JP7405417B2 - Manufacturing method of anisotropic phantom member for MRI imaging device - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act May 29, 2019, https://www. ncbi. nlm. nih. gov/pubmed/31144164, https://link. springer. com/article/101007/s10334-019-00761-3

The present invention provides anisotropy for MRI imaging devices, such as phantoms used for performance evaluation and calibration during measurement in MRI devices, and markers used as position standards. The present invention relates to a method of manufacturing a phantom member , and particularly relates to a method of manufacturing an anisotropic phantom member that is used when taking diffusion-weighted images in MRI and whose characteristics vary depending on the direction.

2. Description of the Related Art In medical settings, MRI devices (Magnetic Resonance Imaging devices) are used, which do not affect patients with radiation exposure or the like. In an MRI device, hydrogen nuclei (protons) contained in each cell of the human body are excited by applying a high-frequency magnetic field that corresponds to the spin of the protons, and the excited protons emit light when they return to their original state (relaxation). Based on electromagnetic waves, it is possible to obtain an image in which areas with different proton densities (for example, water and fat) are represented by shading. The MRI apparatus herein refers to an apparatus that applies compact MRI or magnetic resonance technology used in animal experiments, without limiting the imaging target to humans.

Conventional MRI images include T1-weighted images based on longitudinal relaxation of spins (T1 relaxation) and T2-weighted images based on transverse relaxation of spins (T2 relaxation). The contrast of these images is obtained based on the MRI-specific values of each human tissue. In recent years, relatively new imaging methods include a technology called diffusion MRI, such as diffusion tensor analysis, diffusion kurtosis analysis, and tractography. Diffusion MRI is a type of MRI sequence, and is a technique for obtaining a diffusion-weighted image that visualizes the diffusion motion of water molecules.
Diffusion tensor analysis applies the concept of tensor and can analyze the direction of diffusion motion of water molecules inside the human body. In addition, diffusion kurtosis analysis analyzes the diffusion pattern of water molecules using kurtosis, which is a statistical element, and has the potential to reflect a more detailed structure of human tissue.

Here, since the MRI apparatus uses a magnetic field in measurement, it may be affected by the environment in which it is installed. Additionally, there are individual differences in the distribution and strength of the magnetic field depending on the device, which may affect the measurement results. Therefore, when performing imaging with an MRI apparatus, it is necessary to perform calibration depending on the environment. When performing calibration, a member called a phantom whose characteristics are known in advance is used.
Currently, there are isotropic phantoms that can be used for T1-weighted images and T2-weighted images, but when capturing diffusion-weighted images, if an isotropic phantom is used during calibration, the diffusion phenomenon will be the same in all directions. This makes it difficult to observe the shading, so it is necessary to use an anisotropic phantom.

Although academic research is being conducted on anisotropic phantoms that can be used in diffusion MRI, there are few practical ones. This is because diffusion MRI differs from conventional imaging methods in that it analyzes the diffusion of water to produce an image, and a useful anisotropic phantom material that restricts the diffusion of water has not been reported.
Currently, in diffusion MRI research, asparagus, a low-priced and easily available vegetable, is sometimes used as an anisotropic phantom that has tissues similar to a simulated human body, including brain nerve tissue. (See Patent Document 1). When using asparagus as a phantom, asparagus is boiled in water to impregnate the asparagus with water.
In addition, the techniques described in Patent Document 1 and Non-Patent Documents 1 to 4 below are conventionally known as anisotropic phantoms.

Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2014-223546) discloses that a plurality of thin glass plates (1) are stacked as an anisotropic diffusion phantom for calibration, and H ₂ O of 10 μm between the glass plates (1) is stacked. A structure separated by layer (2) is described. WO 2005/000001 also describes configurations in which the capillary bundle is filled with water, hydrogel, or other substances containing hydrogen.

Non-Patent Document 2 describes that wood can be analyzed in diffusion weighted images in MRI and that it is possible to develop a phantom for diffusion MRI using wood.
Non-Patent Document 3 describes that body surface markers made of wood can be used in various MRI imaging methods including diffusion MRI.
Non-patent document 4 describes a fractional anisotropy map (FA) obtained by diffusion MRI imaging method.
It is stated that body surface markers made of wood can be observed on the map).

JP2014-223546A ("0007"-"0008", "0039"-"0040", Figure 1)

Tetsuhiro Sato and 1 other person, “MR microscope diffusion tensor measurement of anisotropic phantom”, Biomedical Engineering Symposium, 44(4):735-738, 2006 M. Suzuki et al., “Development of an anisotropic phantom for diffusion tensor imaging: Determining wood species of materials”, The 45th Annual meeting of the Japanese Society for Magnetic Resonance in Medicine(JSMRM) Sep 14-16, 2017 M. Suzuki et al., “Surface marker localization devices withsufficient signal-to-noise ratio: verification with wood.”, The 44th Annual meeting of the Japanese Society for Magnetic Resonance in Medicine(JSMRM) Sep 9-11, 2016 M. Suzuki et al., “Development of a Surface Marker for Fractional Anisotropy Maps using Wood in a Phantom Study.”, Magn Reson Med Sci. 2019 Jan 10;18(1):70-74

(Problems with conventional technology)
Asparagus, which is currently used as an anisotropic phantom, is easily perishable and may be difficult to obtain depending on the season (harvest time or season).
Anisotropic phantoms such as those described in Patent Document 1 that have a capillary shape or require control of gaps of 10 μm require advanced technology to manufacture, are expensive, and are difficult to obtain easily. . Furthermore, the configuration described in Patent Document 1 also has a problem in that it tends to generate false images (artifacts) due to differences in magnetic susceptibility. Furthermore, the configuration described in Patent Document 1 has the problem that only a single analysis value can be provided, and there is also a problem that it cannot provide an analysis value according to the region when calibrating according to the region to be imaged with the MRI apparatus.
Furthermore, there are few reports on markers that can be used in diffusion MRI, and no examples have been found where the position can be directly confirmed on a diffusion-weighted image. Currently, the position can only be estimated by comparing a T1-weighted image, a T2-weighted image, and a diffusion-weighted image.

The anisotropic phantom made of wood described in Non-Patent Documents 2-4 can be imaged with an MRI apparatus, and the possibility of the anisotropic phantom as an anisotropic phantom has been academically proposed. A phantom made of wood is less likely to rot than asparagus (easily maintains its properties over a long period of time), and has the advantage of being lower in cost than the phantom of Patent Document 1.
However, there is no established manufacturing method for wood phantoms as anisotropic phantoms, and there is a risk of variations in performance and time-consuming manufacturing.

The first technical problem of the present invention is to provide a manufacturing technique that improves the stability of the performance of a wooden detected member and reduces manufacturing time.
A second technical object of the present invention is to provide a processing technique that suppresses the generation of false images.

In order to solve the above technical problem, a method for manufacturing an anisotropic phantom member for an MRI imaging apparatus according to the invention according to claim 1 includes:
A method for manufacturing an anisotropic phantom member for an MRI imaging device that captures a diffusion weighted image using proton magnetic resonance conditions, the method comprising:
A wooden anisotropic phantom member impregnated with water is obtained by performing a boiling process of boiling a piece of wood soaked in water and a depressurization process of reducing the pressure of the wood piece that has undergone the boiling process to a pressure lower than atmospheric pressure. It is characterized by manufacturing.

The invention according to claim 2 is a method for manufacturing an anisotropic phantom member for an MRI imaging apparatus according to claim 1, comprising:
the boiling step of boiling the wood pieces soaked in water while pressurizing;
It is characterized by carrying out.

The invention according to claim 3 is a method for manufacturing an anisotropic phantom member for an MRI imaging apparatus according to claim 1 or 2 , comprising:
The method is characterized in that boiling and depressurizing the wood chips are repeated multiple times.

The invention according to claim 4 is a method for manufacturing an anisotropic phantom member for an MRI imaging apparatus according to any one of claims 1 to 3 , comprising:
Before impregnating the wood piece with water, compressing the wood piece from a direction crossing the direction in which the vascular bundles of the wood piece extend to adjust the diameter of the vascular bundle to a predetermined diameter;
It is characterized by carrying out.

According to the invention described in claim 1 , the cut piece of wood can be impregnated with water in a short time, and the manufacturing time of the wooden anisotropic phantom member can be shortened. According to the first aspect of the invention, each step can be carried out so that the anisotropic phantom member achieves the desired performance, and the stability of the performance of the wooden anisotropic phantom member can be improved.
According to the invention described in claim 2, water can be impregnated into the wood pieces more easily than when the wood pieces are not pressurized during the boiling process.
According to the third aspect of the invention , by repeating each step until the desired performance is achieved, it is possible to stably supply the wooden anisotropic phantom member having the desired performance.
According to the fourth aspect of the invention , the performance of the wooden anisotropic phantom member can be stabilized compared to the case where the diameter of the vascular bundle is not adjusted.

FIG. 1 is an explanatory diagram of a magnetic resonance imaging apparatus according to a first embodiment of the present invention. FIG. 2 is an enlarged view of the main part of the piece of wood. FIG. 3 is a schematic explanatory diagram of a wood piece forming apparatus. FIG. 4 is an explanatory diagram of an experimental example, and is a graph in which the vertical axis represents the weight of the wood piece and the horizontal axis represents time. FIG. 5 is an explanatory diagram of the experimental results of Experimental Example 2, FIG. 5A is an explanatory diagram of Comparative Example 2, and FIG. 5B is an explanatory diagram of the results of Experimental Example 2. FIG. 6 is an explanatory diagram of the weight change of the wooden phantom of Experimental Example 2.

Next, specific examples of embodiments of the present invention (hereinafter referred to as examples) will be described with reference to the drawings, but the present invention is not limited to the following examples.
In addition, in the following explanation using the drawings, illustrations of members other than those necessary for the explanation are appropriately omitted for easy understanding.

FIG. 1 is an explanatory diagram of a magnetic resonance imaging apparatus according to a first embodiment of the present invention.
In FIG. 1, a magnetic resonance imaging apparatus (MRI apparatus) 1 according to a first embodiment as an example of an imaging apparatus of the present invention has a magnet section 2 as an example of a magnetic field generating apparatus. A through hole 3 is formed in the magnet portion 2 and extends horizontally through the inside thereof. A bed 6 on which a sleeping subject 4 is supported can pass through the through hole 3 .
The magnet section 2 includes a static magnetic field generating magnet 11 as an example of a static magnetic field applying member. Note that a superconducting electromagnet or a permanent magnet can be used as the static magnetic field generating magnet. A gradient magnetic field generating coil 12, which is an example of a gradient magnetic field applying member, is arranged inside the static magnetic field generating magnet 11. A high-frequency magnetic field generating coil 13, which is an example of an excitation magnetic field applying member, is arranged inside the gradient magnetic field generating coil 12. A receiving coil 14 that receives electromagnetic waves is arranged inside the high-frequency magnetic field generating coil 13 as an example of a receiving section.

A computer device 21 as an example of an information processing device is electrically connected to the magnet section 2 via a cable Cb. Therefore, the computer device 21 is configured to be able to transmit and receive control signals for the static magnetic field generating magnet 11 and the like, detection signals for the receiving coil 14, and the like with the magnet unit 2. The computer device 21 includes a computer main body 22, a display 23 as an example of a display section, and a keyboard 24 and a mouse 25 as examples of an input section. In the first embodiment, the computer device 21 and the magnet unit 2 are connected by the cable Cb, but the present invention is not limited to this, and any wireless connection such as a mobile phone line, Bluetooth (registered trademark), wireless LAN, etc. It is also possible to send and receive information using a communication method.

The computer main body 22 of the first embodiment stores an I/O (input/output interface) for inputting/outputting signals to/from the outside, adjusting input/output signal levels, etc., and programs and data for performing necessary startup processing. ROM (read-only memory), RAM (random access memory) for temporarily storing necessary data and programs, a CPU (central processing unit) that performs processing according to the startup program stored in the ROM, etc.; It is composed of a computer device having a clock oscillator, etc., and can realize various functions by executing programs stored in the ROM, RAM, etc.
The computer main body 22 stores basic software that controls basic operations, a so-called operating system, an MRI imaging program as an example of an application program, and other software (not shown).
The MRI imaging program of the first embodiment controls the gradient magnetic field generating coil 12 and the high frequency magnetic field generating coil 13, and derives a diffusion weighted image based on the detection signal received by the receiving coil 14. Note that the method and program for deriving the diffusion weighted image are conventionally known, and various configurations can be adopted, so a detailed explanation will be omitted.

(Description of manufacturing method of wood phantom)
(Explanation of forming process of wood pieces)
FIG. 2 is an enlarged view of the main part of the piece of wood.
In the MRI apparatus 1 of the first embodiment, a wooden phantom is used as an anisotropic phantom (an example of a detected member) used for performance evaluation and calibration when capturing a diffusion weighted image. In Example 1, in order to create a wooden phantom, a piece of wood is first cut out from a tree. Taking a typical coniferous tree as an example, tracheids also have a large-diameter part called earlywood and a small-diameter part called latewood. When using these as phantom materials, in order to achieve uniform anisotropy, it is desirable to separate earlywood and latewood and cut the wood pieces so that earlywood and latewood do not mix.
In a wooden phantom, the smaller the diameter of the vascular bundle, the more difficult it is for water to penetrate, and the more anisotropic it is. When the vascular bundle diameter is large, the characteristics are opposite. In order to stabilize the performance of the detected member, it is desirable to make the diameters of the vascular bundles the same. Therefore, in manufacturing the detected member, it is desirable to separate the portions of the vascular bundles surrounded by circles in FIG. 2 with large diameters and the portions of vascular bundles with small diameters surrounded by squares so that they do not coexist.

FIG. 3 is a schematic explanatory diagram of a wood piece forming apparatus.
Note that due to individual differences in wood, the type of wood, etc., the diameter of the vascular bundle may vary widely, or the diameter may be so large that sufficient anisotropy may not be obtained. In this case, it is also possible to mold a piece of wood. In FIG. 3, a cut piece of wood 31 is placed in a mold 32 so that the direction in which the vascular bundles and the like extend (the direction in which the wood is vertically divided) is horizontal. From this state, the wood piece 31 is pressed and compressed with the press die 33 in a direction intersecting the direction in which the vascular bundles, etc. extend (direction of cutting the wood into rounds), thereby reducing the diameter of the vascular bundles, etc. It is possible to adjust the diameter and density to desired values determined in advance through experiments or the like. Note that wood is weak in tension and easily breaks, but strong in compression, and compression processing is relatively easy.

Note that the smaller the diameter of the vascular bundle, the higher the anisotropy. The higher the anisotropy, the higher the signal strength on the diffusion MRI image. There are various types of human tissues, ranging from tissues with high anisotropy to tissues with low anisotropy. By shaping the wood piece 31 and adjusting the anisotropy of the wood, it is possible to create a phantom that is more equivalent to a human body. That is, it is possible to adjust the anisotropy by adjusting the diameter of the vascular bundle, etc., depending on the region to be measured.
It is also possible to create a phantom with a certain quality by eliminating individual differences in natural wood (variations in the diameter of vascular bundles, variations in anisotropy, etc.) through this molding process.

In addition, the vascular bundle has door structures called wall holes at regular intervals. When the wall holes are closed, it is difficult for moisture to penetrate beyond them. Although it is expected that the wall holes will open due to the pressure and depressurization described later, it is also expected that the wall holes will physically open due to the external force associated with compression during molding, which may make it easier for water to penetrate in the later process. You can expect it.
The shape of the piece of wood can be any shape, such as a cylinder or a square prism, including bending. Note that the shape of the wood can be made into a desired shape when cutting a piece of wood from the wood, or it can be processed into the desired shape after the forming process in the forming devices 32 to 33.

(Explanation of water impregnation process)
In the water impregnation step, first, a boiling step is performed in which the shaped wood piece 31 is immersed in water and boiled. In the boiling step of Example 1, the pieces of wood soaked in water are boiled while being pressurized.
As a result of the inventors' research, it was found that when distilled water or pure water was used as the water in which the piece of wood 31 was immersed, wood-decaying fungi were observed to occur on the wood surface; It has been confirmed that this method can remove wood-decaying fungi that have occurred in the past, and can suppress the further occurrence of wood-decaying fungi. Therefore, it is preferable to use water that has been subjected to antiseptic treatment such as chlorine disinfection that is equivalent to or better than tap water. Therefore, by using tap water, it is possible to preserve the wooden phantom for a long time, that is, to use it as a phantom even after a long period of time has passed.
Next, the wood piece 31 that has undergone the boiling process is subjected to a depressurization process in which the wood piece 31 is held in an environment with a pressure lower than atmospheric pressure.
A wooden phantom was created in which the wood piece 31 was impregnated with water through a water impregnation process consisting of the boiling process and the decompression process.

Wooden phantoms have a structure that allows water and air to easily flow in the direction (in the direction in which the tree is split vertically) along the wood's tracheids (gymnosperms, etc.) and vascular bundles (angiosperms) such as vessels and phloem. Therefore, it is difficult for water to flow in the direction that intersects the direction in which the vascular bundles, etc. extend (the direction in which the tree is sliced into rings). The fact that the ease with which water flows differs depending on the direction is called anisotropy.
However, if air instead of water is present inside a vascular bundle or the like, it is difficult to measure with an MRI apparatus that utilizes the magnetic resonance phenomenon of protons (hydrogen ions). Therefore, it is necessary to fill the inside of the vascular bundle etc. with water.

In Example 1, the air is expanded by heating in the boiling step, so that the air inside the vascular bundle and the like is easily exhausted to the outside.
Further, in Example 1, pressurization is applied in the boiling process, thereby making it easier for the pressurized water to enter the inside of the vascular bundle, etc., than when no pressure is applied.
Further, in the pressure reduction step, by reducing the pressure, the air remaining in the vascular bundle or the like expands due to the pressure difference and is easily exhausted from the vascular bundle to the outside.
As described above, in the water impregnation process of Example 1, by performing the boiling process and the depressurization process, it is possible to stably manufacture and supply a phantom impregnated with more water than when these processes are not performed. It is possible to do so. Furthermore, by impregnating with a large amount of water, the performance as a phantom is also improved.

Note that it is also possible to impregnate the wood piece 31 with more water by repeatedly performing the boiling process and the decompression process multiple times. That is, depending on the material of the wood, the desired degree of anisotropy, the shape and size of the wood piece 31, and the cut portion, water impregnation may not be sufficient with one boiling step and one depressurization step. In such a case, it is possible to repeatedly perform the boiling step and the pressure reduction step until the desired anisotropy is obtained. On the other hand, if the desired anisotropy can be obtained by performing the boiling step and the decompression step once each, it is sufficient to perform the boiling step and the decompression step once each.
Further, in Example 1, the case where pressurization is applied in the boiling process is illustrated, but the present invention is not limited to this. Depending on the material of the wood and the desired degree of anisotropy, heating (boiling) alone may be enough to allow water to enter the vascular bundles and achieve the desired anisotropy without applying pressure. be. In such a case, it is also possible not to apply pressure during the boiling process.

Furthermore, in Example 1, it is possible to impregnate the wood piece 31 with water to some extent even if only the pressure reduction step is performed, as will be shown in the explanation of the experimental results described below. Therefore, if the desired anisotropy can be achieved without the boiling process depending on the material of the wood, etc., the configuration should be such that only the depressurization process is performed without the boiling process (pressurization and boiling). is also possible. Conversely, if the desired anisotropy can be sufficiently achieved only with the boiling process, it is also possible to adopt a configuration in which only the boiling process is performed without performing the pressure reduction process.
Further, in Example 1, the decompression step was performed after the boiling step, but the method is not limited to this. As will be shown in the explanation of the experimental results to be described later, it is also possible to adopt a configuration in which the pressure reduction step is performed first, and then the boiling step is performed.

(Experiment example 1)
Next, an experiment was conducted regarding the water impregnation process.
As the wood piece 31, "cedar" wood was used.
In the boiling step, as an example, a commercially available pressure cooker (for cooking) was used, and the wood pieces 31 were boiled for 30 minutes at a pressure of about 2 atmospheres while completely immersed therein.
In addition, in the depressurization process, for example, a container in which the wood chips 31 are submerged in water is placed in a desiccator, and the inside of the desiccator is kept under vacuum with a vacuum pump (-0.1 MPa with a vacuum meter 62-2986-21 manufactured by As One Corporation). After maintaining the reduced pressure state for 24 hours (a low pressure state such as ""), it was released to atmospheric pressure. More specifically, first, the pressure inside the desiccator is reduced to -0.1 MPa, the vacuum pump is stopped, and the vacuum pump is left standing for about 2 to 3 hours. degree decreases. When the degree of vacuum decreases, the vacuum pump is operated to reduce the pressure to -0.1 MPa again and leave it still. This depressurization and standing still were repeated about three times. Then, 24 hours after the pressure was reduced, the pressure was released to atmospheric pressure.
After the boiling process and the depressurization process, the wood piece 31 was left immersed in water for one week, and its weight was measured. This treatment was carried out for 6 weeks.
In the experiment, boiling was performed without pressurization (comparative example), case where only the boiling process was performed without depressurization (experimental example), case where only the depressurization process was performed for 3 weeks, and case where the boiling process was also performed after the depressurization process. And so I did.
The experimental results are shown in Figure 4.

FIG. 4 is an explanatory diagram of an experimental example, and is a graph in which the vertical axis represents the weight of the wood piece and the horizontal axis represents time.
In FIG. 4, the increase in weight of the wood piece 31 was the least when boiling alone (the preparation method of Non-Patent Documents 2 to 4) was used. That is, it was confirmed that the amount of water impregnated into the wood piece 31 was small. Therefore, it was confirmed that there is a limit to the impregnation of water into vascular bundles and the like by boiling alone, or that it takes a long time to sufficiently impregnate water.
In comparison, it was confirmed that the boiling process alone can increase water impregnation, and it was confirmed that the depressurization process (until the third week) alone resulted in even more water impregnation than the boiling process alone. Furthermore, it was confirmed that when the heating and boiling process and the depressurizing process were performed (after the third week), the amount of water impregnated was the largest and was the most effective.

Note that, theoretically, it is possible to completely impregnate the wood piece 31 with water by leaving the wood piece 31 in water and taking a long period of time. In experiments conducted by the present inventors, it was confirmed that a piece of wood 31 found in underground water excavated from a ruin more than 1,000 years ago was almost completely impregnated with water, and that good measurement results could be obtained when measured with an MRI device. Ta. However, it takes a long time to manufacture such a piece of wood 31 and it is difficult to have a stable supply, and from the perspective of the archaeological value of the piece of wood 31, it is difficult to use it as an anisotropic phantom for medical use. It is.
Therefore, when creating an anisotropic phantom as in Example 1, it is possible to impregnate the wood piece 31 with water in a short time by performing one or both of the boiling process and the decompression process. It is possible to shorten the time span from at least 1000 years to several weeks or months. Therefore, it is possible to stably supply wooden phantoms from cut wood. In particular, if thinned wood is used, it is expected to contribute to environmental protection.

Furthermore, in the first embodiment, it is possible to select the combination of the heating and boiling process and the decompression process and the number of repetitions until the desired performance is achieved, depending on the performance and specifications required of the wooden phantom. Therefore, it is possible to provide a wooden phantom with stable performance.
Furthermore, as mentioned above, when tap water is used in Example 1, it can be used for several months. However, with the conventional technology that uses boiled asparagus, the asparagus spoils in a few days (doesn't last a week), so when performing performance evaluation or calibration, it is necessary to repeatedly purchase asparagus. Ta. In contrast, Example 1 can be used repeatedly over a long period of time and is advantageous in terms of cost. In particular, as a result of the inventor's experiment, the wood piece 31 produced by the manufacturing method of Example 1 was found to be usable because the change in signal value was within the measurement error range even after one year had passed.

Note that depending on the material of the wood, the ease/difficulty of water impregnation differs, so if the material is difficult to impregnate, the impregnation can be progressed by repeating the boiling process and depressurization process more times. If the material is easy to clean, it is possible to shorten the manufacturing period by shortening the standing period. Moreover, the pressure at the time of pressurization and depressurization is not limited to the illustrated pressure, but can be changed. That is, a high effect can be expected by using an industrial pressure device capable of achieving high pressure instead of a pressure cooker as the pressure device.
From the results in Figure 4, an efficient treatment would be to completely submerge the dried wood in water and leave it there for as long as possible under as low a pressure as possible. It is desirable to pressurize as much as possible after that. By doing so, it is possible to apply pressure to the voids inside the wood piece 31 that has been deaerated by reducing the pressure and allow water to penetrate even without boiling.
On the other hand, if the boiling process is performed first, air can dissolve in the water, so it is better to let the boiled water penetrate into the wood piece 31 first, so that the water can penetrate more into the wood piece 31. It can also be considered easy.

In addition, in addition to the experimental examples shown, the inventor similarly impregnated 75 types of wood and captured diffusion weighted images, and confirmed that all of the wood could be used. At this time, many of the woods with high anisotropy were those that were difficult for water to penetrate.
Although there is no limit to the size of the wood piece 31, if the wood piece 31 is thick in the direction of the wood fibers (the direction in which the vascular bundles, etc. extend), the vascular bundles etc. will become long and water will not easily penetrate. Preferably, a thin piece of wood 31 is used.
Furthermore, some vascular plants have wall holes between their tube structures, making it difficult for water to penetrate. Therefore, it is thought that impregnation treatment can be carried out efficiently by using wood that does not have wall holes or whose wall holes are not closed.
Furthermore, in the first embodiment, an example of an anisotropic phantom used for performance evaluation and calibration in capturing diffusion weighted images of an MRI apparatus has been described, but the present invention is not limited thereto. For example, by utilizing the fact that a piece of wood 31 impregnated with water can be detected by an MRI device, a marker (an example of a member to be detected) is fixed to the body surface of the subject 4 to observe the reference position. It is also possible to use the wood piece 31 of Example 1 as a material.

(Explanation of silicon embedding process)
In Example 1, the prepared wooden phantom was embedded in silicone and stored with the surface of the wooden phantom covered with silicone.
In a wooden phantom, the magnetic susceptibility changes rapidly at the boundary between wood and air. If there is a sudden change in magnetic susceptibility, there is a problem in that artifacts occur. In contrast, in Example 1, the surface of the wooden phantom is covered with silicone. Therefore, the sudden change in magnetic susceptibility at the boundary with air at the outer edge of the wooden phantom is alleviated by silicon. Therefore, it is possible to provide a high-performance wooden phantom that is less likely to generate false images.

(Experiment example 2)
Next, we conducted an experiment to confirm the effect of silicon embedding.
In Experimental Example 2, "VM001 Mr. Silicone" manufactured by GSI Creos Co., Ltd. was used as the silicon.
In Experimental Example 2, first, silicone was poured into a Tupperware (container) deep enough to completely hide the piece of wood 31 (wooden phantom) to a thickness of about 10 mm and hardened. Next, using the solidified silicon as a base, a piece of wood 31 was placed on top of it, and silicon was injected from above until the piece of wood 31 was completely hidden (until it was embedded). Then, the wood piece 31 was sealed with this silicone and stored. Then, it was encapsulated in silicone resin and imaged with an MRI apparatus without being taken out.
As Comparative Example 2, a phantom was prepared in which water was used as the embedding material instead of silicon.
The experimental results are shown in Figure 5.

FIG. 5 is an explanatory diagram of the experimental results of Experimental Example 2, FIG. 5A is an explanatory diagram of Comparative Example 2, and FIG. 5B is an explanatory diagram of the results of Experimental Example 2.
In FIG. 5A, in the case of the wooden phantom with water as the embedding material, the captured image was distorted as if the sides of the phantom were falling down, and the upper part was also deformed and signal value abnormalities (false images, artifacts) were observed. In MRI imaging, particularly diffusion MRI imaging, false images are formed at the boundary between an imaging target such as human tissue and the surrounding air. This is because the magnetic susceptibility changes rapidly at the interface.

On the other hand, in the wooden phantom in which silicon was used as the embedding material, as shown in FIG. 5B, no distortion as shown in FIG. 5A was observed. In FIG. 5B, the white trapezoid in the center is a piece of wood, the gray around it is silicone resin, and the black frame around it is air.
Therefore, by embedding with silicone resin, the surface of the piece of wood 31 is covered with silicone, and a sudden change in magnetic susceptibility at the boundary between wood and air is suppressed. In particular, silicone resin has an extremely low NMR (Nuclear Magnetic Resonance) signal, is difficult to appear in images, and is unlikely to have an adverse effect on image quality.

FIG. 6 is an explanatory diagram of the weight change of the wooden phantom of Experimental Example 2.
In Figure 6, the weight of the wooden phantom embedded in the silicone resin of Experimental Example 2 was measured for 9 months, and the weight change during that period was 1.5 g at most, which was 125.5 g of the weight at the time of sample preparation. .2%. Furthermore, the weight change was not a constant change but a vertical movement, which is considered to be a measurement error.
Therefore, in Experimental Example 2, it was confirmed that by embedding a wooden phantom in silicone, it was possible to store the phantom in a stable state over a long period of time without deteriorating its performance.

(Example of change)
Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various changes can be made within the scope of the gist of the present invention as described in the claims. Is possible. Modifications (H01) to (H03) of the present invention are illustrated below.
(H01) In the embodiment described above, a magnetic resonance imaging apparatus in which the magnet portion 2 is ring-shaped, that is, a so-called tunnel type is illustrated, but the present invention is not limited to this. For example, it is also applicable to a so-called open-type magnetic resonance imaging apparatus in which the magnet portion 2 is U-shaped.
(H02) In the above embodiments and experimental examples, the specific numerical values, product names, etc. illustrated can be arbitrarily changed depending on the design, specifications, etc.
(H03) In the above embodiments, the shape of the phantom is not limited to a simple shape such as a cylinder or a quadrangular prism, but the shape can be freely deformed and processed (cut out, etc.). For example, it is possible to make it close to the shape of a human brain, to make it close to the shape of an organ to be measured, or to make it the same shape as a performance evaluation phantom for MRI that is currently commercially available. It is also possible to create a phantom that mimics the branching of nerve fibers by using the parts where branches branch from the trunk of a tree.

1...MRI device 31...piece of wood, member to be detected.

Claims (4)

A method for manufacturing an anisotropic phantom member for an MRI imaging device that captures a diffusion weighted image using proton magnetic resonance conditions, the method comprising:
A wooden anisotropic phantom member impregnated with water is obtained by performing a boiling process of boiling a piece of wood soaked in water and a depressurization process of reducing the pressure of the wood piece that has undergone the boiling process to a pressure lower than atmospheric pressure. A method for manufacturing an anisotropic phantom member for an MRI imaging device, comprising: manufacturing an anisotropic phantom member for an MRI imaging device. the boiling step of boiling the wood pieces soaked in water while pressurizing;
2. The method of manufacturing an anisotropic phantom member for an MRI imaging apparatus according to claim 1, wherein: The method for manufacturing an anisotropic phantom member for an MRI imaging apparatus according to claim 1 or 2, characterized in that boiling and depressurizing the wood piece are repeated multiple times. Before impregnating the wood piece with water, compressing the wood piece from a direction crossing the direction in which the vascular bundles of the wood piece extend to adjust the diameter of the vascular bundle to a predetermined diameter;
4. The method of manufacturing an anisotropic phantom member for an MRI imaging apparatus according to claim 1 , wherein:

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