CN113156350B - Non-invasive light opaque micron-sized living tissue magnetic resonance tomography method and system - Google Patents

Non-invasive light opaque micron-sized living tissue magnetic resonance tomography method and system Download PDF

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CN113156350B
CN113156350B CN202110318850.6A CN202110318850A CN113156350B CN 113156350 B CN113156350 B CN 113156350B CN 202110318850 A CN202110318850 A CN 202110318850A CN 113156350 B CN113156350 B CN 113156350B
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辛学刚
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Abstract

A non-invasive light non-transparent micron-sized living tissue magnetic resonance tomography method is realized by controlling the following three conditions: A. applying a uniform unidirectional ultrahigh magnetic field main magnetic field to living biological tissues; B. on the basis of a main magnetic field, a superimposed gradient magnetic field with intensity gradient distribution of more than 10000mT/m is respectively adopted for X, Y, Z three directions, and elements with spin angular momentum are spatially encoded, so that the spin frequencies of the elements at different spatial positions are different; C. and (3) exciting the imaging object by adopting a radio frequency electromagnetic field vertical to the main magnetic field, picking up an energy level conversion radio frequency signal emitted by the imaging object after the excitation is cancelled, and reconstructing and decoding the radio frequency signal to obtain the tomography. The non-invasive in vivo tissue tomography with the spatial resolution up to 1 micron scale and the subcellular structure resolution capability can be realized.

Description

Non-invasive light opaque micron-sized living tissue magnetic resonance tomography method and system
Technical Field
The invention relates to the technical field of biomedical in-vivo imaging, in particular to a magnetic resonance tomography method and a magnetic resonance tomography system for non-invasive light opaque micron-sized in-vivo tissues.
Background
In the field of biomedical imaging, the main imaging techniques for biological tissues and/or cells are optical imaging, ultrasound imaging, X-ray imaging (including X-ray CT), nuclear medicine imaging, photoacoustic imaging, electromagnetic microwave imaging, magnetic resonance imaging, and the like.
Subcellular structures (i.e., intracellular organelles) can be observed using optical imaging techniques such as confocal laser imaging, but the object of observation must be a single isolated cell that has been detached from non-transparent tissue. For living biological tissues with opaque light, because light cannot penetrate through an imaging object, single cell imaging in the living biological tissues cannot be realized by adopting an optical imaging means, and in most cases, the living biological tissues have the characteristic of non-light transparency, for example, light cannot penetrate through bodies of mice and rats and cannot penetrate through human bodies.
Ultrasonic imaging, although having a certain penetrating power and being capable of penetrating tissues having a thickness of several tens of centimeters or more, cannot observe each single cell in a living tissue due to various limitations such as ultrasonic emission beams, ultrasonic probes, and the like. Ultrahigh frequency ultrasound imaging, which is currently being developed, can achieve a resolution lower than 1mm, but still cannot achieve living body imaging at a resolution level of 1 micron; and the penetration capacity of the ultrasonic tomography device is rapidly reduced along with the increase of the frequency, and at present, the ultrasonic tomography device cannot realize the tomography of the living tissues of rats and mice at the resolution level of 1 micron.
The existing X-ray CT technology can achieve a resolution of about 1mm, but cannot achieve a resolution of 1 micron. In addition, the soft tissue resolving power of X-rays is relatively poor, and tomographic imaging at a resolution level of 1 μm cannot be achieved for large and small mouse living tissues.
Nuclear medicine images have the advantage of higher sensitivity, but have poorer spatial resolution of imaging, lower than that of CT imaging, and far from that required by tomography with a resolution level of 1 micron.
The photoacoustic imaging uses light as an excitation source to excite tissues to generate ultrasonic waves, and imaging is realized by detecting the ultrasonic waves, and the resolution of the photoacoustic imaging does not substantially exceed that of ultrasonic imaging.
The electromagnetic microwave imaging has the advantage of no ionizing radiation, but the resolution is poor, often in the order of centimeters or even coarser, and a practical system with high resolution cannot be formed at present.
The magnetic resonance imaging has the advantages of strong penetrating power and high soft tissue imaging resolution, but the existing magnetic resonance imaging system cannot realize the tomography of 1 micron resolution level in vivo, and the minimum animal magnetic resonance imaging system with the highest resolution can reach 20 at most～The spatial resolution of 40um, the condition that a plurality of cells appear as a pixel point on the image can appear under this resolution.
In summary, no biomedical imaging technology means available today can achieve non-invasive tomographic imaging at the level of 1 micron resolution on the living body level, and the morphology and function of a single cell cannot be observed and measured non-invasively on the living body.
Therefore, it is necessary to provide a non-invasive optically opaque micron-sized magnetic resonance tomography method for living tissue to overcome the deficiencies of the prior art.
Disclosure of Invention
The invention aims to avoid the defects of the prior art and provides a non-invasive optical non-transparent micron-sized living body tissue magnetic resonance tomography method, which can realize the tomography of 1 micron-level resolution level on the living body tissue level in a non-invasive manner.
The object of the invention is achieved by the following technical measures.
The magnetic resonance tomography method of the non-invasive light opaque micron-sized living tissue is realized by controlling the following three conditions:
A. applying a uniform unidirectional ultrahigh-magnetic-field-strength main magnetic field to a living biological tissue serving as an imaging object;
B. on the basis of a main magnetic field, a gradient field is applied to a 1 micron scale imaging area according to an imaging standard with the imaging spatial resolution of 1 micron scale, and the method specifically comprises the following steps: for X, Y, Z three directions, respectively adopting a superposition gradient magnetic field with intensity gradient distribution of more than 10000mT/m to spatially encode elements with spin angular momentum, so that the spin frequencies of the elements at different spatial positions are different;
C. and (3) exciting the imaging object by adopting a radio frequency electromagnetic field vertical to the main magnetic field, picking up an energy level conversion radio frequency signal emitted by the imaging object after the excitation is cancelled, and reconstructing and decoding the radio frequency signal to obtain the tomography.
Preferably, in the above non-invasive light opaque micron-sized living tissue magnetic resonance tomography method, in a, the magnetic field strength of the main magnetic field is not less than 9.4 tesla.
Preferably, in the method for magnetic resonance tomography of non-invasive light-opaque micron-sized living tissue, in step B, a gradient field is applied according to an imaging standard with an imaging spatial resolution of 1 micron, specifically:
in the Z direction, narrowing the frequency-selecting bandwidth to be below 20KHz, and adopting a superimposed gradient magnetic field with the intensity of 10000mT/m to 50000mT/m to realize the Z-direction layer selection with the resolution of 1 micron-scale thickness;
in the X direction, a superposed gradient magnetic field with the strength of 20000mT/m to 50000mT/m and a receiving spectrometer with the frequency resolution of 0.8KHz to 3.0KHz are adopted to achieve the resolution of 1 micron-sized pixels in the X direction;
wherein the frequency resolution of the spectrometer satisfies the formula (1):
Δf＝γ*(GxΔ x) … … formula (1);
in the formula (1), Δ f is the frequency resolution of the spectrometer, γ is the gyromagnetic ratio, and GxThe gradient field intensity of the superimposed gradient magnetic field in the X direction, and deltax is the scale of reaching the pixel resolution in the X direction;
in the Y direction, a superimposed gradient magnetic field with the strength of 10000mT/m to 50000mT/m is adopted to control the gradient opening time in the Y direction, the step length is set to be 4.7us to 4.7 × 5us, and the phase coding of pixels with the resolution of 1 micron scale is realized;
wherein the gradient opening time in the Y direction satisfies formula (2):
Figure BDA0002992359840000031
in the formula (2), GyIs the gradient field strength of the superimposed gradient magnetic field in the Y direction, deltay is the scale for achieving pixel resolution in the Y direction, deltay is not more than 1 micron,
Figure BDA0002992359840000032
is the gradient on time in the Y direction.
Preferably, in the above magnetic resonance tomography method for non-invasive light opaque micron-sized living tissue, in B, a superimposed gradient magnetic field with an intensity of 20000mT/m is used in the X direction, and a receiving spectrometer with a frequency resolution of 852Hz is used to achieve a resolution of 1 micron pixel in the X direction.
Preferably, in the non-invasive light opaque micron-sized living tissue magnetic resonance tomography method, in the step B, a superimposed gradient magnetic field with the intensity of 50000mT/m is adopted in the X direction, and a receiving spectrometer with the frequency resolution of 2.5KHz is adopted to achieve the resolution of 1 micron-sized pixels in the X direction.
Preferably, in the above non-invasive light opaque micron-sized living tissue magnetic resonance tomography method, in B,
in the Y direction, a superimposed gradient magnetic field with the strength of 10000mT/m is adopted, the gradient opening time in the Y direction is controlled to be 2.35ms, and the step length is set to be 4.7 us; or
In the Y direction, a superimposed gradient magnetic field with the strength of 50000mT/m is adopted, the gradient opening time in the Y direction is controlled to be 2.35ms, and the step size is set to be 4.7 × 5 us.
Preferably, the non-invasive light opaque micron-sized living tissue magnetic resonance tomography method adopts an imaging region linkage tomography method for the whole imaging object, wherein the imaging region linkage tomography method is that the imaging region and the imaging resolution are adjusted in a variable state to perform tomography;
the tomography range is 10 +/-5 cm, and when the required imaging range is large, a Zoom out (Zoom out) mode is adopted for imaging; conversely, when the required imaging range is small, imaging is performed in Zoom in (magnification) mode; at least the selected interested area is used as a 1 micron scale imaging area, a gradient field is applied according to the standard of the 1 micron scale imaging area, the imaging spatial resolution of the interested area is 1 micron scale, and the upper limit value of the data size of a single tomographic image is controlled to be between 100kB and 100 MB.
Preferably, when the imaging range is large, imaging is performed by adopting a Zoom out mode, and an initial region of interest is obtained by using the imaging result of the Zoom out mode;
then judging whether the initial region of interest meets the 1 micron scale imaging condition, if so, carrying out 1 micron scale resolution tomography on the initial region of interest; if the sub-imaging area does not meet the 1 micron scale imaging condition, dividing the initial region of interest into a plurality of sub-imaging areas meeting the 1 micron scale imaging condition, and respectively carrying out 1 micron scale resolution tomography on the plurality of sub-imaging areas;
the 1 micron scale imaging conditions were: the upper limit value of the data size of a single tomographic image obtained by imaging with the image spatial resolution of 1 micron scale is between 100kB and 100 MB;
the tomography with the resolution of 1 micron is implemented by applying a gradient field according to the imaging standard with the imaging spatial resolution of 1 micron and imaging.
Preferably, the 1 micron scale refers to a resolution range of 0.1 micron to 2 microns.
Preferably, in the above non-invasive light opaque micron-sized living tissue magnetic resonance tomography method, the signal enhancement sequence used in condition C is: and adding a positive 90-degree radio frequency pulse before the next negative 90-degree radio frequency pulse to shorten the TR time, reduce the attenuation of the T2 signal and improve the signal-to-noise ratio.
Preferably, the non-invasive light opaque micron-sized living tissue magnetic resonance tomography method has a tomography range of 10 +/-2 cm.
The magnetic resonance tomography method of the non-invasive light opaque micron-sized living tissue is realized by controlling the following three conditions: A. applying a uniform and unidirectional main magnetic field with ultrahigh magnetic field intensity to living biological tissues; B. on the basis of a main magnetic field, a superimposed gradient magnetic field with intensity gradient distribution of more than 10000mT/m is respectively adopted for X, Y, Z three directions, and elements with spin angular momentum are spatially encoded, so that the spin frequencies of the elements at different spatial positions are different; C. and (3) exciting the imaging object by adopting a radio frequency electromagnetic field vertical to the main magnetic field, picking up an energy level conversion radio frequency signal emitted by the imaging object after the excitation is cancelled, and reconstructing and decoding the radio frequency signal to obtain the tomography. The invention can realize the tomography of 1 micron level resolution ratio level on the light-opaque living tissue layer surface in a non-invasive way, and can realize the non-invasive living tissue tomography with the spatial resolution ratio reaching 1 micron scale and the subcellular structure resolution capability. The technical problem that the existing biomedical imaging technical means can not realize the noninvasive realization of the tomography with the resolution of 1 micron level on the living tissue layer is solved.
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The invention is further illustrated by means of the attached drawings, the content of which is not in any way limiting.
FIG. 1 is a sequence diagram of a signal enhancement sequence of a non-invasive optical opaque micro-scale in vivo tissue magnetic resonance tomography method of the present invention.
Detailed Description
The invention is further illustrated by reference to the following examples.
Example 1.
A non-invasive light opaque micron-sized living tissue magnetic resonance tomography method is realized by controlling the following A, B, C conditions.
A. The magnetic field with uniform and unidirectional ultrahigh magnetic field intensity is applied to living biological tissues. It should be noted that the ultra-high magnetic field main magnetic field mentioned in the present invention refers to a main magnetic field with a magnetic field strength of not less than 9.4 tesla, such as 9.4T, 10.5T, 16T, etc. The implementation of the main ultra-high magnetic field strength field may be achieved by means of an associated magnetic resonance apparatus, which is well known in the art and will not be described further herein.
The micron-scale of the invention refers to the resolution of imaging about 1 micron, and specifically refers to the resolution range of 0.1 micron to 2 microns, such as 1 micron resolution or slightly less than 1 micron resolution. The elements of spin angular momentum contained in the living organism tissue include protons, phosphorus elements, sodium elements, and the like. The spin direction of an element having spin angular momentum contained in a living body biological tissue can be made uniform by using a main magnetic field having an ultrahigh magnetic field strength in a uniform single direction. When the biological tissue is under the action of a strong external magnetic field, the vector direction of the spin angular momentum of the element is consistent with the direction of the external magnetic field (or 180 degrees is opposite). The design of the A condition is a key for ensuring the realization of micrometer-scale resolution tomography.
B. On the basis of a main magnetic field, when a target region to be imaged needs to realize 1 micron-scale tomography (the target region is a 1 micron-scale imaging region), a gradient field is applied according to an imaging standard with the imaging spatial resolution of 1 micron scale, and the method comprises the following specific steps: for X, Y, Z, superimposed gradient magnetic fields with intensity gradient distribution of more than 10000mT/m are respectively adopted to spatially encode elements with spin angular momentum, so that the spin frequencies of the elements at different spatial positions are different.
The method specifically comprises the following steps: in the Z direction, the frequency-selecting bandwidth is narrowed to be less than 20KHz, and a superimposed gradient magnetic field with the strength of 10000mT/m to 50000mT/m is adopted to realize the Z-direction layer selection with the resolution of 1 micron-scale thickness.
In the X direction, according to the relation of the formula (1), a superimposed gradient magnetic field with the intensity of 20000mT/m to 50000mT/m is adopted, a receiving spectrometer with the frequency resolution of 0.8KHz to 3.0KHz is adopted, and the resolution of the pixel with the scale of 1 micron is achieved in the X direction;
wherein the frequency resolution of the spectrometer satisfies the formula (1):
Δf＝γ*(GxΔ x) … … formula (1);
in the formula (1), Δ f is the frequency resolution of the spectrometer, γ is the gyromagnetic ratio, and GxThe gradient field strength of the superimposed gradient magnetic field in the X direction, Δ X being the dimension at which the resolution of the pixel is achieved in the X direction.
For example, in the X direction, the gyromagnetic ratio of gamma to 42.6MHzT for hydrogen nuclei-1To achieve a resolution of 1 micron in pixels in the X-direction, for frequency encoding, in terms of gradient field strength GxGreater than 20000mT/m calculation, using gradient frequency coding rule to calculate, when the pixel is 1 micron, the frequency resolution of the corresponding spectrometer is:
Δf＝γ*(Gx*Δx)＝42.6×106HzT-1×20Tm-1×10-6the result is that if the frequency resolution of the receiving spectrometer can reach 852Hz (about 1KHz), the frequency coding with 1 micron pixel (X-direction imaging) can be realized, and the current spectrometer can completely reach the frequency resolution level; if the gradient field strength G continues to increasexAnd 50000mT/m, the frequency resolution requirement of the receiving spectrometer is lower, namely about 2.5 KHz.
It should be noted that, according to the relationship of the formula (1), the gradient field strength of the superimposed gradient magnetic field in the X direction and the frequency resolution of the spectrometer are regulated and controlled, and the 1 micron-scale spatial resolution imaging can be realized. The method of the present invention is suitable for not only hydrogen nuclei but also other elements having spin characteristics suitable for magnetic resonance.
In the Y direction, according to the relation of formula (2), a superimposed gradient magnetic field with the strength of 10000mT/m to 50000mT/m is adopted, the opening time of the gradient in the Y direction is controlled, the step length is set to be 4.7us to 4.7 x 5us, and the phase encoding of pixels with the resolution of 1 micrometer scale is realized;
wherein the gradient opening time in the Y direction satisfies formula (2):
Figure BDA0002992359840000071
in the formula (2), GyIs the gradient field strength of the superimposed gradient magnetic field in the Y direction, deltay is the scale for achieving pixel resolution in the Y direction, deltay is not more than 1 micron,
Figure BDA0002992359840000072
is the gradient on time in the Y direction.
For example, in the Y direction, also for hydrogen nuclei, the gyromagnetic ratio γ is 42.6mhz t-1The gradient field intensity Gy in the Y direction is calculated according to 10000mT/m, and within the range that the linear length r in the Y direction of the imaging area is 1mm,
Figure BDA0002992359840000073
is the gradient on duration in the y direction, also requiring the resolution of the imaging to be 1um, then it needs to satisfy:
Figure BDA0002992359840000074
namely:
Figure BDA0002992359840000075
meaning that the phase encoding needs of pixels with a resolution of 1um can be achieved by controlling the gradient on-time to only 2.35ms, and the step size can be set to 4.7 us. The gradient strength in the y direction is generally between 10000mT/m and 50000 mT/m. If G is increasedyTo 50000mT/m, the step size requirement can be relaxed accordingly, so that the step size is 4.7us 5.
It should be noted that, according to the relationship of the formula (2), the gradient field strength, the gradient opening time, and the step length of the superimposed gradient magnetic field in the Y direction are regulated and controlled, and the 1 micron-scale spatial resolution imaging can be realized. The method of the present invention is suitable for not only hydrogen nuclei but also other elements having spin characteristics suitable for magnetic resonance.
C. Adopting a radio frequency electromagnetic field vertical to a main magnetic field to excite the imaging object by the radio frequency electromagnetic field, picking up an energy level conversion radio frequency signal emitted by the imaging object after excitation cancellation, and reconstructing and decoding the radio frequency signal to obtain tomography; the range of tomography is 10 + -5 cm, the preferred range is 10 + -2 cm, and the imaging spatial resolution of the region of interest is 1 micrometer scale.
The radio frequency electromagnetic field adopts a design mode of transmitting and receiving, and the specific winding can adopt a 8-channel or 16-channel cage structure, a columnar coil partially overlapped surrounding covering structure and the like to cover the whole imaging object.
And aiming at the whole imaging object, adopting an imaging region linkage deformation tomography method. The imaging region linkage change tomography method is that the imaging region and the imaging resolution ratio are adjusted in a linkage change state to carry out tomography. Namely, the imaging area and the imaging resolution are dynamically adjusted, and the upper limit value for controlling the data size of a single tomographic image is between 100kB and 100 MB.
When the required imaging range is large, Zoom out (Zoom out) mode imaging is adopted; conversely, when the required imaging range is small, imaging is performed in Zoom in (magnification) mode; at least the selected interested area is used as a 1 micron scale imaging area and a gradient field is applied according to the standard of the 1 micron scale imaging area, the imaging space resolution of the interested area is 1 micron scale, and the upper limit value of the data size of a single tomographic image is controlled to be between 100kB and 100 MB.
This method is proposed for the first time by the applicant, and the most essential characteristics thereof are as follows: the imaging area and the imaging resolution are jointly changed, the size of the image data of the formed tomography is controlled within a required range. Specifically, when the required imaging range is large, a gradient coil and a current control and driving mode corresponding to a Zoom out mode (reduction mode) are adopted; conversely, when the required imaging range is small, the gradient coils corresponding to the Zoom in mode (magnification mode) and the current control and drive mode are used. The Zoom out mode may provide localization assistance for the Zoom in mode, and the gradient field strength in the Zoom out mode is less than the gradient field strength corresponding to the Zoom in mode. In the innovative tomography mode, different parameter combinations are set to match with different imaging areas (FOVs) and imaging resolution requirements, and the set rules are as follows: controlling the data of each tomographic image within the set size range of the image data; the data size of a single tomographic image is generally set to be 100kB to 100 MB. For example, if the imaging FOV is set to 5cm by 5cm, which is the case if the imaging reconstruction with a horizontal resolution of 1um by 1um is performed directly over the entire FOV, the pixel size of each tomographic image will reach 2500MB, which is obviously not suitable. Therefore, by controlling gradient change, a large FOV is segmented into a small FOV, and the process similar to the process of 'imaging region linkage fault' is realized, so that the reasonable collocation of the pixel size of the reconstructed image and the resolution requirement is realized.
The imaging method of the invention takes account of the problem of calculated amount. For a specific imaging target, if the data of a single tomographic image is too large, the image operation processing amount performed by the computer is increased in geometric level, so that the method of the scheme cannot be effectively realized. The invention designs an imaging region linkage change tomography method, which dynamically adjusts an imaging region and corresponding resolution ratio according to the actual condition of an imaging range so as to reduce the operation amount of pictures. For a smaller imaging range, a magnification mode imaging is adopted, and then a related gradient field can be set, and a tomography image realizing 1 micron scale resolution can be realized. When the imaging range is large, the tomography of the whole 1 micron scale resolution ratio is avoided from being carried out on the whole range, but the interested region is selected, the tomography of the 1 micron scale resolution ratio is only carried out on the interested region, and the tomography of the larger scale resolution ratio can be carried out on the non-interested region. And the selection of the region of interest can provide a region of interest positioning reference function by utilizing Zoom out mode imaging.
The following lists a process of setting the region of interest and imaging when the imaging range is large: when the imaging range is large, imaging in a Zoom out mode is adopted, and an initial region of interest is obtained by using the imaging result of the Zoom out mode;
then judging whether the initial region of interest meets the 1 micron scale imaging condition, if so, carrying out 1 micron scale resolution tomography on the initial region of interest; if the sub-imaging area does not meet the 1 micron scale imaging condition, dividing the initial region of interest into a plurality of sub-imaging areas meeting the 1 micron scale imaging condition, and respectively carrying out 1 micron scale resolution tomography on the plurality of sub-imaging areas;
wherein, the 1 micron scale imaging conditions are: the upper limit value of the data size of a single tomographic image obtained by imaging with the image space resolution of 1 micron is between 100kB and 100 MB;
the tomography with the resolution of 1 micron is implemented by applying a gradient field according to the imaging standard with the imaging spatial resolution of 1 micron and imaging.
It should be noted that the size of the imaging range can be flexibly set according to actual needs. The method of the invention is generally suitable for imaging in the range of 10 + -5 cm. The boundary between the large imaging range and the small imaging range can be flexibly set according to actual requirements. As in some cases, a case where the imaging range is small may be set in which the imaging range is 5cm or less, and a case where the imaging range is greater than 5cm may be regarded as a case where the imaging range is large.
In the aspect of the implementation method of the imaging technology, besides a conventional mode, the invention also improves the signal-to-noise ratio of imaging by adopting an acquisition sequence with high signal-to-noise ratio. On the premise of meeting the resolution requirement, the scanning time of the sequence is considered. The signal enhancing sequences employed in condition C are: the positive 90-degree radio frequency pulse is added before the next negative 90-degree radio frequency pulse to shorten the TR time, reduce the attenuation of the T2 signal and improve the signal-to-noise ratio. The timing diagram of the signal enhancement sequence of the invention is shown in fig. 1, Slice refers to layer thickness, phase refers to phase encoding, read refers to readout gradient, RF radio frequency pulse, TE echo time, and TR refers to repetition time. According to the sequence, the TR time can be greatly shortened by adding a 90-degree Radio Frequency (RF) pulse (combination: minus 90 degrees + plus 90 degrees) before the next 90-degree RF pulse, the attenuation of a T2 signal is reduced, the signal-to-noise ratio is improved, the signal-to-noise ratio is ensured, and the imaging speed is also improved.
For biological living tissue or organs which are not transparent to light, the current biomedical imaging technical means cannot realize the tomography of 1 micron resolution level on the living tissue level in a non-invasive way. The specific reasons for the above-mentioned disadvantages are: in order to be able to achieve non-invasive tomographic imaging at the level of 1 micron resolution at the level of the living body, the following three requirements must be technically met at the same time: (1) the key media of imaging (such as light, X-ray, ultrasound, electromagnetic wave, etc.) requires non-invasive, light-penetrating, opaque living tissue; (2) the spatial resolution reaches the scale of 1 micron or less than 1 micron; (3) corresponding information is simultaneously obtained for all imaged individual elements within the imaged area at a resolution level on the scale of 1 micron or less than 1 micron. By means of all the existing technical means, the technical requirements of the three aspects cannot be met simultaneously, so that the existing biomedical imaging technical means cannot realize the tomography of 1 micron resolution level on the living tissue level in a non-invasive manner.
The non-invasive light opaque micron-sized living body tissue magnetic resonance tomography method is designed under three conditions of A, B, C. The tomography of 1 micron level resolution ratio level can be achieved noninvasively on the light-opaque living body tissue layer, and the noninvasive living body tissue tomography with the spatial resolution ratio reaching 1 micron scale and with the subcellular structure resolution capability can be achieved. The technical problem that the existing biomedical imaging technical means can not realize the noninvasive realization of the tomography with the resolution of 1 micron level on the living tissue layer is solved.
Example 2.
The non-invasive light opaque micron-sized living body tissue magnetic resonance tomography method of the invention is used for carrying out 1 micron or less than 1 micron scale ultrahigh resolution tomography which contains the structure and the function of all single cells in an imaging region on an opaque living body organism, namely oogenesis biological fertilized egg.
According to the design technical method, a high magnetic field intensity such as 16T static magnetic field is selected, on the basis of the static magnetic field, a strong gradient magnetic field in X, Y and Z directions is applied, the gradient field intensity is in the Z direction, a superimposed gradient magnetic field with the intensity of more than 10000mT/m is adopted, and the Z direction layer selection with the resolution of 1 micron can be achieved by narrowing the frequency selection bandwidth to be 20KHz or less;
the gradient field intensity is in the X direction, a superimposed gradient magnetic field with the intensity of more than 20000mT/m is adopted, the frequency resolution of a receiving spectrometer can reach 852Hz (about 1KHz), and the resolution in the X direction with the resolution of 1 micron can be achieved;
in the Y direction, the gradient field intensity adopts a superposed gradient magnetic field with the intensity of more than 10000mT/m, the opening time of the gradient is controlled to be 2.35ms, and the step length is set to be 4.7us, so that the phase coding of the pixel with the resolution of 1um can be realized.
The imaging method of 'imaging region linkage variation fault' is adopted, the acquisition sequence with high signal-to-noise ratio is adopted to improve the signal-to-noise ratio of imaging, the imaging region and the imaging resolution ratio are linked and varied, and the size of image data of the formed fault imaging is controlled within a required range, generally within 100 MB.
The invention realizes the non-invasive tomographic imaging technology which can perform the steps of generating oosperm in an optically opaque living organism, performing the ultra-high resolution on the scale of 1 micron or less than 1 micron, and containing the structures and the functions of all single cells in an imaging area through a series of innovative technical means and combinations.
It should be noted that the method of the present invention can non-invasively realize high resolution imaging of 1 micron scale for light-opaque living bodies such as mice, fruit flies, oosperm, etc.
Example 3.
The condition of brain cells of a white mouse needs to be observed, and the brain of one white mouse is subjected to 1 micron-scale tomography. The head size of the mice was approximately 3cm by 3 cm.
The thickness of the longitudinal fault is 1 micron, the XY plane imaging range is 3cm by 3cm, the 1 micron spatial resolution imaging is also carried out, and the upper limit value of the data size of a single fault image is in the range of 100kB-100 MB.
A high magnetic field intensity 10.5T static magnetic field is selected, on the basis of the static magnetic field, strong gradient magnetic fields in the X direction, the Y direction and the Z direction are applied, the gradient field intensity is in the Z direction, a superposed gradient magnetic field with the intensity of more than 10000mT/m is adopted, the frequency-selecting bandwidth is narrowed to 20KHz, and the Z direction layer selection of the thickness with the resolution of 1 micron is achieved.
The gradient field intensity is in the X direction, the superimposed gradient magnetic field with the intensity of more than 20000mT/m is adopted, the frequency resolution of the receiving spectrometer is 1KHz, and the resolution in the X direction with the resolution of 1 micron is achieved.
In the Y direction, the gradient field intensity adopts a superposed gradient magnetic field with the intensity of more than 30000mT/m, the opening time of the gradient is controlled to be 2.35ms, and the step length is set to be 4.7 × 3us, so that the phase coding of the pixel with the resolution of 1um can be realized.
And (3) exciting the imaging object by adopting a radio frequency electromagnetic field vertical to the main magnetic field, picking up an energy level conversion radio frequency signal emitted by the imaging object after the excitation is cancelled, and reconstructing and decoding the radio frequency signal to obtain the tomography. Because the upper limit value of the data size of a single tomographic image is in the range of 100kB-100MB, the calculation amount is small, and micron-scale imaging can be realized.
In the aspect of the implementation method of the imaging technology, besides the conventional practice, the invention also improves the signal-to-noise ratio of the imaging by adopting the acquisition sequence with high signal-to-noise ratio. On the premise of meeting the resolution requirement, the scanning time of the sequence is considered. The signal enhancing sequences employed in condition C are: the positive 90-degree radio frequency pulse is added before the next negative 90-degree radio frequency pulse to shorten the TR time, reduce the attenuation of the T2 signal and improve the signal-to-noise ratio. The timing diagram of the signal enhancement sequence of the present invention is shown in fig. 1. The sequence can greatly shorten TR time, reduce attenuation of T2 signals and improve signal-to-noise ratio by adding 90-degree Radio Frequency (RF) pulses (combination: minus 90 degrees + plus 90 degrees) before the next 90-degree RF pulses, thereby ensuring the signal-to-noise ratio and improving the imaging speed.
The method of the invention can carry out micron-scale imaging on the living body object in a non-traumatic state. Can observe and analyze the cell structure of the living tissue on the basis of cell level, and provides an advanced analysis means for cell research.
Example 4.
The observation and study of the somatic condition of a large object is needed, and the part of the object to be measured, such as the hand, is small in size, and some parts are large in size, such as the chest.
One of the smaller dimension sites to be observed is approximately 2cm by 1cm in size and one of the larger dimension sites to be observed is approximately 20cm by 20 cm.
And imaging a part with a smaller size, wherein the thickness of a longitudinal fault can be controlled to be 1 micrometer, the XY plane imaging range is 2cm by 2cm, 1 micrometer spatial resolution imaging is also carried out, and the upper limit value of the data size of a single fault image is within the range of 100kB-100 MB.
For a larger part, the thickness of a longitudinal fault can be controlled to be 1 micrometer, the XY plane imaging range is 20cm by 20cm, the data size of a single fault image reaches 40000MB, the data volume of the fault image is huge, and the imaging result cannot be effectively obtained. Therefore, for a larger part, an interested area is searched as a 1 micron-scale imaging area through the imaging area linkage tomography method, a gradient field is applied according to the standard of the 1 micron-scale imaging area, the imaging spatial resolution of the interested area is 1 micron scale, and the upper limit value of the data size of a single tomography image is controlled to be between 100kB and 100 MB.
And in the process of finding the region of interest, a Zoom out mode imaging is utilized to provide a region of interest positioning reference function. Imaging an imaging range in a Zoom out mode, and obtaining an initial region of interest by using an imaging result of the Zoom out mode;
then judging whether the initial region of interest meets the 1 micron scale imaging condition, if so, carrying out 1 micron scale resolution tomography on the initial region of interest; and if the initial region of interest does not meet the requirements, dividing the initial region of interest into a plurality of sub-imaging regions meeting the 1 micron scale imaging conditions, and performing 1 micron scale resolution tomography on the plurality of sub-imaging regions respectively.
It should be noted that, two examples are taken here to illustrate that the imaging range is not passed, and for different positions of an actual imaging object, according to the imaging region linkage tomography method of the present invention, an imaging region and a spatial resolution are dynamically linked, and a correspondingly applied gradient field is adjusted, so as to realize at least 1 micrometer scale imaging on an interested region; the non-interested region can be imaged by selecting the 1 micron scale, and an imaging mode with larger resolution can also be adopted.
In terms of the implementation method of the imaging technology, besides the conventional method, the invention also improves the signal-to-noise ratio of the imaging by adopting the acquisition sequence with high signal-to-noise ratio. On the premise of meeting the resolution requirement, the scanning time of the sequence is considered. The signal enhancing sequences employed in condition C are: the positive 90-degree radio frequency pulse is added before the next negative 90-degree radio frequency pulse to shorten the TR time, reduce the attenuation of the T2 signal and improve the signal-to-noise ratio. The timing diagram of the signal enhancement sequence of the present invention is shown in fig. 1. The sequence can greatly shorten TR time, reduce attenuation of T2 signals and improve signal-to-noise ratio by adding 90-degree Radio Frequency (RF) pulses (combination: minus 90 degrees + plus 90 degrees) before the next 90-degree RF pulses, thereby ensuring the signal-to-noise ratio and improving the imaging speed.
The embodiment can realize the tomography of 1 micron-level resolution ratio on the light-opaque living tissue layer surface in a non-invasive way, and can realize the non-invasive living tissue tomography with the spatial resolution ratio reaching 1 micron scale and the subcellular structure resolution capability.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims (7)

1. A non-invasive light non-transparent micron-sized living tissue magnetic resonance tomography method is characterized in that the method is realized by controlling the following three conditions:
A. applying a uniform unidirectional ultrahigh-magnetic-field-strength main magnetic field to a living biological tissue serving as an imaging object;
B. on the basis of a main magnetic field, a gradient field is applied to a 1 micron scale imaging area according to an imaging standard with the imaging spatial resolution of 1 micron scale, and the method specifically comprises the following steps: for X, Y, Z three directions, respectively adopting a superposition gradient magnetic field with intensity gradient distribution of more than 10000mT/m to spatially encode elements with spin angular momentum, so that the spin frequencies of the elements at different spatial positions are different;
C. adopting a radio frequency electromagnetic field vertical to a main magnetic field to excite the imaging object by the radio frequency electromagnetic field, picking up an energy level conversion radio frequency signal emitted by the imaging object after excitation cancellation, and reconstructing and decoding the radio frequency signal to obtain tomography;
in A, the magnetic field intensity of the main magnetic field is not lower than 9.4 Tesla;
in B, applying a gradient field according to an imaging standard with an imaging spatial resolution of 1 micron scale, specifically:
in the Z direction, narrowing the frequency-selecting bandwidth to be below 20KHz, and adopting a superimposed gradient magnetic field with the intensity of 10000mT/m to 50000mT/m to realize the Z-direction layer selection with the resolution of 1 micron-scale thickness;
in the X direction, according to the relation of the formula (1), a superimposed gradient magnetic field with the intensity of 20000mT/m to 50000mT/m is adopted, a receiving spectrometer with the frequency resolution of 0.8KHz to 3.0KHz is adopted, and the resolution of the pixel with the scale of 1 micron is achieved in the X direction;
wherein the frequency resolution of the spectrometer satisfies the formula (1):
Δf＝γ*(GxΔ x) … … formula (1);
in the formula (1), delta f is the frequency resolution of the spectrometer, gamma is the gyromagnetic ratio, and GxThe gradient field intensity of the superimposed gradient magnetic field in the X direction, and deltax is the scale of reaching the pixel resolution in the X direction;
in the Y direction, according to the relation of formula (2), a superimposed gradient magnetic field with the strength of 10000mT/m to 50000mT/m is adopted, the opening time of the gradient in the Y direction is controlled, the step length is set to be 4.7us to 4.7 x 5us, and the phase encoding of pixels with the resolution of 1 micrometer scale is realized;
wherein the gradient opening time in the Y direction satisfies formula (2):
Figure FDA0003590652600000021
in the formula (2), GyIs the gradient field strength of the superimposed gradient magnetic field in the Y direction, deltay is the dimension reaching the resolution of the pixel in the Y direction, deltay is not more than 1 micron,
Figure FDA0003590652600000022
is the gradient on time in the Y direction.
2. The non-invasive optical opaque micro-scale in vivo tissue magnetic resonance tomography method of claim 1, wherein: in B, in the X direction, a superimposed gradient magnetic field with the strength of 20000mT/m and a receiving spectrometer with the frequency resolution of 852Hz are adopted, and the resolution of 1 micron pixel is achieved in the X direction.
3. The non-invasive optically opaque micron-sized in vivo tissue magnetic resonance tomography method of claim 1, wherein: in the step B, a superposed gradient magnetic field with the strength of 50000mT/m and a receiving spectrometer with the frequency resolution of 2.5KHz are adopted in the X direction, and the resolution of pixels with the size of 1 micron is achieved in the X direction.
4. The non-invasive optically opaque micro-scale in vivo tissue magnetic resonance tomography method of any one of claims 1 to 3, wherein: in the step (B), the first step is carried out,
in the Y direction, a superimposed gradient magnetic field with the strength of 10000mT/m is adopted, the gradient opening time in the Y direction is controlled to be 2.35ms, and the step length is set to be 4.7 us; or
In the Y direction, a superimposed gradient magnetic field with the strength of 50000mT/m is adopted, the gradient opening time in the Y direction is controlled to be 2.35ms, and the step size is set to be 4.7 × 5 us.
5. The non-invasive optically opaque micron-sized living tissue magnetic resonance tomography method as claimed in any one of claims 1 to 3, wherein: aiming at the whole imaging object, an imaging region linkage tomography method is adopted, wherein the imaging region linkage tomography method is used for carrying out tomography by adjusting the imaging region and the imaging resolution in a linkage changing state;
when the required imaging range is large, imaging in a Zoom out mode is adopted; on the contrary, when the required imaging range is small, imaging is carried out by adopting a Zoom in mode; at least the selected interested area is used as a 1 micron scale imaging area, a gradient field is applied according to the standard of the 1 micron scale imaging area, the imaging spatial resolution of the interested area is 1 micron scale, and the upper limit value of the data size of a single tomographic image is controlled to be between 100kB and 100 MB.
6. The non-invasive optically opaque micron-sized in vivo tissue magnetic resonance tomography method of claim 5, wherein:
when the imaging range is large, imaging by adopting a Zoom out mode, and obtaining an initial region of interest by utilizing the imaging result of the Zoom out mode;
then judging whether the initial region of interest meets the 1 micron scale imaging condition, if so, carrying out 1 micron scale resolution tomography on the initial region of interest; if the sub-imaging area does not meet the 1 micron scale imaging condition, dividing the initial region of interest into a plurality of sub-imaging areas meeting the 1 micron scale imaging condition, and respectively carrying out 1 micron scale resolution tomography on the plurality of sub-imaging areas;
the 1 micron scale imaging conditions were: the upper limit value of the data size of a single tomographic image obtained by imaging with the image spatial resolution of 1 micron scale is between 100kB and 100 MB;
the tomography with the resolution of 1 micron is implemented by applying a gradient field according to the imaging standard with the imaging spatial resolution of 1 micron and imaging.
7. The non-invasive optically opaque micron-sized in vivo tissue magnetic resonance tomography method of claim 5, wherein: the 1 micron scale refers to the 0.1 micron to 2 micron resolution range.
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