JP2015134106A - X-ray computer tomographic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray computer tomographic apparatus improved in accuracy in dose value calculation.SOLUTION: The X-ray computer tomographic apparatus which reconstitutes an X-ray CT image on the basis of projection data collected by scanning a subject by an X-ray tube 101 and an X-ray detector 103, includes: a table memory part 120 storing a calibration table where a plurality of calibration values for calibrating a dose value determined by a plurality of photographing conditions to be set in scanning are associated with a plurality of values relating to at least one photographing condition of the plurality of photographing conditions; a dose value calculation part 122 calculating a dose value on the basis of the photographing condition set in the scanning, and calibrating the dose value by a calibration value specified from the calibration table; a display part 116 displaying the calibrated dose value; and an update processing part 121 repeatedly updating the calibration table on the basis of actually measured data.

Description

  Embodiments described herein relate generally to an X-ray computed tomography apparatus.

  Examination of an X-ray computed tomography apparatus (X-ray CT apparatus) is widely used for image diagnosis. For example, in order to obtain a CT image, the detector receives X-rays that have passed through the subject, and the data obtained by A / D conversion is stored in a memory or a hard disk built into the main body of the apparatus using an optical cable or the like. It is stored as data, and further, a CT image is reconstructed using a dedicated or general-purpose computer for image reconstruction, displayed on a monitor, and diagnosed.

  In recent X-ray CT apparatuses, the operator mainly uses the imaging conditions as information for confirming whether or not the imaging conditions are appropriate as the exposure (dose) to the subject before the CT examination. It has a function to display the dose value calculated as the inspection condition and the dose value after the inspection on the console, and a display function to warn and warn when the dose value preset in the inspection is exceeded.

  In addition, the necessity of dose management at the individual level has been said in recent years, and for the purpose of individual dose management, an X-ray CT apparatus having a function capable of outputting dose values for each examination to an external database as DICOM data has come out. ing.

  The dose in the X-ray CT apparatus described here is a general dose index called CTDI (CT DOSE INDEX), and is handled as a dose index value obtained by averaging the CT examination range. Therefore, normally this value is prepared in advance with a dose calibration table as the design value of the device and a basic value in advance, and imaging conditions (tube voltage, tube current, irradiation time, imaging slice width, A dose calibration table is created as a constant according to the X-ray tube focus size (Focus), patient body type (phantom size), filter type (Filter type, etc.), and the dose is calculated. Therefore, a constant table is created as a design value for each item affecting the dose in advance in the apparatus.

First, it is necessary to create a table as a reference dose. This is a table showing the reference dose values determined by determining the reference imaging conditions from the imaging conditions. is there. In this example, a reference dose value table is created based on tube voltage and FOV (imaging size). As for imaging conditions other than tube voltage and FOV (imaging size), a relative value table (table) in which ratios of numerical values assumed when changing one or two imaging conditions with the same reference condition is set. ) In advance, it is possible to calculate a dose value (index value) that matches the imaging conditions by ratio calculation.

Specifically, the case of the following imaging conditions is illustrated.
120kV / 300mA / 1s / FOV S / Slice 4mm / Number of rows 4 rows / Focus S / Phantom 160mm / Filter S
In this example, a single reference dose value table and two tables of relative values reflecting other conditions are created, so that combinations of imaging conditions can be easily tabulated, and complicated dose calculation processing can be avoided. . In this case, the tube current and the irradiation time are not determined as the imaging conditions at the time of calculation, but since these two elements are known to be proportional to the dose, the setting values of the imaging conditions for this condition Can be used to calculate dose. As a result, the dose value (index value) can be expressed by the following calculation formula.

Value from standard dose table (mGy / mAs) x tube current (mA) x irradiation time (s) X constant 1 X constant 2
And when actually calculating | requiring a dose value, the numerical value which was initially in tube voltage & FOV from the reference | standard dose value table, and 0.09 (mGy / mAs) are selected in this table | surface. Next, 1.00 corresponding to the number of slices and columns is selected from the relative value table 1 for the phantom type / focus size, and 1.00 corresponding to the phantom type / tube voltage is selected from the relative value table 2 for the filter type. Finally, the current tube current and irradiation time are determined to be 300 mA and 1 s, which are the numerical values of the imaging conditions.

Now that the values and constants for dose calculation have been determined, applying these to the above equation to obtain the dose value (index value) yields 27.0 mGy as shown below. Used for recording dose values.
Dose value (index value) = 0.09 (mGy / mAs) x 300 (mA) x 1.0 (s) x 1.00 x 1.00 = 27.0 mGy
In the current device, these dose values are determined by measuring the actual values with the device, so basically, in the case of the same device, unless the dose values are affected by changes in the device specifications during the process, etc. No matter where the equipment is installed, these dose values will not change. In other words, the dose value of the device is the design value of the device, which presents a general and average value.

  For this reason, differences between individual CT devices, such as differences in design specifications that affect the dose even between CT devices, such as differences in X-ray tube focus size and collimator width, and differences in output adjustment of X-ray high-voltage devices, As a dose index, it naturally appears as an error. Therefore, the error of the general dose value in the CT apparatus is set to about 20% of the displayed value, and the X-ray output change (decrease) due to aging etc. (the target of the tube deteriorates and the dose decreases) Considering the fact that the dose value changes due to aging of the equipment, etc., it is assumed that it contains a larger error.

Furthermore, in the X-ray CT apparatus, since there is no other appropriate index used as information for personal dose management, an error dependent on this apparatus is not considered and is treated as a dose value (index value). .

Furthermore, there is an X-ray tube device as one of the factors that are important for the dose, and it is generally found that when used up to the guaranteed slice limit due to aging, the X-ray output is reduced by about 5-7% compared to the new product. It is a consumable item.

  In addition, at present, apparatuses having AEC (automatic X-ray irradiation control) have become common, and in these apparatuses, when the X-ray tube apparatus has been used up to the guaranteed slice limit, the dose value (index value) ) Does not change because it is as designed, but in order to compensate for the drop in the value of the image SD even if the dose is reduced due to relative changes over time, the imaging conditions are re-established in the direction of increasing the dose. May be set. Of course, this state shows a bad condition of increased dose from the viewpoint of the protection of the subject. There is an advantageous working aspect. However, on the other hand, if the estimated dose is lower than the actual dose, the image quality is deteriorated as a CT examination, which may affect the effectiveness of the examination due to insufficient dose.

  Therefore, it is necessary to provide the CT apparatus with a value with as little error as possible regarding the dose to the subject in the CT examination.

JP 2012-148028 JP 2009-42247

  The purpose is to improve the accuracy of dose value calculation in an X-ray computed tomography apparatus.

  The present embodiment is an X-ray computed tomography apparatus that reconstructs an X-ray CT image based on projection data acquired by scanning an object with an X-ray tube and an X-ray detector. A table storage unit for storing a calibration table in which a plurality of calibration values for calibrating dose values determined by a plurality of imaging conditions to be performed are associated with a plurality of values related to at least one imaging condition of the plurality of imaging conditions; A dose value is calculated based on the imaging conditions set in the scan, the dose value calculation unit that calibrates the dose value based on the calibration value specified from the calibration table, and a display unit that displays the calibrated dose value And an update processing section for repeatedly updating the calibration table based on the actual measurement data.

It is a figure which shows the structure of the X-ray computed tomography apparatus which concerns on this embodiment. FIG. 2 is a view showing an appearance of a gantry part in FIG. It is a figure which shows an example of the reference dose value table memorize | stored in the reference dose value table memory | storage part of FIG. It is a figure which shows an example of the conversion value table memorize | stored in the reference | standard dose value table memory | storage part of FIG. It is a figure which shows an example of the conversion value table memorize | stored in the reference | standard dose value table memory | storage part of FIG. It is a figure which shows an example of the calibration value table memorize | stored in the calibration value table memory | storage part of FIG. It is a figure which shows an example of the reference dose value table in the state which pinches only air, without pinching the phantom etc. which are memorize | stored in the reference dose value table memory | storage part of FIG. It is a figure which shows an example of the calibration value table memorize | stored in the calibration value table memory | storage part of FIG. It is a figure which shows an example of the calibration value table memorize | stored in the calibration value table memory | storage part of FIG. In this embodiment, it is a figure which shows the flow of the process of imaging | photography work. It is a figure which shows an example of the display screen regarding the dose value displayed by process S13 of FIG. It is a figure which shows an example of the caution warning screen displayed by process S17 of FIG.

  The X-ray computed tomography apparatus according to this embodiment will be described below with reference to the drawings. The X-ray computed tomography apparatus includes a rotation / rotation method in which an X-ray tube and an X-ray detector are rotated as one body, and a large number of X-ray detectors in a ring shape. A fixed / rotating method in which only the X-ray tube rotates around the subject, a plurality of X-ray tubes are arranged on the ring, and a plurality of X-ray detectors are similarly arranged on the ring. There are various methods such as a fixed method, and any method is applicable. Regarding the rotation / rotation method, a single tube type in which a pair of X-ray tubes and X-ray detectors are mounted on a rotating frame, and a plurality of pairs of X-ray tubes and X-ray detectors are mounted on the rotating frame. Although there are so-called multi-tube types, any type is applicable. Regarding the X-ray detector, an indirect conversion type in which X-rays transmitted through a subject are converted into light by a phosphor such as a scintillator and then converted into electric charge by a photoelectric conversion element such as a photodiode, and electrons in a semiconductor by X-rays There is a direct conversion type using the generation of a hole pair and its movement to the electrode, that is, a photoconductive phenomenon, and any type may be adopted.

  FIG. 1 is a block diagram showing the configuration of the X-ray computed tomography apparatus according to this embodiment. FIG. 2 shows the appearance of the gantry part of FIG. 1 together with the bed part. The scan main body 100 includes an annular rotating frame 102 that is rotatably supported around a rotation axis (Z axis) and is driven to rotate by a gantry driving unit 107. The subject placed on the bed 200 is arranged in the imaging region so that the body axis substantially coincides with the Z axis. For example, an X-ray tube 101 that generates, for example, a cone beam X-ray and a two-dimensional detector 103 are disposed on the rotating frame 102 so as to face each other. The cone-beam X-ray tube 101 generates X-rays upon receiving application of tube voltage, supply of filament current, and the like from the high voltage generator 109 via the slip ring 108. The generated X-rays are shaped into a quadrangular pyramid at the radiation port 113 and output.

  The two-dimensional detector 103 is connected to a data acquisition system 104 generally called a DAS (data acquisition system). The data acquisition system 104 includes an IV converter that converts a current signal of each channel of the two-dimensional detector 103 into a voltage, and an integration that periodically integrates the voltage signal in synchronization with an X-ray exposure period. And an analog / digital converter for converting the output signal of the preamplifier into a digital signal are provided for each channel. A pre-processing device 106 is connected to the output of the DAS 104 via an optical or electromagnetic non-contact data transmission device 105. The pre-processing device 106 corrects non-uniform sensitivity between channels with respect to projection data detected by the DAS 104, and causes an extreme decrease in signal intensity or signal dropout due to an X-ray strong absorber, mainly a metal part. Pre-processing such as correction is performed. The projection data that has been corrected by the pre-processing device 106 is stored in the storage device 112, and is also used by the volume reconstruction processing unit 118 to reconstruct volume data.

  The host controller 110 stably rotates the rotating frame 102 at a constant speed in order to perform a projection data collecting operation, that is, a scan, and generates a high voltage and the like from the high voltage generator 109. Controls related to scanning, such as causing the DAS 104 to perform a collection operation in synchronization with the occurrence, are supervised.

  The X-ray dose is determined by determining the optimum dose value (upper limit value) for each type of examination and for each subject and performing CT examination. Among these, the dose value (or its index value) is the most important material for determining whether or not it is appropriate to irradiate the subject with X-rays in the examination. The reference dose value table storage unit (ROM) 117 stores the reference dose value table shown in FIGS. The reference dose value table shown in FIG. 3 includes a plurality of typical tube voltages (for example, 80 kV, 100 kV, and 120 kV) and a plurality of typical FOVs (for example, imaging field sizes (for example, SS, S, M, Conversion value converted from the standard dose value per 1 mA for each of multiple combinations of size categories (2 categories: SS / S / M and / L / LL) for L and LL sizes) As unit mGy / mAs.

  In the example of FIG. 3, at a tube voltage of 80 kV, when the FOV is any of the sizes LL / L, the converted value is given 0.040, and when the FOV is any of the sizes SS / S / M, the converted value is 0.030 is given. When the tube voltage is 100 kV, when the FOV is any of the sizes LL / L, the converted value is given 0.070, and when the FOV is any of the sizes SS / S / M, the converted value is given 0.060. When the tube voltage is 120 kV, when the FOV is any of the sizes LL / L, the converted value is given as 0.110, and when the FOV is any of the sizes SS / S / M, the converted value is given as 0.090.

  In the example of FIG. 7, when the tube voltage is 80 kV, when the FOV is any of the sizes LL / L, the converted value is given as 0.058, and when the FOV is any of the sizes SS / S / M, the converted value is 0.053 is given. When the tube voltage is 100 kV, when the FOV is any of the sizes LL / L, the converted value is given as 0.110, and when the FOV is any of the sizes SS / S / M, the converted value is given as 0.101. When the tube voltage is 120 kV, when the FOV is any of the sizes LL / L, the converted value is given 0.177, and when the FOV is any of the sizes SS / S / M, the converted value is given 0.162.

As a dose value (index value), CTDI _{free air} as CTDI in a state where a phantom or the like is not arranged in an imaging region between the X-ray tube 101 and the X-ray detector 103 is used instead of the above CTDI _w. It may be used. As shown in FIG. 7, a similar reference dose value table (CTDI _{free air} ) as a design value is prepared. The reference dose value table in FIG. 3 requires a phantom, but this is easy because it does not require a phantom.

  The dose value calculation unit 122 multiplies the reference dose specified using the reference dose value table by the tube current, the irradiation time, etc., and further specifies the slice thickness, the number of columns, etc. from the conversion value table illustrated in FIGS. The actual dose value is calculated by converting according to the converted value. When actually determining the dose value, first, a numerical value corresponding to the tube voltage and FOV, for example, 0.09 (mGy / mAs) is selected from the reference dose value table.

Value from standard dose value table (mGy / mAs) x tube current (mA) x irradiation time (s)
The dose value calculation unit 122 uses the conversion value a corresponding to the slice / number of columns from the relative value table 1 for the phantom type / focus size illustrated in FIG. 4 and the relative value table 2 for the filter type illustrated in FIG. Select the conversion value b that matches the phantom type and tube voltage. A plurality of relative value tables 1 are prepared in advance. A plurality of relative value tables 1 illustrated in FIG. 4 are respectively associated with a plurality of combinations related to the phantom type and the focus size. Examples of the number of detector rows on the imaging conditions are 16, 8, 4, and 2. The slice thicknesses are 1 mm, 2 mm, 3 mm, and 4 mm. When the number of rows is 16, conversion values of 1.05 and 1.02 are given for slice thicknesses of 1 mm and 2 mm, respectively. When the number of rows is 8, conversion values of 1.20, 1.09, 1.00, and 1.00 are given for slice thicknesses of 1 mm, 2 mm, 3 mm, and 4 mm, respectively. When the number of columns is 4, conversion values of 1.80, 1.25, 1.00, and 1.00 are given for slice thicknesses of 1 mm, 2 mm, 3 mm, and 4 mm, respectively. When the number of columns is 2, conversion values of 2.75, 1.62, 1.00, and 1.00 are given for slice thicknesses of 1 mm, 2 mm, 3 mm, and 4 mm, respectively. Of course, the conversion value of 1.00 means that the conversion is not substantially performed.

  The dose value calculation unit 122 selects the relative value table 1 according to the phantom type and focus size unique to the apparatus, and the converted value a corresponding to the slice / column number set as the imaging condition from the selected relative value table 1. Is identified. The plurality of relative value tables 2 shown in FIG. 5 are associated with a plurality of filter types, respectively. The dose value calculation unit 122 selects the relative value table 2 according to the filter type, and specifies the conversion value b corresponding to the phantom type and tube voltage set as the imaging conditions from the selected relative value table 2. Examples of the phantom species are those having a diameter of 160 mm and those having a diameter of 320 mm. As for the phantom type having a diameter of 160 mm, the converted value is 1.00, that is, not converted regardless of the tube voltage 80 kV, 100 kV, 120 kV. As for the phantom type having a diameter of 320 mm, conversion values of 2.39, 2.29, and 2.22 are given for tube voltages of 80 kV, 100 kV, and 120 kV, respectively. The dose value is calculated as follows:

Dose value = reference dose value (mGy / mAs) x tube current (mA) x irradiation time (s) x converted value a x converted value b
Furthermore, the dose value calculation unit 122 calibrates the calculated dose value with the calibration value specified from the calibration value table stored in the calibration value table storage unit (nonvolatile memory) 120. By the calibration process, an actual dose value is calculated in consideration of a variation factor due to aging of the apparatus.

For example, when the standard shooting conditions are 120 kV / 100 mA / 1 s / FOV S or L / slice 4 mm / number of columns 4 columns / Focus S / Phantom 160 mm / Filter S, the same shooting conditions are measured and FOV S measurement value (CTDI _w) 9.20mGy, and to give a dose of the measured values (CTDI _w) 11.44mGy when the FOV L. At that time, compared with the reference dose value (index value), the actual measured value of the apparatus is higher by 2% for FOV S and 4% for FOV L. Therefore, as the calibration value table 3 (FIG. 6), a new relative value table 3 for correcting the values as 2% and 4% higher than the reference dose value is prepared, and when 1.02 or 1.04 obtained as a relative value is input, A calibration value table 3 of values (index values) is obtained. The calibration value table 3 associates a plurality of calibration values with a plurality of combinations relating to tube voltage and FOV as the same imaging conditions as the reference dose value table. In the example of FIG. 6, when the FOV is any of the sizes LL / L, the conversion value is given as 1.04 regardless of the tube voltage, and when the FOV is any of the sizes SS / S / M, Regardless, the conversion value is given as 1.02. The calibration value c is extracted from the calibration value table 3 according to the imaging conditions, and the dose value is calibrated. In addition, the measurement is not limited to two points for each FOV, but it is also possible to create a relative value by actually measuring each tube voltage. At that time, individually obtained calibration values are input to the calibration value table 3. Of course, when dose measurement is not performed, the calibration value table 3 is prepared as a default value of 1.00, and the constant 3 can be treated as a constant in dose calculation if it is modified and changed only during measurement. The calculation formula here is as follows.

Calibrated dose value = reference dose value (mGy / mAs) x tube current (mA) x irradiation time (s) x converted value a x converted value b x calibration value c
The calibration value table 4 shown in FIG. 8 is used together with the reference dose value table of FIG. 7, and defines calibration values corresponding to fluctuation values due to aging obtained from the output of the reference detector for each tube voltage. . In the example of FIG. 8, when the tube voltage is 80 kV, the fluctuation value / basic value is given by 1.05, when the tube voltage is 100 kV, the fluctuation value / basic value is given by 1.06, and when the tube voltage is 120 kV, the fluctuation value is obtained. The value / base value is given by 1.07.

  The calibration value update control unit 119 displays a message for prompting the update process of the calibration value table 3 on a semi-annual basis or X-ray tube replacement time on the display device 116. When an update program is activated on the user side in response to a message prompting update processing, update shooting is executed with two types of FOVs at each tube voltage while switching between a plurality of (here, three) tube voltages using a phantom. . The calibration value update unit 121 calculates the calibration value by comparing the measured dose value with the reference dose value, and updates the calibration value table shown in FIG. In addition, it is difficult to provide feedback after frequent dosimetry. It is desirable to reflect fluctuations in a shorter period of time in the dose calculation, and fluctuations can be confirmed by using what affects dose measurement in a short cycle.

  As is well known, the X-ray CT has a reference detector for ensuring the accuracy of the CT value. This is generally provided inside the collimator, and the data can be used when the X-ray from the X-ray tube 101 is directly detected. Moreover, automatic data calibration is performed regularly (daily, weekly, monthly), and the data is collected on a daily basis. Therefore, by creating a calibration value table similar to the value at the time of dose measurement from the fluctuation of the collected data in this reference detector, it can be used as a constant for dose calculation. Specifically, the estimated number of photons after reference correction can be obtained, and this is the number of photons collected at the time of X-ray tube replacement (basic value) and the number of photons from automatic air calibration ( (Variation value) is created as a conversion value table in which a conversion ratio similar to that in the dose measurement is calculated. The number of photons is calculated by the following formula.

Photon count = (N / S) After ref correction = K / √Np Np: Number of photons On the other hand, as a matter of course, as the reference detector is also used, the detectability will deteriorate, In this case, it is desirable to use the dose calculation in a form that complements the converted value a, the converted value b, and the calibration value c, instead of handling them alone.
Calibrated dose value = reference dose value (mGy / mAs) x tube current (mA) x irradiation time (s) x converted value a x converted value b x calibration value c x calibration value d
As constants for improving the accuracy of dose calculation, even if the calibration value c × calibration value d assuming the above-mentioned change with time is not set, the tube current value and irradiation which are previously set as design values as variables for each apparatus Since the time value has a value unique to the apparatus, it can be developed in the same manner. In this case, the ratio between the actually measured value and the set value (design value) is created as a calibration value d as a calibration value table (FIG. 9). In the example of FIG. 9, the measured value / set value is given as 1.01 regardless of the irradiation time of 0.5 seconds, 1.0 seconds, and 1.5 seconds.

This calculation formula is given as follows.
Calibrated dose value = reference dose value (mGy / mAs) x tube current (mA) x irradiation time (s) x converted value a x converted value b x calibration value c x calibration value d x calibration value e
FIG. 10 shows a flow in the X-ray CT examination under the control of the host controller 110. Subject information is supplied from the in-hospital information system (HIS) or radiation information system (RIS) to the X-ray CT host controller 110 together with the examination request information (S10), and the subject is displayed on the screen for the imaging plan according to the information. Information is set (S11). The examination engineer confirms the subject information and the examination request information, and selects an imaging plan including a plurality of imaging conditions (S12). When an imaging plan is selected, the dose calculation unit 122 calculates a dose value from the reference dose table in FIG. 3 or FIG. 7 and the converted value table in FIG. 4 and FIG. Calibration is performed using the calibration value table of FIG. The calibrated dose value is displayed in the imaging condition confirmation step (S13) by the operator as illustrated in FIG. The laboratory technician confirms the displayed dose value and permits the start of imaging (S14). The host controller 110 determines whether or not the calculated dose value exceeds a value (set dose value) preset by the operator (S15), and when the calculated dose value exceeds the set value, FIG. A display window showing a caution / warning illustrated in Fig. 6 is displayed (S17). The operator determines whether to continue processing (S16) or cancel (S19).

  In addition to the device-specific dose values (index values), elements that affect the dose at the device level have a function to input relevant data at the actual use stage. Calibration value tables 3, 4 and 5 (FIGS. 6, 8, and 9) are created and incorporated into the calculation function in the same manner as the current dose calculation. As a result, information for each device other than the design value can be incorporated as a table of dose values (index values), so that the accuracy of the dose values (index values) can be increased.

  The process from the shooting condition confirmation (S14) to the shooting (S16) is repeated while additional or continuous shooting processes remain (S18). After the end of imaging (S19), the imaging information outputs and records the dose values for each examination as DICOM data in the internal or external database for personal dose management (S20), and the examination ends (S21).

  Regarding the calibration value, the dose can be calculated by calculating the variation for each device by setting the necessary values corresponding to the dose-related items in the manufacturing, installation, and operation stages of the device. They can be input from the operator or manufacturer side, and on the other hand, it is also possible to automatically convert the calibration data into the calibration value data from the daily related collected data and apply the data. In other words, the dose value at the manufacturing, installation, and operation stages is used by using the calibration value for correcting the dispersion of each device, as well as calculating the dose by setting the converted value of the design value as before. It is possible to improve the accuracy by calibrating the value to be a constant and reflecting it in the dose value (index value).

  As described above, a dose value (index value) based on the design value of the device has a table that calibrates the amount of change of the device during manufacturing, installation, and operation. The (index value) can be provided to the operator, and the dose value (index value) for personal dose management can be provided to the subject with higher accuracy. As a result, a more appropriate dose value (index value) is provided as apparatus information, and therefore an X-ray CT apparatus capable of providing a safer CT examination is provided.

  Rather than keeping the dose value (index value) in the device as a design value only, the dose calculation for each device can be performed so that the dose value during manufacture, installation, and use can be continuously reflected by the device alone. By providing them as constants, it is possible to provide the operator with appropriate dose values (index values) that can be used not only as design values but also as device unit information, and to provide more accurate information for individual dose management of the subject. By doing so, an X-ray computed tomography apparatus capable of undergoing a safe CT examination can be provided.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 100 ... Scan main body, 200 ... Bed, 101 ... X-ray tube, 102 ... Rotating frame, 103 ... Two-dimensional detector, 104 ... Data acquisition system, 105 ... Non-contact data transmission device 106 ... Pre-processing device 108 ... Slip ring 109 ... High voltage generator 110 ... Host controller 112 ... Storage device 113 ... Radiation port 117 ... reference dose value table storage unit (ROM), 118 ... volume reconstruction processing unit, 119 ... calibration value update control unit, 120 ... calibration value table storage unit (non-volatile memory), 121... Calibration value update unit, 122... Dose value calculation unit.

Claims (6)

In an X-ray computed tomography apparatus for reconstructing an X-ray CT image based on projection data acquired by scanning an object with an X-ray tube and an X-ray detector,
A table storing a calibration table in which a plurality of calibration values for calibrating dose values determined by a plurality of imaging conditions to be set in the scan are respectively associated with a plurality of values related to at least one imaging condition of the plurality of imaging conditions A storage unit;
Calculating a dose value based on the imaging conditions set in the scan, and a dose value calculation unit that calibrates the dose value with the calibration value specified from the calibration table;
A display for displaying the calibrated dose value;
An X-ray computed tomography apparatus comprising: an update processing unit that repeatedly updates the calibration table based on actual measurement data.   The X-ray computed tomography apparatus according to claim 1, wherein the calibration table associates a plurality of calibration values with a plurality of combinations of tube voltage and FOV.   The X-ray computed tomography apparatus according to claim 1, wherein the calibration value represents a dose value fluctuation rate due to aging.   The X-ray computed tomography apparatus according to claim 1, wherein the calibration table associates a plurality of calibration values with a plurality of irradiation times. A reference detector for directly detecting X-rays from the X-ray tube;
2. The calibration table subjected to the update process, wherein a calibration value corresponding to a change over time in the number of photons specified from a detection value of the reference detector is associated with a tube voltage or other imaging conditions. X-ray computed tomography apparatus.   The X-ray computed tomography apparatus according to claim 1, further comprising an output unit that outputs data relating to the calibration table to be updated as DICOM data.

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