JP2010193940A - X-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus capable of changing a condition for radiography by simple operation if clipping occurs in a predetermined allowable range of tube current quantity. <P>SOLUTION: A system control device 401 computes a tube current modulation curve 153 to be fed to an X-ray tube based on a condition for radiography set by an operator and a target image quality, and computes and displays an image quality index changing curve 173 from the computed tube current modulation curve 153. The system control device 401 analyzes the image quality index changing curve 173, and determines whether there is clipping of the tube current or a part deviating from the allowable range of the target image quality. If there is clipping of the tube current or a part deviating from the allowable range of the target image quality, the system control device 401 computes and displays a candidate for correction of the condition for radiography for achieving the target image quality. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an X-ray CT apparatus that optimizes an X-ray dose irradiated to a subject.

The X-ray CT apparatus irradiates X-rays from around the subject, collects transmitted X-ray data, which is information related to the intensity of the X-rays transmitted through the subject, with an X-ray detector, and collects the transmitted X-ray data collected Is a device for creating a reconstructed image inside a subject based on the above.
In the above X-ray CT apparatus, in order to reduce the exposure dose in the subject while achieving the image quality required for the reconstructed image, the X-ray dose that modulates the X-ray dose irradiated from the X-ray tube during a series of imaging. Optimization techniques have been proposed.

  For example, in Patent Document 1, in order to reduce the exposure dose while maintaining a low noise level and a good CNR (contrast-noise ratio), it is appropriate to use the physique, attenuation index, and desired image noise characteristics of the subject. An X-ray CT apparatus is disclosed that calculates an appropriate tube current value and determines an appropriate tube voltage in combination with desired noise and contrast characteristics. In Patent Document 2, a three-dimensional model of a subject is estimated from scanogram projection data, and an imaging target can be identified from the three-dimensional model, the size of the subject, and standard imaging conditions stored in advance. An X-ray CT apparatus that calculates a CNR to be calculated and calculates an optimum tube current and tube voltage for achieving the CNR is disclosed.

  In Patent Document 3, a target image quality level (image SD) of a tomographic image to be reconstructed can be selected based on a slice thickness, an inspection region, and an inspection purpose set by an operator. An X-ray CT apparatus is disclosed that controls an X-ray irradiation dose by a tube current calculated based on a level. Also, in Patent Document 4, for the convenience of the operator, how is the image quality of the portion corresponding to the region of interest different between when the irradiation X-ray dose optimization function is used and when it is not used? An X-ray CT apparatus for displaying is also disclosed.

JP 2004-073865 A International Publication No. 2007/13879 JP 2003-033346 A International Publication No. 2007/032462

  On the other hand, in a general X-ray CT apparatus, an upper limit value and a lower limit value of a tube current amount that can be stably supplied are determined. Therefore, depending on the physique of the subject, the amount of tube current obtained by the optimization calculation exceeds the upper limit value, rounded to the upper limit value, conversely, lower than the lower limit value and rounded to the lower limit value, Such clipping will occur. When clipping occurs due to the upper limit value, the necessary X-ray dose cannot be irradiated, and as a result, the image quality index value (SD value or CNR value) preset as a target cannot be achieved. In addition, when clipping occurs due to the lower limit value, the X-ray dose to be irradiated becomes excessive and the exposure dose increases.

  When tube current clipping occurs, the imaging conditions may have to be changed in order to suppress the effect on the image quality, but in the conventional X-ray CT apparatus, what conditions are to be changed to what extent? It was left to the operator's experience and was difficult for an unfamiliar operator.

  The present invention has been made in view of the above problems, and an X-ray CT apparatus capable of changing imaging conditions with a simple operation when clipping occurs in a predetermined tube current allowable range. It is intended to provide.

  In order to achieve the above-described object, the present invention calculates a tube current amount to be supplied to the X-ray tube based on the set imaging conditions and target image quality, and based on the calculated tube current amount and the imaging conditions. In an X-ray CT apparatus that performs X-ray imaging of a subject, a determination unit that determines whether or not the tube current amount deviates from a predetermined allowable range, and the determination unit deviates from the allowable range. An X-ray CT apparatus comprising correction candidate presenting means for presenting correction candidates for the imaging conditions for achieving the target image quality when determined.

  According to the present invention, it is possible to provide an X-ray CT apparatus capable of changing imaging conditions with a simple operation when clipping occurs in a predetermined allowable range of tube current.

External view showing the entire configuration of the X-ray CT apparatus 1 Hardware block diagram of X-ray CT apparatus 1 The flowchart which shows the flow of the imaging condition setting process which the system control apparatus 401 performs Shooting condition setting screen 13 Display example of tube current modulation curve 153 Display example of image quality index change curve 173 Correction part in the image quality index change curve 173 Presentation example of photographing condition correction candidate 20 (example 1) Presentation example of shooting condition correction candidate 21 (example 2) Setting example of correction priority 23 for shooting conditions Example of presenting shooting condition correction candidate 22 (when “other (detailed setting)” of correction candidate 20 of example 1 is selected)

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, with reference to FIGS. 1-2, the structure of the X-ray CT apparatus 1 of this Embodiment is demonstrated.
In the present embodiment, a case where there is one X-ray tube will be described, but the present invention can also be applied to a multi-ray source type X-ray CT apparatus. In addition, the X-ray CT apparatus is a rotation-rotation method (Rotate-Rotate method) in which an X-ray tube and an X-ray detector rotate together while irradiating a wide fan beam covering the entire subject, There are an electron beam scanning system (Scanning Electron Beam system) in which the target electrode is applied while being deflected, and other systems, but the present invention is applicable to any system of X-ray CT apparatus.

  As shown in FIG. 1, the X-ray CT apparatus 1 includes a scanner 2, a bed 3, an operation console 4, a top 5 provided on the bed 3, a display device 7, and an operation device 8. The X-ray CT apparatus 1 acquires transmission X-ray data of the subject 6 by carrying the subject 6 fixed to the top plate 5 on the bed 3 into the opening of the scanner 2 and scanning.

  As shown in FIG. 2, the scanner 2 includes an X-ray tube 201, an X-ray tube control device 202, a collimator 203, a collimator control device 204, an X-ray detector 205, a data collection device 206, a rotating plate 207, and a rotating plate driving device 208. , A rotation control device 209, and a drive transmission system 210.

  The X-ray tube 201 is an X-ray source, and is controlled by the X-ray tube control device 202 to irradiate the subject 6 with X-rays continuously or intermittently. The X-ray tube control device 202 applies the X-ray tube voltage and the X-ray tube current to be applied to or supplied to the X-ray tube 201 according to the X-ray tube voltage and the X-ray tube current determined by the system control device 401 of the console 4. Control. Hereinafter, the X-ray tube current is referred to as tube current.

  The collimator 203 irradiates the subject 6 with X-rays radiated from the X-ray tube 201 as X-rays such as a cone beam (conical or pyramidal beam), for example, and is controlled by the collimator controller 204. . X-rays transmitted through the subject 6 enter the X-ray detector 205.

  The X-ray detector 205 includes, for example, about 1000 X-ray detection element groups configured by, for example, a combination of a scintillator and a photodiode in the channel direction (circumferential direction), for example, about 1-320 in the column direction (body axis direction). They are arranged and arranged so as to face the X-ray tube 201 through the subject 6. The X-ray detector 205 detects X-rays emitted from the X-ray tube 201 and transmitted through the subject 6, and outputs the detected transmitted X-ray data to the data acquisition device 206.

  The data collection device 206 is connected to the X-ray detector 205, collects transmission X-ray data detected by the individual X-ray detection elements of the X-ray detector 205, and outputs it to the image reconstruction device 402.

  An X-ray tube 201, a collimator 203, an X-ray detector 205, and a data collection device 206 are mounted on the rotating plate 207. The rotating plate 207 is rotated by the driving force transmitted through the drive transmission system 210 from the rotating plate driving device 208 controlled by the rotation control device 209.

The bed 3 shown in FIG. 2 includes a top plate 5, a bed control device 301, a vertical movement device 302, and a top plate driving device 303.
The bed control device 301 controls the vertical movement device 302 to make the height of the bed 3 appropriate, and also controls the tabletop driving device 303 to move the tabletop 5 back and forth in the body axis direction. Thereby, the subject 6 is carried into and out of the X-ray irradiation space of the scanner 2.

  The console 4 includes a display device 7, an operation device 8, a system control device 401, an image reconstruction device 402, and a storage device 404. The console 4 is connected to the scanner 2 and the bed 3.

  The display device 7 includes a display device such as a liquid crystal panel and a CRT monitor, and a logic circuit for executing display processing in cooperation with the display device, and is connected to the system control device 401. The display device 7 displays a reconstructed image and a scanogram image output from the image reconstructing device 402 and various information handled by the system control device 401.

  The operation device 8 includes, for example, an input device such as a keyboard, a mouse, and a numeric keypad, and various switch buttons. The operation device 8 outputs various instructions and information input by the operator to the system control device 401. The operator interactively operates the X-ray CT apparatus 1 using the display device 7 and the operation device 8. For example, the operation device 8 performs an input operation of a target value of an image quality index value (for example, an image SD value, a contrast-noise ratio, etc.) based on a scanogram image obtained by the image reconstruction device 402, and various photographing conditions (tube voltage). Image slice thickness, collimation thickness, scan speed, spiral pitch (bed movement speed), reconstruction filter, image filter, image FOV (Field of View, etc.) input operation, etc. are accepted.

  The system control device 401 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The system control device 401 controls the X-ray tube control device 202, the collimator control device 204, the data acquisition device 206, the X-ray detector 205, and the rotation control device 209 in the scanner 2, and the bed control in the bed 3. The apparatus 301 is controlled.

  Further, the system control apparatus 401 executes an imaging condition setting process (see FIG. 3) described later at the start of imaging in the X-ray CT apparatus 1. In the imaging condition setting process, the system controller 401 uses a time-dependent change curve of the tube current supplied to the X-ray tube 201 in a series of scans based on the imaging conditions input by the operator, the target image quality, and the like. A certain tube current modulation curve 153 (tube current amount) is calculated (see FIGS. 3 and 5). Further, a change curve 173 of the image quality index value obtained when photographing is performed with the tube current modulation curve 153 (see FIG. 6). Further, the system control apparatus 401 determines whether or not there is an image quality degradation portion or the like due to tube current clipping (deviation from the allowable range), and if there is an image quality degradation portion, presents an imaging condition correction candidate. .

  The image reconstruction device 402 acquires transmission X-ray data collected by the data collection device 206 in the scanner 2 under the control of the system control device 401. At the time of scanogram imaging, a scanogram image is created using the scanogram projection data collected by the data collection device 206. At the time of scanning, a tomographic image is reconstructed using transmission X-ray data of a plurality of views collected by the data collection device 206.

  The storage device 404 is configured by a hard disk or the like, and is connected to the system control device 401. The storage device 404 stores scanogram projection data and scanogram images collected by the data collection device 206, photographing conditions input from the operation device 8, target image quality index values, and the like. In addition to these various data, a tomographic image generated by the image reconstruction device 402, a program for realizing the functions of the X-ray CT apparatus 1, and the like are stored. In addition, the storage device 404 stores in advance the correction priority order of each condition item of the shooting condition, the correction priority order for each mode, and the like that are referred to when presenting correction candidates for the shooting condition in the shooting condition setting process. ing.

  Next, the operation of the X-ray CT apparatus 1 will be described with reference to the flowchart of FIG. 3 and FIGS. 4 to 11.

  The system control apparatus 401 of the X-ray CT apparatus 1 according to the present embodiment executes an imaging condition setting process shown in FIG. 3 when imaging of the subject 6 is started. In other words, the system control apparatus 401 reads out the program and data related to the shooting condition setting process from the storage device 404 and executes the shooting condition setting process based on the program and data.

  In the imaging condition setting process of FIG. 3, first, the system control apparatus 401 performs scanogram imaging of the subject 6 to acquire scanogram projection data (step S101). The system control device 401 sends the acquired scanogram projection data to the image reconstruction device 402. The image reconstruction device 402 creates a scanogram image 11 based on the scanogram projection data, stores it in the storage device 404 and displays it on the display device 7.

  Next, the system control device 401 causes the display device 7 to display a shooting condition input frame 13 for inputting shooting conditions and target image quality, and receives input of shooting conditions and target image quality from the operator. Based on the displayed scanogram image 11, the operator inputs shooting conditions and target image quality using the operation device 8 (step S102).

  Here, the imaging conditions specifically include the condition items for the scanner and bed such as the body axis direction imaging range (z position range), collimation thickness, helical pitch, scanning speed, image slice thickness, tube voltage, etc. , Image FOV, and reconstruction items such as a reconstruction filter.

The scanogram image 11 photographed / generated in step S101 and the photographing condition input frame 13 displayed in step S102 are displayed as shown in FIG. 4, for example.
The operator clicks on desired positions 11a and 11b in the scanogram image 11 shown in FIG. 4 by using the operation device 8 such as a mouse, and inputs an imaging range. The photographing condition is input by inputting a desired numerical value into the condition item.

  In addition, the operator uses the operation device 8 to input a target value of a desired image quality index value. As the image quality index value, for example, an image SD (Standard Deviation) value, a CNR (contrast-noise ratio), an identifiable diameter (radius of an abnormal shadow that can be identified) under a predetermined CNR, or an SNR (signal-noise ratio) Etc. are used. In the following description, an image SD value is used as an image quality index value as an example.

The system control device 401 calculates the tube current modulation curve 153 based on the input shooting conditions and the target image quality (step S103; see FIG. 5).
In calculating the tube current modulation curve 153, the system control apparatus 401, for example, approximates the human body of the subject from the projection position distribution (for example, the projection value maximum height, the projection value area, etc.) at each position in the body axis direction of the scanogram projection data. A model (elliptical approximation model, modified elliptical approximation model, etc.) is generated, and based on this, tube current modulation is performed to achieve the target image quality in consideration of various shooting conditions such as tube voltage, reconstruction filter, and image slice thickness. A curve 153 is created. Details about the calculation of the tube current modulation curve 153 may be performed by using a known method such as the above-mentioned Patent Documents 1 to 4, and the description thereof will be omitted.

  The dotted lines 11a and 11b in FIG. 5 are the imaging ranges set in step S102, and the tube current modulation curve 153 corresponding to the body axis direction range indicated by the dotted lines 11a and 11b is calculated. In FIG. 5, 151 is a lower limit value of the tube current, 152 is an upper limit value of the tube current, 153 is a tube current change curve, 154 is a clipping portion based on the upper limit value, and 155 is a clipping portion based on the lower limit value.

  When the calculated tube current modulation curve 153 exceeds the allowable range determined by the lower limit value 151 or the upper limit value 152, the system control device 401 corrects the calculated value to the lower limit value 151 and the upper limit value 152. A tube current modulation curve 153 is created. Here, the upper limit value 152 and the lower limit value 151 of the tube current are ranges in which the tube current can be output stably and accurately, and are values determined depending on the performance of the high voltage generator of the X-ray CT apparatus 1 or the like. Alternatively, the value is determined by the operation of the operator.

  Next, the system control device 401 calculates an image quality index change curve 173 estimated to be obtained when scanning based on the calculated tube current modulation curve 153 and the input imaging conditions, It is displayed side by side with the scanogram image 11 (step S104; see FIG. 6). At this time, the portions 154 and 155 where the tube current is clipped, that is, the portion where the tube current is out of the allowable range may be characterized and displayed.

  By the process of step S104, the image quality index change curve 173 corresponding to the body axis direction range indicated by the dotted lines 11a and 11b of the scanogram image 11 of FIG. 6 is calculated. In FIG. 6, reference numeral 170 denotes a target image quality index value, 171 denotes a lower limit value of the allowable range of the image quality index value, 172 denotes an upper limit value of the allowable range of the image quality index value, 173 denotes an image quality index change curve, and A and B denote image quality index values. This is a part where the index value has deviated from the allowable range.

  In the example of FIG. 6, the image SD value is used as the image quality index value. The image SD value increases as the noise increases. In order to obtain good visibility, it is desirable that the image SD value is low. In the example of FIG. 6, it can be seen that the image quality is deteriorated in the portion A where the tube current amount is clipped by the upper limit value.

  Next, the system control apparatus 401 analyzes the image quality index change curve 173 and determines whether there is a portion where the target image quality is not achieved on the tube current clipping or the image quality index change curve 173. That is, it is determined whether or not the image quality index change curve 173 is within the range of the image quality index allowable value, and a portion that does not satisfy the image quality index allowable value, that is, the tube current deviates from the allowable range and clipping occurs. If there is a part, the process proceeds to step S106. If there is no portion where clipping has not occurred (step S105; no clipping), the process proceeds to step S107.

  Here, as shown in FIG. 7, a portion A or B that deviates from the allowable range of the image quality index change curve 173 may be designated by an operator's mouse operation or the like.

  If there is a part that does not achieve the target image quality (step S105; with clipping), or if a part of the image quality index change curve 173 is specified by the operator's mouse operation or the like, the process proceeds to step S106. In step S106, the system control apparatus 401 calculates and presents shooting condition correction candidates (condition items and correction values of the condition items).

  In the following description, it is assumed that the part A of the image quality index change curve 173 is selected by operating the mouse or the like.

As a first example of presenting correction candidates in step S106, the correction value of each condition item and the cautionary notes on the influence of the correction are displayed in a list as in the correction candidate 20 shown in FIG.
Specifically, in the correction candidate 20 in FIG. 8, the condition item “image slice thickness” presents the current value “0.625” and the correction value “1.25”, and “ "Axis resolution degradation" is presented. Similarly, for the condition item “scan speed”, the current value “0.35” and the correction value “0.5” are presented, and “scan time extension / motion artifact increase” is presented as a caution. .

  When the operator increases the image slice thickness from 0.625 mm to 1.25 mm by referring to the correction candidate 20 as shown in FIG. 8, the body axis resolution deteriorates, and the scan time is reduced to 0. In the case of correcting from .35 seconds to 0.5 seconds, it can be understood that there is an effect that artifacts due to movement of the subject increase. For example, in abdominal imaging, artifacts due to peristaltic movement of the intestinal tract are likely to occur, so that it is easier to determine that it is better to correct the slice thickness than the scan time.

Similarly, for each condition item such as “collimation thickness”, “reconstruction filter”, and “spiral pitch”, a current value, a correction value, and a caution are presented.
The calculation of the correction value will be described later.

  Further, FIG. 8 includes an item for the operator to manually set a correction value of an arbitrary condition item as “other (detailed setting)”. Details of the manual setting will be described later.

  When displaying the correction candidates 20, it is not necessary to display all the condition items, and only one or a plurality of condition items may be selectively displayed. In that case, for condition items other than the displayed condition items, correction candidates may be presented according to the operator's designation operation.

  Moreover, when displaying the correction candidate 20, you may make it show the correction candidate which changes two or more simultaneously. For example, by changing both the scanning speed related to the temporal resolution and the image slice thickness related to the spatial resolution, it is possible to avoid the major deterioration of either one. Further, by changing both the reconstruction filter related to the spatial resolution in the axial plane and the image slice thickness related to the spatial resolution in the slice direction (body axis direction), deterioration other than the spatial resolution can be avoided. .

  When a desired condition item is selected from the correction candidates 20 shown in FIG. 8 by the operator's operation (step S107; Yes), the process returns to step S102, and the system control device 401 sets the corrected value. The imaging conditions are reset, and the tube current modulation curve 153 and the image quality index change curve 173 are calculated again.

  Further, as a second example of the presentation of correction candidates, as in the correction candidate 21 shown in FIG. 9, for example, “image quality emphasis mode”, “shooting time emphasis mode”, “balance setting mode”, etc. The contents to be emphasized in shooting are set to be selectable, and the condition items corresponding to the selected mode are corrected and presented.

Here, as shown in FIG. 10, the correction priority 23 of each condition item of the photographing condition is preset for each mode.
In the example illustrated in FIG. 10, in “standard priority”, “collimation thickness” is priority “1”, “spiral pitch” is priority “2”, “scan speed” is priority “3”, and “image slice” “Thickness” is set to priority “4”, “tube voltage” is set to priority “5”, and “reconstruction filter” is set to priority “6”.

  In the “image quality emphasis mode”, “spiral pitch” has a priority “1”, “image slice thickness” has a priority “2”, “collimation thickness” has a priority “3”, and “scan speed” has a priority. “4” is set. Similarly, in the “shooting time emphasis mode”, “image slice thickness” has a priority “1”, “collimation thickness” has a priority “2”, “reconstruction filter” has a priority “3”, and “tube voltage”. Is set to priority “4”. In “balance setting mode”, “image slice thickness” is priority “1”, “collimation thickness” is priority “2”, and “spiral pitch” is priority “3”. “Scanning speed” is set to priority “4”.

  Any one of these modes may be set as a default, or may be set in advance by an operator's selection operation.

  In the case of correcting the shooting conditions for a plurality of condition items based on these priorities, first the correction candidates are presented based on the condition of priority “1”, and then the contents presented by the operator are displayed. When an operation for correction is performed (step S107; Yes), the process returns to step S102, and the shooting condition of the corrected condition item is corrected to the correction value presented. Thereafter, the system control device 401 again calculates the tube current modulation curve 153 and the image quality index change curve 173, and analyzes the image quality index change curve 173 (steps S103 to S105).

  At this stage, if there is still clipping, a correction value is calculated and displayed for the condition item of priority “2”.

  Further, as a third example of presenting correction candidates, an operator may select a condition item and input each condition item of shooting conditions as in the correction candidate 22 shown in FIG.

For example, when “other (detailed setting)” in the correction candidate 20 shown in FIG. 8 is selected (step S107; “other” is selected), a correction value input frame 22 as shown in FIG. 11 is displayed. A desired correction value may be input for the condition item selected by the operator.
In the example of FIG. 11, “helical pitch” and “image slice thickness” are selected, and correction values such as “13.0” and “1.00” are input in the correction value input frames.

Next, calculation of the correction value for each item of the shooting condition will be described.
First, the system control device 401, for a portion where clipping occurs in the tube current modulation curve, the tube current when clipping does not occur, that is, the calculated necessary tube current mA_n and the tube current mA_c limited by clipping. The ratio mA_r is calculated. The ratio mA_r is calculated by the following equation (1) and is called a correction ratio.

      mA_r = mA_n / mA_c (1)

  The correction value of each item of the shooting condition is calculated by multiplying the setting value of each condition item by the correction ratio mA_r calculated by the equation (1).

  For example, when correcting the image slice thickness, the corrected image slice thickness it_a is calculated by multiplying the correction ratio mA_r by the uncorrected image slice thickness it_b, as shown in the following equation (2).

      ith_a = ith_b * mA_r (2)

  Similarly, when correcting the scan speed, the corrected scan speed st_a is calculated by multiplying the correction ratio mA_r by the scan speed st_b before the correction, as shown in the following formula (3).

      st_a = st_b * mA_r (3)

  Similarly, when correcting the collimation thickness, the corrected collimation thickness cth_a is calculated by multiplying the correction ratio mA_r by the uncorrected collimation thickness cth_b as shown in the following equation (4).

      cth_a = cth_b * mA_r (4)

  Similarly, when correcting the helical pitch, as shown in the following formula (5), the corrected helical pitch hp_a is calculated by multiplying the correction ratio mA_r by the uncorrected helical pitch hp_b.

      hp_a = hp_b * mA_r (5)

  When correcting the reconstruction filter, a reference SD value for each settable reconstruction filter is obtained in advance, and the currently set reference SD value of the reconstruction filter and the corrected reconstruction filter reference A reconstructed filter after correction can be determined such that the square of the ratio to the SD value exceeds the correction ratio mA_r.

  Here, the reference SD value is an image SD value at the center of the image obtained by reconstruction using each reconstruction filter when the reference phantom is imaged under the reference imaging conditions. Reference imaging conditions are, for example, a tube voltage of 120 kV, a scanning speed of 1.0 s / rotation, a tube current of 200 mA, an image slice thickness of 2.5 mm, a collimation thickness of 2.5 mm, a helical pitch of 15.0, an image FOV of 250 mm, and a reference phantom. For example, a φ240 water phantom may be used.

  Similarly, when correcting the tube voltage, for example, a reference SD value is obtained in advance for each settable tube voltage, and the currently set tube voltage reference SD value and the corrected tube voltage reference SD are obtained. A tube voltage such that the square of the ratio to the value exceeds the correction ratio mA_r can be determined as the corrected tube voltage.

  The reference SD value in this case is, for example, a scanning speed of 1.0 s / rotation, a tube current of 200 mA, an image slice thickness of 2.5 mm, a collimation thickness of 2.5 mm, a reconstruction filter F34, a helical pitch of 15. The image SD may be 0 and the image FOV is 250 mm, and the image SD value at the center of the reconstructed image obtained by photographing a reference phantom such as a φ240 water phantom, for example, may be indicated at each settable voltage.

  When the shooting condition is not corrected, or when the image quality index change curve 173 according to the corrected shooting condition is confirmed and no further correction is performed (step S107; No), the system control device 401 is set. Based on the tube current modulation curve 153 calculated based on the imaging conditions and the target image quality, the main imaging process of the subject 6 is executed (step S108).

  As described above, in the X-ray CT apparatus of the present embodiment, the system control apparatus 401 uses the tube current modulation curve 153 supplied to the X-ray tube 201 based on the imaging conditions and the target image quality set by the operator. And an image quality index change curve 173 is calculated from the calculated tube current modulation curve 153 and displayed. Further, the system control device 401 analyzes the image quality index change curve 173 and determines whether there is a clipping of the tube current or whether there is a portion that deviates from the allowable range of the target image quality. When there is a part that deviates from the allowable range of the clipping of the tube current or the target image quality, the system control apparatus 401 calculates and presents a correction candidate for the imaging condition for achieving the target image quality.

  Therefore, even when the tube current amount calculated from the shooting conditions set by the operator and the target image quality exceeds the allowable range, correction candidates for the shooting conditions are presented, so that the operator can easily perform the shooting condition setting operation. And it becomes possible to carry out quickly. Further, it is possible to confirm the image quality in advance by referring to the image quality index change curve 173 before photographing.

In addition, you can select a shooting condition from the suggested correction candidates and select a new shooting condition or keep the original shooting condition, which enables flexible operation for each shooting. it can.
In addition, it is possible to designate an arbitrary part of the image quality index change curve 173 and present a correction candidate for the imaging condition in that part, so that the interest is low as it is added to the imaging range simply to grasp the position of the target part. The image quality of only the region of interest can be improved without intentionally changing the imaging conditions for the region, and the imaging quality can be improved.

  Furthermore, since the priority order of the condition items to be corrected among the respective condition items of the shooting conditions is determined in advance, the correction value can be accurately calculated even when correcting a plurality of condition items. In addition, since it is possible to select a mode that is important for imaging, more flexible imaging conditions can be set according to the inspection content.

  The preferred embodiment of the X-ray CT apparatus according to the present invention has been described above, but the present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, the gantry type X-ray CT apparatus has been described, but a C-arm type X-ray CT apparatus may be used. Moreover, the example of presentation of the correction candidate and the example of the correction value in the above-described embodiment are merely examples, and other correction values may be presented according to the examination contents and the photographing contents. Similarly, the method of giving priority, the contents of modes, the method of giving priority in each mode, and the like can be changed as needed. In addition, it is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea disclosed in the present application, and these naturally belong to the technical scope of the present invention. It is understood.

DESCRIPTION OF SYMBOLS 1 ... X-ray CT apparatus 2 ... Scanner 3 ... Sleeper 4 ... Operation desk 5 ... Top plate 6 ... Test subject 7. ···· Display device 8 ··· Operating device 201 ··· X-ray tube
205: X-ray detector 401 ... System control device 402 ... Image reconstruction device 404 ... Storage device 11 ... Scanogram image 151 ... Upper limit value of tube current 152 ... Tube Lower limit value of current 153... Tube current modulation curve 154, 155... Clipping portion of tube current 17... Display frame of image quality index change curve 170... Target image quality 171. Value 172 ... Lower limit value of image quality index value 173 ... Image quality index change curve 20 ... Correction candidate list (first example)
21... Correction candidate list (second example)
22 .... Correction value input frame 23 ... Setting example of modification priority by mode

Claims (6)

X-ray CT that calculates a tube current amount to be supplied to the X-ray tube based on the set imaging conditions and target image quality, and performs X-ray imaging of the subject based on the calculated tube current amount and the imaging conditions In the device
Determination means for determining whether or not the tube current amount deviates from a predetermined allowable range;
Correction candidate presenting means for presenting correction candidates for the shooting conditions for achieving the target image quality when it is determined by the determining means to deviate from the allowable range;
An X-ray CT apparatus comprising: An image quality index value display means for calculating and displaying a change curve of the image quality index value obtained based on the tube current amount and the imaging conditions;
Select whether to set one shooting condition selected from one or more correction candidates presented by the correction candidate presenting means as a new shooting condition or to maintain the original shooting condition Selecting means for
2. The X-ray CT apparatus according to claim 1, wherein the tube current amount supplied to the X-ray tube is calculated again based on the imaging condition selected by the selection means and the target image quality. An image quality index value display means for calculating and displaying a change curve of the image quality index value obtained based on the tube current amount and the imaging conditions;
Designating means for designating an arbitrary part on the change curve of the image quality index value displayed by the image quality index value display means,
The correction candidate presenting means includes
The X-ray CT apparatus according to claim 1, wherein correction candidates of imaging conditions for improving an image quality index value at a site specified by the specifying unit are presented.   The X-ray CT apparatus according to claim 1, wherein the correction candidate presenting unit presents a corrected value of the imaging condition and an influence of the correction.   The X-ray CT apparatus according to claim 1, wherein the correction candidate presenting unit presents correction values of condition items in order of a predetermined priority among the condition items of the imaging conditions. It further comprises a mode selection means for selecting contents important for photographing,
The X-ray imaging apparatus according to claim 1, wherein the correction candidate presenting unit presents a correction value for a condition item corresponding to a mode selected by the mode selection unit among the imaging conditions.

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