JP5277452B2 - MRI equipment - Google Patents

Description

  The present invention relates to an MRI apparatus suitable for determining a mask image used for mask processing on an absolute value image.

  The MRI apparatus applies an RF pulse having a specific frequency to the magnetic moment of a nucleus placed in a static magnetic field, and measures the natural scientific information of the substance using the magnetic resonance phenomenon generated thereby, As a device to visualize as. In recent MRI apparatuses, imaging is mainly performed using a receiving multiple array coil (MAC coil) composed of a plurality of coil elements, and high-speed, high S / N, wide-range imaging taking advantage of its characteristics. Is possible. Various proposals have been made regarding how to use the MAC coil. For example, there are Patent Documents 1 and 2. Patent Document 1 provides means for selecting a coil to be used in accordance with the imaging range.

Patent Document 2 is provided with a MAC coil for sensitivity distribution detection, a MAC coil for measurement, and a coil for whole body, and mask threshold detection at the time of mask processing such as image contour extraction is performed for whole body. A coil is used for sensitivity detection when detecting a sensitivity distribution, and a MAC coil for measurement is used for measurement.
JP 10-290793 A JP 2002-315731 A

  There are several purposes for using a MAC coil, one of which is to obtain a high S / N. Therefore, in many cases, the coil element is a surface coil having a small diameter, and the MAC coil is a set thereof. The image obtained from this has a large signal intensity difference between the portion where the surface coil is present and the portion where the surface coil is not present, and the image has a large signal strength unevenness unless special equalization processing is performed. On the other hand, special arithmetic processing is performed to create various types of MRI images, and a result image is output. For example, when contour extraction is necessary, a mask process using a mask image is used as a simple method, and it is assumed that an appropriate mask image is obtained for the mask process. Although the mask image is obtained from the absolute value image data, the mask image calculated from the absolute value image data is often not appropriate due to the influence of the local variation of the signal value. As a result, the extraction of the region of interest or the processing region using the mask image is caused to fail. Here, the absolute value image refers to an absolute image value that does not depend on the phase since the MRI image has a phase component.

  The above-mentioned Patent Document 2 presents one solution to such a problem. A coil for whole body is provided, and mask image calculation is performed from an absolute value image obtained using this coil. . Such a method has a problem that, in order to calculate a mask image using a whole body coil, extra imaging is required for that purpose, and the entire imaging time is extended.

An object of the present invention is to provide an MRI apparatus capable of calculating an appropriate mask image without extending the entire imaging time.
A further object of the present invention is to provide an MRI apparatus that can be used in a vertical magnetic field method and enables calculation of an appropriate mask image.

The present invention provides an MRI apparatus that has a plurality of receiving coils and obtains a first MRI absolute value image by combining these measurement NMR signals.
A part of the plurality of receiving coils is selected, a second absolute value image is obtained using a measurement NMR signal of the selected receiving coil, a mask image is obtained from the second absolute value image, and the mask image is used. An MRI apparatus that performs mask processing of the first MRI absolute value image is disclosed.

In addition, the present invention is a vertical magnetic field type receiving coil having two types of receiving coils, that is, a MAC coil and a solenoid coil, or having a solenoid coil as a part of the MAC coil and including the solenoid coil. In an MRI apparatus that obtains a first MRI absolute value image by combining signals,
A second absolute value image is obtained using the measured NMR signal of the solenoid coil, a mask image is obtained from the second absolute value image, and the mask processing of the first absolute value image is performed using the mask image. An intended MRI apparatus is disclosed.

  According to the present invention, it is possible to calculate an appropriate mask image that is not affected by variations in signal values existing in the absolute value image obtained from the MAC coil during mask processing, and avoid inappropriate mask processing results. I can do it.

Embodiments of the present invention will be described below with reference to the drawings.
First, general mask processing will be described. Mask processing using a mask image is used for image contour extraction and the like. In an MRI image, a mask image is widely used as a filter when it is desired to separate the background and the region of interest using the result of contour extraction and to perform selective computation. As a specific method for calculating the mask image, a method of performing threshold processing using the signal intensity of the absolute value image is simple. For example, a dark portion 1a and the light portion 1b and its When the image 1 having an intermediate dark portion 1c at an appropriate threshold TH ₁ performs threshold processing higher than the threshold value TH ₁ or less, as shown in FIG. 2 (a) As shown in FIGS. 2B and 2C, images 2 and 3 in which the signal area and the background area are easily separated can be obtained. Therefore, for the mask processing for extracting only a high signal area than the threshold TH _1, create a mask image for masking only the lower background area than the threshold value TH _1, may, combined over the mask image to the absolute value image. However, if the threshold setting is inappropriate, an unintended mask processing result is obtained. As shown in FIGS. 3B and 3C, the signal difference caused by the structure of the imaging target is different from the image 1 in FIG. May also divide the area. In order to calculate an appropriate mask process, it is desirable to prepare an image suitable for threshold processing. Generally, an image with a small signal difference between tissues in a signal region or a signal difference between a signal region and a background region is required. A large image is desirable. These are requests for avoiding severe threshold processing, and the above-described image is preferable in order to obtain a certain threshold processing effect in various scenes.

Next, an image obtained when the MAC coil is used will be described. As a method of applying a static magnetic field, there are a horizontal magnetic field type and a vertical magnetic field type. Each of the MAC coils used in the horizontal magnetic field type MRI apparatus is composed of a small-diameter coil capable of obtaining a high S / N. In addition, since the MAC coil is often installed in contact with the surface to be imaged, a local high signal is exhibited in the image in a place where a coil pattern as an outer edge (shape) of the coil exists. When threshold processing is performed on such an image, as shown in FIG. 4A, if there is a high signal portion 1d due to a coil, the threshold TH ₃ is raised due to an increase in the maximum signal value of the absolute value image. For this reason, in FIG. 2, what has been successfully processed with the same threshold setting may not be possible as shown in FIGS. 4B and 4C. Although it is conceivable to lower the threshold setting as a measure to avoid such a situation, a threshold that is too low may pick up artifacts such as signal flow due to blood flow and noise areas, so it is a perfect countermeasure It can not be said.

The present invention is preferably applied to a vertical magnetic field type MRI apparatus. FIG. 1 shows a configuration example of a QD coil applied to a vertical magnetic field method. The QD coil refers to a coil configuration in which coils are arranged so as to be orthogonal to each other and reception sensitivity is increased. The QD coil shown in FIG. 1 includes a MAC coil 10 arranged one-dimensionally in the body axis direction (x) and a solenoid coil 11 arranged in a direction (z) orthogonal to the MAC coil 10. The solenoid coil is also a part of the MAC coil, but is treated as another name in this embodiment. The MAC coil 10 has four planar arrangement examples, and overlaps with each other at the end so that the mutual signal is minimized. There are cases where the number of turns of the solenoid coil 11 is one time, and there are cases where the number of turns is two or more.

  The MAC coil 10 in FIG. 1 has four cases, but there are five or more cases and various arrangements and shapes. In addition, although the solenoid coil is perpendicular to the planar arrangement coil, there is also a planar arrangement example. In addition to an example in which a part of the MAC coil has a solenoid coil, there is an example in which a solenoid coil is provided separately from the MAC coil.

The QD coil of FIG. 1 uses coils 10 and 11 in cooperation to acquire MRI measurement information (NMR signal) from a subject. Specifically, the four received NMR signals of the MAC coil 10 and the received NMR signal of the solenoid coil 11 are combined to obtain an MRI image by reconstruction.
Therefore, in the present invention, attention is paid to the solenoid coil 11, and an image of the coil 11 is to be used for mask image extraction.

  This point will be described in detail. FIG. 5A shows an example of an image obtained by synthesizing NMR signals from the MAC coil 10 and the solenoid coil 11 shown in FIG. A high-luminance image component P appears at the left and right ends of the image. This is due to the influence of the coil pattern of the MAC coil 10. When this is projected horizontally, profile information as shown in FIG. 5B is obtained, making it difficult to calculate an appropriate mask image.

  Solenoid coils are generally known to have a wide sensitivity region and high uniformity sensitivity. As described in Patent Document 2. Therefore, the solenoid coil 11 is used as a measurement NMR signal for synthesis and also for mask image calculation.

FIG. 6 shows the processing flow. In flow F1, the NMR signals of both coils 10 and 11 are acquired. In flow F2, an NMR absolute value image G2 is obtained by reconstruction using only the NMR signal of the solenoid coil. In the flow F3, threshold processing is performed on the absolute value image G2 using the threshold TH to obtain a mask image. In flow F4, mask processing is performed using the mask image on the NMR absolute value image G1 or the NMR phase image obtained by synthesizing both signals . In the flow F5, an image G3 (absolute value image or phase image) from which only the region of interest is extracted is acquired.

  FIG. 7 shows an example of image processing according to this embodiment. FIG. 7A is an image of only the solenoid coil of the MAC coil, and the profile is as shown in FIG. It can be seen that the use of such an image facilitates appropriate mask image calculation.

  According to the present invention described above, the mask image is calculated using the absolute value image using only the data of the solenoid coil that is one of the elements constituting the MAC coil. This makes it possible to perform mask processing without being affected by a local high signal generated in the absolute value image when the MAC coil is used, and a good mask processing result can be obtained.

The above is an example having a vertical magnetic field type solenoid coil. Cases can be included.
For example, there is an example of the MAC coil 100 as shown in FIG. This is an example in which the coil elements # 1 to # 6 having a small diameter and the coil element # 7 around the planar arrangement thereof are provided. In this example, the coil element # 7 has a wider area than the coil elements # 1 to # 6 as a sense area. In the MAC coil 100, the coil element # 7 is not a solenoid coil, but has a flatter characteristic than the coil elements # 1 to # 6. Therefore, even if it is not as uniform as the solenoid coil, it is the most uniform among the MAC coils 100 and is used. Since # 1 to # 6 have a small diameter, they are highly matured, and the absolute value image synthesized from # 1 to # 7 has a large signal value. However, if only # 7 having a large diameter is used, a relatively uniform absolute value image can be obtained, and a satisfactory result can be obtained when performing absolute value processing.

It is a figure which shows the QD coil example in the perpendicular magnetic field type of this invention. It is a conceptual diagram of the contour extraction by threshold processing. It is a conceptual diagram of the contour extraction by threshold value processing when a threshold value is inappropriate. It is a conceptual diagram at the time of performing the contour extraction by threshold processing about the image which has a high signal part locally. It is the image obtained when a MAC coil is used with a perpendicular magnetic field MRI apparatus, and its profile. It is a processing flowchart of the present invention. It is the image and its profile which are obtained when only a solenoid coil is used in a vertical magnetic field MRI apparatus. It is another MAC coil example figure.

Explanation of symbols

1, 2, 3 Image 10 MAC coil 11 Solenoid coil

Claims (3)

In an MRI apparatus that obtains a first absolute value image by combining measurement NMR signals from a plurality of receiving coils,
A part of the plurality of receiving coils is selected, a second absolute value image is obtained using a measurement NMR signal of the selected receiving coil, a mask image is obtained from the second absolute value image, and the mask image is used. An MRI apparatus that performs mask processing of the first absolute value image. The MRI apparatus according to claim 1, wherein a reception coil having a uniform sensitivity region in a relatively wide range is selected as the selection reception coil from the plurality of reception coils. A vertical magnetic field type receiving coil with two types of receiving coils, MAC coil and solenoid coil, or a part of the MAC coil with a solenoid coil, and synthesizing the measured NMR signal including the solenoid coil In the MRI apparatus for obtaining the first MRI absolute value image,
A second absolute value image is obtained using the measured NMR signal of the solenoid coil, a mask image is obtained from the second absolute value image, and the mask processing of the first absolute value image is performed using the mask image. The intended MRI system.

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