JPS60376A - Rf coil device of nuclear magnetic resonance imaging device - Google Patents

Abstract

PURPOSE:To use a small-sized detecting coil and to improve the catching ratio of signals and the SN ratio by synthesizing outputs from amny detecting coils arranged close to the periphery of a subject to receive a magnetic response from the subject. CONSTITUTION:A uniform static magnetic field H0 and an RF magnetic field Hrf are applied to a slice 41 to be tested in the vertical direction and a radial direction around the axis of the H0 respectively. Two pairs of exciting coils 51a, 51b and 52a, 52b are arranged rectangularly and properly used to excite the magnetic fields. On the other hand, outputs from respective coils 53 arranged close to the periphery of the subject 41 are inputted to a weighing factor unit 55 through a receiving amplifier 54. When the respective outputs are to be selectively used, weights to be applied to the respective outputs are varied by the factor unit 55, and when all the outputs are to be used uniformly, respective weights are uniformed. All outputs from the weighing factor unit 55 are uniformly added to an additional amplifier 56 and outputted as one signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to nuclear magnetic resonance (Nuclear Magnetic Resonance).
An NMR signal (FID: Free I
RF that detects
Related to coil devices.

2. Description of the Related Art NMR imaging apparatuses that use NMR techniques to obtain tomographic images of a subject focusing on specific atomic nuclei have been known. First, an outline of the principle of this NMR imaging apparatus will be briefly explained.

When a biaxial static field 1o is applied to a specific substance such as hydrogen, its atomic nucleus precesses around the Z-axis at an angular velocity ω as shown in the following equation.

ω-γHa (Larmor angular velocity) However, γ: gyromagnetic ratio When an electromagnetic wave (usually a radial wave: RF signal) with a frequency corresponding to the angular velocity ω is applied to a system in this state, resonance occurs, and the atomic nucleus is determined by the spin quantum number. Transition to the higher energy level in energy units. There are several types of atomic nuclei with nuclear spin angular momentum), and each nucleus has a different gyromagnetic ratio γ, so the resonant frequencies are different, so it is possible to extract only the resonance of a specific atomic nucleus. . Furthermore, by measuring the strength of the resonance, it is possible to determine the amount of atomic nuclei present. Also, after resonance, the atomic nucleus excited to a higher unit returns to a lower unit during a time determined by a time constant called relaxation time. Among these relaxation times, the spin-interstitial relaxation time called T1 is a time constant that depends on the way each compound binds, and it is known that the value differs greatly between normal tissues and malignant tumors. ing.

Therefore, by using this NMR, and using the same principle as X-ray CT, we excite protons in a virtual cross section of the subject, and the NMR signals corresponding to each projection are observed in many directions of the subject. By measuring the NMR signal intensity at each position using a reconstruction method, it is possible to obtain a tomographic image of the subject focusing on a specific atomic nucleus.

FIG. 1 is a waveform diagram illustrating an example of an inspection method in such a conventional device. First, place the first
As shown in Figure (B), the RF pulse (9) has a narrow frequency spectrum (f) as shown in Figure 1.
06 pulse) is applied. In this case, Larmor angular velocity If
If the plane of only the plane where ω-γ (Ho→-△GZ) is excited, and the magnetization M is expressed on a rotating coordinate system rotating at θ] as shown in Figure 2 (a), then y ' The direction is changed by 90 degrees in the axial direction. Next, as shown in Figure 1 (c) and (d), an X gradient magnetic field Qx and a y gradient magnetic field Gy are applied, thereby creating a two-dimensional gradient magnetic field and generating an NMR signal as shown in (e). Detected. Here, as shown in Figure 2, the magnetization M is x I , due to the inhomogeneity of the magnetic field.
As it gradually disperses in the direction of the arrow within the y1 plane, the NMR signal eventually decreases and disappears after one hour as shown in FIG. 1 (e). If the NMR signal obtained in this manner is subjected to 7-lier transformation, it becomes a projection in the direction perpendicular to the gradient magnetic field synthesized by the × gradient magnetic field GX and the V gradient magnetic field GV.

Hereafter, in the same way, the predetermined time τ′ is set.
Repeat the following sequence. In each sequence,
Change GX, G, and V little by little. Thereby, NMR signals corresponding to each projection can be tracked in many directions of the subject.

The Li storage coil portion in this case is constructed as shown in FIG. That is, a cylinder 1 in which the subject is placed.
A static magnetic field coil 2. which provides a uniform static magnetic field (in the -1 direction) around the . A gradient It field coil consisting of a tc second gradient Iit & field coil, an X gradient magnetic field coil, and an An excitation coil 4 that provides NM as an electromagnetic field, NM from the subject
Detection coils 5 for detecting the R signal are installed respectively.

By the way, in such a conventional device, the static magnetic field 1-
Even if the accuracy of the perturbation components such as the uniformity of 10 and the gradient magnetic field is good, there is a problem that the RF coil of the detection coil 5 is too sensitive. , 3~5M1-1z (800G
Even if it resonates at ~1.2KG), it will resonate at about 0.7~1.
It has a diameter of 0+11φ and is wound vi times, and the wire material A is also formed using a thick copper band or a wire rod shaped like a vibrator. Roughly speaking, the energy density of a coil when magnetic energy enters the space surrounding it is small. Therefore, the exchange of energy between the spins becomes rough in the T1 culm of the Okawa method, and the detection sensitivity becomes low. However, with the Okawa method, the Qo can be increased accordingly, so the decrease in detection sensitivity can actually be suppressed to a small amount. However, large-sized detection coils are very inconvenient and cumbersome to manufacture and install.

The present invention has been made in view of these points, and its purpose is to provide an NMR imaging system that avoids large-sized detection coils, has good signal capture efficiency, and can also improve S/N ratio. An object of the present invention is to provide an RF coil device for a device.

The present invention achieves this object by arranging a large number of detection coils close to the circumference of the subject, connecting a receiving amplifier to each of them, and uniformly distributing the output of the receiving amplifier. The present invention is characterized in that it is configured to receive the magnetic response of the subject while combining it into a single signal using only a part of the magnetic response as needed.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 4 is a schematic diagram showing an embodiment of the present invention.

In the figure, the perturbation coil 1o is omitted, but 1o is horizontal and the RFWl field Hrf is vertical with respect to the sample slice 41 of the subject (the thickness of which is determined by selective excitation). In such a state, a large number of small detection coils 42 are arranged as shown in the figure, and their outputs are taken out through the receiving amplifiers 43, and the outputs are all used uniformly or selectively. It has become. Each detection coil 42 is placed near the subject slice 41 and is coupled to a shallow portion of the slice 41, so each detection coil 42 can be excited even if a large excitation coil 44 is used for specific excitation. It is possible to use this detection coil 42.

FIG. 5 is a diagram of another embodiment. In this case, t-1o is applied to the subject slice 41 in a vertical direction, and Hrf is applied in a radial direction centered on the axis of Ho. [100 signals can be observed from all directions perpendicular to Ha, so excitation can be received from any direction. However, excitation with only 90' pulse creates a blind spot, so excitation with 90' pulse and 180' pulse
If the ° pulse is used in combination as appropriate, or if imaging is performed only at 90°, two orthogonal sets of excitation-only coils 51a, 51b and 528, 52b are arranged and used as appropriate. In the case of this figure, the individual detection
Because it is strongly coupled to the shallow part of the slice directly below it, it is suitable for performing precise imaging of a specific region. Incidentally, the output of each detection coil 53 may be used uniformly or selectively at any number of points after passing through the receiving amplifier 54. When used selectively, Weighting 1) Weighting is performed by varying the weight given to each output by the coefficient unit 55. When using all of them uniformly, it is sufficient to make each weight of the weighting coefficient unit 55 equal.The outputs of the weighting coefficient unit 55 are all uniformly added together by an adding amplifier and made into one signal. Output.

Adding in this manner creates the need to ensure proper phase matching. And once proper phase matching is ensured,
This leads to an improvement in the noise figure of the overall detection.The fact that the size (volume) of the sensitive area is significantly smaller (approximately 1/10 or less) compared to the conventional one also improves the S/N. It can be seen that this leads to an improvement in

The method of using the FID signal thus obtained and the method of imaging reconstruction are the same as in the conventional method.

In addition, although each detection coil is shown in a fixed arrangement in FIG. 5, as shown in FIG. 6, each detection coil can be moved as a probe coil in the radial direction shown using a plunger 1761 such as an air cylinder. It is also possible to freely configure the structure so that each detection coil is pressed against the surface of the subject.

With this configuration, it is possible to image the area just below the opposing surface without being subject to the restrictions of the thickness and shape of the object. In addition, the probe can also be placed on the object mounting table 62. A coil may be arranged.

As explained above, according to the present invention, by using a large number of detection coils, not only the manufacturing and installation of the coils are easy, but also the signal capture efficiency is improved, the S/N is
The NMR imaging limb device RF coil device can also be improved.

[Brief explanation of the drawing]

Fig. 1 is a waveform diagram for explaining an example of an inspection method in conventional NMR eyebrow placement, Fig. 2 is a diagram for explaining the direction of magnetization M by the method of Fig. 1, and Fig. 3 is a diagram for explaining the direction of magnetization M in the method of Fig. FIG. 4 is a block diagram showing one embodiment of the present invention, and FIGS. 5 and 6 are block diagrams showing other embodiments of the present invention. 1...Cylinder 2...Static magnetic field coil 3...Gradient (
A-field coil 4... Excitation coil 5.42.53... Detection coil Patent applicant: Yokogawa Medical Systems Co., Ltd. Agent
Person Patent Attorney Shinsuke Kozawa Figure 3 Figure 4 Figure 5

Claims (2)

[Claims] (1) A large number of detection coils are placed close to the periphery of the subject, a reception amplifier is connected to each of them, and the output of the reception amplifier is applied uniformly to all or only a part as necessary.
1. An RF coil device in a nuclear magnetic resonance imaging apparatus, characterized in that the RF coil device is configured to receive a magnetic response of a subject while combining it into two signals. (2) The RF coil device in the nuclear magnetic resonance imaging apparatus according to claim 1, wherein the detection coil is also capable of excitation of the subject. (3) The detection coil is configured to be movable and can be placed in contact with the surface of the subject or moved at a close distance. RF in nuclear magnetic resonance imaging equipment
coil device.