A magnetic resonance method for online measurement and drawing of viscosity-shear rate curves

Abstract

The present invention discloses a magnetic resonance method for online measurement and drawing of viscosity-shear rate curve, measuring the systolic and diastolic pressures of arteries; deploying a pulse gating system and a radio frequency coil supporting an MRI instrument; performing magnetic resonance imaging, dividing the cardiac cycle into a plurality of sub-intervals in the time dimension, and obtaining grouped image results; obtaining the distribution of blood flow velocity in radial and time dimensions; calculating viscosity and shear rate, and making a one-to-one correspondence between viscosity and shear rate according to radial position and time, and obtaining a viscosity-shear rate scatter plot. The present invention belongs to a non-contact measurement method, and can realize the measurement of viscosity-shear rate without affecting the normal operation of the fluid.

Description

Technical Field

[0001] The present invention belongs to the field of magnetic resonance imaging, and in particular relates to a magnetic resonance method for online measurement and drawing of viscosity-shear rate curves, which is suitable for online measurement of the viscosity-shear rate curve of any non-Newtonian fluid under known fluid pressure drop conditions. Background Art

[0002] Computational Fluid Dynamics (CFD) is an interdisciplinary subject between mathematics, mechanics and computer science that emerged with the development of computers. Its main research content is to simplify some known fluid mechanics problems into a set of equations to be solved through a series of abstract means, and then use the powerful high-speed parallel computing function of computers to solve the set of equations through numerical methods and finally obtain a series of parameters used to describe the flow process and fluid state.

[0003] Computational fluid dynamics is widely used in aerospace, chemical engineering, vehicles, water conservancy, and biomedicine. The objects of analysis in chemical engineering and biomedicine are often the flow of liquid in the lumen. Such problems often focus on the fluid flow process and the force between the fluid and the tube wall, and the fluid as the research object involves non-Newtonian properties. Therefore, in the research of these two fields, the accuracy of the viscosity-shear rate curve used to describe the viscosity properties of non-Newtonian fluids is a prerequisite for obtaining true and correct results.

[0004] The measurement method of fluid viscosity depends on the viscosity properties of the fluid. The viscosity of Newtonian fluids is only affected by the temperature of the fluid, and a capillary viscometer (such as a Saybolt viscometer) is often used in conjunction with a water bath to measure the viscosity; while among non-Newtonian fluids, generalized Newtonian fluids are only affected by the temperature and shear rate of the fluid, and using capillary viscometers of different specifications cannot produce consistent results. Therefore, a rotational viscometer with controllable shear rate (such as a Brookfield viscometer) is often used to measure the viscosity-shear rate curve of generalized Newtonian fluids at different shear rates.

[0005] However, in actual applications, there are often factors such as different fluid states online and offline (such as blood), too harsh online conditions that are not suitable for viscometer operation (such as high temperature), or dangerous properties of the fluid itself that are not suitable for sampling (such as toxicity and corrosiveness). Whether in the chemical or biomedical fields, a method for online measurement of fluid viscosity-shear rate curves is needed. Previously, there was a magnetic resonance sequence (loc_presat_FLASH) that can observe the flow velocity distribution of fluid inside the lumen. By post-processing the image results produced by this method, the relative viscosity of the coaxially distributed two-phase mixed fluid can be obtained, but the absolute viscosity of the fluid cannot be directly obtained. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a magnetic resonance method for online measurement and drawing of viscosity-shear rate curves. The method can realize online in-situ detection of fluid viscosity characteristics. Compared with the traditional offline measurement method, the method proposed by the present invention is applicable to a wider range of fluid conditions and is suitable for measuring the viscosity properties of special fluids with high temperature, corrosive or unstable properties.

[0007] The above-mentioned purpose of the present invention is achieved by the following technical means:

[0008] A magnetic resonance method for online measurement and drawing of viscosity-shear rate curves comprises the following steps:

[0009] Step 1: Measure the systolic blood pressure of the artery 收缩 With diastolic blood pressure 舒张 ;

[0010] Step 2: Deploy the pulse gating system and radio frequency coil that are compatible with the MRI instrument;

[0011] Step 3, performing magnetic resonance imaging to obtain continuous sampling signals of measurement points of the portion of the common carotid artery that vertically passes through the saturation layer;

[0012] Step 4, dismantle the pulse gating system and the radio frequency coil;

[0013] Step 5: divide the cardiac cycle into multiple sub-intervals in the time dimension, and then group the samples according to the sub-intervals of the sampling enable signal generated in each sampling process within a single cardiac cycle to obtain sampling signals grouped according to the sub-intervals, and reconstruct the grouped sampling signals to obtain the corresponding grouped image results;

[0014] Step 6: Obtain the radial distribution of blood flow velocity corresponding to each group, and further obtain the distribution v of blood flow velocity in radial and time dimensions. z (r, t, z = 0), r is the distance from the measuring point to the pipe axis, t is the time, z is the axial distance, the z = 0 plane represents the plane on the fluid inflow side of the saturated layer boundary, and the z plane is the plane passing through the axial position z and perpendicular to the axial direction;

[0015] Step 7, calculate the viscosity μ(r, t, z=0) and shear rate τ(r, t, z=0) at the radial position r at time t in the z=0 plane, and make a one-to-one correspondence between the viscosity and the shear rate according to the radial position r and the time t to obtain a viscosity-shear rate scatter plot;

[0016]

[0017]

[0018] Where p(t,z) is the cross-sectional pressure on the z plane at time t, v z (r, t, z) is the distribution of blood flow velocity in the radial and time dimensions on the z plane, v r (r, t, z) is the radial component distribution function of the flow velocity in the z = 0 plane, ρ is the fluid density, and dr is the radial resolution.

[0019] As mentioned above, step 3 includes the following steps:

[0020] The specific position of the carotid artery in the image space is obtained by an MRI instrument, and the loc_presat_FLASH sequence is executed in the MRI instrument, and the field of view selection is adjusted to meet the following conditions: the imaging selection is adjusted to a set size, the imaging selection includes three blood vessels, namely the common carotid artery, the internal carotid artery and the external carotid artery, the common carotid artery is parallel to the frequency encoding direction of the field of view, the saturation layer is set to a layer with a preset thickness and a length and width exceeding the imaging selection, the common carotid artery passes vertically through the saturation layer, and the portion of the common carotid artery passing vertically through the saturation layer is the sampling measurement point; and continuous sampling signals of the measurement points of the portion of the common carotid artery passing vertically through the saturation layer are obtained.

[0021] As mentioned above, the grouping in step 5 is based on the following method:

[0022] The mth sampling is located in the bth subinterval of the ath cardiac cycle, and the nth sampling is located in the dth subinterval of the cth cardiac cycle. If b=d, the mth and nth samplings are in the same group according to the sampling order, otherwise they are in different groups.

[0023] Step 6 as described above includes the following steps:

[0024] Step 6.1, cropping the image result obtained in step 5, retaining the blood vessel area inside the saturated layer;

[0025] Step 6.2, binarize the cropped image result and use the Sobel operator to obtain the image edge coordinates;

[0026] Step 6.3, the delay time T used when scanning through the loc_presat_FLASH sequence delay The radial distribution of blood flow velocity in the six images is inferred from the edge coordinates of the images;

[0027] Step 6.4: Based on the time information contained in the six image results, the distribution v of blood flow velocity in radial and time dimensions is obtained. z (r, t, z = 0).

[0028] As mentioned above in step 7:

[0029]

[0030]

[0031] Among them, PWV represents the velocity of the pulse wave along the blood vessel, A max With A min are the maximum and minimum values ​​of the blood vessel cross-sectional area A(t) at time t in a single cardiac cycle, and C is a constant correction term.

[0032] As mentioned above in step 7:

[0033]

[0034]

[0035]

[0036]

[0037]

[0038] As mentioned above, step 7 also includes the following steps: grouping the data points in the viscosity-shear rate scatter plot according to the shear rate size, weighted averaging the volume element sizes corresponding to all the data points in each group into an average point, and performing curve fitting on all the average points of the viscosity-shear rate scatter plot to obtain the final viscosity-shear rate curve.

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] 1. The present invention is a non-contact measurement method, which can realize the measurement of viscosity-shear rate without affecting the normal operation of the fluid.

[0041] 2. The present invention has a wide application range and is suitable for measuring the viscosity of Newtonian fluids under laminar flow and the viscosity-shear rate curve of generalized Newtonian fluids.

[0042] 3. The present invention can measure the mathematical relationship between fluid viscosity and shear rate online, and can be combined with open source or non-open source computational fluid dynamics methods to more accurately predict the motion behavior of the fluid and quantify the interaction between the fluid and the pipe wall. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a flow chart of the present invention;

[0044] Figure 2 It is a time dimension arrangement sequence diagram of the image acquisition of the present invention. DETAILED DESCRIPTION

[0045] In order to facilitate those skilled in the art to understand and implement the present invention, the present invention is further described in detail below in conjunction with embodiments. It should be understood that the implementation examples described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0046] Example 1: Measurement of viscosity-shear rate curves in healthy Sprague-Dawley rats

[0047] This embodiment is the most complex applicable situation of the method described in the present invention, so this example is selected to introduce the detailed process of the method, and other simplified situations can be simplified by the process of this example. The healthy SD rats used in this example weigh about 230g and are female. Personnel protection (lab coat, operating gloves, goggles, etc.) should be fully done before the experiment. A magnetic resonance method for online measurement and drawing of viscosity-shear rate curves described in the present invention is implemented near the carotid sinus of the rat. Specifically comprising the following steps:

[0048] Step 1: Anesthesia, blood pressure measurement and fixation of rats

[0049] The rats were weighed and anesthetized, and the systolic pressure of the rat tail artery was measured using the tail pressure method. 收缩 With diastolic blood pressure 舒张 As the blood pressure reference interval [p 舒张 ,p 收缩 After the blood pressure measurement, the rat was fixed on the rat bed matched with the MRI instrument in a supine position without pillow, with the head tilted to the left. A surface coil with a diameter of 3 cm was placed on the upper left side of the chest cavity, with the lower side of the surface coil tangent to the ribs, and the rat was placed head first on the rat bed, so that the shoulder and neck of the rat were located in the center of the magnet of the MRI instrument.

[0050] Step 2: Hardware and software adjustments before the experiment

[0051] Connect and start the pulse gating system of the MRI instrument, and use the tail sleeve to fix the sensor on the abdominal side of the rat's tail root according to the operation process of the pulse gating system. Use a three-way connector to separate the sampling enable signal of the MRI instrument and introduce it into the sampling input interface of the pulse gating system. Using such a connection can determine the specific position of all signal sampling in the cardiac cycle during the MRI scan, and the deployment of the pulse gating system can be completed. At this time, the monitoring end of the pulse gating system can see the pulse curve of the rat's tail artery and the sampling enable signal of the MRI instrument at the same time.

[0052] Step 3: Magnetic resonance imaging

[0053] After completing the above steps, magnetic resonance imaging is started. First, the specific position of the carotid artery in the image space is obtained through the MRI instrument. Then the loc_presat_FLASH sequence is executed in the MRI instrument. The specific setting parameters of the loc_presat_FLASH sequence are as follows: Matrix = 128*96, Field of View = 2*1.4cm 2 , repetition time / echo time (TR / TE) = 25ms / 2.826ms, number of repetitions (NR) = 4, post-saturation delay (T delay )=15ms, slice thickness (Thickness of Slices)=2mm, saturation pulse flip angle (Sat.FA)=90deg, excitation pulse flip angle (FA)=40deg, saturation slice thickness (Thickness of Sat.Slices)=5mm. Then adjust the field of view selection to meet the following conditions: imaging selection is (2*1.4*0.2)cm 3 The image selection area contains three blood vessels: the common carotid artery, the internal carotid artery and the external carotid artery. The common carotid artery is parallel to the frequency encoding direction of the visual field (2 cm long side). The saturation layer is a layer with a thickness of 5 mm and a length and width exceeding the image selection area. The common carotid artery passes vertically through the saturation layer, and the part where the common carotid artery passes vertically through the saturation layer is the sampling measurement point. After the sampling is completed, a series of continuous sampling signals will be obtained.

[0054] If the result is to be used in the computational fluid dynamics-magnetic resonance imaging method, the vascular wall should also be imaged by the MRI instrument in this step. Since the vascular wall imaging step does not affect the result and execution of the method described in the present invention, it will not be described in detail here.

[0055] Step 4: End imaging

[0056] After completing the above steps, the imaging needs to be terminated, the rat is taken out of the MRI apparatus, and the connection between the radio frequency coil and the pulse gating system is disconnected.

[0057] Step 5: Data transfer and reconstruction

[0058] The sampling enable signal obtained in step 2, the pulse curve of the rat tail artery and the sampling signal obtained in step 3 are exported to the data processing terminal. For this embodiment, MRI performs a total of 96 (derived from the Matrix parameter) * 4 (derived from the number of repetitions NR) signal samplings, each sampling generates a sampling enable signal, and obtains the sampling signal obtained by sampling. The sampling enable signal is synchronized with the pulse curve through the pulse gating system. The pulse curve produces rhythmic oscillations under the influence of the heart beat, and the time for one oscillation cycle is defined as a cardiac cycle. In order to obtain MRI images of different stages in a single cardiac cycle, in this embodiment, all cardiac cycles are equally divided into 6 sub-intervals in the time dimension. Then, according to the sub-intervals of the sampling enable signal generated by each sampling process in a single cardiac cycle, each sampling is grouped to obtain the sampling signal grouped according to the sub-interval. The specific grouping method is as follows: the m-th sampling is located in the b-th sub-interval of the a-th cardiac cycle, and the n-th sampling is located in the d-th sub-interval of the c-th cardiac cycle. If b = d, the mth and nth samples are grouped together according to the sampling order, otherwise they are not grouped together. This is irrelevant to the values ​​of a and c.

[0059] Six groups of sampling signals are obtained by the above grouping method. Each group of sampling signals is reconstructed according to the Cartesian sampling mode, and finally six images of loc_presat_FLASH sequence scans in different sub-intervals are obtained. The six image results contain the time information of the cardiac cycle and record the fluid flow events occurring in their respective sub-intervals.

[0060] It should be noted that in this step, when dividing the sub-intervals, the order of each sub-interval in the cardiac cycle should be taken into consideration (e.g. Figure 2 The 6 images are arranged in this order in the subsequent steps.

[0061] Step 6: Extraction of velocity profile

[0062] For blood vessels, especially straight arteries without branches, since they have good cylindrical symmetry, it is more concise to use cylindrical coordinates to describe blood flow in steps 6 and 7.

[0063] The image result obtained in step 5 is processed, and the specific steps are as follows:

[0064] Step 6.1, firstly crop the image result obtained in step 5, and retain the blood vessel area inside the saturated layer;

[0065] Step 6.2, then use 0.45 as the threshold to binarize the cropped image result, and use the Sobel operator to obtain the image edge coordinates;

[0066] Step 6.3: Since the image edge coordinates are directly related to the radial distribution of blood flow velocity, the delay time T used in the loc_presat_FLASH sequence scan can be used. delay The radial distribution of blood flow velocity in the six images is deduced from the edge coordinates of the images.

[0067] Step 6.4: Because the six images output in step 5 contain time information, the distribution of blood flow velocity in radial and time dimensions can be obtained. z (r, t, z = 0). z The three coordinates represent the distance r from the measuring point to the tube axis, the time t, and the axial position z. The z=0 plane is defined here to represent the plane on the fluid inflow side of the saturated layer boundary (hereinafter referred to as the z=0 plane). From the description of the saturated layer in step 3, it can be seen that the z=0 plane is always perpendicular to the direction of the common carotid artery. Similarly, the z=z0 plane represents a plane that is also perpendicular to the common carotid artery but is located downstream of the z=0 plane and at a distance of z0. The z plane is a plane that passes through the axial position z and is perpendicular to the axial direction (the direction of the common carotid artery). In order to improve the accuracy of subsequent calculations, v is defined here. z Bicubic interpolation is performed so that the resulting resolution in the radial dimension r is dr = 1 μm and the resolution in the temporal dimension t is dt = 1 ms.

[0068] Step 7: Calculation of viscosity-shear rate curve

[0069] The calculation expression of viscosity is simplified from the Navier-Stokes equation, which is:

[0070]

[0071] Each of these items is calculated as follows:

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079] Among them, v z (r, t, z) is the distribution of blood flow velocity in the radial and time dimensions on the z plane, v z(r, t, z = 0) is the distribution of blood flow velocity in the radial and time dimensions on the z = 0 plane, r represents the radial position of the measurement point (the distance from the measurement point to the tube axis), t represents the time at the measurement point, and z represents the distance from the measurement point to the z = 0 plane (the axial position of the measurement point). The wave equation (3) is used to expand the measured data in the z = 0 plane to three dimensions: r, t, and z. p(t, z) is the cross-sectional pressure on the z plane at time t, and p(t, z = 0) is the cross-sectional pressure on the z = 0 plane at time t. The domain is expanded to two dimensions: t and z by the wave equation (2).

[0080] In formula (1), fluid density ρ = 1050 kg / m 3 , μ(r,t,z=0) represents the viscosity at the radial position r at time t in the z=0 plane;

[0081] In formula (2-4), PWV represents the velocity of the pulse wave along the blood vessel, and for rats, PWV = 5.326 m / s;

[0082] In formula (5), τ(r, t, z = 0) represents the shear rate of the radial position r at time t in the z = 0 plane, and v z (r+dr,t,z=0) represents the flow velocity of the adjacent measuring point in the radial direction at the radial position r at the time t in the z=0 plane, and dr is the radial resolution of the interpolation in step 6 dr=1μm;

[0083] Formula (6) is the differential approximation of the second-order differential of the velocity profile along the radial direction, where τ(r+dr,t,z=0) represents the velocity of the adjacent measuring point in the radial direction at the radial position r at time t in the z=0 plane;

[0084] Formula (7) is the radial component distribution function v of the velocity in the z=0 plane r The specific solution method of (r, t, z = 0) is derived from the continuity equation and can be combined with equation (3) to form a differential form. i represents the radial position of the i-th measurement point, represents the partial differential of the velocity in the z direction at the radial i-th point at time t. Substituting the boundary conditions (9) into the equation, we can solve it;

[0085] Formula (8) is the time difference form of the velocity profile. The numerator represents the velocity difference between the measurement point at position r at time t and the next time t+dt in the z=0 plane; the denominator is the time interval between the two times dt=1ms.

[0086]

[0087] In formula (9), R represents the flow radius of the fluid, that is, the radius of the blood vessel lumen. The radius of the blood vessel lumen can be obtained by the following method: First, the blood flow velocity distribution vz (r, t, z = 0) with v z =0.005m / s is the threshold for segmentation. At this time, v z The part >0.005m / s is the vascular lumen. The radial coordinate of the segmentation boundary at time t is the vascular lumen radius R(t), and R(t+dt) is the vascular lumen radius at the next adjacent time point t+dt, and the corresponding cross-sectional area is A(t) (calculated using a circular cross-section approximation, A(t)=πR(t) 2 ). The pressure p(t,z=0) described in equation (2) can be calculated by the vascular compliance condition of equation (10):

[0088]

[0089] In formula (10), p 收缩 With p 舒张 is the systolic and diastolic blood pressure measured in step 1, A max With A min is the maximum and minimum value of the cross-sectional area A(t) of the blood vessel at time t in a single cardiac cycle, A(t) is the cross-sectional area of ​​the blood vessel at time t, and C is a constant correction term. This method does not require the full measurement of the pressure curve of the elastic tube, but only requires the measurement of the maximum and minimum values ​​of the cross-sectional area A(t) of the blood vessel in a single cardiac cycle.

[0090] v r The solution of (r, t, z = 0) and p(t, z = 0) is applicable to the case of elastic pipe wall. For rigid pipe wall, its v r (r, t, z = 0) = 0, the pressure is linearly related to the flow velocity at the pipe axis position, that is, p(t, z = 0) = k × v(r = 0, t, z = 0) + C. Among them, k is the proportionality coefficient, C is a constant, and at this time v(r = 0, t, z = 0) represents the flow velocity at the pipe axis position at time t in the z = 0 plane.

[0091] Through the above calculations, the spatiotemporal distribution of viscosity μ(r, t, z=0) and the spatiotemporal distribution of shear rate τ(r, t, z=0) at the measuring point can be obtained. Based on this, the viscosity and shear rate can be matched one by one according to the radial position r and time t, thereby obtaining a viscosity-shear rate scatter plot.

[0092] In order to suppress the fluctuation of viscosity results caused by measurement noise, the data points in the viscosity-shear rate scatter plot can be grouped according to the shear rate size, and the volume element size corresponding to each data point is weighted averaged as an average point (the number of groups can be determined according to demand. Generally, the more groups, the more accurate the results, but too many groups are not conducive to suppressing measurement noise). Finally, the final viscosity-shear rate curve can be obtained by curve fitting all the average points of the viscosity-shear rate scatter plot. (The viscosity-shear rate curve drawing method is applicable to the case of generalized Newtonian fluids. For Newtonian fluids, the viscosity is independent of the shear rate, and the global volume-weighted average viscosity can be directly calculated. ).

[0093] The above embodiments mainly introduce the situation where the pressure at the measuring point fluctuates greatly. If the measured system is at a constant pressure, the viscosity μ(r) is calculated by formula (11):

[0094]

[0095] At this time, the differential of pressure with respect to the axial coordinate is measured by the two-point method (12):

[0096]

[0097] where p i (i=1,2) is the pressure measurement value of the i-th measuring point, and z2-z1 is the axial distance between the two measuring points. is the second-order differential of blood flow velocity with respect to the radial direction. The algorithm is shown in formula (6).

[0098] Embodiment 2:

[0099] A device for online measurement and drawing of viscosity-shear rate curve, comprising a data transfer and reconstruction module, a velocity profile extraction module, and a viscosity-shear rate curve calculation module.

[0100] The data transfer and reconstruction module is used to implement step 5 of Example 1, that is, to divide the cardiac cycle into multiple sub-intervals in the time dimension, and then group each sample according to the sub-interval of the sampling enable signal generated by each sampling process within a single cardiac cycle, obtain the sampling signal grouped according to the sub-interval, and reconstruct the grouped sampling signal to obtain the corresponding grouped image result.

[0101] The specific groups are:

[0102] The mth sampling is located in the bth subinterval of the ath cardiac cycle, and the nth sampling is located in the dth subinterval of the cth cardiac cycle. If b=d, the mth and nth samplings are in the same group according to the sampling order, otherwise they are in different groups.

[0103] The flow velocity profile extraction module is used to implement step 6 of embodiment 1, that is, to obtain the radial distribution of the blood flow velocity corresponding to each group, and further obtain the distribution v of the blood flow velocity in the radial direction and time dimension. z (r, t, z = 0), r is the distance from the measuring point to the pipe axis, t is the time, z is the axial distance, the z = 0 plane represents the plane on the fluid inflow side of the saturated layer boundary, and the z plane is the plane passing through the axial position z and perpendicular to the axial direction.

[0104] Specifically:

[0105] The image results obtained by the data transfer and reconstruction module are cropped to retain the blood vessel area inside the saturated layer;

[0106] Binarize the cropped image result and use the Sobel operator to obtain the image edge coordinates;

[0107] The delay time T used when scanning through the loc_presat_FLASH sequence delay The radial distribution of blood flow velocity in the six images is inferred from the edge coordinates of the images;

[0108] According to the time information contained in the 6 images, the distribution v of blood flow velocity in radial and time dimensions is obtained. z (r, t, z = 0).

[0109] A viscosity-shear rate curve calculation module is used to implement step 7 of Example 1, that is, to calculate the viscosity μ(r, t, z=0) and the shear rate τ(r, t, z=0) at the radial position r at time t in the z=0 plane, and to make a one-to-one correspondence between the viscosity and the shear rate according to the radial position r and the time t to obtain a viscosity-shear rate scatter plot;

[0110]

[0111]

[0112] Where p(t,z) is the cross-sectional pressure on the z plane at time t, v z (r, t, z) is the distribution of blood flow velocity in the radial and time dimensions on the z plane, v r (r, t, z) is the radial component distribution function of the flow velocity in the z = 0 plane, ρ is the fluid density, and dr is the radial resolution.

[0113]

[0114]

[0115]

[0116]

[0117]

[0118] The data points in the viscosity-shear rate scatter plot are grouped according to the shear rate size, and the volume element sizes corresponding to all the data points in each group are weighted averaged as an average point. The final viscosity-shear rate curve can be obtained by curve fitting all the average points of the viscosity-shear rate scatter plot.

[0119] It should be noted that the specific embodiments described in the present invention are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the attached claims.

Claims

1. A magnetic resonance method for online measurement and drawing of viscosity-shear rate curves, characterized in that: The following steps are involved: Step 1: Measure the systolic blood pressure of the artery 收缩 With diastolic blood pressure 舒张 ; Step 2: Deploy the pulse gating system and radio frequency coil that are compatible with the MRI instrument; Step 3, performing magnetic resonance imaging to obtain continuous sampling signals of measurement points of the portion of the common carotid artery that vertically passes through the saturation layer; Step 4, dismantle the pulse gating system and the radio frequency coil; Step 5: divide the cardiac cycle into multiple sub-intervals in the time dimension, and then group the samples according to the sub-intervals of the sampling enable signal generated in each sampling process within a single cardiac cycle to obtain sampling signals grouped according to the sub-intervals, and reconstruct the grouped sampling signals to obtain the corresponding grouped image results; Step 6: Obtain the radial distribution of blood flow velocity corresponding to each group, and further obtain the distribution v of blood flow velocity in radial and time dimensions. z (r, t, z = 0), r is the distance from the measuring point to the pipe axis, t is the time, z is the axial distance, the z = 0 plane represents the plane on the fluid inflow side of the saturated layer boundary, and the z plane is the plane passing through the axial position z and perpendicular to the axial direction; Step 7, calculate the viscosity μ(r, t, z=0) and shear rate τ(r, t, z=0) at the radial position r at time t in the z=0 plane, and make a one-to-one correspondence between the viscosity and the shear rate according to the radial position r and the time t to obtain a viscosity-shear rate scatter plot; Where p(t,z) is the cross-sectional pressure on the z plane at time t, v z (r, t, z) is the distribution of blood flow velocity in the radial and time dimensions on the z plane, v r (r, t, z) is the radial component distribution function of the flow velocity in the z = 0 plane, ρ is the fluid density, and dr is the radial resolution.

2. A magnetic resonance method for online measurement and drawing of viscosity-shear rate curve according to claim 1, characterized in that: The step 3 comprises the following steps: The specific position of the carotid artery in the image space is obtained by an MRI instrument, and the loc_presat_FLASH sequence is executed in the MRI instrument, and the field of view selection is adjusted to meet the following conditions: the imaging selection is adjusted to a set size, the imaging selection includes three blood vessels, namely the common carotid artery, the internal carotid artery and the external carotid artery, the common carotid artery is parallel to the frequency encoding direction of the field of view, the saturation layer is set to a layer with a preset thickness and a length and width exceeding the imaging selection, the common carotid artery passes vertically through the saturation layer, and the portion of the common carotid artery passing vertically through the saturation layer is the sampling measurement point; and continuous sampling signals of the measurement points of the portion of the common carotid artery passing vertically through the saturation layer are obtained.

3. A magnetic resonance method for online measurement and drawing of viscosity-shear rate curve according to claim 2, characterized in that: The grouping in step 5 is based on the following method: The mth sampling is located in the bth subinterval of the ath cardiac cycle, and the nth sampling is located in the dth subinterval of the cth cardiac cycle. If b=d, the mth and nth samplings are in the same group according to the sampling order, otherwise they are in different groups.

4. A magnetic resonance method for online measurement and drawing of viscosity-shear rate curve according to claim 3, characterized in that: The step 6 comprises the following steps: Step 6.1, cropping the image result obtained in step 5, retaining the blood vessel area inside the saturated layer; Step 6.2, binarize the cropped image result and use the Sobel operator to obtain the image edge coordinates; Step 6.3, the delay time T used when scanning through the loc_presat_FLASH sequence delay The radial distribution of blood flow velocity in the six images is inferred from the edge coordinates of the images; Step 6.4: Based on the time information contained in the six image results, the distribution v of blood flow velocity in radial and time dimensions is obtained. z (r, t, z = 0).

5. A magnetic resonance method for online measurement and drawing of viscosity-shear rate curve according to claim 4, characterized in that: In step 7: Among them, PWV represents the velocity of the pulse wave along the blood vessel, A max With A min are the maximum and minimum values ​​of the blood vessel cross-sectional area A(t) at time t in a single cardiac cycle, and C is a constant correction term.

6. A magnetic resonance method for online measurement and drawing of viscosity-shear rate curve according to claim 5, characterized in that: In step 7:

7. A magnetic resonance method for online measurement and drawing of viscosity-shear rate curve according to claim 1, characterized in that: The step 7 also includes the following steps: grouping the data points in the viscosity-shear rate scatter plot according to the shear rate size, weighted averaging the volume element sizes corresponding to all the data points in each group into an average point, and performing curve fitting on all the average points of the viscosity-shear rate scatter plot to obtain the final viscosity-shear rate curve.

Images