Gx and Gy, respectively, Gx and Gy are integrated. Determine the k-space dice (kx, ky) as

First, FIG. 2A will be described with reference to FIGS. 2A, 2B, and Equation 1. FIG. The area of the hatched pulses of FIGS. 2B and 3B is the same, the slope is determined according to the size of the pulse without hatching, and the scan direction is determined by the increase and decrease of the integral of the two pulses over time. The value of kx, which is an integral value of 211 pulses, decreases with time and is scanned in the 201 direction, and is again scanned in the 202 direction by 212 pulses having twice the width of 211 pulses. Reference numeral 214 indicates that the slope with respect to the kx axis is twice as large as that for 213 pulses.

In the case of the reference numerals 204 and 215, the inclination of the scanning line changes with respect to the ky axis when the inclination of the scanning line with respect to the kx axis is 45 degrees or more and 135 degrees or less. Reference numeral 203 denotes a value obtained by integrating 216 pulses to determine the k-space resolution.

If the slope with respect to the kx axis is greater than 135 ° and less than 180 °, the slope is changed with respect to the kx axis as before.

FIG. 3B is a pulse train for performing a second scan between the scan lines of FIG. 2A. Reference numeral 301 of FIG. 3A gives the ky tilt magnetic field pulse to be 1/2 of reference numeral 203 of FIG. 2A. Reference numeral 303 of FIG. 3A corresponds to the size of reference numeral 203 of FIG. 2A.

4 illustrates a k-space scanning method of the interlaced scanning line projection echo planner image generating method, in which a solid line represents a first scan line and a dotted line represents a second scan line.

According to the present invention, a high-speed EPI method is used to obtain LPI data for a motile part, and interlaced scanning reduces signal loss due to a difference in susceptibility, and continuously displays images of a motile part with high SNR and high resolution. When shooting, no artifacts are created, ensuring continuity.

Claims (4)

When the magnetic resonance signal is discrete Fourier transformed and then the 2D video screen to which the converted signal is scanned is called k-space, Applying a predetermined gradient magnetic field when performing the eco-planner image generating method, which is a high speed magnetic resonance image generating method, and scanning a scan line generated by the gradient magnetic field to rotate the k-space by a predetermined angle; And And generating a magnetic resonance image by scanning the scan line generated in the scanning step so as to pass a zero point of the k-space at every scan. The method of claim 1, wherein the gradient magnetic field A first inclination magnetic field in which positive and negative pulses of a constant amplitude and pulse width are alternated; And And a second inclination magnetic field, which is a pulse string having an amplitude, a pulse width, and a pulse polarity, so that a magnetic resonance signal is scanned while rotating the k-space by a predetermined angle corresponding to each pulse of the first gradient magnetic field. Line projection echo planner image generation method. The method of claim 1, A line projection echo planner image generating method further comprising: interlacing the scan line produced by each step. The method of claim 1, wherein the scanning line is When the x-axis gradient field is Gx and the y-axis gradient field is Gy, k-space dice (kx, ky) are expressed as Line projection echo planner image generating method, characterized in that determined as follows.