JP2001224572A - Transmitting method and apparatus for magnetic resonance signal and magnetic resonance imaging instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a transmitting method and apparatus for magnetic resonance signal which are hardly influenced by noises, and a magnetic resonance imaging instrument equipped with such a transmitting apparatus. SOLUTION: A magnetic resonance signal is encoded in a received position 202, and the encoded signal is transmitted to a data collection part 150.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance signal transmission method and apparatus, and a magnetic resonance imaging apparatus.
The present invention relates to a method and a device for transmitting a magnetic resonance signal from its receiving location to a location for processing it, and to a magnetic resonance imaging device equipped with such a transmitting device.

[0002]

2. Description of the Related Art Magnetic resonance imaging (MRI: Magneti)
c Resonance Imaging) device
An object to be imaged is loaded into an internal space of a magnet system, that is, a space in which a static magnetic field is formed, and a gradient magnetic field and a high-frequency magnetic field are applied to generate a magnetic resonance signal in the object. Based on the received signal, To generate (reconstruct) a tomographic image.

[0003] A magnet system is a scan room provided with shielding against electromagnetic waves and magnetism.
A signal processing device installed in m) for processing the received magnetic resonance signal is installed outside the scan room, and both are connected by a signal cable.

[0004]

The transmission of the received signal from the magnet system to the signal processing device is performed by RF (radii).
The transmission signal is performed as it is, but the transmission signal is a signal having a low level of, for example, about mV, and thus is susceptible to noise.

Therefore, an object of the present invention is to provide a method and apparatus for transmitting a magnetic resonance signal which is less susceptible to noise.
An object of the present invention is to realize a magnetic resonance imaging apparatus including such a transmission device.

[0006]

Means for Solving the Problems (1) According to one aspect of the invention for solving the above-described problems, a magnetic resonance signal is received, and the magnetic resonance signal is encoded at the location where the magnetic resonance signal is received. A magnetic resonance signal transmission method characterized by transmitting a converted signal.

In the invention according to this aspect, since the magnetic resonance signal is encoded at the receiving location and the encoded signal is transmitted, it is possible to perform signal transmission that is less affected by noise.

(2) According to another aspect of the invention for solving the above-mentioned problems, the encoding is an analog-to-digital conversion. .

In the invention according to this aspect, since the magnetic resonance signal is converted from analog to digital at the receiving location and the digital signal is transmitted, signal transmission that is less affected by noise can be performed.

(3) According to another aspect of the present invention, there is provided a magnetic resonance signal transmission method according to (1), wherein the encoding is pulse width modulation.

In the invention according to this aspect, since the magnetic resonance signal is subjected to pulse width modulation at the receiving location and the pulse width signal is transmitted, it is possible to perform signal transmission that is less affected by noise.

(4) The invention according to another aspect for solving the above-mentioned problem is the method of transmitting a magnetic resonance signal according to (1), wherein the encoding is pulse density modulation.

In the invention according to this aspect, since the magnetic resonance signal is subjected to pulse density modulation at the receiving location and the pulse density signal is transmitted, it is possible to perform signal transmission that is less affected by noise.

(5) Another aspect of the invention for solving the above-mentioned problem is the magnetic resonance signal transmission method according to (1), wherein the encoding is frequency modulation.

According to the invention in this respect, the magnetic resonance signal is frequency-modulated at the receiving location and the frequency signal is transmitted, so that signal transmission that is less affected by noise can be performed.

(6) According to another aspect of the present invention, there is provided a receiving means for receiving a magnetic resonance signal, an encoding means for encoding the magnetic resonance signal at the location where the magnetic resonance signal is received, A transmission unit for transmitting the encoded signal.

In the invention according to this aspect, since the magnetic resonance signal is encoded by the encoding means at the receiving location and the encoded signal is transmitted, it is possible to perform signal transmission that is less affected by noise.

(7) According to another aspect of the invention for solving the above-described problem, the encoding is an analog-to-digital conversion. .

In the invention according to this aspect, the magnetic resonance signal is converted from analog to digital at the receiving location and the digital signal is transmitted, so that signal transmission that is less affected by noise can be performed.

(8) According to another aspect of the present invention, there is provided a magnetic resonance signal transmitting apparatus according to (6), wherein the encoding is pulse width modulation.

According to the invention from this viewpoint, the magnetic resonance signal is pulse-width modulated at the receiving location and the pulse-width signal is transmitted, so that signal transmission that is less affected by noise can be performed.

(9) According to another aspect of the present invention, there is provided a magnetic resonance signal transmitting apparatus according to (6), wherein the encoding is pulse density modulation.

In the invention according to this aspect, since the magnetic resonance signal is pulse-density-modulated at the receiving location and the pulse-density signal is transmitted, it is possible to perform signal transmission that is less affected by noise.

(10) According to another aspect of the invention for solving the above-described problem, the encoding is frequency modulation. The magnetic resonance signal transmission device according to (6).

In the invention according to this aspect, the frequency of the magnetic resonance signal is modulated at the receiving location and the frequency signal is transmitted, so that the signal transmission which is less affected by noise can be performed.

(11) According to another aspect of the present invention, there is provided a receiving means for receiving a magnetic resonance signal;
Encoding means for encoding the magnetic resonance signal at the received location; transmission means for transmitting the encoded signal; receiving means for receiving the transmitted signal; and an image based on the received signal. A magnetic resonance imaging apparatus comprising: an image generation unit that generates an image.

In the invention according to this aspect, since the magnetic resonance signal is encoded at the receiving location by the encoding means and the encoded signal is transmitted, it is possible to perform signal transmission which is less affected by noise. A high-quality image can be generated based on such a transmission signal.

(12) According to another aspect of the invention for solving the above-mentioned problem, the encoding is an analog-to-digital conversion. The magnetic resonance imaging apparatus according to (11), wherein

According to the invention from this viewpoint, the magnetic resonance signal is converted from analog to digital at the receiving location and this digital signal is transmitted, so that signal transmission that is not easily affected by noise can be performed. A high-quality image can be generated based on such a transmission signal.

(13) According to another aspect of the invention for solving the above-described problem, the encoding is pulse width modulation, and the magnetic resonance imaging apparatus according to (11) is provided.

In the invention according to this aspect, since the magnetic resonance signal is pulse-width modulated at the receiving location and the pulse width signal is transmitted, it is possible to perform signal transmission that is less affected by noise. A high-quality image can be generated based on such a transmission signal.

(14) According to another aspect of the invention for solving the above-mentioned problem, the encoding is pulse density modulation, wherein the magnetic resonance imaging apparatus is described in (11).

According to the invention in this respect, the magnetic resonance signal is pulse-density-modulated at the receiving location and the pulse-density signal is transmitted, so that signal transmission that is not easily affected by noise can be performed. A high-quality image can be generated based on such a transmission signal.

(15) According to another aspect of the invention for solving the above-described problem, the encoding is frequency modulation, and the encoding is frequency modulation.

In the invention according to this aspect, the frequency of the magnetic resonance signal is modulated at the receiving location and the frequency signal is transmitted, so that the signal transmission that is less affected by noise can be performed. A high-quality image can be generated based on such a transmission signal.

[0036]

Embodiments of the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiment. FIG. 1 shows a block diagram of the magnetic resonance imaging apparatus. This device is an example of an embodiment of the present invention. The configuration of the present apparatus shows an example of an embodiment relating to the apparatus of the present invention. An example of an embodiment of the method of the present invention is shown by the operation of the present apparatus.

As shown in FIG. 1, the present apparatus has a magnet system 100. The magnet system 100 includes a main magnetic field coil unit 102 and a gradient coil unit 106
And an RF (radio frequency) coil unit 108. Each of these coil portions has a substantially cylindrical shape and is arranged coaxially with each other. A generally cylindrical internal space of the magnet system 100 (bore: bor)
e), the subject 300 to be photographed is a cradle
e) loaded and unloaded by transport means (not shown) mounted on the 500;

The main magnetic field coil section 102 forms a static magnetic field in the internal space of the magnet system 100. The direction of the static magnetic field is substantially parallel to the direction of the body axis of the object 300. That is, a so-called horizontal magnetic field is formed. The main magnetic field coil unit 102 is configured using, for example, a superconducting coil. It is needless to say that not only the superconducting coil but also a normal conducting coil may be used.

The gradient coil section 106 generates a gradient magnetic field for giving a gradient to the static magnetic field strength. The generated gradient magnetic fields are a slice gradient magnetic field, a readout gradient magnetic field, and a phase encode gradient magnetic field. The gradient coil unit 1 corresponds to these three types of gradient magnetic fields.
Reference numeral 06 has three gradient coils (not shown).

The RF coil unit 108 controls the object 3 in the static magnetic field space.
A high-frequency magnetic field for exciting spins in the body of 00 is formed. Hereinafter, forming a high-frequency magnetic field is referred to as transmission of an RF excitation signal. The RF coil unit 108 also receives an electromagnetic wave generated by the excited spin, that is, a magnetic resonance signal.

The RF coil unit 108 has a transmitting coil and a receiving coil (not shown). The same coil is used for the transmitting coil and the receiving coil, or a dedicated coil is used for each. RF coil unit 10
The receiving coil in FIG. 8 is an example of an embodiment of the receiving means in the present invention.

The gradient coil unit 106 includes a gradient driving unit 130
Is connected. The gradient driving unit 130 is a gradient coil unit 1
A drive signal is given to 06 to generate a gradient magnetic field. The gradient drive unit 130 has three drive circuits (not shown) corresponding to the three gradient coils in the gradient coil unit 106.

The RF coil section 108 includes an RF drive section 140
Is connected. The RF driving unit 140 is the RF coil unit 1
08, a drive signal is given, an RF excitation signal is transmitted, and the target 3
Excite the spins in the body of 00.

The data collection unit 150 is connected to the RF coil unit 108. The data collection unit 150
The received signal received by the F coil unit 108 is fetched, and the received signal is collected as view data. The capture of the received signal will be described later.

A control unit 160 is connected to the gradient driving unit 130, the RF driving unit 140, and the data collection unit 150. The control unit 160 controls the gradient driving unit 130 to the data collection unit 150 to perform photographing.

The output side of the data collection unit 150 is connected to the data processing unit 170. The data processing unit 170 is configured using, for example, a computer. The data processing unit 170 includes a memory (me
(money). The memory stores a program for the data processing unit 170 and various data. The function of the present apparatus is realized by the data processing unit 170 executing a program stored in the memory.

The data processing unit 170 includes the data collection unit 15
The data taken from 0 is stored in the memory. A data space is formed in the memory. The data space is two-dimensional
It constitutes a Fourier space. The data processing unit 170 performs two-dimensional inverse Fourier transform on the data in the two-dimensional Fourier space to generate an image of the target 300 (reconstruction).
I do. Two-dimensional Fourier space is converted to k-space (k-spac
Also referred to as e).

The data processing section 170 is connected to the control section 160. The data processing unit 170 is at a higher level than the control unit 160 and controls it. A display unit 180 and an operation unit 190 are connected to the data processing unit 170. The display unit 180 displays a graphic display (gr).
aphic display). The operation unit 190 is a pointing device (pointing device).
keyboard with device
d) and the like.

The display section 180 displays the reconstructed image output from the data processing section 170 and various kinds of information. The part consisting of the data processing unit 170 and the display unit 180
5 is an example of an embodiment of an image generating unit according to the present invention. The operation unit 190 is operated by an operator, and inputs various commands and information to the data processing unit 170. The operator operates the present apparatus interactively through the display unit 180 and the operation unit 190.

FIG. 2 is a block diagram showing another type of magnetic resonance imaging apparatus. This device is an example of an embodiment of the present invention. The configuration of the present apparatus shows an example of an embodiment relating to the apparatus of the present invention.

The apparatus shown in FIG. 2 has a magnet system 100 'which is different from the apparatus shown in FIG.
Except for the magnet system 100 ', the configuration is the same as that of the apparatus shown in FIGS. 1 and 2, and the same parts are denoted by the same reference numerals and description thereof will be omitted.

The magnet system 100 'has a main magnetic field magnet unit 102', a gradient coil unit 106 ', and an RF coil unit 108'. These main magnetic field magnet units 1
02 ′ and each of the coil portions are formed of a pair of coils opposing each other across a space. Each of them has a substantially disk shape and is arranged so as to share a central axis. The object 300 is mounted on the cradle 500 and is carried in and out of the internal space (bore) of the magnet system 100 ′ by carrying means (not shown).

The main magnetic field magnet section 102 'forms a static magnetic field in the internal space of the magnet system 100'. The direction of the static magnetic field is substantially perpendicular to the body axis direction of the object 300. That is, a so-called vertical magnetic field is formed. The main magnetic field magnet unit 102 'is configured using, for example, a permanent magnet. It is needless to say that the present invention is not limited to the permanent magnet and may be configured using a superconducting electromagnet or a normal conducting electromagnet.

The gradient coil section 106 'generates a gradient magnetic field for giving a gradient to the intensity of the static magnetic field. The generated gradient magnetic fields are a slice gradient magnetic field, a readout gradient magnetic field, and a phase encode gradient magnetic field. The gradient coil unit 106 'has three types of gradient coils (not shown) corresponding to these three types of gradient magnetic fields. .

The RF coil unit 108 ′ transmits an RF excitation signal for exciting spins in the body of the subject 300 to the static magnetic field space. The RF coil unit 108 'also receives a magnetic resonance signal generated by the excited spin. The RF coil unit 108 'has a transmitting coil and a receiving coil (not shown). The same coil is used for the transmitting coil and the receiving coil, or a dedicated coil is used for each. The receiving coil in the RF coil unit 108 'is an example of the embodiment of the receiving means in the present invention.

The magnet system 100 is installed in a scan room (not shown) provided with electromagnetic and magnetic shielding. The gradient driving unit 130 or the operation unit 190 is installed outside the scan room. The gradient driving unit 130, the RF driving unit 140, and the data collecting unit 150 are respectively connected to the magnet system 100 by a signal cable.

FIG. 3 shows a block diagram of a reception signal transmission system in the present apparatus. As shown in the figure, a magnet system 100 is installed in a scan room, and a data collection unit 150 and the like are installed outside the scan room, with a partition 700 provided with electromagnetic and magnetic shielding in the scan room as a boundary. You.

The magnet system 100 has an RF receiving circuit 200. The magnetic resonance signal received by the RF coil unit 108 is input to the RF receiving circuit 200 as an RF signal. The RF receiving circuit 200 amplifies the RF input signal and downconverts the frequency.
(Vert) to shift the frequency band of the received signal to a lower band, encode the received signal whose band has been shifted, and transmit it to the data collection unit 150 through the transmission line 400. The RF receiving circuit is
It is an example of embodiment of the encoding means in this invention.
The transmission line 400 is an example of an embodiment of a transmission unit according to the present invention.

FIG. 4 shows an example of a block diagram of the RF receiving circuit 200. As shown in FIG.
The RF signal of frequency f0 input from the RF amplifier (R
(Amplifier) 202. An output signal of the RF amplifier 202 is supplied to a bandpass filter (band).
-Pass filter) 204, the frequency f
The signal is input to the multiplier 206 as a signal of a predetermined band centered on 0.

The multiplier 206 is supplied with a reference signal having a frequency F1. By multiplying the reference signal, the frequency f0 of the input signal is down-converted to f1. The signal whose frequency is down-converted to f1 is input to the multiplier 210 through the band-pass filter 208 as a signal of a predetermined band centered on the frequency f1.

The reference signal of the frequency F2 is input to the multiplier 210, and the frequency f1 of the input signal is down-converted to f2 by multiplication with the reference signal. In addition,
The frequency down-conversion does not necessarily have to be performed in two steps, but is performed in one step at a time.
Needless to say, down-conversion may be performed up to 2, or down-conversion may be performed in three or more stages.

The signal whose frequency is down-converted to f2 is supplied to an anti-aliasing filter (anti-a
, a coding filter 214 as a signal from which an aliasing component has been removed.
Is input to

The encoding circuit 214 receives the input analog signal (an
alog) converts the signal into an encoded signal and outputs it to the transmission line 400. As the encoding circuit 214, for example, an analog-to-digital converter (analog-to-digital conv)
erter) is used. Thus, the input signal is converted (encoded) into a digital signal and transmitted.

The encoding circuit 214 is not limited to an A / D converter, but may be a pulse width modulation (PWM).
dth Modulation) circuit. In that case, the input signal is converted (encoded) into a pulse width signal and transmitted.

The encoding circuit 214 also performs pulse density modulation (PDM).
ation) circuit. In that case, the input signal is converted (encoded) into a pulse density signal and transmitted.

The encoding circuit 214 also performs frequency modulation (FM).
It may be a circuit. In that case, the input signal is converted (coded) into a frequency signal and transmitted.

The magnet system 1 in the scan room
Since the signal transmitted from 00 to the data collection unit 150 outside the scan room is such an encoded signal, it is extremely resistant to noise mixed in during transmission, as compared with the conventional method of transmitting the RF signal as it is. Can be stronger.

FIG. 5 shows an example of a pulse sequence used for magnetic resonance imaging. This pulse sequence is a pulse sequence based on a gradient echo (GRE) method.

That is, (1) is the RF in the GRE method.
A sequence of α ° pulses for excitation, (2)
(3), (4) and (5) are the sequences of the slice gradient Gs, readout gradient Gr, phase encode gradient Gp and gradient echo MR, respectively. The α ° pulse is represented by the center signal.
The pulse sequence proceeds from left to right along the time axis t.

As shown in the figure, α ° excitation of the spin is performed by the α ° pulse. Flip angle (flip
angle) α ° is 90 ° or less. At this time, a slice gradient Gs is applied, and selective excitation for a predetermined slice is performed.

After the α ° excitation, the phase encode gradient Gp
Performs phase encoding of the spin. next,
The spin is first dephased by the readout gradient Gr, and then the spin is rephased (r
ephase) to generate a gradient echo MR. The signal strength of the gradient echo MR is α °
It becomes maximum at the time point after the echo time (echo time) TE from the excitation. The gradient echo MR is collected by the data collection unit 150 as view data.

Such a pulse sequence has a period TR
(Repetition time) is repeated 64 to 512 times. The phase encoding gradient Gp is changed for each repetition, and a different phase encoding is performed each time. As a result, view data of 64 to 512 views filling the k space is obtained.

FIG. 6 shows another example of the pulse sequence for magnetic resonance imaging. This pulse sequence is a pulse sequence of a spin echo (SE: Spin Echo) method.

That is, (1) is a sequence of 90 ° and 180 ° pulses for RF excitation in the SE method, and (2), (3), (4) and (5) are slice gradients, respectively. Gs, readout gradient G
r, phase encoding gradient Gp and spin echo M
This is a sequence of R. Note that a 90 ° pulse and 18
Each 0 ° pulse is represented by a center signal. The pulse sequence proceeds from left to right along the time axis t.

As shown in the figure, 90 ° excitation of spin is performed by a 90 ° pulse. At this time, the slice gradient G
s is applied to perform selective excitation for a predetermined slice. After a predetermined time from the 90 ° excitation, 180 ° excitation by a 180 ° pulse, that is, spin inversion is performed. Also at this time, the slice gradient Gs is applied, and selective inversion is performed for the same slice.

During the period between the 90 ° excitation and the spin inversion, the readout gradient Gr and the phase encode gradient Gp
Is applied. The spin dephase is performed by the readout gradient Gr. The phase encoding of the spin is performed by the phase encoding gradient Gp.

After the spin inversion, the spin is rephased with the readout gradient Gr to generate a spin echo MR.
The signal intensity of the spin echo MR becomes maximum at a point after TE from the 90 ° excitation. The spin echo MR is collected by the data collection unit 150 as view data. Such a pulse sequence is repeated 64 to 512 times in the period TR. Phase encoding gradient Gp for each iteration
And perform different phase encoding each time. As a result, view data of 64 to 512 views filling the k space is obtained.

The pulse sequence used for photographing is G
The method is not limited to the RE method or the SE method.
E (Fast Spin Echo) method, Fast Recovery FSE (Fast Recovery Fast)
Spin Echo method, Echo Planar Imaging (EPI: Echo Planar Imaging)
g) or any other suitable technique.

The data processing unit 170 reconstructs a tomographic image of the object 300 by performing two-dimensional inverse Fourier transform on the view data in the k space. The reconstructed image is stored in the memory and displayed on the display unit 180.

Since the input signal transmitted from the magnet system 100 to the data collection unit 150 is extremely resistant to noise due to being encoded, the SNR (s
good signal-to-noise ratio)
A high quality reconstructed image can be obtained.

[0081]

As described above in detail, according to the present invention, a magnetic resonance signal transmission method and apparatus which are not easily affected by noise and a magnetic resonance imaging apparatus provided with such a transmission apparatus are realized. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram of a device according to an example of an embodiment of the present invention.

FIG. 2 is a block diagram of an apparatus according to an embodiment of the present invention.

FIG. 3 is a block diagram of a reception signal transmission system in the device shown in FIG. 1 or FIG.

FIG. 4 is a block diagram of the RF receiving circuit shown in FIG. 3;

FIG. 5 is a diagram showing an example of a pulse sequence executed by the device shown in FIG. 1 or 2;

FIG. 6 is a diagram showing an example of a pulse sequence executed by the device shown in FIG. 1 or FIG.

[Explanation of symbols]

 100, 100 'Magnet system 102 Main magnetic field coil unit 102' Main magnetic field magnet unit 106, 106 'Gradient coil unit 108, 108' RF coil unit 130 Gradient driving unit 140 RF driving unit 150 Data collection unit 160 Control unit 170 Data processing unit 180 display section 190 operation section 200 RF receiving circuit 202 RF amplifier 204, 208 bandpass filter 206, 210 multiplier 212 anti-aliasing filter 214 coding circuit 300 target 400 transmission line 500 cradle 700 partition

Claims (15)

[Claims] 1. A method of transmitting a magnetic resonance signal, comprising: receiving a magnetic resonance signal; encoding the magnetic resonance signal at the location where the signal is received; and transmitting the encoded signal. 2. The method according to claim 1, wherein the encoding is an analog-to-digital conversion. 3. The method according to claim 1, wherein the encoding is pulse width modulation. 4. The method according to claim 1, wherein the encoding is pulse density modulation. 5. The method according to claim 1, wherein the encoding is frequency modulation. 6. A receiving means for receiving a magnetic resonance signal, an encoding means for encoding the magnetic resonance signal at the location where the magnetic resonance signal is received, and a transmitting means for transmitting the encoded signal. Characteristic magnetic resonance signal transmission device. 7. The magnetic resonance signal transmission device according to claim 6, wherein the encoding is an analog-to-digital conversion. 8. The magnetic resonance signal transmission device according to claim 6, wherein the encoding is pulse width modulation. 9. The magnetic resonance signal transmission device according to claim 6, wherein the encoding is pulse density modulation. 10. The magnetic resonance signal transmission device according to claim 6, wherein the encoding is frequency modulation. 11. A receiving unit for receiving a magnetic resonance signal, an encoding unit for encoding the magnetic resonance signal at the location where the magnetic resonance signal is received, a transmitting unit for transmitting the encoded signal, and the transmitted signal. A magnetic resonance imaging apparatus comprising: a receiving unit that receives an image; and an image generating unit that generates an image based on the received signal. 12. The magnetic resonance imaging apparatus according to claim 11, wherein said encoding is an analog-to-digital conversion. 13. The magnetic resonance imaging apparatus according to claim 11, wherein the encoding is pulse width modulation. 14. The encoding is pulse density modulation.
The magnetic resonance imaging apparatus according to claim 11, wherein: 15. The magnetic resonance imaging apparatus according to claim 11, wherein the encoding is frequency modulation.