JP2002034951A - Method for taking image of length information in magnetic resonance image and method for correcting image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect distortion inside the field of vision(FOV) of imaging and to correct the distortion. SOLUTION: Rulers with a hollow part filled with a material which can be imaged by the MRI are disposed adjacent to a subject, and the images of rulers are taken in the image of the subject. Then by detecting the distortion in the image of the hollow part of the ruler, the distortion in the MRI image is detected and corrected. By using rulers with graduation units having a hollow part filled with a material which can be imaged by the MRI, and integrating the graduation units three-dimensionally to be brought into contact with the subject by each unit, the image of the graduations can be always picked up in any MRI slice image surface. The rulers may be disposed at right angles to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of imprinting length information on images of magnetic resonance images for medical use and research and development, and a method for detecting and correcting the imaged magnetic resonance images.

[0002]

2. Description of the Related Art Magnetic resonance imaging (MRI, Magnetic Reso
nance Imaging) device uses RF (Radio F)
The object is irradiated with a (reqency, high frequency) magnetic field, and a signal returned from protons in the object is measured by a receiving coil. Position information of protons in the subject is obtained from a gradient magnetic field formed using the gradient magnetic field. Field of view (FOV: fi
If non-uniformity occurs within the eld of view), the resulting M
The position of the RI image is distorted.

When installing an MRI apparatus or changing the setting of imaging conditions (parameters), a phantom is installed in an imaging space, an image of the phantom is taken, and the imaging data is processed to calculate a plurality of magnetic field correction coils (SHIM coils). Is calculated, and the current of the magnetic field correction coil is corrected by the correction value to correct the magnetic field distortion. The correction of the magnetic field is performed by software, and this operation is called shimming. The photographer can control the size of the shimming range from the center of the FOV. However, if the range is too small, a large distortion occurs around the obtained image, and if the range is too large, the accuracy of correction decreases.

[0004]

It is apparent that only the method of changing the image parameters of the MRI apparatus by phantom imaging is affected by the magnetic field exerted by the subject itself, and how much distortion-free images are actually obtained. Was not. An object of the present invention is to solve this problem.

[0005]

SUMMARY OF THE INVENTION The present invention is characterized in that a ruler in which a substance which can be clearly imaged by an MRI apparatus is sealed in a hollow portion is arranged within the range of magnetic resonance image imaging and a magnetic resonance image is taken. And a method for imprinting length information on a magnetic resonance image.

The present invention also provides a three-dimensionally integrated plurality of graduation units provided on a central axis of a hollow part in which a substance which can be clearly imaged by an MRI apparatus is enclosed in the hollow part, and the ruler unit has a hollow part. Is provided so as to be in contact with a subject, and a method of imprinting length information on any MRI slice plane image in the vicinity of the subject. Furthermore, a method of imprinting length information on a magnetic resonance image characterized in that a plurality of sets of blocks each including a plurality of scale units are arranged in a different direction close to the subject, for example, at right angles.

Further, when these rulers are arranged in different directions, for example, at right angles, distortion in the vertical and horizontal components of MRI can be detected. When non-uniformity of the magnetic field is detected when imaging the subject using the MRI apparatus, data can be provided to an algorithm for correcting the length, and the captured image can be corrected.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows one of the rulers used in the present invention.
An example will be described. Reference numeral 1 denotes an object, 2 and 2R denote nonmagnetic rulers, and 3 denotes a hollow portion filled with a substance that can be imaged by an MRI apparatus, for example, water, copper sulfate aqueous solution, oil, or the like. The plurality of hollow portions 3 have a structure in which meter lengths are arranged in parallel with the rulers 2 and 2R at a fixed length and a fixed interval. The ruler 2 and the ruler 2R are installed at right angles to each other and are supported near the subject 1. One ruler may be provided, and ruler 2 and ruler 2R may be supported at the same height or at different heights.

FIGS. 2A and 2B show another embodiment of the ruler used in the present invention. (A) Ruler 4 is an example in which a member in which hollow portions 3 filled with a substance which can be imaged by an MRI apparatus are arranged in parallel at a fixed length and a fixed interval in an L-shaped curved shape. The ruler 5 shown in FIG. 3B is an example in which a member having a U-shaped hollow portion 6 filled with a substance that can be imaged by an MRI apparatus is arranged at a right angle. In the present specification and the drawings, members denoted by the same reference numerals represent the same members.

FIG. 3 shows still another embodiment of the ruler used in the present invention. (A) shows a scale unit having a hollow portion filled with a substance that can be imaged by MRI, and (b) shows a ruler 9 composed of the scale unit of (a). In FIG.
Denotes a scale unit, and 8 denotes a hollow portion filled with a substance that can be imaged by an MRI apparatus. The hollow portion 8 has a fixed length, and is configured to be in contact with one end face of a central axis in the longitudinal direction of a ruler unit.

In the ruler 9 of FIG. 3, a plurality of graduation units 7 of the same shape are stacked vertically and horizontally with the direction of the hollow portion 8 aligned.
The interval between the hollow portions is determined by the width direction of the scale unit. FIG.
In the example, the scale unit is a rectangular parallelepiped, but may be cylindrical, and any structure may be used as long as the interval between the hollow portions 8 serving as scales is kept constant when stacked. Since the scale unit is movable in the axial direction, the hollow-side end surface of each hollow portion can be brought into contact with the subject 3.

Referring to FIG. 4, the relationship between the ruler 9 and the subject 1 in FIG. 3 used in the present invention will be described. As shown in FIG. 4, the hollow portion 8 of each scale unit 7 is brought into contact with the subject 1 to support the ruler 9. The hollow portion 8 filled with the MRI-capable substance is photographed together with the subject 1 on each tomographic plane S1, S2, S3,... Of the MRI image as a ruler scale. Also, in the MRI images of the inclined tomographic planes S1 ', S2', S3 ',..., The hollow scale is designed to be long, so that it is captured with the subject at regular intervals. Another ruler 9 is arranged at a right angle to the ruler 9 in the figure, and the hollow portion 8 of the ruler is
May be imprinted. Of course, the rulers 2, 2R, 4, and 5 may be combined and imprinted.

The shape of the hollow portion of the ruler used in the present invention is not limited to the above-described embodiment, but is a line segment, a U-shape, or a lightning pattern or a square shape in which the end point of the hollow portion is easily detected. ,
What is necessary is just to have length information, such as a parallel line segment group of a predetermined length with a fixed interval. Also, a plurality of rulers (FIG. 1,
Instead of arranging a plurality of sets (FIG. 2) or a plurality of scale units (FIG. 3) at right angles, they may be arranged in different directions. The ruler is supported in close proximity to the subject by the non-magnetic material support within the imaging range.

FIG. 5 shows an example of an MRI tomographic reconstruction image according to the present invention. Fixed interval (1cm) shown in Fig. 6
A white line 11 is an image of a ruler scale (hollow portion filled with a substance that can be imaged by MRI), which coincides with the display scale of the mechanical scale 12 of the MRI apparatus on the image. Since the interval between the white lines 11 is constant and not distorted, it can be confirmed that proper shimming is performed.

FIG. 6 shows another example of an MRI tomographic reconstruction image according to the present invention. Since the white line 13a shown in the lower right end of FIG. 7 is not parallel to the other white lines 13, it can be seen that the magnetic field is distorted outside the shimming range. Further, it can be confirmed that the magnetic field is not distorted in the part on the left, in which the brain is shown.

Next, a method for correcting distortion of an MRI image according to the present invention will be described with reference to FIG. When the imaging conditions of the MRI apparatus are changed (step S1), the phantom is imaged (step S2), and shimming is repeated until the magnetic field distortion is within the allowable range (steps S3 and S4), and the magnetic field distortion is within the allowable range. , The correction ends and the subject is imaged in the next step. The above is the conventional correction method of the magnetic field distortion.

The correction method according to the present invention is a method for correcting a magnetic field distortion caused by the subject itself. 1 to 4
The length information (ruler) together with the subject is
Imprinted on the RI image (step S5), the distortion of the magnetic field due to the subject is detected based on the MRI imaging data (step S5).
6). If the distortion of the magnetic field is out of the allowable range, first, it is determined whether the distortion is within a range that can be corrected only by the image processing (step S7). If it is determined that it is within the range that can be corrected only by image processing, the photographing data is corrected by known image processing (step S9), and an MRI image is obtained (step S10).
If not, the correction is performed by shimming (step S8). If the distortion of the magnetic field is within the allowable range in step S7 (for example, the image example in FIG. 5), an MRI image is created from the photographed data (step S10).

If the photographing data of the subject and the ruler are those of the image shown in FIG. 5, the determination in step S6 of "Is distortion acceptable?" Is set to "YES", and the correction ends. When the imaging data of the subject and the ruler are those of the image of FIG.
In the determination of step S6, "is distortion allowable range?" Is set to "NO", and the process shifts to the determination of step S7 (if it is determined that there is no magnetic distortion in a portion where image data is actually required, the determination of step S6 is performed. "Is distortion acceptable?" May be set to "YES".) The criterion for determining whether or not to correct only with the image in the determination step S7 is determined by an error of the photographed length information with respect to the real thing.

This error in the length information is sufficient for practical use even if the photographing data is corrected according to a known computer process.
When the I image is within the range that can be obtained, for example,
When the length or angle of one graduation is calculated to be an error of 20% or less based on the photographic data of the graduation, the MRI image is corrected only by the image. If this error is equal to or greater than this value, the magnetic field is corrected by shimming (step S8), and the degree of magnetic field distortion is calculated again based on the imaging data of the subject and the ruler, and it is determined whether the distortion is an allowable range (step S8).
6).

[0020]

While the magnetic field has been adjusted only by prior phantom imaging, the present invention allows the magnetic field to be checked at the same time as the imaging of the subject, and if necessary, corrects the distortion after the fact. it can. To be able to confirm that there is no distortion in the obtained nuclear magnetic resonance image or to correct the distortion,
In particular, in head photographing, matching of an image with a brain chart becomes easy, and more accurate treatment and R & D can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an arrangement of a ruler example including length information of the present invention.

FIG. 2 is a diagram showing an arrangement of another ruler example including length information of the present invention.

FIG. 3 is a diagram showing an arrangement of another ruler example including length information of the present invention.

FIG. 4 is a diagram showing the relationship between the ruler of FIG. 3 including length information of the present invention and an MRI slice.

FIG. 5 is a diagram showing an example (Example 1) in which no distortion is detected in an image captured by the method of the present invention.

FIG. 6 is a diagram illustrating an example (Example 2) of detecting distortion in an image captured by the method of the present invention.

FIG. 7 is a flowchart illustrating a method of correcting an MRI image according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Subject 2, 2R ruler 3, 6, 8 Hollow part 4, 5, 9 Ruler 7 Scale unit 11 Hollow part image 13, 13a Hollow part image

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kenji Kono 1-1-4 Umezono, Tsukuba City, Ibaraki Prefecture Inside the Electronic Technology Research Laboratory, Industrial Technology Institute (72) Inventor Kenzo Kigami 1-1-1 Umezono Tsukuba City, Ibaraki Prefecture 4 Within the Institute of Electronic Technology, National Institute of Industrial Science (72) Inventor Kenji Shinsaku 1-8-1 Ihana, Chuo-ku, Chiba-shi, Chiba F-term (reference) 4C096 AA01 AB05 AB32 AB45 AC01 AD08 CA21 DC02 DC22 FA03 FA06 FA07

Claims (5)

[Claims] 1. A magnetic resonance image is taken by placing a ruler in which a substance that can be clearly photographed by a magnetic resonance imaging device is sealed in a hollow portion arranged at a predetermined interval or a predetermined shape within a range of magnetic resonance image photographing. A method of imprinting length information on a magnetic resonance image. 2. A method of imprinting length information on a magnetic resonance image, wherein a plurality of the rulers according to claim 1 are arranged in different directions. 3. A plurality of graduation units each having a hollow portion enclosing a substance which can be clearly photographed by a magnetic resonance imaging apparatus and having a central axis provided on one end side, and the one end of the hollow portion side is brought into contact with a subject to form a three-dimensional image. A method of imprinting length information on a magnetic resonance image, characterized in that the magnetic resonance image is photographed with the magnetic resonance images arranged in a horizontal direction. 4. A method for imprinting length information on a magnetic resonance image, wherein a plurality of sets of blocks each comprising a plurality of scale units according to claim 3 are arranged in different directions close to a subject. 5. An image correction method, comprising detecting and correcting distortion of an image of a subject taken based on image data of length information imprinted together with the subject on a magnetic resonance image.