JPH03139329A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PURPOSE:To contrive improvements in picture qualities such as slice characteristics, S/N ratio and unevenness of image density by carrying out a digital operation processing of correction data at least to either one digital signal out of a high frequency pulse signal to be transmitted and a magnetic resonance signal to be received. CONSTITUTION:A transmission system 6 and a reception system 7, which transmits a high frequency pulse signal to a subject for exciting a magnetic resonance and receives a magnetic resonance signal emitted from the subject by the aforementioned excitation respectively, are installed. Furthermore, a device 8, which corrects a linearity of at least either one out of the high frequency pulse signal to be transmitted and the magnetic resonance signal to be received, is also installed. This device 8 holds a correction data beforehand and carries out a digital operation processing of this holding data to a digital mode signal. It is possible, as a result, to form a signal of high accuracy, therefore, to contrive improvements in picture qualities such as slice characteristics, S/N ratio and unevenness of image density.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to magnetic resonance (MR) technology.
The present invention relates to a magnetic resonance imaging apparatus that obtains morphological information and functional information such as spectroscopy of a subject by using the phenomenon (sonance).

(Prior art) Magnetic resonance is a phenomenon in which an atomic nucleus with non-zero spin and magnetic moment placed in a static magnetic field resonantly absorbs and emits only electromagnetic waves of a specific frequency. The angular frequency ω0 (ωo”2πν0. ) shown in

; Larmor frequency) ν It resonates with me.

ω0−γHO Here, γ is the gyromagnetic ratio of solid H based on the type of nucleus.

Ho is the unevenness of image density, and Ho is the static magnetic field strength.

An apparatus that performs biological diagnosis using the above-mentioned principle processes electromagnetic waves of the same frequency as above that are induced after the above-mentioned resonance absorption, and calculates nuclear density, longitudinal relaxation time T1. Transverse relaxation time T2. Diagnostic information that reflects information such as flow and chemical shift, such as slice images of a subject, can be obtained non-invasively.

Collecting diagnostic information by magnetic resonance can excite all parts of a subject placed in a static magnetic field and collect signals, but there are limitations in the equipment configuration and clinical requirements for imaging images. Therefore, in an actual device, a specific part is excited and its signal is collected.

In this case, the specific region to be imaged is generally a sliced region with a certain thickness;
Magnetic resonance signals (MR multiplied signals) of echo signals and FID signals from this slice site are collected by performing a data encoding process many times, and these data groups are subjected to image reconstruction processing using, for example, a two-dimensional Fourier transform method. By doing so, an image of the specific slice region is generated.

Two factors that determine image evaluation, such as slice characteristics, S/N ratio 1, and image density unevenness, include transmission characteristics and reception characteristics. In other words, in terms of transmission characteristics, this means that the characteristics of the ideal high-frequency pulse irradiated to the subject differ from the actual high-frequency pulse, and in terms of reception characteristics, there is a difference between the actual magnetic resonance signal induced from the subject and the actual high-frequency pulse. This means that the characteristics differ from those of the magnetic resonance signal.

(Problem to be Solved by the Invention) The above-mentioned transmission and reception characteristics are determined by the nonlinearity of analog circuits such as amplifiers that constitute the transmitter and receiver, and are determined by the slice characteristics and the S/N ratio of 1. This is an issue that needs to be improved in order to improve image quality, such as unevenness in image density.

Therefore, the purpose of the present invention is to improve slice characteristics, S/N ratio 1
An object of the present invention is to provide a magnetic resonance imaging apparatus capable of improving image quality such as uneven image density.

[Structure of the Invention] (Means for Solving the Problems) The present invention has a structure in which the following means are taken to solve the above problems and achieve the objects.

That is, the present invention provides a magnetic resonance imaging apparatus having a transmission/reception system that transmits a high frequency pulse signal for magnetic resonance excitation to a subject and receives a magnetic resonance signal generated from the subject due to the excitation. means for correcting the linearity of at least one of the high frequency pulse signal to be received and the magnetic resonance signal to be received; The method is characterized in that lr1 pressure data is held and the held data is digitally processed into the digital 1-like signal.

(Function) According to such a configuration, a highly accurate signal can be generated by digitally processing the correction data into a digital signal of at least one of the high frequency pulse signal and the magnetic resonance signal to be received. This makes it possible to improve image quality such as slice characteristics and S/N ratio 1 image density unevenness.

(Example) An example of a magnetic resonance imaging apparatus according to the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram showing the configuration of a magnetic resonance imaging apparatus according to the present embodiment, and FIG. 2 is a diagram showing the contents of the transmission/reception correction process in the same embodiment.

In FIG. 1, there is a static magnetic field magnet 2. Gradient magnetic field coils that generate gradient magnetic fields along the X, Y, and Z axis directions3. A probe 4, such as a transmitter/receiver coil for the whole body embedded in the main body, having a transmitter coil and a receiver coil is built in, and a space is formed inside of these to introduce a subject (not shown), and a The magnetic field allows the generation of magnetic resonance phenomena and the collection of magnetic resonance signals.

Further, the gradient magnetic field coil 3 is driven by a gradient magnetic field controller 5, and the probe 4 is driven by a transmitter 6 and a receiver 7. Gradient magnetic field controller5. Transmitter 6.
The receiver 7 is under the control of a sequencer 9, which in turn is under the control of a computer system 10.

And probe 4. The magnetic resonance signals obtained through the receiver 7 are sent to a computer system 10, where image reconstruction processing is performed using two-dimensional and three-dimensional Fourier transform methods, and display is performed.

Next, the transmitter 6. which constitutes the transmitting and receiving system which is the main part of this embodiment. The receiver 7 and the correction data generator 8 will be explained. The transmitter 6 transmits a 1rNc modulated wave for generating a high frequency pulse signal such as a 90° pulse or a 180" pulse.
An RF wave generator 6a that holds a function as digital waveform data, a multiplier 6b that multiplies the output of the RF wave generator 6a by correction data provided from the correction data generator 8, and this multiplier 6b. A lookup memory 6C that holds the output of , a D/A converter 6d that converts the data held in the lookup memory 6c into an analog signal, and an analog S that is the output of the D/A converter 6d.
It is comprised of a modulator 6e that modulates an internally generated high frequency using an ING waveform, and an amplifier 6f that amplifies the output of this modulator 6e and irradiates it to the subject through the probe 4.

The receiver 7 also includes an amplifier 7a that amplifies the magnetic resonance signal induced from the subject and captured by the probe 4, and a detector that detects the magnetic resonance signal amplified by the amplifier 7a using an orthogonal phase shift detection method or the like. 7b, an A/D converter 7C that converts the detection output from the detector 7b into a digital signal, and a correction data generator 8 that outputs a signal from the correction data generator 8 to the digitized detection output output from the A/D converter 7C. Multiplier 7d for multiplying correction data and interface 7e
and a lookup memory 7f.

Further, the correction data generator 8 is configured to generate data indicating the correction characteristic CC shown in FIG. 2, for example. Data indicating this correction characteristic CC is generated as follows. That is, by calculating the function g, (f) indicating the actual characteristic AC in advance, and using the function f indicating the ideal characteristic, f/g,
(f) is calculated, and the calculation result is used as the correction function g, (f). Correction data will be generated based on this correction function gc (f).

Here, for example, a transmission waveform correction process will be explained with reference to FIG. 2.

That is, assuming that the analog equivalent waveform of the RF wave output from the RF wave generator 6a is the original waveform OW shown in FIG. 2, if no correction processing is performed, the D/A converter 6c, modulator 6d, The waveform irradiated to the subject through the amplifier 6e and the probe 4 has a corrected front waveform A shown in FIG.
It becomes W.

This is due to the actual characteristic AC, which is a non-linear characteristic due to analog circuits such as the amplifier 6e. Of course, analog circuits should originally exhibit linear characteristics.

On the other hand, when performing correction processing, the correction data generator 8 stores in advance correction data that will result in a correction characteristic CC that is approximately the inversion of the actual characteristic AC shown in FIG. As a result, the original waveform OW is corrected based on the correction characteristic CC through digital processing in the multiplier 6b and the lookup memory 6C, and as a result,
A correction waveform BW is generated, and the correction waveform BW passes through the D/A converter 6d, the modulator 6e, the amplifier 6f, and the probe 4, and is subjected to the action of the nonlinear characteristic AC.As a result, the ideal waveform tW is applied to the subject. will be irradiated.

Correction processing of the received waveform is performed by holding correction data in the correction data generator 8 and lookup memory 7f to compensate for non-linear characteristics of analog circuits such as the amplifier 7a, and digitally processing the received waveform in the multiplier 7d. , a magnetic resonance signal close to an ideal waveform is obtained at the interface 7e.

As described above, according to this embodiment, by digitally processing the correction data of the digital signal into the RF pulse and magnetic resonance signal, which are digital signals, a highly accurate signal with non-linearity compensated for is obtained. This can generate slicing properties.

With an S/N ratio of 9, image quality such as unevenness in image density can be improved.

Note that the correction data held in the correction data generator 8 may be generated by simulating the transmitting/receiving system, or
It is preferable that the information is generated by actual driving and updated periodically.

In addition, in the correction process, in the case of transmission, the selected excitation pulse may be constant, so the data is held in the lookup memory 6C at the beginning of the sequence and used every time the sequence is executed, and in the case of reception, the selected excitation pulse is kept constant. , a lookup memory 7f for received data each time a sequence is executed.
Perform correction processing using

Further, in the above example, correction processing is performed for both transmission and reception, but only one of them may be performed.

The present invention is not limited to the above embodiments, but can be implemented with various modifications without departing from the gist of the present invention.

[Effects of the Invention] As described above, the present invention includes means for correcting the linearity of at least one of the high-frequency pulse signal to be transmitted and the magnetic resonance signal to be received, and the means holds correction data in advance. , by digitally processing the retained data on the signal in a digital format, so that the correction data is applied to at least one digital signal of the high frequency pulse signal and the magnetic resonance signal to be received.
By performing digital arithmetic processing, it is possible to generate highly accurate signals, thereby making it possible to improve image quality such as slice characteristics, S/N ratio 1 ratio image density, etc.

Therefore, according to the present invention, the Rice characteristic, S/N ratio 2
It is possible to provide a magnetic resonance imaging apparatus that can improve image quality such as uneven image density.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of a magnetic resonance imaging apparatus according to the present invention, and FIG. 2 is a diagram showing the contents of transmission/reception correction processing in the embodiment. DESCRIPTION OF SYMBOLS 1... Main body, 2... Static magnetic field magnet, 3... Gradient magnetic field coil, 4... Probe, 5... Gradient magnetic field controller, 6... Transmitter, 6a... RF wave generation container, 6b... multiplier, 6C... lookup memory,
6d...D/A converter, 6e...Modulator, 6f...
・Amplifier, 7...Receiver, 7a...Amplifier, 7b...
・Detector, 7C.../D converter, 7d... Multiplier,
7e...Interface, 7f...Lookup memory, 8...Correction data generator, 9...Sequencer, 10...Funputer system.

Claims (1)

[Claims] In a magnetic resonance imaging apparatus having a transmission/reception system that transmits a high frequency pulse signal for magnetic resonance excitation to a subject and receives a magnetic resonance signal generated from the subject due to the excitation, the high frequency pulse signal to be transmitted and the reception comprising means for correcting the linearity of at least one of the magnetic resonance signals to be detected, the means holding correction data in advance and digitally processing the held data on the signal in a digital manner. Features of magnetic resonance imaging equipment.