A water model and calibration method for gradient nonlinear error calibration of DWI quantitative analysis

Abstract

The present invention proposes a DWI quantitative analysis gradient nonlinear error calibration water model, the structure of which includes a plurality of layers of water model solution tubes (1), a sealing plate (2), and a liquid injection box (3); wherein the plurality of layers of water model solution tubes (1) are placed parallel to each other, one end of the plurality of layers of water model solution tubes (1) is connected to the sealing plate (2), the other end of the plurality of layers of water model solution tubes 1 is connected to the liquid injection box (3), the liquid injection box (3) is provided with a liquid injection box seal (4), and the other end of each water model solution tube (1) is connected to the liquid injection box (3). A method for calibrating using a DWI quantitative analysis gradient nonlinear error calibration water model, the method comprising calibrating an ADC calculated by DWI using a DWI quantitative analysis gradient nonlinear error calibration water model; the present invention can effectively avoid standing wave artifacts, and can calibrate the ADC deviation caused by gradient nonlinearity through a single test.

Description

Technical Field

[0001] The invention discloses a DWI quantitative analysis gradient nonlinear error calibration water model and a calibration method, belonging to the technical field of magnetic resonance imaging. Background Art

[0002] MRI (magnetic resonance imaging) is a commonly used imaging technique in clinical practice. Its significant advantages are no ionizing radiation, multi-sequence, and multi-directional imaging.

[0003] DWI (diffusion weighted imaging) is a quantitative MRI method widely used in clinical practice. It can measure the diffusion rate of water molecules in human tissue for the diagnosis of diseases. Clinically, DWI can provide images for qualitative diagnosis of diseases on the one hand, and calculate quantitative parameters such as ADC (apparent diffusion coefficient) for disease diagnosis and treatment efficacy evaluation on the other hand.

[0004] DWI uses the diffusion sensitivity gradient to measure the diffusion rate of water molecules in human tissues, and controls the degree of water molecule diffusion through the diffusion sensitivity factor (b value). A low b-value and a high b-value DWI image (or multiple high b-value DWI images) can be collected, and the ADC can be calculated using a single exponential model to characterize the speed of water molecule diffusion in tissues. The single exponential model is based on the assumption that the tissue has a single diffuse component and that water molecules move freely. It is the most commonly used data analysis method for DWI and has the advantage of fast calculation.

[0005] Clinical MRI equipment is mainly based on superconducting systems with an aperture of 60 cm-70 cm. Gradient nonlinearity has a great influence on DWI quantitative parameters, causing the ADC error of tissue to reach 20%. In order to improve the accuracy of DWI quantitative analysis, gradient nonlinearity error detection is required, and the ADC is calibrated by certain methods (such as water phantom test) to improve the accuracy of calculated ADC. In the water phantom used for DWI calibration, the shape and filling of the model need to be considered in order to design DWI tests for specific purposes.

[0006] The water phantom for DWI calibration that has been reported frequently is the ice-water mixture temperature-controlled water phantom developed by the Radiological Society of North America (RSNA) and the Quantitative Imaging Biomarkers Alliance (QIBA). The water phantom is spherical in design, with a diameter of about 20 cm, and multiple test tubes are implanted inside to store test solutions, such as polyvinylpyrrolidone (PVP) solution. The water phantom is filled with an ice-water mixture and temperature equilibrium is achieved to control the temperature of the test solution to 0 0 C. The test solution has a known ADC (standard value) at this temperature, and the gradient nonlinear error is calculated by the difference between the ADC measured value and the standard value. It is worth noting that the design of this water phantom is mainly for intracranial DWI research. When imaging body DWI, a wider imaging field of view is required, and the imaging range is larger than the head. The reported water phantom needs to be repeatedly tested by moving the water phantom position multiple times to evaluate the gradient nonlinear error. Moving the water phantom position and repositioning will bring new errors. In addition, if the existing water phantom size is changed to the size of the abdomen, standing wave artifacts will be generated. In order to overcome the shortcomings of the existing technology, designing a body DWI calibration water phantom is of great significance to improving the accuracy of body DWI quantitative parameters. At the same time, when designing the water phantom, it is also necessary to consider the cost, ease of use and other characteristics. Summary of the invention

[0007] The present invention proposes a DWI quantitative analysis gradient nonlinear error calibration water phantom and a calibration method, which is intended to be used for calibrating the apparent diffusion coefficient of diffusion weighted imaging.

[0008] The technical solution of the present invention is: a DWI quantitative analysis gradient nonlinear error calibration water model, whose structure includes several layers of water model solution tubes 1, a sealing plate 2, and a liquid injection box 3; wherein the several layers of water model solution tubes 1 are placed parallel to each other, one end of the several layers of water model solution tubes 1 is connected to the sealing plate 2, the other end of the several layers of water model solution tubes 1 is connected to the liquid injection box 3, the liquid injection box 3 is provided with a liquid injection box seal 4, and the other end of each water model solution tube 1 is connected to the liquid injection box 3.

[0009] Furthermore, each layer of the several layers of water-model solution tubes 1 has several water-model solution tubes 1, and the number of water-model solution tubes 1 in each layer of the several layers of water-model solution tubes 1 first gradually increases and then gradually decreases from the bottom layer to the top layer, and the number of water-model solution tubes 1 in the top layer is equal to the number of water-model solution tubes 1 in the bottom layer; the side wall of the liquid injection box 3 connected to the several layers of water-model solution tubes 1 is an inner sealing plate 6 of the liquid injection box, and the inner sealing plate 6 of the liquid injection box is fixedly connected to the other end of the several layers of water-model solution tubes 1, and the inner sealing plate opening 5 of the liquid injection box is provided on the inner sealing plate 6 of the liquid injection box near the top of each water-model solution tube 1; the water-model solution tubes 1 are filled with water-model filling material; the liquid injection box seal 4 is located at the top of the liquid injection box 3.

[0010] Furthermore, the plurality of layers of water-modeled solution tubes 1 are N layers, N is an odd number, and the bottom layer is the first layer; from the first layer to the (N+1) / 2th layer, the number of water-modeled solution tubes 1 in each layer is one less than the number of water-modeled solution tubes 1 in the previous layer; the number of water-modeled solution tubes 1 in the (N-1) / 2th layer is one less than the number of water-modeled solution tubes 1 in the (N+1) / 2th layer; from the (N+1) / 2th layer to the Nth layer, the number of water-modeled solution tubes 1 in each layer is one more than the number of water-modeled solution tubes 1 in the previous layer.

[0011] Furthermore, the several layers of water-model solution tubes 1 are 7 layers, and the numbers of water-model solution tubes 1 from the 1st layer to the 7th layer are 6, 7, 8, 9, 8, 7, and 6 respectively, with a total of 51 water-model solution tubes 1; each water-model solution tube 1 is a cylindrical tube, and the length of each water-model solution tube 1 is 300 mm and the inner diameter is 29 mm; the several layers of water-model solution tubes 1, the sealing plate 2, and the liquid injection box 3 are all made of acrylic material.

[0012] Further, every three adjacent water phantom solution tubes 1 in the several layers of water phantom solution tubes 1 are stacked in a "pin" shape, and a standing wave artifact elimination area 7 is formed between the three water phantom solution tubes 1 stacked in a "pin" shape; the standing wave artifact elimination area 7 formed between the three water phantom solution tubes stacked in a "pin" shape is surrounded by three arc-shaped side walls; when the magnetic resonance imaging device performs MRI imaging, the radiofrequency field emitted by the magnetic resonance imaging device enters the DWI quantitative analysis gradient nonlinear error calibration water phantom from the air, and the incident direction of the radiofrequency field is perpendicular to the length direction of the water phantom solution tube 1. When the radiofrequency field passes through a water phantom solution tube 1 perpendicular to the length direction of the water phantom solution tube 1, the radiofrequency field does not directly enter the adjacent water phantom solution tube 1, but enters the adjacent standing wave artifact elimination area 7. Since the interface between the standing wave artifact elimination area 7 and each water phantom solution tube 1 is the arc-shaped interface formed by the tube wall of the water phantom solution tube 1, when the electromagnetic wave in the radiofrequency field passes through the arc-shaped interface, the incident angles between the electromagnetic waves at different positions and the arc-shaped interface are different, so that the electromagnetic waves in the radiofrequency field are transmitted into the standing wave artifact elimination area 7 at different angles respectively. After passing through the standing wave artifact elimination area 7, the electromagnetic waves in the radiofrequency field enter the next standing wave artifact elimination area 7 at different angles respectively. At the same time, the amplitude of the reflected electromagnetic wave in the water phantom solution tube 1 decreases, so that the radiofrequency field emitted by the magnetic resonance imaging device cannot form a standing wave during the propagation process in the entire DWI quantitative analysis gradient nonlinear error calibration water phantom.

[0013] Further, the inside of the standing wave artifact elimination area 7 is air; each water phantom solution tube 1 in the several layers of water phantom solution tubes 1 is a cylindrical tube, each water phantom solution tube 1 in the several layers of water phantom solution tubes 1 is horizontally placed, and the different water phantom solution tubes 1 are parallel to each other, and the size specifications of the different water phantom solution tubes 1 are the same; the cylindrical tube walls of two adjacent water phantom solution tubes 1 are tangent to each other.

[0014] A calibration method using a DWI quantitative analysis gradient nonlinear error calibration water phantom, the method includes calibrating the ADC calculated by DWI using the DWI quantitative analysis gradient nonlinear error calibration water phantom;

[0015] The calibration of the ADC calculated by DWI using the DWI quantitative analysis gradient nonlinear error calibration water phantom specifically includes:

[0016] 1. Inject the water phantom filling material into the injection tank 3 through the injection tank seal 4, and the water phantom filling material enters each water phantom solution tube 1 through the injection tank 3;

[0017] 2. Perform DWI scanning on the DWI quantitative analysis gradient nonlinear error calibration water phantom through a magnetic resonance imaging device;

[0018] 3. Use the DWI quantitative analysis obtained by scanning to calibrate the water model DWI data for gradient nonlinear error and calculate the apparent diffusion coefficient of the water model filling material;

[0019] 4. Calculate the three-dimensional spatial deviation of the apparent diffusion coefficient Bias 3d ;

[0020] 5. Calibrate the apparent diffusion coefficient of clinical MRI scan subjects.

[0021] Furthermore, the DWI quantitative analysis of the gradient nonlinear error obtained by scanning is used to calibrate the water model DWI data to calculate the apparent diffusion coefficient of the water model filling material, specifically including using a voxel-based single exponential model for calculation, as shown in formula (3):

[0022] (3);

[0023] Where ADC is the apparent diffusion coefficient, is the diffusion sensitivity factor, for The DWI signal intensity when the value is 0, for DWI signal intensity when value> 0; diffusion sensitivity factor It is calculated by the following formula (4):

[0024] (4);

[0025] in, is the gyromagnetic ratio of the proton, is the applied diffusion gradient strength, is the duration of the applied diffusion gradient, Refers to the time interval between two diffusion gradients.

[0026] Furthermore, the three-dimensional spatial deviation Bias of the calculated apparent diffusion coefficient 3d , including:

[0027] 4-1. Calculation of ADC Bias of water model filling material in magnetic coordinate system based on voxel analysis method voxel ;

[0028] 4-2. ADC Bias of water model filling material in magnetic coordinate system voxel Polynomial fitting to calculate the three-dimensional bias of the apparent diffusion coefficient 3d ;

[0029] The step 4-1 calculates the ADC deviation Bias of the water model filling material in the magnetic coordinate system based on the voxel analysis method. voxel, specifically including the calculation using the following formula (5):

[0030] (5);

[0031] Where ADC is the measured value of the apparent diffusion coefficient of the water model filling material of each voxel in the magnetic coordinate system obtained by DWI test, and ADC true is the standard value of the apparent diffusion coefficient of the water model filling material, Bias voxel is the ADC deviation of the water model filling material for each voxel in the magnet coordinate system;

[0032] The step 4-2 is for the ADC bias of the water model filling material in the magnet coordinate system voxel Polynomial fitting to calculate the three-dimensional bias of the apparent diffusion coefficient 3d Specifically, according to the actual magnetic coil characteristics, select fitting function 1 or fitting function 2 for Bias 3d Calculation of

[0033] The fitting function 1 adopts a second-order polynomial fitting, while considering the cross terms, as shown in formula (6):

[0034] (6);

[0035] Where X, Y, and Z represent the spatial position coordinates of the magnet coordinate system, b0 is a constant term, and b1, b2, b3, b4, b5, b6, b7, b8, and b9 are coefficients of each term; b0, b1, b2, b3, b4, b5, b6, b7, b8, and b9 are determined by multivariate linear regression of the ADC deviation of the water model filling material of all voxels in the magnet coordinate system, as shown in the following formula (7):

[0036] (7);

[0037] Wherein, X1, Y1, Z1, X2, Y2, Z2, ..., Xn, Yn, Zn represent the spatial position coordinates of each voxel of the water model filling material in the magnetic coordinate system, n is an integer, and the size of n is determined by the DWI scanning parameters; the DWI scanning parameters include the imaging field of view, imaging matrix, layer thickness, and layer spacing of the image in the DWI scanning parameters; b0 is a constant term, and b1, b2, b3, b4, b5, b6, b7, b8, and b9 are coefficients of each term; , ,……, They are the ADC deviations of the water model filling materials corresponding to the voxels at different spatial position coordinates in the magnet coordinate system;

[0038] The fitting function 2 adopts a second-order polynomial fitting and does not contain cross terms, as shown in formula (8):

[0039] (8);

[0040] Where X, Y, and Z represent the spatial position coordinates of the magnet coordinate system, b0 is a constant term, and b1, b2, b3, b4, b5, and b6 are coefficients of each term. b0, b1, b2, b3, b4, b5, and b6 are determined by multivariate linear regression of the ADC deviation of the water model filling material of all voxels in the magnet coordinate system, as shown in the following formula (9):

[0041] (9);

[0042] Wherein, X1, Y1, Z1, X2, Y2, Z2, ..., Xn, Yn, Zn represent the spatial position coordinates of each voxel of the water model filling material in the magnetic coordinate system, n is an integer, and the size of n is determined by the DWI scanning parameters; the DWI scanning parameters include the imaging field of view, imaging matrix, layer thickness, and layer spacing of the image in the DWI scanning parameters; b0 is a constant term, and b1, b2, b3, b4, b5, and b6 are coefficients of each term; , ,……, They are the ADC deviations of the water model filling material corresponding to the voxels at different spatial position coordinates in the magnet coordinate system.

[0043] Furthermore, the calibrating the apparent diffusion coefficient of the MRI clinical scan subject specifically includes:

[0044] The calibrated apparent diffusion coefficient ADC is calculated by the following formula (10): correct :

[0045] (10);

[0046] Among them, ADC correct is the apparent diffusion coefficient of the calibrated clinical subject, ADC patient It is the raw, uncalibrated apparent diffusion coefficient obtained from MRI examination of clinical subjects.

[0047] Beneficial effects of the present invention:

[0048] 1) The present invention can effectively avoid standing wave artifacts and solve the serious problem of standing wave artifacts in the water model traditionally used for DWI calibration;

[0049] 2) Through further design, the DWI quantitative analysis gradient nonlinear error calibration water phantom designed in the present invention is similar to the characteristics of the human body, and has significant advantages such as simple production, low cost, and easy use; it can be applied to body (including pelvic) DWI quality control, quantitative parameter error analysis, clinical image calibration, etc.; the ADC deviation caused by gradient nonlinearity can be calibrated through a single test. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Attached Figure 1 It is a schematic diagram of the overall structure of the water model for calibration of gradient nonlinear error in DWI quantitative analysis.

[0051] Attached Figure 2 It is a schematic diagram of the arrangement and distribution of several layers of water model solution tubes and the structure of the sealing plate.

[0052] Attached Figure 3 It is a schematic diagram of the arrangement and distribution of several layers of water model solution tubes and the structure of the sealing plate inside the liquid injection box.

[0053] Attached Figure 4 This is a schematic diagram of the apparent diffusion coefficient change curve of ultrapure water in the temperature range of 15℃-30℃.

[0054] Attached Figure 5 The DWI quantitative analysis gradient nonlinear error calibration water phantom cross-sectional ADC image calculated by formula (3).

[0055] Attached Figure 6 This is an example of a transverse image of the water phantom Bias3d calculated using formula (8) for the DWI quantitative analysis gradient nonlinear error calibration.

[0056] Attached Figure 7 It is a structural schematic diagram of the standing wave artifact elimination area.

[0057] Attached Figure 8 Yes Figure 7 A partial enlarged view of part A shown in FIG.

[0058] In the attached drawings, 1 is a water model solution tube, 2 is a sealing plate, 3 is a liquid injection box, 4 is a sealing of the liquid injection box, 5 is an opening of a sealing plate inside the liquid injection box, 6 is a sealing plate inside the liquid injection box, and 7 is a standing wave artifact elimination area. DETAILED DESCRIPTION

[0059] Referring to the accompanying drawings, a DWI quantitative analysis gradient nonlinear error calibration water model, its structure includes several layers of water model solution tubes 1, a sealing plate 2, and a liquid injection box 3; wherein, the several layers of water model solution tubes 1 are placed parallel to each other, one end of the several layers of water model solution tubes 1 is connected to the sealing plate 2, the other end of the several layers of water model solution tubes 1 is connected to the liquid injection box 3, the liquid injection box 3 is provided with a liquid injection box seal 4, and the other end of each water model solution tube 1 is connected to the liquid injection box 3.

[0060] Each layer of the several layers of water-model solution tubes 1 has several water-model solution tubes 1, and the number of water-model solution tubes 1 in each layer of the several layers of water-model solution tubes 1 gradually increases and then gradually decreases from the bottom layer to the top layer, and the number of water-model solution tubes 1 in the top layer is equal to the number of water-model solution tubes 1 in the bottom layer.

[0061] Preferably, the number of layers of water-modeled solution tubes 1 is N layers, N is an odd number, and the bottom layer is the first layer; from the first layer to the (N+1) / 2th layer, the number of water-modeled solution tubes 1 in each layer is one less than the number of water-modeled solution tubes 1 in the previous layer; the number of water-modeled solution tubes 1 in the (N-1) / 2th layer is one less than the number of water-modeled solution tubes 1 in the (N+1) / 2th layer; from the (N+1) / 2th layer to the Nth layer, the number of water-modeled solution tubes 1 in each layer is one more than the number of water-modeled solution tubes 1 in the previous layer.

[0062] Preferably, the number of layers of water-model solution tubes 1 is 7 layers, and the number of water-model solution tubes 1 from the 1st layer to the 7th layer is 6, 7, 8, 9, 8, 7, and 6 respectively, with a total of 51 water-model solution tubes 1; each water-model solution tube 1 is preferably a cylindrical acrylic tube, and each water-model solution tube 1 is preferably 300 mm in length and 29 mm in inner diameter, and is arranged in 7 rows according to a certain rule (such as the attached Figure 1 ).

[0063] The several layers of water-based solution tubes 1 , the sealing plate 2 , and the liquid injection box 3 are preferably made of acrylic material.

[0064] The side wall of the injection box 3 connected to the several layers of water model solution tubes 1 is an inner sealing plate 6 of the injection box. The inner sealing plate 6 of the injection box is fixedly connected to the other end of the several layers of water model solution tubes 1. The inner sealing plate opening 5 of the injection box is provided on the inner sealing plate 6 near the top of each water model solution tube 1. The aperture of the inner sealing plate opening 5 of the injection box is preferably 5 mm; the inner sealing plate opening 5 of the injection box is used to fill the water model filling material into the water model solution tube 1 through the injection box 3.

[0065] Each of the plurality of layers of water-mold solution tubes 1 is filled with a water-mold filling material; the water-mold filling material is preferably ultrapure water.

[0066] Among the several layers of water phantom solution tubes 1, every three adjacent water phantom solution tubes 1 are stacked in a "pin" shape, and a standing wave artifact elimination area 7 is formed between the three water phantom solution tubes 1 stacked in a "pin" shape; the standing wave artifact elimination area 7 formed between the three water phantom solution tubes stacked in a "pin" shape is surrounded by three arcs; when the magnetic resonance imaging device performs MRI imaging, the radiofrequency field emitted by the magnetic resonance imaging device enters the DWI quantitative analysis gradient nonlinear error calibration water phantom from the air, and the incident direction of the radiofrequency field is perpendicular to the length direction of the water phantom solution tube 1. When the radiofrequency field passes through a water phantom solution tube 1 perpendicular to the length direction of the water phantom solution tube 1, the radiofrequency field does not directly enter the adjacent water phantom solution tube 1, but enters the adjacent standing wave artifact elimination area 7. Since the interface between the standing wave artifact elimination area 7 and each water phantom solution tube 1 is a circular arc interface formed by the tube wall of the water phantom solution tube 1, when the electromagnetic wave in the radiofrequency field passes through the circular arc interface, the incident angles between the electromagnetic waves at different positions and the circular arc interface are different, so that the electromagnetic waves in the radiofrequency field are transmitted into the standing wave artifact elimination area 7 at different angles respectively. After passing through the standing wave artifact elimination area 7, the electromagnetic waves in the radiofrequency field enter the next standing wave artifact elimination area 7 at different angles respectively. At the same time, the amplitude of the reflected electromagnetic waves in the water phantom solution tube 1 is greatly reduced, so that the radiofrequency field emitted by the magnetic resonance imaging device cannot form a standing wave during the propagation process in the entire DWI quantitative analysis gradient nonlinear error calibration water phantom, so that the radiofrequency field can smoothly pass through the entire DWI quantitative analysis gradient nonlinear error calibration water phantom and avoid forming standing wave artifacts.

[0067] The inside of the standing wave artifact elimination area 7 is air; preferably, no other substances are filled in the standing wave artifact elimination area 7 except air.

[0068] Each water phantom solution tube 1 in the several layers of water phantom solution tubes 1 is a cylindrical tube. Each water phantom solution tube 1 in the several layers of water phantom solution tubes 1 is horizontally placed and parallel to each other, and the size specifications of different water phantom solution tubes 1 are the same; the cylindrical tube walls of two adjacent water phantom solution tubes 1 are tangent to each other.

[0069] The liquid injection box seal 4 is located at the top of the liquid injection box 3. The liquid injection box seal 4 is preferably a hole with a diameter of 10 mm; during use, the water phantom filling material is injected into the liquid injection box 3 through the liquid injection box seal 4; when using the DWI quantitative analysis gradient nonlinear error calibration water phantom for experiments, a thermometer can be used to measure the temperature of the water phantom filling material through the liquid injection box seal 4.

[0070] A plastic sealing screw and a leather gasket are configured at the liquid injection box seal 4. The plastic sealing screw and the leather gasket are used to seal the liquid injection box seal 4 after the water phantom filling material is filled into the liquid injection box 3 (such as Figure 1 )

[0071] The size of the DWI quantitative analysis gradient nonlinear error calibration water phantom is preferably similar to the size of the human body; further preferably, the overall width of the DWI quantitative analysis gradient nonlinear error calibration water phantom is preferably 350 mm, and the overall height is preferably 240 mm.

[0072] The DWI quantitative analysis gradient nonlinear error calibration water phantom is used to simulate the characteristics of the human body, and the DWI quantitative analysis gradient nonlinear error calibration water phantom is used to calibrate the ADC calculated by DWI.

[0073] The DWI quantitative analysis gradient nonlinear error calibration water phantom of the present invention can be used for calibrating ADC in DWI quantitative analysis of various MRI devices in clinical practice. When in use, the DWI quantitative analysis gradient nonlinear error calibration water phantom is first placed in the MRI magnet room for more than 24 hours, so that the water phantom filling material reaches temperature equilibrium; secondly, a DWI test is performed, and a thermometer is used to measure the temperature of the water phantom filling material through the injection box seal 4, and the standard value ADC of the apparent diffusion coefficient of the water phantom filling material is calculated. true Then the ADC of the water-filled material measured by DWI test is compared with the standard value ADC of the apparent diffusion coefficient of the water-filled material. true By comparison, the three-dimensional spatial deviation Bias of ADC in the magnet coordinate system of the MRI device is obtained. 3d ; When calibrating the ADC of human body tissue, DWI is used to quantitatively analyze the gradient nonlinear error and calibrate the ADC three-dimensional spatial deviation Bias calculated by the water model 3d Calibration is performed to obtain the calibration value ADC of the apparent diffusion coefficient of human body tissue correct .

[0074] The standard value of the apparent diffusion coefficient ADC of the ultrapure water true For existing known data, such as Figure 5 In the example, when the test measurement temperature is 23.0℃, the standard value of the apparent diffusion coefficient of ultrapure water is 2.187x10 -3 mm 2 / s.

[0075] When the magnetic resonance imaging device performs MRI imaging, when the radio frequency field enters the DWI quantitative analysis gradient nonlinear error calibration water phantom or the imaging tissue of the object being tested from the air, the wavelength of the radio frequency field will change, satisfying the following formula (1):

[0076] (1);

[0077] in is the wavelength of the RF field in the water phantom filling material or imaging tissue, is the speed of light (3×10 8 m / s), is the RF field frequency (127.8 MHz for 3.0-T field strength and 63.9 MHz for 1.5-T field strength), is the dielectric constant of the water phantom filling material or the imaged tissue.

[0078] When the size of the water-model filling material or the imaging tissue is comparable to the wavelength size of the radio frequency field in the water-model filling material or the imaging tissue, an obvious standing wave effect will be generated, which will cause obvious artifacts in the image during MRI imaging; the present invention can effectively reduce the standing wave artifacts by placing a plurality of water-model solution tubes 1 in parallel with each other, and the water-model filling material is isolated by the material of the water-model solution tube 1 and the air between the water-model solution tubes 1; at the same time, the diameter of the water-model solution tube 1 is much smaller than the wavelength of the radio frequency field in the water-model filling material, which can further reduce the standing wave artifacts.

[0079] During operation, each of the several layers of water-model solution tubes 1 is filled with water-model filling material; the apparent diffusion coefficient ADC of ultrapure water at different temperatures true is known (such as Figure 4 ), the apparent diffusion coefficient ADC of ultrapure water at different temperatures true Calculated by formula (2):

[0080] (2);

[0081] Where: ADC true represents the apparent diffusion coefficient of ultrapure water, and T represents temperature (in Kelvin).

[0082] Ultrapure water at 0 0 C. 20 0 C. 37 0 The dielectric constants at 0°C are 88, 80, and 73 respectively; thus, the dielectric constants at 0°C can be calculated. 0 C–37 0 C range: 3.0-T field strength: 25.0 cm-27.5 cm for RF field in ultrapure water, 1.5-T field strength: 0 0 C–37 0 The wavelength of the radio frequency field in ultrapure water within the C range is 50.0cm-55.0cm; under the field strength of clinical MRI equipment, preferably, the inner diameter of the water model solution tube 1 is 29 mm, which is much smaller than the wavelength of the radio frequency field in ultrapure water, and can further significantly reduce standing wave artifacts.

[0083] A method for calibrating using a DWI quantitative analysis gradient nonlinear error calibration water model, the method comprising calibrating an ADC calculated by DWI using a DWI quantitative analysis gradient nonlinear error calibration water model.

[0084] The method of using the DWI quantitative analysis gradient nonlinear error calibration water model to calibrate the ADC calculated by DWI specifically includes:

[0085] 1. Inject water model filling material into the injection box 3 through the injection box seal 4, and the water model filling material enters each water model solution tube 1 through the injection box 3; the water model filling material is preferably ultrapure water;

[0086] 2. Perform DWI scans on the DWI quantitative analysis gradient nonlinear error calibration water phantom using magnetic resonance imaging equipment;

[0087] 3. Use the DWI quantitative analysis obtained by scanning to calibrate the water model DWI data for gradient nonlinear error and calculate the apparent diffusion coefficient of the water model filling material;

[0088] 4. Calculate the three-dimensional spatial deviation of the apparent diffusion coefficient Bias 3d ;

[0089] 5. Calibrate the apparent diffusion coefficient of clinical MRI scan subjects.

[0090] The method of using the DWI quantitative analysis gradient nonlinear error calibration water model DWI data obtained by scanning to calculate the apparent diffusion coefficient of the water model filling material specifically includes using a voxel-based single exponential model for calculation, as shown in formula (3):

[0091] (3);

[0092] Where ADC is the apparent diffusion coefficient, is the diffusion sensitivity factor, for The DWI signal intensity when the value is 0, for DWI signal intensity when value> 0; diffusion sensitivity factor It is calculated by the following formula (4):

[0093] (4);

[0094] in, is the gyromagnetic ratio of the proton, is the applied diffusion gradient strength, is the duration of the applied diffusion gradient, Refers to the time interval between two diffusion gradients.

[0095] The three-dimensional spatial deviation Bias of the apparent diffusion coefficient is calculated 3d , including:

[0096] 4-1. Calculation of ADC Bias of water model filling material in magnetic coordinate system based on voxel analysis method voxel ;

[0097] 4-2. ADC Bias of water model filling material in magnetic coordinate system voxel Polynomial fitting to calculate the three-dimensional bias of the apparent diffusion coefficient 3d .

[0098] The step 4-1 calculates the ADC deviation Bias of the water model filling material in the magnetic coordinate system based on the voxel analysis method. voxel , specifically including the calculation using the following formula (5):

[0099] (5);

[0100] Where ADC is the measured value of the apparent diffusion coefficient of the water model filling material of each voxel in the magnetic coordinate system obtained by DWI test, and ADC true is the standard value of the apparent diffusion coefficient of the water model filling material, Bias voxel is the ADC deviation of the water phantom filling material for each voxel in the magnet coordinate system.

[0101] The step 4-2 is for the ADC bias of the water model filling material in the magnet coordinate system voxel Polynomial fitting to calculate the three-dimensional bias of the apparent diffusion coefficient 3d Specifically, according to the actual magnetic coil characteristics, select fitting function 1 or fitting function 2 for Bias 3d Calculation.

[0102] The fitting function 1 adopts second-order polynomial fitting while considering cross terms, as shown in formula (6):

[0103] (6);

[0104] Where X, Y, and Z represent the spatial position coordinates of the magnet coordinate system, b0 is a constant term, and b1, b2, b3, b4, b5, b6, b7, b8, and b9 are coefficients of each term; b0, b1, b2, b3, b4, b5, b6, b7, b8, and b9 are determined by multivariate linear regression of the ADC deviation of the water model filling material of all voxels in the magnet coordinate system, as shown in the following formula (7):

[0105] (7);

[0106] Wherein, X1, Y1, Z1, X2, Y2, Z2, …, Xn, Yn, Zn represent the spatial position coordinates of each voxel of the water model filling material in the magnetic coordinate system, n is an integer, and the size of n is determined by the imaging field of view, imaging matrix, slice thickness, and slice spacing of the image in the DWI scanning parameters; b0 is a constant term, and b1, b2, b3, b4, b5, b6, b7, b8, and b9 are coefficients of each term; , ,……, They are the ADC deviations of the water model filling material corresponding to the voxels at different spatial position coordinates in the magnet coordinate system.

[0107] The fitting function 2 adopts a second-order polynomial fitting and does not contain cross terms, as shown in formula (8):

[0108] (8);

[0109] Where X, Y, and Z represent the spatial position coordinates of the magnet coordinate system, b0 is a constant term, and b1, b2, b3, b4, b5, and b6 are coefficients of each term. b0, b1, b2, b3, b4, b5, and b6 are determined by multivariate linear regression of the ADC deviation of the water model filling material of all voxels in the magnet coordinate system, as shown in the following formula (9):

[0110] (9);

[0111] Wherein, X1, Y1, Z1, X2, Y2, Z2, …, Xn, Yn, Zn represent the spatial position coordinates of each voxel of the water model filling material in the magnetic coordinate system, n is an integer, and the size of n is determined by the imaging field of view, imaging matrix, slice thickness, and slice spacing of the image in the DWI scanning parameters; b0 is a constant term, and b1, b2, b3, b4, b5, and b6 are coefficients of each term; , ,……, They are the ADC deviations of the water model filling material corresponding to the voxels at different spatial position coordinates in the magnet coordinate system.

[0112] The present invention measures the apparent diffusion coefficient measurement value ADC and the standard value (ADC) of the water model filling material through DWI test. true ) ratio and polynomial fitting to calculate the three-dimensional spatial deviation Bias of the apparent diffusion coefficient of the water model filling material in the magnet coordinate system 3d ; When calibrating the apparent diffusion coefficient of human body tissue, the three-dimensional spatial deviation Bias of the apparent diffusion coefficient of the water model filling material is used 3d Complete the calibration of the apparent diffusion coefficient of MRI clinical scan subjects.

[0113] The calibrating of the apparent diffusion coefficient of the MRI clinical scan subject specifically includes:

[0114] 5-1. Based on the DWI data obtained from clinical scanning of the subject, the apparent diffusion coefficient ADC of the subject is calculated using formula (3): patient ;

[0115] 5-2. Calculate the calibrated apparent diffusion coefficient ADC using the following formula (10): correct :

[0116] (10);

[0117] Among them, ADC correct is the apparent diffusion coefficient of the calibrated clinical subject, ADC patient It is the raw, uncalibrated apparent diffusion coefficient obtained from MRI examination of clinical subjects.

Claims

1. A DWI quantitative analysis gradient nonlinear error calibration water model, characterized in that: It includes several layers of water phantom solution tubes (1), a sealing plate (2), and a liquid injection tank (3); among them, several layers of water phantom solution tubes (1) are placed parallel to each other. One end of several layers of water phantom solution tubes (1) is connected to the sealing plate (2), and the other end of several layers of water phantom solution tubes (1) is connected to the liquid injection tank (3). There is a liquid injection tank seal (4) on the liquid injection tank (3), and the other end of each water phantom solution tube (1) is communicated with the liquid injection tank (3); the side wall of the liquid injection tank (3) connected to several layers of water phantom solution tubes (1) is the inner sealing plate of the liquid injection tank (6), and the inner sealing plate of the liquid injection tank (6) is fixedly connected to the other end of several layers of water phantom solution tubes (1). There are openings (5) on the inner sealing plate of the liquid injection tank (6) at positions close to the top of each water phantom solution tube (1); the water phantom solution tube (1) is filled with water phantom filling material; the liquid injection tank seal (4) is located at the top of the liquid injection tank (3); there are 7 layers of the several layers of water phantom solution tubes (1); every 3 adjacent water phantom solution tubes (1) in the several layers of water phantom solution tubes (1) are stacked in a "pin" shape, and a standing wave artifact elimination area (7) is formed between the 3 water phantom solution tubes stacked in a "pin" shape; the standing wave artifact elimination area (7) formed between the 3 water phantom solution tubes stacked in a "pin" shape is surrounded by 3 arc-shaped side walls; The standing wave artifact elimination area (7) is filled with air; each water phantom solution tube (1) in the several layers of water phantom solution tubes (1) is a cylindrical tube. Each water phantom solution tube (1) in the several layers of water phantom solution tubes (1) is horizontally placed and parallel to each other between different water phantom solution tubes (1), and the size specifications of different water phantom solution tubes (1) are the same; the cylindrical tube walls of two adjacent water phantom solution tubes (1) are tangent to each other.

2. A DWI quantitative analysis gradient nonlinear error calibration water model according to claim 1, characterized in that: Each layer of the several layers of water phantom solution tubes (1) has several water phantom solution tubes (1). The number of water phantom solution tubes (1) in each layer of the several layers of water phantom solution tubes (1) gradually increases first and then gradually decreases from the bottom layer to the top layer, and the number of water phantom solution tubes (1) in the top layer is equal to the number of water phantom solution tubes (1) in the bottom layer.

3. A DWI quantitative analysis gradient nonlinear error calibration water model according to claim 1, characterized in that: The number of water phantom solution tubes from the 1st layer to the 7th layer in the several layers of water phantom solution tubes (1) is 6, 7, 8, 9, 8, 7, 6 respectively, and there are a total of 51 water phantom solution tubes (1); the length of each water phantom solution tube (1) is 300 mm and the inner diameter is 29 mm; the several layers of water phantom solution tubes (1), the sealing plate (2), and the liquid injection tank (3) are all made of acrylic material.

4. A DWI quantitative analysis gradient nonlinear error calibration water model according to claim 1, characterized in that: When MRI imaging is performed using a magnetic resonance imaging device, the radio frequency field emitted by the magnetic resonance imaging device enters the DWI quantitative analysis gradient nonlinear error calibration water model from the air, and the incident direction of the radio frequency field is perpendicular to the length direction of the water model solution tube (1). When the radio frequency field passes through a water model solution tube (1) perpendicular to the length direction of a water model solution tube (1), the radio frequency field does not directly enter the adjacent water model solution tube (1), but enters the adjacent standing wave artifact elimination area (7). Since the interface between the standing wave artifact elimination area (7) and the water model solution tube (1) is an arc formed by the wall of the water model solution tube (1), When the electromagnetic waves in the radio frequency field pass through the arc-shaped interface, the incident angles between the electromagnetic waves at different positions and the arc-shaped interface are different, so that the electromagnetic waves in the radio frequency field are transmitted into the standing wave artifact elimination area (7) at different angles. After passing through the standing wave artifact elimination area (7), the electromagnetic waves in the radio frequency field enter the next standing wave artifact elimination area (7) at different angles. At the same time, the amplitude of the reflected electromagnetic waves in the water model solution tube (1) is reduced, so that the radio frequency field emitted by the magnetic resonance imaging device cannot form a standing wave during the propagation process of the entire DWI quantitative analysis gradient nonlinear error calibration water model.

5. A method for calibrating using the DWI quantitative analysis gradient nonlinear error calibration water model according to any one of claims 1 to 4, characterized in that: The method includes calibrating the ADC calculated by DWI using a DWI quantitative analysis gradient nonlinear error calibration water model; The method of using the DWI quantitative analysis gradient nonlinear error calibration water model to calibrate the ADC calculated by DWI specifically includes: 1) injecting water model filling material into the liquid injection box (3) through the sealing opening (4) of the liquid injection box, and the water model filling material enters each water model solution tube (1) through the liquid injection box (3); 2) Perform DWI scans on the DWI quantitative analysis gradient nonlinear error calibration water phantom using magnetic resonance imaging equipment; 3) Use the DWI quantitative analysis obtained by scanning to calibrate the water model DWI data for gradient nonlinear error and calculate the apparent diffusion coefficient of the water model filling material; 4) Calculate the three-dimensional spatial deviation of the apparent diffusion coefficient Bias 3d ; 5) Calibrate the apparent diffusion coefficient of clinical MRI scan subjects.

6. The calibration method according to claim 5, characterized in that: The method of using the DWI quantitative analysis gradient nonlinear error calibration water model DWI data obtained by scanning to calculate the apparent diffusion coefficient of the water model filling material specifically includes using a voxel-based single exponential model for calculation, as shown in formula (3): Where ADC is the apparent diffusion coefficient, b is the diffusion sensitivity factor, s0 is the DWI signal intensity when b value is 0, S b is the DWI signal intensity when b value>0; the diffusion sensitivity factor b is calculated by the following formula (4): b=c 2 G 2 d 2 (D-d / 3) (4); Where γ is the gyromagnetic ratio of the protons, G is the strength of the applied diffusion gradient, δ is the duration of the applied diffusion gradient, and Δ refers to the time interval between two diffusion gradients.

7. The calibration method according to claim 5, characterized in that: The three-dimensional spatial deviation Bias of the apparent diffusion coefficient is calculated 3d , specifically including: Step 4-1) Calculate the ADC deviation Bias of the water model filling material in the magnetic coordinate system based on the voxel analysis method voxel ; Step 4-2) ADC deviation Bias of water model filling material in the magnetic coordinate system voxel Polynomial fitting to calculate the three-dimensional bias of the apparent diffusion coefficient 3d ; The step 4-1) calculates the ADC bias Bias of the water model filling material in the magnetic coordinate system based on the voxel analysis method voxel , specifically including the calculation using the following formula (5): Bias voxel =ADC / ADC true (5); Where ADC is the measured value of the apparent diffusion coefficient of the water model filling material of each voxel in the magnetic coordinate system obtained by DWI test, and ADC true is the standard value of the apparent diffusion coefficient of the water model filling material, Bias voxel is the ADC deviation of the water model filling material for each voxel in the magnet coordinate system; The step 4-2) is to determine the ADC deviation Bias of the water model filling material in the magnet coordinate system. voxel Polynomial fitting to calculate the three-dimensional bias of the apparent diffusion coefficient 3d Specifically, according to the actual magnetic coil characteristics, select fitting function 1 or fitting function 2 for Bias 3d Calculation of The fitting function 1 adopts a second-order polynomial fitting, while considering the cross terms, as shown in formula (6): <h2 style=";text-align:left;direction:ltr">Bias<h2 style=";text-align:left;direction:ltr"> 3d <h2 style=";text-align:left;direction:ltr"> (X, Y, Z) = b0 + b1X + b2Y + b3Z + b4X<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +b5Y<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> b6Z<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +b7XY+b8XZ+b9YZ (6); Where X, Y, and Z represent the spatial position coordinates of the magnet coordinate system, b0 is a constant term, and b1, b2, b3, b4, b5, b6, b7, b8, and b9 are coefficients of each term; b0, b1, b2, b3, b4, b5, b6, b7, b8, and b9 are determined by multivariate linear regression of the ADC deviation of the water model filling material of all voxels in the magnet coordinate system, as shown in the following formula (7): Bias voxel (X1,Y1,Z1)=b0+b1X1+b2Y1+b3Z1+b4X1 2 +b5Y1 2 +b6Z1 2 +b7X1Y1+b8X1Z1+b9Y1Z1 <h2 style=";text-align:left;direction:ltr">Bias<h2 style=";text-align:left;direction:ltr"> voxel <h2 style=";text-align:left;direction:ltr"> (X2,Y2,Z2) = b0 + b1X2 + b2Y2 + b3Z2 + b4X2<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +b5Y2<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +b6Z2<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +b7X2Y2+b8X2Z2+b9Y2Z2 …… Bias voxel (Xn,Yn,Zn)=b0+b1Xn+b2Yn+b3Zn+b4Xn 2 +b5In 2 +b6Zn 2 +b7XnYn+b8XnZn+b9YnZn(7); Wherein, X1, Y1, Z1, X2, Y2, Z2, …, Xn, Yn, Zn represent the spatial position coordinates of each voxel of the water model filling material in the magnetic coordinate system, n is an integer, and the size of n is determined by the DWI scanning parameters; b0 is a constant term, b1, b2, b3, b4, b5, b6, b7, b8, b9 are coefficients of each term; Bias voxel (X1, Y1, Z1), Bias voxel (X2, Y2, Z2),……,Bias voxel (X n , Y n , Z n ) are the ADC deviations of the water model filling materials corresponding to the voxels at different spatial position coordinates in the magnet coordinate system; The fitting function 2 adopts a second-order polynomial fitting, which does not contain cross terms, as shown in formula (8): <h2 style=";text-align:left;direction:ltr">Biasv<h2 style=";text-align:left;direction:ltr"> 3d <h2 style=";text-align:left;direction:ltr"> (X, Y, Z) = b0 + b1X + b2Y + b3Z + b4X<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +b5Y<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +b6Z<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> (8); Where X, Y, and Z represent the spatial position coordinates of the magnet coordinate system, b0 is a constant term, and b1, b2, b3, b4, b5, and b6 are coefficients of each term. b0, b1, b2, b3, b4, b5, and b6 are determined by multivariate linear regression of the ADC deviation of the water model filling material of all voxels in the magnet coordinate system, as shown in the following formula (9): Bias voxel (X1,Y1,Z1)=b0+b1X1+b2Y1+b3Z1+b4X1 2 +b5Y1 2 +b6Z1 2 <h2 style=";text-align:left;direction:ltr">Bias<h2 style=";text-align:left;direction:ltr"> voxel <h2 style=";text-align:left;direction:ltr"> (X2,Y2,Z2)=b0+b1X2+b2Y2+b3Z2+b4X2<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +b5Y2<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +b6Z2<h2 style=";text-align:left;direction:ltr"> 2 …… Bias voxel (Xn,Yn,Zn)=b0+b1Xn+b2Yn+b3Zn+b4Xn 2 +b5In 2 +b6Zn 2 (9); Wherein, X1, Y1, Z1, X2, Y2, Z2, …, Xn, Yn, Zn represent the spatial position coordinates of each voxel of the water model filling material in the magnetic coordinate system, n is an integer, and the size of n is determined by the DWI scanning parameters; b0 is a constant term, b1, b2, b3, b4, b5, b6 are coefficients of each term; Bias voxel (X1, Y1, Z1), Bias voxel (X2, Y2, Z2),……,Bias voxel (X n , Y n , Z n ) are the ADC deviations of the water model filling materials corresponding to the voxels at different spatial position coordinates in the magnet coordinate system.

8. The calibration method according to claim 5, characterized in that: The calibrating of the apparent diffusion coefficient of the MRI clinical scan subject specifically includes: The calibrated apparent diffusion coefficient ADC is calculated by the following formula (10): correct : ADC correct =ADC patient / Bias 3d (10); Among them, ADC correct is the apparent diffusion coefficient of the calibrated clinical subject, ADC patient It is the raw, uncalibrated apparent diffusion coefficient obtained from MRI examination of clinical subjects.

Images