JP2693429B2 - Magnetic resonance imaging equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention utilizes a magnetic resonance (MR) phenomenon to identify a specific atomic nucleus in a specific cross section of a subject (living body). The density distribution of spins can be computed using a so-called computed tomography (CT) method.
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MRI apparatus (magnetic resonance imaging apparatus) that performs imaging as a tomogram and performs a biopsy on the basis of this image, and particularly to a magnetic resonance imaging apparatus in which the configuration of a magnetic field generator is improved. (Prior Art) An example of a conventional magnetic resonance imaging apparatus will be described with reference to FIG. That is, in FIG. 4, an examinee P is placed on a bed top (not shown), and the examinee P is the uniform static magnetic field generating coils 1A and 1B as a uniform static magnetic field generator.
And the gradient magnetic field generating coil 2 as a main element. Uniform static magnetic field generating coil 1A, 1
The gradient magnetic field generated by the gradient magnetic field generating coil 2 is superimposed on the uniform static magnetic field generated by B to form a superimposed magnetic field, and the subject P is placed in this superimposed magnetic field. The transmission / reception coil 3 is applied to the subject P, and the MR phenomenon is caused in the subject P by applying an excitation rotating magnetic field by the transmission / reception coil 3, and the induced MR signal is detected by the transmission / reception coil 3. By performing image reconstruction processing by an image processing device (not shown) or the like, information such as a tomographic image at the position of the subject P to which the transmission / reception coil 3 is applied is obtained, and image display or the like is performed. In this case, since the gradient magnetic field generating coil 2 and the transmitting / receiving coil 3 maintain a positional relationship such that they are not coupled,
The gradient magnetic field generating coil 2 is used for the reason such as suppressing noise generated by electromagnetic force due to energization of the gradient magnetic field generating coil 3 and obtaining a large subject access cavity formed in the gradient magnetic field generating coil 3. The fixed static magnetic field generating coils 1A and 1B, which are magnetic field forming spaces, are fixed at fixed positions and are in contact with the inner circumference. However, the following problems have been raised in such a configuration. That is, this type of magnetic resonance imaging apparatus is not satisfied with the short-time imaging request required as a medical diagnostic apparatus, and requires a relatively long imaging time. One method for solving this is to generate a strong magnetic field to act on a desired imaging region of the subject, to speed up the rising speed, and the like. In order to realize this, the gradient magnetic field generating coil 2 needs to have a small self-inductance, and there are conditions such as reducing the coil diameter, increasing the current, and reducing the number of coil windings.
However, these conditions are different from the conventional configuration in which the gradient magnetic field generating coil 2 is fixed to the uniform static magnetic field generating coils 1A and 1B so as to be in a fixed position and in contact with the inner circumference in the following points. It cannot be entered. That is, when it is attempted to obtain a large subject access cavity in order to secure a desired imaging region including the whole body, the gradient magnetic field generating coil 2 has a diameter that contacts the inner circumference of the uniform static magnetic field generating coils 1A and 1B. Need to have. In this case, the distance between the gradient magnetic field generating coil 2 and the subject becomes large, so the magnetic field that can act on the desired imaging region becomes weak, and it is necessary to reduce the size of the gradient magnetic field generating coil 2 in order to strengthen the magnetic field. Yes, and eventually the subject's access cavity is small. (Problems to be Solved by the Invention) As described above, in the conventional technique, since the gradient magnetic field generation device is fixedly installed with a diameter such that it is in contact with the static magnetic field generation device, it is possible to access a large subject. If you secure a cavity,
There is a problem in that the strength of the gradient magnetic field that can act on the desired imaging region of the subject becomes weak, and the demand for short-time imaging or the like cannot be realized. Therefore, an object of the present invention is to secure a desired subject access cavity and to make the strength of the gradient magnetic field that can act on the desired imaging region of the subject strong so that a request for short-time imaging or the like can be realized. To provide. [Structure of the Invention] (Means for Solving Problems) The present invention has the following structure in order to solve the problems and achieve the object. That is, the present invention causes a magnetic resonance phenomenon in the subject by applying a static magnetic field, a gradient magnetic field and an excitation magnetic field to the subject, detects a magnetic resonance signal induced from the subject, and reconstructs an image. In the magnetic resonance imaging apparatus for obtaining the image information of the subject by performing a process, the means for generating the gradient magnetic field is a first gradient magnetic field generating means for applying a gradient magnetic field of a predetermined magnitude and the first gradient magnetic field generation. A second gradient magnetic field generating means which provides a gradient magnetic field area smaller than that of the means and which is provided with a transmission / reception coil integrally, and the first gradient magnetic field generating means and the second gradient according to the imaging region of the subject. It is characterized in that the magnetic field generating means is selectively used. (Operation) According to such a configuration, the first gradient magnetic field generating means is used for imaging a large imaging region, and the second transmitting / receiving coil is integrally provided for imaging a small imaging region. By using the gradient magnetic field generating means, a strong gradient magnetic field can be applied to the imaged regions of different sizes. Moreover, the second gradient magnetic field generating means and the transmission / reception coil can be integrated to maintain a positional relationship in which coupling between the two does not occur. In the case of a small imaging region, the strong gradient magnetic field described above is used. Therefore, there is no adverse effect such as sensitivity unevenness due to the cubbling. Further, under the application of the gradient magnetic field by the second gradient magnetic field generating means, the integrated transmission / reception coil enables effective signal collection from a local site. These advantages greatly contribute to high precision diagnosis. (Embodiment) Hereinafter, an embodiment of a magnetic resonance imaging apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing the configuration of the same embodiment. In FIG. 1, a uniform static magnetic field generating coil is provided in the main body 4.
1A and 1B are arranged, and the inner diameter portions of the uniform static magnetic field generating coils 1A and 1B are hollow as a uniform static magnetic field forming space. A photographing unit 7 to be inserted into the cavity is detachably attached to an end portion of a top plate 6 which is slidable on the bed 5 toward the main body. The imaging unit 7 includes a gradient magnetic field generating coil 7a, a transmission / reception coil 7b that is inserted inside the gradient magnetic field generating coil 7a and is located close to the imaging region of the subject.
The gradient magnetic field generating coil 7 and the mounting base 7c on which the transmitting / receiving coil 7b is mounted.
a, the transmission / reception coil 7b has an appropriate diameter corresponding to a desired imaging region, and the gradient magnetic field generation coil 7a and the transmission / reception coil 7b
Is fixed by a fixture or the like (not shown) in a positional relationship such that coupling does not occur. Of course, the apparatus of this embodiment has a control system and an image processing system (not shown) to control the excitation of the uniform static magnetic field generating coils 1A and 1B and the gradient magnetic field generating coil 7a, and to transmit / receive the transmitting / receiving coil 7b. Thus, the signal processing of the detection signal is performed, and image information such as a tomographic image is obtained. Next, the operation of this embodiment configured as described above will be described. According to this embodiment, since the gradient magnetic field generating coil 7a and the transmission / reception coil 7Ab in the imaging unit 7 are fixed in fixed positions, the gradient magnetic field generation coil 7a and the transmission / reception coil 7b are set in a positional relationship so as not to be coupled. And it can be held. According to the present embodiment, since the photographing unit 7 is configured to be attachable to and detachable from the top plate 6, as shown in FIG. 2, a large-diameter inclination with respect to the cavities of the uniform static magnetic field generating coils 1A and 1B. A large-diameter imaging unit having a magnetic field generation coil 7Aa, a transmission / reception coil 7Ab, and a mounting base 7Ac can be arranged, and a small-diameter imaging unit having a small-diameter gradient magnetic field generation coil 7Ba, transmission / reception coil 7Bb, and mounting base 7Bc is arranged. Will be able to. A large diameter object can be used for a large object, and a small diameter object can be used for a small object. That is, a gradient magnetic field generating coil 7Aa having a large diameter and a gradient magnetic field generating coil 7Ba having a small diameter are used according to the size of the photographing region, and the photographing region and the gradient magnetic field generating coil 7A are used.
Since the distance to a can be made sufficiently small, a strong magnetic field can be applied to the imaging region close to the gradient magnetic field generating coil 7a. This is because even if it is smaller than the conventional one, it is possible to apply a strong magnetic field, realize short-time shooting, and generate a small electromagnetic force.
The fixing mechanism can be simplified and noise can be reduced. According to the present embodiment, it is possible to employ the small-diameter gradient magnetic field generating coil 7a that can apply a strong magnetic field to a desired imaging region, so that the number of coil windings can be reduced, which can reduce the self-inductance. This realizes weight reduction. Another embodiment of the present invention is shown in FIG. The structure shown in FIG. 3 has a groove 8 in the cavity of the uniform static magnetic field generating coils 1A and 1B of the main body 4a.
A spacer 8 having a formed therein is provided, and a groove 8 is formed in the spacer 8.
The configuration is such that the imaging unit 10 of the gradient magnetic field generating coil 9a with the protrusion 9a 'and the transmitting / receiving coil 9b corresponding to a can be inserted. According to this configuration, the spacers 8 having different diameters
By changing the combination of the imaging unit 9 and the imaging unit 9, it becomes possible to apply the gradient magnetic field generating coil 9a and the transmitting / receiving coil 9b of various sizes described above. The present invention is not limited to the above-described embodiments. For example, in addition to the configuration in which the gradient magnetic field generating coil and the transmission / reception coil are fixed together as an imaging unit, the transmission / reception coil may be separated from the imaging unit to be portable As a uniform static magnetic field generating device, of course, a device using four magnets other than the structure using two electromagnet coils shown in FIG. The present invention can be applied and variously modified without departing from the scope of the present invention. [Advantages of the Invention] As described above, in the magnetic resonance imaging apparatus according to the present invention, the means for generating the gradient magnetic field includes the first gradient magnetic field generating means and the first gradient magnetic field generating means for providing the gradient magnetic field of a predetermined magnitude. And a second gradient magnetic field generating means for providing a small gradient magnetic field region and a transmission / reception coil integrally provided, the first gradient magnetic field generating means and the second gradient magnetic field generating according to an imaging region of the subject. Since the means is selectively used, the first gradient magnetic field generating means is used to image a large imaging area, and the transmitting and receiving coils are integrally provided to image a small imaging area. Second
By using the gradient magnetic field generating means, a strong gradient magnetic field can be applied to the imaged regions of different sizes. Moreover, the second gradient magnetic field generating means and the transmission / reception coil can be integrated with each other to maintain a positional relationship in which coupling between the two does not occur. Therefore, there is no adverse effect such as uneven sensitivity due to coupling. Further, under the application of the gradient magnetic field by the second gradient magnetic field generating means, the integrated transmission / reception coil enables effective signal collection from a local site. These advantages greatly contribute to high precision diagnosis. Therefore, it is possible to provide a magnetic resonance imaging apparatus capable of fulfilling requirements such as short-time imaging.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing the configuration of an embodiment of a magnetic resonance imaging apparatus according to the present invention, FIG. 2 is a view showing the operation of the same embodiment, and FIG. FIG. 4 is a diagram showing the configuration of the embodiment of FIG. 4, and FIG. 4 is a diagram showing the configuration of the conventional example. 1A, 1B ... uniform static magnetic field generating coil, 2 ... gradient magnetic field generating coil, 7 ... imaging unit, 7a ... gradient magnetic field generating coil, 7b ... transmitting and receiving coil, 7c ... mounting base.

Claims (1)

(57) [Claims] By causing a magnetic resonance phenomenon in the subject by applying a static magnetic field, a gradient magnetic field and an excitation magnetic field to the subject, detecting a magnetic resonance signal induced from the subject, by performing an image reconstruction process, In the magnetic resonance imaging apparatus for obtaining image information of a subject, the means for generating the gradient magnetic field is a first gradient magnetic field generating means for providing a gradient magnetic field of a predetermined magnitude and a gradient magnetic field smaller than the first gradient magnetic field generating means. A second gradient magnetic field generating means that provides a region and is integrally provided with a transmission / reception coil, and selectively selects the first gradient magnetic field generating means and the second gradient magnetic field generating means according to an imaging region of the subject. A magnetic resonance imaging apparatus characterized by being used for.