Method for generating air correction table in CT system, computer program and readable storage medium

Abstract

The invention discloses a method for generating an air correction table in a CT (Computed Tomography) system, a computer program, a readable storage medium and computed tomography equipment. To avoid generating all tables in a short period of time, air correction tables are grouped into a base correction table, a sub-base table, and a differential table. According to the method for generating the air correction table in the CT system, the computer program, the readable storage medium and the computed tomography equipment, the table making time is greatly shortened as long as one or two basic air correction tables are frequently generated according to the CT system, and the image quality does not obviously become poor.

Description

[0001] Nouns and pronouns relating to persons in this patent application are not limited to a specific gender. Technical Field

[0002] The present invention relates to computed tomography and, more particularly, to air correction tables. Background Art

[0003] In CT, air correction is used to correct for the different signal responses of different detector units. The table used in this step is called an air correction table. Since the signal response of the detector unit changes over time, the air correction table must be repeatedly generated after a period of time. Because there are a large number of tables, it takes a lot of time. In order to shorten the table generation time, currently, the air correction table is divided into a basic correction table and a differential correction table, and only the basic correction table needs to be updated in the short term. However, because there is one or two or even three tables in the basic correction table according to each collimation of the CT system, it still takes several minutes. Summary of the invention

[0004] In view of this, the present invention proposes a method for generating an air correction table in a CT system, a computer program, a readable storage medium, and a computer tomography device.

[0005] According to a first aspect of the present invention, there is provided a method for generating an air correction table in a CT system, comprising:

[0006] At maximum collimation, an air scan is performed with a typical tube voltage, typical rotation time, typical filter setting, and typical focal spot size to obtain the signal S air (z, k, r, p), and according to the signal S air (z, k, r, p) calculates the basic correction table bascal; where z represents the row, k represents the channel, r represents the reading, and p represents the projection;

[0007] For each combination of collimation and focal size, an air scan is performed with a typical tube voltage, a typical rotation time, and a typical filter setting. The temporary table temptab is calculated in the same way as the basic correction table bascal, and the subbasic table subbascal is calculated according to the following formula:

[0008] subbascal = temptab-bascal;

[0009] For each combination of collimation and focus size, an air scan is performed with each tube voltage, each rotation time, and each filter setting, and the second temporary table temptab2 is calculated in the same way as the basic correction table bascal, and the difference table diffcal is calculated according to the following formula:

[0010] diffcal=temptab2-subbascal-bascal;

[0011] Among them, the sub-basic table subbascal, the differential table diffcal and the second temporary table temptab2 have only one parameter different and have the same collimation and focus size, the sub-basic table subbascal and the basic table bascal have the same tube voltage, rotation time, and filter setting; when there is a basic table bascal with a different focus size, the sub-basic table subbascal and the basic table bascal also have the same focus size.

[0012] In one embodiment, each of the combinations of collimation and focus size is different from the combination of collimation and focus size of the basic correction table bascal.

[0013] In one embodiment, the basic correction table bascal, the sub-basic table subbascal, and the difference table diffcal correspond to signals of the same row.

[0014] According to a second aspect of the present invention, a computer program is provided, which can implement the steps of the above method when executed by a processor.

[0015] According to a third aspect of the present invention, there is provided a computer-readable storage medium having a computer program stored thereon, which can implement the steps of the above-mentioned method when executed by a processor.

[0016] According to a fourth aspect of the present invention, there is provided a computer tomography device comprising the computer readable storage medium as described above.

[0017] The method, computer program, readable storage medium and computer tomography device of the present invention for generating an air correction table in a CT system only need to regularly generate one or two basic air correction tables according to the CT system, thereby greatly shortening the table making time without significantly deteriorating the image quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the above and other features and advantages of the present invention will be more apparent to those skilled in the art. In the accompanying drawings:

[0019] Figure 1 Schematic diagram of the difference in signal response variation between an edge row of 1×5 mm collimation and the same row of 64×0.6 mm collimation and the shift in signal response differential on the same row of 1×5 mm collimation according to an embodiment of the present invention.

[0020] Figure 2Schematic diagram of the high-pass portion of the difference in signal response change between an edge row of 1×5 mm collimation and the same row of 64×0.6 mm collimation and the high-pass portion of the shifted signal response difference on the same row of 1×5 mm collimation according to an embodiment of the present invention.

[0021] Figure 3 The present invention is a schematic flowchart of a method for generating an air correction table according to an embodiment of the present invention.

[0022] Figure 4A Schematic diagram of a tomographic image of a water phantom reconstructed using an air correction table in the prior art.

[0023] Figure 4B To use Figure 3 Schematic representation of the method for generating an air correction table for reconstructing a tomographic image of a water phantom.

[0024] Figure 4C for Figure 4B The tomographic images and Figure 4A Schematic diagram of the difference in tomographic images.

[0025] Figure 4D A schematic diagram of the CT value distribution of tomographic images obtained by scanning a water phantom with 40 CT machines in the prior art. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail with reference to the following embodiments.

[0027] Although the inhomogeneity of the detector channel response is inevitable, it has been greatly improved with the improvement of processing technology and scintillating materials. This makes the difference in the signal response change of the detector channel under large and small collimation comparable to the difference in the signal response change of the same channel under the small collimation. This means that the signal response change of the detector channel under large collimation can be used as the signal response change of the detector channel under small collimation.

[0028] Figure 1 is the difference d between the signal response variation of the edge row of 1×5 mm collimation and the same row of 64×0.6 mm collimation according to the embodiment of the present invention. src (Indicated by signal response change diff in the figure, Figure 2 The same) and the signal response differential deviation d on the same row of 1×5mm collimation (indicated by diffcal deviation in the figure, Figure 2 The same is true for the schematic diagram of the LP circuit, where LP stands for low pass.

[0029] d src=(S(64×0.6,t1)-S(1×5,t1,2))-(S(64×0.6,t2)-S(1×5,t2,2))

[0030] d=(S(1×5,t1,1)-S(1×5,t1,2))-(S(1×5,t2,1)-S(1×5,t2,2))

[0031] S(1×5, t1, 1) is the signal obtained on the edge row by using 1×5 mm collimation for the first scan at around time t1 of the first table making;

[0032] S(64×0.6, t1) is the signal obtained on the row using 64×0.6mm collimation at around time t1 of the first table making;

[0033] S(1×5, t1, 2) is the signal obtained on the row by changing the scanning parameters by using 1×5 mm collimation to perform the second scan at around time t1 of the first table making;

[0034] S(64×0.6, t2) is the signal obtained on the row using 64×0.6mm collimation at around time t2 of the second table making;

[0035] S(1×5, t2, 1) is the signal obtained on this row by using 1×5 mm collimation for the first scan at around time t2 of the second table making;

[0036] S(1×5, t2, 2) is the signal obtained on the row by changing the scanning parameters and performing the second scan using 1×5 mm collimation at around time t2 of the second table making;

[0037] Let subbascal(t1)=S(64×0.6, t1)-S(1×5, t1, 2), which represents the signal response change on the row at time t1 for 1×5 mm collimation and 64×0.6 mm collimation.

[0038] Let subbascal(t2)=S(64×0.6, t2)-S(1×5, t2, 2), which represents the signal response change on the row at time t2 for 1×5 mm collimation and 64×0.6 mm collimation.

[0039] Let diffcal(t1)=S(1×5, t1, 1)-S(1×5, t1, 2), which represents the signal response difference on the row at time t1 for 1×5 mm collimation.

[0040] Let diffcal(t2)=S(1×5, t2, 1)-S(1×5, t2, 2), which represents the signal response difference on the row at time t2 for 1×5 mm collimation.

[0041] The low pass portion of the variation and shift is caused by the different shifts from the optimum collimation slot position. Because all air correction tables are generated within the Z control tolerance, the low pass portion is acceptable and should be excluded when comparing the difference in signal response variation and the shift in signal response differential. Figure 2 Schematic diagram of the high-pass portion of the difference in signal response variation between 1×5 mm collimation and 64×0.6 mm collimation and the high-pass portion of the shift in the signal response difference of 1×5 mm collimation according to an embodiment of the present invention, wherein HP represents high-pass. Figure 2 As shown, the difference in the signal response variation of the detector channel under large and small collimation is comparable to the offset of the signal response difference of the same channel under small collimation. Therefore, the signal response variation of the detector channel under large collimation can be used as the response variation of the same channel under small collimation.

[0042] To avoid generating all the tables in a short time, the air correction tables are grouped into basic correction tables, sub-basic tables and differential tables. The basic correction table has maximum collimation and no filters (this is the typical filter setting) and is generated during general adjustment, daily inspection, and calibration. The sub-basic table reflects the quasi-long-term factors collimation and focus size. The differential table reflects the long-term factors, including rotation time, filter settings and tube voltage. The sub-basic table and differential table are generated during general adjustment. Optionally, the sub-basic table is also generated during calibration.

[0043] Figure 3 FIG. 1 is a schematic flow chart of a method 100 for generating an air correction table according to an embodiment of the present invention. Figure 3 As shown, the method 100 for generating an air correction table in a CT system includes step S102, step S104, and step S106. It should be noted that the original data in the present invention are all offset corrected, decoded, logarithmic, and monitor normalized data, and the tube current is used as a configurable parameter.

[0044] In step S102, an air scan is performed at maximum collimation with a typical tube voltage, a typical rotation time, a typical filter setting, and a typical focal spot size to obtain a signal S air (z, k, r, p), and according to the signal S air (z, k, r, p) calculates the basic correction table bascal. S air (z, k, r, p) is the offset corrected, decoded, logarithmic, and monitor normalized data. SFor each angular partition, the data is averaged and the wedge vector is removed to obtain the basic correction table bascal. In which z represents the row, k represents the channel, r represents the reading, and p represents the projection. In this embodiment, the basic correction table bascal is bascal(64×600_120_500_small).

[0045] In step S104, for each combination of collimation and focal size, an air scan is performed with a typical tube voltage, a typical rotation time, and a typical filter setting, and a temporary table temptab is calculated in the same manner as the basic correction table bascal, and a subbasic table subbascal is calculated according to the following formula:

[0046] subbascal=temptab-bascal

[0047] Only the rows corresponding to the maximum collimation are used in the calculation.

[0048] The subbasic table subbascal stores the difference between the air scan and the basic correction table bascal on the corresponding row. In this embodiment, the scan is performed in mode 1x5000_120_500_small (this mode means: collimation is 1x5mm, rotation time (the time for the tube to rotate one circle) is 500ms, tube voltage is 120kV, and small focus), and the temporary table temptab is calculated in the same way as the basic correction table bascal. Then, the subbasic table subbascal is calculated by the above formula, that is:

[0049] subbascal(1×5000_120_500_small)

[0050] =temptab(1×5000_120_500_small)-bascal(64×600_120_500_small)

[0051] In step S106, for each combination of collimation and focus size, air scanning is performed with each tube voltage, each rotation time, and each filter setting, and a second temporary table temptab2 is calculated in the same manner as the basic correction table bascal, and a difference table diffcal is calculated according to the following formula:

[0052] diffcal=temptab2-subbascal-bascal;

[0053] When calculating, only the row corresponding to the maximum collimation is used. In this embodiment, each combination of collimation and focus size is different from the combination of collimation and focus size in the basic correction table bascal.

[0054] Among them, the sub-basic table subbascal and the differential table diffcal and the second temporary table temptab2 have only one parameter different and have the same collimation and focus size. The sub-basic table subbascal and the basic table bascal have the same tube voltage, rotation time, and filter setting. When there is a basic table bascal with different focus sizes, the sub-basic table subbascal and the basic table bascal also have the same focus size. In this embodiment, the mode 1x5000_80_500_small (this mode means: collimation is 1x5mm, rotation time is 500ms, tube voltage is 80kV, small focus) is used for scanning, and the second temporary table temptab2 is calculated in the same way as the basic correction table bascal. Then, the differential table diffcal is calculated by the above formula, that is:

[0055] diffcal(1×5000_80_500_small)=temptab2(1×5000_80_500_small)-subbascal(1×5000_120_500_small)-bascal(64×600_120_500_small);

[0056] The basic correction table bascal, the subbasic table subbascal, and the difference table diffcal correspond to signals of the same row.

[0057] When applying the air correction table of the present invention, in order to obtain the correct air correction table for a specific scanning mode, it is necessary to add the basic correction table and the related sub-basic table and differential table. For example:

[0058] airtab(1×5000_80_1000_small)=bascal(64×600-120_500_small)+subbascal(1×5000_120_500_small)+diffcal(1×5000_80-500_small)+diffcal(1×5000_120_1000_small)

[0059] To verify the performance of the present invention, a scan was performed immediately after air correction, with the same parameters as used in the prior art to generate an air correction table with a collimation of 1x5mm. The air correction table of the present invention and the air correction table of the prior art were each used to reconstruct the image. To generate the table of the present invention, two tables (1×5000_120_500_small and 64×600_120_500_small, used to generate the sub-basic table of the present invention) air-corrected 12 days ago and one table (64×600_120_500_small, used as the basic correction table of the present invention) air-corrected recently were used.

[0060] Figure 4A Schematic diagram of a tomographic image of a water phantom reconstructed using an air correction table in the prior art. Figure 4B To use Figure 3 Schematic representation of the method for generating an air correction table for reconstructing a tomographic image of a water phantom. Figure 4C for Figure 4B The tomographic images and Figure 4A Schematic diagram of the difference in tomographic images. Figure 4A , 4B As shown, both images have no visible artifacts, only a slight shift in the CT values ​​is noticed, which is mainly caused by the limited accuracy of the Z control (tolerance is 10um) resulting in different collimation slit offsets relative to the optimal collimation slit position during air correction.

[0061] Figure 4D The figure is a schematic diagram of the CT value distribution of tomographic images obtained by scanning a water phantom with 40 CT machines in the prior art, which scan a water phantom with a diameter of 20 cm with a collimation of 1x5 mm. Figure 4A , 4B As can be seen from Figures 4C and 4D, the CT value deviation caused by the air correction table of the present invention is within the normal range.

[0062] In one embodiment, the present invention further provides a computer program, which can implement the steps of the method 100 for generating an air correction table when executed by a processor.

[0063] In one embodiment, the present invention further provides a computer-readable storage medium having a computer program stored thereon, which can implement the steps of the method 100 for generating an air correction table when the program is executed by a processor.

[0064] In one embodiment, the present invention further provides a computer tomography device, comprising the computer readable storage medium described above.

[0065] The method, computer program, readable storage medium and computer tomography device of the present invention for generating an air correction table in a CT system only need to regularly generate one or two basic air correction tables based on the CT system, thereby greatly shortening the table making time without significantly deteriorating the image quality.

[0066] 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, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for generating an air correction table in a CT system, comprising: At maximum collimation, an air scan is performed with a typical tube voltage, typical rotation time, typical filter setting, and typical focal spot size to obtain the signal S air (z, k, r, p), and according to the signal S air (z, k, r, p) calculates the basic correction table bascal; where z represents the row, k represents the channel, r represents the reading, and p represents the projection; For each combination of collimation and focal size, an air scan is performed with a typical tube voltage, a typical rotation time, and a typical filter setting. The temporary table temptab is calculated in the same way as the basic correction table bascal, and the subbasic table subbascal is calculated according to the following formula: subbascal = temptab-bascal; For each combination of collimation and focus size, an air scan is performed with each tube voltage, each rotation time, and each filter setting, and the second temporary table temptab2 is calculated in the same way as the basic correction table bascal, and the difference table diffcal is calculated according to the following formula: diffcal=temptab2-subbascal-bascal; Among them, the sub-basic table subbascal, the differential table diffcal and the second temporary table temptab2 have only one parameter different and have the same collimation and focus size, the sub-basic table subbascal and the basic table bascal have the same tube voltage, rotation time, and filter setting; when there is a basic table bascal with a different focus size, the sub-basic table subbascal and the basic table bascal also have the same focus size.

2. The method according to claim 1, characterized in that: Each of the combinations of collimation and focus size is different from the combination of collimation and focus size of the basic correction table bascal.

3. The method according to claim 1, characterized in that: The basic correction table bascal, the subbasic table subbascal, and the difference table diffcal correspond to signals of the same row.

4. A computer program, which, when executed by a processor, can implement the steps of the method according to any one of claims 1 to 3.

5. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method described in any one of claims 1 to 3 can be implemented.

6. A computer tomography apparatus comprising the computer readable storage medium according to claim 5.

Images