A magnetic resonance method for observing the blood flow velocity distribution characteristics inside isolated blood vessels

Abstract

The present invention discloses a magnetic resonance method for observing the characteristics of blood flow velocity distribution inside an isolated blood vessel. The surface coil is fixed on a subject, and the subject is sent into an MRI instrument; the workstation supporting the MRI instrument is debugged; the scanned visual field selection covering the common carotid artery is positioned; according to the positioned visual field selection covering the common carotid artery, an improved FLASH sequence is loaded to obtain a free induction decay signal; the MRI instrument performs bed withdrawal; the free induction decay signal is reconstructed to obtain a cross-sectional projection diagram of the blood flow; and the viscosity ratio of the inner and outer layers of the blood and the proportion of the inner layer diameter are obtained. The present invention can realize non-invasive detection of the blood flow state near the carotid sinus. The whole blood viscosity and plasma viscosity under the shear rate of this part can also be further analyzed in combination with blood pressure data.

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 observing the blood flow velocity distribution characteristics inside an isolated blood vessel, which is suitable for in-situ measurement of the blood flow velocity distribution of deep blood vessels without relying on mathematical model description. Background Art

[0002] Since 1931, when Swedish physicians R. Fahraeus and T. Lindquist proposed the Fahraeus-Lindquist effect, people began to realize that blood is actually a non-Newtonian fluid, and its flow behavior is much more complicated than the Newtonian fluid previously believed. With the development of various measuring instruments and the application of computers, it is now possible to simulate the deformation and movement behavior of a single red blood cell in the blood flow, the overall movement trend of all red blood cells in a section of blood vessels, and the blood velocity distribution under arterial wall stenosis. There are currently two main recognized laminar flow models of blood in a cylindrical lumen: one is a two-phase flow model with a Casson fluid as the inner layer, and the other is a two-phase flow model with a Newtonian fluid as the inner layer. The main difference between the two is whether there is a flow core structure at the center of the tube axis. In the case of a flow core, the former has higher fitting accuracy, and in the case of no flow core or uncertainty about whether there is a flow core, the latter requires fewer parameters and calculations in the fitting process. However, these two models have only been verified in the microcirculation of living bodies. The reason is that the blood flow velocity distribution data used to verify the model is obtained based on optical means. Optical methods generally have the characteristics of high accuracy but low penetration depth, making it difficult to obtain blood flow information in deep blood vessels. Summary of the invention

[0003] 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 observing the blood flow velocity distribution characteristics inside isolated blood vessels. The high penetration depth characteristics of magnetic resonance imaging are utilized to supplement the insufficient penetration depth of the existing optical methods, and finally realize the non-invasive detection of blood flow status in key locations such as the vicinity of the carotid sinus. The whole blood viscosity and plasma viscosity under the shear rate of the location can also be further analyzed in combination with blood pressure data.

[0004] A magnetic resonance method for observing the blood flow velocity distribution characteristics inside an isolated blood vessel comprises the following steps:

[0005] Step 1: The surface coil is fixed on the subject, and the subject is placed in the MRI machine;

[0006] Step 2: Debug the workstation supporting the MRI instrument;

[0007] Step 3, positioning the scanned visual field selection area covering the common carotid artery;

[0008] Step 4: According to the selected visual field covering the common carotid artery, the improved FLASH sequence is loaded to obtain the free induction decay signal;

[0009] Step 5: The MRI machine is removed from the bed;

[0010] Step 6, reconstructing the free induction decay signal to obtain a cross-sectional projection diagram of the blood flow;

[0011] Step 7: Calculate the viscosity ratio of the inner and outer layers of blood and the proportion of the inner layer diameter based on the cross-sectional projection diagram of the blood flow.

[0012] As described above, step 2 includes the following steps: creating a new first scan, loading the positioning image pulse sequence, starting the tuning mode, adjusting the knob on the surface coil so that the lowest point of the reflection curve displayed on the workstation coincides with the center frequency, and adjusting the value of the lowest point of the reflection curve to less than 5%.

[0013] As mentioned above, step 3 includes the following steps:

[0014] In the first scan established, run the positioning image pulse sequence to obtain transverse positioning images, coronal positioning images, and sagittal positioning images. The transverse image should cover all the subject images as much as possible, and the coronal and sagittal images should roughly select the shoulder and neck position to determine the field of view selection for the next scan;

[0015] Create a new second scan, load the FLASH sequence, and determine the field of view selection covering the common carotid artery for the next scan;

[0016] Create a third scan, adjust the FLASH sequence parameters, and determine the field of view selection covering the common carotid artery for the next scan.

[0017] As described above in step 3, the parameters of the FLASH sequence in the second scan include: slice direction: axial, slice number = 9, slice thickness = 1.5 mm, sampling matrix = 256*192, repetition time = 350 ms, echo time = 5.4 ms, average number = 1, excitation pulse is 0.9 ms hermite pulse, flip angle = 40 degrees;

[0018] In step 3, the parameters of the FLASH sequence in the third scan include: slice direction: sagittal, number of slices = 1, slice thickness = 3 mm, sampling matrix = 256*192, repetition time = 100 ms, echo time = 3.926 ms, average times = 20, excitation pulse is 3 ms hermite pulse, flip angle = 40 degrees.

[0019] As mentioned above, the improved FLASH sequence timing in step 4 is as follows:

[0020] Step 4.1, applying an excitation pulse of the gradient magnetic field coil in the readout direction, improving the FLASH sequence so that all the excitation pulses of the gradient magnetic field coils are square waves, and considering their rising and falling edges, and applying a 90° radio frequency pulse at the same time;

[0021] Step 4.2, applying a gradient magnetic field coil excitation pulse orthogonal to the readout direction to form a gradient magnetic field;

[0022] Step 4.3: Wait for a set delay time T delay , under the effect of the delay time, static tissues will not be affected; but the flowing blood will flow from outside the saturation zone into the saturation zone through the blood vessels, and the saturation state of some saturation zone areas will be destroyed to an excitable state;

[0023] Step 4.4, applying an excitation pulse of the gradient magnetic field coil in the slice selection direction and a 40° radio frequency pulse, the excitation pulse of the gradient magnetic field coil in the slice selection direction and the 40° radio frequency pulse are applied simultaneously to perform radio frequency excitation on the imaging layer;

[0024] Step 4.5: Apply reverse excitation pulses of the gradient magnetic field coils in the slice selection direction and the readout direction and excitation pulses of the gradient magnetic field coils in the phase direction, and perform phase encoding while completing the slice gradient echo operation. The polarities of the reverse excitation pulses in the slice selection direction and the readout direction are opposite to the polarities of the corresponding excitation pulses.

[0025] The magnitude of the reverse excitation pulse in the slice selection direction is half the magnitude of the excitation pulse of the gradient magnetic field coil in the slice selection direction in step 4.4;

[0026] The magnitude of the reverse excitation pulse in the readout direction is half the magnitude of the excitation pulse of the readout direction gradient magnetic field coil applied in the subsequent readout step 4.6;

[0027] The magnitude of the excitation pulse in the phase direction is the same as the magnitude of the reverse excitation pulse of the phase direction gradient magnetic field coil applied in the subsequent phase refocusing step 4.7, but the polarity is opposite, and they both change with the number of cycles;

[0028] Step 4.6, applying an excitation pulse of the readout direction gradient magnetic field coil to perform frequency encoding while sampling the signal, to obtain a free induction decay signal;

[0029] Step 4.7, applying a reverse excitation pulse of the phase direction gradient magnetic field coil in the phase direction, refocusing the phase while destroying the residual uncollected signal with the excitation pulse of the readout direction gradient magnetic field coil.

[0030] As described above, the viscosity of the inner and outer layers of blood in step 7 is obtained by the following steps:

[0031] Step 7.1. The following 5 points of the white bulge outline in the cross-sectional projection diagram: Point 1. The intersection point where the side of the white bulge close to the left tube wall intersects with the saturation band boundary for the first time along the bulge direction of the white bulge, with coordinates (x1, y1); Point 2. The inflection point on the left side of the white bulge, with coordinates (x2, y2); Point 3. The point with the longest displacement in the white bulge, with coordinates (x3, y3); Point 4. The inflection point on the right side of the white bulge, with coordinates (x4, y4); Point 5. The intersection point where the side of the white bulge close to the right tube wall intersects with the saturation band boundary for the first time along the bulge direction of the white bulge, with coordinates (x5, y5), record

[0032] Step 7.2, divide the coordinates of the five points into {(x i1 ,y i1 )|i1=1,2,4,5} and {(x i2 ,y i2 )|i2=2,3,4} two groups, forming a matrix and matrix Set the rotation angles θ1 and θ2, and assign the iteration initial value 0;

[0033] Step 7.3, calculate the rotation matrix separately and

[0034] The rotated matrix P1 is the point coordinate matrix

[0035] The rotated matrix P2 is the point coordinate matrix

[0036] Step 7.4: For the first set of coordinates {(x i1 ,y i1 )|i1=1,2,4,5}, construct the independent variable matrix from the point coordinate matrix P′1 And the dependent variable matrix Yv1 = [y1′ y2′ y4′] T , coefficient matrix A1 = [a1 b1 c1] T , solve the matrix equation X′1A1=Y′1 about the coefficient matrix A1;

[0037] Step 7.5: For the second set of coordinates {(x i2 ,y i2 )|i2=2,3,4},

[0038] Calculate the coefficient matrix A2 = [a2 b2 c2] T ,

[0039] in b2=-2a2x″3,

[0040] Step 7.6: Calculate the error value

[0041] Step 7.7: When E1≥0.05, let the new θ1=θ1-E1×10 -4 ;

[0042] When E2≥0.05, let the new θ2=θ2-E2×10 -4 ;

[0043] If E1 ≥ 0.05 or E2 ≥ 0.05, repeat steps 7.3-7.6;

[0044] If both E1 and E2 are less than 0.05, proceed to step 7.8;

[0045] Step 7.8, calculate the viscosity ratio a1 / a2 of the inner and outer layers of blood.

[0046] As mentioned above in step 7

[0047] in, They are the coordinates of point 1, point 2, point 3, point 4, and point 5 respectively, and “-” is a vector operator.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] 1. Higher penetration depth than optics, ensuring detection of deep blood vessels.

[0050] 2. In-situ detection, the results are closer to the actual flow of blood in the living body.

[0051] 3. While obtaining the blood flow properties, the vascular morphology and structure can be intuitively seen in the results.

[0052] 4. The method used does not rely on any blood flow-related mathematical model from signal acquisition to reconstruction, but directly obtains the flow velocity at various locations on the same cross-section of the blood vessel. The mathematical model description of other blood flow phenomena can also be verified and applied using this imaging method. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is the improved FLASH sequence timing diagram of the present invention;

[0054] Figure 2 It is a flowchart of the algorithm of the present invention;

[0055] Figure 3 This is a transverse positioning image of the rat's neck;

[0056] Figure 4 This is a coronal positioning image of the rat's neck;

[0057] Figure 5 This is a sagittal localization image of the rat's neck;

[0058] Figure 6 This is one of the multi-layer images of the transverse section of the neck (a total of 9 layers, the shapes are roughly similar but the positions of the bright spots arranged in a straight line vertically in the image are slightly different);

[0059] Figure 7 This is the carotid artery positioning image;

[0060] Figure 8 This is a schematic diagram of the selected point location;

[0061] Fig. 9 Effect diagram of bit data processing results;

[0062] Fig.10 The storage structure of the raw data required for the data processing of the present invention requires that the conventional K-space Cartesian sampling + two-dimensional Fourier transform reconstruction algorithm be used to obtain an image at the data processing terminal before running the data processing method of the present invention;

[0063] Fig.11 Schematic diagram of the two-phase flow model of blood. DETAILED DESCRIPTION

[0064] In order to facilitate those skilled in the art to understand and implement the present invention, Figures 1 to 11 The present invention is further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0065] Example: Determination of the ratio of inner layer diameter to inner and outer layer viscosity ratio in healthy Sprague-Dawley rats

[0066] This example uses a 7T small animal MRI instrument from Bruker, the workstation operating system is Cent OS, the supporting software platform is ParaVision5.1, and the data processing terminal operating system is Windows 10. The healthy SD rats used weigh about 320 g. The two-phase flow model is selected as the fitting model. Personnel protection should be fully done before the experiment.

[0067] A magnetic resonance method for observing the blood flow velocity distribution characteristics inside an isolated blood vessel comprises the following steps:

[0068] Step 1: Anesthesia and fixation of rats

[0069] The rats were weighed and anesthetized, and fixed on the rat bed with the MRI instrument in a supine position without a 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 rats were placed head first on the rat bed, so that the shoulder and neck of the rats were located at the center of the magnet of the MRI instrument.

[0070] Step 2: Adjustment before experiment

[0071] Start ParaVision5.1, create a new Patient and Study, create the first scan Scan1 and load the positioning image pulse sequence (1-TriPilot-ig). Start the tuning (wobble) mode, adjust the knob on the surface coil so that the lowest point of the reflection curve displayed on the ParaVision5.1 interface of the workstation coincides with the center frequency, and adjust the value of the lowest point of the reflection curve to less than 5%. After completion, click the STOP button to prepare to start the experiment.

[0072] Step 3: Positioning

[0073] In the first scan Scan1, run the scout pulse sequence. The MRI instrument will automatically execute the scout pulse sequence after frequency shimming and gain adjustment to obtain the following Figure 3-5 The three orientations of the positioning images shown include the transverse positioning image ( Figure 3 ), coronal positioning image ( Figure 4 ), sagittal localization image ( Figure 5 ), the white box is the field of view selection for the next scan. The transverse section is required to cover all rat images as much as possible, and the coronal and sagittal sections can be roughly located at the shoulder and neck position.

[0074] Create a second scan Scan2 and load the FLASH sequence (the workstation's ParaVision5.1 comes with a FLASH sequence) using the following parameters: Slice Orientation: axial, Number of Slices = 9, Slice Thick = 1.5 mm, Sampling Matrix = 256*192, Repetition Time = 350 ms, Echo Time = 5.4 ms, Numbers of Average = 1, Excitation Pulse (0.9 ms, hermite pulse), Flip Angle = 40 degrees). Figure 6 The transverse multi-layer image shown (such as Figure 6), the white frame is the visual field selection area covering the common carotid artery in the next scan. In this step, the common carotid artery is the left common carotid artery. The image actually includes 9 images of different layers but similar shapes. The bright spot in the white frame (visual field selection area) is the left common carotid artery. The position of the bright spot in the image of different layers is slightly moved. The position needs to be adjusted so that the visual field selection area covers as many bright spots between different layers as possible.

[0075] Finally, create a third scan Scan3, load the FLASH sequence, and adjust the FLASH sequence parameters as follows: Slice Orientation: sagittal, Number of Slices = 1, Slice Thick = 3mm, Sampling Matrix = 256*192, Repetition Time = 100ms, Echo Time = 3.926ms, Numbers of Average = 20, Excitation Pulse (3ms, hermite pulse), Flip Angle = 40deg). Note that during the layer selection process of the third scan Scan3, the layers must include all the common carotid artery areas of the second scan Scan2 results. Finally, execute the third scan Scan3, and the resulting common carotid artery positioning map is as shown below. Figure 7 As shown, the white rectangle is the field of view selection covering the common carotid artery in the next scan, and the oblique line area is the saturation band selection.

[0076] Step 4: Formal Scan

[0077] Clone the third scan Scan3 to the fourth scan Scan4, change the parameters: sampling matrix (Matrix) = 128 * 96, field of view (Field of View) = 2 * 1.4cm 2 , and load the improved FLASH sequence (loc_presat_FLASH) at the same time. The improved FLASH sequence timing is as follows:

[0078] Step 4.1, applying the excitation pulse of the gradient magnetic field coil in the readout direction, improving the excitation pulses of all the gradient magnetic field coils of the FLASH sequence to be square waves, and considering the rising and falling edges, applying a 90° RF pulse at the same time, the envelope shape of the 90° RF pulse can be selected between hermite and sinc according to the hardware conditions and imaging effects, to achieve selective RF excitation of a certain layer in space perpendicular to the readout direction;

[0079] Step 4.2: After spatial excitation, apply a gradient magnetic field coil excitation pulse orthogonal to the readout direction to form a gradient magnetic field. The gradient magnetic field destroys the signal of the excited layer in step 4.1. At this time, the excited layer is in a saturated state where it cannot be excited and does not generate signals, and is displayed as a black strip on the image, while other parts are not affected;

[0080] Step 4.3: Wait for a set delay time T after the excitation pulse of the gradient magnetic field coil delay Under the effect of the delay time, static tissues will not be affected; however, flowing blood will flow into the saturated zone from outside the saturated zone through blood vessels, causing the saturated state of some saturated zone areas to be destroyed and turned into an excitable state. The greater the degree of saturated zone destruction, the closer the grayscale value of the corresponding position in the result image is to the FLASH image, and the scope of the destruction, that is, the blood in T delay The range of blood flow during the period. Since the blood flow in the straight vessels has been proven to be laminar, and the common carotid artery is a straight line with a circular cross-section when the neck is stretched on this side, the outline of this range is a cross-sectional projection of the blood flow. In the subsequent steps, the FLASH sequence was used to visualize this range;

[0081] Step 4.4, the layer selection excitation step follows the original excitation step of the FLASH sequence. In the layer selection excitation step, the excitation pulse of the layer selection direction gradient magnetic field coil and the 40° radio frequency pulse are applied simultaneously to perform radio frequency excitation on the imaging layer;

[0082] Step 4.5: The gradient echo step uses the short echo mode of the FLASH sequence. The gradient echo step applies the reverse excitation pulses of the gradient magnetic field coils in the layer selection direction and the readout direction and the excitation pulses of the gradient magnetic field coils in the phase direction. Phase encoding is performed while completing the layer gradient echo operation. The polarity of the reverse excitation pulses in the layer selection direction and the readout direction is opposite to the polarity of the corresponding excitation pulses.

[0083] The magnitude of the reverse excitation pulse in the slice selection direction is half the magnitude of the excitation pulse of the gradient magnetic field coil in the slice selection direction in step 4.4;

[0084] The magnitude of the reverse excitation pulse in the readout direction is half the magnitude of the excitation pulse of the readout direction gradient magnetic field coil applied in the subsequent readout step 4.6;

[0085] The magnitude of the excitation pulse in the phase direction is the same as the magnitude of the reverse excitation pulse of the phase direction gradient magnetic field coil applied in the subsequent phase refocusing step 4.7, but the polarity is opposite, and they both change with the number of cycles.

[0086] The above-mentioned “size” refers to the integral of the current intensity curve corresponding to the pulse (reverse excitation pulse, excitation pulse) during the application period. For example, the size of the reverse excitation pulse refers to the integral of the current intensity curve corresponding to the reverse excitation pulse during the application period. The size of the excitation pulse of the layer selection direction gradient magnetic field coil refers to the integral of the current intensity curve corresponding to the excitation pulse of the layer selection direction gradient magnetic field coil during the application period.

[0087] Step 4.6: The sampling step follows the FLASH sampling step. While sampling the signal, an excitation pulse of the readout direction gradient magnetic field coil is applied to perform frequency encoding to obtain a free induction decay signal.

[0088] Step 4.7, the destruction step follows the short echo mode of FLASH, applies the reverse excitation pulse of the phase direction gradient magnetic field coil in the phase direction, and destroys the residual uncollected signal with the excitation pulse of the readout direction gradient magnetic field coil while refocusing the phase, preventing this part of the signal from entering the next cycle process;

[0089] After loading the improved FLASH sequence, change the positioning settings of the fourth scan Scan4 as follows Figure 7 As shown, that is, the saturation band is rotated so that the plane where the saturation band is located is perpendicular to the direction of the blood vessel. Figure 7 The area covered by the thin oblique line is shown, and the upper and lower positions of the saturation band are adjusted so that the center of the saturation band is located about 8 to 10 mm from the common carotid artery to the carotid sinus, and the width of the saturation band is adjusted to 5 mm. Figure 7 The hollow rectangular part has a rectangular size of 2mm*1.4mm, which is the field of view set by the parameters. The imaging field of view frame selection area should include the carotid sinus area, the saturated zone area near the carotid sinus, and the common carotid artery near the carotid sinus, and the readout direction is specified as the head-to-foot direction. In this embodiment, the head-to-foot direction is the long side direction of the imaging field of view.

[0090] The saturation band region is subjected to a pre-saturation pulse before imaging ( Figure 1 The static tissue signal in the saturation band area is completely eliminated, while the moving blood will generate Figure 1 Medium delay time T delay In the parameter setting interface of ParaVision software, a delay time T is given. delay After the scan is completed, the total scanning time is 3min12s. The cross-sectional projection diagram of the blood flow obtained by scanning is displayed in the workstation as shown in the following figure. Figure 8 If you need to perform multiple scans, you can directly clone Scan4 to a new Scan and then perform the scan.

[0091] Step 5: Remove the rat

[0092] After completing the above steps, the MRI machine will exit the bed, remove the rat from the magnet cavity and remove the radio frequency coil. Put the rat back into the cage and clean and remove the animal bed.

[0093] Step 6: Data transfer and reconstruction

[0094] Transfer the data folder from the workstation to the data processing terminal. The structure of the data folder is as follows: Fig.10 As shown in the figure, the data folder contains the folders of each scan Scan under Study used for imaging. Each scan Scan contains at least pdata folder, acqp file, fid file, method file and pulseprogram file. The fid file in the fourth scan Scan4 is the free induction decay signal of the cross-sectional projection diagram of blood flow. After the transfer is completed, the free induction decay signal is reconstructed and the following is obtained at the data processing terminal: Figure 8 The cross-sectional projection of the blood flow is shown. The white protrusion in the saturation band is the blood flow at the delay time T Delay The longer the distance of the white bulge is, the more blood at that location flows in during the delay time T Delay The greater the internal displacement, the faster the flow velocity. Figure 8 It can be seen that the flow velocity in the pipe axis is the fastest and the flow velocity in the pipe wall is the slowest. The distribution is consistent with the two-phase flow model and the inflection point described in the model does exist.

[0095] Step 7: Model fitting and calculation of inner and outer layer viscosity ratio

[0096] Step 7.1, import the fourth scan Scan4 imaging result generated in step 6 - the cross-sectional projection of blood flow, and mark the white raised contours in the cross-sectional projection of blood flow in sequence ( Figure 8 The following 5 points (such as Figure 8 ): Point 1. Along the bulge direction of the white bulge, the first intersection of the side of the white bulge close to the left wall and the saturation zone boundary, the coordinates are (x1, y1); Point 2. The inflection point on the left side of the white bulge, the coordinates are (x2, y2); Point 3. The point with the longest displacement in the white bulge, the coordinates are (x3, y3); Point 4. The inflection point on the right side of the white bulge, the coordinates are (x4, y4); Point 5. Along the bulge direction of the white bulge, the first intersection of the side of the white bulge close to the right wall and the saturation zone boundary, the coordinates are (x5, y5). Obtain the plane coordinates corresponding to the cross-sectional projection diagram of the blood flow The processing process is as follows:

[0097] Step 7.2, divide the coordinates of the five points into {(x i1 ,y i1 )|i1=1,2,4,5} and {(xi2 ,y i2 )|i2=2,3,4} two groups, forming a matrix and matrix Set the rotation angles θ1 and θ2, and assign the iteration initial value 0;

[0098] Step 7.3, calculate the rotation matrix separately and

[0099] The rotated matrix P1 is the point coordinate matrix

[0100] The rotated matrix P2 is the point coordinate matrix

[0101] Step 7.4: For the first set of coordinates {(x i1 ,y i1 )|i1=1,2,4,5}, construct the independent variable matrix from the point coordinate matrix P′1 And the dependent variable matrix Y′1=[y1′ y2′ y4′] T , coefficient matrix A1 = [a1 b1 c1] T Solve the matrix equation X′1A1=Y′1 about the coefficient matrix A1

[0102] Step 7.5: For the second set of coordinates {(x i2 ,y i2 )|i2=2,3,4},

[0103] Calculate the coefficient matrix A2 = [a2 b2 c2] T ,

[0104] in b2=-2a2x″3,

[0105] Step 7.6: Calculate the error value

[0106] Step 7.7, determine E respectively i3 <0.05,i3=1,2,

[0107] When E1≥0.05, let the new θ1=θ1-E1×10 -4 ,

[0108] When E2≥0.05, let the new θ2=θ2-E2×10 -4 ,

[0109] If E1 ≥ 0.05 or E2 ≥ 0.05, repeat steps 7.3-7.6;

[0110] If both E1 and E2 are less than 0.05, proceed to step 7.8;

[0111] Step 7.8, end, record the coefficient matrix A1, coefficient matrix A2, rotation angle θ1, and rotation angle θ2. The recorded data can be used for drawing and calculating the viscosity ratio of the inner and outer layers of blood (a1 / a2).

[0112] Step 8: Calculation of the inner layer diameter ratio

[0113] The points marked in step 7 can be used to calculate the inner diameter ratio, the formula is

[0114] Among them, D i is the inner diameter, which is the same as the inner diameter of the blood vessel D vessel The ratio is defined as the inner diameter ratio. The numerator of the formula is the vector inner product of the inner diameter of the blood vessel and the inner diameter of the blood flow, which is then divided by the second norm of the inner diameter vector (that is, the length) to obtain the projection length of the inner diameter of the blood flow in the direction perpendicular to the direction of the blood vessel. This calculation can offset the deviation caused by the inner layer deviating from the axis during the physiological flow of blood. The inner diameter ratio is then obtained by dividing the projection length of the inner diameter of the blood flow by the inner diameter of the blood vessel. are the coordinates of points 1, 2, 3, 4, and 5 marked in step 7. The “-” in this step is a vector operator.

[0115] This embodiment also provides a magnetic resonance device for observing the blood flow velocity distribution characteristics inside an isolated blood vessel, comprising module 1, module 2, module 3, module 4, module 5, module 6, module 7, and module 8. The above steps 1-8 are implemented by modules 1-8 respectively.

[0116] The specific embodiments described herein are merely examples of the present invention. A person skilled in the art may make various modifications, additions or substitutions to the specific embodiments described, but will not deviate from the essence of the present invention or exceed the scope defined by the appended claims.

Claims

1. A magnetic resonance method for observing the blood flow velocity distribution characteristics inside an isolated blood vessel, characterized in that: The following steps are involved: Step 1: The surface coil is fixed on the subject, and the subject is placed in the MRI machine; Step 2: Debug the workstation supporting the MRI instrument; Step 3, positioning the scanned visual field selection area covering the common carotid artery; Step 4: According to the selected visual field covering the common carotid artery, the improved FLASH sequence is loaded to obtain the free induction decay signal; Step 5: The MRI machine is removed from the bed; Step 6, reconstructing the free induction decay signal to obtain a cross-sectional projection diagram of the blood flow; Step 7: Calculate the viscosity ratio of the inner and outer layers of blood and the proportion of the inner layer diameter according to the cross-sectional projection diagram of the blood flow. In step 7, the viscosity of the inner and outer layers of blood is obtained by the following steps: Step 7.

1. The following 5 points of the white bulge outline in the cross-sectional projection diagram: Point 1. The intersection point where the side of the white bulge close to the left tube wall intersects with the saturation band boundary for the first time along the bulge direction of the white bulge, with coordinates (x1, y1); Point 2. The inflection point on the left side of the white bulge, with coordinates (x2, y2); Point 3. The point with the longest displacement in the white bulge, with coordinates (x3, y3); Point 4. The inflection point on the right side of the white bulge, with coordinates (x4, y4); Point 5. The intersection point where the side of the white bulge close to the right tube wall intersects with the saturation band boundary for the first time along the bulge direction of the white bulge, with coordinates (x5, y5), record Step 7.2, divide the coordinates of the five points into {(x i1 ,y i1 )|i1=1,2,4,5} and {(x i2 ,y i2 )|i2=2,3,4} two groups, forming a matrix and matrix Set the rotation angles θ1 and θ2, and assign the iteration initial value 0; Step 7.3, calculate the rotation matrix separately and The rotated matrix P1 is the point coordinate matrix The rotated matrix P2 is the point coordinate matrix Step 7.4: For the first set of coordinates {(x i1 ,y i1 )|i1=1,2,4,5}, construct the independent variable matrix from the point coordinate matrix P′1 And the dependent variable matrix Y′1=[y1′ y2′ y4′] T , coefficient matrix A1 = [a1 b1 c1] T , solve the matrix equation X′1A1=Y′1 about the coefficient matrix A1; Step 7.5: For the second set of coordinates {(x i2 ,y i2 )|i2=2,3,4}, Calculate the coefficient matrix A2 = [a2 b2 c2] T , in b2=-2a2x″3, Step 7.6: Calculate the error value Step 7.7: When E1≥0.05, let the new θ1=θ1-E1×10 -4 ; When E2≥0.05, let the new θ2=θ2-E2×10 -4 ; If E1 ≥ 0.05 or E2 ≥ 0.05, repeat steps 7.3-7.6; If both E1 and E2 are less than 0.05, proceed to step 7.8; Step 7.8, calculate the viscosity ratio of the inner and outer layers of blood a1 / a2, in, They are the coordinates of point 1, point 2, point 3, point 4, and point 5 respectively, and "-" is a vector operator.

2. A magnetic resonance method for observing the blood flow velocity distribution characteristics inside an isolated blood vessel according to claim 1, characterized in that: The step 2 includes the following steps: creating a new first scan, loading a positioning image pulse sequence, starting a tuning mode, adjusting the knob on the surface coil so that the lowest point of the reflection curve displayed on the workstation coincides with the center frequency, and adjusting the value of the lowest point of the reflection curve to less than 5%.

3. The magnetic resonance method for observing the blood flow velocity distribution characteristics inside an isolated blood vessel according to claim 1, characterized in that: The step 3 comprises the following steps: In the first scan established, run the positioning image pulse sequence to obtain transverse positioning images, coronal positioning images, and sagittal positioning images. The transverse image should cover all the subject images as much as possible, and the coronal and sagittal images should select the shoulder and neck position to determine the field of view selection for the next scan; Create a new second scan, load the FLASH sequence, and determine the field of view selection covering the common carotid artery for the next scan; Create a third scan, adjust the FLASH sequence parameters, and determine the field of view selection covering the common carotid artery for the next scan.

4. A magnetic resonance method for observing the blood flow velocity distribution characteristics inside an isolated blood vessel according to claim 3, characterized in that: In step 3, the parameters of the FLASH sequence in the second scan include: slice direction: axial, slice number = 9, slice thickness = 1.5 mm, sampling matrix = 256*192, repetition time = 350 ms, echo time = 5.4 ms, average number = 1, excitation pulse is 0.9 ms hermite pulse, flip angle = 40 degrees; In step 3, the parameters of the FLASH sequence in the third scan include: slice direction: sagittal, number of slices = 1, slice thickness = 3 mm, sampling matrix = 256*192, repetition time = 100 ms, echo time = 3.926 ms, average times = 20, excitation pulse is 3 ms hermite pulse, flip angle = 40 degrees.

5. The magnetic resonance method for observing the blood flow velocity distribution characteristics inside an isolated blood vessel according to claim 1, characterized in that: The improved FLASH sequence timing in step 4 is as follows: Step 4.1, applying an excitation pulse of the gradient magnetic field coil in the readout direction, improving the FLASH sequence so that all the excitation pulses of the gradient magnetic field coils are square waves, and considering their rising and falling edges, and applying a 90° radio frequency pulse at the same time; Step 4.2, applying a gradient magnetic field coil excitation pulse orthogonal to the readout direction to form a gradient magnetic field; Step 4.3: Wait for a set delay time T delay , under the effect of the delay time, static tissues will not be affected; but the flowing blood will flow from outside the saturation zone into the saturation zone through the blood vessels, and the saturation state of some saturation zone areas will be destroyed to an excitable state; Step 4.4, applying an excitation pulse of the gradient magnetic field coil in the slice selection direction and a 40° radio frequency pulse, the excitation pulse of the gradient magnetic field coil in the slice selection direction and the 40° radio frequency pulse are applied simultaneously to perform radio frequency excitation on the imaging layer; Step 4.5: Apply reverse excitation pulses of the gradient magnetic field coils in the slice selection direction and the readout direction and excitation pulses of the gradient magnetic field coils in the phase direction, and perform phase encoding while completing the slice gradient echo operation. The polarities of the reverse excitation pulses in the slice selection direction and the readout direction are opposite to the polarities of the corresponding excitation pulses. The magnitude of the reverse excitation pulse in the slice selection direction is half the magnitude of the excitation pulse of the gradient magnetic field coil in the slice selection direction in step 4.4; The magnitude of the reverse excitation pulse in the readout direction is half the magnitude of the excitation pulse of the readout direction gradient magnetic field coil applied in the subsequent readout step 4.6; The magnitude of the excitation pulse in the phase direction is the same as the magnitude of the reverse excitation pulse of the phase direction gradient magnetic field coil applied in the subsequent phase refocusing step 4.7, but the polarity is opposite, and they both change with the number of cycles; Step 4.6, applying an excitation pulse of the readout direction gradient magnetic field coil to perform frequency encoding while sampling the signal, to obtain a free induction decay signal; Step 4.7, applying a reverse excitation pulse of the phase direction gradient magnetic field coil in the phase direction, refocusing the phase while destroying the residual uncollected signal with the excitation pulse of the readout direction gradient magnetic field coil.

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