JPS6244235A - Magnetic resonance imaging apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to magnetic resonance (MR: ma() netiCre
sonance (hereinafter referred to as rMRJ) phenomenon is used to obtain information based on the density distribution of specific atomic nuclear spins in a specific cross section of the object using so-called computer tomography (CT).
C by computed tomoc+raphy)
The present invention relates to a magnetic resonance imaging apparatus called an MRI apparatus that images as a T image (COMPLIted tomogram).

[Technical Background of the Invention] For example, in a diagnostic MRI apparatus, in order to obtain a tomographic image at a specific position of a subject, a highly uniform scan is performed on the subject P along the Z-axis direction as shown in FIG. A static magnetic field Ha is applied, and a linear magnetic field gradient Gz is added to the static magnetic field Ha by a pair of gradient magnetic field coils 1A and 'IB. For a static magnetic field Ha, a specific atomic nucleus has each frequency ω expressed by the following equation.
Resonates at 0.

ωo=THo...(1)
In this equation (1), T is the gyromagnetic ratio, which is unique to the type of atomic nucleus. Therefore, a rotating magnetic field H1 having an angular frequency ωO that causes only specific atomic nuclei to resonate is applied to the subject P via a pair of transmitting coils 2A and 2B provided in the probe head.

In this way, the linear magnetic field gradient Gz selectively acts only on the illustrated x-y plane portion selectively set in the Z-axis direction, and a specific slice portion S (a portion on a plane) from which a tomographic image is obtained. In reality, the MR phenomenon occurs only with a certain thickness.

This MR phenomenon is caused by free induction attenuation (FI
D: free 1induction decay
) signal (hereinafter referred to as "rFID signal"), and by Fourier transforming this signal, a single spectrum can be obtained for the rotational frequency of a specific nuclear spin. CTf the cut JfN image! ! In order to obtain this, projection images of the slice portion S in multiple directions within the X-y plane are required. Therefore, after exciting the slice portion S to cause the MR phenomenon, the magnetic field HO is applied to X′ as shown in FIG.
When a linear magnetic field gradient GXV having a linear gradient in the axial direction (coordinate system rotated by an angle θ from the The line E is a straight line, and the rotational frequency of a specific atomic nuclear spin on this isomagnetic field line E is given by the above equation (1). Here, for convenience of explanation, the isomagnetic field lines E are referred to as E1 to En, and it is assumed that the magnetic fields on these isomagnetic field lines E1 to En generate signals D1 to Dn, which are a type of FID signal, respectively. The amplitudes of the signals D1 to Dn are respectively the slice portion S.
It is proportional to the spin density of a specific atomic nucleus on the isomagnetic field lines E1 to En passing through the . However, the FI actually observed
The D signal is a composite FI that adds all signals @D1 to Dn.
It becomes D signal. Therefore, by Fourier transforming this composite FID signal, projection information (one-dimensional image) PD of the slice portion S onto the X' axis is obtained. This X-axis is rotated in the x-y plane (the rotation of this magnetic field gradient GXV is, for example, 2
Create a magnetic field gradient Gxy as a composite magnetic field of magnetic field gradients GX and G\ in the X and y directions by a pair of gradient magnetic field coils,
By changing the composite ratio of the magnetic field gradients GX and Gy), projection information in each direction within the x-y plane is obtained in the same manner as above, and a CT image is created based on this information. Can be synthesized.

[Problems with Background Art] By the way, in this type of MR imaging device, since the MR multiplied signal detected by the probe head is very weak, this signal is generally amplified through a preamplifier and then subjected to arithmetic processing. The probe head 1 is of a saddle coil type or a solenoid type, and is equipped with a preamplifier. Therefore, the signal cable and the power cable for supplying power to the preamplifier are pulled out from the probe head. Although the S/N ratio can be improved by bringing the probe head closer to the subject, the presence of the preamplifier and cable causes an inconvenience in that the patient feels uncomfortable.

[Object of the Invention] The present invention has been made in view of the above circumstances, and its purpose is to increase the MR signal height S from a specific part of the subject without causing discomfort to the subject (patient). The object of the present invention is to provide a magnetic resonance imaging apparatus that can receive data at a /N ratio, is easy to position, and is effective in imaging that emphasizes only a specific part of a subject.

[Summary of the Invention] The outline of the present invention for achieving the above object is to place a subject in a uniform static magnetic field generated by a static magnetic field generating coil, and superimpose a gradient magnetic field on this uniform static Wi field. , and applying an excitation rotating magnetic field to cause a magnetic resonance phenomenon in the subject, detecting the induced magnetic resonance signal with a probe head, and performing image reconstruction processing to obtain image information of the subject. In a magnetic resonance imaging apparatus, a magnetic resonance signal enhancement means that includes at least a coil and that enhances a magnetic resonance signal from a specific region of a subject is provided on a propagation path of a magnetic resonance signal and before the probe head. It is characterized by being placed in

[Embodiments of the invention] Hereinafter, the present invention will be specifically explained with reference to Examples.

FIG. 1 is an explanatory diagram showing the relationship between a probe head and magnetic resonance signal enhancement means in a magnetic resonance imaging apparatus according to an embodiment of the present invention. FIG. 4 shows a probe head, which receives the MR multiplied signal from the subject P, similar to the conventional apparatus. A resonant circuit is formed by this probe head 4 and a capacitor 5 connected to the probe head 4, and is amplified by an MR multiplier signal preamplifier 6 which has achieved resonance. The amplified MR multiplied signal is subjected to image reconstruction processing. The image reconstruction process is the same as that of the conventional apparatus, so a description thereof will be omitted.

A magnetic resonance signal enhancing means 7 is arranged between the subject P and the probe head 4. The magnetic resonance signal enhancing means 7 is for enhancing the MR multiplied signal from a specific part of the subject P, and is composed of a coil 7a and a capacitor 7b.

Figure 2 shows the equivalent circuit of Figure 1, with coil 7
a and capacitor 7b to LC#,! A circuit is formed.

With this configuration, the MR multiplied signal from a specific region of the subject P, that is, near the magnetic resonance signal enhancement means 7, is first received by the magnetic resonance signal enhancement means 7, and thereby an induced current 11 is applied to the LC co-imaging circuit. flows. This induced current 1
An induced current 12 flows through the probe head 4 due to the magnetic flux generated by the magnetic flux 1 and the MR multiplied signal from the subject P. Therefore, the MR multiplied signal and induced current 11 from a specific part of the subject P
The magnetic flux generated by the probe head 4
will be received by. Therefore, the S/N ratio of the MR multiplied signal from the vicinity of the magnetic resonance signal enhancement means 7 of the subject P is improved, and it becomes possible to reconstruct a high-quality lateral MR image.

Next, the results of an experiment conducted by the inventor of the present application will be explained with reference to FIG.

FIG. 3 is a characteristic diagram of the MR signal reception intensity with respect to the depth from the surface of the subject, 8 is a case where a surface coil is used (preamplifier is used), and 9 is a case where magnetic resonance signal enhancement means 7 is arranged. In case 1Q, the magnetic resonance enhancement means 7 is not used and only the probe head 4 is used. When magnetic resonance enhancement means 7 is not used (curve 10)
Compared to , when magnetic resonance enhancement means 7 is used (curve 9)
The MR signal reception strength is higher in this case. In the case of using a surface coil (curve 8), the MR signal reception strength increases considerably, but the presence of the cable gives the patient a sense of discomfort. In this respect, since the magnetic resonance signal enhancement means 7 does not use a preamplifier, there is no need for a signal cable or a power cable, and even if it is worn quite close to the patient, the patient will not feel uncomfortable.

In this embodiment, since the magnetic resonance signal enhancement means 7 is disposed between the subject P and the probe head 4, the apparatus of this embodiment can be used without causing discomfort to the subject (patient). The MR multiplied signal from the specific part of the subject can be received with high sensitivity, that is, with a high S/N ratio, and the image quality of the specific part of the subject is improved in the MR image reconstructed based on the received MR multiplied signal. Also, unlike when using surface coils,
Since the entire image including the vicinity of the magnetic resonance signal enhancement means 7 can be reconstructed at the same time, positioning becomes very easy. Furthermore, M from any part of the subject P
Whether or not to enhance the R-fold signal is determined by the size, shape, etc. of the coil 7a constituting the magnetic resonance signal enhancement means 7, and therefore it is very easy to change the high-sensitivity ocular region.

Although one embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the gist of the present invention.

In the above embodiment, the magnetic resonance signal emphasizing means 7 is constructed from the coil 7a and the capacitor 7b, but the magnetic resonance signal emphasizing means 7 can also be constructed from only the coil 7a without using the capacitor 7b. . This is because even if a closed loop is formed only by the coil 7a, an induced current flows in the coil 7a. Therefore, even if the magnetic resonance signal emphasizing means 7 is composed of only a closed loop coil, the same effects as in the above embodiment can be obtained.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to receive signals at an S/N ratio twice as high as the MR signal from a specific part of the subject without causing discomfort to the subject (patient). , it is possible to provide a magnetic resonance imaging apparatus that is easy to position and is effective in imaging that emphasizes only a specific part of a subject.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the relationship between a probe head and magnetic resonance signal enhancement means in a magnetic resonance imaging apparatus according to an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram of FIG. 1, and FIG.
The figure is a characteristic diagram of the MR signal reception intensity with respect to the depth from the surface of the subject, Figure 4 is an explanatory diagram showing the principle configuration of a magnetic resonance imaging device, and Figure 5 is a diagram of the principle of obtaining projection information by magnetic resonance phenomena. be. 4...probe head,

Claims (3)

[Claims] (1) A subject is placed in a uniform static magnetic field generated by a static magnetic field generating coil, a gradient magnetic field is superimposed on this uniform static magnetic field, and an excitation rotating magnetic field is applied to cause magnetic resonance in the subject. A magnetic resonance imaging apparatus that generates a phenomenon, detects the induced magnetic resonance signal with a probe head, and obtains image information of the subject by performing image reconstruction processing, comprising at least a coil, and A magnetic resonance imaging apparatus, characterized in that a magnetic resonance signal enhancing means for enhancing magnetic resonance signals from a specific region of a subject is disposed on a propagation path of the magnetic resonance signals and upstream of the probe head. (2) The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic resonance signal enhancement means is an LC resonance circuit consisting of a coil and a capacitor. (3) The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic resonance signal enhancement means is a closed loop coil.