Small animal sciatic nerve magnetic resonance coil and imaging method

Abstract

The application provides a small animal sciatic nerve magnetic resonance coil and an imaging method, and the method comprises the following steps: filling a high-concentration sugar syrup solution at the bottom of the magnetic resonance coil and performing constant temperature control; placing a small animal in a prone position in the high-concentration sugar syrup solution and discharging air in the gap between the lower limbs and below the abdomen of the small animal; after performing magnetic resonance positioning scanning to determine the main sequence scanning range, starting the main sequence scanning, suppressing the flow tissue signal through a pre-pulse combination, exciting the tissue by using a radio frequency pulse with preset parameters, acquiring echo signals by combining a fast spin echo technology and filling K space, and obtaining scanning original data; performing preprocessing on the scanning original data and accurate segmentation of the sciatic nerve and spinal nerve to obtain a segmentation result; and completing three-dimensional model reconstruction, optimization and multi-modal fusion visualization based on the segmentation result to obtain an image scanning result. The application is suitable for small animals, is accurate in imaging, can effectively suppress various kinds of artifacts, and can be widely applied to sciatic nerve imaging scenarios of small animals.

Description

Technical Field

[0001] This invention relates to the field of magnetic resonance imaging technology, and in particular to a magnetic resonance coil for the sciatic nerve of a small animal and an imaging method thereof. Background Technology

[0002] The sciatic nerve is a relatively large mixed peripheral nerve in the body, mainly responsible for motor control and sensory conduction. The integrity of its structure and function is an important anatomical and functional basis for evaluating the degree of nerve damage and the effect of repair. Especially in the study of spinal and nerve root injury models, it can directly reflect whether there is damage such as compression, contusion or rupture of the lumbosacral spinal nerve root.

[0003] Similar to the needs of human clinical diagnosis and treatment, small animals also have a practical need for sciatic nerve imaging, whether for basic medical experimental research (such as the construction and evaluation of rat nerve injury models) or for application in pet clinical diagnosis and treatment. Magnetic resonance imaging (MRI) technology is currently the core method for sciatic nerve imaging, but its imaging effect is affected by a variety of factors such as coil design, scanning parameters, and artifact suppression.

[0004] However, currently, there is no magnetic resonance imaging coil or corresponding imaging method specifically designed for sciatic nerve imaging in small animals. Conventional magnetic resonance coils and imaging schemes are mainly designed for humans or large animals, and cannot be adapted to the body characteristics of small animals (such as rats). They also cannot solve problems such as magnetic susceptibility artifacts, tissue signal interference, and hypothermia that occur during small animal scanning, resulting in poor image quality, inability to clearly delineate the sciatic nerve structure, and difficulty in meeting the needs of experimental research and clinical diagnosis for precise sciatic nerve imaging. Summary of the Invention

[0005] Therefore, it is necessary to provide a magnetic resonance coil and imaging method for the sciatic nerve in small animals to address the above-mentioned technical problems.

[0006] A method for magnetic resonance imaging of the sciatic nerve in small animals includes the following steps:

[0007] A high-concentration syrup solution was used to fill the bottom of the magnetic resonance coil, and the magnetic resonance coil was subjected to constant temperature control.

[0008] The anesthetized small animal to be tested was placed prone on the high-concentration syrup solution, and the air in the lower abdomen and between the two lower limbs of the small animal to be tested was expelled.

[0009] After determining the main sequence scanning range by performing magnetic resonance localization scanning on the small animal to be tested, the main sequence scanning is started. The flow tissue signal is suppressed by pre-pulse combination, the tissue is excited by radio frequency pulses with preset parameters, and the echo signal is collected and filled with K space by combining fast spin echo technology to obtain the original scan data.

[0010] The raw scan data is preprocessed and the sciatic nerve and spinal nerve are precisely segmented to obtain the segmentation results;

[0011] Based on the segmentation results, the 3D model is reconstructed, optimized, and visualized using multimodal fusion to obtain the image scanning results.

[0012] In one embodiment, the components and mass percentages of the high-concentration syrup solution are: fructose 40%-50%, glucose 20%-40%, and water 10%-25%;

[0013] The high-concentration syrup solution has a freezing point of -5℃ to -10℃, and is a clear, transparent, and homogeneous liquid above 37℃.

[0014] In one embodiment, the prepulse combination is a combination of multiple 90°, 180°, and -90° radio frequency pulses, and gradients of the same magnitude but opposite polarity are applied on both sides of the 180° pulse; the prepulse combination is applied in the head-to-foot direction, left-right direction, and front-back direction, respectively.

[0015] In one embodiment, the radio frequency pulse with preset parameters is a 180° radio frequency pulse with a bandwidth of not less than 2500Hz, which reverses the longitudinal magnetization vector of the tissue to the opposite direction to the main magnetic field.

[0016] In one embodiment, the acceleration factor of the fast spin echo technology is set to 5-15 in 2D scanning mode and 30-50 in 3D scanning mode; the K space is filled linearly to fill the center of the K space with the intermediate echo signal, and the arrival time of the intermediate echo is set to 90ms-170ms; the interval between two adjacent excitations is set to 2200ms-5000ms.

[0017] In one embodiment, it further includes:

[0018] When acquiring echo signals, a gradient-adjusted focusing pulse is used. Initially, a small-angle focusing pulse is used, and as the tissue relaxes laterally, the focusing pulse angle is gradually increased to 180°.

[0019] In one embodiment, preprocessing includes image rearrangement, contrast enhancement, and noise suppression;

[0020] The contrast enhancement employs a neural optimal window width and window level algorithm to calculate the optimal window level and optimal window width and perform grayscale linear mapping.

[0021] The noise suppression employs nonlocal mean filtering combined with edge protection constraints.

[0022] In one embodiment, the precise segmentation of the sciatic nerve and spinal nerve employs a three-level progressive segmentation strategy, including:

[0023] Global threshold initial screening: Set the grayscale threshold range to 70GV-800GV to extract high signal regions;

[0024] Based on the high-signal region, seed points are set at the spinal nerve root exit and the intervertebral foramen area, and region growth is performed according to gray-level similarity and spatial connectivity criteria to obtain the grown region.

[0025] The manual editing signal is received, the key layers of the growth region are contoured, and the surface jaggedness is eliminated through smoothing to obtain the segmentation result.

[0026] In one embodiment, the 3D model optimization includes: micropore closure, internal cavity filling, mesh optimization and resampling, and independent entity output;

[0027] The multimodal fusion visualization includes: surface reconstruction, maximum intensity projection and stereo rendering, to achieve continuous display of the sciatic nerve throughout its entire course, verification of segmentation accuracy and three-dimensional stereoscopic display.

[0028] A magnetic resonance coil for sciatic nerve in small animals includes a main body of the coil. The bottom of the main body of the coil is provided with a filling cavity for containing a high-concentration syrup solution. The filling cavity is equipped with a heating device, either internally or externally, for maintaining the temperature of the syrup solution and the body temperature of the small animal to be tested. The main body of the coil is used in conjunction with a magnetic resonance imaging system to perform a magnetic resonance imaging method for sciatic nerve in small animals as described above.

[0029] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: the present invention is adapted to the body size of small animals, the imaging is accurate and clear, it can effectively suppress various artifacts, it is easy to operate, and it can be widely used in sciatic nerve imaging scenarios of small animals such as laboratory rats. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating a method for magnetic resonance imaging of the sciatic nerve in a small animal, as described in one embodiment.

[0031] Figure 2 This is a schematic diagram of the radio frequency pre-pulse combination sequence before the main sequence is started in one embodiment;

[0032] Figure 3 This is a comparison diagram of conventional 90° RF pulse excitation and ultra-high bandwidth 180° RF pulse excitation in one embodiment;

[0033] Figure 4 This is a schematic diagram of the 180° focused pulse master sequence in one embodiment;

[0034] Figure 5 This is a schematic diagram of the main sequence for adjusting the focus pulse angle in one embodiment;

[0035] Figure 6 This is a comparison chart showing the results of applying a conventional standard gradient field and applying a bipolar gradient field of equal magnitude but opposite direction in one embodiment;

[0036] Figure 7 This is a schematic diagram illustrating the import of a dicom metafile in one embodiment;

[0037] Figure 8 This is a schematic diagram illustrating the application of a nonlocal mean filtering formula to reduce background noise in one embodiment.

[0038] Figure 9 This is a schematic diagram illustrating the application of a global threshold mask in one embodiment;

[0039] Figure 10 This is a schematic diagram of the output MASK1 mask after the seed point 26-neighborhood region is grown in one embodiment;

[0040] Figure 11 This is a schematic diagram of obtaining the final segmentation mask in one embodiment;

[0041] Figure 12 This is a schematic diagram of a three-dimensional neural model after applying micropore closure and internal cavity filling in one embodiment;

[0042] Figure 13 This is a schematic diagram of the surface reconstruction of the full-length sciatic nerve path in one embodiment;

[0043] Figure 14 A VR rendering schematic diagram of the sciatic nerve of a rat in one embodiment;

[0044] Figure 15 This is a schematic diagram of the maximum intensity projection (MIP) of the sciatic nerve in a rat in one embodiment of the prior art;

[0045] Figure 16 This is a VR rendering of a 3D stereoscopic image of the sciatic nerve of a rat in one embodiment of the prior art. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0047] It should be noted that, unless otherwise defined, the technical or scientific terms used in one or more embodiments of this specification should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in one or more embodiments of this specification do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word covers the element or object listed following the word and its equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0048] For ease of understanding, the terms used in the embodiments of this invention are explained below:

[0049] Magnetic susceptibility artifacts: In magnetic resonance imaging, the difference in magnetic susceptibility between tissue and the surrounding medium (such as air) leads to local magnetic field inhomogeneity, resulting in image distortion and signal abnormalities. In this invention, the air gaps are filled with a high-concentration syrup solution, which can effectively suppress this type of artifact.

[0050] Longitudinal magnetization vector: refers to the magnetization vector formed by protons in the tissue aligning along the direction of the main magnetic field under the influence of the main magnetic field. The changes in its direction and intensity are the core principle of magnetic resonance imaging. Radio frequency pulses can change its direction and intensity.

[0051] Lateral relaxation: refers to the process by which the transverse magnetization vector gradually decays and disappears after being excited by a radio frequency pulse. It is represented by the transverse relaxation time (T2). The transverse relaxation time is different for different tissues and is an important basis for image comparison.

[0052] Longitudinal relaxation: refers to the process by which the longitudinal magnetization vector gradually recovers from the direction deviating from the main magnetic field to its initial state after the radio frequency pulse stops. It is represented by the longitudinal relaxation time (T1) and affects the image signal intensity and contrast.

[0053] Gray-scale threshold: In image segmentation, the gray-scale threshold used to distinguish target regions (such as the sciatic nerve) from background regions.

[0054] Region growing: An image segmentation algorithm that uses a preset seed point as the center and gradually expands the growing region based on criteria such as gray-level similarity and spatial connectivity to finally obtain a complete segmented region of the target tissue (sciatic nerve, spinal nerve).

[0055] Voxel: The basic unit of a three-dimensional magnetic resonance image, corresponding to a tiny volume element in three-dimensional space. Its gray value reflects the magnetic resonance signal intensity of the tissue within that volume element. The accuracy of voxels directly affects the accuracy of imaging and segmentation.

[0056] Multimodal fusion visualization: Information from different imaging methods (such as original MRI images and 3D reconstruction models) is registered and superimposed, and through various post-processing methods (surface reconstruction, stereo rendering, etc.), the target tissue (sciatic nerve) is displayed clearly and intuitively from multiple angles.

[0057] Off-resonance effect: refers to the phenomenon that the resonant frequency of protons in the tissue deviates from the frequency of the radio frequency pulse applied by the magnetic resonance system, resulting in insufficient signal excitation or signal attenuation. Different types of refocusing pulses have different sensitivities to this effect.

[0058] MRI: Magnetic Resonance Imaging, also known as magnetic resonance imaging, is a technology that uses magnetic fields and radio frequency pulses to generate images of human (or small animal) tissues by detecting the magnetic resonance signals of protons within the tissue. It is the core imaging method of this invention.

[0059] SAR: Specific Absorption Rate, refers to the radio frequency electromagnetic power absorbed per unit mass of small animal tissue. Excessively high SAR values ​​may stimulate small animals, causing them to twitch and affecting the scanning results.

[0060] TSE: Turbo Spin Echo, a sequence technology for rapidly acquiring magnetic resonance echo signals, whose core function is to shorten scan time.

[0061] TE: Echo Time, which refers to the time from the excitation of a radio frequency pulse to the acquisition of a valid echo signal.

[0062] TR: Repetition Time, refers to the interval between two consecutive radio frequency pulse excitations.

[0063] Venc: The full name of the English word is Velocity Encoding. It is used to quantify the intensity of motion-sensitive gradients. Its value is inversely proportional to the intensity of the motion-sensitive gradient and can be flexibly adjusted according to the velocity of the blood flow to be inhibited, so as to achieve precise inhibition of blood flow signals at different velocities.

[0064] TE prep: English full name Echo Time Preparation Time, Chinese name echo time preparation time, refers to the preparation time in the pre-pulse combination module from pulse excitation to the generation of effective echo signal, which directly affects scanning efficiency and image contrast.

[0065] DICOM: Digital Imaging and Communications in Medicine, is a universal storage and transmission format for medical images (including magnetic resonance images). In this invention, the raw scan data is exported in this format to facilitate subsequent preprocessing and segmentation.

[0066] CNR: Contrast to Noise Ratio, is used to evaluate the ability of a target tissue (such as the sciatic nerve) to distinguish itself from surrounding tissues (such as muscles) and the background in an MRI image. The higher the value, the better the image contrast and the clearer the target tissue.

[0067] CPR: Curved Planar Reconstruction, a post-processing technique for magnetic resonance imaging that can automatically generate curved images along the entire length of the sciatic nerve, straightening the tortuous nerve and achieving continuous display throughout.

[0068] MIP stands for Maximum Intensity Projection, an image post-processing technique that extracts the maximum intensity of high-signal regions (such as neural tissue) in an image and generates a projection image to verify segmentation accuracy and neural course continuity.

[0069] VR: Full name Volume Rendering, a three-dimensional image visualization technology that uses lighting and transparency settings on a three-dimensional model to achieve a three-dimensional display of the sciatic nerve and spinal nerve plexus, which can be rotated and scaled at will for observation.

[0070] GV: Gray Value, used to quantify the signal intensity of voxels in magnetic resonance images, reflecting the magnetic resonance signal characteristics of tissues. In this invention, it is used to set gray value thresholds and determine tissue gray value similarity.

[0071] In one embodiment, such as Figure 1 As shown, a method for magnetic resonance imaging of the sciatic nerve in small animals is provided, including the following steps:

[0072] Step S101: A high-concentration syrup solution is filled into the bottom of the magnetic resonance coil, and the magnetic resonance coil is subjected to constant temperature control.

[0073] Specifically, a high-concentration syrup solution is prepared, and the high-concentration syrup solution is filled into the bottom of the magnetic resonance coil. The coil is shaken or vibrated repeatedly and then left to stand to observe whether there are any air bubbles. The magnetic resonance coil is then subjected to constant temperature control.

[0074] Based on this, the components and mass percentages of the high-concentration syrup solution are: fructose 40%-50%, glucose 20%-40%, and water 10%-25%;

[0075] The high-concentration syrup solution has a freezing point of -5℃ to -10℃, and is a clear, transparent, and homogeneous liquid above 37℃.

[0076] Specifically, the preparation process of high-concentration syrup solutions can be carried out according to conventional syrup preparation processes (the specific preparation steps can be adjusted according to actual needs, the core is to ensure that the proportion of each component meets the standards). A small amount of unavoidable impurities may be generated during the preparation process, mainly oligosaccharides (such as maltose), trace amounts of dextrin, sucrose, etc. that were not fully converted during the production process. These impurities do not affect the use effect of the syrup solution or the quality of magnetic resonance imaging.

[0077] High-concentration syrup solutions have the following key characteristics, making them suitable for magnetic resonance imaging (MRI) of small animals:

[0078] ① Safety and compatibility: Colorless, non-toxic and odorless, it does not irritate or damage the small animals being tested, and it is non-corrosive to magnetic resonance equipment. After use, the coil can be cleaned with warm water. It is easy to operate.

[0079] ② Excellent physical properties: Low freezing point (approximately -5~-10℃), adaptable to different ambient temperatures; at temperatures above 37℃, it is a clear and transparent thin liquid, without suspended particles, flocculent matter, or crystal precipitation. The overall system is homogeneous and will not separate, precipitate, or crystallize even after prolonged standing, thus avoiding interference with imaging.

[0080] ③ Good fluidity: When the container is tilted, it can quickly flow down the container wall; when poured into the bottom filling cavity of the coil, there is no serious sticking to the wall, and it can be leveled by gently shaking the container, which is convenient for filling operation. It can also fully penetrate into the air gaps under the abdomen and fur of the small animal to be tested, and completely expel the air.

[0081] ④ Magnetic Resonance Compatibility: Although the high-concentration syrup solution contains a small amount of water (H2O) and a large number of hydrogen protons, it does not produce a magnetic resonance signal regardless of the magnetic resonance pulse sequence used to excite it. It is speculated that this is because the hydrogen protons are bound by the macromolecular groups of the syrup and will not interfere with the imaging signal of the small animal tissue to be detected. At the same time, it can fill the air gaps and reduce artifacts.

[0082] The purpose of isothermal control is to maintain the temperature of both the syrup solution and the animal being tested, preventing hypothermia that may occur during prolonged scanning of anesthetized animals. It also ensures that the high-concentration syrup solution maintains good fluidity and effectively fills air gaps at temperatures above 37°C. The isothermal control temperature can be flexibly adjusted according to the body temperature of different animals, ideally between 37°C and 42°C. For example, the isothermal control temperature for laboratory rats can be set to 37°C-39°C, consistent with the normal body temperature of rats.

[0083] In this embodiment, the small animal being scanned is typically in a curled-up, prone position during MRI scanning. This position contains a large amount of air in areas such as the lower abdomen and between the hind limbs, making it highly susceptible to magnetic susceptibility artifacts. Filling the bottom of the MRI coil with a high-concentration syrup solution, and then placing the anesthetized animal prone on top of it for scanning, eliminates air interference from the lower abdomen. Furthermore, by placing a heating plate or slowly passing hot water through the bottom of the MRI coil, a constant temperature is maintained between the coil and the animal's body temperature (37°C-42°C, depending on the animal's temperature), preventing hypothermia during prolonged scanning after anesthesia. A temperature above 37°C also allows the high-concentration syrup to maintain better fluidity, fully penetrating the air gaps in the lower abdomen and fur of the animal.

[0084] Step S102: Place the anesthetized small animal to be tested face down on the high-concentration syrup solution and expel the air from the lower abdomen and between the two lower limbs of the small animal to be tested.

[0085] Specifically, the animal to be tested is anesthetized and placed prone on the syrup. During the operation, care is taken to expel as much air as possible from the lower abdomen and between the hind limbs before sending it into the center of the main magnetic field for scanning.

[0086] Step S103: After determining the main sequence scanning range by performing magnetic resonance localization scanning on the small animal to be tested, the main sequence scanning is started. The flow tissue signal is suppressed by pre-pulse combination, the tissue is excited by radio frequency pulse with preset parameters, and the echo signal is collected and filled with K space by combining fast spin echo technology to obtain the original scan data.

[0087] Specifically, a rapid localization scanning sequence is used to acquire sagittal, coronal, and transverse localization images. Based on the acquired localization images, the final scanning range of the main sequence is determined, ensuring that the anteroposterior direction includes the entire lumbar spine and thigh, while avoiding fluid signals from the gastrointestinal tract as much as possible. The main sequence scan is initiated, and pre-pulse combinations are used to suppress flowing tissue signals. Radiofrequency pulses with preset parameters are used to excite the tissue, and echo signals are acquired using rapid spin echo technology and filled into the K-space to obtain the raw scan data.

[0088] Based on this, the prepulse combination consists of multiple 90°, 180°, and -90° radio frequency pulse combinations, with gradients of the same magnitude but opposite polarity applied on both sides of the 180° pulse; the prepulse combinations are applied to the head-to-foot direction, left-right direction, and front-back direction, respectively.

[0089] Specifically, before the main sequence is initiated, multiple combinations of 90°, 180°, and -90° radio frequency pulses are introduced, and gradients of the same magnitude but opposite polarity are applied on both sides of the 180° pulse. This pre-pulse combination causes the moving proton group (mainly cluttered blood flow) to dephased, thereby suppressing its signal; while the phase of stationary tissue remains unchanged, improving image quality and reducing artifacts. The specific steps are as follows.

[0090] like Figure 2 As shown, firstly, a 90° radio frequency pulse is applied along the x-axis of the rotating coordinate system, flipping all magnetization vectors (including those of stationary tissue and flowing blood) to the xy plane. Then, a gradient is applied, causing the protons in stationary tissue and flowing tissue to dephased. Next, a 180° refocusing pulse is applied along the y-axis of the coordinate system, followed by a gradient of the same magnitude but opposite polarity. After the second gradient, the dephasing and convergence of stationary protons are equal, and their phases are restored to consistency, while the phases of flowing protons cannot be restored to consistency, resulting in dephasing. Subsequently, after the second reverse 90° pulse, the longitudinal relaxation of stationary protons returns to its initial state, while the longitudinal relaxation of flowing protons fails to return to its initial state, thereby suppressing the signal of flowing tissue.

[0091] To further optimize the inhibitory effect of the pre-pulse combination, the relevant parameters of the pre-pulse combination can be optimized (using white rats as the research subjects):

[0092] ① Number of Refocusing Pulses: Adding extra refocusing pulses can better help correct phase shift in stationary tissues, especially suitable for MRI machines with high field strength, scanning fields off-center from the main magnetic field center, and scenarios where magnetic susceptibility artifacts are prone to occur. However, increasing the number of refocusing pulses will increase scanning time and SAR value (which may stimulate the small animal being examined, causing it to twitch and affecting the scanning effect). Based on the syrup filling and precise positioning design of this invention, only one refocusing pulse is needed to achieve a good suppression effect, balancing imaging quality and scanning safety.

[0093] ② Refocusing Pulse Type: There are two types: Composite and Adiabatic. The Composite type is more sensitive to off-resonance effects and has a shorter TE prep time; the Adiabatic type is less sensitive to off-resonance effects but has a longer TE prep time. Considering the imaging requirements of this invention, selecting the Composite type satisfies the need for suppressing flowing tissue signals while shortening the scan time.

[0094] ③ Gradient direction of motion sensitivity: Gradients are applied in three directions: head-foot, left-right, and front-back, to ensure comprehensive suppression of tissue flow signals and avoid local signal interference.

[0095] ④ Flow velocity encoding value (Venc): Venc is inversely proportional to the intensity of the motion-sensitive gradient. A smaller Venc value indicates a stronger motion-sensitive gradient, which can suppress slower blood flow signals; a larger Venc value indicates a weaker motion-sensitive gradient, suitable for suppressing fast blood flow signals. In this invention, the Venc value can be set between 0 and 30, where 0 indicates no motion-sensitive gradient is applied, 0.1 indicates the strongest motion-sensitive gradient is applied, and 30 indicates the weakest motion-sensitive gradient is applied. Considering that the blood flow velocity in rats is faster than in humans, the specific settings are: 10 in the head-to-foot direction, 8 in the left-right direction, and 2 in the front-back direction, which can accurately suppress chaotic blood flow signals in rats.

[0096] ⑤ Interval time: The interval between the pre-pulse combination module and the subsequent imaging sequence is set to 35-100 ms, which can avoid the interference of the pre-pulse on the main sequence and introduce an appropriate amount of T2 contrast to improve image contrast.

[0097] Based on this, the preset radio frequency pulse is a 180° radio frequency pulse with a bandwidth of not less than 2500Hz, which reverses the longitudinal magnetization vector of the tissue to the opposite direction to the main magnetic field.

[0098] Specifically, a 180° radio frequency pulse with a large bandwidth (above 2500Hz) is selected to excite the tissue within the defined scanning range, deflecting the longitudinal magnetization vector of all tissues by 180°, i.e., deflecting it in the opposite direction to the main magnetic field. Compared to conventional 90° pulse excitation, 180° pulse excitation results in a longer longitudinal relaxation process, increasing the difference in longitudinal relaxation between tissues, further enhancing the signal contrast between different tissues (such as the sciatic nerve, muscle, and fat), facilitating clearer differentiation of the sciatic nerve from surrounding tissues, and improving imaging clarity. Figure 3As shown in the figure, the vertical axis represents the longitudinal magnetization vector (Mz), and the horizontal axis represents time (ms). The thick line represents tissue A, and the thin line represents tissue B. Figure A shows that after conventional 90° radio frequency pulse excitation, the longitudinal magnetization vectors of both tissues gradually recover from 0 to 100%. The vertical arrow indicates the maximum difference in longitudinal relaxation that can be achieved between the two tissues—that is, the maximum contrast that can be achieved in the later images. Figure B shows that after ultra-high bandwidth 180° radio frequency pulse excitation, the longitudinal magnetization vectors of both tissues gradually recover from -100% to 100%. The vertical arrow indicates the maximum difference in longitudinal relaxation that can be achieved between the two tissues—that is, the maximum contrast that can be achieved in the later images.

[0099] After the above operations, the longitudinal magnetization vector of all tissues gradually decreased from -100% to zero, and then gradually increased from zero to 100%. During this process, at the moment when the longitudinal magnetization vector of the adipose tissue just returned to zero, a 90° radio frequency pulse was applied to all tissues to redirect the longitudinal magnetization vector to the transverse direction. At this point, the adipose tissue, lacking a longitudinal magnetization vector, would not generate a transverse magnetization vector signal. Specifically, taking the scanning of rats on a 3.0T device as an example, this time was set to 180ms-250ms, and this time was defined as TI.

[0100] Based on this, the acceleration factor of the fast spin echo technology is set as follows: 5-15 in 2D scanning mode and 30-50 in 3D scanning mode; the K space adopts a linear filling method to fill the center of the K space with the intermediate echo signal, and the arrival time of the intermediate echo is set to 90ms-170ms; the interval between two adjacent excitations is set to 2200ms-5000ms.

[0101] Specifically, the core function of fast spin echo technology is to rapidly acquire echo signals, shorten scanning time, and ensure image quality. The acceleration factor setting needs to balance scanning speed and image resolution: 2D scanning mode is suitable for routine sciatic nerve imaging, with an acceleration factor set to 5-15, which can shorten scanning time while ensuring image clarity; 3D scanning mode is suitable for scenarios requiring three-dimensional reconstruction, with an acceleration factor set to 30-50, enabling rapid three-dimensional scanning to meet the needs of subsequent three-dimensional model reconstruction.

[0102] The advantage of linear K-space filling (also known as sequential filling) is that it fills the center of the K-space with the echo signal located in the middle. Since the center of the K-space determines the image contrast, this filling method can effectively improve image contrast and clearly distinguish the sciatic nerve from surrounding tissues. The intermediate echo arrival time (TE) is set to 90ms-170ms. This range can adapt to the needs of sciatic nerve imaging in small animals and avoid the problems of insufficient signal contrast due to an excessively short TE and signal attenuation due to an excessively long TE.

[0103] The interval between two consecutive excitations (defined as TR) is set to 2200ms-5000ms. This is to allow all tissues sufficient time to recover to their initial state between excitations, avoiding signal superposition and interference, ensuring accurate and clear signals acquired with each excitation, while balancing scan time and imaging quality. Specifically, the complete master sequence is shown below. Figure 4 As shown.

[0104] In addition to this, it also includes:

[0105] When acquiring echo signals, a gradient-adjusted focusing pulse is used. Initially, a small-angle focusing pulse is used, and as the tissue relaxes laterally, the focusing pulse angle is gradually increased to 180°.

[0106] Specifically, in conventional fast spin echo technology, all focusing pulses use 180° pulses, which has two main drawbacks: First, the transverse magnetization vector after the 90° pulse will continue to decay over time, causing the echo signal amplitude generated by the 180° focusing pulse to gradually decrease, eventually leading to a certain degree of image blurring; second, the 180° pulse has high energy, and using 180° pulses for focusing will cause a significant increase in SAR value, which may cause irritation symptoms in the small animal to be tested, causing unnecessary twitching and leading to scan failure.

[0107] This invention effectively solves the above-mentioned defects by adjusting the focusing pulse angle through gradient: at the beginning of echo signal acquisition, a focusing pulse with a small angle is used so that the proton group is not completely phase-focused, reducing the intensity of the initial echo; as the tissue relaxes laterally, the lateral magnetization vector decays continuously, and the focusing pulse angle is gradually increased until it reaches 180°, so that the intensity of each echo tends to be similar, avoiding image blurring caused by excessive differences in echo signal amplitude, while reducing the overall SAR value, reducing stimulation to the small animals being tested, and improving the scanning success rate.

[0108] by Figure 5 As shown, taking 5 focusing pulses as an example, the focusing pulse angles can be set sequentially to 145°, 160°, 170°, 175°, and 180° to achieve a smooth transition in echo signal intensity and improve image clarity.

[0109] Based on this, during the main sequence scanning process, gradient fields are applied to the gradient coils in the three directions of the main magnetic field to perform gradient field spatial encoding. Specifically, the direction of the coronal plane of the animal to be detected is taken as the layer direction, the left and right directions of the animal to be detected are taken as the phase encoding direction, and the head and foot directions of the animal to be detected are taken as the frequency encoding direction.

[0110] Specifically, taking rats as an example, the coronal plane of the rat is used as the slice direction, the left and right direction of the rat is used as the phase encoding direction, and the head-foot direction of the rat is used as the frequency encoding direction. The slice thickness is set to 1.2-2mm. This gradient field spatial encoding setting can significantly optimize scanning efficiency and imaging quality, while adapting to the anatomical course of the sciatic nerve.

[0111] In this embodiment, the beneficial effects of the gradient field spatial encoding setting are as follows:

[0112] ① Shortening Scanning Time: The scanning time of the main sequence is positively correlated with the number of scanning layers and the coding step level in the phase coding direction. That is, the more scanning layers and the higher the coding step level in the phase coding direction, the longer the scanning time. This invention combines the anatomical characteristics of the sciatic nerve—the sciatic nerve mainly runs along the coronal plane of the animal being tested—and sets the coronal plane direction as the layer direction and the left and right directions as the phase coding direction. While ensuring complete coverage of the sciatic nerve scanning range, it can reasonably reduce the number of scanning layers and the coding step level in the phase coding direction, thereby effectively shortening the overall scanning time. This avoids problems such as hypothermia and agitation in anesthetized animals due to prolonged scanning, and improves the scanning success rate.

[0113] ② Improve image signal-to-noise ratio while ensuring reconstruction effect: Since the coronal plane is the main direction of the sciatic nerve, setting this direction as the slice direction allows for an appropriate increase in slice thickness (1.2-2mm). This increase in slice thickness reduces noise interference during scanning, improves the image signal-to-noise ratio, and makes the sciatic nerve signal clearer. At the same time, the coronal plane is consistent with the course of the sciatic nerve, so even if the slice thickness is increased appropriately, the small volume effect will not affect the overall morphological display of the sciatic nerve, nor will it interfere with the accuracy of subsequent 3D model reconstruction, thus achieving a balance between scanning efficiency, imaging quality, and reconstruction effect.

[0114] Building upon this, to further eliminate the interference of cerebrospinal fluid artifacts on imaging quality, a symmetrical bipolar gradient is applied in the head-foot direction, as follows:

[0115] By applying a symmetrical bipolar gradient in the head-to-foot direction and alternating between positive and negative gradient fields of varying areas multiple times, the phase shift caused by the uniformly flowing cerebrospinal fluid proton groups is canceled out, achieving phase refocusing. This completely eliminates the thin, high-signal artifacts caused by cerebrospinal fluid flow, ensuring clear visualization of the spinal nerve roots and sciatic nerve. This provides a high-quality original image foundation for subsequent precise segmentation and 3D reconstruction, further improving the reliability and accuracy of the imaging method of this invention. Figure 6As shown, for a stationary proton, these additional gradients cancel each other out and have no effect. However, for a proton moving at a constant velocity, if a standard GRE readout gradient is applied, the accumulated phase is not zero at the midpoint of the echo (blue circle), which will lead to signal loss. Applying bipolar gradient fields of equal magnitude and opposite direction yields the following result: the first gradient field introduces a positive phase shift, and the second gradient field introduces a very large negative phase shift. When the signal readout occurs, the applied gradient fields restore the phase shift to zero (orange circle), thus eliminating the phase shift and removing flow artifacts.

[0116] Step S104: Preprocess the original scan data and accurately segment the sciatic nerve and spinal nerve to obtain the segmentation result.

[0117] Specifically, the raw scan data is exported in DICOM 3.0 format, imported into MIMICS 26.0 software, preprocessed, and precisely segmented for the sciatic nerve and spinal nerve to obtain the segmentation results.

[0118] Based on this, preprocessing includes image rearrangement, contrast enhancement, and noise suppression;

[0119] The contrast enhancement employs a neural optimal window width and window level algorithm to calculate the optimal window level and optimal window width and perform grayscale linear mapping.

[0120] The noise suppression employs nonlocal mean filtering combined with edge protection constraints.

[0121] Specifically, the raw scan data may contain issues such as image misalignment, insufficient signal contrast, and background noise, which can affect subsequent segmentation and imaging results. Therefore, preprocessing is necessary, and the specific steps are as follows:

[0122] 1. Image rearrangement: such as Figure 7 As shown, the original scan data was exported to DICOM 3.0 format and imported into MIMICS 26.0 software. Using MIMICS' "Re-slice" function, the images were rearranged based on the sciatic nerve course to ensure spatial alignment of coronal, sagittal, and axial images, avoiding segmentation errors caused by image misalignment.

[0123] 2. Contrast Enhancement: Employing a neural optimal window width and level algorithm, the system automatically calculates the optimal window level and width, and performs linear grayscale mapping to maximize nerve-muscle contrast, ensuring the sciatic nerve structure is clearly discernible. The specific formula is shown below:

[0124] ① The formula for calculating the optimal window level is: ,in This indicates the optimal window level (which controls the central grayscale value of the MRI image display). Indicates the MRI signal intensity (image grayscale value) of neural tissue. Indicates the MRI signal intensity (image grayscale value) of muscle tissue;

[0125] ②The formula for calculating the optimal window width is: ,in This indicates the optimal window width (which controls the grayscale range displayed in the MRI image). Indicates the MRI signal intensity (image grayscale value) of neural tissue. Indicates the MRI signal intensity (image grayscale value) of the background tissue;

[0126] ③ The formula for calculating the contrast-to-noise ratio is: ,in This represents the contrast-to-noise ratio (used to evaluate the ability to distinguish nerves from muscle / background). Indicates the average signal intensity of neural tissue. This represents the average signal intensity of muscle tissue. This represents the standard deviation of background noise. The algorithm described above ensures that the contrast-to-noise ratio meets imaging requirements, clearly distinguishing the sciatic nerve from surrounding tissues.

[0127] 3. Noise suppression: such as Figure 8 As shown, by applying nonlocal mean filtering combined with edge protection constraints, background noise is significantly reduced while preserving nerve edge details, thus preventing noise from interfering with the recognition of the sciatic nerve structure. The specific formula is shown below:

[0128] ① The core calculation formula for filtering is: ,in, Represents the filtered pixels The final grayscale value, Represented in pixels The search neighborhood centered on the center, Represents pixels With pixels The weighting coefficients between them Represents pixels in the original image grayscale value;

[0129] ②The formula for calculating the weighting coefficient is: ,in This represents the natural exponential function. Represents pixels The local neighborhood gray vector, Represents pixels The local neighborhood gray vector, The squared Euclidean distance representing the difference in gray levels among neighbors. This represents the filtering smoothing parameter (controlling the noise reduction intensity). This filtering algorithm effectively removes background noise while avoiding the loss of neural edge details.

[0130] Based on this, a three-level progressive segmentation strategy is adopted for precise segmentation of the sciatic nerve and spinal nerves, including:

[0131] Global threshold initial screening: Set the grayscale threshold range to 70GV-800GV to extract high signal regions;

[0132] Based on the high-signal region, seed points are set at the spinal nerve root exit and the intervertebral foramen area, and region growth is performed according to gray-level similarity and spatial connectivity criteria to obtain the grown region.

[0133] The manual editing signal is received, the key layers of the growth region are contoured, and the surface jaggedness is eliminated through smoothing to obtain the segmentation result.

[0134] Specifically, the three-level progressive segmentation strategy can achieve precise segmentation of the sciatic nerve and spinal nerves, avoiding interference from irrelevant tissues. The specific implementation process is as follows:

[0135] 1. Global Thresholding Initial Screening: Based on the high signal characteristics of neural tissue, a grayscale threshold range of 70GV-800GV is set (this range is approximately 1.5-2.0 times the relative signal intensity of muscle). The "Thresholding" function of MIMICS is used to extract all high-signal areas, including spinal nerve roots and the sciatic nerve, while excluding some low-signal irrelevant tissues. The specific calculation formula is as follows:

[0136] ① The relative signal strength of the nerve satisfies: ,in This represents the relative signal-to-noise ratio of the nerve (a measure of the signal difference between nerves and muscles). Indicates the MRI signal intensity of neural tissue. Indicates the reference signal intensity of muscle tissue. It must satisfy ∈ [1.5, 2.0];

[0137] ② Extract high-signal regions using a global threshold, such as Figure 9 As shown, the initial mask is calculated using the following formula: ,in This represents the initial mask obtained from the threshold screening. Represents the three-dimensional spatial coordinates of an image voxel. express The grayscale value (GV) is defined as follows: 70GV is the lower limit of the grayscale threshold (GV_low), and 800GV is the upper limit of the grayscale threshold (GV_high).

[0138] 2. Seed point region growth: such as Figure 10 As shown, seed points were manually placed at the spinal nerve root exit and intervertebral foramen region on axial and coronal images (this location is the connection between the sciatic nerve and the spinal nerve, with obvious signal characteristics, ensuring accurate growth direction). Using the seed points as centers, region growth was performed based on gray-level similarity and spatial connectivity criteria to further screen the sciatic nerve and spinal nerve regions, excluding irrelevant high-signal tissue remaining from the initial screening. The specific calculation formula is as follows:

[0139] ① Gray-scale similarity criterion: ,in Indicates the voxel to be judged grayscale value, This represents the grayscale value of the seed dot voxel. This indicates the allowable grayscale deviation (set to ±10GV in this method) to ensure that the grayscale of the growth area is consistent with that of the neural tissue.

[0140] ② Spatial connectivity criterion: ,in Voxel representation The set of connected neighborhoods, This represents two adjacent voxels to be judged. express and Manhattan distance, Indicates the neighborhood determination distance; when When the neighborhood is 6-neighborhood (face adjacent); When the edges are adjacent, the neighborhood is 18-neighborhood. At this time, it is a 26-neighborhood (points are adjacent). The appropriate neighborhood type can be selected according to the imaging accuracy requirements. The 26-neighborhood is preferred to ensure the continuity of the growth area.

[0141] ③ Region growth output mask: ,in This represents the mask output after region growing. This represents the region growing algorithm function. This represents the initial mask obtained from the threshold screening. This indicates a seed point that was placed manually. Indicates the grayscale deviation threshold. Represents spatial connectivity rules.

[0142] 3. Manual Editing and Smoothing: Using MIMICS' "Multiple Slice Edit" tool, perform layer-by-layer contour correction at key levels (nerve root entry into the spinal cord, dorsal root ganglion, and nerve plexus confluence) to remove residual irrelevant tissue and supplement missing nerve segments; use the "Smoot" tool, setting the iteration count to 3-5 and the intensity factor to 0.5, to eliminate jagged edges on the segmented area surface, maintaining the anatomical accuracy of the sciatic and spinal nerves, ultimately obtaining the final segmentation mask (Mask_final), as shown below. Figure 11 As shown, this is the segmentation result.

[0143] Step S105: Based on the segmentation results, complete the 3D model reconstruction, optimization, and multimodal fusion visualization to obtain the image scanning results.

[0144] Specifically, based on the segmentation result, i.e. the final neural segmentation mask (Mask_final), the 3D Calculate voxel reconstruction function of MIMICS26.0 software is used to generate three-dimensional entities of target structures such as the sciatic nerve and spinal nerve roots with voxel-level precision, thus completing the initial three-dimensional model construction.

[0145] Based on this, the 3D model optimization includes: sealing of micropores, filling of internal voids, mesh optimization and resampling, and output of independent entities;

[0146] The multimodal fusion visualization includes: surface reconstruction, maximum intensity projection and stereo rendering, to achieve continuous display of the sciatic nerve throughout its entire course, verification of segmentation accuracy and three-dimensional stereoscopic display.

[0147] Specifically, the implementation process is as follows:

[0148] To ensure the anatomical integrity and surface smoothness of the model, the following optimization processes were performed sequentially:

[0149] ① Sealing of minute pores: Using MIMICS' Wrap function, tiny gaps and pinhole-like defects on the surface of the initial model are automatically sealed to avoid discontinuities in the reconstructed structure and ensure the integrity of the model.

[0150] ② Internal cavity filling: Using MIMICS' Cavity Fill function, cavities inside the model caused by image noise or partial volume effect are filled to ensure the uniformity and closure of neural entities.

[0151] ③ Mesh optimization and resampling: Convert the voxel model into a standard triangular mesh, perform Remesh remeshing, set the target side length to 0.1–0.15 mm, and unify the mesh density, eliminate jagged edges and burrs, and improve the smoothness of the model while preserving subtle anatomical features (such as nerve branches and thickness variations).

[0152] ④ Independent Entity Output: Irrelevant tissue interference is removed from the model to generate an independent 3D neural entity model containing only the sciatic nerve and spinal nerve roots, meeting the needs of subsequent multimodal visualization, morphological measurement, and virtual simulation. The 3D neural model after applying micropore closure and internal cavity filling is shown below. Figure 12 As shown.

[0153] The reconstructed 3D neural model is registered and fused with the original MRI images. Through various post-processing methods, a clear, intuitive, and multi-angle display of the neural structure is achieved, meeting the needs of morphological assessment, result presentation, and experimental reporting. Specifically, this includes:

[0154] ① Curved Surface Reconstruction (CPR): Automatically generates curved surface reconstruction images along the entire length of the sciatic nerve, straightening the tortuous nerve and achieving continuous display from the nerve root exit to the distal end of the nerve. This allows for intuitive assessment of nerve morphology, thickness variations, compression sites, and injury areas. Examples of curved surface reconstruction images of the entire sciatic nerve path include... Figure 13 As shown;

[0155] ② Maximum Intensity Projection (MIP): Generates a high-intensity projection image of the neural network, which is overlaid on the 3D segmentation model. The original image signal and the reconstructed structure are compared in the same view to quickly verify the segmentation accuracy, neural course continuity and boundary consistency.

[0156] ③ Realistic 3D Rendering (VR): Utilizing the Phong lighting model for realistic 3D rendering, material transparency is set to 0.6–0.8, and background culling depth is enabled to ≥10 mm. This highlights the main neural structure while minimizing background interference, achieving a three-dimensional display of the sciatic nerve and spinal nerve plexus. The image can be freely rotated and scaled for observation, meeting the standards for clinical diagnosis and scientific drawing. An example of a 3D VR rendering of the rat sciatic nerve is shown below. Figure 14 As shown.

[0157] Figure 15 This is the maximum intensity projection MIP image of the sciatic nerve in rats using current technology. Figure 16 The existing technology for creating a three-dimensional VR rendering of the sciatic nerve in rats suffers from excessive ghosting and insufficient clarity. In contrast, the small animal sciatic nerve imaging method of this invention provides a three-dimensional VR rendering of the sciatic nerve in rats that achieves precise and clear imaging, accurately separates the sciatic nerve from the spinal nerve, and clearly displays the anatomical morphology of the nerve.

[0158] Based on the same inventive concept, corresponding to any of the above embodiments, the present invention also provides a small animal sciatic nerve magnetic resonance coil, including a magnetic resonance coil body, a filling cavity for containing a high-concentration syrup solution at the bottom of the magnetic resonance coil body, and a heating device internally or externally connected to the filling cavity for maintaining the temperature of the syrup solution and the small animal to be tested; the coil body cooperates with a magnetic resonance imaging system to perform a small animal sciatic nerve magnetic resonance imaging method.

[0159] Specifically, the coil body is designed to fit the body shape of the animal being tested (such as a rat), ensuring comfortable placement while guaranteeing complete coverage of the lumbar spine and thigh (the main pathway of the sciatic nerve) within the scanning area. The shape of the filling cavity matches the bottom of the coil body, and its depth can be designed according to actual filling needs, ensuring sufficient high-concentration syrup solution to fully fill the air area below the abdomen and between the lower limbs of the animal being tested. The inner wall of the filling cavity is made of a smooth, corrosion-resistant material, facilitating the filling and cleaning of the syrup solution and preventing syrup residue from adhering to the walls.

[0160] The heating device can take the form of a heating plate, hot water pipes, etc. Built-in heating devices can be directly integrated into the bottom of the filling cavity, while external heating devices can be connected to the filling cavity via pipes to achieve precise temperature control. The heating device is connected to a temperature control system, which can flexibly adjust the heating temperature according to the body temperature requirements of different animals being tested, ensuring a stable temperature between 37℃ and 42℃ to prevent hypothermia in the animals and coagulation of the syrup solution.

[0161] The connection between the coil body and the magnetic resonance imaging system adopts the conventional magnetic resonance coil connection method to ensure that the coil can normally receive and transmit magnetic resonance signals, and complete the scanning imaging of the sciatic nerve of the small animal to be tested in conjunction with the imaging method.

[0162] Compared with the prior art, the present invention has the following advantages:

[0163] It fills the gap in the existing technology of magnetic resonance coils and imaging methods specifically for imaging the sciatic nerve in small animals. It is adapted to the body characteristics of small animals and can achieve accurate and clear imaging of the sciatic nerve in small animals, meeting the needs of medical experiments and clinical diagnosis and treatment.

[0164] By filling the bottom of the coil with a high-concentration syrup solution and combining it with constant temperature control, not only can the air in the lower abdomen and between the lower limbs of the small animal be completely expelled, effectively suppressing magnetic susceptibility artifacts, but also the hypothermia that may occur during long-term scanning of the anesthetized small animal can be avoided. At the same time, the syrup solution has no magnetic resonance signal and will not interfere with tissue imaging, making it highly safe and compatible.

[0165] By combining pre-pulse, optimizing radio frequency pulse parameters, and using gradient-adjusted focusing pulses, interference from flowing tissue signals and fat signals is effectively suppressed, increasing the signal contrast between tissues, improving image clarity, and reducing the scan failure rate.

[0166] A three-level progressive segmentation strategy is adopted, combined with preprocessing and multimodal fusion visualization, to achieve accurate segmentation of the sciatic nerve and spinal nerve. It can clearly display the anatomical morphology, course and detailed features of the nerve. At the same time, after the 3D model is optimized, it can meet the subsequent needs such as morphological measurement and virtual simulation.

[0167] The entire imaging method is easy to operate, and the scanning parameters can be flexibly adjusted according to the needs of different small animals. The coil structure is simple, easy to clean and maintain, and highly practical. It can be widely used in sciatic nerve imaging scenarios of small animals such as laboratory rats.

[0168] It should be noted that the above description describes some embodiments of the present invention. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps described in the claims may be performed in a different order than that shown in the above embodiments and still achieve the desired results. Furthermore, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0169] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of the invention as described above, which are not provided in the details for the sake of brevity.

[0170] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0171] While specific details have been set forth to describe exemplary embodiments of the invention, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details or with variations thereof. Therefore, these descriptions should be considered illustrative rather than restrictive. Although the invention has been described in conjunction with specific embodiments thereof, many substitutions, modifications, and variations of these embodiments will be apparent to those skilled in the art based on the foregoing description.

[0172] The embodiments of this invention are intended to cover all such substitutions, modifications, and variations falling within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this invention should be included within the protection scope of this invention.

Claims

1. A method for magnetic resonance imaging of the sciatic nerve in small animals, characterized in that, include: A high-concentration syrup solution was used to fill the bottom of the magnetic resonance coil, and the magnetic resonance coil was subjected to constant temperature control. The anesthetized small animal to be tested was placed prone on the high-concentration syrup solution, and the air in the lower abdomen and between the two lower limbs of the small animal to be tested was expelled. After determining the main sequence scanning range by performing magnetic resonance localization scanning on the small animal to be tested, the main sequence scanning is started. The flow tissue signal is suppressed by pre-pulse combination, the tissue is excited by radio frequency pulses with preset parameters, and the echo signal is collected and filled with K space by combining fast spin echo technology to obtain the original scan data. The raw scan data is preprocessed and the sciatic nerve and spinal nerve are precisely segmented to obtain the segmentation results; Based on the segmentation results, the 3D model is reconstructed, optimized, and visualized using multimodal fusion to obtain the image scanning results.

2. The method for magnetic resonance imaging of the sciatic nerve in small animals according to claim 1, characterized in that, The components and mass percentages of the high-concentration syrup solution are: fructose 40%-50%, glucose 20%-40%, and water 10%-25%. The high-concentration syrup solution has a freezing point of -5℃ to -10℃, and is a clear, transparent, and homogeneous liquid above 37℃.

3. The method for magnetic resonance imaging of the sciatic nerve in small animals according to claim 1, characterized in that, The prepulse combination consists of multiple sets of 90°, 180°, and -90° radio frequency pulse combinations, with gradients of the same magnitude but opposite polarity applied on both sides of the 180° pulse; the prepulse combinations are applied in the head-to-foot direction, left-right direction, and front-back direction, respectively.

4. The method for magnetic resonance imaging of the sciatic nerve in small animals according to claim 1, characterized in that, The preset parameters are 180° radio frequency pulses with a bandwidth of not less than 2500Hz, which reverse the longitudinal magnetization vector of the tissue to the opposite direction to the main magnetic field.

5. The method for magnetic resonance imaging of the sciatic nerve in small animals according to claim 1, characterized in that, The acceleration factor of the fast spin echo technology is set as follows: 5-15 in 2D scanning mode and 30-50 in 3D scanning mode; the K space adopts a linear filling method, filling the center of the K space with the intermediate echo signal, and the arrival time of the intermediate echo is set to 90ms-170ms; the interval between two adjacent excitations is set to 2200ms-5000ms.

6. The method for magnetic resonance imaging of the sciatic nerve in small animals according to claim 1, characterized in that, Also includes: When acquiring echo signals, a gradient-adjusted focusing pulse is used. Initially, a small-angle focusing pulse is used, and as the tissue relaxes laterally, the focusing pulse angle is gradually increased to 180°.

7. The method for magnetic resonance imaging of the sciatic nerve in small animals according to claim 1, characterized in that, The preprocessing includes image rearrangement, contrast enhancement, and noise suppression; The contrast enhancement employs a neural optimal window width and window level algorithm to calculate the optimal window level and optimal window width and perform grayscale linear mapping. The noise suppression employs nonlocal mean filtering combined with edge protection constraints.

8. The method for magnetic resonance imaging of the sciatic nerve in small animals according to claim 1, characterized in that, The precise segmentation of the sciatic nerve and spinal nerves employs a three-level progressive segmentation strategy, including: Global threshold initial screening: Set the grayscale threshold range to 70GV-800GV to extract high signal areas; Based on the high-signal region, seed points are set at the spinal nerve root exit and the intervertebral foramen area, and region growth is performed according to gray-level similarity and spatial connectivity criteria to obtain the grown region. The manual editing signal is received, the key layers of the growth region are contoured, and the surface jaggedness is eliminated through smoothing to obtain the segmentation result.

9. The method for magnetic resonance imaging of the sciatic nerve in small animals according to claim 1, characterized in that, The 3D model optimization includes: sealing of micropores, filling of internal voids, mesh optimization and resampling, and output of independent entities; The multimodal fusion visualization includes: surface reconstruction, maximum intensity projection and stereo rendering, to achieve continuous display of the sciatic nerve throughout its entire course, verification of segmentation accuracy and three-dimensional stereoscopic display.

10. A magnetic resonance coil for the sciatic nerve of a small animal, characterized in that, The device includes a magnetic resonance coil body, the bottom of which is provided with a filling cavity for containing a high-concentration syrup solution. The filling cavity is equipped with a heating device, either internally or externally, for maintaining the temperature of the syrup solution and the body temperature of the small animal to be tested. The coil body is used in conjunction with a magnetic resonance imaging system to perform a magnetic resonance imaging method for the sciatic nerve of a small animal as described in any one of claims 1 to 9.

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