CN112345989B - Tumor tissue magnetic characteristic imaging method - Google Patents
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Abstract
A tumor tissue magnetic characteristic imaging method comprises the following steps: firstly, magnetic resonance flat scanning measurement of radio frequency magnetic field distribution to obtain amplitude and phase image data of a magnetic field; substituting the multichannel magnetic field data into a human-electric characteristic reconstruction algorithm to respectively solve the conductivity, dielectric constant and related spatial gradient items of the human body; thirdly, intravenous injection of gadolinium contrast agent as contrast agent to human body, and magnetic resonance enhancement scanning to obtain new amplitude and phase data; and fourthly, substituting the human body conductivity and the dielectric constant obtained in the second step and the magnetic field data obtained in the third step into a human magnetic characteristic reconstruction algorithm to solve the magnetic permeability distribution of the focus area of the human body after the gadolinium contrast agent nano particles are dispersed.
Description
Technical Field
The invention relates to a magnetic characteristic imaging method for human tissues, in particular to a magnetic characteristic imaging method based on nuclear magnetic resonance scanning.
Background
Tumor diseases are a great threat to human health, and existing diagnostic and therapeutic methods include X-ray tomography, magnetic resonance imaging, pathological examination, chemotherapy, radiation therapy, and the like. Magnetic resonance imaging is a non-invasive imaging examination technique that can reconstruct proton density distribution images of tissues, thereby judging and obtaining morphological information such as tumor position, tumor size, etc. However, as with other medical imaging techniques, anatomical images have limited information reflecting changes in physiology and pathology. The electromagnetic characteristic difference between normal tissues and tumor tissues is remarkable, and the early diagnosis of tumor diseases is expected to be realized through measurement and reconstruction of electric characteristic and magnetic characteristic parameters.
The traditional medical electrical impedance imaging technology is to attach electrode plates on a body surface to inject current, and inversion is carried out on the measured potentials at different positions to obtain the conductivity distribution inside the tissue. Chinese patent 201310583583.0 'electrical impedance tomography method integrated with skull resistivity non-uniform distribution information' utilizes anatomical structure information provided by CT data of the head of a measured object, thickness of a barrier layer of a skull plate and statistical parameters of skull resistivity values to establish a head two-dimensional finite element model containing skull resistivity non-uniform distribution, and realizes electrical impedance tomography reconstruction based on the model. The method can improve the positioning accuracy and the image space resolution of an imaging target, but a patient needs to wear an electrode device, and the injection current cannot exceed the safety limit value of a human body by 15mA.
As a new multi-physical field imaging method, 2012, chen Ruijuan proposed a ring electrode electrical impedance imaging method (DOI 10.19650/j.cnki.cjsi.2012.10.016) for a developed magnetic resonance system, which changes the phase distribution of proton precession by injecting current to cause a change in the main magnetic field, and reconstructs the conductivity distribution from the relationship between phase and conductivity. Simulation experiments show that in the annular electrode mode, the distribution of current density in the main magnetic field direction component is basically consistent with the distribution of conductivity, and the gray distribution of the electrical impedance image obtained after the simulation experiment is carried out in a 0.36T magnetic resonance system is more uniform. Although the magnetic resonance electrical impedance imaging greatly increases the known measurement quantity on the reconstruction algorithm and reduces the known pathological condition, the imaging scanning still depends on electrode pasting and exciting current injection on the surface of the patient body, and the limit value limits the further clinical application of the technology.
In order to overcome the limitation of the electrode injection current mode to the electrical impedance imaging technology, the radio frequency excitation magnetic field of Fourier transform imaging is utilized, and the magnetic resonance electrical characteristic imaging directly reconstructs the conductivity and the dielectric constant of human tissues by magnetic resonance scanning. Chinese patent 201510222241.5, "equipment for monitoring dielectric characteristics of human tissues in real time and method for obtaining dielectric characteristic parameters of human tissues", wherein the equipment comprises an electromagnetic wave signal generator, a power distributor, a directional coupler, a coaxial transmission line, a main processor and the like; the method for detecting the dielectric characteristic parameter comprises the following steps: the electromagnetic wave signal generator generates a broadband electromagnetic wave signal, the broadband electromagnetic wave signal is distributed by the power distributor to form a reference signal and a test signal, the reference signal is input to the amplitude phase processing unit, the test signal is transmitted to the tissue of the body to be tested through the directional coupler by the coaxial transmission line, and reflected waves are generated at the tissue of the body to be tested; the directional coupler transmits the reflected wave signal generated by the part to be detected to the amplitude phase processing unit, compares the reflected wave signal generated by the part to be detected with the reference signal, inputs the compared signal to the main processor and calculates the dielectric characteristics of human tissues. The technology works by relying on a standard water model and a known dielectric property database of tumor tissues, and the use of a current injection electrode plate is abandoned, but in the establishment process of a related tumor tissue reference database, measurement is carried out on the ex-situ tissue under the condition of an ex-situ state, and the corresponding relation between the dielectric property and the dielectric property under the pathological condition of a body is quite complex, so that the dielectric property value obtained by the technology is difficult to be used as the basis of clinical diagnosis.
U.S. patent 15/186759 "transpose and method of reconstruction of electrical characteristic images based on magnetic resonance" discloses a method of measuring brain tissue conductivity and permittivity distribution. In the traditional magnetic resonance electrical characteristic reconstruction algorithm, because the differentiation operation of magnetic field data introduces larger errors to the electrical characteristic result, the patent technology calculates the electrical characteristic based on the ratio of the image water content signal, and can improve the signal-to-noise ratio of the image. But improving the accuracy of the measurement of the relevant water signal remains a problem to be solved.
Therefore, because the existing measurement technology of the electrical characteristic parameters of human tissues is not enough, the differential diagnosis of the tumor diseases based on the electrical characteristic parameters is difficult to realize, and a new comprehensive measurement and imaging technology of the electrical characteristic parameters and the magnetic characteristic parameters of human tissues is necessary. Based on the magnetic resonance multichannel radio frequency coil, a plurality of groups of known magnetic field quantities are acquired, so that the problem of excessive unknown quantities in an electrical characteristic parameter reconstruction algorithm can be solved.
Disclosure of Invention
In order to overcome the defect that the existing magnetic resonance electrical characteristic imaging can only reconstruct the electrical characteristic parameters of a human body and is difficult to realize the differential diagnosis of tumor diseases based on the electrical characteristic parameters, the invention provides a magnetic resonance magnetic characteristic imaging method based on the current electrical characteristic imaging. The magnetic characteristic image under paramagnetic contrast condition is obtained through two magnetic field measurement and reconstruction, and is used for evaluating the quality of the magnetic resonance contrast enhancement image and assisting in early diagnosis of tumor diseases.
The principle of the imaging method based on the magnetic resonance electrical characteristics and the magnetic characteristics is as follows: the human body enters a static magnetic field of the magnetic resonance magnet, a radio frequency pulse excitation magnetic field acts on the human body under the time sequence coordination of a gradient magnetic field, the human body generates an alternating induction magnetic field, related signals are detected and processed by a coil and a spectrometer, and then the electrical characteristics are obtained through inversion of pixel data; then, gadolinium contrast agent is injected into the human body, the pixel data of the radio frequency magnetic field are obtained through scanning again, and the magnetic characteristic distribution image is obtained after inversion.
The invention discloses an imaging method based on nuclear magnetic resonance scanning electric characteristic and magnetic characteristic parameter reconstruction, which solves the technical problems by adopting the following specific steps: firstly, magnetic resonance flat scanning measurement of radio frequency magnetic field distribution to obtain amplitude and phase image data of a magnetic field; substituting the multichannel magnetic field data into a human-electric characteristic reconstruction algorithm to respectively solve the conductivity, dielectric constant and related spatial gradient items of the human body; thirdly, intravenous injection of gadolinium contrast agent as contrast agent to human body, and magnetic resonance enhancement scanning to obtain new amplitude and phase data; and fourthly, substituting the human body conductivity and the dielectric constant obtained in the second step and the magnetic field data obtained in the third step into a magnetic characteristic reconstruction algorithm to solve the magnetic permeability distribution of the focus area of the human body after the gadolinium contrast agent nano particles are dispersed.
The concrete explanation is as follows:
The first step: acquiring magnetic resonance flat scanning radio frequency magnetic field distribution data of human body
And scanning the tumor part by using a rapid gradient echo imaging sequence to obtain the amplitude and phase data of the alternating magnetic field. The receiving coil is a multichannel transmitting coil, and the acquired transmitting magnetic field data does not contain proton density distribution information.
And a second step of: reconstruction of electrical characteristic parameter distribution
For clinical application of tumor focus examination, the magnetic permeability μ of the human body is close to the air μ 0, which is a known quantity. The invention adopts an electrical characteristic parameter distribution reconstruction algorithm, and obtains the magnetic field space distribution interacted with tissues by utilizing magnetic resonance measurement and then according to ampere lawAnd Faraday's law/>Inversion calculation of the spatial distribution of conductivity and permittivity,/>Is a magnetic flux density vector, i is an imaginary unit,/>For electric field strength, ω is the resonant angular frequency, ε c is the complex permittivity of the human body, ε c =ε -i (σ/ω), ε is the permittivity, σ is the conductivity,/>For the rotation operator. And (3) solving the rotation on both sides of the ampere law and carrying the ampere law into the Faraday law to obtain a relation equation of the magnetic field and the complex dielectric constant, wherein the relation equation is shown in a formula (1). Emitted magnetic field flux density rotation component scalar/>Sign '-' to show the difference between the emitted magnetic field at the later permeability distribution measurement step,/>The equation of relation with electrical characteristics is:
Wherein x, y, z are the spatial position coordinates, For the gradient operator, let/>AndThe gradients of epsilon c along the z-direction and xy-combined direction are shown, respectively.
For the multichannel coil and a specific imaging body, an equation set can be obtained based on the equation (1), and parameter distribution of complex dielectric constants epsilon c, m, n and the like of the human body can be reconstructed.
And a third step of: contrast enhancement agent is injected to change the magnetic permeability distribution of focus area
Injecting paramagnetic nanoparticle contrast enhancer solution into human body, and scanning tumor part again by using the same imaging sequence as in the first step to obtain amplitude and phase data of alternating magnetic field. Due to the presence of the contrast enhancing agent, the distribution of the main magnetic field in the body is changed, and thus the magnetic field and the reconstructed image are also changed under the same imaging conditions. The obtained magnetic field data contains distribution information of magnetic permeability mu in human body.
Fourth step: reconstructing magnetic characteristic parameter distribution
For magnetic resonance imaging scanning, the radio frequency magnetic field excited and detected lies in a plane perpendicular to the main magnetic field direction and is a rotating magnetic field. After the spatial distribution of the magnetic field interacting with the tissue is obtained by magnetic resonance measurement, the magnetic characteristic parameter distribution is reconstructed by using an algorithm based on the following formula (2). Unlike in the case of electrical property reconstruction, the permeability μ of the tissue at the site of administration in the human body after injection of the reinforcing agent is no longer approximately equal to the vacuum permeability μ 0.
Magnetic flux density of emitted magnetic field during scanning after injection of reinforcing agentThe equation of relation with magnetic properties is:
wherein mu is the spatial distribution of the magnetic permeability in the human body after the injection of the reinforcing agent, namely the reconstruction parameter.
Based on the formula (2), the complex permittivity epsilon c of the human body is obtained by reconstruction in the second step, and the magnetic flux density of the emitted magnetic field is obtained by scanning after the injection of the reinforcing agentThe permeability distribution mu can be reconstructed.
The human tissue magnetic resonance electrical characteristic and magnetic characteristic parameter distribution reconstruction imaging method provided by the invention can be used for non-invasively measuring the electromagnetic characteristic spatial distribution of tumor disease focus tissues in situ. Compared with pathological results of tissue sections of living body examination, the method has the advantages that the obtained electrical characteristic and magnetic characteristic parameter difference of normal tissues and tumor tissues is more obvious than the morphological difference of the normal tissues and tumor tissues on anatomical structure images obtained by the existing enhancement scan, and tissue electrical characteristic and magnetic characteristic information is expected to be used for differential diagnosis of different stages of tumor evolution.
Drawings
The invention will be further described with reference to the drawings and examples.
Fig. 1 is a schematic diagram of a signal acquisition device applying the tumor tissue magnetic characteristic imaging method of the invention, wherein the signal acquisition device comprises a1 excitation source, a2 transmitting coil, a 3-target imaging body, a4 receiving coil, a 5 detection device, a 6 upper computer and a 7 magnet.
FIG. 2 is a flow chart of a method for imaging the magnetic properties of tumor tissue according to the present invention.
Detailed Description
As shown in fig. 1, in a device of a tumor tissue magnetic characteristic imaging method, an excitation source 1 is connected with a transmitting coil 2, the transmitting coil 2 and a detecting coil are arranged close to a target imaging body 3, the transmitting coil 2 is used for exciting the target imaging body 3 with a magnetic field, and the detecting coil 4 detects a magnetic field signal generated by the target imaging body; the detection coil is connected with the detection device 4, the detection device 4 is used for amplifying, filtering, demodulating and analog-to-digital converting magnetic field signals, the detection device 4 is connected with the upper computer 6, and the upper computer 6 completes Fourier transformation, electric characteristic and magnetic characteristic parameter distribution image reconstruction of the magnetic field digital signals. The transmitting coil 2, the target imaging body and the receiving coil 4 are arranged in the magnet, the static magnetic field generated by the magnet magnetizes the target imaging body, the spin system in the target imaging body resonates under the combined action of the exciting magnetic field generated by the transmitting coil 2, and the receiving coil 4 receives the free induction attenuation magnetic field signal. The target imaging volume may be human tumor tissue.
In the embodiment shown in fig. 1, the specific steps of the tumor tissue magnetic property imaging method of the present invention are as follows: after a tumor disease patient pushes in a magnet 7, firstly, carrying out magnetic resonance flat scanning on a normal tissue target imaging body, measuring radio frequency magnetic field distribution, enabling an excitation source 1 to generate a magnetic field through a transmitting coil 2 to act on the target imaging body, and after a magnetic resonance signal is acquired by a detecting coil, processing the magnetic resonance signal by a detecting device 4 and transmitting the magnetic resonance signal to an upper computer 6 to obtain amplitude and phase image data of the magnetic field; substituting the multichannel magnetic field data into an electrical characteristic reconstruction algorithm to respectively solve the conductivity, dielectric constant and related spatial gradient items of the human body; thirdly, intravenous injection of gadolinium contrast agent into a target imaging body, magnetic resonance enhancement scanning is carried out, and the method involves that an excitation source 1 applies a pulse electromagnetic field to the target imaging body through a transmitting coil, a generated free induction attenuation magnetic field signal is acquired and processed by a detecting coil and a detecting device and then is transmitted to an upper computer 6, and new amplitude and phase data are obtained through inverse Fourier transformation; and fourthly, substituting the human body conductivity and the dielectric constant obtained in the second step and the magnetic field data obtained in the third step into a magnetic characteristic reconstruction algorithm to solve the magnetic permeability distribution in the target imaging body after gadolinium contrast agent nano particles are dispersed.
The following is a specific description in connection with the imaging method flowchart shown in fig. 2:
The first step: acquiring magnetic resonance flat scanning radio frequency magnetic field distribution data of human body
And scanning the tumor part by using a rapid gradient echo imaging sequence to obtain the amplitude and phase data of the alternating magnetic field. The receiving coil is a multichannel transmitting coil, and the acquired transmitting magnetic field data does not contain proton density distribution information.
And a second step of: reconstruction of electrical characteristic parameter distribution
For clinical application of tumor focus examination, the magnetic permeability mu 0 of the human body is close to that of air, which is a known quantity. The electrical characteristic parameter distribution reconstruction algorithm is to measure the spatial distribution of the magnetic field interacted with the tissue by using magnetic resonance or other methods, and then calculate the spatial distribution of the conductivity and the dielectric constant according to ampere law and Faraday law inversion.
Scalar quantity of magnetic flux density rotation component of emitted magnetic fieldSign '-' to show the difference between the emitted magnetic field at the later permeability distribution measurement step,/>The equation of relation with electrical characteristics is:
Wherein, Is a magnetic flux density vector, ω is a resonance angular frequency, x, y, z is a spatial position coordinate, ε c is a complex permittivity of human body, ε c =ε -i (σ/ω), ε is a permittivity, σ is a conductivity, i is an imaginary unit, and/>Mu 0 is the permeability in vacuum for gradient operator, let/>And/>The gradients of epsilon c along the z-direction and xy-combined direction are shown, respectively.
For the multichannel coil and a specific imaging body, an equation set can be obtained based on the equation (1), and parameter distribution of complex dielectric constants epsilon c, m, n and the like of the human body can be reconstructed.
And a third step of: contrast enhancement agent is injected to change the magnetic permeability distribution of focus area
Injecting paramagnetic nanoparticle contrast enhancer solution into human body, and scanning tumor part again by using the same imaging sequence as in the first step to obtain amplitude and phase data of alternating magnetic field. Due to the presence of the contrast enhancing agent, the distribution of the main magnetic field in the body is changed, and thus the magnetic field and the reconstructed image are also changed under the same imaging conditions. The obtained magnetic field contains distribution information of magnetic permeability mu in human body.
Fourth step: reconstructing magnetic characteristic parameter distribution
For magnetic resonance imaging scanning, the radio frequency magnetic field excited and detected lies in a plane perpendicular to the main magnetic field direction and is a rotating magnetic field. And (3) using a magnetic characteristic parameter distribution reconstruction algorithm, obtaining the spatial distribution of a magnetic field interacted with the tissue by magnetic resonance measurement, and then calculating the spatial distribution of magnetic permeability according to ampere law and Faraday law inversion. Unlike in the case of electrical property reconstruction, the permeability μ of the tissue at the site of administration in the human body after injection of the reinforcing agent is no longer approximately equal to the vacuum permeability μ 0.
Magnetic flux density of emitted magnetic field during scanning after injection of reinforcing agentThe equation of relation with magnetic properties is:
wherein mu is the spatial distribution of magnetic permeability in human body after injection of the reinforcing agent, namely reconstruction parameters;
based on equation (2), the ε c parameters are reconstructed in the second step, obtained by The permeability distribution mu can be reconstructed.
Claims (1)
1. The imaging method of the magnetic characteristics of the tumor tissue is characterized by comprising the following steps:
The first step, magnetic resonance flat scan measurement radio frequency magnetic field distribution, obtain amplitude and phase image data of the magnetic field, including: scanning the tumor part by using a rapid gradient echo imaging sequence to obtain amplitude and phase data of an alternating magnetic field;
secondly, substituting the multichannel magnetic field data into a human-electric characteristic reconstruction algorithm to respectively solve the conductivity, dielectric constant and related spatial gradient items of the human body, wherein the method comprises the following steps:
adopting an electrical characteristic parameter distribution reconstruction algorithm, obtaining the spatial distribution of a magnetic field interacted with a tissue by utilizing magnetic resonance measurement, and then inverting and calculating the spatial distribution of the conductivity and the dielectric constant according to ampere law and Faraday law;
Scalar quantity of magnetic flux density rotation component of emitted magnetic field Sign '-' to show the difference between the emitted magnetic field at the later permeability distribution measurement step,/>The equation of relation with electrical characteristics is:
Wherein, Is a magnetic flux density vector, ω is a resonance angular frequency, x, y, z is a spatial position coordinate, ε c is a human complex permittivity, ε c =ε -i (σ/ω), ε is a permittivity, σ is a conductivity, i is an imaginary unit, and δ is a gradient operator, μ 0 is a permeability in vacuum, and/>And/>Representing the gradient of epsilon c along the combined z-direction and xy-direction, respectively;
For the multichannel coil and a specific imaging body, an equation set can be obtained based on the formula (1), and the parameter distribution of complex dielectric constants epsilon c, m and n of the human body can be reconstructed;
Thirdly, intravenous injection of gadolinium contrast agent as contrast agent to human body, magnetic resonance enhancement scanning to obtain new amplitude and phase data, comprising: injecting paramagnetic nanoparticle contrast enhancer solution into human body, and scanning tumor part again by using the same imaging sequence as in the first step to obtain amplitude and phase data of alternating magnetic field; the obtained magnetic field data contains distribution information of magnetic permeability mu in human body;
Fourthly, substituting the human body conductivity and the dielectric constant obtained in the second step and the magnetic field data obtained in the third step into a human magnetic characteristic reconstruction algorithm to solve the magnetic permeability distribution of a human focus area after gadolinium contrast agent nano particles are dispersed, wherein the method comprises the following steps:
For magnetic resonance imaging scanning, the excited and detected radio frequency magnetic field is located in a plane perpendicular to the main magnetic field direction and is a rotating magnetic field; after magnetic resonance measurement is carried out to obtain magnetic field space distribution interacted with tissues by using a magnetic characteristic parameter distribution reconstruction algorithm, the space distribution of magnetic permeability is calculated according to ampere law and Faraday law inversion;
magnetic flux density of emitted magnetic field during scanning after injection of reinforcing agent The equation of relation with magnetic properties is:
wherein mu is the spatial distribution of magnetic permeability in human body after injection of the reinforcing agent, namely reconstruction parameters;
based on the formula (2), the magnetic flux density of the magnetic field Reconstructing magnetic permeability distribution mu; ω is the resonant angular frequency, x, y, z is the spatial position coordinates, ε c is the complex permittivity of the human body, ε c =ε -i (σ/ω), ε is the permittivity, σ is the conductivity, and i is the imaginary unit.
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