JPS63292949A - Rf coil for nuclear magnetic resonance imaging apparatus - Google Patents

Abstract

PURPOSE:To reduce the load of a protection circuit and to certainly protect a preamplifier, by providing receiving points at the feed position of a loop element and at a position excepting the almost 180 deg.-position starting from said position. CONSTITUTION:A transmitting port is provided at the position of a condenser 5a and a receiving port is provided at the position of a condenser 5b and the condenser 5b is present at the +90 deg.-position starting from the position (a) of the condenser 5a. The space between the transmitting port and the output terminal of a power amplifier 6 is n.lambda/2 (n:1, 2, 3...) and the space between the receiving port and the input terminal of a preamplifier 8 is (2n-1).lambda/4. When a high frequency signal is applied to an RF coil 1 from the power amplifier 6 at the time of transmission, a cross diode 7 is turned ON the drive a coil 1. At this time, there is almost no attenuation due to the diode 7 and a standing wave is generated in loop elements 2, 3 and the signals at + or -90 deg.-positions from the transmitting port become zero.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an RF coil that performs transmission and reception in a nuclear magnetic resonance imaging apparatus (hereinafter referred to as MRf).

(Prior Art) MRI, which uses nuclear magnetic resonance (hereinafter referred to as NMR) development to obtain a tomographic image of a subject focusing on specific atomic nuclei, has been known for a long time. Also, the RF coil used in this MRl is also known. This is known. Fig. 5 shows an example thereof.

1 is an r(F coil, which is usually called a bird gauge type RF coil. There are bypass types and low-pass types of this RF coil, but the bypass type is shown here. 2 and Reference numeral 3 denotes a conductive loop element having a substantially circular shape, the surfaces of which are arranged parallel to each other, and form an opening for accommodating the subject. Reference numeral 4 denotes a conductive segment along the periphery of each of the loop elements 2 and 3. The two are connected at a separate point. 5 is a capacitor, which is inserted in series between the connection points of loop elements 2 and 3 with segment 4. 6 is a power amplifier, and its output end is connected to a cross diode 7. via RF
Connected to the feeding point (transmission port) of coil 1. The transmitting boat is composed of both ends of a capacitor 5a (one of the capacitors 5), and also serves as a power receiving point (receiving boat) for the RF coil 1. Reference numeral 8 designates a low-noise preamplifier, the input end of which is connected to a receiving port, and protection circuits 9 and 10 are arranged between them. The wavelength λ of the signal flowing through the RF coil 1 is set to be an integral multiple of λ/2 between the output end of the power amplifier 6 and the transmitting port, and between the receiving port and the input end of the preamplifier 8, respectively.

In the above configuration, during transmission, a high frequency signal of several kilowatts amplified by the power amplifier 6 is applied to the transmission port of the loop element 2 (both ends of the capacitor 5a). At this time, the cross diode 7 is turned on and there is almost no attenuation of the high frequency signal. Further, the input side of the preamplifier 8 is protected by, for example, duplicated protection circuits 9 and 10. on the other hand,
During reception (the supply of high-frequency signals is suspended), an NMR signal of several μW is received by the R[coil 1]. NM at the receiving port of loop element 2 (both ends of capacitor 5a)
Since the cross diode 7 is not turned on by the R signal, the NMR signal is guided to the preamplifier 8 and taken out to an external circuit.

(Problems to be Solved by the Invention) As described above, since the transmitting boat and the receiving boat are shared, it is necessary to strengthen the protection circuit (that is, to make it redundant here) to protect the preamplifier. However,
This protixcon circuit also operates in a direction that results in loss of the received signal. There is a problem in that this tendency increases when a complicated configuration such as duplexing is used. That is, even if a low-noise preamplifier (one with good NF) is used, there is a problem in that the NF<noise index of system interruption is deteriorated.

The present invention has been made in view of the above points, and its purpose is to provide an MRr RF coil that can reduce the burden on the protection circuit (simplify the protection circuit) and that can reliably protect the preamplifier. It is about realization.

<Means for Solving the Problems> The present invention, which solves the above-mentioned problems, includes a pair of conductive loop elements arranged at a distance from each other and substantially orthogonal to a common vertical axis;
a plurality of conductive segments disposed substantially parallel to the longitudinal axis, the segments electrically connecting the loop elements to each other at spaced apart points along the periphery of each of the loop elements; A capacitor is arranged in series between the loop element and the connection point with the segment, and in an RF coil with both ends of one capacitor as the feeding point, the feeding point position of the loop element and approximately 180° from this position as the starting point. The feature is that the power receiving point is provided at a position other than the position.

(Function) In the RF coil of the present invention, the power feeding position of the loop element (the transmitting boat) and the receiving boat located at a position approximately 180° from the position as a starting point are connected to the transmitting signal. Maximum potential does not appear. Therefore, the influence of the transmitted signal on the preamplifier side is reduced.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram of an RF coil showing an embodiment of the present invention. In the figure, the same parts as in FIG. 5 are given the same reference numerals, and the explanation thereof will be omitted. Reference numeral 11 denotes a bird gauge type coil, and its basic configuration is the same as that shown in Fig. 5, but its unique feature is that the transmitting port is provided at the position of the capacitor 5a, and the receiving port is provided at the position of the capacitor 5b. . Capacitors 5a and 5b are both one of the capacitors 5 arranged on loop element 2, and capacitor 5b is located at +900 position from position a of capacitor 5a. The distance between the transmitting boat (position a) and the output end of the power amplifier 6 is n·λ/2 (however, n: 1, 2, 3...), and the distance between the receiving boat (position b) and the input of the preamplifier 8 The relationship between the ends is (2n-1>.lambda./4).Only the protection circuit 9 is provided on the input side of the preamplifier 8.

Note that C and d in the figure indicate positions of +180' and -4-270' from position a.

In the above configuration, at the time of transmission, from the power amplifier 6 to R
When a high frequency signal of several kilowatts is applied to the F coil 1, the cross diode 7 is turned on and the RF coil 1 is driven.

At this time, there is almost no attenuation due to the cross diode 7, and standing waves as shown in FIG. 2 are generated in the loop elements 2 and 3. Figure 2 (marks @a, b, ... are the positions a, b in Figure 1)
,...), it is clear that ±90"(90' or 1.t
The signal at the position 270'') is zero. That is, the receiving boat (position b) is not affected by the transmitted signal.

In reality, the signal at the receiving boat is not zero, but several +
Although a signal that is attenuated by dBilji appears, the load on the protection circuit is reduced by the amount of attenuation.

Therefore, the preamplifier 8 can be sufficiently protected by the one-stage protection circuit 9. NMR when receiving
Since the signal ranges from several μVp-p to several tens of meters VP-P, the cross diode 7 is turned off and the received signal is guided to the preamplifier 8.

FIG. 3 is a schematic diagram of a so-called quadrature reception system, which is another embodiment of the present invention. In FIG. 3, position 1ia indicates the position of the transmitting boat, and e and f indicate the positions of the two receiving boats. Receiving boats e and f are ±45″ from position a
, and an angular difference of 90' is formed between e and f. In this configuration, the standing waves in the loop element 2 during transmission are as shown in FIG. Each reference numeral is assigned corresponding to each position in FIG. As is clear from Fig. 4, the signals appearing on receiving boats e and f have a magnitude of 1/(1) of the transmitting signal. Kill by reducing the burden.

Note that the present invention is applicable to all types of RF coils that generate standing waves, and is not limited to the above embodiments. Further, the position of the receiving boat may be any position other than the position of the transmitting boat and a position approximately 180@ from this position as a starting point.

(Effects of the Invention) As described above, according to the present invention, the transmitted signal is reliably attenuated at the position of the receiving boat, so that the burden on the protection circuit can be reduced.

Therefore, the protection circuit can be simplified, and
Loss of received signals can be reduced.

That is, the NF of the entire system can be improved.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing one embodiment of the present invention, and Fig. 2 is a schematic diagram showing an embodiment of the present invention.
FIG. 3 is a schematic diagram showing another embodiment of the present invention; FIG. 4 is a diagram showing standing waves in the conductive loop element of FIG. 3; FIG. The figure is a schematic diagram showing a conventional example. 1... RF coil 2, 3... Conductive loop element 4... Conductive segment 5.5a, 5C... Capacitor 6... Power amplifier 7... Cross diode 8
...Preamplifier 9.10...BuO chikujoun circuit patent applicant Yokogawa Medical Systems Co., Ltd. Figure 1 Figure 2 Figure 3 Solution Figure 4 Figure 5 Figure 2 No j

Claims (3)

[Claims] (1) A pair of conductive loop elements arranged substantially perpendicularly to a common longitudinal axis and spaced apart from each other, and a plurality of conductive segments arranged substantially parallel to the longitudinal axis, the segments comprising the loop The loop elements are electrically connected to each other at spaced apart points along the periphery of each element, and a capacitor is disposed in the loop element in series between the connection points with the segment, and both ends of one capacitor are connected to each other. An RF coil for a nuclear magnetic resonance imaging apparatus, characterized in that, in the RF coil used as a power feeding point, a power receiving point is provided at a position other than the feeding point position of the loop element and a position approximately 180° from the position as a starting point. (2) The nuclear magnetic resonance imaging apparatus according to claim 1, wherein the power receiving point of the loop element is located near a position approximately 90° or 270° from the power feeding position of the loop element. RF coil for (3) Nuclear magnetic resonance according to claim 1, wherein the power receiving point of the loop element performs quadrature reception at both positions approximately ±45° from the power feeding position of the loop element. RF coil for imaging equipment.