A voltage prediction method for a variable voltage CT scan

Abstract

This invention relates to the technical field of CT imaging, specifically to a voltage prediction method for variable voltage CT scanning, comprising: 1. setting the desired minimum transmittance t0 for CT projection scanning; 2. determining the value of the minimum voltage adjustment range ΔU; 3. testing and determining the initial angle acquisition voltage; 4. for the nth angle, based on the voltage U of the (n-1)th angle... n‑1 The lowest transmittance t of the X-ray image at the (n-1)th angle n‑1 and the corresponding b n‑1 Value, calculate the voltage U' required at the nth angle. n 5. Collect projection data for the nth angle; 6. Calculate b n Value: 7. Repeat steps 4, 5, and 6 until the projection acquisition at the last angle is completed. The voltage prediction formula of this invention has high accuracy and limits the voltage interval, fixing the voltage value to a few values, thus eliminating the need for further adjustment of the predicted value.

Description

Technical Field

[0001] This invention relates to the technical field of CT imaging, and more specifically, to a voltage prediction method for variable voltage CT scanning. Background Technology

[0002] In CT imaging, radiographic images of the object are acquired in 360-degree directions around its circumference, and the projection is calculated. For industrial parts with large aspect ratios or complex structures, the thickness varies significantly in different directions. When using traditional fixed-voltage CT technology, overexposure occurs in the thinner directions and underexposure occurs in the thicker directions, affecting the reconstruction quality of the CT image. During the rotation of complex structural components, the effective thickness changes rapidly. Using fixed-energy imaging results in a mismatch between energy and effective thickness at different angles. At angles with large thickness, the dose is insufficient, leading to high noise levels; at angles with small thickness, scattering is significant, resulting in severe information loss and preventing the achievement of high-quality CT imaging. Summary of the Invention

[0003] The present invention provides a voltage prediction method for variable voltage CT scanning, which does not require pre-scanning and does not require voltage readjustment at each angle, thus overcoming some of the defects of the prior art.

[0004] A voltage prediction method for variable voltage CT scanning according to the present invention includes the following steps:

[0005] 1. Set the minimum transmittance t0 for the desired CT projection scan;

[0006] 2. Determine the value of the minimum voltage adjustment range ΔU;

[0007] III. Test and determine the initial angle by sampling voltage;

[0008] IV. For the nth angle, based on the voltage U at the (n-1)th angle... n-1 The lowest transmittance t of the X-ray image at the (n-1)th angle n-1 and the corresponding coefficient b n-1 Value, calculate the voltage U' required at the nth angle. n ;

[0009] V. Take U n =[U' n / ΔU+0.5]ΔU, collect the projection data of the nth angle;

[0010] VI. Calculate the coefficient b n value:

[0011] 7. Repeat steps 4, 5, and 6 until the projection data is collected from the last angle.

[0012] Preferably, the formula for calculating the minimum transmittance t of the X-ray image at each angle is:

[0013]

[0014] Where I 最小 I represents the minimum value of the current X-ray image. 背景 This represents the image value obtained under the current imaging conditions when X-rays have no attenuation.

[0015] Preferably, step three includes the following steps:

[0016] 3.1 Acquire two X-ray images when the voltage is U and U' = U + ΔU, calculate the minimum transmittance corresponding to the X-ray images under the two voltages, and denot them as t. U and t ΔU ;

[0017] 3.2. According to the following formula:

[0018]

[0019] Calculate the value of coefficient b1, and then apply the voltage prediction formula:

[0020]

[0021] Calculate the voltage U1' corresponding to the lowest transmittance t0;

[0022] 3.3. Take U1 = [U'1 / ΔU + 0.5]ΔU, where [] indicates rounding, and collect the projection data under voltage U1.

[0023] Preferably, in step four, the voltage prediction formula is used:

[0024]

[0025] Calculate the voltage U' required at the nth angle. n , take U n =[U' n / ΔU+0.5]ΔU。 .

[0026] Preferably, in step six, b is calculated. n The value includes the following steps:

[0027] 6.1 If U n =U n-1 Then b n =b n-1 ;

[0028] 6.2 If U n ≠U n-1Calculate the minimum transmittance t of the X-ray image at the current angle. n According to the following formula:

[0029]

[0030] Calculate b n value.

[0031] Existing methods rely entirely on grayscale for voltage prediction, resulting in a simplistic and crude formula with insufficient accuracy. This leads to significant deviations in the predicted voltage image grayscale values, necessitating multiple voltage adjustments at a single angle. Our proposed method employs a more accurate voltage prediction formula and limits the voltage interval, fixing the voltage value to a limited set of values, thus eliminating the need for further adjustments to the predicted value. Attached Figure Description

[0032] Figure 1 This is a flowchart of a voltage prediction method for variable voltage CT scanning in Example 1;

[0033] Figure 2 This is a schematic diagram showing the variation of the minimum X-ray transmittance of the phantom under different voltages with angle in Example 1;

[0034] Figure 3 This is a schematic diagram illustrating the change in minimum X-ray transmittance under the predicted acquisition strategy in Example 1;

[0035] Figure 4 This is a schematic diagram of the voltage change under the predictive acquisition strategy in Example 1;

[0036] Figure 5 This is a diagram showing the dimensions of the wedge block in Example 1;

[0037] Figure 6(a) shows the X-ray image and transmittance change diagram under 60kV voltage in Example 1;

[0038] Figure 6(b) shows the X-ray image and transmittance change diagram under 80kV voltage in Example 1;

[0039] Figure 6(c) shows the X-ray image and transmittance change diagram under 100kV voltage in Example 1;

[0040] Figure 6(d) shows the X-ray image and transmittance change diagram under 120kV voltage in Example 1;

[0041] Figure 6(e) shows the X-ray image and transmittance change at 150kV voltage in Example 1;

[0042] Figure 6(f) shows the X-ray image and transmittance change at 180kV voltage in Example 1;

[0043] Figure 7(a) is a schematic diagram of the relative error of the predicted voltage at the first location point in Example 1;

[0044] Figure 7(b) is a schematic diagram of the relative error of the predicted voltage at the second location point in Example 1;

[0045] Figure 7(c) is a schematic diagram of the relative error of the predicted voltage at the third location point in Example 1;

[0046] Figure 7(d) is a schematic diagram of the relative error of the predicted voltage at the fourth location point in Example 1;

[0047] Figure 7(e) is a schematic diagram of the relative error of the predicted voltage at the fifth location point in Example 1;

[0048] Figure 7(f) is a schematic diagram of the relative error of the predicted voltage at the sixth location point in Example 1. Detailed Implementation

[0049] To further understand the content of this invention, a detailed description of the invention will be provided in conjunction with the accompanying drawings and embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0050] Example 1

[0051] like Figure 1 As shown, this embodiment provides a voltage prediction method for variable voltage CT scanning, which includes the following steps:

[0052] I. Set the desired minimum transmittance t0 for CT projection scanning. Generally, t0 ≥ 0.15 is chosen; here, t0 = 0.2 is selected. The formula for calculating the minimum transmittance t of the X-ray image at each angle is:

[0053]

[0054] Where I 最小 I represents the minimum value of the current X-ray image. 背景 This represents the image value obtained under the current imaging conditions when X-rays have no attenuation;

[0055] 2. Determine the value of the minimum voltage adjustment range ΔU; generally, the value is taken as an integer multiple of 5kV, here we take ΔU=10kV;

[0056] III. Test and determine the initial angle (first angle) and collect voltage;

[0057] 3.1 Acquire two X-ray images when the voltage is U and U' = U + ΔU, calculate the minimum transmittance corresponding to the X-ray images under the two voltages, and denot them as t. U and t ΔU ;

[0058] 3.2. According to the following formula:

[0059]

[0060] Calculate the coefficient b1 value of the voltage prediction formula, and then follow the voltage prediction formula:

[0061]

[0062] Calculate the voltage U1' corresponding to the lowest transmittance t0;

[0063] 3.3. Take U1 = [U'1 / ΔU + 0.5]ΔU, where [] indicates rounding, and collect the projection data under voltage U1;

[0064] IV. For the nth angle (n≥2 and n is an integer), based on the voltage U of the (n-1)th angle... n-1 The lowest transmittance t of the X-ray image at the (n-1)th angle n-1 and the corresponding coefficient b n-1 Value, according to the voltage prediction formula:

[0065]

[0066] Calculate the voltage U' required at the nth angle. n ;

[0067] V. Take U n =[U' n / ΔU+0.5]ΔU, collect the projection data of the nth angle;

[0068] VI. Calculate the coefficient b n value:

[0069] 6.1 If U n =U n-1 Then b n =b n-1 ;

[0070] 6.2 If U n ≠U n-1 Calculate the minimum transmittance t of the X-ray image at the current angle. n According to the following formula:

[0071]

[0072] Calculate b n value;

[0073] 7. Repeat steps 4, 5, and 6 until the projection data is collected from the last angle.

[0074] A validation experiment was conducted on the YXLON FF20 microfocus CT system in the laboratory, using microfocus imaging mode. The minimum voltage amplitude change was set to 10kV for acquisition strategy validation. The phantom diameter was 20mm. The changes in the minimum projected transmittance of the phantom at 360 angles under different voltages are shown below. Figure 2 The lowest X-ray transmittance using a projection acquisition strategy employing predicted voltage is as follows: Figure 3 As shown, the collected voltage is as follows Figure 4 As shown, the desired minimum transmittance t = 0.2 is taken, and the initial acquisition voltage for the first angle is set to 80kV or 90kV.

[0075] Experimental results show that, under the voltage prediction strategy, the minimum X-ray transmittance variation is between [0.1732, 0.2264], which is about 50% smaller than the transmittance variation range under a single voltage: [0.1057, 0.2023] (70kV), [0.1352, 0.24433] (80kV), [0.1594, 0.2732] (90kV), [0.1787, 0.2893] (100kV), [0.1952, 0.321] (110kV), [0.2115, 0.3406] (120kV), indicating a significant reduction.

[0076] There is no need to repeatedly adjust the voltage at each angle; simply collect the voltage once according to the predicted voltage.

[0077] In the formula accuracy verification experiment, the error between the predicted value and the actual value of this method is less than 4%.

[0078] The verification model uses 3D-printed wedge blocks, with specifications as follows: Figure 5 As shown, the thickness is 1 cm. The laboratory's YXLON FF20 microfocus CT system was used, with microfocus imaging mode selected, probe size of 0.127×0.127 mm, and imaging every 10 kV from 60 kV to 180 kV. Some X-ray images are shown in Figures 6(a), 6(b), 6(c), 6(d), 6(e), and 6(f).

[0079] Selecting a subset of image points, their transmittance was calculated. Using the first two voltage data points, the voltage prediction formula was applied to predict the voltage at the current transmittance, and the prediction was compared with the actual voltage to verify the formula. Six different points were selected from left to right (50, 95, 195, 445, 745, and 945 pixels from the left boundary). The results and errors are shown in Figures 7(a), 7(b), 7(c), 7(d), 7(e), and 7(f). Experimental results show that the error between the predicted and actual voltages is less than 4%, meeting application requirements.

[0080] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A voltage prediction method for variable voltage CT scanning, characterized in that: Includes the following steps:

1. Set the desired minimum transmittance for CT projection scans. t 0; II. Determine the minimum voltage adjustment range Δ U The value; III. Test and determine the initial angle by sampling voltage; Step three includes the following steps: 3.1, Data collection when the voltage is... U and U’ = U +Δ U Two X-ray images were taken at different voltages. The minimum transmittance corresponding to the X-ray images at the two voltages was calculated and denoted as follows: t U and t ΔU ; 3.

2. According to the following formula: ； Calculate coefficients b 1 value, then according to the voltage prediction formula: ； Calculate at the lowest transmittance t Voltage corresponding to 0 U 1 ’ ; 3.3, Take U 1=[ U’ 1 / Δ U +0.5]Δ U [ ] indicates rounding, and the sampled voltage is... U 1. Projection data; IV. For the nth angle, based on the voltage at the (n-1)th angle... U n-1 The lowest transmittance of the X-ray image at the (n-1)th angle t n-1 and the corresponding coefficients b n-1 Value, calculate the first n Voltage required at each angle U’ n ; In step four, according to the voltage prediction formula: ； Calculate the first n Voltage required at each angle U’ n ,Pick U n =[ U’ n / Δ U +0.5]Δ U ; V. Take U n =[ U’ n / Δ U +0.5]Δ U , collect the first n Projection data from each angle; VI. Calculation of Coefficients b n ; In step six, calculate b n The value includes the following steps: 6.1 If U n = U n-1 ,but b n = b n-1 ; 6.2 If U n ≠ U n-1 Calculate the minimum transmittance of the X-ray image at the current angle. t n According to the following formula: ； calculate b n value; 7. Repeat steps 4, 5, and 6 until the projection data is collected from the last angle.

2. The voltage prediction method for variable voltage CT scanning according to claim 1, characterized in that: Minimum transmittance of X-ray images at each angle t The formula for calculating 0 is: ； in This represents the minimum grayscale value of the current X-ray image. This represents the image grayscale value obtained under the current imaging conditions when X-rays have no attenuation.

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