JP2001087243A - Magnetic resonance diagnostic system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide a wide dynamic range and a wide frequency band characteristic with simple constitution in a receiver of a magnetic resonance diagnostic system. SOLUTION: In a magnetic resonance diagnostic system for generating living body information on the basis of a received signal by receiving a signal radiated from an examinee P by a receiver 6 via an RF coil 3 after a magnetic resonance phenomenon, the receiver 6 has a first receiving system 34 being connected to the RF coil 3 and having an amplifying and AD converting function and a second receiving system 35 being arranged in parallel to the first receiving system 34 to the RF coil 3 and having an amplifying and AD converting function different in an amplifying rate from the first receiving system 34 to correct a signal part of a period of causing an overflow in the first receiving system 34 on the basis of a signal part of the period outputted from the second receiving system 35.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance diagnostic apparatus for imaging in-vivo information of a subject using a magnetic resonance phenomenon.

[0002]

2. Description of the Related Art As is well known, magnetic resonance phenomena occur when a group of nuclei having a unique magnetic moment is placed in a uniform static magnetic field, and a high frequency magnetic field rotating at a specific frequency. This is the phenomenon of absorbing energy resonantly.

In order to use such a phenomenon to image chemical and structural microscopic information of a substance in a living body, it is necessary to identify the source of a magnetic resonance signal. As a general method, a two-dimensional Fourier transform method (2DFT method) is generally used.

In the 2DFT method, first, by applying an RF pulse together with a slice selection gradient magnetic field, only the magnetization of a specific nucleus existing in a specific slice is selectively excited, and the transverse magnetization component is reduced. generate. This RF
When a gradient magnetic field for phase encoding is applied for a certain time after the pulse, the magnetization rotates at a frequency corresponding to the magnetic field at that location, but this frequency difference is preserved as a phase difference even after the magnetic field is turned off. .

[0005] Thereafter, the magnetic resonance signal guided to the RF coil while the frequency encoding gradient magnetic field is applied is first amplified by an amplifier in a receiver, converted into a digital signal by an A / D converter, and output. I do. The magnetization is rotated by the frequency encoding gradient magnetic field pulse at a frequency corresponding to the magnetic field at that location, but this difference in frequency is directly reflected in the frequency of the magnetic resonance signal.

Such a procedure is repeated while changing the phase encoding little by little, and a large number of magnetic resonance signals are collected. For each of the collected magnetic resonance signals f (t),
First, a projection F (ωx) on the X axis can be obtained by performing a Fourier transform on the frequency encoding axis.
By performing a Fourier transform on these F (ωx) with respect to the phase encode axis, a final spatial distribution F (ωx, ωy) of chemical and structural microscopic information of the substance in the living body can be obtained.

By the way, the amplification factor of the amplifier of the receiver is set to an appropriate value such that the maximum value of the amplified signal does not exceed the dynamic range of the A / D converter and that the dynamic range can be utilized as much as possible. It needs to be adjusted in advance. However, in recent 3D photographing and the like, an extremely high signal level is required, and accordingly, an A / D converter having a wide dynamic range is required. Further, in magnetic resonance diagnosis, not only a wide dynamic range but also a wide frequency band is required, and an A / D converter that guarantees both of them has a complicated circuit configuration and is very expensive.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a receiver for a magnetic resonance diagnostic apparatus, which has a wide dynamic range and a wide frequency band characteristic with a simple configuration and at low cost.

[0009]

(1) According to the present invention, a signal emitted from a subject after a magnetic resonance phenomenon is received by a receiver via an RF coil, and biological information is generated based on the received signal. In the magnetic resonance diagnostic apparatus, the receiver includes:
A first receiving system connected to the RF coil and having an amplification and A / D conversion function, and arranged in parallel with the first receiving system with respect to the RF coil; At least one second receiving system having amplification and A / D conversion functions having different rates and a signal portion in a period where an overflow has occurred in the first receiving system are transmitted to the second receiving system.
And a compensating means for compensating based on a signal portion during the synchronization output from the receiving system. (2) The present invention is the apparatus according to (1), wherein the amplification factor of the first reception system is higher than the amplification factor of the second reception system. (3) The present invention is the device of (1), wherein the signal portion S1 in a period during which an overflow occurs in the first receiving system.
S1 = (A1 / A2) · S2 + (− C2 + C1), where S2 is a signal portion during the synchronization output from the second receiving system, A1 is an amplification factor of the first receiving system, A2
Is the amplification factor of the second reception system, C1 is the DC offset of the first reception system, and C2 is the D offset of the second reception system.
C offset. (4) The present invention is the device according to (3), wherein a reference signal generator for generating a reference signal for the first reception system and the second reception system, and the reference signal generator corresponding to the reference signal. Based on the output of the first reception system and the output of the second reception system, the amplification factor A1 of the first reception system, the amplification factor A2 of the second reception system, and the amplification factor A2 of the first reception system And a calculator for calculating a DC offset C1 and a DC offset C2 of the second reception system. (5) The present invention is the device according to (1), wherein the correction means generates a correction signal based on a signal output from the second reception system, A selector for selectively outputting a signal output from a receiving system and the correction signal, and comparing a level of the signal output from the first receiving system with an overflow level, and selecting the selector according to a result of the comparison. And a control circuit for controlling (6) The present invention is the device according to (1), further comprising a distributor for distributing an output signal of the RF coil to the first receiving system and the second receiving system. I do. (7) The present invention relates to a magnetic resonance diagnostic apparatus that receives a signal emitted from a subject after a magnetic resonance phenomenon via an RF coil by a receiver and generates biological information based on the received signal. Comprises: a plurality of amplifiers having different amplification factors arranged in parallel with the RF coil; a plurality of A / D converters individually arranged with respect to the plurality of amplifiers; One specific A / D in the vessel
A correction circuit is provided which compensates for a signal portion during a period in which an overflow occurs in the converter based on a signal portion during a period output from another A / D converter. (8) The present invention relates to a magnetic resonance diagnostic apparatus which receives a signal emitted from a subject after a magnetic resonance phenomenon via an RF coil by a receiver and generates biological information based on the received signal. Represents an amplifier connected to the RF coil, an A / D converter connected to the output of the amplifier, and a signal portion of a period during which the A / D converter overflows, is a signal before and after the period. And a calculator for estimating based on the portion. (9) The present invention is the apparatus according to (8), wherein the computer estimates a signal portion in a period in which an overflow has occurred in the A / D converter from a signal portion before and after the period by spline interpolation. It is characterized by the following. (10) The present invention is the apparatus according to (8), wherein the computer calculates a signal portion in a period in which an overflow has occurred in the A / D converter from a gradient of a signal portion before and after the period in a quadratic curve. It is characterized by estimation by approximation.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic resonance diagnostic apparatus according to the present invention will be described below in detail with reference to the drawings. (First Embodiment) FIG. 1 shows a configuration of a magnetic resonance diagnostic apparatus according to the present embodiment. The magnet device 14 includes a static magnetic field coil unit 1, a gradient magnetic field coil unit 2, and an RF coil 3. The static magnetic field coil unit 1 receives power supply from the static magnetic field control device 4 and has a substantially cylindrical imaging region 1 into which the subject P placed on the bed 13 at the time of imaging is inserted.
A static magnetic field is generated in 6. Gradient magnetic field coil unit 2
Receives power from the gradient magnetic field power supplies 7, 8, and 9 to generate three types of gradient magnetic fields having different magnetic field gradient directions in the imaging region 16;
There are three types of coils so that they can be generated individually in the inside.

If the RF coil 3 is a transmission / reception type, it is connected to a transmitter 5 that generates a high-frequency current at the time of transmission, and amplifies a magnetic resonance signal induced at the RF coil 3 at the time of reception. It is connected to a receiver 6 that converts the signal. Of course, the RF coil 3 is not limited to the transmission / reception type. The transmission coil fixedly connected to the transmitter 5 and the reception coil fixedly connected to the receiver 6 are separately provided. May be provided. The RF coil 3 is connected to a tuning device 15 having a variable capacitor constituting a C-type resonance circuit together with the RF coil 3 so that the resonance frequency can be changed according to the target nucleus at the time of transmission and reception. It has become.

The sequence controller 10 controls the transmitter 5, the receiver 6, the gradient power supplies 7, 8, 9 and the tuning device 15 to execute a desired pulse sequence. The computer system 11 generates image data by, for example, the 2DFT method based on the digital signal output from the receiver 6. The display unit 12 displays an image according to the image data generated by the computer system 11.

FIG. 2 shows the configuration of the receiver 6 shown in FIG. The receiver 6 includes a first receiving system 3 including an amplifier 22 and a general and relatively inexpensive A / D converter 23.
4, an amplifier 24 having an amplification factor lower than that of the amplifier 22.
And a second receiving system 35 including an A / D converter 25 equivalent to the A / D converter 23. The same signal is supplied from the signal distributor 27 to these two reception systems.

To the signal distributor 27, a magnetic resonance signal from the subject P guided to the RF coil 3 and a reference signal from a reference signal generator 26 are selectively supplied by a signal switch 28. It has become. The signal switch 28
In accordance with a control signal from the computer system 11, the reference signal generator 26 is connected to the signal distributor 27 when measuring the reception characteristics (amplification rate, DC offset) of each of the first reception system 34 and the second reception system 35. On the other hand, during imaging for actually collecting a magnetic resonance signal from the subject P, RF
The coil 3 is connected to the signal distributor 27.

When measuring the reception characteristics, the characteristic calculator 29 calculates
Based on the output of the A / D converter 23 of the first receiving system 34, the receiving characteristics of the first receiving system 34 (amplification factor; A1, DC
Offset; C1), and based on the output of the A / D converter 25 of the second receiving system 35, the second receiving system 35
(A2, DC offset; C2) of the first and second receiving systems 34 and 35 calculated here are stored in the characteristic memory 30.
Is held.

FIG. 2 shows a supplementary diagram of the reception characteristic calculation.
An example of a waveform of an output signal of the first receiving system 34 or the second receiving system 35 is shown. The amplification factor (A1) of the first receiving system 34 is calculated as a difference value between the maximum value and the minimum value of the output signal of the first receiving system 34, and the DC offset (C1) is It is calculated as the sum of the maximum value and the minimum value of the output signal. Second receiving system 35
Similarly, the amplification factor (A2) of the second receiving system 35 is
It is calculated as the difference between the maximum value and the minimum value of the output signal of the second receiving system 35, and the DC offset (C2) is
It is calculated as the sum of the maximum value and the minimum value of the output signal of the second reception system 35.

At the time of photographing, the correction signal generator 31 includes first and second receiving systems 35 held in the characteristic memory 30.
The output signal S2 of the second receiving system 35 is corrected based on the reception characteristic data of the second receiving system 35, and the corrected signal S2 'is changed to S2' = (A1 / A2) .S2 + (-C2 + C1) where S2 is the second reception A signal output from the system 35,
A1 is calculated by the amplification factor of the first reception system 34, A2 is calculated by the amplification factor of the second reception system 35, C1 is the DC offset of the first reception system 34, and C2 is the DC offset of the second reception system 35. And output. This correction signal S2 '
As can be seen from the above equation, the output signal S1 of the first receiving system 34 whose amplification factor is set high is converted from the output signal S2 of the second receiving system 35 whose amplification factor is set low to the second receiving system 35. Are estimated based on the difference between the reception characteristics of the first reception system and the like.

At the time of photographing, the correction signal S2 'calculated by the correction signal generator 31 and the output signal S
1 is selectively output to the computer system 11 through the selector 32. The control of the selector 32 is performed by a selection control circuit 33.

The selection control circuit 33 includes a first reception system 34
, And compares the signal level with an overflow level (threshold) that is equal to or slightly lower than the upper limit of the dynamic range of the A / D converter 23 of the first receiving system 34, When the signal level of the output signal S1 has reached the overflow level, the first
The selector 32 is controlled so as to output the correction signal S2 'calculated by the correction signal generator 31 instead of the output signal S1 of the reception system. Of course, when the signal level of the output signal S1 has not reached the overflow level, the output signal S1 of the first reception system 34 is output from the selector 32.

Under the control of the selection control circuit 33, as shown in FIG.
During a period in which no overflow occurs in the / D converter 23, the output signal S of the first reception system 34 is output from the receiver.
1 is output, and during the period (t1 to t2) in which the overflow occurs, the output signal S of the first reception system 34 is output.
In place of 1, the correction signal S2 'for the period (t1 to t2) in FIG. 4B is output.

As described above, according to the present embodiment,
Using an inexpensive A / D converter having a relatively narrow dynamic range, a signal having a wide dynamic range can be handled without deterioration.

(Second Embodiment) FIG. 5 shows a configuration of a receiver of a magnetic resonance diagnostic apparatus according to a second embodiment. The overall configuration of the magnetic resonance diagnosis apparatus according to the present embodiment is the same as that in FIG. This receiver is equipped with only one receiving system consisting of an amplifier 42 and a general and relatively inexpensive A / D converter 43. A / D converter 43
Is temporarily stored in the memory 44. Calculator 4
In 5, in the same manner as in the first embodiment, the period in which the A / D converter 43 has caused an overflow is specified by comparing the signal level with the overflow level using the signal held in the memory 44. The signal part of the overflow period is interpolated from the signal parts before and after the same period.

As this interpolation method, a spline interpolation method is used. This spline interpolation method has various specific calculation methods due to differences in calculation efficiency and the like. For example, as shown in FIG. Signal parts 51,5
The second and third order differential coefficients are filled so as to maintain continuity.

Further, as another interpolation method, the following is preferable.
As shown in FIG. 5B, the signal portion (the broken line portion) of the overflow period is estimated by the quadratic curve approximation from the rising gradient G1 and the falling gradient of the signal portions 51 and 52 before and after the overflow period.

As described above, according to the present embodiment, a signal having a wide dynamic range can be handled without deterioration using an inexpensive A / D converter having a relatively narrow dynamic range.

The present invention can of course be carried out in various modifications without being limited to the above embodiment.

[0027]

The present invention has first and second receiving systems having different amplification factors. When an overflow occurs in the first receiving system, the signal portion in that period is transmitted to the second receiving system. Since the output signal of the system is used to compensate, even if the dynamic range of the A / D converter alone is narrow, a signal having a wide dynamic range can be handled without deterioration.

Also, according to the present invention, when an overflow occurs in the A / D converter, the signal portion in that period is estimated based on the signal portions before and after the same period.
Even if the dynamic range of the / D converter alone is narrow, a signal having a wide dynamic range can be handled without deterioration.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a magnetic resonance diagnostic apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of the receiver in FIG. 1;

FIG. 3 is a supplementary diagram of reception characteristics calculated by the characteristic calculator of FIG. 2;

4A is a diagram showing an output of the selector in FIG. 2; FIG.
3 is a diagram showing an output of the correction signal generator of FIG.

FIG. 5 is a configuration diagram of a receiver of the magnetic resonance diagnosis apparatus according to the second embodiment of the present invention.

6A is a diagram showing a correction signal estimated by the computer of FIG. 5 according to the first method, and FIG. 6B is a diagram showing a correction signal estimated by the computer of FIG. 5 according to the second method;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Static magnetic field coil unit, 2 ... Gradient magnetic field coil unit, 3 ... RF coil unit, 4 ... Static magnetic field control device, 5 ... Transmitter, 6 ... Receiver, 7 ... X-axis gradient magnetic field power supply, 8 ... Y-axis tilt Magnetic field power supply, 9: Z-axis gradient magnetic field power supply, 10: Sequence controller, 11: Computer system, 12: Display unit, 13: Bed, 14: Magnet device, 15: Tuning device, 22: Amplifier, 23: A / D conversion 24, an amplifier, 25, an A / D converter, 26, a reference signal generator, 27, a signal distributor, 28, a signal switcher, 29, a characteristic calculator, 30, a characteristic memory, 31, a correction signal generator, 32: selector, 33: selection control circuit.

Continued on the front page (72) Inventor Naoki Sasaki 1385-1, Shimoishigami, Otawara-shi, Tochigi F-term in Toshiba Nasu Plant (reference) 4C096 AB42 AB50 AD12 CD01 DA02 DA04 DA05 DA14 DA30

Claims (10)

[Claims] 1. A magnetic resonance diagnostic apparatus which receives a signal emitted from a subject after a magnetic resonance phenomenon via an RF coil at a receiver and generates biological information based on the received signal, wherein the receiver comprises: Amplified and connected to the RF coil
A first receiving system having a / D conversion function, and an amplification and A / D conversion function which are arranged in parallel with the first receiving system with respect to the RF coil and have different amplification factors from the first receiving system. At least one second receiving system having: and correcting means for compensating for a signal portion in a period in which an overflow has occurred in the first receiving system based on a signal portion during the synchronization output from the second receiving system. And a magnetic resonance diagnostic apparatus comprising: 2. The magnetic resonance diagnostic apparatus according to claim 1, wherein an amplification factor of the first reception system is higher than an amplification factor of the second reception system. 3. A signal portion S1 in a period during which an overflow occurs in the first receiving system is: S1 = (A1 / A2) · S2 + (− C2 + C1) where S2 is output from the second receiving system. A1 is an amplification factor of the first reception system, A2 is an amplification factor of the second reception system, C1 is a DC offset of the first reception system, and C2 is a second reception system. The magnetic resonance diagnostic apparatus according to claim 1, wherein the DC offset is calculated by: 4. A reference signal generator for generating a reference signal for the first receiving system and the second receiving system, an output of the first receiving system corresponding to the reference signal, and a second
The amplification factor A1 of the first reception system, the amplification factor A2 of the second reception system, the DC offset C1 of the first reception system, and the amplification factor A1 of the second reception system 4. The magnetic resonance diagnostic apparatus according to claim 3, further comprising a calculator for calculating the DC offset C2. 5. The correction means includes: a correction signal generator that generates a correction signal based on a signal output from the second reception system, a signal output from the first reception system, and the correction signal. And a selector for selectively outputting
And a control circuit for comparing the level of the signal output from the receiving system and the overflow level, and controlling the selector according to the comparison result.
The magnetic resonance diagnostic apparatus according to claim 1. 6. The magnetic resonance diagnostic apparatus according to claim 1, further comprising a distributor that distributes an output signal of the RF coil to the first receiving system and the second receiving system. 7. A magnetic resonance diagnostic apparatus which receives a signal emitted from a subject after a magnetic resonance phenomenon via an RF coil by a receiver and generates biological information based on the received signal, wherein the receiver comprises: A plurality of amplifiers having different amplification factors arranged in parallel with the RF coil, a plurality of A / D converters individually arranged for the plurality of amplifiers, and a plurality of A / D converters And a correction circuit for compensating for a signal portion during a period in which an overflow occurs in one of the specified A / D converters, based on a signal portion during a synchronization output from another A / D converter. Magnetic resonance diagnostic apparatus. 8. A magnetic resonance diagnostic apparatus which receives a signal emitted from a subject after a magnetic resonance phenomenon via an RF coil at a receiver and generates biological information based on the received signal, wherein the receiver comprises: An amplifier connected to the RF coil;
An A / D converter connected to the output of the amplifier;
A magnetic resonance diagnostic apparatus comprising: a computer for estimating a signal portion in a period in which an overflow occurs in the / D converter based on signal portions before and after the period. 9. The magnetic device according to claim 8, wherein the computer estimates a signal portion in a period where the overflow has occurred in the A / D converter from a signal portion before and after the period by spline interpolation. Resonance diagnostic device. 10. The computer according to claim 1, wherein the computer estimates a signal portion in a period in which the A / D converter overflows from a slope of a signal portion before and after the period by quadratic curve approximation. 9. The magnetic resonance diagnostic apparatus according to 8.