KR101475685B1 - Magnetic resonance imaging apparatus and method for generating susceptibility weighted image using thereof - Google Patents

Abstract

A method of generating a magnetic susceptibility-emphasized image of an object in an MRI apparatus, comprising: obtaining at least one first complex number data corresponding to an RF signal using an RF signal received from a target object; Applying at least one first complex number data to a predetermined filter to obtain at least one second complex number data; Generating a magnetic susceptibility enhancement mask using at least one second complex number data; And generating a magnetic susceptibility-emphasized image by applying a magnetic susceptibility-enhancing mask to an MRI image of a target object.

Description

TECHNICAL FIELD [0001] The present invention relates to an MRI apparatus and a method of generating a magnetic susceptibility-emphasized image using the MRI apparatus and a magnetic susceptibility-

The present invention relates to an MRI apparatus. More specifically, the present invention relates to an MRI apparatus for generating a magnetic susceptibility-emphasized image of a subject and a magnetic susceptibility-emphasized image generating method using the same.

The MRI (Magnetic Resonance Imaging) system is noninvasive, has excellent contrast of the tissue as compared with the CT apparatus, and has no advantage of artifact caused by the bone tissue. In addition, the MRI system is widely used with other imaging diagnostic devices because it can capture various sections according to a desired direction without changing the position of the object.

In order to enhance the contrast of MRI images, the MRI system generates MRI images using the characteristic differences between the tissues of the object. In other words, the difference in characteristics between the tissues of the subject is reflected in the MRI image, allowing the examiner to easily distinguish the tissues from the MRI image.

Susceptibility Weighted Imaging is an image that enhances the contrast of MRI images by reflecting the difference of susceptibility between tissues of the subject. Specifically, since gray matter and white matter, iron-containing tissues and surrounding tissues, and vein blood vessels and surrounding tissues have different susceptibility rates, this difference in susceptibility is reflected in MRI images MRI images with high contrast can be obtained.

An object of the present invention is to provide an apparatus and a method for efficiently removing artifacts generated by phase wrapping in a magnetic susceptibility-emphasized image using an MRI apparatus and a magnetic susceptibility- do.

According to an embodiment of the present invention, there is provided a method of generating a susceptibility-

A method of generating a magnetic susceptibility-emphasized image of an object in an MRI apparatus, the method comprising: obtaining at least one first complex number data corresponding to the RF signal using an RF signal received from the object; Obtaining at least one second complex data by applying a predetermined filter to the at least one first complex data; Generating a magnetic susceptibility enhancement mask using the at least one second complex data; And applying the susceptibility enhancing mask to the MRI image of the subject to generate the susceptibility enhancing image.

Wherein generating the susceptibility enhancement mask comprises: obtaining a magnitude value of each of the at least one second complex data; And generating the susceptibility enhancement mask using the obtained magnitude value.

Wherein the obtaining of the at least one second complex data comprises: setting a magnitude value of the at least one first complex data to a predetermined constant value; And applying the high-frequency filter to the at least one first complex number data whose magnitude value is set to a predetermined constant value to obtain the at least one second complex number data.

Generating the susceptibility enhancement mask comprises: obtaining at least one third complex number data by applying a low pass filter to the at least one first complex number data whose magnitude value is set to a predetermined constant value; And generating the susceptibility enhancement mask using a value obtained by subtracting the predetermined constant value from a value obtained by adding the magnitude value of the at least one second complex data to the magnitude value of the at least one third complex data. have.

The step of generating the susceptibility enhancement mask may include normalizing the magnitude value of the at least one second complex data to a value between 0 and 1.

The normalizing step may include normalizing a magnitude value of the at least one second complex data by dividing the magnitude value of the at least one second complex data by a value obtained by multiplying the predetermined constant value by two.

Wherein the step of generating the susceptibility enhancement mask comprises the step of subtracting the predetermined constant value from a value obtained by adding the magnitude value of the at least one second complex number data and the magnitude value of the at least one third complex number data to the predetermined constant value By 2, and normalizing the value to a value between 0 and 1.

The obtaining of the at least one second complex data may comprise applying the high frequency filter to imaginary data of the at least one first complex data to obtain the at least one second complex data.

The generating of the magnetic susceptibility emphasis image may include generating the magnetic susceptibility emphasis image by multiplying the magnetic susceptibility enhancing mask by an MRI image of the subject a predetermined number of times.

According to another aspect of the present invention, there is provided an MRI apparatus comprising:

A first data obtaining unit obtaining at least one first complex number data corresponding to the RF signal using an RF signal received from a target object; A second data acquiring unit acquiring at least one second complex data by applying a predetermined filter to the at least one first complex data; A mask generator for generating a magnetic susceptibility enhancement mask using the at least one second complex data; And an image generating unit for applying the magnetic susceptibility enhancing mask to the MRI image of the subject to generate the magnetic susceptibility emphasis image.

The mask generator may generate the susceptibility enhancement mask using a magnitude value of each of the at least one second complex data.

Wherein the second data obtaining unit sets a magnitude value of the at least one first complex number data to a predetermined constant value and applies a high frequency filter to the at least one first complex number data whose magnitude value is set to a predetermined constant value, One second complex number data can be obtained.

Wherein the second data obtaining unit obtains at least one third complex number data by applying a low frequency filter to the at least one first complex number data whose magnitude value is set to a predetermined constant value, 2 magnitude value of the complex number data and the magnitude value of the at least one third complex number data minus the predetermined constant value.

The mask generator may normalize the magnitude value of the at least one second complex data to a value between 0 and 1.

The mask generator may normalize the magnitude value of the at least one second complex data by dividing the magnitude value of the at least one second complex data by a value obtained by multiplying the predetermined constant value by two.

The mask generation unit may multiply the predetermined constant value by 2 by subtracting the predetermined constant value from a value obtained by adding the magnitude value of the at least one second complex number data and the magnitude value of the at least one third complex number data And can be normalized to a value between 0 and 1.

The second data obtaining unit may obtain the at least one second complex data by applying the high-frequency filter to imaginary data of the at least one first complex data.

The image generating unit may generate the magnetic susceptibility emphasis image by multiplying the magnetic susceptibility enhancing mask by an MRI image of the subject a predetermined number of times.

A program for executing the method of generating the susceptibility-emphasized image can be recorded on a computer-readable recording medium.

1 is a view for explaining the operation principle of the MRI system.
2 (a) is a diagram showing the phase values of RF signals emitted from the respective regions of the object when a gradient magnetic field is applied to the cross section of the object.
Fig. 2 (b) is a diagram showing the phase values in the respective regions changed by the macroscopic magnetic field change and the micro magnetic field change.
3 is a block diagram showing a configuration of an MRI apparatus according to an embodiment of the present invention.
4 is a diagram showing first complex number data of an RF signal emitted from at least one region of a target object in an MRI apparatus according to an embodiment of the present invention.
FIG. 5 is a diagram for explaining a difference between first complex data according to a difference in phase values of respective regions of a target object in an MRI apparatus according to an embodiment of the present invention. FIG.
6 is a diagram showing second complex data obtained by applying a high-frequency filter to first complex data in an MRI apparatus according to an embodiment of the present invention.
FIG. 7A is a view showing an MRI image of a subject, and FIG. 7B is a diagram showing a magnetic susceptibility emphasis image generated according to an embodiment of the present invention.
8A is a diagram showing first complex number data of an RF signal emitted from at least one region of a target object in an MRI apparatus according to another embodiment of the present invention.
8B is a diagram showing magnitude values of at least one third complex data and at least one third complex data obtained by applying a low-pass filter to the first complex data of FIG. 8A.
8C is a diagram showing the magnitude values of at least one second complex data and at least one second complex data obtained by applying a high-frequency filter to the first complex data of high 8a.
8D is a diagram showing a value obtained by adding a magnitude value of the third complex number data of FIG. 8B and a magnitude value of the second complex number data of FIG. 8C minus a predetermined constant value.
9 is a diagram for explaining a range of a value obtained by adding a magnitude value of a second complex number data and a magnitude value of a third complex number data minus a predetermined constant value.
FIG. 10 is a diagram showing a magnetic susceptibility enhancing mask produced according to the method described with reference to FIGS. 8A-8D. FIG.
11 is a view for explaining a difference of imaginary data according to a difference in phase values of respective regions of a target object when a high-frequency filter is applied to imaginary data of first complex data in an MRI apparatus according to another embodiment of the present invention.
12 is a flowchart showing a procedure of a method of generating a susceptibility-emphasized image according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

The term " part " used in this embodiment means a hardware component such as software, FPGA, or ASIC, and 'part' performs certain roles. However, 'minus' is not limited to software or hardware. The " part " may be configured to be in an addressable storage medium and configured to play back one or more processors. Thus, by way of example, and by no means, the terms " component " or " component " means any combination of components, such as software components, object- oriented software components, class components and task components, Subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays and variables. The functions provided in the components and parts may be combined into a smaller number of components and parts or further separated into additional components and parts.

1 is a view for explaining the operation principle of the MRI system. Referring to FIG. 1, an MRI system generally includes an RF coil 10, a body coil 20, a gradient coil 30, and a main magnet 40 in a shield room, And a control device 50. The central control unit 50 may include a display (not shown), which allows the inspector to view the MRI image through the display or to control the MRI system.

The patient is examined in a cylindrical gantry in a shielded room where an external RF signal is shielded. A magnetic field is formed in the gantry by a main magnet 40, and a gradient coil 30 A magnetic field gradient pulse is transmitted to form a magnetic gradient field. When a magnetic field is formed on the outside of the body, atomic nuclei in the body move along the direction of the magnetic field. The frequency (resonance frequency) of this wash motion is proportional to the intensity of the external magnetic field according to the Lamor equation. If the transmission of the RF pulse is stopped after transmitting the RF pulse of the same frequency as the resonance frequency toward the nucleus which carries out the kinetic motion with the resonance frequency, the nuclear nucleus emits energy absorbed from the RF pulse to the outside, and the MRI system emits And acquires an MRI image using the RF signal. The RF coil 10 or the body coil 20 applies an RF pulse at a resonance frequency to the patient to obtain an MRI image and receives an RF signal generated from a specific part of the patient, To the central control unit 50 of the separate operating room. The RF signal is finally converted into an MRI image through a signal processing process. On the other hand, the gradient coil 30 forms an inclined magnetic field, and the gradient magnetic field induces different resonance frequencies of the respective parts in the body. MRI systems can identify the location of each region of the body through differently induced resonance frequencies. FIG. 1 shows a schematic configuration of a general MRI system, and the present invention can be applied to various MRI systems within a range that is obvious to a person skilled in the art.

2 (a) is a diagram showing the phase values of RF signals emitted from the respective regions of the object when a gradient magnetic field is applied to the cross section of the object. The phase value in each region is mapped to a phase value between -π and π.

As used herein, the term "subject" refers to various parts of the body or an animal, or a specific part of the body or an animal, from which an MRI image is to be acquired.

As shown in Fig. 2 (a), the object may include 25 regions (a to y regions), and each region may correspond to each pixel of the MRI image. Although FIG. 2 (a) shows an object as including 25 regions, it is obvious to a person skilled in the art that it can include different numbers of regions.

The phase value displayed in each region of the object represents the phase value of the RF signal emitted from each region at a predetermined point, and it can be seen from FIG. 2 (a) that the phase value of each region has a value of 8? / 9.

Fig. 2 (b) is a diagram showing the phase values in the respective regions changed by the macroscopic magnetic field change and the micro magnetic field change.

Referring to the i region and q region in Fig. 2 (b), it can be seen that the phase values of the i region and q region in Fig. 2 (a) are changed.

First, a change in the phase value occurs due to the non-uniformity of the magnetic field formed by the main magnet 40 shown in Fig.

Secondly, the phase value changes due to the difference in the susceptibility of the atoms contained in each region. That is, the phase value changes due to the difference in magnetic susceptibility between the respective tissues of the object, or the phase value changes due to the difference in the magnetic susceptibility between the air and the tissue adjacent to the air.

The change in the phase value due to the nonuniformity of the magnetic field and the change in the phase value due to the difference in the magnetic susceptibility between the air and the tissue adjacent to the air are referred to as a phase value change due to the change in the macroscopic magnetic field, The change in the value is referred to as a change in the phase value due to the change in the micro magnetic field.

Since the magnetic susceptibility-emphasized image is an MRI image using magnetic susceptibility difference between tissues of a subject, micro-magnetic field change should be considered, but macroscopic magnetic field change should be excluded. Generally, a macroscopic magnetic field change causes a small change rate of phase value change (i.e., a low frequency phase change), and a micro magnetic field change causes a large change rate of phase value change (i.e., a high frequency phase change).

Referring to Figs. 2 (a) and 2 (b), it can be seen that the phase value of the i-th region in Fig. 2 (b) is changed by? / 9 from the phase value of the i-region in Fig. That is, the phase value of the i-region in Fig. 2 (b) increases from the phase value of the i-region in Fig. 2 (a) by? / 9 and has a phase value of-?.

It can also be seen that the phase value of the q region in Fig. 2 (b) is changed by 8? / 9 from the phase value of the q region in Fig. 2 (a). That is, the phase value of the q area in Fig. 2 (b) increases from the phase value of the q area in Fig. 2 (a) by 8? / 9 and has a phase value of -2? / 9.

It is possible to determine that a phase change of a predetermined value or more is caused by a micro-magnetic field change, and a phase change that is smaller than the predetermined value can be determined to be caused by a macro-magnetic field change. For example, the predetermined value may include 5? / 9. Thus, the change in the phase value in the i region in FIG. 2 (b) can be regarded as a result of a change in the macroscopic magnetic field. The change of the phase value in the magnetic field can be regarded as the change of the micro magnetic field.

In the conventional method of generating the magnetic susceptibility emphasis image, the phase values of the respective regions of the object are used to generate the magnetic susceptibility enhancing mask. Specifically, a high frequency filter is applied to the phase value of each region of the object to generate a mask that emphasizes regions having a large difference in phase value from the surrounding regions, and the generated mask is applied to the MRI image of the object, Respectively.

Referring to FIG. 2B, the phase value of the i region in FIG. 2B is changed by? / 9 from the phase value of the i region in FIG. 2 (a) The difference of the phase values between the i regions of 2 (b) is 17? / 9 (= 8? / 9 - (-9? / 9) / 9 (= 8? / 9 - (-2? / 9)). Therefore, when a high-frequency filter is applied to the phase values of the respective regions shown in Fig. 2 (b), the i region and the q region having a large difference in phase value from other adjacent regions are emphasized. The change in the phase value of the i-region in Fig. 2 (b) is due to the change in the macroscopic magnetic field and should be excluded. However, if the conventional method for generating the magnetic susceptibility enhanced image generates the magnetization rate image in which the i-region is emphasized, a problem arises. This problem is because the phase values in each region are mapped to discontinuous values of -π to pi. That is, the conventional method of generating a magnetic susceptibility emphasis image may include artifacts due to phase wrapping.

The MRI apparatus 300 according to an embodiment of the present invention and a method of generating a magnetic susceptibility emphasis image using the MRI apparatus 300 may use a complex data difference in each region of a target body instead of a phase value difference in each region of the target body Since a magnetic susceptibility enhancing mask is generated, artifacts due to phase overlapping can be prevented.

3 is a block diagram showing the configuration of an MRI apparatus 300 according to an embodiment of the present invention.

3, an MRI apparatus 300 according to an embodiment of the present invention includes a first data acquisition unit 310, a second data acquisition unit 320, a mask generation unit 330, and an image generation unit 340 ).

The MRI apparatus 300 according to an embodiment of the present invention may be included in the central controller 50 shown in FIG. 1 and may include a first data acquiring unit 310, a second data acquiring unit 320, The unit 330 and the image generating unit 340 may be configured as a microprocessor.

The first data obtaining unit 310 obtains at least one first complex number data for the object using the RF signal received from the object.

The central controller 50 of the MRI system determines an appropriate echo delay time (TE) in consideration of the difference in susceptibility between the tissues of the object and outputs RF pulse (s) to the tissue of the object according to a GRE (gradient echo) And controls the RF coil 10 or the body coil 20 so that the RF coil 10 or the body coil 20 is transmitted.

The first data obtaining unit 310 obtains the k-space data using the RF signal received by the RF coil 10 and applies at least one of the first complex data by applying an inverse Fourier transform to the k-space data can do. At least one first complex number data may be represented by a magnitude value and a phase value of complex number data.

The second data obtaining unit 320 obtains at least one second complex data by applying a predetermined filter to at least one first complex data. The predetermined filter may include a high-frequency filter. The high-frequency filter may be applied by subtracting the values obtained by applying a low-pass filter to at least one first complex data to at least one first complex data.

When a high frequency filter is applied to a predetermined region having a large difference between adjacent regions and first complex number data, the predetermined region is more emphasized than other regions in which the difference between the adjacent regions and the first complex number data is relatively smaller .

In the present specification, "difference between two complex data" means a magnitude value of complex data obtained as a result of subtracting another complex data from any one of two complex data.

Since the magnitude values of the first complex data in each of at least one region of the object can be different for each region, the second data obtaining unit 320 sets the magnitude value of at least one first complex data to a predetermined constant value And a high-frequency filter may be applied to the first complex-valued data whose magnitude value is set to a predetermined constant value. The predetermined constant value may be set to one.

4 is a diagram showing first complex data obtained from an RF signal emitted from at least one region of a target object in an MRI apparatus 300 according to an embodiment of the present invention. The phase value of the first complex data shown in FIG. 4 is the same as the phase value shown in FIG. 2B. The magnitude value of the first complex data shown in FIG. 4 is set to a constant value r. In Fig. 4, i represents an imaginary number.

In the conventional method of generating a magnetic susceptibility emphasis image, a high-frequency filter is applied to the phase value itself shown in FIG. 2 (b), but an embodiment of the present invention applies a high-frequency filter to the first complex- Thereby preventing artifacts due to phase overlapping.

5 is a diagram for explaining the difference of the first complex data according to the phase difference between the respective regions of the object in the MRI apparatus 300 according to the embodiment of the present invention.

As described above, the change in the phase value of the i-region in Fig. 4 is due to the change in the macroscopic magnetic field, which is to be excluded when generating the mask, and the change in the phase value of the q- This is something to consider.

5 shows a coordinate plane in which the real axis is the x-axis and the imaginary axis is the y-axis. The real axis corresponds to cosΦ and the imaginary axis corresponds to sinΦ. Here, phi denotes a phase value.

In Fig. 5, point A corresponds to the first complex number data of the h area and p area, point B corresponds to the first complex number data of the i area, and point C corresponds to the first complex number data of the q area .

5, the phase difference between the points A and B is 17? / 9, but the difference (p) of the first complex data is smaller than the difference (q) of the first complex data between the points B and C It can be seen that it is very small. That is, the phase difference between the points A and B is larger than the phase difference between the points B and C, but the first complex data difference (p) between the points A and B is between the points B and C Is smaller than the first complex data difference (q), the q region can be more emphasized than the i region by applying a high-frequency filter to the first complex data shown in Fig.

FIG. 6 is a diagram showing second complex data obtained by applying a high-frequency filter to first complex data in the MRI apparatus 300 according to an embodiment of the present invention. The result shown in Fig. 6 can be obtained by applying a low-pass filter to the first complex data shown in Fig. 4, and then subtracting the first complex data subjected to the low-pass filter from the first complex data. The result shown in FIG. 6 was obtained assuming that the first complex data of the regions other than the regions (a to y regions) shown in FIG. 4 is r (cos 8? / 9 + isin 8? / 9).

When a low-pass filter is applied to the first complex data shown in FIG. 4, the first complex number data of the predetermined area shown in FIG. 4 and the first complex number data of eight areas adjacent to the predetermined area are determined as the values of the predetermined area . The number of adjacent regions can be variously set within a range obvious to a person skilled in the art.

For example, if a low-pass filter is applied to the i-region of FIG. 4, the value of the i-region to which the low-pass filter is applied can be determined by Equation 1 below. The following c ', d', e ', h', i ', j', m ', n', o 'can be set to 1 as a weight for obtaining an average value, It may be set to various values.

[ Equation  One]

first complex number data + i '* i area of the first complex number data + d' * d area of the first complex number data + e '* e area of the first complex number data + A first complex number data of a first complex number data + j '* j area + a first complex number data of a m' * m area + a first complex number data of a n '* n area + / 9

The regions excluding the q region are filtered by the high-frequency filter to have the second complex data having a magnitude value close to 0 or zero. The magnitude value of the second complex number data of each area is larger as the difference from the first complex number data of the adjacent areas is larger. Meanwhile, in the embodiment of the present invention, in addition to the low-frequency filter and the high-frequency filter described above, a low-frequency filter and a high-frequency filter obvious to those skilled in the art in the image processing field can be used.

The mask generation unit 330 generates a susceptibility enhancement mask using the magnitude value of at least one second complex data. For example, the magnitude value of the second complex data of x + yi may be obtained by the following equation (2).

[ Equation  2]

The mask generator 330 may normalize the obtained magnitude value to a value between 0 and 1 to generate a magnetic susceptibility enhancing mask. When the high-frequency filter is applied to the first complex-valued data whose magnitude is set to r, since the magnitude of the first complex-valued data to which the high-frequency filter is applied has a value of 0 to 2r, The magnitude value of the second complex data can be normalized by dividing the magnitude value by 2r. The fact that the magnitude value of the second complex data has a value of 0 to 2r is described below with reference to Fig.

The magnetic susceptibility enhancing mask generated by using the magnitude value of the normalized second complex data will function to brighten an area having a large difference between the magnetic susceptibility and the adjacent area. However, the magnetic susceptibility enhancing mask may be obtained by subtracting the magnitude value of the second complex number data normalized at 1 Will function to darken a region having a large difference in magnetic susceptibility.

The image generating unit 340 applies the magnetic susceptibility enhancing mask to the MRI image of the object to generate a magnetic susceptibility emphasis image. The MRI image of the object may be generated using the magnitude value of the first complex data obtained from the RF signal received from at least one region of the object.

In addition, the image generating unit 340 may generate a magnetic susceptibility emphasis image by multiplying the magnetic susceptibility enhancing mask by a predetermined number of times to enhance the contrast to noise ratio (CNR) of the magnetic susceptibility emphasis image. For example, the predetermined number of times may be 3 to 5 times.

FIG. 7A is a view showing an MRI image of a subject, and FIG. 7B is a diagram showing a magnetic susceptibility emphasis image generated according to an embodiment of the present invention. Referring to FIG. 7 (b), it can be seen that the contrast between the tissues of the object is improved as compared with FIG. 7 (a).

Although not shown in FIG. 3, the MRI apparatus according to an embodiment of the present invention may further include a display unit, and the display unit may display the generated magnetic susceptibility-emphasized image.

On the other hand, in the above description, the difference in the phase value due to the change in the macroscopic magnetic field causes the low frequency phase change. However, the high frequency phase change can also occur due to the change in the macroscopic magnetic field. For example, a change in the phase value due to the difference in susceptibility between the inside of the ear and the air adjacent to the inside of the ear may cause a high frequency phase change.

8A is a diagram showing first complex number data of an RF signal emitted from at least one region of a target object in an MRI apparatus according to another embodiment of the present invention. It is assumed that the first complex data of the areas other than the areas (a to y areas) shown in FIG. 8A is cos 8? / 9 + isin 8? / 9.

If the phase values of the regions d, e, i, j, n and o are due to differences in the magnetic susceptibility between the air and the tissues adjacent to the air, the change in phase value due to the macroscopic magnetic field change can not be excluded merely by the high- .

In order to solve this problem, first, the second data obtaining unit 320 obtains at least one third complex data by applying a low-pass filter to at least one first complex data set with a size r. In Fig. 8A, r is set to 1.

8B is a diagram showing magnitude values of at least one third complex data and at least one third complex data obtained by applying a low-pass filter to the first complex data of FIG. 8A. The values written in the parentheses of the respective regions in Fig. 8B represent the magnitude values of the third complex data in the respective regions.

Generally, the range in which the phase value changes due to the change in the micro magnetic field is narrower than the range in which the phase value changes due to the macroscopic magnetic field variation. This is because the venous blood in which the phase value changes is much smaller than the air adjacent to the tissue. The third complex number data of the q area in FIG. 8B is not different from the third complex number data of the adjacent areas, but the large area d, e, i, j, n , it can be seen that the third complex data of the o area still has a difference from the third complex data of the adjacent areas. 8B, the magnitude values of the third complex data in the regions d, e, i, j, n and o in FIG. 8B are relatively small compared to the magnitude values of the third complex data in the other regions .

When a high-frequency filter is applied to the first complex data in FIG. 8A, the region having a large difference between the adjacent regions and the first complex data is emphasized. 8C is a diagram showing magnitude values of second complex data and second complex data obtained by applying a high-frequency filter to first complex data of high 8a.

Referring to FIG. 8C, it can be seen that the magnitude values of the second complex data in the regions d, e, i, j, n, o and q are relatively larger than those in the other regions.

When the third complex number data is obtained by applying the low frequency filter to the first complex number data whose magnitude value is set to r, the size value of the third complex number data has a value from 0 to r, so that the magnitude value of the third complex number data The magnitude value of the third complex number data will be inverted. 8B, when the magnitude value of the third complex number data of the area d, e, i, j, n, o having a size value of the third complex number data is smaller than that of the other area, , the magnitude value of the third complex data of the j, n, o area will be relatively large compared to other areas.

If the magnitude value of the third complex number data whose magnitude value is inverted from the magnitude value of the second complex number data is subtracted, then only the q area will have a relatively larger value than the other areas. FIG. 8D shows a value obtained by adding a magnitude value of the third complex number data of FIG. 8B and a magnitude value of the second complex number data of FIG. 8C minus a predetermined constant value. The mask generation unit 330 may generate a susceptibility enhancement mask using a value obtained by adding a magnitude value of the second complex data and a magnitude value of the third complex data minus a predetermined constant value.

On the other hand, since the value obtained by subtracting the predetermined constant value from the value obtained by adding the magnitude value of the second complex data to the magnitude of the third complex data has a value of 0 to 2r, the mask generator 330 calculates the magnitude Value obtained by subtracting the predetermined constant value from a value obtained by adding the value of the third complex data to the value of the third complex data is divided by 2r and normalized to a value of 0 to 1.

9 is a diagram for explaining a range of a value obtained by adding a magnitude value of a second complex number data and a magnitude value of a third complex number data minus a predetermined constant value.

9A, the v1 vector represents first complex number data of a predetermined area, and the v2 vector represents first complex number data of a predetermined area and average complex number data of first complex number data of areas adjacent to the predetermined area . The magnitude value of the first complex number data in the predetermined area is set to r. The v2 vector is complex data obtained by applying a low-pass filter to a predetermined area. The v2 vector has a magnitude value of 0 to r, and its phase can be any value. When a high-frequency filter is applied to the first complex number data in a predetermined area, a v3 vector obtained by subtracting the v2 vector from the v1 vector is acquired.

since the sum of the lengths of the two sides in the triangle having the v1 vector, the v2 vector and the v3 vector as three sides is always larger than the length of the other side, the size value of the second complex data and the size value of the data of the third complex number The value obtained by subtracting r from the sum of values is always greater than zero.

As shown in FIG. 9 (b), if the magnitude of the v2 vector obtained by applying the low-pass filter to the v1 vector is r and the magnitude of the vector is 180 degrees to the v1 vector, v3 The size value of the vector will be 2r. 9C, if the magnitude of the v2 vector obtained by applying the low-pass filter to the v1 vector is r and the magnitude of the v2 vector is the same phase as the v1 vector, the v3 vector, which is the difference between the v1 vector and the v2 vector, The magnitude value of 0 will be zero. As a result, the magnitude value of the second complex data obtained by applying the high-frequency filter to the first complex data has a value of 0 to 2r.

The value 2r will be obtained by subtracting r from the magnitude value of the v2 vector shown in FIG. 9 (b) and the magnitude value of the v3 vector obtained by subtracting the v2 vector from the v1 vector. Subtracting r from the magnitude value of the v2 vector and the magnitude value of the v3 vector obtained by subtracting the v2 vector from the v1 vector will yield zero. As a result, the value obtained by subtracting r from the magnitude value of the second complex data and the magnitude value of the third complex data has a range of 0 to 2r.

FIG. 10 is a diagram showing a magnetic susceptibility enhancing mask produced according to the method described with reference to FIGS. 8A-8D. FIG.

FIG. 11 is a graph illustrating the difference in imaginary data according to the phase difference of each region of a target object when a high-frequency filter is applied to imaginary data of the first complex data in the MRI apparatus 300 according to another embodiment of the present invention. FIG.

In the present specification, "difference between two imaginary data" means a magnitude value of imaginary data obtained as a result of subtracting one imaginary data from one of two imaginary data.

In the MRI apparatus 300 according to another embodiment of the present invention, the second data acquisition unit 320 may acquire second complex data by applying a high-frequency filter only to imaginary data of the first complex data.

Fig. 11 is a diagram showing a graph of sin? Versus phase value?, Where sin? Means imaginary data which is the imaginary part of the first complex data.

Referring to the phase values of the respective regions shown in FIG. 4, a point is a point representing imaginary data of the h region and a p region, and a point b is a point representing imaginary data of the i region. The point c is the point representing the imaginary data of the q area.

Referring to FIG. 11, it can be seen that the imaginary data difference between points a and c is larger than the imaginary data difference between points a and b. Therefore, it is possible to apply the high-frequency filter only to the imaginary data of the first complex data shown in FIG. 4, and to generate the susceptibility enhancing mask using the magnitude value of the imaginary data to which the high-frequency filter is applied. Thereby, the q area can be more emphasized than the i area.

In this embodiment, since the high-frequency filter is applied only to the imaginary data of the first complex data, the amount of calculation for generating the magnetic susceptibility enhancing mask can be reduced.

12 is a flowchart showing a procedure of a method of generating a susceptibility-emphasized image according to an embodiment of the present invention. Referring to FIG. 12, the method for generating the susceptibility-emphasized image according to an embodiment of the present invention includes steps that are processed in a time-series manner in the MRI apparatus 300 shown in FIG. Therefore, it is understood that the above description about the MRI apparatus 300 shown in FIG. 3 applies to the method of generating the magnetic susceptibility-emphasized image of FIG. 12, even if omitted from the following description.

First, in step S1210, the MRI apparatus 300 acquires at least one first complex number data using the RF signal received from the object.

Specifically, the MRI apparatus 300 may acquire k-space data using the RF signal received from at least one region of the object, and obtain first complex data by performing inverse Fourier transform on the k-space data.

In step S1220, the MRI apparatus 300 applies a predetermined filter to at least one first complex number data. As described above, the MRI apparatus 300 may set a magnitude value of at least one first complex-valued data to a predetermined constant value, and apply a high-frequency filter to the first complex-valued data whose magnitude is set to a constant value.

In step S1230, the MRI apparatus 300 acquires at least one second complex data for the object.

In step S1240, the MRI apparatus 300 generates a susceptibility enhancement mask for the object using the magnitude value of the second complex data. The MRI apparatus 300 may normalize the magnitude value of the second complex data to a value between 0 and 1.

In step S1250, the MRI apparatus 300 applies the magnetic susceptibility enhancing mask to the MRI image of the object to generate the magnetic susceptibility emphasis image. The MRI apparatus 300 may generate a magnetic susceptibility emphasis image by multiplying the magnetic susceptibility enhancing mask by a predetermined number of times in order to improve the CNR of the magnetic susceptibility emphasis image.

The above-described embodiments of the present invention can be embodied in a general-purpose digital computer that can be embodied as a program that can be executed by a computer and operates the program using a computer-readable recording medium.

The computer readable recording medium may be a magnetic storage medium such as a ROM, a floppy disk, a hard disk, etc., an optical reading medium such as a CD-ROM or a DVD and a carrier wave such as the Internet Lt; / RTI > transmission).

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

300: MRI apparatus
310: first data acquisition unit
320: second data acquisition unit
330: mask generation unit
340:

Claims (20)

A method of generating a magnetic susceptibility-emphasized image of an object in an MRI apparatus,
Obtaining at least one first complex number data including real data and imaginary data corresponding to the RF signal using an RF signal received from the object;
Obtaining at least one second complex data including real data and imaginary data by applying a predetermined filter to the Cartesian coordinate form of the at least one first complex data;
Generating a magnetic susceptibility enhancement mask using the at least one second complex data; And
And applying the magnetic susceptibility enhancing mask to the MRI image of the subject to generate the susceptibility enhancing image.
A method of generating a magnetic susceptibility-emphasized image of an object in an MRI apparatus,
Obtaining at least one first complex number data corresponding to the RF signal using an RF signal received from the object;
Obtaining at least one second complex data by applying a predetermined filter to the at least one first complex data;
Generating a magnetic susceptibility enhancement mask using the at least one second complex data; And
And applying the magnetic susceptibility enhancing mask to the MRI image of the subject to generate the susceptibility enhancing image,
Wherein the step of generating the susceptibility enhancing mask comprises:
Obtaining a magnitude value of each of the at least one second complex data; And
And generating the magnetic susceptibility enhancement mask using the obtained magnitude value.
A method of generating a magnetic susceptibility-emphasized image of an object in an MRI apparatus,
Obtaining at least one first complex number data corresponding to the RF signal using an RF signal received from the object;
Obtaining at least one second complex data by applying a predetermined filter to the at least one first complex data;
Generating a magnetic susceptibility enhancement mask using the at least one second complex data; And
And applying the magnetic susceptibility enhancing mask to the MRI image of the subject to generate the susceptibility enhancing image,
Wherein obtaining the at least one second complex data comprises:
Setting a magnitude value of the at least one first complex number data to a predetermined constant value; And
And applying the high-frequency filter to the at least one first complex number data whose magnitude value is set to a predetermined constant value to obtain the at least one second complex number data.
The method of claim 3,
Wherein the step of generating the susceptibility enhancing mask comprises:
Applying a low-pass filter to the at least one first complex number data whose magnitude value is set to a predetermined constant value to obtain at least one third complex number data; And
And generating the susceptibility enhancement mask using a value obtained by subtracting the predetermined constant value from a value obtained by adding the magnitude value of the at least one second complex data and the magnitude value of the at least one third complex data. A method of generating a magnetic susceptibility-emphasized image.
The method of claim 3,
Wherein the step of generating the susceptibility enhancing mask comprises:
And normalizing the magnitude value of the at least one second complex data to a value between 0 and 1.
6. The method of claim 5,
Wherein the normalizing step comprises:
And normalizing a magnitude value of the at least one second complex data by dividing the magnitude value of the at least one second complex data by a value obtained by multiplying the predetermined constant value by 2, .
5. The method of claim 4,
Wherein the step of generating the susceptibility enhancing mask comprises:
A value obtained by subtracting the predetermined constant value from a value obtained by adding the magnitude value of the at least one second complex number data and the magnitude value of the at least one third complex number data to a value obtained by multiplying the predetermined constant value by 2, To a value between < RTI ID = 0.0 > a < / RTI >
A method of generating a magnetic susceptibility-emphasized image of an object in an MRI apparatus,
Obtaining at least one first complex number data corresponding to the RF signal using an RF signal received from the object;
Obtaining at least one second complex data by applying a predetermined filter to the at least one first complex data;
Generating a magnetic susceptibility enhancement mask using the at least one second complex data; And
And applying the magnetic susceptibility enhancing mask to the MRI image of the subject to generate the susceptibility enhancing image,
Wherein obtaining the at least one second complex data comprises:
And applying the high-frequency filter to the imaginary data of the at least one first complex-valued data to obtain the at least one second complex-valued data.
A method of generating a magnetic susceptibility-emphasized image of an object in an MRI apparatus,
Obtaining at least one first complex number data corresponding to the RF signal using an RF signal received from the object;
Obtaining at least one second complex data by applying a predetermined filter to the at least one first complex data;
Generating a magnetic susceptibility enhancement mask using the at least one second complex data; And
And applying the magnetic susceptibility enhancing mask to the MRI image of the subject to generate the susceptibility enhancing image,
Wherein the step of generating the susceptibility-
And generating the magnetic susceptibility emphasis image by multiplying the magnetic susceptibility enhancing mask by an MRI image of the object a predetermined number of times.
A first data acquiring unit acquiring at least one first complex data including real data and imaginary data corresponding to the RF signal using an RF signal received from an object;
A second data acquiring unit for acquiring at least one second complex data including real data and imaginary data by applying a predetermined filter to the Cartesian coordinate format of the at least one first complex data;
A mask generator for generating a magnetic susceptibility enhancement mask using the at least one second complex data; And
And an image generating unit for applying the magnetic susceptibility enhancing mask to the MRI image of the subject to generate a magnetic susceptibility emphasis image.
A first data obtaining unit obtaining at least one first complex number data corresponding to the RF signal using an RF signal received from a target object;
A second data acquiring unit acquiring at least one second complex data by applying a predetermined filter to the at least one first complex data;
A mask generator for generating a magnetic susceptibility enhancement mask using the at least one second complex data; And
And an image generating unit for applying the magnetic susceptibility enhancing mask to the MRI image of the subject to generate a magnetic susceptibility enhancing image,
Wherein the mask generator comprises:
Wherein the magnetic susceptibility enhancing mask is generated using magnitude values of the at least one second complex data.
A first data obtaining unit obtaining at least one first complex number data corresponding to the RF signal using an RF signal received from a target object;
A second data acquiring unit acquiring at least one second complex data by applying a predetermined filter to the at least one first complex data;
A mask generator for generating a magnetic susceptibility enhancement mask using the at least one second complex data; And
And an image generating unit for applying the magnetic susceptibility enhancing mask to the MRI image of the subject to generate a magnetic susceptibility enhancing image,

Wherein the second data obtaining unit comprises:
The at least one first complex number data is set to a predetermined constant value and the at least one second complex number data is set to a predetermined constant value by applying a high frequency filter to the at least one first complex number data, The MRI apparatus comprising:
13. The method of claim 12,
Wherein the second data obtaining unit comprises:
Applying a low-pass filter to the at least one first complex number data whose magnitude value is set to a predetermined constant value to obtain at least one third complex number data,
Wherein the mask generator comprises:
Wherein the magnetic susceptibility enhancing mask is generated by using a value obtained by subtracting the predetermined constant value from a magnitude value of the at least one second complex data and a magnitude value of the at least one third complex data. .
13. The method of claim 12,
Wherein the mask generator comprises:
And normalizes the magnitude value of the at least one second complex data to a value between 0 and 1.
15. The method of claim 14,
Wherein the mask generator comprises:
And normalizes the magnitude value of the at least one second complex number data by dividing the magnitude value of the at least one second complex number data by a value obtained by multiplying the predetermined constant value by two.
14. The method of claim 13,
Wherein the mask generator comprises:
A value obtained by subtracting the predetermined constant value from a value obtained by adding the magnitude value of the at least one second complex number data and the magnitude value of the at least one third complex number data to a value obtained by multiplying the predetermined constant value by 2, Wherein the MRI apparatus normalizes the MRI apparatus to a value between the MRI apparatus and the MRI apparatus.
A first data obtaining unit obtaining at least one first complex number data corresponding to the RF signal using an RF signal received from a target object;
A second data acquiring unit acquiring at least one second complex data by applying a predetermined filter to the at least one first complex data;
A mask generator for generating a magnetic susceptibility enhancement mask using the at least one second complex data; And
And an image generating unit for applying the magnetic susceptibility enhancing mask to the MRI image of the subject to generate a magnetic susceptibility enhancing image,
Wherein the second data obtaining unit comprises:
And applies the high-frequency filter to the imaginary data of the at least one first complex-valued data to obtain the at least one second complex-valued data.
A first data obtaining unit obtaining at least one first complex number data corresponding to the RF signal using an RF signal received from a target object;
A second data acquiring unit acquiring at least one second complex data by applying a predetermined filter to the at least one first complex data;
A mask generator for generating a magnetic susceptibility enhancement mask using the at least one second complex data; And
And an image generating unit for applying the magnetic susceptibility enhancing mask to the MRI image of the subject to generate a magnetic susceptibility enhancing image,
The image generation unit may include:
Wherein the magnetic susceptibility enhancing mask is multiplied by a predetermined number of times with the MRI image of the subject to generate the magnetic susceptibility enhancing image.
A computer-readable recording medium having recorded thereon a program for executing the method of generating a susceptibility-emphasized image according to any one of claims 1 to 9. 11. The method of claim 10,
Wherein the mask generator comprises:
Wherein the magnetic susceptibility enhancing mask is generated using magnitude values of the at least one second complex data.

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