JP4699585B2 - X-ray CT system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray CT apparatus, and more specifically, includes a rotating anode type X-ray tube and an X-ray detector facing each other with a subject interposed therebetween, and the subject's subject is based on projection data collected from the X-ray detector. The present invention relates to an X-ray CT apparatus for reconstructing a CT tomogram.
[0002]
Today, so-called rotating anode type X-ray tubes are widely used in X-ray CT apparatuses. However, when X-rays are continuously exposed, high heat is accumulated in the rotating anode. The following is desirable from the viewpoint of extending the life of the X-ray tube.
[0003]
[Prior art]
FIG. 5 is a view for explaining a conventional rotary anode type X-ray tube, partially showing a cross-sectional view. In the figure, 11 is a rotary anode type X-ray tube, 61 is an envelope that keeps the inside of the tube in a vacuum, 62 is a filament, 63 is a focusing electrode, 64 is a cathode sleeve, 65 is a target made of an umbrella-shaped tungsten disk, etc. , 66 is a focal point that is an X-ray generation source, 67 is a rotary anode that rotates and supports the target 65, 68 is a bearing that supports the rotary anode 67, and 69 is an anode shaft that supports the anode side of the X-ray tube. is there. The rotating anode 67 rotates at high speed by a magnetic field (rotating magnetic field or the like) applied from a stator (not shown) provided around the envelope 61. Further, the X-ray tube 11 is forcibly cooled by covering the periphery of the X-ray tube 11 with a housing 70 made of aluminum or the like, and circulating cooling oil from the outside.
[0004]
With such a configuration, the thermoelectrons generated in the filament 62 are accelerated and focused at a high pressure and collide with a small focal point 66 on the target 65 to generate X-rays. However, the conversion efficiency into X-rays is generally as low as several percent or less, so that most of the energy is converted into heat, and high heat is generated at the focal point 66. Therefore, the rotary anode 67 (target 65) is rotated around the anode shaft 69 at a high speed (about 130 to 160 Hz), thereby expanding the effective area of the focal point 66 and obtaining the required X-ray output. However, even if such a rotating anode type X-ray tube 11 is continuously exposed, high heat is accumulated in the target 65, leading to failure or breakage of the X-ray tube 11. Therefore, there is a means for avoiding such a situation. Desired.
[0005]
Conventionally, the virtual anode accumulated heat amount increase value of the X-ray tube 11 is obtained based on the next scheduled exposure parameter, and if this is predicted to exceed the allowable heat amount upper limit value, the imaging is not permitted (locked) and An X-ray apparatus that displays a waiting time until permission for imaging is known (Japanese Patent Laid-Open No. 10-335092). The contents are outlined below.
[0006]
FIG. 6 is a diagram showing a rise in anode accumulated heat and a cooling curve. The amount of heat accumulated in the anode St of the X-ray tube 11 increases with the exposure time t, and the degree of increase is substantially proportional to the input power P (tube voltage kV × tube current mA) and the like. Qlm represents the allowable maximum stored heat amount value of the X-ray tube 11, and Ct represents the cooling characteristic from the allowable maximum stored heat amount value Qlm.
[0007]
The amount of heat accumulated in the anode St of the X-ray tube 11 can be approximated based on the exposure parameters (tube voltage, tube current, focus size, anode rotation speed, etc.) to the X-ray tube 11 and its cooling characteristics Ct. Synchronously with the actual driving / stopping of the tube 11, the current accumulated anode heat value St is calculated momentarily. In this case, various parameters affecting the calorific value calculation are corrected functions {correction function K (p) depending on anode input power P, correction function L (T) depending on exposure duration T, X-ray focal spot size. Correction is performed with a correction function M (f) depending on f, a correction function N (r) depending on the anode rotation speed value r, etc.} to ensure the accuracy of the calculation.
[0008]
When the next scheduled exposure parameter is determined, the next scheduled anode input heat value Qsn is predicted based on the anode input power value P and the X-ray exposure duration value T. This is added to the current anode accumulated heat quantity value Qt (= St), and the next scheduled anode accumulated heat quantity reached value Qs is obtained. Depending on whether Qs <Qlm or not, the next scheduled shooting is permitted / not permitted, and the waiting time until the next shooting is possible using the cooling curve Ct (Qs <Qlm) is displayed on the screen. indicate. Hereinafter, an example of the operation will be specifically described.
[0009]
FIG. 7 is a diagram for explaining the transition of the amount of accumulated anode heat accompanying X-ray imaging. Now, assuming that the situation at point A in the figure is reached at time ta, the anode accumulated heat value at this time = Qa. Assuming that the next scheduled exposure parameter is anode input power P = P0 and X-ray exposure duration T = Tac, the next scheduled anode input calorific value Qsn is calculated. You can see it. At this time, the accumulated amount of heat accumulated in the anode Qs = Qc1. In this case, since Qc1> Qlm, the next X-ray exposure is not permitted (locked).
[0010]
On the other hand, if the transition is made to the point B after the time Tab has elapsed since the current time ta, the anode accumulated heat value Qt = Qb at that time decreases, so that the exposure time Tbc (= Tac) when the next exposure is performed from there. Qc2 after the elapse of ()) is exactly equal to Qlm, so that the next exposure is possible from this point. Therefore, the waiting time Tab is obtained by calculation and displayed on the display device. If this waiting time becomes 0, the next exposure can be automatically started.
[0011]
[Problems to be solved by the invention]
However, if the system simply informs the user of permission / non-permission of photographing and the waiting time as in the conventional case, for example, even if photographing according to the next scheduled condition is not permitted, other photographing conditions are possible. It was not easy to determine what kind of shooting conditions are possible. For example, when it is desired to quickly acquire an X-ray tomographic image by carrying in an emergency patient, conventionally, if the imaging conditions (50 images, etc.) do not match, the imaging is not permitted, and the waiting is not allowed. The time was only displayed. However, even in this case, if the number of images is reduced to 30 images can be taken immediately, a conventional operator cannot easily grasp such a photographing possible limit condition.
[0012]
There is also a method for the operator to change the number of images (exposure time) for the next time, but the operator does not know the possible limit condition (number of images that can be captured) at that time, so the setting is changed. For example, 45 sheets were set and disallowed, and then 40 sheets were set and disallowed. In some cases, 20 sheets were suddenly set and allowed. In the latter case, the number is 10 times lower than the imaging limit condition, and it cannot be said that the X-ray apparatus is effectively used. Further, the operation of repeating the trial operation as described above is very complicated, and there is a problem from the viewpoint of quick diagnosis.
[0013]
In addition, it is relatively easy to change the number of images (exposure time) as described above, but there are other factors (power, focus size, rotation speed, etc.) in the exposure parameters that affect the amount of heat accumulated in the anode. In addition, since the power and focus size of these have an effect on the image quality, it has been extremely difficult to search for possible limit conditions for each of these elements or combinations thereof.
[0014]
The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide an X-ray CT apparatus that can easily grasp a possible limit condition for exposing an X-ray tube.
[0015]
[Means for Solving the Problems]
The above problem is solved by the configuration of FIG. That is, the X-ray CT apparatus of the present invention (1) includes a rotating anode type X-ray tube and an X-ray detector facing each other with a subject interposed therebetween, and the subject is based on projection data collected from the X-ray detector. In an X-ray CT apparatus for reconstructing a CT tomogram of a specimen, the X-ray tube is synchronized with the actual driving / stopping of the X-ray tube based on the accumulated heat amount increase characteristic of the rotating anode by the exposure parameter of the X-ray tube and its cooling characteristic. The current stored heat amount calculating means 51 for obtaining the anode accumulated heat amount value Qt every moment, the anode accumulated heat amount value Qt at the current ta determined by the current accumulated heat amount calculating means 51 and the next scheduled exposure parameter are used. The next stored heat amount predicting means 52 for obtaining the virtual stored heat amount reached value Qc when the exposure starts at the current ta, and the virtual stored heat amount reached value Qc exceeds the allowable heat amount upper limit value Qlm of the X-ray tube. Accumulated heat quantity reaches value Qc of those and a substitute parameter calculation means 53 for determining the exposure parameters Ps / Ts / Fs / Rs alternative to not exceed the allowable heat limit Qlm the X-ray tube.
[0016]
According to the present invention (1), the alternative parameter calculation means 53 determines that the next accumulated heat amount reaching value Qc is X when the next scheduled virtual accumulated heat amount reaching value Qc exceeds the allowable heat amount upper limit value Qlm of the X-ray tube. With the configuration to obtain alternative exposure parameters (Ps / Ts / Fs / Rs, etc.) so as not to exceed the allowable heat amount upper limit value Qlm of the tube, the operator can easily grasp the next photographing possible limit condition as a result, Easy to assemble next workaround. Therefore, such an X-ray CT apparatus can be used effectively (no waiting time etc.).
[0017]
Preferably, in the present invention (2), in the present invention (1), the substitute parameter calculation means 53 sets any one of the next scheduled exposure parameters as an unknown and the remaining exposure. The unknown is used to satisfy the parameters up to the allowable heat amount upper limit value Qlm of the X-ray tube by directly adopting the parameters. For example, the exposure time parameter Ts is set to the unknown X, and the remaining exposure parameters (power Ps, focus size Fs, rotation speed Rs) are adopted as scheduled next time to the allowable heat amount upper limit value Qlm of the X-ray tube. The unknown number X for satisfying the above is obtained. Accordingly, it can be easily understood that, for example, 30 images can be imaged under the next scheduled imaging condition.
[0018]
Other exposure parameters (power Ps, focus size Fs, or rotation speed Rs) can be set to the unknown X. In that case, all the exposure parameters are sequentially set as unknowns X (however, the remaining parameters are scheduled for the next time), and the limit values of all the unknown parameters are obtained simultaneously, and these can be provided to the operator. . In this case, the operator can judge (select) at once whether to compromise by the number of sheets or to compromise by electric power. Further, the electric power Ps can be divided into a tube voltage kV and a tube current mA.
[0019]
Preferably, in the present invention (3), the present invention (2) further includes parameter setting means capable of arbitrarily changing the remaining exposure parameters other than the unknown.
[0020]
Therefore, for example, after the number of shots that was the unknown number X (corresponding to the exposure time Ts) = 30 is obtained, the target to be the unknown number X is changed to the power Ps, and the number of shots to be found = 30 is set. It is possible to change the setting to 40 sheets and further obtain the electric power Ps that can satisfy this. That is, the operator can easily know how much power Ps should be used as an alternative to capturing 40 images instead of the 30 images obtained. Similarly, various combinations of limit parameters can be searched easily and easily.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. Note that the same reference numerals denote the same or corresponding parts throughout the drawings. FIG. 2 is a configuration diagram of a main part of the X-ray CT apparatus according to the embodiment. In the figure, 10 is a scanning gantry for performing Axial / Hericl scanning / reading of the subject 100 by the X-ray fan beam, and 19 is the subject 100 mounted thereon. An imaging table 40 that is moved in the body axis direction is an operation console operated by the user.
[0022]
In the scanning gantry 10, 11 is a rotary anode type X-ray tube, 12 is an X-ray control unit for controlling the tube voltage kV, tube current mA, exposure time Sec, etc. of the X-ray tube 11, and 13 is the X-ray fan direction. And a collimator for limiting the exposure range in the body axis direction, 14 is a collimator control unit, 16 is an X-ray detector array in which a large number (about 1000) of X-ray detectors are arranged in an arc, and 17 is an X-ray. A data collection unit (DAS) 15 that collects detection data (projection data) of the detector array, 15 is a rotation control unit that rotates the scanning gantry 10 around the body axis of the subject 100.
[0023]
In the operation console 40, 41 is a central processing unit that performs main control and processing (scan control, CT tomographic image reconstruction processing, alternative parameter calculation processing according to the present invention) of the X-ray CT apparatus, 41a is its CPU, The main memory (MEM) used by the CPU 41a, 42 is an input device such as a keyboard or mass, 43 is an imaging parameter for imaging planning (tube voltage kV, tube current mA, scan time Sec, detection of subject body axis direction) A display device (CRT) 44 for displaying a CT thickness image and the like of the imaging result, and the like, and exchange of various control signals C and monitor signals SD between the CPU 41a and the scanning gantry 10 or imaging table 19. The control interface to be used, 45 is a data collection buffer for storing projection data from the data collection unit 17, and 46 is necessary for the operation of the X-ray CT apparatus. Such stores various data and application programs by which the secondary storage device (disk), 47 is a common bus of CPU 41a.
[0024]
An outline of the X-ray imaging operation is as follows. Fan beams from the X-ray tube 11 are incident on the X-ray detector array 16 all at once through the subject 100. The data collection unit 17 scans and collects projection data of the subject 100 from the X-ray detector array 16 and stores it in the data collection buffer 45. Further, imaging similar to the above is performed at a position (view) where the scanning gantry 10 is slightly rotated, and the collected data is accumulated. Hereinafter, similarly, projection data for one rotation of the scanning gantry 10 is collected and accumulated, and the imaging table 19 is moved intermittently / continuously in the body axis direction of the subject 100 in accordance with the Axial / Hericl scan method. All projection data for the required imaging region of the subject 100 is collected and accumulated. Then, the CPU 41 a reconstructs a CT tomographic image of the subject 100 based on the obtained all projection data and displays it on the display device 43.
[0025]
In addition, an inset (a) shows functional blocks related to the present invention realized by executing the program of the CPU 41a. In the figure, 51 indicates the anode accumulated heat quantity value Qt in synchronization with actual driving / stopping of the X-ray tube 11 based on the accumulated heat quantity rise characteristic St of the rotating anode according to the exposure parameter of the X-ray tube 11 and its cooling characteristic Ct. A current stored heat amount calculation unit 52 that is obtained every moment, 52 is a virtual when the current start of exposure using the current stored anode heat value Qt obtained by the current stored heat amount calculation unit 51 and the next scheduled exposure parameter. The next stored heat amount predicting unit 53 for obtaining the stored heat amount reached value Qe of the next, when the virtual stored heat amount reached value Qe exceeds the allowable heat amount upper limit value Qlm of the X-ray tube 11, the next stored heat amount reached value Qe becomes the X-ray tube. 11 is an alternative parameter calculation unit that obtains an alternative exposure parameter that does not exceed 11 allowable heat amount upper limit value Qlm. It should be noted that the calculation relating to the accumulated heat amount increase characteristic St of the rotating anode and the cooling characteristic Ct according to the exposure parameter of the X-ray tube 11 approximates a well-known calculation formula or a characteristic curve obtained by actual measurement in advance for the X-ray tube 11 to be used. Can be used.
[0026]
Hereinafter, the alternative photographing operation and the alternative parameter setting process according to the embodiment will be described in detail. FIG. 3 is a diagram illustrating an operation screen of the display device 43 according to the embodiment. However, the figure mainly shows the part related to the exposure parameters of the X-ray tube 11. When the X-ray CT apparatus is powered on, a predetermined operation panel column 61 is displayed on the screen of the display device 43 after completing the required initialization process. When the operator presses (clicks) a shooting mode selection button (icon), the corresponding shooting (exposure) parameters are collectively displayed. The figure shows the exposure parameters when button [3] is pressed. At first, since the X-ray tube 11 is sufficiently cooled, imaging according to this exposure parameter is possible, and the “READY” lamp is lit.
[0027]
When the operator presses the “START” button, shooting according to the shooting protocol is started. Eventually, when the required shooting (exposure) time elapses, shooting is terminated, the “START” button is turned off, and the “STOP” button is turned on instead. On the other hand, the anode accumulated heat value Qt of the X-ray tube 11 rises due to this exposure, and thereafter it is gradually cooled along the cooling curve Ct. The current accumulated heat amount calculation unit 51 obtains the current anode accumulated heat amount value Qt from time to time, and thus tracks the actual anode accumulated heat amount value Qt.
[0028]
Next, when the operator sets the imaging parameter scheduled for the next time (may be the same as the previous time), the next stored heat amount prediction unit 52 determines the anode accumulated heat amount value at the present time (for example, ta) obtained by the current stored heat amount calculation unit 51. Using Qa and the next scheduled exposure parameter, a virtual accumulated heat amount reaching value Qe (= Qc1) that is expected to be reached when the exposure is started from this state (current time ta) is obtained. Then, when the obtained accumulated heat amount reaching value Qe exceeds the allowable heat amount upper limit value Qlm of the X-ray tube 11, “WAIT” is turned on in the same manner as in the conventional case, and the accumulated heat amount reaching value Qe is set to the allowable heat amount upper limit value. The waiting time Tab until it does not exceed Qlm is displayed every moment.
[0029]
In this state, if the operator presses the “alternate” button or the [START] button, the operation shifts to an alternative search mode, and the alternative parameter column 62 and preferably the anode accumulated heat amount transition graph column 63 are displayed on the screen. Is also displayed. On the other hand, the alternative parameter calculation unit 53 obtains an alternative exposure parameter for preventing the next accumulated heat amount reaching value Qe from exceeding the allowable heat amount upper limit value Qlm of the X-ray tube 11. Details of this processing will be described later with reference to FIG.
[0030]
The first substitute parameter is a copy of the contents of the next scheduled exposure parameter. However, the alternative exposure (possible) time Ts (= 1.0 second) obtained by the alternative parameter calculation unit 53 is displayed in the column of the unknown parameter (initially, exposure time T by default setting). This means that if the exposure parameter of the next scheduled time is adopted, the photographing is permitted for 1.0 second. For this, referring to the anode accumulated heat amount transition graph column 63, the exposure possible time Ts = 1.0 until the accumulated heat amount Qt started from the accumulated heat amount Qa at the imaging start time point ta (point A) reaches the allowable upper limit value Qlm. Represents seconds. In this way, the operator can easily understand the next scheduled shooting situation by graphic display.
[0031]
By the way, the obtained alternative exposure time Ts (= 1.0 second) is not always satisfactory. If the imaging area of the subject is large, longer exposure times are desired, even at the expense of some image quality. In order to make this possible, it is necessary to make the rising curve of the anode accumulated heat quantity Qt more gradual, and as parameters related thereto, the power (tube voltage × tube current) Ps, the focus size Fs or the rotation speed Rs is changed. It is possible to do. The change image of the curve in this case is shown in the anode accumulated heat amount transition graph 63.
[0032]
Now, paying attention to the tube current among the alternative parameters, if the tube current is reduced from 30 mA to 20 mA, the amount of anode heat generation per unit time decreases, and the rising curve of the graph changes from C1 to C3 in the figure. It is possible. Therefore, the operator changes the setting of the tube current = 30 mA in the alternative parameter column 62 to 20 mA. Although not shown, this automatically changes to an alternative exposure time Ts = 2.0 seconds, and this exposure time is satisfactory. The same applies when other parameters are changed. At this time, the operator can easily recognize the validity of his / her changing operation by displaying the rising curve after changing each setting in a graph.
[0033]
Or, conversely to the above, there is a way to ask how many tube currents should be used in order to set the exposure time Ts = 2.0 seconds. In this case, the operator changes the column for the unknown number of substitution parameters from the exposure time T to the tube current mA column, and changes the setting to the exposure time Ts = 2.0 seconds. As a result, the tube current As = 20 mA that satisfies the conditions is automatically changed to satisfy the requirement. In this way, various exposure parameters that can satisfy the allowable upper limit Qlm and combinations thereof can be easily tried.
[0034]
FIG. 4 is a flowchart of alternative parameter calculation processing according to the embodiment. When the “alternate” button on the operation panel 61 is pressed, or when the “START” button is pressed while “WAIT” is lit, an input is made to this process. In step S1, the contents of the next scheduled shooting parameter are copied to the alternative parameter column. The next shooting parameters in this example are tube voltage Vn = 120 kV, tube current An = 30 mA, exposure time Tn = 4.0 seconds, focus size Fn = 3 mm, and rotation speed Rn = 140 Hz. In step S2, the current anode accumulated heat value Qt is set in the start temperature storage register Qb. In step S3, the allowable heat amount upper limit value Qlm of the X-ray tube 11 is set in the end temperature storage register Qe, and the current unknown parameter X is obtained. The first unknown parameter X is the exposure time Ts by default setting.
[0035]
In step S4, the parameter of the calculation result (initially the exposure time Ts) is set as an alternative parameter. For the rest, the next scheduled exposure parameters are used as they are. In step S5, an alternative parameter is displayed. In step S6, it is determined whether or not the “START” button has been pressed. If not, it is further determined in step S7 whether or not parameter settings have been changed. The operator can change the item that is unknown in this section, or can arbitrarily change the parameter setting values other than the unknown item. If the parameter setting is not changed in step S7, the process returns to step S2. If the parameter setting is changed, the contents of the changed parameter are set in the alternative parameter corresponding column in step S8, and the process returns to step S2.
[0036]
In this way, by arbitrarily changing the parameter setting values other than the unknown number column and the unknown number column, an unknown parameter that can satisfy the allowable heat amount upper limit value Qlm of the X-ray tube 11 even when imaging is started at that time is automatically obtained. Then, when it is determined that “START” has been pressed in the determination of step S6, the process is terminated. Thereafter, photographing using this alternative parameter is started.
[0037]
In the above-described embodiment, the alternative parameters that satisfy the thermal conditions are obtained one by one according to the operation, but the present invention is not limited to this. For example, in the first stage, all the alternative parameters may be obtained by sequentially setting each parameter as an unknown, and these may be displayed on the screen all at once. In this case, the substitution parameter Ts = 1.0 seconds when the exposure time is an unknown, and the tube current is an unknown (however, the original next time parameter Tn = 4.0 seconds is adopted). The alternative parameter As = 15 mA at the time is displayed all at once. Accordingly, the operator in this case can quickly select any one of a plurality of alternative proposals.
[0038]
In the above embodiments, application examples to the X-ray CT apparatus have been mainly described. However, the present invention is not limited to various other X-ray apparatuses (X-ray transmission photography apparatus, X-ray television apparatus) using an X-ray tube. Etc.).
[0039]
Moreover, although the application example to the rotating anode type X-ray tube has been described in the above embodiment, the present invention can be applied to other types of X-ray tubes.
[0040]
Further, although the preferred embodiment of the present invention has been described, it goes without saying that various changes can be made to the configuration, control, and combination of each part without departing from the spirit of the present invention.
[0041]
【The invention's effect】
As described above, according to the present invention, the operator can grasp the limit condition for exposure from the present time of the X-ray tube whose anode calorific value Qt changes from moment to moment specifically and easily. Therefore, it is possible to easily adopt the next best measure of the next four-handed photographing or other purpose photographing, and thus the X-ray CT apparatus can be used safely and fully.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating the principle of the present invention.
FIG. 2 is a configuration diagram of a main part of an X-ray CT apparatus according to an embodiment.
FIG. 3 is a diagram illustrating an operation screen according to an embodiment.
FIG. 4 is a flowchart of alternative parameter calculation processing according to the embodiment.
FIG. 5 is a diagram illustrating an example of a conventional rotary anode X-ray tube.
FIG. 6 is a diagram showing an increase in anode accumulated heat and a cooling curve.
FIG. 7 is a diagram for explaining the transition of the amount of accumulated anode heat associated with X-ray imaging.
[Explanation of symbols]
51 Current Accumulated Heat Calculation Unit 52 Next Accumulated Heat Amount Prediction Unit 53 Alternative Parameter Calculation Unit 61 Operation Panel 62 Alternative Parameter Field 63 Anode Accumulated Heat Quantity Transition Graph Field

Claims (4)

In an X-ray CT apparatus comprising an X-ray tube and an X-ray detector facing each other with a subject interposed therebetween, and reconstructing a CT tomographic image of the subject based on projection data collected from the X-ray detector,
Current stored heat amount calculation means for obtaining the anode stored heat amount value every moment in synchronism with actual driving / stopping of the X-ray tube based on the characteristics of increasing the stored heat amount of the rotating anode according to the exposure parameters of the X-ray tube and its cooling characteristics; ,
Next stored heat amount prediction means for obtaining a virtual stored heat amount arrival value when the current exposure start is performed using the current anode stored heat amount value obtained by the current stored heat amount calculation means and the next scheduled exposure parameter. When,
Any one of the exposure parameters related to slowing the increase in the anode accumulated heat amount due to exposure when the virtual accumulated heat amount reaching value exceeds the allowable upper limit value of the X-ray tube Is determined as an unknown number, and an alternative value is obtained for the exposure parameter with the unknown value so that the next accumulated heat amount reaching value does not exceed the allowable upper limit value of the X-ray tube even if imaging is started without waiting time. An alternative parameter calculation means;
An X-ray CT apparatus comprising: The exposure parameters associated with moderating the increase in anode stored heat due to the exposure include x-ray tube voltage, x-ray tube current, focal spot size, and rotational speed. X-ray CT system. Alternate parameter calculating means, the exposure parameters other than exposure parameters determined as unknowns, the values of the next scheduled on that relied, determine the value of one alternative for exposure parameters and the unknown The X-ray CT apparatus according to claim 1, wherein the X-ray CT apparatus is an apparatus. The substitute parameter calculating means is a means for changing an item of the exposure parameter determined as the unknown after obtaining one alternative value for the exposure parameter set as the unknown and / or the exposure parameter set as the unknown. 4. Parameter setting means capable of arbitrarily setting and changing the value of an exposure parameter other than the exposure parameter determined as an unknown after obtaining one alternative value for The X-ray CT apparatus as described in any one.

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