JP4342004B2 - X-ray CT system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray CT apparatus including a measurement detection unit and a reference detection unit, and particularly has a means for determining whether or not a part of a subject protrudes from an effective visual field, depending on the state of protrusion. The present invention relates to an X-ray CT apparatus capable of appropriately performing reference correction.
[0002]
[Prior art]
FIG. 4 shows an outline of a detection unit of a conventional X-ray CT apparatus to which the present invention is applied as an example of a rotation / rotation type X-ray CT apparatus.
[0003]
In FIG. 4, the X-ray tube 101 and the X-ray detector 100 are arranged to face each other, and the subject 121 can be arranged between them. The X-ray detector 100 is provided with a multi-channel measurement detection unit 102 and reference detection units 103L and 103R including channels on both sides of the X-ray detector 100. The X-ray detector 100 straddles the reference detection unit and the measurement detection unit. The protrusion determination units 104L and 104R each having 8 channels are set. This protrusion determination unit detects whether or not the subject 121 protrudes from the effective visual field 120 formed by the X-ray tube and the X-ray detector.
[0004]
FIG. 2 shows an outline of processing contents and a reference corrector in an image processing apparatus in a conventional X-ray CT apparatus. As shown in (1) of FIG. 2, output data from the X-ray detector is read and sent to the image processing apparatus (data read). The output data of this detector does not become zero even when X-rays are not emitted and has a certain value. Therefore, offset correction for correcting the read data is performed based on the data obtained by the offset measurement.
[0005]
The offset corrected data is log-transformed. Reference correction is performed on the log-converted data. The intensity of X-rays emitted from the X-ray tube is not always constant and varies with each irradiation. Therefore, the intensity of the X-rays irradiated to the subject is measured by the reference detection unit, and the error of the measurement data due to the fluctuation of the X-ray intensity is corrected using this value. This correction is a reference correction.
[0006]
The reference corrected data is subjected to air calibration correction. The sensitivity of the detector to the intensity of X-rays irradiated differs for each channel, and therefore the output voltage of the preamplifier section varies even under the same conditions. The air calibration correction corrects the difference in sensitivity of the detectors that differ for each channel based on the value of each channel of the air measurement.
[0007]
Image reconstruction is performed based on the data after the above processing, and the obtained image data is sent to a storage device and a display device.
[0008]
FIG. 2 (2) shows a block diagram of the reference correction processing. In the figure, reference numeral 1 denotes an input data memory, which stores log-converted data of output data of the measurement detector. The data 20L from the left reference detection unit and the data 20R from the right reference detection unit are extracted from the input data memory and input to the reference average value calculator 7 to obtain the average value 20 on both sides. Further, log-converted data 110 of the output data of the measurement detection unit is taken out from the memory 1, and reference correction is performed by the above-described 20, 110 in the reference subtractor 91, and the corrected data 111 is stored in the output data memory 10. Stored.
[0009]
FIG. 3 shows a block diagram of a reference corrector with a protrusion judgment according to the prior art.
[0010]
The left-side protrusion determination unit data 1a (for 8 channels) is extracted from the log-converted data fetched into the input data memory 1, corrected by the air calibration data Ic by the air calibration subtractor, and selected for the maximum and minimum values. Input to the device 2. Here, a maximum value and a minimum value are selected from the corrected data for eight channels, and a difference value between them is obtained by a differentiator. This difference value is compared with the threshold value 3a by the protrusion determination flag generator 3, and if it is within the threshold value, a flag signal of 0 is output as no protrusion, and if it exceeds the threshold value, a flag signal of 1 is output as an protrusion. This is input to the protrusion determination flag synthesizer 6.
[0011]
Next, the right-side protrusion determination part data 1b (for 8 channels) is taken out from the input data memory 1, and is determined by comparing with the threshold value by the protrusion determination flag generator in the same manner as described above. If it exceeds 0 and the threshold value, a signal 2 is generated and input to the OR circuit of the overhang determination flag synthesizer 6.
[0012]
This synthesizer 6 outputs a signal 0 when there is no protrusion on the left and right, 1 when there is protrusion on the left side, 1 when there is protrusion only on the right side, and 3 when there is protrusion on both sides. To do.
[0013]
On the other hand, the data 20L and 20R (for each channel) from the left and right reference detection units are taken out from the input data memory 1 and input to the reference average value calculator 7, where both side average values, left side average values, and right side averages are input. The value is calculated and input to the reference correction amount selector 9.
[0014]
In the reference correction amount selector 9, when the output value of the above-described protrusion determination flag synthesizer 6 is 0, the average value on both sides is obtained, when the output value is 1, the average value on the right side is obtained, and when the output value is 2, the left side average value is obtained. When the output value is 3, since there is a protrusion on both the left and right sides, the reference correction is not performed.
[0015]
Based on the selected reference correction amount, 110 is corrected from the log-converted data extracted from the input data memory by the reference subtractor 91 and stored in the output data memory 10.
[0016]
[Problems to be solved by the invention]
In the prior art shown in FIG. 2, regardless of whether or not the subject protrudes from the effective field of view, the average value on both sides is obtained from the data from the left and right reference detectors, and the reference correction is performed by this. Therefore, there is a problem that accurate reference correction cannot be performed when the subject protrudes.
[0017]
Further, in the prior art shown in FIG. 3, the right and left protrusions of the subject are determined, and reference correction is correctly performed accordingly. However, there is a problem that the reference correction cannot be performed when both right and left protrusions occur. The determination of the presence or absence of protrusion is made based on whether the difference between the maximum value and the minimum value of the detection values in the right and left determination units is within the threshold value or exceeds the threshold value. This determination method has a problem that when the amount of protrusion increases, the difference between the channels of the determination unit decreases, and correct determination cannot be made. An object of the present invention is to accurately determine the protruding state of the subject from the effective visual field, perform correct reference correction according to the protruding state, and obtain an accurate image.
[0018]
[Means for Solving the Problems]
The invention of the present application for achieving the above object is as follows.
(1) An X-ray tube and an X-ray detector that are arranged on both sides of the subject and rotate integrally around the subject, a measurement detector that constitutes the X-ray detector, and both left and right sides thereof A reference detection unit provided on the right side, a protrusion determination unit provided on the left and right sides across the reference detection unit and the measurement detection unit, an input data memory for storing log-converted data of detection data of the X-ray detection unit, and a protrusion Means for determining the state of protrusion of the subject from the effective visual field based on the data from the determination unit, and reference correction amount selection means for correcting the data in the input data memory with the reference correction value selected based on the determination result In the X-ray CT apparatus comprising: a means for determining the state of protrusion of the subject from the effective visual field, the difference between the maximum value and the minimum value of the left and right protrusion determination unit data The difference between the first determination means for determining whether or not the threshold value is within the threshold value, and the average value of the right and left protrusion determination unit data and the average value of the average value when there is no protrusion is within the threshold value. The determination result of the second determination means, the third determination means for determining whether or not the difference between the left and right average values of the protrusion determination unit is within the threshold value, and the determination results of the three determination means An X-ray CT apparatus comprising: a protrusion determination combining unit that comprehensively determines a protrusion state of a subject based on the determination result.
[0019]
(2) An X-ray tube and an X-ray detector that are arranged on both sides of the subject and rotate integrally with the subject, a measurement detector that constitutes the X-ray detector, and both left and right sides thereof A reference detection unit provided on the right side, a protrusion determination unit provided on the left and right sides across the reference detection unit and the measurement detection unit, an input data memory for storing log-converted data of detection data of the X-ray detection unit, and a protrusion Means for determining the state of protrusion of the subject from the effective visual field based on the data from the determination unit, and reference correction amount selection means for correcting the data in the input data memory with the reference correction value selected based on the determination result In the X-ray CT apparatus provided with the reference, the reference for calculating the respective reference average values of the left side, the right side, and both sides based on the detection data of the reference detection unit An average value calculator, means for calculating a temporary reference correction amount by accumulating the values selected by the reference correction amount selection means and correcting the data in the input data memory, and a reference based on the determination result of the protrusion determination means X-ray CT comprising reference correction amount selection means for selecting one of each average value calculated by an average value calculator and a temporary reference correction amount and correcting data in the input data memory apparatus.
[0020]
(3) An X-ray tube and an X-ray detection unit that are arranged on both sides of the subject and rotate integrally with the subject, a measurement detection unit that constitutes the X-ray detection unit, and both left and right sides thereof A reference detection unit provided on the right side, a protrusion determination unit provided on the left and right sides across the reference detection unit and the measurement detection unit, an input data memory for storing log-converted data of detection data of the X-ray detection unit, and a protrusion Means for determining the state of protrusion of the subject from the effective visual field based on the data from the determination unit, and reference correction amount selection means for correcting the data in the input data memory with the reference correction value selected based on the determination result In the X-ray CT apparatus provided with the first determination means for determining whether or not the difference between the maximum value and the minimum value of the left and right protrusion determination unit data is within a threshold value; Means for calculating the average value of each protrusion determination unit data, means for calculating a cumulative average value of the average value when no protrusion occurs, and whether the difference between the average value and the cumulative average value is within a threshold value Based on the determination results of the second determination means for determining whether or not, the third determination means for determining whether or not the difference between the left and right average values of the protrusion determination portion is within the threshold value, and the above three determination means A protrusion determination / synthesis unit that comprehensively determines the protrusion state of the subject, a reference average value calculator that calculates the reference average values of the left side, right side, and both sides based on the detection data of the reference detection unit, and the reference correction amount selection Means for calculating a temporary reference correction amount by cumulatively averaging values obtained by correcting the data in the input data memory selected by the means, and a reference based on the determination result of the protrusion determination combining means X-ray CT comprising reference correction amount selection means for selecting one of each average value calculated by an average value calculator and a temporary reference correction amount and correcting data in the input data memory apparatus.
[0021]
(4) In the above (3), the same means as the means for detecting whether the tube voltage and tube current of the X-ray tube at the start of the next scan are the same as in the previous scan after the end of a series of processes in each scan An X-ray CT apparatus comprising means for holding the cumulative average value and the temporary reference correction amount of the protrusion determination unit as they are, and updating them to 0 when they are not the same.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
The contents of the present invention will be specifically described with reference to the embodiment shown in FIG. The left-side protrusion determination unit data 1a (for eight channels) is extracted from the log-converted data fetched into the input data memory 1, and is corrected by the air calibration subtractor 1 ′ using the air calibration data Ic. The corrected data is input to the maximum value / minimum value selector 2, where the maximum value and minimum value in the input data are selected, and the difference value between them is obtained by the differencer 2 ′. This difference value is compared with the threshold value 3a by the protrusion determination flag generator 3, and if it is within the threshold value, the signal 0 is output as no protrusion, and if it exceeds the threshold value, the flag signal 1 is output as protrusion. The signal A is input to the OR circuit F of the protrusion determination flag synthesizer.
[0023]
Next, the right-side protrusion determination unit data 1b (for eight channels) is taken out from the input data memory 1, and is determined by comparing with the threshold value by the protrusion determination flag generator in the same manner as described above. A signal 0 is output as no protrusion, and a signal 2 is output as a protrusion if the threshold is exceeded, and this is input to one of the OR circuits G of the protrusion determination flag synthesizer 6 as a signal C.
[0024]
Next, the left protrusion determination unit data Ia-Ic corrected by the air calibration data Ic is input to the protrusion determination unit average value calculator 4 to obtain the average value a. The average value a and the protrusion determination unit cumulative average value 5a in the protrusion determination unit cumulative average value calculator 5 are input to the differentiator 4 ′ to determine the difference Δa.
[0025]
The difference Δa is compared with the threshold value 3b by the protrusion determination flag generator 30, and if the difference is within the threshold value, the signal 0 is output as no protrusion, and if it is outside the threshold value, the signal 1 is output as the protrusion. These signals are input to the other side of the OR circuit F as B.
[0026]
The right-side protrusion determination unit data 1b is processed in the same manner to obtain the difference (Δb) between the average value (b) and the cumulative average value (5b). If the value is out of the threshold value, the signal 2 is output as a protrusion, and these signals are input as D to the other of the OR circuit G.
[0027]
Next, the difference between the left and right average values a and b of the above-described protrusion determination unit is calculated by the difference unit 4 ″, and the difference is compared with the threshold value 3c by the protrusion determination flag generator 300 (E). If the value is within the value, signal 0 is set as no protrusion, signal 1 is set when the difference is outside the threshold value and the left side is large, and signal 2 is set when the value is outside the threshold value and the right side is large. Is output and is input to one of the OR circuits I of the protrusion determination flag synthesizer 6.
[0028]
The contents of the synthesis (logical sum) in the protrusion determination flag synthesizer 6 are shown in Table 1 and will be briefly described below. On the left side, in the circuit F that processes the signals A and B from the headline determination unit, if both the signals A and B are 0 (within the threshold value), the signal 0 is output, and either A or B is 1 ( If it is outside the threshold value, a signal 1 is output and input to one of the OR circuits H.
[0029]
In the circuit G that processes the signals C and D from the right-side protrusion determination unit, if both the signals C and D are 0 (within the threshold value), the signal 0 is output, and either C or D is 2 (threshold). If the value is out of value, the signal 2 is output and input to the other side of the OR circuit H.
[0030]
In the circuit H, the processing signals 0 and 1 for the left side protrusion determination unit from the circuit F and the processing signals 0 and 2 for the right side protrusion determination unit from the circuit G are processed. When the signal protrudes, the signal 1 is output only when the signal protrudes from the right side, and when the signal protrudes from the left and right, the signal 3 is output.
[0031]
In the circuit I, the signal from the circuit H and the signal from the protrusion determination flag generator 300 (E) are received and processed as shown in Table 1, and 0 is output as the output signal from the protrusion determination flag synthesizer 6 (the right and left are not protruding). ), 1 (with protrusion on the left side), 2 (with protrusion on the right side), or 3 (with protrusion on both the left and right sides) is output and sent to the reference correction amount selector 9.
[0032]
On the other hand, the data 20L and 20R (each channel) from the left and right reference detection units are taken out from the input data memory 1 and input to the reference average value calculator 7, where both side average values, left side average values, and right side average values are input. Is calculated and input to the reference correction amount selector 9.
[0033]
The reference correction amount selector 9 selects the average value on both sides when the output signal of the protrusion determination flag synthesizer 6 is 0, selects the right average value when the output signal is 1, and outputs 2 When the output signal is 3, the temporary reference correction amount 8a is selected from the temporary reference correction amount calculator, and the selected correction amount is used to load the input data memory 1 when the output signal is 3. The log converted data 110 is corrected by the reference amount subtracter 91. The reference-corrected data is stored in the output data memory 10.
[0034]
In the temporary reference correction amount calculator 8 shown in FIG. 1, in the first view of the measurement scan, the value stored in the previous result storage unit is 0, and in the second view, the cumulative average is the reference correction amount in the first view. The value selected by the selector 9 is directly taken as a cumulative average, and this is sent to the selector 9 as a previous result. From the next view onward, the selection result (value) in the selector 9 is returned to the cumulative average value calculation unit, half of the value is added, and the previous (calculation) result in the calculator is returned. A cumulative average value is calculated by adding one-half of the value. Further, the previous result is initialized to 0 by a reset signal after the end of each measurement scan.
[0035]
Further, in the protrusion determination unit cumulative average value calculator 5 shown in FIG. 1, the previous result is 0 in the first view of the measurement scan. In the second view, the value selected in response to the output signal (0) of the protrusion determination flag synthesizer 6 becomes the cumulative average value as it is, and this is sent to the differentiator 4 ′ as the previous result at the next view. In subsequent views, when the signal from the protrusion determination flag synthesizer 6 does not protrude, the signal 0 is received and the accumulated average value 5a is updated. That is, the average value a of the protrusion determination unit at the time of the current measurement is selected, and the previous calculation result 5a is returned, and the cumulative average value is updated by adding ½ each. This update is performed for each of the left and right blocks for data processing of the left and right protrusion determination unit. When the signal from the overhang determination flag synthesizer 6 is overhanging, the selection selects 5a of the previous result, adds 1/2 of the selected 5a and 1/2 of the previous result 5a, and the cumulative average value is If the reset signal is given after the measurement scan is completed, the previous result is initialized to 0. For each view, the average value of the protrusion detection unit and the previous result are selected.
[0036]
As described above, when the previous result in the cumulative average value calculator 5 and the correction amount calculator 8 is initialized to 0 after the end of scanning, the previous result becomes 0 in the first view of the next scan. The protrusion determination based on the difference between the average value of the determination unit and the cumulative average value cannot be performed. Further, even if the judgment by the overhang determination flag synthesizer 6 has overhang on both sides, there is a problem that the reference correction cannot be performed because the temporary reference correction reference is 0.
[0037]
Therefore, in the present invention, this problem is solved by taking the following processing means. That is, after a series of processing is completed, at the start of the next scan (scan), it is determined whether or not the tube voltage / tube current of the X-ray tube is the same as the previous condition. The value 5a and the temporary reference correction amount 8a are not reset (cleared to 0) (in cases other than the above, they are reset as usual).
[0038]
As a result, the first view measurement of the next scan becomes the same as the next view of the last view of the previous scan, and even if the subject protrudes during the first view, the protrusion determination using 5a is performed in the same way as the protrusion during the scan. The processing by the flag generator 30 and the processing by the reference correction amount selector 9 using the temporary reference correction amount can be performed, and even when the second and subsequent scans protrude from both sides over the entire circumference, the reference according to the protrusion determination process and the determination result Correction is possible.
[0039]
Further, by scanning in advance with the same tube voltage and current sensitivity as the imaging conditions of the subject before putting the subject into the X-ray CT apparatus, the left and right protrusion determination unit cumulative average values 5a and provisional reference correction amount Since 8a can be set as a default, it is possible to perform a protrusion determination process and a reference correction process even during the first view of the first scan.
[0040]
【The invention's effect】
In the present invention, with respect to the detection value of the protrusion determination unit composed of a plurality of channels provided on the left and right sides of the measurement detection unit, the difference between the left and right maximum values and the minimum value, the difference between the average value of the detection values and the cumulative average value, and the left and right For the three differences between the average values of each judgment section, it is checked whether the threshold value is exceeded, and the presence or absence of protrusion is comprehensively judged, so the judgment system is significantly improved compared to the conventional technology. Can be made.
[0041]
In addition, the reference correction values selected for each measurement view are cumulatively averaged and prepared as a temporary reference correction amount so that appropriate reference correction can be performed even when both sides protrude.
[0042]
In addition, even when resetting the temporary reference correction amount and the overhang determination unit cumulative average value for each measurement scan, if the tube voltage and tube current of the X-ray tube do not change from the previous scan, hold them as they are and scan the next scan. Since the protrusion determination and reference correction at the top view can be performed without any trouble, a more accurate X-ray image can be obtained.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an embodiment of the present invention.
FIG. 2 is a prior art explanatory diagram of reference correction in an X-ray CT apparatus.
FIG. 3 is an explanatory diagram of a conventional example of reference correction with protrusion determination.
FIG. 4 is a schematic view of an installation state of an X-ray detector in an X-ray CT apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Input data memory 1a Left side protrusion determination part data 1b Right side protrusion determination part data 2 Maximum value minimum value selector 3, 30, 300 Overflow determination flag preparation device 4 Overflow determination part average value calculator 5 Overflow determination part accumulation average calculator 5a Overflow determination unit cumulative average value 6 Overflow determination flag synthesizer 7 Reference average value calculator 8 Temporary reference correction amount calculator 8a Temporary reference correction amount 9 Reference correction amount selector 10 Output data memory 20L Left reference detection unit data 20R Right reference detection Part data 100 X-ray detector 101 X-ray tube 102 Measurement detector 103L Left reference detector 103R Right reference detector 104L Left protrusion determination part 104R Right protrusion determination part 110 Log converted input data 120 Effective field of view 121 Covered Body [Table 1]

Claims (3)

An X-ray tube and an X-ray detector that are arranged on both sides of the subject and rotate integrally around the subject, a measurement detector that constitutes the X-ray detector, and both sides thereof Reference detection units, protrusion determination units provided in each of the reference detection units, and threshold values that are set in advance based on data from these protrusion determination units And a reference correction amount selection unit that selects a reference correction value based on the protruding state determined by the determination unit, and corrects the data of the effective visual field by the selected reference correction value. In the X-ray CT apparatus provided,
The determination means is a first determination means for determining whether or not a difference between the maximum value and the minimum value of each data of the protrusion determination unit is within the threshold value;
Second determination means for determining whether or not a difference between an average value of each data of the protrusion determination unit and a cumulative average value of the average value when there is no protrusion is within the threshold value;
Third determination means for determining whether or not the difference between the average values of the protrusion determination portions is within the threshold value, and the protrusion state of the subject based on the determination results of the three determination means To determine
The cumulative average value is 0 as an initial value,
When the determination means determines that there is no protrusion, 1/2 of the average value of each data of the protrusion determination unit is added to the previous result,
When said determination means determines that there is protruding is, X-rays CT apparatus characterized by remains of the previous results. An X-ray tube and an X-ray detector that are arranged on both sides of the subject and rotate integrally around the subject, a measurement detector that constitutes the X-ray detector, and both sides thereof Reference detection units, protrusion determination units provided in each of the reference detection units, and threshold values that are set in advance based on data from these protrusion determination units And a reference correction amount selection unit that selects a reference correction value based on the protruding state determined by the determination unit, and corrects the data of the effective visual field by the selected reference correction value. Prepared,
The determination means is a first determination means for determining whether or not a difference between the maximum value and the minimum value of each data of the protrusion determination unit is within the threshold value;
Second determination means for determining whether or not a difference between an average value of each data of the protrusion determination unit and a cumulative average value of the average value when there is no protrusion is within the threshold value;
Third determination means for determining whether or not the difference between the average values of the protrusion determination units is within the threshold value,
In the X-ray CT apparatus for determining the protruding state of the subject based on the determination results of the three determination means,
Provisional reference correction amount calculation means for calculating a temporary reference correction amount based on the output of the reference correction amount selection means,
An X-ray CT apparatus, wherein the reference correction amount selection means selects the temporary reference correction amount as a reference correction value when the determination means determines that both left and right are protruding. The X-ray CT apparatus according to claim 2,
X-ray irradiation condition determination means for determining whether or not the X-ray irradiation condition of the scan is the same as the previous scan,
An X-ray CT apparatus characterized in that, when the X-ray condition determining means determines that the same X-ray conditions are used, the temporary reference correction amount is set to a value at the previous scan.

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