JP3589769B2 - X-ray CT system - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is to emit X-rays and measurement position location around the oppositely disposed X-ray tube and the X-ray detector from the X-ray tube with rotating around the measurement position in the object, The present invention relates to an X-ray CT apparatus that detects the transmitted X-rays with an X-ray detector and measures and displays a tomographic image of a diagnostic site of a subject . In particular, an X-ray transmission image ( The present invention relates to an X-ray CT apparatus capable of suppressing mottled artifacts generated in a “scanogram image”.
[0002]
[Prior art]
As shown in FIG. 3, a conventional X-ray CT apparatus of this type includes a subject table 3 for placing a subject 2 on a top 1 and moving the subject 2 to a measurement position. The X-ray tube 4 and the X-ray detector 5 are arranged facing each other around the subject 2 and rotated around the subject 2 to emit X-rays from the X-ray tube 4 to the subject 2. A scanner 6 for detecting transmitted X-rays with an X-ray detector 5, a high-voltage generator 7 for applying a high voltage to the X-ray tube 4, and controlling the emission of X-rays from the X-ray tube 4. An X-ray control device 8, an image processing device 9 that performs image processing using measurement data obtained by digitizing a detection signal from the X-ray detector 5, and an image signal from the image processing device 9 is displayed as an image. And an operation console 10 for inputting operation commands and measurement conditions.
[0003]
The X-ray tube 4 and the X-ray detector 5 of the scanner 6 are mounted at opposite positions on a rotating disk 11 having an opening for inserting the subject 2 in the center. The drive unit 12 rotates in a predetermined direction. The X-ray beam 13 emitted from the X-ray tube 4 is restricted in the slice direction by a collimator 13 ′, passes through the subject 2, and the transmitted X-rays are detected by a multi-channel X-ray detector 5. The detection signal is detected, amplified by the measurement circuit 14 and A / D-converted, and converted into numerical data. The image processing device 9 includes a logarithmic converter 15 that performs logarithmic conversion on the measurement data input from the measurement circuit 14, an air corrector 16 that performs air correction on output data from the logarithmic converter 15, A two-dimensional filtering unit 17 that performs two-dimensional filtering processing such as contour enhancement on the output data from the air corrector 16. Reference numeral 18 denotes a scanner / table controller that sends control signals to the scanner 6 and the subject table 3. Reference numeral 19 denotes a display device such as a television monitor installed on the console 10.
[0004]
Next, a method of measuring a scanogram image in the conventional X-ray CT apparatus shown in FIG. 3 will be described with reference to a flowchart shown in FIG. First, the operator uses the console 10 shown in FIG. 3 to input various operation commands and measurement conditions necessary for measuring a scanogram image of the subject 2 (step A). Next, necessary control signals based on these input operation commands and measurement conditions are sent to the X-ray controller 8 and the scanner / table controller 18 via the image processing device 9 to perform a measurement preparation operation (step B). . Next, a control signal is sent from the X-ray controller 8 and the scanner / table controller 18 to the subject table 3, the scanner 6, the X-ray tube 4, etc., so that a scanogram image can be measured under predetermined conditions. , And waits for a measurement start command (step C). Then, when the operator inputs a measurement start command using the console 10, the above step C proceeds to the "YES" side to enter step D, and starts measurement of a scanogram image along the body axis direction of the subject 2. I do.
[0005]
As a result, X-rays are emitted from the X-ray tube 4 in FIG. 3, the X-ray beam 13 transmits through the subject 2, and the transmitted X-rays are detected by the X-ray detector 5 and sent to the measurement circuit 14. The measurement circuit 14 measures the output of each channel of the multi-channel X-ray detector 5 at a predetermined sampling point in the moving direction (slice direction) of the top 1 and converts it into numerical data by A / D conversion. The above is transferred to the image processing device 9 (step E). At this time, the output data of the measurement circuit 14 is represented by the following equation (1).
Here, xi, j indicates output data of the measurement circuit 14 when the channel number of the X-ray detector 5 is i and the sampling point in the moving direction of the top 1 is j.
Ii indicates an average value of xi, j when there is no attenuator such as the subject 2 and the top 1.
e indicates the base of the natural logarithm.
Si, j indicates the X-ray transmission path when the channel number of the X-ray detector 5 is i and the sampling point in the moving direction of the top 1 is j, and μ (s) is the X-ray transmission path Si, j. The upper X-ray absorption coefficient distribution is shown above, and ds is an integral line element on Si, j.
[0006]
In the image processing apparatus 9, the logarithmic converter 15 performs logarithmic conversion on the input measurement data (step F). This logarithmic conversion process is represented by the following equation (2).
Here, logxi, j and logIi do not lose generality even if they mean taking a natural logarithm. Ii appearing in the above formulas (1) and (2) can be easily obtained by measuring the X-ray beam 13 in the absence of the attenuating body such as the subject 2 and the top 1 in advance.
[0007]
Next, the measurement data logarithmically converted by the logarithmic converter 15 is input to an air corrector 16 and subjected to air correction (step G). That is, using Ii obtained in advance, air correction processing is performed on yi, j shown in the above equation (2) by the following equation (3).
As is apparent from the equation (3), the data zi, j after the air correction depends only on the distribution of the X-ray absorption coefficient on the X-ray transmission path Si, j (when xi, j> 0) ).
[0008]
In the next step H, it is determined whether or not the scanogram image measurement operation has been completed for the subject 2 by a predetermined distance in the slice direction. When the image processing device 9 determines that the measurement operation of the scanogram image has been completed, the above-described step H proceeds to the “YES” side and proceeds to step I. Then, an appropriate two-dimensional filtering process such as contour enhancement is performed by the two-dimensional filtering device 17 (step I) to create a scanogram image. Thereafter, the scanogram image thus created is transferred from the image processing device 9 to the console 10 (step J), sent to the display device 19, and displayed on the screen thereof. Thus, the measurement of the scanogram image is finally completed. Then, based on the scanogram image displayed on the display device 19, the position of the tomographic image measurement of the diagnosis site is planned in advance while observing the positional relationship of the skeleton, the organ, and the like, and the tomographic image is measured according to the plan.
[0009]
[Problems to be solved by the invention]
However, in such a conventional X-ray CT apparatus, in the measurement of a scanogram image of the subject 2, the X-ray detector 5 depends on measurement conditions such as the size of the subject 2, the slice thickness, the X-ray tube current, and the like. When the amount of incident X-rays is very small, black and white mottled artifacts may occur in the corresponding portions of the scanogram image, making it impossible to read images of skeletons and organs. That is, if the amount of X-rays incident on the X-ray detector 5 is extremely small, there may be a case where xi, j ≦ 0 in the above-mentioned equation (2) due to various noise effects. In this case, the logarithmic converter 15 Logarithmic conversion cannot be performed.
[0010]
In such a case, the values of xi, j are replaced with appropriate positive values in the logarithmic converter 15. For example, when the measurement data xi, j is “0” or negative, the logarithmic conversion is performed by replacing the measurement data xi, j with a value of “1” or more. As a result, the measurement data xi, j does not reflect the original information, and in the above equation (3), zi, j becomes a value irrelevant to the distribution of the X-ray absorption coefficient on the X-ray transmission path Si, j. Sometimes happened. When such a portion appears everywhere, a mottled artifact is generated in the scanogram image. In this case, the anatomical structure of the part of the subject 2 is not known, and the diagnosis site cannot be correctly positioned.
[0011]
Therefore, the present invention addresses such a problem and provides an X-ray CT apparatus capable of suppressing a mottled artifact occurring in a scanogram image for determining a position for measuring a tomographic image of a diagnostic site of a subject. The purpose is to provide.
[0012]
[Means for Solving the Problems]
To achieve the above object, X-rays CT device according to the invention, and the object table is moved to the measurement position by Neno the subject on the top plate, X-rays tube around the said measuring position location a scanner in which an X-ray detector emits X-rays is rotated from the X-ray tube to the object around the measurement position is opposed to detect the transmitted X-rays by the X-ray detector and the upper Symbol X In an X-ray CT apparatus having an image processing apparatus that performs image processing using measurement data obtained by digitizing a detection signal from a line detector and a display apparatus that displays an image signal from the image processing apparatus as an image, Bias addition means for adding a predetermined amount of bias value b to the input measurement data is provided at a preceding stage of logarithmic conversion means for performing logarithmic conversion on measurement data input in the image processing apparatus, and the bias value b is X-ray detector channel No. sampling points in the moving direction of the a i top plate as j the measurement data x i in the case of performing measurement without X-ray irradiation from the X-ray tube, a j, each channel of the X-ray detector When the standard deviation at the channel number i when the standard deviation is calculated for each channel is σ i, and the maximum value of the standard deviation σ i with respect to the channel number i is max ( σ i) , it is expressed by Equation 1. Before measuring the tomographic image of the diagnostic site of the subject, the X-ray incident on the X-ray detector is measured at the time of measuring the X-ray transmission image for determining the position for measuring the tomographic image. In order to suppress artifacts that occur when the dose is small, the bias adding means performs a bias adding process .
[0013]
Further, the bias adding means may change the amount of the bias value according to the value of the input measurement data, and may add the bias value to the measurement data.
[0014]
Further, the bias adding means may determine a minimum value of the input measurement data within a predetermined period, optimize the bias value based on the minimum value, and add the bias value to the measurement data.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram of an overall configuration showing an embodiment of an X-ray CT apparatus according to the present invention. The X-ray CT apparatus, and around the measurement position location oppositely disposed X-ray tube and the X-ray detector to the subject of the measurement position from the X-ray tube with rotating around the measurement position X-rays are emitted, and the transmitted X-rays are detected by an X-ray detector to measure and display a tomographic image of a diagnostic site. As shown in FIG. It comprises a voltage generator 7, an X-ray controller 8, an image processor 9, and a console 10.
[0016]
The subject table 3 lays the subject 2 on the top 1 and moves the subject 2 to a measurement position of a scanner 6 described later. The top 1 is moved back and forth as indicated by arrows P and Q. It is possible to move in the direction. The scanner 6 emits X-rays and detects transmitted X-rays of the subject 2 laid on the top plate 1 and moved in the direction of the arrow P, and inserts the subject 2 at the center. The X-ray tube 4 and the X-ray detector 5 are arranged opposite to each other on a rotating disk 11 having an opening, and the rotating disk 11 is rotated in a predetermined direction by a scanner driving device 12. Thereby, the X-ray tube 4 and the X-ray detector 5 are rotated around the subject 2, and the X-ray beam 13 emitted from the X-ray tube 4 is restricted in the slice direction by the collimator 13 '. The transmitted X-rays that pass through the subject 2 are detected by the multi-channel X-ray detector 5. The detection signal output from the X-ray detector 5 is amplified and A / D-converted by the measurement circuit 14, converted into numerical data, and output.
[0017]
The high voltage generator 7 applies a high voltage to the X-ray tube 4 in the scanner 6 and operates according to a control signal sent from an X-ray controller 8 described later, for example, a high voltage pulse of 2 to 5 ms. Is applied to the X-ray tube 4. The X-ray control device 8 controls the emission of X-rays from the X-ray tube 4, and receives a control signal required for CT scanning via the image processing device 9, and controls the tube voltage and tube current. A control signal is sent to the high voltage generator 7.
[0018]
The image processing device 9 performs image processing using measurement data obtained by digitizing a detection signal output from the X-ray detector 5 in the scanner 6 by a measurement circuit 14. A logarithmic converter 15 for performing logarithmic conversion on the measured data obtained, an air corrector 16 for performing air correction on output data from the logarithmic converter 15, and an edge enhancement for the output data from the air corrector 16. A two-dimensional filtering unit 17 for performing a two-dimensional filtering process.
[0019]
Further, the console 10 receives the image signal created and output by the image processing device 9 and displays the image as an image, and also inputs various operation commands and measurement conditions. The display device 19 is provided. In FIG. 1, reference numeral 18 denotes a scanner / table controller that sends control signals to the scanner 6 and the object table 3.
[0020]
Here, in the present invention, a predetermined amount of bias value is added to the input measurement data before the logarithmic converter 15 as means for performing logarithmic conversion on the measurement data input in the image processing device 9. A bias adder 20 is provided as a means for performing this. The bias adder 20 adds a predetermined amount of numerical data in advance so that the measured data input to the logarithmic converter 15 does not become “0” or a negative value. Then, before the measurement of the tomographic image of the diagnostic site of the subject, the amount of X-rays incident on the X-ray detector 5 is small when measuring the X-ray transmission image for determining the position for measuring the tomographic image. In order to suppress artifacts that occur in the case, the bias adder 20 performs a bias addition process.
[0021]
Next, a method for measuring a scanogram image in the X-ray CT apparatus of the present invention thus configured will be described with reference to the flowchart shown in FIG. The method of measuring a scanogram image according to the present invention is almost the same as that of the conventional apparatus shown in FIG. 4, except that a step E ′ is inserted between steps E and F. In the following description, the description of the same steps as the procedure shown in FIG. 4 will be omitted, and the procedure will be described for the differences due to the insertion of the step E '.
[0022]
First, the processing proceeds in steps A → B → C → D → E, and in step E, the measurement data xi, j shown in the above-described equation (1) is output from the measurement circuit 14 shown in FIG. You. The measurement data xi, j transferred to the image processing device 9 is input to the bias adder 20, and the process of bias addition is performed (step E '). The process of the bias addition is represented by the following equation (4).
Here, b indicates a predetermined amount of bias value (> 0).
qi, j indicates the output data (> 0) after the bias addition at the channel number i of the X-ray detector 5 and the sampling point j in the moving direction of the top 1.
[0023]
The predetermined amount of the bias value b in the above equation (4) is expressed, for example, as in equation (5).
Here, σi is the measurement data xi, j in the case where measurement is performed without X-ray irradiation from the X-ray tube 4 and the channel number i in the case where the standard deviation is calculated for each channel of the X-ray detector 5. The standard deviation at is shown.
[0024]
The output data qi, j after the bias addition by the bias adder 20 is input to the next logarithmic converter 15 and subjected to logarithmic conversion (step F). The logarithmic conversion process is represented by the following equation (6) using the above equations (4) and (1).
Here, ui, j indicates output data after logarithmic conversion.
[0025]
Next, the data ui, j output by logarithmic conversion by the logarithmic converter 15 are input to an air corrector 16 and subjected to air correction (step G). This air correction process is expressed by the following equation (7) using the above equation (6).
Here, ri and j indicate output data after air correction. Here, if Ii≫b, that is, if the attenuation of X-rays is not remarkable,
And the above equation (7) becomes
Which is almost equivalent to the above-mentioned equation (3).
[0026]
Thereafter, in the same manner as the procedure shown in FIG. 4, the process proceeds from step H → I → J, and in step J, the scanogram image is transferred from the image processing device 9 to the console 10 and sent to the display device 19 to display the scanogram image on the screen. I do. At this time, the logarithmic conversion in step F is performed by performing logarithmic conversion processing on the positive data to which the bias value has been added at a uniform rate by the bias addition in step E ′. Can be suppressed. From this, the operator can observe the anatomy with a scanogram image of good image quality, and can correctly position the diagnostic site.
[0027]
As another embodiment of the present invention, the bias adder 20 in the image processing apparatus 9 shown in FIG. 1 is used to adjust the amount of the bias value in accordance with the magnitude of the measurement data input from the measurement circuit 14 in the scanner 6. And the bias value may be added to the input measurement data. That is, the input unit in the bias adder 20 may be provided with a judgment selecting means such as a table for checking the value of the input measurement data and selecting an appropriate bias value according to the magnitude of the value. At this time, the range of the bias value b to be changed is a range as shown in the above equation (5). In this case, since the bias value is determined according to the value of the input measurement data, the image processing can be executed in a state that is not far from the original information.
[0028]
Further, as still another embodiment of the present invention, the bias adder 20 in the image processing apparatus 9 shown in FIG. 1 calculates a minimum value within a predetermined period of measurement data input from the measurement circuit 14 in the scanner 6. The bias value may be optimized based on the minimum value and added to the input measurement data. That is, the input unit in the bias adder 20 may be provided with an arithmetic unit or the like for obtaining the minimum value of the input measurement data within the period from the start of the measurement to the present and optimizing the bias value based on the minimum value. Also in this case, since the bias value is optimized according to the minimum value of the input measurement data, the image processing can be executed in a state that is not far from the original information.
[0029]
【The invention's effect】
Since the present invention is configured as described above, according to the first aspect of the present invention, the input measurement data is provided before the logarithmic conversion means for performing logarithmic conversion on the input measurement data in the image processing apparatus. Is provided with a bias adding means for adding a predetermined amount of bias value b in a range represented by Expression 1, and the bias adding means performs a bias adding process, thereby obtaining a bias value before measurement of a tomographic image of a diagnostic site of a subject. Thus, when measuring an X-ray transmission image for determining a position for measuring the tomographic image, it is possible to suppress an artifact that occurs when the amount of X-ray incident on the X-ray detector is small. At this time, since the logarithmic conversion process is performed on the positive data to which the bias value b has been added , the occurrence of mottled artifacts occurring in the X-ray transmission image (scanogram image) for determining the position for measuring the tomographic image is generated. Can be suppressed. From this, the operator can observe the anatomy with a scanogram image of good image quality, and can correctly position the diagnostic site.
According to the second aspect of the present invention, the bias adding means changes the amount of the bias value according to the value of the input measurement data, and adds the bias value to the measurement data. As a result, the bias value is determined according to the value of the input measurement data, so that the image processing can be executed in a state that is not far from the original information.
Further, according to the third aspect of the present invention, the bias adding means obtains a minimum value of the input measurement data within a predetermined period, optimizes the bias value based on the minimum value, and adds the bias value to the measurement data. By doing so, the bias value is optimized according to the minimum value of the input measurement data, so that the image processing can be executed in a state that is not far from the original information.
[Brief description of the drawings]
FIG. 1 is a block diagram of an overall configuration showing an embodiment of an X-ray CT apparatus according to the present invention.
FIG. 2 is a flowchart showing a procedure of a scanogram image measuring method in the X-ray CT apparatus of the present invention.
FIG. 3 is a block diagram of an overall configuration showing a conventional X-ray CT apparatus.
FIG. 4 is a flowchart showing a procedure of a scanogram image measuring method in a conventional X-ray CT apparatus.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 top 2 subject 3 subject table 4 X-ray tube 5 X-ray detector 6 scanner 7 high-voltage generator 8 X-ray controller 9 image processor 10 console 14 ... Measurement circuit 15 ... Logarithmic converter 19 ... Display device 20 ... Bias adder

Claims (3)

And the object table is moved to the measurement position by Neno the subject on the top plate, rotated around the around the said measuring position location and the X-ray tube and the X-ray detector disposed facing the measuring position image using a scanner that detected by radiating X-rays from the X-ray tube to the subject the transmitted X-rays by the X-ray detector, the measurement data obtained by digitizing a detection signal from the upper Symbol X-ray detector In an X-ray CT apparatus having an image processing device for performing processing and a display device for displaying an image signal from the image processing device as an image,
In the preceding stage of the logarithmic conversion means for performing logarithmic conversion on the measurement data input in the image processing apparatus, a bias addition means for adding a predetermined amount of bias value b to the input measurement data is provided ,
The bias value b is measured data x when measurement is performed without X-ray irradiation from the X-ray tube, where i is the channel number of the X-ray detector and j is the sampling point in the moving direction of the tabletop. i, a j, the standard deviation of the channel number i in the case where the standard deviation calculated for each channel of the X-ray detector and sigma i, the maximum values for the channel number i of the standard deviation sigma i max (sigma when you and i),
It shall be in the range represented by
Before the measurement of the tomographic image of the diagnostic site of the subject, when measuring the X-ray transmission image for determining the position for measuring the tomographic image and when the incident X-ray dose to the X-ray detector is small. An X-ray CT apparatus , wherein a bias addition process is performed by the bias addition means in order to suppress an artifact that occurs . 2. The X-ray CT according to claim 1, wherein said bias adding means changes the amount of the bias value in accordance with the value of the input measurement data, and adds the bias value to the measurement data. apparatus. 2. The apparatus according to claim 1, wherein said bias adding means obtains a minimum value within a predetermined period of the input measurement data, optimizes a bias value based on the minimum value, and adds the bias value to the measurement data. X-ray CT apparatus.