Method for improving data sampling trigger signal precision based on CT scanning frame

Abstract

The invention relates to a method for improving the precision of a data sampling trigger signal based on a CT scanning frame. The method comprises the following steps: a static control panel controller processes A and B orthogonal pulse information transmitted from an encoder module of a slip ring and converts the information into a data acquisition system sampling trigger signal; the static control board controller processes the first n sampling trigger signals by using an expected threshold value to generate improved first n sampling trigger signals; the static control panel controller sequentially generates an improved nth sampling trigger signal by using improved Kalman filtering; the static control panel controller transmits the signals to the rotary control panel through the slip ring command ring, and then the signals are transmitted to the data acquisition system through the rotary control panel to serve as trigger signals for sampling. The improved Kalman filtering is adopted to improve the precision of a data sampling trigger signal, the real-time performance is higher than that of average value filtering, abnormal extreme measurement values are removed, data can be smoothed, and unnecessary fluctuation caused by the abnormal extreme values is eliminated.

Description

Technical Field

[0001] The invention relates to the technical field of radiological diagnosis, and in particular to a method for improving the accuracy of data sampling trigger signals based on a CT scanning frame. Technical Background

[0002] CT (Computed Tomography) is a medical imaging technology that uses precise X-ray beams and highly sensitive detectors to scan the human body layer by layer. The data obtained from the scan is processed by a computer to generate high-resolution images of the body's internal cross-section, coronal or sagittal planes. CT images reflect the degree of X-ray absorption by organs and tissues in different grayscales, have high density resolution, and can clearly display soft tissue and bone structures. CT is widely used in clinical diagnosis, treatment planning, and disease monitoring, and is particularly valuable in the diagnosis of tumors, vascular lesions, trauma, and infection.

[0003] The CT machine is composed of a control console, a scanning frame, a scanning bed and a power cabinet. The scanning frame of the CT machine is composed of a stationary part and a rotating part. The stationary part includes a stationary frame, a display screen, a control operation panel, a static control circuit board and a stationary part of the slip ring; the rotating part is composed of a rotating control board, a rotating part of the slip ring, a high-voltage generator, an X-ray tube, a collimator, a data acquisition system (DAS for short), etc. The slip ring is composed of a data receiving module 1, a slip ring disk 2, a carbon brush module 3, a data sending module 4, an encoder module 5, and an encoding belt 6 on the slip ring disk. Figure 2 , Figure 3 , Figure 4 shown.

[0004] At the beginning of scanning, the X-ray tube on the rotating body rotates 360 degrees around the center of the ISO aperture, and the X-rays emitted by the tube are also emitted 360 degrees to the detection part. The X-rays pass through the detection object and reach the data acquisition system. The encoder module on the slip ring collects the information of the encoding belt, generates A, B phase orthogonal differential pulses and one Z phase differential pulse per circle, and sends the A, B, Z phase pulses to the static control board. The static control board converts them into sampling trigger signals of the data acquisition system after processing, which constitutes the sampling frequency of the data acquisition system, which records the angle information and speed information of the rotation. The sampling frequency of the data acquisition system during one revolution of the rotating body determines the time resolution of CT. Time resolution and spatial resolution are one of the important parameters of the CT system. In multi-slice spiral CT, it is related to the scanning coverage and reconstruction method, the sampling time of each frame image, the reconstruction time, and the ability of continuous imaging. The time resolution determines the most important parameter of the imaging quality of the heart and surrounding large blood vessels. The fundamental frequency of the time resolution is generated by the slip ring encoding belt on the rotating body or by the encoder on the rotating motor of the static part. Most manufacturers use encoders on rotating bodies because they directly determine the 360-degree sampling angle. Due to the precision and difficulty of mechanical processing, the baseband frequency is generally around 1K, and then multiplied to 2K, 4K, 6K, etc. by the controller.

[0005] Patent CN201310732682 only discloses a slip ring encoder and its encoding method, and uses redundant sensors to improve the stability of encoding. During the scanning process of the computed tomography system (CT), due to the mechanical error on the encoding belt on the slip ring and the slight error collected by the encoder module, the accuracy of the sampling trigger signal of the data acquisition system will eventually deteriorate, thereby causing the image quality of the heart and surrounding large blood vessels to decrease. Therefore, it is also necessary to improve the accuracy of the sampling trigger signal of the data acquisition system. Summary of the invention

[0006] The purpose of the present invention is to propose a method for improving the accuracy of data sampling trigger signals based on a CT scanning frame, thereby improving the quality of imaging of the heart and surrounding large blood vessels.

[0007] The present invention is realized by the following technical scheme: a method for improving the accuracy of data sampling trigger signal based on CT scanning frame, comprising the following steps:

[0008] The static control board controller collects the A, B orthogonal pulses and Z pulses of the encoder module on the slip ring; and converts the A, B orthogonal pulses into data sampling trigger signals after processing;

[0009] For the first n sampling trigger signals, an improved first n sampling trigger signal is generated by processing the first n sampling trigger signals by using the expected threshold value;

[0010] The sampling trigger signal is output through the improved Kalman filter: the average output of the first n improved sampling trigger signals is calculated as the initial estimate; the improved n+i-th trigger signal measurement value is used as the improved Kalman measurement value, and the i-th improved Kalman filter is performed, and the obtained filter estimate value is output as the n+i-th improved sampling trigger signal.

[0011] The method of generating improved first n sampling trigger signals by processing the first n sampling trigger signals with expected thresholds comprises the following steps:

[0012] Read n sampling trigger signal values ​​and compare each measured value with the expected value;

[0013] If the n measured values ​​are within the threshold of the expected value, the n sampling trigger signal values ​​are output as the improved sampling trigger signal;

[0014] If a value among the n measured values ​​is greater than the threshold of the expected value, the expected value plus the threshold of the expected value is output as an improved sampling trigger signal;

[0015] If any value of the n measured values ​​is smaller than the threshold of the expected value, the expected value minus the threshold of the expected value is output as the improved sampling trigger signal.

[0016] The threshold of the expected value is a% of the expected value; a≦10.

[0017] The threshold value of a certain value greater than the expected value is used to indicate that the mechanical hole of the coding belt is blocked; the threshold value of a certain value less than the expected value is used to indicate that the mechanical hole of the coding belt is screened.

[0018] The method of outputting a sampling trigger signal by improving the Kalman filter comprises the following steps:

[0019] 1) Calculate the average value of the first n sampled trigger signals Z(n) after improvement as the initial estimate

[0020] X i-1 =(Z1+Z2+…+Z n ) / n; i=1,2,…

[0021] 2) Determine whether the measured value of the n+i-th sampling trigger signal is within a% of the expected value D; if it is within a% of the expected value D, the measured value of the n+i-th sampling trigger signal is used as the measured value Z of the improved Kalman n+i ; If it is greater than a% of the expected value D, then Z n+i =D*(1+a%); if it is less than a% of the expected value D, then Z n+i =D*(1-a%);

[0022] 3) According to the improved Kalman gain K i and the previous estimate X i-1 , calculate the next estimate X i =X i-1 +K i *(Z n+i -X i-1 );X i As the n+ith improved data sampling trigger signal, T n+i＝ X i ;

[0023] According to the improved Kalman gain K i and the estimated error e est(i-1) Calculate the next estimated error e esti ;

[0024] e esti =(1-K i )*e est(i-1)

[0025] According to the measurement error e mea and the estimated error e esti Find the next improved Kalman gain K i+1 ;

[0026] K i+1 =e esti / (e esti +e mea )

[0027] 4) Through steps 2)-3), the generated estimated value X i+1 As the output of data sampling trigger signal, T n+i+1 =X i+1 .

[0028] The sampling trigger signal is transmitted to the rotating control board through the slip ring command ring, and then transmitted to the data acquisition system for sampling by the rotating control board.

[0029] A system for improving the accuracy of data sampling trigger signals based on a CT scanning frame, applied to a static control panel controller; comprising:

[0030] The sampling trigger signal generation module is used to collect the A, B orthogonal pulses and Z pulses of the encoder module on the slip ring; and convert the A, B orthogonal pulses into data sampling trigger signals after processing; for the first n sampling trigger signals, the expected threshold value is used to generate the improved first n sampling trigger signals;

[0031] The sampling trigger signal optimization module is used to output the sampling trigger signal through the improved Kalman filter: the average output value of the first n improved sampling trigger signals is calculated as the initial estimate value; the improved n+i-th trigger signal measurement value is used as the improved Kalman measurement value, and the i-th improved Kalman filter is performed, and the obtained filter estimate value is output as the n+i-th improved sampling trigger signal.

[0032] Compared with the prior art, the present invention has the following beneficial effects and advantages:

[0033] The improved Kalman filter is used to improve the accuracy of the data sampling trigger signal, which is more real-time than the average value filter. Adding the removal of abnormal extreme measurement values ​​can further smooth the data and eliminate unnecessary fluctuations caused by abnormal extreme values ​​compared to the standard Kalman filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flow chart of the present invention;

[0035] Figure 2 This is the front view of the slip ring;

[0036] Figure 3 This is the back side composition diagram of the slip ring;

[0037] Figure 4 This is a partial enlarged view of the coding belt of the slip ring;

[0038] Among them, 1 data receiving module, 2 slip ring disk, 3 carbon brush module, 4 data sending module, 5 encoder module, 6 encoding belt on the slip ring disk;

[0039] Figure 5 This is the data sampling trigger signal before the improved Kalman filter is added, with 1S exposure time and 2320 view integration time diagram;

[0040] Figure 6 This is the data sampling trigger signal after adding the improved Kalman filter, 1S exposure time, and 2320 view integration time diagram. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below in conjunction with the embodiments.

[0042] like Figure 1As shown, a method for improving the accuracy of data sampling trigger signals based on a CT scanning frame includes: a static control board controller processes A and B orthogonal pulse information transmitted from an encoder module of a slip ring and converts the information into a sampling trigger signal of a data acquisition system; the static control board controller processes the first n sampling trigger signals using an expected threshold value to generate improved first n sampling trigger signals; the static control board controller sequentially generates improved sampling trigger signals after the nth sampling trigger signal using an improved Kalman filter; the static control board controller transmits these signals to a rotating control board through a slip ring command ring, and then the rotating control board transmits them to the data acquisition system as trigger signals for sampling, thereby improving the quality of imaging of the heart and surrounding large blood vessels.

[0043] The implementation steps of the present invention include:

[0044] 1. The controller on the static control board collects the A, B, and Z pulse information transmitted from the encoder module of the slip ring. The controller on the static control board processes the A and B pulse information and converts it into a data sampling trigger signal.

[0045] 2. The controller on the static control board reads n measurement data sampling trigger signal values, and compares each value of the n measurement sampling trigger signals with the expected value. If the n measurement values ​​are within the threshold of the expected value, these signals are output as improved sampling trigger signals; if any value among the n measurement values ​​is greater than the threshold of the expected value, the expected value plus the threshold of the expected value is output as the improved sampling trigger signal; if any value among the n measurement values ​​is less than the threshold of the expected value, the expected value minus the threshold of the expected value is output as the improved sampling trigger signal.

[0046] 3. Calculate the average value of the first n improved sampling trigger signal outputs as the initial estimated value; use the improved (n+1)th trigger signal measurement value as the improved Kalman measurement value, perform the first improved Kalman filter, and use the estimated value as the (n+1)th improved sampling trigger signal output, and then use the improved Kalman filter characteristics to iterate and obtain the sampling trigger signal output in turn.

[0047] 4. The command signal is transmitted to the rotary control board through the slip ring, and then transmitted to the data acquisition system for sampling.

[0048] During the entire rotation process, the measured value greater than the expected value threshold represents the blockage of the encoder belt mechanical small hole, and the measured value less than the expected value threshold represents the sieve hole of the encoder belt mechanical small hole. The purpose of this is to eliminate the influence of a relatively large abnormal extreme measurement value of a blockage or sieve hole on the improved Kalman filter.

[0049] Example:

[0050] 1. The static control board collects the A, B orthogonal pulses and Z pulses transmitted from the encoder module on the slip ring. The static control board processes the A, B orthogonal pulses and converts them into data sampling trigger signals.

[0051] 2. The static control board reads n data sampling trigger signals and puts them into the array Z(n). In this example, the small holes on the encoder belt of the slip ring are square holes. Square holes are more conducive to encoder module sampling, but square holes are more difficult to process. The encoder belt of the slip ring has 2320 mechanical small holes in one circle. When the CT scanner starts scanning, the rotating motor starts to drive the slip ring to rotate. The encoder collects the rising and falling edges of the mechanical small holes on the encoder belt, generates orthogonal A and B orthogonal pulses, and sends them to the static control board. After being processed by the static control board, it is converted into data sampling trigger signal input.

[0052] In this example, n is 4, and the threshold of the expected value D of the sampling trigger signal is set to 3%. If the four measured values ​​are within 3% of the expected value D, the first four data sampling trigger signals use the actual measured signals, T1 = Z1, T2 = Z2, T3 = Z3, T4 = Z4; if any of the four measured values ​​is greater than 3% of the expected value D, that value is changed to the expected value D plus 3% of the expected value; if any of the four measured values ​​is less than 3% of the expected value D, that value is changed to the expected value D minus 3% of the expected value; these four signals are output as improved sampling trigger signals.

[0053] 3. The static control board controller uses the improved Kalman filter to sequentially generate the improved n-th sampling trigger signal sampling trigger signal.

[0054] 1) Calculate the average value of Z(n) as the initial estimate X0 = (Z1 + Z2 + Z3 + Z4) / 4.

[0055] 2) According to the measurement error e mea and estimated language difference e est0 Calculate the current improved Kalman gain K1. Measurement error e mea In this example, 0.1us is taken and the estimated error e est0 Take 3us, where the measurement error e mea is a fixed value;

[0056] K1=e est0 / (e est0+ e mea )=3 / (3+0.1)=0.968

[0057] 3) According to the improved Kalman gain K1 and the initial estimated value X0, take the next data sampling trigger signal measurement value to determine whether this measurement value is within 3% of the expected value. If it is within this range, this measurement value is used as the improved Kalman measurement value Z n+1; If it is greater than 3% of the expected value D, then Z n+1 =D*(1+3%); if it is less than 3% of the expected value D, then Z n+1 =D*(1-3%); Calculate the estimated value X1 using the formula;

[0058] X1=X0+K1*(Z n+1 -X0)

[0059] X1 represents the n+1th improved data sampling trigger signal, T n+1＝ X1;

[0060] 4) According to the improved Kalman gain K1 and the estimated language difference e est0 Calculate the next estimated error to generate e est1 ;

[0061] e est1 =(1-K1)*e est0 =(1-0.968)*3=0.096

[0062] According to the measurement error e mea and estimated language difference e est1 Calculate the next improved Kalman gain K2.

[0063] K2=e est1 / (e est1+ e mea )=0.096 / (0.096+0.1)=0.490

[0064] 5) According to the improved Kalman gain K2 and the initial estimated value X1, take the next data sampling trigger signal measurement value to determine whether this measurement value is within 3% of the expected value. If it is within this range, this measurement value is used as the improved Kalman measurement value Z n+1 ; If it is greater than 3% of the expected value D, then Z n+2 =D*(1+3%); if it is less than 3% of the expected value D, then Z n+2 =D*(1-3%); Calculate the estimated value X2 using the formula.

[0065] X2=X1+K2*(Z n+2 -X1)

[0066] X2 represents the n+1th improved data sampling trigger signal, T n+2＝ X2;

[0067] 6) Repeat 4) to 5) and keep iterating to generate estimated values ​​X3, X4, X5, etc. m ;

[0068] X3, X4, X5...Xm As the output of the data system sampling trigger signal, T n+3 =X3,T n+4 =X 4, T n+5 =X5……T n+m =X m .

[0069] 4. The command signal is transmitted to the rotary control board through the slip ring, and then transmitted to the data acquisition system for sampling.

[0070] Furthermore, when the computer tomography is being scanned (the speed is 1S in this example), the rotating motor starts to rotate, and the static control board will receive the data sampling trigger signal from the encoder of the slip ring. The first four data acquisition system sampling trigger signals of the static control board are output with the measured value after the threshold judgment of the expected value, and the fifth and subsequent data sampling trigger signals use the estimated value after the improved Kalman filter as the data sampling trigger signal. When the rotating part of the scanning frame reaches 1S, the exposure starts. At this time, the sampling accuracy of the data sampling trigger signal has become very high after multiple iterations of the improved Kalman filter, achieving the expected purpose.

[0071] Furthermore, the system was tested when the CT scanner was running at 1S speed, 2320VIEW, and 1S exposure. Figure 5 The difference in data sampling time of the Kalman filter of the traditional slip ring without improvement = 0.450-0.420 = 0.030ms.

[0072] Figure 6 The difference in data sampling time of the improved Kalman filter of the traditional slip ring is 0.4329-0.4304=0.0025ms.

[0073] like Figure 5 , Figure 6 As shown in the figure, the horizontal axis represents the sampling point and the vertical axis represents the sampling time. Figure 5 , Figure 6 By comparison, it can be seen that the accuracy of the data sampling trigger signal after the improved Kalman filter processing is 12 times higher than that of the unimproved Kalman filter processing.

Claims

1. A method for improving the accuracy of data sampling trigger signals based on a CT scanning frame, characterized in that , including the following steps: The static control board controller collects the A, B orthogonal pulses and Z pulses of the encoder module on the slip ring; and converts the A, B orthogonal pulses into data sampling trigger signals after processing; For the first n sampling trigger signals, an improved first n sampling trigger signal is generated by processing the first n sampling trigger signals by using the expected threshold value; Output the sampling trigger signal through the improved Kalman filter: calculate the output average value of the first n sampling trigger signals after the improvement as the initial estimation value; The improved n+i-th trigger signal measurement value is used as the improved Kalman measurement value, and the i-th improved Kalman filter is performed, and the obtained filter estimation value is output as the n+i-th improved sampling trigger signal.

2. A method for improving the accuracy of data sampling trigger signals based on a CT scanning frame according to claim 1, characterized in that , for the first n sampling trigger signals, using the expected threshold processing to generate the improved first n sampling trigger signals, including the following steps: Read n sampling trigger signal values ​​and compare each measured value with the expected value; If the n measured values ​​are within the threshold of the expected value, the n sampling trigger signal values ​​are output as the improved sampling trigger signal; If a value among the n measured values ​​is greater than the threshold of the expected value, the expected value plus the threshold of the expected value is output as an improved sampling trigger signal; If any value of the n measured values ​​is smaller than the threshold of the expected value, the expected value minus the threshold of the expected value is output as the improved sampling trigger signal.

3. The method for improving the accuracy of data sampling trigger signals based on a CT scanning frame according to claim 1, characterized in that: The threshold of the expected value is a% of the expected value; a≦10.

4. The method for improving the accuracy of data sampling trigger signals based on a CT scanning frame according to claim 1, characterized in that: The threshold value of a certain value greater than the expected value is used to indicate that the mechanical hole of the coding belt is blocked; the threshold value of a certain value less than the expected value is used to indicate that the mechanical hole of the coding belt is screened.

5. The method for improving the accuracy of data sampling trigger signals based on a CT scanning frame according to claim 1, characterized in that: The method of outputting a sampling trigger signal by improving the Kalman filter comprises the following steps: 1) Calculate the average value of the first n sampled trigger signals Z(n) after improvement as the initial estimate X i-1 =(Z1+Z2+…+Z n ) / n;i=1,2,… 2) Determine whether the measured value of the n+ith sampling trigger signal is within a% of the expected value D; if it is within a% of the expected value D, the measured value of the n+ith sampling trigger signal is used as the measured value Z of the improved Kalman n+i ; If it is greater than a% of the expected value D, then Z n+i =D*(1+a%); if it is less than a% of the expected value D, then Z n+i =D*(1-a%); 3) According to the improved Kalman gain K i and the previous estimate X i-1 , calculate the next estimate X i =X i-1 +K i *(Z n+i -X i-1 );X i As the n+ith improved data sampling trigger signal, T n+i＝ X i ; According to the improved Kalman gain K i and the estimated error e est(i-1) Calculate the next estimated error e esti ; yes esti =(1-K i )*e est(i-1) According to the measurement error e mea and the estimated error e esti Find the next improved Kalman gain K i+1 ; K i+1 =and esti / (And esti +e mea ) 4) Through steps 2)-3), the generated estimated value X i+1 As the output of data sampling trigger signal, T n+i+1 =X i+1 .

6. The method for improving the accuracy of data sampling trigger signals based on a CT scanning frame according to claim 1, characterized in that: The sampling trigger signal is transmitted to the rotating control board through the slip ring command ring, and then transmitted to the data acquisition system for sampling by the rotating control board.

7. A system for improving the accuracy of data sampling trigger signals based on a CT scanning frame, characterized in that , applied to static control panel controller; including: The sampling trigger signal generation module is used to collect the A, B orthogonal pulses and Z pulses of the encoder module on the slip ring; and convert the A, B orthogonal pulses into data sampling trigger signals after processing; for the first n sampling trigger signals, the expected threshold value is used to generate the improved first n sampling trigger signals; The sampling trigger signal optimization module is used to output the sampling trigger signal through the improved Kalman filter: the average output value of the first n improved sampling trigger signals is calculated as the initial estimate value; the improved n+i-th trigger signal measurement value is used as the improved Kalman measurement value, and the i-th improved Kalman filter is performed, and the obtained filter estimate value is output as the n+i-th improved sampling trigger signal.

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