Wide temperature correction method for CT detector module and CT using the same

Abstract

This invention, applicable to the field of computed tomography (CT) scanning, provides a wide-temperature correction method for CT detector modules and a CT system employing the method. By adding a corresponding temperature sensor to each detector module, the method collects detector sensitivity at different temperatures and establishes a temperature-sensitivity correction table. This correction table is then used to calibrate the projection data output during the actual imaging process, effectively eliminating ring artifacts in tomographic images and enhancing the imaging system's adaptability to various environments.

Description

Technical Field

[0001] The present invention belongs to the technical field of computerized tomography, and in particular relates to a wide temperature correction method for a CT detector module and a CT using the same. Background Art

[0002] The CT detector system primarily consists of a collimator, detector modules, a data acquisition module, a control board, a fan, and the mechanical structure that houses and secures these components. Each detector module corresponds to a data acquisition module. Various chips are soldered to the data acquisition module. When the detector system is operating, these chips generate significant heat, causing the internal temperature of the detector to rise continuously.

[0003] For the photodiodes within the detector module, the charge carriers are primarily excited by thermal motion, and their energy distribution follows the Boltzmann distribution. Rising temperature leads to an increase in carrier concentration. A temperature increase of just a few degrees can increase the carrier concentration dozens of times. To prevent temperature fluctuations from causing asynchronous changes in the sensitivity of the detector modules, the CT system is typically placed in a constant temperature environment. Alternatively, the high-power chips (AD chips, FPGA chips) on the data acquisition module are positioned so that they are directly exposed to the strong airflow generated by the rear fan, improving heat dissipation efficiency and ensuring minimal temperature fluctuations within the CT system.

[0004] However, the former requires an additional heating device, which increases system power consumption, increases power requirements, and complicates the structure, hindering the miniaturization of the imaging system and the entire CT machine. While the latter facilitates miniaturization, due to the different positions of the detector modules within the detector system, even in environments with drastic temperature fluctuations, the detector modules may experience asynchronous temperature changes, leading to ring artifacts. Existing technologies have shortcomings. Summary of the Invention

[0005] The purpose of the present invention is to provide a wide temperature correction method for a CT detector module, aiming to establish a correction table for the sensitivity of each detector at different temperatures, so as to avoid the ring artifact problem of tomographic images when imaging in a wide temperature environment through correction.

[0006] In one aspect, the present invention provides a method for wide temperature calibration of a CT detector module, the method comprising the following steps:

[0007] F1. Collect the output signal strength of each detector module in the CT at different temperatures, calculate the corresponding temperature-sensitivity correction coefficient, and establish a temperature-sensitivity correction table;

[0008] F2. Correct the projection data of each detector module based on the temperature-sensitivity correction table in an actual environment.

[0009] Furthermore, the step F1 includes the following steps:

[0010] S1. Turn off the CT, place the CT in a preset temperature environment, and calibrate the corresponding temperature sensors of each detector module;

[0011] S2. Turn on the CT machine and record the dark current of each detector module before exposure; perform air exposure; record the X-ray source tube current, the output signal intensity of each detector module, and the corresponding ambient temperature during exposure;

[0012] S3. Raise the ambient temperature and continue air exposure; record the output signal intensity and dark current of each detector module at different temperatures, as well as the corresponding X-ray source tube current;

[0013] S4. After completing the data collection within the working temperature range, the data is processed into a table to create a temperature-sensitivity correction table.

[0014] Furthermore, the step F2 includes the following steps:

[0015] T1. Collect the actual ambient temperature of each detector module to calculate the average ambient temperature;

[0016] T2. The average ambient temperature is used as the reference temperature to transform the temperature-sensitivity correction table;

[0017] T3. Correct the projection data of each detector module at the actual ambient temperature using the converted temperature-sensitivity correction table.

[0018] On the other hand, the present invention also provides a CT operating in a wide ambient temperature range, comprising a turntable and an X-ray source and a detection system respectively fixed at two ends of the turntable, and adopting the wide temperature correction method of the CT detector module as described in any one of the above items.

[0019] Furthermore, the detection system includes a plurality of detector modules; the plurality of detector modules are arranged in an arc shape, and the center of the arc is the focus of the X-ray source;

[0020] The detector module is provided with a scintillator, a photodiode, a substrate and a connector in sequence in the direction of the X-ray; and a temperature sensor is provided on a surface of the substrate facing the X-ray source.

[0021] Furthermore, the operating temperature range of the temperature sensor is -50 degrees Celsius to 100 degrees Celsius, with an accuracy greater than 0.5 degrees Celsius.

[0022] The present invention provides a solution for establishing a temperature-sensitivity correction table, specifically for use in CT projection data correction. First, in hardware, by adding a corresponding temperature sensor to each detector module, the actual operating temperature of each detector module can be accurately detected under different ambient temperatures. Then, based on the detector module output, a correction table is established that reflects the relationship between temperature and sensitivity. Finally, during the actual imaging process, the projection data of each detector module is individually corrected based on this correction table. This allows all detector modules to output projection data based on a single standard temperature when CT is used in a wide range of temperature environments, effectively eliminating ring artifacts in tomographic images and enhancing the imaging system's ability to adapt to different environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of an implementation method for wide temperature correction of a CT detector module provided in the first embodiment of the present invention;

[0024] Figure 2 This is a flowchart for implementing the construction of a correction table in the wide temperature correction method for a CT detector module provided in the first embodiment of the present invention;

[0025] Figure 3 This is a flowchart for implementing the application of the correction table in the wide temperature correction method for the CT detector module provided in the first embodiment of the present invention;

[0026] Figure 4 It is a schematic diagram of the structure of a detector module of a CT provided in the second embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] The following describes the specific implementation of the present invention in detail with reference to specific embodiments:

[0029] Example 1:

[0030] Figure 1 The following illustrates the implementation process of the wide temperature calibration method for a CT detector module provided in the first embodiment of the present invention. For ease of illustration, only the portion related to the embodiment of the present invention is shown. The details are as follows:

[0031] The present invention provides a wide temperature calibration method for a CT detector module, the method comprising the following steps:

[0032] F1. Collect the output signal strength of each detector module in the CT at different temperatures, calculate the corresponding temperature-sensitivity correction coefficient, and establish a temperature-sensitivity correction table;

[0033] F2. In the actual environment, based on the temperature-sensitivity correction table, calibrate the projection data of each detector module.

[0034] like Figure 2 As shown, step F1 includes the following steps:

[0035] S1. Turn off the CT, place it in a preset temperature environment, and calibrate the corresponding temperature sensors of each detector module;

[0036] S2. Turn on the CT and record the dark current of each detector module before exposure; perform air exposure; record the X-ray source tube current, the output signal intensity of each detector module, and the corresponding ambient temperature during exposure;

[0037] S3. Raise the ambient temperature and continue air exposure; record the output signal intensity and dark current of each detector module at different temperatures, as well as the corresponding X-ray source tube current;

[0038] S4. After completing the data collection within the working temperature range, the data is processed into a table to create a temperature-sensitivity correction table.

[0039] Furthermore, step S4 includes the following steps:

[0040] S41. Deduct the dark current of the output signal intensity of each detector module at different preset temperatures to obtain the net signal intensity:

[0041] d k,n =D k,n -B k,n ;

[0042] Where d is the net signal intensity, D is the output signal intensity, B is the dark current, k is the preset temperature, and n is the detector module number;

[0043] S42. Perform normalization correction on the X-ray source tube current at each preset temperature to obtain the tube current correction coefficient:

[0044]

[0045] Where a is the correction coefficient of the tube current; I is the tube current; k is the preset temperature; I1 is the standard current;

[0046] S43. Use the tube current correction coefficient to normalize the net signal strength of each detector module at each temperature to eliminate the effect of tube current fluctuations on detector sensitivity:

[0047]

[0048] Among them, a k is the correction coefficient of the tube current at temperature k, C is the signal intensity output by the detector when the tube current is normalized to the standard current, and C k,n is the net signal intensity of the nth detector module when exposed at the preset temperature k;

[0049] S44. Select a preset temperature from a plurality of preset temperatures as a reference temperature, normalize the sensitivity of each detector module at each preset temperature, and construct a temperature-sensitivity correction table.

[0050] Furthermore, the normalization process in step S44 is as follows:

[0051]

[0052] Where kB is the reference temperature selected from a preset range, and f is the temperature-sensitivity correction factor for the detector module. A temperature-sensitivity correction factor table constructed by constructing correction factors for different temperatures based on a ratio of a reference temperature facilitates reference temperature conversion (i.e., when a new temperature is needed as the reference temperature, all correction factors in the table are simultaneously divided by the corresponding factor for that temperature. In other words, the correction factor for the new reference temperature is 1). This allows for application in real-world environments with a wide temperature range.

[0053] In a preferred embodiment, when executing step F1, when the detector module is in an appropriate low-temperature environment and does not generate dark current, step S4 constructs a temperature-sensitivity correction table by using the ratio of the output signal intensity to the signal intensity output by the detector when the tube current is normalized to the standard current as the temperature-sensitivity correction coefficient of the detector module.

[0054] Specifically: In this way, the speed of constructing the temperature-sensitivity correction table can be effectively improved.

[0055] Furthermore, the step interval of the temperature increase in step S3 is 1 degree Celsius.

[0056] like Figure 3 As shown, step F2 includes the following steps:

[0057] T1. Collect the actual ambient temperature of each detector module to calculate the average ambient temperature;

[0058] T2. Transform the temperature-sensitivity correction table using the average ambient temperature as the reference temperature;

[0059] T3. Use the converted temperature-sensitivity correction table to calibrate the projection data of each detector module at the actual ambient temperature.

[0060] Furthermore, step T3 includes the following steps:

[0061] T31. Calculate the net signal strength output by each detector module at the actual ambient temperature;

[0062] T32. Based on the converted temperature-sensitivity correction table, multiply the net signal intensity at the actual ambient temperature by the ratio of the correction coefficient at the average temperature to the correction coefficient at the actual ambient temperature to obtain the projection data of the corresponding detector module after temperature effect correction:

[0063]

[0064] Among them, f kB,n The temperature in the temperature-sensitivity correction table after conversion is the correction coefficient of the reference temperature with the average ambient temperature as the reference temperature;

[0065] f kT,n is the correction coefficient of the measured temperature T of the detector module n in the temperature-sensitivity correction table after transformation;

[0066] d kT,n is the net signal strength output by detector module n at the measured temperature T;

[0067] E n This is the projection data after temperature effect correction.

[0068] In a preferred embodiment, if the average temperature of each detector module in the CT operating environment is exactly the same as the reference temperature used to construct the temperature-sensitivity correction table, the table conversion step can be skipped and used directly to calibrate the projection data of each detector module. This allows the output of each detector module in the same CT to be uniformly maintained at the same temperature, thus avoiding ring artifacts.

[0069] The following table is a temperature-sensitivity correction table established with 25 degrees Celsius as the reference temperature during specific implementation. The specific table is:

[0070] Module 1 Module 2 …… Module N Temperature 1 <![CDATA[f 1,1 ]]> <![CDATA[f 1,2 ]]> <![CDATA[f 1,N ]]> Temperature 2 <![CDATA[f 2,1 ]]> <![CDATA[f 2,2 ]]> <![CDATA[f 2,N ]]> …… 25 degrees Celsius 1 1 1 1 …… Temperature K <![CDATA[f K,1 ]]> <![CDATA[f K,2 ]]> <![CDATA[f K,N ]]>

[0071] In step S3, the temperature increase step interval is 1 degree Celsius. Therefore, the above table records the correction coefficients corresponding to the reference temperature of 25 degrees Celsius for all detector modules (1, 2...N) in the CT starting from temperature 1 and stepping 1 degree Celsius up to temperature K.

[0072] In the specific implementation, suppose that due to a large change in ambient temperature, the temperature of each detector module inside the CT cannot reach the same level in a short time. For example, the temperature of module 1 is 22 degrees Celsius, and the output net signal strength is d 22℃，1 , the temperature of module 2 is 24 degrees Celsius, and the output net signal strength is d 24℃，2 , ... The temperature of module N is 28 degrees Celsius, and the output net signal strength is d 28℃，N etc.

[0073] Since the operating temperatures of all detector modules are distributed around 25 degrees Celsius, a temperature-sensitivity correction table using 25 degrees Celsius as the reference temperature is used to calibrate the output of each detector module. Here, the reference temperature can also be obtained by calculating the average temperature of all detector modules.

[0074] Specifically, according to the formula:

[0075]

[0076] The net signal intensity of each detector module is corrected to obtain projection data with a unified temperature standard:

[0077] Module 1:

[0078] Module 2:

[0079] …

[0080] Module N: Ultimately, all detector modules in the CT are calibrated to the same temperature to ensure the uniformity of the output data and avoid ring artifacts in the tomographic images.

[0081] This embodiment uses the tube current correction coefficient to normalize the net signal strength of each detector module at each temperature to obtain the net signal strength correction coefficient. Based on the net signal strength correction coefficient, the sensitivity of each detector module at other temperatures is normalized to obtain the detector module correction coefficient. Once the reference temperature is determined, a temperature-sensitivity correction table can be constructed.

[0082] Because the correction coefficients are ratios, the reference temperature in the correction table, along with the corresponding correction coefficients for other temperatures, can be easily converted by multiplication based on the average temperature of each CT detector module in the actual ambient temperature. This temperature-sensitivity correction table allows for correction of projection data collected under varying ambient temperatures during the actual imaging process, effectively eliminating ring artifacts in tomographic images and enhancing the imaging system's ability to adapt to different environments.

[0083] When temperature changes are inevitable, the computed tomography correction method in the prior art generally obtains a first air correction table corresponding to a first temperature of the detector; when the detector is at a second temperature, performs an air scan, and obtains a second air correction table based on the air scan and the first air correction table; and uses the second air correction table to correct the image obtained at the second temperature.

[0084] The CT detector must be stable at the second temperature; that is, the temperature of each detector module must be the same at both second temperatures. This is easily achieved for large CT scans in a CT room with a stable ambient temperature. However, for mobile CT scans in complex and changing outdoor environments, because the temperature field of each detector module varies in a new ambient temperature, achieving a stable temperature distribution through heat transfer requires a significant amount of time. This conflicts with the requirement for mobile CT scans to quickly scan and produce images on-site. Therefore, existing solutions cannot meet practical needs.

[0085] The temperature-sensitivity correction table creation method of the present invention quickly and effectively corrects the detector gain when the detector temperature is not the first temperature, generating a second air correction table at the second temperature. Using the correction table corresponding to the actual temperature, the system can operate in a wide range of open ambient temperatures, such as -20°C (winter in Northeast China) to 40°C (summer in Southern China).

[0086] Example 2:

[0087] Figure 4 A CT operating in a wide ambient temperature range provided by a second embodiment of the present invention is shown, comprising a turntable and an X-ray source and a detection system respectively fixed at both ends of the turntable, and adopting a wide temperature correction method for a CT detector module as described in any of the above items.

[0088] Furthermore, the detection system includes a plurality of detector modules; the plurality of detector modules are arranged in an arc shape, and the center of the arc is the focus of the X-ray source;

[0089] The detector module is provided with a scintillator, a photodiode, a substrate and a connector in sequence in the direction of the X-ray; and a temperature sensor is provided on the side of the substrate facing the X-ray source.

[0090] Furthermore, the operating temperature range of the temperature sensor is -50 degrees Celsius to 100 degrees Celsius, with an accuracy greater than 0.5 degrees Celsius.

[0091] Because during actual measurement, the greater the difference between the working environment temperature and the reference temperature of the temperature-sensitivity correction table, the greater the cumulative error is likely to be. Therefore, when using the correction table, the principle of proximity is adopted to confirm the temperature of each detector module of the detector system, that is, the average temperature of each detector module is calculated and used as the basis for transforming the correction table.

[0092] At the same time, the present invention can directly obtain the real-time temperature of each detector module in the environment by setting a corresponding temperature sensor for each detector module on the side facing the X-ray source. According to the transformed temperature-sensitivity correction table, the sensitivity of the detector module can be conveniently corrected by looking up the table, and then the tomographic image can be directly reconstructed and quickly output.

[0093] The present invention adds a temperature sensor to each detector module to measure detector sensitivity at different temperatures. This temperature correction table is then created and applied to the collected projection data during the actual imaging process, eliminating ring artifacts in tomographic images caused by ambient temperature. This enhances the mobile CT's adaptability to various environmental temperatures, unlike current clinical CT systems, which require constant temperature operation.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A wide temperature calibration method for a CT detector module, characterized in that: The method comprises the following steps: F1. Collect the output signal strength of each detector module in the CT at different temperatures, calculate the corresponding temperature-sensitivity correction coefficient, and establish a temperature-sensitivity correction table; F2 in the actual environment based on the temperature - sensitivity correction table, calibrate the projection data of each detector module; The step F1 comprises the following steps: S1. Turn off the CT, place the CT in a preset temperature environment, and calibrate the corresponding temperature sensors of each detector module; S2. Turn on the CT machine and record the dark current of each detector module before exposure; perform air exposure; record the X-ray source tube current, the output signal intensity of each detector module, and the corresponding ambient temperature during exposure; S3. Raise the ambient temperature and continue air exposure; record the output signal intensity and dark current of each detector module at different temperatures, as well as the corresponding X-ray source tube current; S4. After completing data collection within the operating temperature range, the data is processed into a table to establish a temperature-sensitivity correction table; The step S4 comprises the following steps: S41. Deduct the dark current of the output signal intensity of each detector module at different preset temperatures to obtain the net signal intensity: d k,n =D k,n -B k,n ; Where d is the net signal intensity, D is the output signal intensity, B is the dark current, k is the preset temperature, and n is the detector module number; S42. Perform normalization correction on the X-ray source tube current at each preset temperature to obtain the tube current correction coefficient: Wherein, a is the correction coefficient of the tube current; I is the tube current; k is the preset temperature; I1 is the standard current; S43. Using the tube current correction coefficient, normalize the net signal strength of each detector module at each temperature to eliminate the effect of tube current fluctuations on detector sensitivity: Among them, a k is the correction coefficient of the tube current at temperature k, C is the signal intensity output by the detector when the tube current is normalized to the standard current, and C k,n The net signal intensity when the tube current is normalized to the standard current is the signal intensity output by the nth detector module during exposure at the preset temperature k; S44. Select one preset temperature from the plurality of preset temperatures as a reference temperature, normalize the sensitivity of each detector module at each preset temperature, and construct a temperature-sensitivity correction table.

2. The method according to claim 1, wherein The normalization process in step S44 is as follows: Wherein, kB is a reference temperature selected from the preset temperatures, and f is a temperature-sensitivity correction coefficient of the detector module.

3. The method according to claim 1, wherein The step interval of the temperature increase in step S3 is 1 degree Celsius.

4. The method according to claim 3, wherein The step F2 comprises the following steps: T1. Collect the actual ambient temperature of each detector module to calculate the average ambient temperature; T2. The average ambient temperature is used as the reference temperature to transform the temperature-sensitivity correction table; T3. Correct the projection data of each detector module at the actual ambient temperature using the converted temperature-sensitivity correction table.

5. The method according to claim 4, wherein Described step T3 comprises the following steps: T31 calculates the net signal strength output by each detector module at the actual ambient temperature; T32. Based on the converted temperature-sensitivity correction table, multiply the net signal intensity at the actual ambient temperature by the ratio of the correction coefficient at the average temperature to the correction coefficient at the actual ambient temperature to obtain the projection data after temperature effect correction for the corresponding detector module: Among them, f kB,n The temperature in the temperature-sensitivity correction table after conversion is the correction coefficient of the reference temperature using the average ambient temperature as the reference temperature; f kT,n is the correction coefficient of the measured temperature T of the detector module n in the converted temperature-sensitivity correction table; d kT,n is the net signal strength output by detector module n at the measured temperature T; E n This is the projection data after temperature effect correction.

6. A CT system operating in a wide range of ambient temperatures, comprising a turntable and an X-ray source and a detection system fixed at opposite ends of the turntable, characterized in that: A wide temperature calibration method for a CT detector module according to any one of claims 1 to 5 is adopted.

7. The CT according to claim 6, wherein: The detection system includes a plurality of detector modules; the plurality of detector modules are arranged in an arc shape, and the center of the arc is the focus of the X-ray source; The detector module is provided with a scintillator, a photodiode, a substrate and a connector in sequence in the direction of the X-ray; and a temperature sensor is provided on a surface of the substrate facing the X-ray source.

8. The CT according to claim 7, wherein: The operating temperature range of the temperature sensor is -50 degrees Celsius to 100 degrees Celsius, with an accuracy greater than 0.5 degrees Celsius.

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