JPH0722573B2 - Magnetic resonance imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention is based on the density distribution of each spin of a specific atom in a specific cross section of an object using a magnetic resonance (MR) phenomenon. Information is called so-called computer tomography (CT: c
CT image (computed tomogra) by omputed tomography
The present invention relates to a magnetic resonance imaging apparatus for imaging as m), and particularly to a magnetic resonance imaging apparatus having an improved probe head configuration.

(Prior Art) For example, in a magnetic resonance imaging apparatus for biomedical diagnosis, in order to obtain a tomographic image of a specific portion of a subject, as shown in FIG. A static magnetic field H ₀ is applied, and a pair of gradient magnetic field coils 1
A linear magnetic field gradient Gx is added to the static magnetic field H ₀ by A and 1B.
Specific nuclei resonate at an angular frequency ω ₀ represented by the following equation with respect to the static magnetic field H ₀ .

ω ₀ = γH ₀ (1) In this equation (1), γ is a gyromagnetic ratio and is unique to the type of atomic nucleus. Therefore, a rotating magnetic field H ₁ having an angular frequency ω ₀ that causes only specific 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 case, the linear magnetic field gradient Gx is selected and set in the Z-axis direction in the illustrated xy direction.
The magnetic resonance phenomenon occurs only in a specific slice portion S (a portion on the plane but actually having a certain thickness) that selectively acts on only the planar portion and obtains a tomographic image. This magnetic resonance phenomenon is generated by a free induction decay signal (FID: free in-flight) via a pair of receiving coils 3A and 3B provided in the probe head.
duction decacy, hereinafter referred to as "FID signal"), and a Fourier transform of this FID signal gives a single spectrum at the rotation frequency of a specific nuclear spin.

To obtain a tomographic image as a CT image, x of the slice portion S
-Projections for multiple directions in the y plane are required. Therefore, the slice part after causing the magnetic resonance phenomenon is excited to S, a 10 x the field H ₀ as shown in FIG 'axis direction (x
When a linear magnetic field gradient Gxy having a linear gradient is applied to a coordinate meter rotated by an angle θ from the axis by a coil or the like (not shown), the equal magnetic field line E in the slice portion S of the subject P becomes a straight line. The rotation frequency of the specific nuclear spin on E is expressed by the above equation (1).

Here, for convenience of explanation, it is considered that the equal magnetic field lines E are E _{1 to} En, and the magnetic fields on the respective equal magnetic field lines E _{1 to} En generate signals D _{1 to} Dn, which are a kind of FID signals. The amplitudes of the signals D _{1 to} Dn are proportional to the specific nuclear spin densities on the isomagnetic field lines E _{1 to} En penetrating the slice portion S, respectively. However,
The FID signal actually observed is a combined FID signal in which all the signals D _{1 to} Dn are added. Then, the composite FID signal is subjected to Fourier transform to obtain projection information (one-dimensional image) PD of the slice portion S on the x ′ axis. This x'axis is rotated in the xy plane (the rotation of this magnetic field gradient Gxy is performed by, for example, two pairs of gradient magnetic field coils in the magnetic field gradients Gx, Gy in the x, y directions.
A magnetic field gradient Gxy is created as a synthetic magnetic field of
By changing the composition ratio of Gy), projection information in each direction in the xy plane can be obtained in the same manner as above, and a CT image can be composed based on these information. .

In this type of magnetic resonance imaging apparatus, the probe head is a transmitter (transmitter coil 2) that generates an exciting rotating magnetic field.
A, 2B) and a receiver (reception coil 3A, 3B) that detects a magnetic resonance signal based on the FID signal. The coil form has a relationship between the static magnetic field and the exciting rotating magnetic field (the magnetic resonance phenomenon There is a surface coil, a saddle coil and a solenoid coil. In addition, it is needless to say that the excitation rotating magnetic field generated in the specific portion of the subject is efficiently generated, and the FID signal detected from the specific portion of the subject is weak, so that it must be efficiently detected.

FIG. 11 (a) shows a situation in which a high frequency power source 5 is connected to the transmitting surface coil 4A and an exciting rotating magnetic field is applied to the subject P close to the transmitting surface coil 4A. Figure 12 (a)
Shows a situation in which the amplifier 6 is connected to the receiving surface coil 4B and the FID signal is detected from the subject P close to the receiving surface coil 4B.

(Problems to be Solved by the Invention) However, the transmission magnetic field distribution in the conventional transmission / reception system shown in FIGS. 11 (a) and 12 (a) is as shown in FIG. 11 (b), and the sensitivity is The distribution is as shown in FIG. 12 (b). That is, in the transmission magnetic field distribution, the same magnetic field distribution is symmetrically generated on the subject side and the non-subject side with the transmitting surface coil A as a boundary. Here, the magnetic field distribution on the subject side is the magnetic field distribution required region, which is the diagnostic region of interest, but the magnetic field distribution on the anti-subject side is the magnetic field generation unnecessary region, which is the diagnostic daily region of interest, and is Powering a car is both pointless and inefficient. Similarly, the same sensitivity distribution is generated symmetrically on the subject side and the non-subject side with the receiving surface coil 4B as a boundary. Here, the sensitivity distribution on the non-subject side is an unnecessary area, and supplying power to this unnecessary area is meaningless and inefficient.

Therefore, an object of the present invention is to provide a magnetic resonance imaging apparatus capable of generating at least one of a magnetic field distribution and a sensitivity distribution only in a necessary area and improving efficiency.

(Means for Solving Problems) The present invention is characterized by taking the following means in order to solve the above problems and achieve the object. That is,
One or more emphasizing means including at least a coil that realizes at least one of emphasizing an excitation rotating magnetic field with respect to the object-specific part and emphasizing a magnetic resonance signal from the object-specific part are provided at the front and rear stages of the probe head, respectively. It is characterized by having been placed.

(Operation) By taking such a means, the emphasizing means can direct at least one of the excitation rotation magnetic field and the magnetic resonance signal, and thus the excitation rotation magnetic field for the specific part of the subject. And at least one of the enhancement of the magnetic resonance signal from the specific part of the subject are realized, and the efficiency of transmission / reception is improved.

(Embodiment) FIG. 1 shows a first embodiment of the present invention, which is an example applied to a surface coil as a probe head and a transmitter coil.

FIG. 1 (a) is a front view of the transmitting surface coil 4A, in which a director 7 made of a closed loop coil made of copper wire or the like is arranged between the transmitting surface coil 4A which is the previous stage and the object P. A reflector 8 composed of a closed loop coil made of copper wire or the like is arranged at the subsequent stage of the coil 4A, and a high frequency power source 5 is provided to the transmitting surface coil 4A.
Are connected and the excitation rotating magnetic field is applied to the subject P close to the transmitting surface coil 4A.

The transmission magnetic field distribution in the transmission system of the first embodiment as described above is as shown in FIG. 1 (b). That is, the transmission magnetic field distribution is generated on the subject side and the non-subject side with the transmitting surface coil 4A as a boundary, but due to the action of the director 7 and the reflector 8 arranged in the front and rear stages of the transmitting surface coil 4A. The directivity is generated in the high-frequency magnetic field distribution, so that it is emphasized on the front side and weakened on the contrary on the rear side. Here, the magnetic field distribution on the subject side is the region of interest for diagnosis, and the non-subject side is the region not necessary for diagnosis, so that power is not substantially supplied to the unnecessary region and efficient transmission characteristics are obtained. It is a thing.

The shapes and sizes of the director 7 and the reflector 8 and the distance between the surface coil 4A for transmission, the director 7 and the reflector 8 and the like are related to the object P and the relationship of the transmission output. Can be selected as appropriate.

FIG. 2 shows a second embodiment of the present invention, which is an example applied to a surface coil as a probe head and a receiver coil.

FIG. 2 (a) shows that a wave director 9 made of a closed loop coil made of copper wire or the like is arranged between the receiving surface coil 4B, which is the preceding stage of the receiving surface coil 4B, and the subject P, and the receiving surface is provided. A reflector 10 formed of a closed loop coil made of a copper wire or the like is arranged at the subsequent stage of the coil 4B, an amplifier 6 is connected to the receiving surface coil 4B, and a magnetic resonance signal is transmitted to a subject P generated by a transmitter (not shown). The FID signal based on it is detected by the receiving surface coil 4B.

The receiving sensitivity distribution in the receiving system of the second embodiment as described above is as shown in FIG. 2 (b). That is, the receiving sensitivity distribution is generated on the subject side and the non-subject side with the receiving surface coil 4B as a boundary, but due to the action of the director 9 and the reflector 10 arranged in the front and rear stages of the receiving surface coil 4B. , The reception sensitivity distribution has directivity, and is therefore emphasized on the front side and weakened on the other side. Here, since the reception sensitivity distribution on the subject side is the region of interest for diagnosis and the non-subject side is the region not necessary for diagnosis, the FID signal from the required region is efficiently received.

The shapes and sizes (coil length) of the director 9 and the reflector 10 and the distance between the receiving surface coil 4B, the director 9 and the reflector 10 and the like are related to the subject P and reception. It can be appropriately selected depending on the output relationship.

The present invention may be configured and practiced as in the third to fifth embodiments shown in FIGS. The third to fifth embodiments are examples in which the probe head is applied to a transmitter.

In the third embodiment shown in FIG. 3, an LC resonance circuit is constructed by providing variable capacitors 11 and 12 for tuning to the director 7 and the reflector 8, respectively.

The fourth embodiment shown in FIG. 4 is a saddle type coil as a transmitter.
As a configuration in which the closed-loop coil directors 14A and 14B are arranged between the subject P and the saddle-shaped coil 13 and the closed-loop coil reflectors 15A and 15B are arranged outside the saddle-shaped coil 13 There is.

The fifth embodiment shown in FIG. 5 is the same as the fourth embodiment, except that
The directors 14A and 14B are connected to form the director 14, and the reflectors 15A and 15B
Is connected to form a reflector 15.

The present invention may be configured and carried out as in the sixth to eighth embodiments shown in FIGS. 6 to 8. The sixth to eighth embodiments are examples in which the probe head is applied to a receiver.

In the sixth embodiment shown in FIG. 6, an LC resonance circuit is constructed by providing variable capacitance capacitors 16 and 17 for tuning to the director 9 and the reflector 10, respectively.

A seventh embodiment shown in FIG. 7 is a saddle type coil as a transmitter.
18, the closed-loop coil directors 19A and 19B are arranged between the subject P and the saddle-shaped coil 18, and the closed-loop coil reflectors 20A and 20B are arranged outside the saddle-shaped coil 18. There is.

The eighth embodiment shown in FIG. 8 is the same as the seventh embodiment.
The directors 19A and 19B are connected to form the director 19, and the reflectors 20A and 20B
Are connected to form a reflector 20.

The present invention is not limited to the above embodiment, and may be applied to a probe head in which the transmitter and the receiver are combined, and according to the drawings, the coil length l of the director, the probe head and the reflector is shown. ₁ , l ₂ , l ₃ satisfy l ₁ <l ₂ <l ₃ but are not limited to this. Besides this, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described in detail above, the magnetic resonance imaging apparatus according to the present invention realizes at least one of the enhancement of the excitation rotating magnetic field with respect to the subject specific region and the enhancement of the magnetic resonance signal from the subject specific region. In this configuration, at least one emphasizing means including at least a coil is arranged in each of the front stage and the rear stage of the probe head.

According to such a configuration, the enhancing means can direct at least one of the excitation rotating magnetic field and the magnetic resonance signal, and thus enhances the excitation rotating magnetic field with respect to the subject specific portion and the subject. At least one of the enhancement of the magnetic resonance signal from the specific portion is realized, and the magnetic resonance imaging apparatus in which the efficiency of transmission / reception is improved can be provided.

[Brief description of drawings]

FIGS. 1 to 8 are configuration diagrams showing first to eighth embodiments of the present invention, FIGS. 9 and 10 are diagrams for explaining the principle of magnetic resonance imaging, FIGS. 11 and 12 Each of the drawings is a configuration diagram showing a conventional example. 4A, 13 …… Transmitter, 4A, 18 …… Receiver, 7,9,14A, 14B, 14,1
9A, 19B, 19 …… Director, 8,10,15A, 15B, 15,20A, 20B, 20…
… Reflectors, 11,12,16,17 …… Variable capacitors.

Claims (4)

[Claims] 1. A subject is placed in a uniform static magnetic field, a gradient magnetic field is superimposed on the uniform static magnetic field, and an exciting rotating magnetic field is applied by a probe head to cause a magnetic resonance phenomenon in the subject. In the magnetic resonance imaging apparatus for detecting the induced magnetic resonance signal by the probe head and performing the image reconstruction processing to obtain the image information of the subject, the enhancement of the excitation rotating magnetic field with respect to the subject specific portion and the subject A magnetic resonance imaging apparatus, wherein one or more emphasizing means including at least a coil for realizing at least one of the enhancement of a magnetic resonance signal from a specific portion is arranged in each of a front stage and a rear stage of the probe head. 2. The magnetic resonance imaging apparatus according to claim 1, wherein the enhancing means is a closed loop coil. 3. The probe head according to claim 1, wherein the probe head is configured so as to serve both as a transmitter for generating an exciting rotating magnetic field and a receiver for detecting a magnetic resonance signal. Magnetic resonance imaging device. 4. The magnetic head according to claim 1, wherein the probe head has a transmitter for generating an exciting rotating magnetic field and a receiver for detecting a magnetic resonance signal, which are separately configured. Resonance imaging device.