A method for improving the accuracy of data sampling trigger signals based on CT scanning gantry

Abstract

This invention relates to a method for improving the accuracy of data sampling trigger signals based on a CT scanner gantry. The method includes: a static control board controller processing A and B quadrature pulse information transmitted from the encoder module of the slip ring and converting it into sampling trigger signals for the data acquisition system; the static control board controller processing the first n sampling trigger signals using a desired threshold to generate improved first n sampling trigger signals; the static control board controller using an improved Kalman filter to sequentially generate the improved nth and subsequent sampling trigger signals; and the static control board controller transmitting these signals through a slip ring command loop to a rotary control board, which then transmits them to the data acquisition system as trigger signals for sampling. The improved Kalman filter improves the accuracy of the data sampling trigger signals, offering higher real-time performance than average value filtering. Furthermore, by removing abnormal extreme measurements, it smooths the data and eliminates unnecessary fluctuations caused by abnormal extreme values.

Description

Technical Field

[0001] This invention relates to the field of radiological diagnostics, and more specifically to a method for improving the accuracy of data sampling trigger signals based on a CT scanning gantry. Technical Background

[0002] CT (Computed Tomography) is a medical imaging technique that uses precise X-ray beams and highly sensitive detectors to scan the human body layer by layer. The computer processes the scan data to generate high-resolution images of the body's internal cross-sections, coronal planes, or sagittal planes. CT images use different gray levels to reflect the degree of X-ray absorption by organs and tissues, possessing high density resolution and clearly displaying soft tissue and bone structures. CT is widely used in clinical diagnosis, treatment planning, and disease monitoring, showing particularly high value in the diagnosis of tumors, vascular diseases, trauma, and infections.

[0003] A CT scanner consists of a control console, gantry, scanning bed, and power supply cabinet. The gantry comprises a stationary section and a rotating section. The stationary section includes the stationary gantry, display screen, control panel, static control circuit board, and slip ring. The rotating section consists of a rotation control board, slip ring rotating section, high-voltage generator, X-ray tube, collimator, and data acquisition system (DAS). The slip ring consists of a data receiving module 1, slip ring disk 2, carbon brush module 3, data transmitting module 4, encoder module 5, and encoding strip 6 on the slip ring disk. Figure 2 , Figure 3 , Figure 4 As shown.

[0004] At the start of the scan, the X-ray tube on the rotating body rotates 360 degrees around the ISO aperture center, emitting X-rays that also propel the X-rays towards the detection area in a 360-degree manner. The X-rays pass through the object being detected and reach the data acquisition system. The encoder module on the slip ring acquires information from the coded band, generating A and B phase quadrature differential pulses and one Z phase differential pulse per revolution. These A, B, and Z phase pulses are then sent to the static control board, which processes them and converts them into sampling trigger signals for the data acquisition system. This constitutes the sampling frequency of the data acquisition system, which records the rotation angle and speed information. The sampling frequency of the data acquisition system during one revolution of the rotating body determines the temporal resolution of the CT scan. Temporal and spatial resolution are among the most important parameters of a CT scanner system. In multi-slice spiral CT, it is related to the scan coverage and reconstruction method, the sampling time per frame, the reconstruction time, and the ability to perform continuous imaging. Temporal resolution is the most important parameter determining the imaging quality of the heart and surrounding large blood vessels. The fundamental frequency of the temporal resolution is generated by the coded band on the slip ring of the rotating body or by the encoder on the rotating motor in the static section. Most manufacturers use encoders on rotating bodies because they directly determine the 360-degree upsampling angle. Due to the precision and difficulty of machining, the base frequency is generally around 1K, and then it is multiplied by the controller to 2K, 4K, 6K, etc.

[0005] Patent CN201310732682 only discloses a slip ring encoder and its encoding method, which uses redundant sensors to improve the stability of the encoding. During the scanning process of a computed tomography (CT) system, due to mechanical errors on the encoding strip on the slip ring and small errors acquired by the encoder module, the accuracy of the sampling trigger signal of the data acquisition system will eventually deteriorate, resulting in a decrease in the image quality of the heart and surrounding large blood vessels. Therefore, it is also very necessary to improve the accuracy of the sampling trigger signal of the data acquisition system. Summary of the Invention

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

[0007] This invention is achieved by the following technical solution: a method for improving the accuracy of data sampling trigger signals based on a CT scanning gantry, comprising the following steps:

[0008] The static control board controller acquires the A and B quadrature pulses and Z pulses from the encoder module on the slip ring; and processes the A and B quadrature pulses into data sampling trigger signals.

[0009] For the first n sampled trigger signals, the improved first n sampled trigger signals are generated by processing with the expected threshold.

[0010] The improved Kalman filter outputs a sampling trigger signal: the average value of the first n improved sampling trigger signals is calculated as the initial estimate; the measured value of the (n+i)th improved trigger signal is used as the measured value of the improved Kalman filter, and the i-th improved Kalman filter is performed. The resulting filtered estimate is used as the (n+i)th improved sampling trigger signal output.

[0011] The step of generating an improved first n sampled trigger signals by processing the first n sampled trigger signals using a desired threshold includes the following steps:

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

[0013] If these n measured values ​​are within the threshold of the expected value, then the n sample trigger signal values ​​will be output as the improved sample trigger signal.

[0014] If any of these n measured values ​​is greater than the threshold of the expected value, then the expected value plus the threshold of the expected value will be used as the improved sampling trigger signal output.

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

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

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

[0018] The improved Kalman filter output sampling trigger signal includes 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 taken as the measured value Z of the improved Kalman algorithm. n+i If Z 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) Based on the improved Kalman gain K i And the previous estimate X i-1 Calculate the next estimated value X i =X i-1 +K i *(Z n+i -X i-1 ); X i As the (n+i)th improved data sampling trigger signal, T n+i＝ X i ;

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

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

[0025] According to the measurement error e mea and estimation 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 is... i+1 As the output of the data sampling trigger signal, T n+i+1 =X i+1 .

[0028] The sampling trigger signal is transmitted to the rotation control board via the slip ring command loop, and then transmitted from the rotation control board to the data acquisition system for sampling.

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

[0030] The sampling trigger signal generation module is used to acquire the A, B quadrature pulses and Z pulses from the encoder module on the slip ring; and to process the A and B quadrature pulses into data sampling trigger signals; for the first n sampling trigger signals, an improved first n sampling trigger signals are generated by processing with the desired threshold.

[0031] The sampling trigger signal optimization module is used to output the sampling trigger signal through the improved Kalman filter: the average value 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, the i-th improved Kalman filter is performed, and the filtered estimate obtained 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 enhances the accuracy of the data sampling trigger signal and offers higher real-time performance than the average value filter. Furthermore, the addition of a function to remove outlier extreme measurements further smooths the data and eliminates unnecessary fluctuations caused by outlier extreme values ​​compared to the standard Kalman filter. Attached Figure Description

[0034] Figure 1 This is a flowchart of the present invention;

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

[0036] Figure 3 This is a diagram showing the back of the slip ring;

[0037] Figure 4 This is a magnified view of the coding strip of the slip ring;

[0038] Among them, 1 is a data receiving module, 2 is a slip ring disk, 3 is a carbon brush module, 4 is a data sending module, 5 is an encoder module, and 6 is an encoding strip on the slip ring disk.

[0039] Figure 5 The data sampling trigger signal before the addition of the improved Kalman filter, with an exposure time of 1 second and an integral time plot of 2320 views;

[0040] Figure 6 The data sampling trigger signal after adding the improved Kalman filter, 1-second exposure time, and 2320 view integral time plot. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to the embodiments.

[0042] like Figure 1As shown, a method for improving the accuracy of data sampling trigger signals based on a CT scanning gantry includes: a static control board controller processing the A and B quadrature pulse information transmitted from the encoder module of the slip ring and converting it into sampling trigger signals for the data acquisition system; the static control board controller processing the first n sampling trigger signals using a desired threshold to generate improved first n sampling trigger signals; the static control board controller using an improved Kalman filter to sequentially generate the improved nth and subsequent sampling trigger signals; and the static control board controller transmitting these signals through a slip ring command loop to a rotary control board, which then 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 this invention include:

[0044] 1. The controller on the static control board acquires 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 data sampling trigger signals.

[0045] 2. The controller on the static control board reads n measurement data sampling trigger signal values. Each of these n measurement sampling trigger signal values ​​is compared with the expected value. If these n measurement values ​​are within the threshold of the expected value, these signals are output as the improved sampling trigger signal. If any of these 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 of these 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 sampled trigger signal outputs after improvement as the initial estimate; use the measured value of the (n+1)th improved trigger signal as the measured value of the improved Kalman filter, perform the first improved Kalman filter, and use the estimated value as the (n+1)th improved sampled trigger signal output. Then, use the characteristics of the improved Kalman filter to iterate and obtain the sampled trigger signal outputs in sequence.

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

[0048] Throughout the rotation process, measurements exceeding the expected threshold represent blockages in the mechanical orifices of the coding tape, while measurements below the expected threshold represent gaps in the mechanical orifices of the coding tape. This is done to eliminate the impact of unusually large orifice or gap values ​​on the improved Kalman filter.

[0049] Example:

[0050] 1. The static control board acquires the A and B quadrature pulses and the Z pulse transmitted from the encoder module via the slip ring. The static control board processes the A and B quadrature 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 array Z(n). In this example, the holes on the encoder strip of the slip ring are square holes. Square holes are more conducive to the encoder module sampling, but square holes are more difficult to process. There are 2320 mechanical holes in one circle of the encoder strip of the slip ring. When the CT scanning gantry starts scanning, the rotary motor starts to drive the slip ring to rotate. The encoder collects the rising and falling edges of the mechanical holes on the encoder strip, generates orthogonal A and B quadrature pulses, and sends them to the static control board. After being processed by the static control board, they are converted into data sampling trigger signal inputs.

[0052] In this example, n is set to 4, and the threshold of the expected value D for 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 these 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 these 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 the improved sampling trigger signals.

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

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

[0055] 2) Based on the measurement error e mea And estimated language difference e est0 Calculate the improved Kalman gain K1. Measurement error e mea In this example, we take 0.1 μs, and the estimation error is e. est0 Take 3µs, where the measurement error e mea It is a fixed value;

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

[0057] 3) Based on the improved Kalman gain K1 and the initial estimated value X0, take the next data sampling trigger signal measurement value and determine whether this measurement value is within 3% of the expected value. If it is within this range, this measurement value is taken as the improved Kalman measurement value Z. n+1If 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+1)th improved data sampling trigger signal, T n+1＝ X1;

[0060] 4) Based on the improved Kalman gain K1 and the estimated speech difference e est0 Calculate the next estimation 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 Find the next improved Kalman gain K2.

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

[0064] 5) Based on the improved Kalman gain K2 and the initial estimated value X1, take the next data sampling trigger signal measurement value and determine whether this measurement value is within 3% of the expected value. If it is within this range, this measurement value is taken 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%); use the formula to calculate the estimated value X2.

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

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

[0067] 6) Repeat steps 4) to 5) iteratively until the estimated values ​​X3, X4, X5...X are generated sequentially. m ;

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

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

[0070] Furthermore, during computed tomography (CT) scanning (at a rotation speed of 1 second in this example), the rotary motor begins to rotate, and the static control board receives data sampling trigger signals from the slip ring encoder. The first four data acquisition system sampling trigger signals from the static control board are output using measured values ​​after threshold judgment based on the expected value. The fifth and subsequent data sampling trigger signals use estimated values ​​after improved Kalman filtering as the data sampling trigger signals. When the rotating part of the scanning carriage reaches 1 second, line exposure begins. At this time, the data sampling trigger signals, after multiple iterations of the improved Kalman filter, have achieved very high sampling accuracy, reaching the expected purpose.

[0071] Furthermore, the system was tested when the CT scanner gantry rotated at 1 second, with a 2320 VIEW and an exposure time of 1 second. Figure 5 The difference in data sampling time for the traditional slip ring without modification of the Kalman filter is 0.450 - 0.420 = 0.030 ms.

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

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

Claims

1. A method for improving the accuracy of data sampling trigger signals based on a CT scanning gantry, characterized in that... This includes the following steps: The static control board controller acquires the A and B quadrature pulses and Z pulses from the encoder module on the slip ring; and processes the A and B quadrature pulses into data sampling trigger signals. For the first n sampled trigger signals, the improved first n sampled trigger signals are generated by processing with the expected threshold. The improved Kalman filter outputs a sampling trigger signal: the average value of the first n improved sampling trigger signals is calculated as the initial estimate; Using the improved (n+i)th trigger signal measurement value as the improved Kalman measurement value, perform the i-th improved Kalman filter, and output the filtered estimate as the (n+i)th improved sampling trigger signal; The improved Kalman filter outputs a sampling trigger signal, which includes 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+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 taken as the measured value Z of the improved Kalman algorithm. n+i If Z 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) Based on the improved Kalman gain K i And the previous estimate X i-1 Calculate the next estimated value X i =X i-1 +K i (Z) n+i -X i-1 ); X i As the (n+i)th improved data sampling trigger signal, T n+i= X i ; According to the improved Kalman gain K i and estimation error e est(i-1) Calculate the next estimation error e esti ; yes esti =(1- K i ) yes est(i-1) According to the measurement error e mea and estimation error e esti Find the next improved Kalman gain K. i+1 ; K i+1 = and esti / ( And esti +e mea ) 4) Using steps 2)-3), the generated estimated value X i+1 As the output of the data sampling trigger signal, T n+i+1 =X i+1 .

2. The method for improving the accuracy of data sampling trigger signals based on a CT scanning gantry according to claim 1, characterized in that... The step of generating an improved first n sampled trigger signals by processing the first n sampled trigger signals using a desired threshold includes the following steps: Read n sampled trigger signal values ​​and compare each measured value with the expected value; If these n measured values ​​are within the threshold of the expected value, then the n sample trigger signal values ​​will be output as the improved sample trigger signal. If any of these n measured values ​​is greater than the threshold of the expected value, then the expected value plus the threshold of the expected value will be used as the improved sampling trigger signal output. If any of these n measured values ​​is less than the threshold of the expected value, the improved sampling trigger signal is output as the expected value minus the threshold of the expected value.

3. The method for improving the accuracy of data sampling trigger signals based on a CT scanning gantry according to claim 2, characterized in that, The threshold for 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 gantry according to claim 2, characterized in that, The threshold value that is greater than the expected value is used to indicate that the mechanical hole of the coding tape is blocked; the threshold value that is less than the expected value is used to indicate that the mechanical hole of the coding tape is sieve.

5. The method for improving the accuracy of data sampling trigger signals based on a CT scanning gantry according to claim 1, characterized in that, The sampling trigger signal is transmitted to the rotation control board via the slip ring command loop, and then transmitted from the rotation control board to the data acquisition system for sampling.

6. A system for improving the accuracy of data sampling trigger signals based on a CT scanner gantry, the system being used to implement the method for improving the accuracy of data sampling trigger signals based on a CT scanner gantry as described in any one of claims 1-5, characterized in that... Applied to static control board controllers; including: The sampling trigger signal generation module is used to acquire the A, B quadrature pulses and Z pulses from the encoder module on the slip ring; and to process the A and B quadrature pulses into data sampling trigger signals; for the first n sampling trigger signals, an improved first n sampling trigger signals are generated by processing with the desired threshold. The sampling trigger signal optimization module is used to output the sampling trigger signal through the improved Kalman filter: the average value 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, the i-th improved Kalman filter is performed, and the filtered estimate obtained is output as the (n+i)-th improved sampling trigger signal.

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