JP3139039B2 - NMR equipment receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an NM for performing imaging or spectroscopy using nuclear magnetic resonance.
Regarding the R device, it is particularly necessary to receive the NMR signal and perform detection and A /
The present invention relates to improvement of a D-conversion receiving apparatus.

[0002]

2. Description of the Related Art A receiving device of a conventional NMR apparatus is usually
It is configured as shown in FIG. An NMR signal from a subject is captured by a receiving coil 1, first amplified by a preamplifier 2, and then sent to a distributor 5 via a variable attenuator 3 and a filter 4. The distributor 5 forms a complex detection circuit together with the balance modulators 6 and 7 and the phase shifter 9. That is, the input of the test wave is distributed by the distributor 5 and sent to the two balanced modulators 6 and 7. The balanced modulators 6 and 7 are provided with a phase shifter 9 for each of the reference signals having a phase difference of 90 degrees. A reference signal from source 8 is being sent. The balanced modulator 6 outputs a real component representing a phase difference from the reference signal, and the balanced modulator 7 outputs an imaginary component having a phase difference of 90 degrees with respect to the real component. These real and imaginary detection outputs are sampled and held by sample and hold circuits 11 and 12, respectively, and then A /
The data is converted into digital data by the D conversion circuits 13 and 14, respectively.

[0003] From the real component and the imaginary component of the detection output from such a complex detection circuit, the phase relationship of the received signal can be grasped as shown in FIG. FIG. 2 shows the magnitude and phase of the received NMR signal on a phase plane based on the phase of the reference signal.

[0004]

However, in the conventional receiving apparatus as shown in FIG. 1, A / D conversion circuits 13 and 14 are used.
There is a problem that the dynamic range of is not effectively used, and quantization noise increases. That is, the received NMR signal has a phase angle as shown by a solid line or a dotted line in FIG. 2 according to the phase relationship with the reference signal. If the phase of the received NMR signal is the angle shown by the solid line in FIG. However, when the phase angle is as shown by the dotted line, the amplitude of the real component is small and the amplitude of the imaginary component is large. Then, the levels of the input signals of the A / D conversion circuits 13 and 14 are greatly different between the real side and the imaginary side, and the smaller amplitude does not effectively use the dynamic range of the A / D conversion circuit.
The proportion occupied by the quantization error increases.

In view of the above, the present invention makes it possible to effectively use the dynamic range of the A / D conversion circuit even when there is a difference between the real component and the imaginary component of the detection output from the complex detection circuit. It is an object of the present invention to provide an NMR apparatus receiving apparatus improved so that data with a small error in a received NMR signal can be obtained.

[0006]

Means for Solving the Problems In order to achieve the above object, a receiver for an NMR apparatus according to the present invention comprises:
A received signal is input to a complex detection circuit as a detection input, and a real component and an imaginary component of a detection output from the complex detection circuit are respectively amplified by an amplifier and then A / D converted by two A / D conversion circuits. Each of the above-mentioned amplifiers is a variable amplification type amplifier, the amplification of which is independently adjusted so as to match the dynamic range of each A / D conversion circuit, and the amplification of the complex detection circuit is performed. A switch is provided for switching the detected wave input from the received signal to the reference signal, and each A / A when the detected wave input of the complex detection circuit is switched from the received signal to the reference signal by the switch.
According to the D conversion circuit output data, each A /
It is characterized in that the output data of the D conversion circuit is corrected. In order to amplify the real component and the imaginary component of the detection output from the complex detection circuit input to each A / D conversion circuit with different amplification factors, the amplification factors are adjusted to the actual real / imaginary components. The adjustment makes it possible to effectively use the dynamic range of each A / D conversion circuit and reduce quantization errors. On the other hand, if the amplification degree of the real and imaginary components is changed as described above, the phase cannot be represented by the data from each A / D conversion circuit. By giving the signal to the circuit, the signal of the reference level can be obtained as real or imaginary. The signals are amplified by amplifiers having different amplification degrees, and then A / D converted to obtain data relating to the amplification degree. , The original amplitude of the real component and the imaginary component can be reproduced, and the original phase relationship can be prevented from being lost.

[0007]

An embodiment of the present invention will be described below in detail with reference to the drawings. In FIG. 3, a receiving coil 1, a preamplifier 2, a variable attenuator 3, a filter 4
1 is the same as that of FIG. 1 except that the output of the filter 4 is input to the distributor 5 via the switch 21.
Also, the complex detection circuit including the distributor 5, the balance modulators 6, 7 and the phase shifter 9, the reference signal source 8, the sample and hold circuits 11, 12, the A / D conversion circuits 13, 14 are the same as those in FIG. is there. Here, the variable amplifier 2 whose amplification degree can be independently varied between the real component of the detection output from the balanced modulator 6 and the imaginary component of the detection output from the balanced modulator 7.
After being amplified by 2 and 23, respectively, they are sent to the sample and hold circuits 11 and 12.

For example, it is assumed that the amplitudes of the real component and the imaginary component of the detection output from the balanced modulators 6 and 7 when the NMR signal is received differ greatly as shown in FIG. In such a case, the amplitudes of both the A / D converters 13, 1
Variable amplifier 2 to match the dynamic range of
The amplification degrees of 2, 23 are independently adjusted. Then
The received NMR signals entering the A / D converters 13 and 14 have the same amplitude as shown in FIG.

After the adjustment of the amplification degrees of the variable amplifiers 22 and 23 is completed, the switch 21 is switched to the reference signal source 8 side, and only when the NMR signal is received, the switch 21 is switched.
Are switched to the filter 4 side, and when the reception of the NMR signal is completed, the data is returned to the reference signal source 8 side to collect the data of the NMR signal. When the switch 21 is switched to the reference signal source 8 side, a reference signal is given as a detection input of the complex detection circuit, and the reference signal is detected by the reference signal itself. And the imaginary component are DC components at the same level. The DC components of the same level are amplified by the variable amplifiers 22 and 23 at different amplification degrees, and the A / D converters 13 and 14
Appears on the input side of.

That is, as shown in FIG. 5, the input sides of the A / D converters 13 and 14 are arranged before and after the received NMR signal.
DC components of the voltages Vr and Vi appear. This DC voltage V
Since r and Vi represent the amplification degrees of the variable amplifiers 22 and 23, these digital data are taken into a host computer (not shown) connected after the A / D converters 13 and 14. Then, by correcting the digital data of the received NMR signal taken into the host computer by the data representing the degree of amplification, the original amplitudes of the real and imaginary components (FIG. 4) can be reproduced. After such correction, the host computer performs a two-dimensional Fourier transform for image reconstruction.

[0011]

As described above, according to the embodiment,
According to the receiver of the NMR apparatus of the present invention, the reception NMR
Regardless of the phase relationship between the signal and the reference signal, the real component and the imaginary component of the complex detection output are always converted to the maximum dynamics of the A / D conversion circuit while maintaining their original amplitudes. A / D conversion can be performed in a range, the amount of quantization error included in collected data during A / D conversion can be minimized, and the accuracy of measurement data can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a conventional example.

FIG. 2 is a diagram showing a received NMR signal in a phase plane.

FIG. 3 is a block diagram of one embodiment of the present invention.

FIG. 4 is a waveform chart of each part in FIG. 3;

FIG. 5 is a waveform chart of each part in FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Receiving coil 2 Preamplifier 3 Variable attenuator 4 Filter 5 Distributor 6, 7 Balanced modulator 8 Reference signal source 9 Phase shifter 11, 12 Sample hold circuit 13, 14 A / D conversion circuit 21 Switching device 22, 23 Variable amplifier

Claims (1)

(57) [Claims] 1. A receiving circuit, a complex detecting circuit that receives a received signal as a detection input and performs complex detection using a reference signal, amplifies a real component and an imaginary component of a detection output from the detecting circuit, and Two amplification-variable amplifiers whose amplifications are independently adjusted so that the amplitudes of the real component and the imaginary component of the detection output at the time of signal input are adapted to a dynamic range of an A / D conversion circuit described later; Two A / D conversion circuits for A / D converting the outputs of these amplifiers; a switch for switching the input of the complex detection circuit from a received signal to a reference signal; Means for correcting output data of each A / D conversion circuit at the time of inputting a received signal by output data of the D conversion circuit.