CN111637962A - Shear wave attenuation coefficient measuring method and system - Google Patents
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Abstract
The embodiment of the invention relates to a method and a system for measuring a shear wave attenuation coefficient, which solve the problem of measurement failure caused by the fact that an ultrasonic detection method cannot penetrate certain media; the shear wave attenuation coefficient measuring method comprises the following steps: the method comprises the following steps: applying a nuclear magnetic resonance pulse sequence to a measured object with stable vibration state, and performing motion coding by matching with a static or controllable gradient magnetic field to detect nuclear magnetic resonance echo signals of at least two different positions of the measured object, and analyzing and processing the nuclear magnetic resonance echo signals to obtain a shear wave attenuation coefficient; the system comprises a magnetic resonance system, a mechanical vibration exciting device and a nuclear magnetic resonance console; the embodiment of the invention is used for measuring the attenuation coefficient of a solid or semisolid in a non-invasive and non-destructive mode based on low-field nuclear magnetic resonance.
Description
Technical Field
The embodiment of the invention relates to a method and a system for measuring a shear wave attenuation coefficient.
Background
The attenuation coefficient is also called attenuation constant. Is the real part of the propagation coefficient. It comprises two parts: classical absorption and molecular absorption. Classical absorption is the dissipation of acoustic energy due to air viscosity, thermal conduction effects, and the rotation of air molecules, etc., the magnitude of which is proportional to the square of the acoustic frequency and is related to air temperature and pressure, and is generally not considered. The molecular absorption is mainly caused by the vibration relaxation effect of oxygen and nitrogen molecules in the air, is closely related to the temperature and the humidity of the air, and also changes along with the increase and the decrease of the frequency of the sound wave, but the change rule is more complex.
The attenuation coefficient describes the attenuation rate of wave propagation in a substance and is an important index reflecting the absorption performance of a material. In medicine, the attenuation coefficient can reflect the parameters of the elasticity, fat content, water content and the like of tissues closely related to the physiological and pathological states.
The calculation of the attenuation coefficient often needs to be done using amplitude data of the shear wave. The attenuation of a shear wave in a medium can be described by the following equation
Wherein A is0The initial amplitude of the shear wave is r, the distance between the position of the measured object and the vibration source, and α is the attenuation coefficient.
Most of the existing attenuation coefficient measurement technologies are improved based on the attenuation model. The measurement technique requires two points in the medium to acquire the amplitude, and then calculates the attenuation coefficient according to the formula (1):
wherein A is1，A2The amplitudes of two points of the wave in the measured object at different distances from the vibration source are respectively, delta r is the distance between the two points, and a is the attenuation coefficient.
Amplitude data of the shear wave needs to be measured. The classification is based on the way shear wave amplitude is collected, and standing wave method and ultrasonic detection method are common.
The standing wave method is the most direct measurement method and is suitable for various mechanical waves. As shown in fig. 1, the signal generated by the generator propagates within a fixed length mediumOf a substantially follows a-a loss in the medium0(1+R)e-αrWherein R is a reflection coefficient, α is an attenuation coefficient of the medium, A and A0The amplitudes are respectively at the position r and the vibration source. Because the generator and the receiver are made of the same material, the output voltage (U) and the receiving voltage (U)0) Proportional to the amplitude. Can obtain the product
The method needs to contain the intercepted substance in a measuring device container or a generating/receiving device to go deep into a medium to measure the amplitude of a propagation signal, and is suitable for gas and liquid.
The ultrasonic detection method is a measurement method based on ultrasonic imaging; suitable for measuring attenuation coefficient in solid body, i.e. applying an external excitation vibration to generate shear wave with frequency omega in tissue, and selecting two points with distance delta r in wave propagation direction to excitation vibration source r1，r2. Two point-by-point ultrasonic probes are excited and collected at the same set frame rate to obtain two vibration curves of mass points along with time, then a signal of vibration frequency omega is extracted from the two vibration curves by Kalman filtering, and the amplitude of the extracted signal is the amplitude of the corresponding position.
The standing wave method is suitable for liquid and gas, a detector needs to be immersed into a substance or a substance sample needs to be intercepted during measurement, and the application range is narrow; the attenuation coefficient of ultrasonic detection has the advantages of low cost, quick quantification and the like, but the penetrability of ultrasonic waves is easily influenced by media, so that the measurement is easy to fail.
Disclosure of Invention
The embodiment of the invention provides a method and a system for measuring a shear wave attenuation coefficient, which solve the problem of measurement failure caused by the fact that an ultrasonic detection method cannot penetrate certain media.
In a first aspect, a method for measuring attenuation coefficient of shear wave includes: applying a nuclear magnetic resonance pulse sequence to a measured object with stable vibration state, matching with a static or controllable gradient magnetic field to perform motion coding so as to detect nuclear magnetic resonance echo signals of at least two different positions of the measured object, and analyzing and processing the nuclear magnetic resonance echo signals to obtain a shear wave attenuation coefficient.
With reference to the first aspect, in a first possible implementation manner, the applying a nuclear magnetic resonance pulse sequence to a measured object with a stable vibration state and performing motion coding in cooperation with a static or controllable gradient magnetic field to detect nuclear magnetic resonance echo signals of at least two different positions of the measured object includes: applying 90 DEG radio frequency pulses to a measured object which is in simple harmonic vibration and is in a gradient magnetic field, determining the application time of at least one 180 DEG radio frequency pulse according to the frequency of a vibration source, and applying the at least one 180 DEG radio frequency pulse to the measured object with stable vibration state at the time.
With reference to the first possible implementation manner of the first aspect, in a second possible implementation manner, the measuring nuclear magnetic resonance echo signals of at least two different positions of the measured object includes detecting nuclear magnetic resonance echo signals of different central frequencies of the measured object;
or detecting nuclear magnetic resonance echo signals at different positions of the magnet and/or the probe and the measured object.
With reference to the second possible implementation manner of the first aspect, in a third possible implementation manner, the measuring the nuclear magnetic resonance echo signals of at least two different positions of the object to be measured includes adjusting the initial phase of the vibration source at equal intervals for each position to obtain a series of nuclear magnetic resonance echo signals at the position.
With reference to the first aspect or the third possible implementation manner of the first aspect, in a fourth possible implementation manner, the adjusting the initial phase of the vibration source at equal intervals for each position includes adjusting the initial phase of the vibration source at equal intervals, and the interval is greater than 2 pi.
With reference to the first aspect or any one of the foregoing possible implementation manners of the first aspect, in a fifth possible implementation manner, the analyzing and processing the nuclear magnetic resonance echo signal to obtain a shear wave attenuation coefficient includes:
setting S1 (theta, n) as the nuclear magnetic resonance echo signal acquired at the first position, S2 (theta, n) as the nuclear magnetic resonance echo signal acquired at the second position, theta represents the initial phase of the vibration source, and the second dimension n represents the number of points of the echo;
respectively performing one-dimensional Fourier transform on the second dimensions of S1 (theta, n) and S2 (theta, n), and respectively obtaining the phase of the lowest frequency part
And
are respectively paired
And
performing one-dimensional phase reverse convolution operation;
respectively calculate
And
i.e. separately calculating
And
to obtain a peak value of
Calculating the amplitude of the shear wave at the first and second locations
In the formulas (5) and (6), G is a motion sensitive gradient, gamma is a Larmor frequency, T is a shear wave vibration period, and N is the number of shear wave periods in the whole motion encoding duration;
the value of attenuation coefficient of shear wave propagating in tissue is calculated according to the following formula (7)
α in the formula (7) is the attenuation coefficient, r1Is the distance from the first position to the vibration source, r2Is the distance of the second location from the source.
In a second aspect, a measuring system for implementing the method for measuring attenuation coefficient of shear wave comprises
The magnetic resonance system is used for transmitting radio frequency pulses according to the nuclear magnetic resonance pulse sequence instruction, positioning the spatial position of a measured object and receiving a nuclear magnetic resonance echo signal;
the mechanical vibration exciting device is used for receiving the radio frequency pulse signal sent by the magnetic resonance system and enabling a measured object to generate simple harmonic vibration according to the signal;
and the nuclear magnetic resonance console is used for controlling the magnetic resonance system to operate a nuclear magnetic resonance pulse sequence instruction, receiving a nuclear magnetic resonance echo signal acquired by the magnetic resonance system and analyzing and processing the nuclear magnetic resonance echo signal.
With reference to the second aspect, in a first possible implementation manner, the magnetic resonance system includes a magnetic resonance spectrometer, a radio frequency power amplifier, a preamplifier, a transceiving switching module, a magnet module, and a radio frequency probe;
the magnetic resonance spectrometer is used for sending a trigger signal to the mechanical vibration exciting device and is connected with the receiving and transmitting switching module through a radio frequency power amplifier;
the receiving and transmitting switching module is used for switching the transmitting state and the receiving state of the magnetic resonance system;
the radio frequency probe is connected with the receiving and transmitting switching module; in the transmitting state, the radio frequency probe is used for transmitting radio frequency pulses to a measured object; in a receiving state, the radio frequency probe is used for receiving a nuclear magnetic resonance echo signal generated after a detection target position of a detected object is excited;
and the magnet module is used for generating a static gradient magnetic field to carry out space positioning on the object to be measured.
With reference to the first possible implementation manner of the second aspect, in a second possible implementation manner, the mechanical vibration excitation device includes a signal generator, a power amplifier and a vibration generator;
the signal generator is used for receiving a trigger signal sent by the magnetic resonance spectrometer and driving the vibration generator to generate simple harmonic vibration according to the trigger signal;
the vibration generator is connected with the transmission rod; the vibration generator acts on the object to be measured through the transmission rod to enable the object to be measured to generate simple harmonic vibration.
With reference to the second possible implementation manner of the second aspect, in a third possible implementation manner, the transceiving switching module is connected to the magnetic resonance spectrometer through a preamplifier; the vibration generator is connected with the signal generator through the power amplifier.
The shear wave attenuation coefficient measuring method and system provided by the embodiment of the invention measure the attenuation coefficient of a solid or a semisolid in a non-invasive and non-destructive mode based on the magnetic resonance principle; obviously, the problem that the ultrasonic detection method cannot penetrate certain media to cause measurement failure is avoided.
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In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings that are required to be used in the description of the embodiments are briefly introduced below.
FIG. 1 is a schematic diagram of the principle of the standing wave method for measuring attenuation coefficient.
Fig. 2 is a schematic flow chart of a measurement method according to an embodiment of the present invention.
Fig. 3 is a schematic system structure according to an embodiment of the present invention.
FIG. 4 is a schematic structural diagram of a gradient adding system according to an embodiment of the present invention.
Fig. 5 is a schematic view of a magnetic field distribution of a magnet module according to an embodiment of the present invention.
FIG. 6 is a schematic diagram of an exemplary NMR pulse sequence.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The embodiment of the invention provides a shear wave attenuation coefficient measuring method and system, which are used for solving the problem that an ultrasonic detection method in the prior art cannot penetrate certain media to cause measurement failure. The method and the system are based on the same inventive concept, and because the principles of solving the problems of the method and the device are similar, the implementation of the device and the method can be mutually referred, and repeated parts are not repeated.
The plural in the present invention means two or more. In the description of the present invention, the terms "first", "second", and the like are used for distinguishing between descriptions and are not intended to indicate or imply relative importance nor order to be construed.
The embodiment of the invention provides a shear wave attenuation coefficient measuring method and system, which are realized based on a low-field nuclear magnetic resonance principle and used for measuring the attenuation coefficient of a solid or semisolid in a non-invasive and non-destructive mode. The measuring method provided by the embodiment of the invention also has the advantages of low cost, short measuring time, accurate positioning and high repeatability of measuring results. The method has the characteristics of being used for industrial detection and medical detection. Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
Referring to fig. 2, an embodiment of the present invention provides a method for measuring a shear wave attenuation coefficient, including: applying a nuclear magnetic resonance pulse sequence to a measured object with stable vibration state, matching with a static or controllable gradient magnetic field to perform motion coding so as to detect nuclear magnetic resonance echo signals of at least two different positions of the measured object, and analyzing and processing the nuclear magnetic resonance echo signals to obtain a shear wave attenuation coefficient.
The nuclear magnetic resonance pulse sequence is applied to a measured object, the measured object is subjected to motion coding, the spatial position of the measured object is positioned, at least two magnetic resonance signals at different positions are collected, and finally, the attenuation coefficient is directly calculated according to information such as phase information of the magnetic resonance signals and the distance between a measured point and a vibration source.
Optionally, the applying a nuclear magnetic resonance pulse sequence to the object to be measured in a stable vibration state and performing motion coding in cooperation with a static or controllable gradient magnetic field to detect nuclear magnetic resonance echo signals of at least two different positions of the object to be measured includes: applying 90 DEG radio frequency pulses to a measured object which is in simple harmonic vibration and is in a gradient magnetic field, determining the application time of at least one 180 DEG radio frequency pulse according to the frequency of a vibration source, and applying the at least one 180 DEG radio frequency pulse to the measured object with stable vibration state at the time.
After the vibration state is stabilized, a 90 ° rf pulse is applied, and due to the presence of the magnetic field gradient, spins within a certain thickness of the ROI are excited, and the timing of the 180 ° pulse application can be determined according to the frequency of the vibration source, as shown in fig. 5. After the 180 ° pulse, the spins converge, echo signals are detected at two different points in the material and transmitted back to the console to complete the calculation. In practice, the signal-to-noise ratio can be improved by shortening the echo time or by adding multiple signals by partial motion coding. Furthermore, to improve the phase signal-to-noise ratio, multiple 180 pulses may be applied.
The spatial location of the object to be measured can be located by using the action of the gradient magnetic field and the object to be measured. The gradient magnetic field is mainly used for space positioning, comprises phase encoding and frequency encoding, and can be used for determining any position in space. The system of the embodiment of the invention adopts a single-side magnet with special magnetic field distribution, and generally, the same purpose can be achieved by adopting a traditional low-field magnetic resonance system or other magnet design schemes.
Optionally, measuring nuclear magnetic resonance echo signals of at least two different positions of the object to be measured, including detecting nuclear magnetic resonance echo signals of different central frequencies of the object to be measured; or detecting nuclear magnetic resonance echo signals at different positions of the magnet and/or the probe and the measured object.
The embodiment of the invention needs to measure the magnetic resonance signals at two positions and can be realized by changing the central frequency or the relative positions of the magnet, the probe and the measured object.
Optionally, the measuring nuclear magnetic resonance echo signals of at least two different positions of the measured object includes adjusting an initial phase of the vibration source at equal intervals for each position to obtain a series of nuclear magnetic resonance echo signals at the position.
Preferably, a set of nuclear magnetic resonance echo signals is acquired for each location; the acquisition of a group of nuclear magnetic resonance echo signals of each position can be obtained by adjusting the initial phase of a vibration source at each position at equal intervals, wherein the equal intervals refer to the fixed difference of each initial phase in each vibration state; preferably, the equally spaced values of the respective initial phases are greater than 2 π.
Optionally, the analyzing and processing the nuclear magnetic resonance echo signal to obtain a shear wave attenuation coefficient includes:
setting S1 (theta, n) as the nuclear magnetic resonance echo signal acquired at the first position, S2 (theta, n) as the nuclear magnetic resonance echo signal acquired at the second position, theta represents the initial phase of the vibration source, and the second dimension n represents the number of points of the echo;
respectively performing one-dimensional Fourier transform on the second dimensions of S1 (theta, n) and S2 (theta, n), and respectively obtaining the phase of the lowest frequency part
And
are respectively paired
And
performing one-dimensional phase reverse convolution operation;
respectively calculate
And
i.e. separately calculating
And
to obtain a peak value of
Calculating the amplitude of the shear wave at the first and second locations
In the formulas (5) and (6), G is a motion sensitive gradient, gamma is a Larmor frequency, T is a shear wave vibration period, and N is the number of shear wave periods in the whole motion encoding duration;
the value of attenuation coefficient of shear wave propagating in tissue is calculated according to the following formula (7)
α in the formula (7) is the attenuation coefficient, r1Is the distance from the first position to the vibration source, r2Is the distance of the second location from the source.
When the number of the measured positions is two, the first position and the second position correspond to the two measured positions one by one; when the measured positions are 3 or more, the first position and the second position are any two of the 3 or more measurement positions.
The embodiment of the invention only describes a method for acquiring two positions to calculate the attenuation coefficient. In fact, more than two positions can be collected, and the attenuation coefficient can be measured by a method similar to the method disclosed by the invention, and the method is also within the protection scope of the invention.
Those of ordinary skill in the art will understand that: all or part of the steps for implementing the embodiments of the method may be implemented by hardware related to program instructions, the program may be stored in a computer-readable storage medium, and when executed, the program performs the steps including the embodiments of the method, and the storage medium includes: various media that can store program codes, such as ROM, RAM, magnetic or optical disks.
As shown in fig. 3, an embodiment of the present invention further provides a measurement system for implementing the shear wave attenuation coefficient measurement method, including a magnetic resonance system, configured to transmit a radio frequency pulse according to a nuclear magnetic resonance pulse sequence instruction, and locate a spatial position of a measured object, where the magnetic resonance system is configured to receive a nuclear magnetic resonance echo signal; the mechanical vibration exciting device is used for receiving the radio frequency pulse signal sent by the magnetic resonance system and enabling a measured object to generate simple harmonic vibration according to the signal; and the nuclear magnetic resonance console is used for controlling the magnetic resonance system to operate a nuclear magnetic resonance pulse sequence instruction, receiving a nuclear magnetic resonance echo signal acquired by the magnetic resonance system and analyzing and processing the nuclear magnetic resonance echo signal.
Optionally, the magnetic resonance spectrometer and the magnet module are both portable for ease of carrying. The magnetic resonance system is a portable low-field magnetic resonance system, so that the whole system is lighter, more convenient and lower in cost.
The nuclear magnetic resonance console sends a nuclear magnetic resonance pulse sequence instruction to the mechanical vibration excitation device, the mechanical vibration excitation device acts on a measured object to enable the measured object to generate simple harmonic vibration, the measured object is positioned in a space position in the magnetic resonance system through a gradient magnetic field, and the magnetic resonance system receives a nuclear magnetic resonance echo signal of the measured object and returns the nuclear magnetic resonance signal to the nuclear magnetic resonance console; the nuclear magnetic resonance console controls the mechanical vibration excitation device to adjust the initial phase of the vibration source at equal intervals at each position through an instruction to obtain a series of nuclear magnetic resonance echo signals to return to the nuclear magnetic resonance console; the nuclear magnetic resonance console can also generate nuclear magnetic resonance echo signals at different positions by instructions and corresponding execution mechanisms in a mode of changing the central frequency or a mode of changing the relative positions of the magnet, the probe and the measured object and return the nuclear magnetic resonance echo signals to the nuclear magnetic resonance console; and analyzing and processing the nuclear magnetic resonance echo signals after the nuclear magnetic resonance console receives a series of nuclear magnetic resonance echo signals at different positions to obtain an attenuation coefficient.
Optionally, the magnetic resonance system includes a magnetic resonance spectrometer, a radio frequency power amplifier, a preamplifier, a transmit-receive switching module, a magnet module, and a radio frequency probe; the magnetic resonance spectrometer is used for sending a trigger signal to the mechanical vibration exciting device and is connected with the receiving and transmitting switching module through a radio frequency power amplifier; the receiving and transmitting switching module is used for switching the transmitting state and the receiving state of the magnetic resonance system; the radio frequency probe is connected with the receiving and transmitting switching module; in the transmitting state, the radio frequency probe is used for transmitting radio frequency pulses to a measured object; in a receiving state, the radio frequency probe is used for receiving a nuclear magnetic resonance echo signal generated after a detection target position of a detected object is excited; and the magnet module is used for generating a static gradient magnetic field to carry out space positioning on the object to be measured.
Preferably, the transceiving switching module is connected with the magnetic resonance spectrometer through a preamplifier; the vibration generator is connected with the signal generator through the power amplifier.
Specifically, as shown in fig. 3, the magnetic resonance spectrometer is connected to the transmit-receive switch through a radio frequency power amplifier; the magnetic resonance spectrometer is connected with the receiving and transmitting change-over switch through a preamplifier; the magnetic resonance spectrometer is connected with the radio frequency probe through a receiving and transmitting change-over switch; the receiving and transmitting switching module is used for switching the portable magnetic resonance system to be in a transmitting state or a receiving state, and the probe transmits radio frequency pulses in the transmitting state; and in the receiving state, the radio frequency probe is used for receiving nuclear magnetic resonance echo signals generated after the target position of the measured object is excited. The magnetic resonance spectrometer is communicated with the mechanical vibration exciting device; the magnetic resonance console is respectively connected with the magnetic resonance spectrometer and the receiving and transmitting change-over switch through a radio frequency power amplifier; the magnet module is arranged on the rear side of the radio frequency probe; the object to be measured is arranged between the radio frequency probe and the transmission rod of the mechanical vibration exciting device; the transmission rod transmits the vibration of the mechanical vibration exciting device to the object to be measured, so that the object to be measured does simple harmonic vibration in the gradient magnetic field of the magnet module.
Preferably, if a static magnetic field is used, the magnetic resonance spectrometer is not provided with a gradient control module, and therefore, a corresponding gradient coil is not required. The magnet module is provided with a single-sided magnet, the back surface of the magnet module is connected with a magnetic yoke, the magnetic field intensity of the back surface is rapidly attenuated, the single-sided magnet generates a static magnetic field, the static magnetic field has linear or approximately linear gradient in an AP-LR plane in the ROI range, and the magnetic field is uniformly and rapidly attenuated outside the ROI range; the magnetic field distribution of the magnet module is shown in fig. 6.
Optionally, if controllable gradient magnetic fields are used, as shown in fig. 4, the magnetic resonance system further comprises a gradient system; the gradient system comprises a gradient amplifier and a gradient coil; the gradient amplifier is communicated with the magnetic resonance spectrometer and is connected with the gradient coil; the gradient coil is arranged between the radio frequency probe and the magnet module and is used for generating a controllable gradient magnetic field to a measured object.
The gradient system consists of a gradient amplifier and a gradient coil, is controlled by a magnetic resonance spectrometer, and forms a gradient magnetic field in the space of the measured object by the gradient coil after the signal is amplified by the gradient amplifier; in this embodiment, in addition to the pulse sequence and the static gradient magnetic field being used for motion encoding, the pulse sequence may also be used in conjunction with a gradient system to perform motion encoding using a controllable gradient magnetic field generated by a gradient coil.
Preferably, the magnetic resonance spectrometer is provided with a transmitting and gating unidirectional signal path, and is connected with the radio frequency power amplifier through the transmitting and gating unidirectional signal path; the magnetic resonance spectrometer is connected with a receiving and transmitting switch through a receiving and transmitting switching gate, the radio frequency power amplifier amplifies a transmitting signal and then is connected with the receiving and transmitting switch, and the receiving and transmitting switch is connected with the radio frequency probe.
Optionally, the mechanical vibration excitation means comprises a signal generator, a power amplifier and a vibration generator; the signal generator is used for receiving a trigger signal sent by the magnetic resonance spectrometer and driving the vibration generator to generate simple harmonic vibration according to the trigger signal; the vibration generator is connected with the transmission rod; the vibration generator acts on the object to be measured through the transmission rod to enable the object to be measured to generate simple harmonic vibration.
Preferably, the signal generator is a waveform generator, the waveform generator sends a 50HZ sine wave to the power amplifier for amplification, the vibration power amplifier is connected with the signal generator, the signal generator is connected with the magnetic resonance spectrometer, a trigger signal sent by the magnetic resonance spectrometer is received and transmitted to the vibration generator by the signal generator, and the vibration generator drives the transmission rod to generate simple harmonic vibration; the simple harmonic vibrator is tightly attached to the adjacent surface of a measured object through the transmission rod to generate vibration and then generate shear waves in the simple harmonic vibrator, the shear waves are transmitted in the AP direction to cause mass points in tissues to do simple harmonic vibration in the LR direction, the nuclear magnetic resonance console is connected with the magnetic resonance spectrometer to control the running of a magnetic resonance pulse sequence instruction and receive nuclear magnetic resonance echo signals collected by the magnetic resonance spectrometer to complete real-time data processing.
As will be appreciated by one of ordinary skill in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments of the present invention without departing from the spirit or scope of the embodiments of the invention. Thus, if such modifications and variations of the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to encompass such modifications and variations.
Claims (10)
1. A shear wave attenuation coefficient measuring method is characterized in that: the method comprises the following steps: applying a nuclear magnetic resonance pulse sequence to a measured object with stable vibration state, matching with a static or controllable gradient magnetic field to perform motion coding so as to detect nuclear magnetic resonance echo signals of at least two different positions of the measured object, and analyzing and processing the nuclear magnetic resonance echo signals to obtain a shear wave attenuation coefficient.
2. A method of measuring attenuation coefficient of shear waves according to claim 1, wherein: the nuclear magnetic resonance pulse sequence is applied to the object to be measured with stable vibration state, and the nuclear magnetic resonance pulse sequence is matched with a static or controllable gradient magnetic field to carry out motion coding so as to detect nuclear magnetic resonance echo signals of at least two different positions of the object to be measured,
the method comprises the following steps: applying 90 DEG radio frequency pulses to a measured object which is in simple harmonic vibration and is in a gradient magnetic field, determining the application time of at least one 180 DEG radio frequency pulse according to the frequency of a vibration source, and applying the at least one 180 DEG radio frequency pulse to the measured object with stable vibration state at the time.
3. A method of measuring attenuation coefficient of shear waves according to claim 2, wherein: the nuclear magnetic resonance echo signals of at least two different positions of the measured object are measured, and the nuclear magnetic resonance echo signals of different central frequencies of the measured object are detected;
or detecting nuclear magnetic resonance echo signals at different positions of the magnet and/or the probe and the measured object.
4. A method of measuring attenuation coefficient of shear waves according to claim 3, wherein: and measuring nuclear magnetic resonance echo signals of at least two different positions of the measured object, wherein the initial phase of the vibration source is adjusted at equal intervals at each position to obtain a series of nuclear magnetic resonance echo signals at the position.
5. A method of measuring attenuation coefficient of shear waves according to claim 4, wherein: and the step of adjusting the initial phase of the vibration source at equal intervals for each position comprises adjusting the initial phase of the vibration source at equal intervals, wherein the interval is greater than 2 pi.
6. A method of measuring attenuation coefficient of shear waves according to any of claims 1 to 5, wherein: the analyzing and processing of the nuclear magnetic resonance echo signal to obtain a shear wave attenuation coefficient includes:
setting S1 (theta, n) as the nuclear magnetic resonance echo signal acquired at the first position, S2 (theta, n) as the nuclear magnetic resonance echo signal acquired at the second position, theta represents the initial phase of the vibration source, and the second dimension n represents the number of points of the echo;
respectively performing one-dimensional Fourier transform on the second dimensions of S1 (theta, n) and S2 (theta, n), and respectively obtaining the phase of the lowest frequency part
And
are respectively paired
And
performing one-dimensional phase reverse convolution operation;
respectively calculate
And
i.e. separately calculating
And
to obtain a peak value of
Calculating the amplitude of the shear wave at the first and second locations
In the formulas (5) and (6), G is a motion sensitive gradient, gamma is a Larmor frequency, T is a shear wave vibration period, and N is the number of shear wave periods in the whole motion encoding duration;
the value of attenuation coefficient of shear wave propagating in tissue is calculated according to the following formula (7)
α in the formula (7) is the attenuation coefficient, r1Is the distance from the first position to the vibration source, r2Is the distance of the second location from the source.
7. A measuring system for implementing the shear wave attenuation coefficient measuring method according to any one of claims 1 to 6, characterized in that: comprises that
The magnetic resonance system is used for transmitting radio frequency pulses according to the nuclear magnetic resonance pulse sequence instruction, positioning the spatial position of a measured object and receiving a nuclear magnetic resonance echo signal;
the mechanical vibration exciting device is used for receiving the radio frequency pulse signal sent by the magnetic resonance system and enabling a measured object to generate simple harmonic vibration according to the signal;
and the nuclear magnetic resonance console is used for controlling the magnetic resonance system to operate a nuclear magnetic resonance pulse sequence instruction, receiving a nuclear magnetic resonance echo signal acquired by the magnetic resonance system and analyzing and processing the nuclear magnetic resonance echo signal.
8. The measurement system of claim 7, wherein: the magnetic resonance system comprises a magnetic resonance spectrometer, a radio frequency power amplifier, a preamplifier, a receiving and transmitting switching module, a magnet module and a radio frequency probe;
the magnetic resonance spectrometer is used for sending a trigger signal to the mechanical vibration exciting device and is connected with the receiving and transmitting switching module through a radio frequency power amplifier;
the receiving and transmitting switching module is used for switching the transmitting state and the receiving state of the magnetic resonance system;
the radio frequency probe is connected with the receiving and transmitting switching module; in the transmitting state, the radio frequency probe is used for transmitting radio frequency pulses to a measured object; in a receiving state, the radio frequency probe is used for receiving a nuclear magnetic resonance echo signal generated after a detection target position of a detected object is excited;
and the magnet module is used for generating a static gradient magnetic field to carry out space positioning on the object to be measured.
9. The measurement system of claim 8, wherein: the mechanical vibration exciting device comprises a signal generator, a power amplifier and a vibration generator;
the signal generator is used for receiving a trigger signal sent by the magnetic resonance spectrometer and driving the vibration generator to generate simple harmonic vibration according to the trigger signal;
the vibration generator is connected with the transmission rod; the vibration generator acts on the object to be measured through the transmission rod to enable the object to be measured to generate simple harmonic vibration.
10. The measurement system of claim 9, wherein: the receiving and transmitting switching module is connected with the magnetic resonance spectrometer through a preamplifier; the vibration generator is connected with the signal generator through the power amplifier.
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