JP2003033346A - X-ray ct system and its control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray CT system that can set a tube current in addition to setting of an inspection region and a slice thickness according to inspection purposes so that dosage of a subject to be examined can be reduced. SOLUTION: The X-ray CT system that reorganizes a tomogram of the subject by irradiating X-ray from an X-ray tube and by detecting the transmitted X-ray is equipped with a first setting means 1002 which sets an inspection region of the subject, a second setting means 1003 which sets a slice thickness, a third setting means 1004 which sets inspection purposes, and a target SD selection means 1005 which selects a target image quality level of a tomogram which is reorganized on the basis of the content set by the first to third set means (1002 to 1004). The system is characterized to control dosage by the tube current that is calculated based on such target image quality level that is selected by the target SD selection means 1005.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an X-ray CT system for obtaining a tomographic image of a subject by X-ray irradiation and a control method therefor.

[0002]

2. Description of the Related Art An X-ray CT system irradiates a subject (patient) with X-rays, detects a difference in X-ray absorption rate of human tissues such as organs, blood, and gray matter with a detector, and detects this difference by a computer. By processing (reconstructing), an image (tomographic image) of the tomographic plane (slice plane) of the examination site is obtained.

A doctor diagnoses a medical condition of a patient based on a tomographic image of the patient at a predetermined examination site reconstructed by the X-ray CT system. Therefore, the reconstructed tomographic image is
It is necessary to be able to accurately identify the difference in X-ray absorption rate of human body tissue and to have an image quality suitable for the purpose of inspection. In order to obtain such image quality, reduction of image noise is indispensable.

Generally, image noise in an X-ray CT system is expressed as a variation in CT value (hereinafter referred to as Image SD) when a homogeneous substance is imaged, and I
The smaller the value of image SD, the higher the quality of the tomographic image, and the larger the value of Image SD, the lower the quality of the tomographic image. In order to reduce the image noise and obtain a high-quality tomographic image (that is, to reduce the Image SD), the transmitted X-ray dose that is transmitted through the subject and detected by the detector must be large. In order to obtain a sufficient transmitted X-ray dose in the detector, the amount of X-ray irradiation applied to the subject must be large.

However, it is not desirable to focus only on the improvement of the image quality and increase the X-ray irradiation amount for irradiating the subject, because the dose of the subject is increased. Therefore, in practice, the minimum X-ray that can secure the desired image quality is X-ray.
It is necessary to control the irradiation from a ray tube.

The X-ray dose emitted from the X-ray tube is controlled by a current flowing through the X-ray tube (hereinafter referred to as a tube current or mA). There is an auto mA function (automatic tube current control function) as a function of controlling the current, which is standardly equipped in the conventional X-ray CT system.

Auto m in the conventional X-ray CT system
The A function irradiates X-rays from a predetermined direction with a predetermined X-ray irradiation amount to a predetermined site for each subject in advance (irradiates X-rays in advance in this manner for each subject to obtain desired data. The sampling function is called the Scout function), and based on the transmission X-ray dose measurement result (basic data) at that time, the Image SD
While calculating the image quality level required for the tomographic image at the time of inspection (the target image quality level as the target is
Called SD) and set Image SD and Target
The tube current at the time of inspection is calculated based on the ratio with t SD.

At this time, the setting of Target SD is
It was decided based on the slice thickness at the time of the examination and the examination site.

FIG. 1 is a functional block diagram of an auto mA function in a conventional X-ray CT system.
Is a Scout extraction means having a Scout function, 102
Is the first setting means for setting the slice thickness, 103 is the second setting means for setting the examination region, 104 is the slice thickness set by the first setting means 102, and is set by the second setting means 103. Tar based on the inspection site
Target SD selecting means for selecting get SD,
Reference numeral 105 denotes the transmission X-ray dose measurement result from the Scout extraction means 101 and Ta from the Target SD selection means 104.
It is a tube current calculation means for calculating a tube current based on the rget SD.

FIG. 2 is a Target SD table used when selecting a Target SD in the conventional Target SD selecting means 104. In FIG. 2, 201 represents a section of an inspection site, and 202 represents a slice thickness. Reference numeral 203 is a Target SD for each examination site and each slice thickness.

[0011]

As described above, the Target SD table (FIG. 2) used in the conventional Target SD selecting means 104 is set on the basis of the slice thickness and the inspection site, and the purpose of the inspection is It did not correspond directly.

However, in reality, even if the same inspection site and the same slice thickness are used, the inspection purpose is diverse, and the required image quality level may differ depending on the inspection purpose. For example, in FIG. 2, when the examination site is the chest and the slice thickness is 10 mm, Target SD is set to 5.4, but when the examination purpose is lung cancer examination or bone mineral amount measurement, the image quality up to that is set. No level is required, and even if the image quality level is lowered, there is no problem in making a diagnosis. The same applies to other inspection parts, as in the conventional Target.
The division of the t SD table has a problem that the tube current is set high for a specific inspection purpose.

The present invention has been made to solve the above problems, and in order to reduce the exposure dose of a subject, it is possible to set the tube current not only according to the examination site and slice thickness but also according to the examination purpose. It is an object to provide a possible X-ray CT system.

[0014]

In order to solve such a problem, for example, an X-ray CT system of the present invention has the following configuration. That is, in an X-ray CT system that reconstructs a tomographic image of the subject by irradiating the subject with X-rays from an X-ray tube and detecting transmitted X-rays, first setting an examination site of the subject. And setting means, second setting means for setting the slice thickness, third setting means for setting the inspection purpose, and reconfiguration based on the contents set by the first to third setting means. Selecting means for selecting the target image quality level of the tomographic image, and the tube current calculated based on the target image quality level selected by the selecting means,
It is characterized by controlling the X-ray irradiation dose.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

(First Embodiment) In describing the X-ray CT system according to the first embodiment of the present invention in detail, the Scout function and the auto mA function of the X-ray CT system will be described.

1. Scout function The Scout function refers to a function that preliminarily collects basic data necessary for calculating the optimum tube current in the Z-axis direction (the body axis direction of a laterally-shaped subject) in the auto mA function for each subject in advance. The outline of the functions will be described below with reference to FIGS. 3 and 4.

In FIG. 3, reference numeral 301 denotes an X-ray tube for irradiating a subject 303 placed on a top plate (hereinafter referred to as a cradle) 304 with X-rays, and 302 denotes an X-ray tube 301 for irradiating the subject. A detector for detecting X-rays transmitted through the specimen 303 is shown. The X-ray tube 301 and the detector 302 are the subject 3
It is possible to move linearly in the directions indicated by the arrows 301a and 302a relative to 03. 301a,
The direction parallel to the direction indicated by the arrow of 302a (that is, the body axis direction of the subject 303) is called the Z-axis direction, and is indicated by 306.

Under such a structure, a predetermined tube current is passed through the X-ray tube 301, so that the direction of 0 degree (just above the object 303) is maintained with respect to the object 303 as shown in FIG. The X-ray of a predetermined X-ray dose is irradiated as it is, and the transmitted X-ray dose at that time is detected over the inspection site in the Z-axis direction. Reference numeral 305 denotes the transmitted X-ray dose at this time, and shows the transmitted X-ray dose distribution of the chest of the subject 303 when the horizontal axis represents the Z-axis direction position and the vertical axis represents the transmitted X-ray dose. S0-1, S0-
2, S0-3, ... Denote the Z-axis direction position, which is equal to the position of the slice plane at the time of inspection.

From the above, it becomes possible to obtain the transmitted X-ray dose in the 0 degree direction of the subject 303 (hereinafter, this measurement result is referred to as the Scout result (0 degree)).

Next, the X-ray tube 301 and the detector 302 are set to 9
By rotating the tube by 0 degree and passing a predetermined tube current through the X-ray tube in the same manner as in the case of the 0 degree direction, X-rays of a predetermined X-ray dose are given to the subject from the direction of 90 degrees (side surface of the subject 303). Irradiate
The transmitted X-ray dose at that time is detected over the inspection site in the Z-axis direction. In FIG. 4, reference numeral 405 denotes a transmitted X-ray dose distribution when the X-ray tube 301 and the detector 302 are rotated 90 degrees and the chest is irradiated with X-rays from the side surface of the subject 303. S
90-1, S90-2, S90-3, ... Denote Z-axis direction positions and are equal to the position of the slice plane at the time of inspection. It is to be noted that, in FIG. 4, the same reference numerals as those in FIG.

From the above, it is possible to obtain the transmitted X-ray dose in the 90-degree direction of the subject 303 over the examination site (hereinafter, such measurement result will be referred to as Scout result (90 degrees)).

As described above, before the inspection, the Sco
By irradiating a predetermined X-ray from a predetermined direction using the ut function and detecting the transmitted X-ray dose at that time, the Scout result (0 degree) and Sc that are different for each subject and inspection site can be obtained.
The out result (90 degrees) can be obtained.

2. Auto mA function The auto mA function is a function for reducing the exposure dose of the subject by optimizing the X-ray irradiation dose.

The auto mA function uses the Scout result (0 degree) and Sco obtained by the Scout function described above.
While the Image SD is calculated based on the ut result (90 degrees), the target image quality level (Target SD) is set, and the necessary image quality of each slice plane in the Z-axis direction is set based on the ratio between the Image SD and the Target SD. Find the tube current. The basic principle of the auto mA function will be described in detail below.

2-1 Calculation of Area Under Projection (1) Basic Formula of Transmitted X-ray Dose The thickness of the subject 303 is x, the X-ray absorption coefficient of the subject 303 is μ, and the X-ray irradiation from the X-ray tube 301 is performed. The amount is I ₀ ,
When the X-ray dose transmitted through the subject 303 (transmission X-ray dose) is I, I ₀ and I can be generally expressed by the following relational expressions.

[0027]

[Equation 1]

(2) Calculation of Area Under Projection If "-ln (I / I ₀ )" shown in the above equation 1 is calculated for each channel of the detector 302 based on the Scout result (0 degree), the result of FIG. Like In FIG. 5A, 3
03 'is the subject 3 at the Z-axis position (for example, S0-1)
5B shows a cross section of No. 03, and FIG.
The right side of Expression 1 when the linear irradiation amount is I ₀ is taken as the vertical axis, and the horizontal axis shows each channel of the detector 302. 5
01 is "-ln (I
/ I ₀ ) ”, which is called the projected area (0 degree) and can be expressed by the following equation.

[0029]

[Equation 2] Here, proj _{0deg i} is the Scout result (0
"-Ln (I / I ₀ )" of the i-th channel of the detector 402 based on

Similarly, Equation 3 is a side (90
Area under projection (90 degrees) when X-ray is irradiated from
Degree).

[0031]

[Equation 3]

The projected area (0 degrees) and projected area (90 degrees) are the Scout result (0 degree) and S, respectively.
It can be calculated for each position in the Z-axis direction based on the cout result (90 degrees).

2-2 Calculation of long-axis / short-axis ratio Based on the Scout result (0 degree), "-ln (I / I) shown in the above equation 1 in the central 100 channels of the detector 302.
₀ ) ”is calculated as shown in FIG. 6 (B). In FIG. 6 (A), 303 ′ is the position in the Z-axis direction (for example, S
0-1) shows a cross section of the subject 303, and FIG.
Is the right-hand side of Equation 1 on the vertical axis and the horizontal axis of the detector 302 on the horizontal axis of the detector 302, where I is the transmitted X-ray dose transmitted through the cross section 303 ′ and I ₀ is the X-ray irradiation dose emitted from the X-ray tube 301. Each channel is taken.

At this time, the area indicated by the arrow is the detector 30.
"-Ln (I / I
₀ ) ”, and the region is called a projected central area (0 degree). An equation for obtaining the projected central area (0 degree) is shown in Equation 4.

[0035]

[Equation 4]

Similarly, when "-ln (I / I ₀ )" in the central 100 channels of the detector 302 is calculated based on the Scout result (90 degrees), it becomes as shown in FIG. 6 (C). In FIG. 6A, reference numeral 303 ′ indicates a cross section of the subject 303 at the position S90-1 in the Z-axis direction.
(C) shows the transmitted X-ray dose transmitted through the cross section 303 ′ as I,
When the X-ray irradiation amount irradiated from the X-ray tube 301 is I ₀ , the right side of Expression 1 is the horizontal axis and the vertical axis is each channel of the detector 302.

At this time, the area indicated by the arrow is the detector 30.
"-Ln (I / I
₀ ) ”, and the region is referred to as a projected central area (90 degrees). An equation for obtaining the projected central area (90 degrees) is shown in Equation 5.

[0038]

[Equation 5]

The ratio between the above equation 4 and the above equation 5 is called the major axis / minor axis ratio and can be expressed by the following equation.

[0040]

[Equation 6]

2-3 General Relationship between Projected Area and Image SD Image SD is the variation in CT value when the subject 403 is imaged, and the projected area has the relationship as shown in FIG. Have.

FIG. 7 is a graph obtained by experimentally determining the change in Image SD when the area under projection is changed under a constant tube current. From Figure 7, Image
SD can be approximated by a quadratic expression shown in Expression 7 using the projected area.

[0043]

[Equation 7] Note that α, β, and γ are predetermined constants. Moreover, the same result can be obtained regardless of whether the projected area is the projected area (0 degree) or the projected area (90 degrees).

2-4 Major / Minor Axis Ratio and Image SD
Relationship with and obtain the Image SD when the major axis / minor axis ratio is 1.0, and the Image S when the value at this time is 1.0
When the ratio to D is SD ratio, when the major axis / minor axis ratio is changed while keeping the projected area constant, the major axis / minor axis ratio and SD ratio have the relationship shown in FIG.

In FIG. 8, the horizontal axis is the (major axis / short axis ratio) ² and the vertical axis is the SD ratio. Therefore,
SD ratio can be approximated by a linear expression shown in Expression 8.

[0046]

[Equation 8] In addition, A and B are predetermined constants.

From 2-1 to 2-4 above, the Image
It became clear that SD increases with an increase in the projected area, and even if the projected area is the same, as the major axis / minor axis ratio increases, the SD also increases. The following equation expresses this relationship.

[0048]

[Equation 9]

2-5 Relationship between Image SD and Tube Current From the above, it was shown that the Image SD can be calculated using the Scout result (0 degree) and the Scout result (90 degree). Therefore, if the Image SD when a predetermined tube current is applied is obtained in advance, Ta
The tube current mA required to obtain the Target SD can be calculated from the following formula from the ratio with the rget SD.

[0050]

[Equation 10] Here, the mAs _reference is the Scout result (0
Degree) and Scout result (90 degrees)
The tube current flowing in the wire tube 301. Further, the scan time means the X-ray tube 301 arranged on the gantry rotating part at the time of inspection.
And the time required for the detector 302 to make one rotation when the detector 302 makes a relative spiral motion around the subject 303.

From the above, if Target SD is set, the basic data (Scou
It was clarified that it is possible to find the required tube current at each position in the Z-axis direction based on the t result (0 degree) and the Scout result (90 degree).

3. Description of Embodiment of the Present Invention An X-ray CT system according to an embodiment of the present invention having the Scout function and the auto mA function will be described below.

FIG. 9 is a system configuration diagram of the X-ray CT system according to the first embodiment of the present invention.

As shown in FIG. 9, the system irradiates the subject (patient) with X-rays and transmits X-rays through the placed subject.
A gantry device 920 for detecting lines, various settings for the gantry device 920, an operation console 900 for reconstructing and displaying a tomographic image based on the data output from the gantry device 920, and a target object. A transport device 94 for placing a sample and transporting it inside the gantry device
It is composed of 0 and.

The gantry device shown at 920 has the following structure including the main controller 922 that controls the entire device.

Reference numeral 921 denotes an interface for communicating with the operation console 900, reference numeral 932 denotes a gantry rotating portion, inside which an X-ray tube 924 (driving controlled by the X-ray tube controller 923) and X-ray irradiation are provided. Collimator 927 that defines the range, adjustment of slit width that defines the X-ray irradiation range of collimator 927, and collimator 927
A collimator motor 926 for adjusting the position of the Z axis (direction perpendicular to the drawing) is provided. The driving of the collimator motor 926 is controlled by the collimator controller 925.

Further, in the gantry rotating part shown at 932,
A detection unit 931 that detects X-rays that have passed through the subject and a data collection unit 930 that collects the data obtained by the detection unit 931 are also provided. X-ray tube 924 and collimator 927
And the detecting section 931 are provided at positions facing each other with the cavity portion 933 interposed therebetween, and the gantry rotating section 932 rotates in a state where the relationship is maintained. This rotation is controlled by the drive signal from the motor controller 928 and the rotation speed of the rotation motor 9 is controlled in a predetermined control cycle.
29.

The main controller 922 uses the I / F 92
The various commands received via 1 are analyzed, and various control signals are output to the X-ray tube controller 923, the collimator controller 925, the motor controller 928, and the data collecting unit 930 based on the analysis. Further, the main controller 922 also performs a process of sending the data collected by the data collecting unit 930 to the operation console 900 via the I / F 921.

The operation console 900 is a so-called workstation, and as shown in the figure, it stores a CPU 905 which controls the entire apparatus, a boot program, and the like.
An OM 906, a RAM 907 functioning as a main storage device, and the following configuration are provided.

The HDD 908 is a hard disk device, and stores a program for giving various instructions to the OS and the gantry device 920 and reconstructing an X-ray tomographic image based on the data received from the gantry device 920. ing. The VRAM 901 is a memory that expands the image data to be displayed, and by expanding the image data or the like here, it can be displayed on the CRT 902. Reference numerals 903 and 904 are a keyboard and a mouse for making various settings. Reference numeral 909 is an interface for communicating with the gantry device 920.

In the above X-ray CT system, Scou
Programs for realizing the t function and the auto mA function are stored in the ROM 906 of the operation console and the ROM (not shown) of the main controller 922, and operate in conjunction with each other. The table of Target SD according to the first embodiment of the present invention is stored in the HDD 908 in the operation console.

FIG. 10 is a functional block diagram of the X-ray CT system according to the first embodiment of the present invention. 1
Reference numeral 001 denotes a Scout extracting means, which is a means for performing an inspection for obtaining the Scout result (0 degree) and the Scout result (90 degree) and extracting basic data for calculating the tube current. 1002 is a first setting means for setting a slice thickness, 1003 is a second setting means for setting an inspection region, 1004 is a third setting means for setting an inspection purpose, 1
Reference numeral 005 is Target according to the slice thickness, inspection site, and inspection purpose set by the first to third setting means.
The Target SD selection means which selects SD is shown.
Reference numeral 1006 is a tube current calculation means, which is the basic data extracted in 1001 and Target SD selected in 1005.
Is a means for obtaining the optimum tube current at each position in the Z-axis direction.

FIG. 11 is a diagram showing the function of the tube current calculating means 1006 in more detail. 1101 is a Scout result (0 degree) reading means, and Scout extraction means 100
Of the basic data extracted in 1, the Scout result (0
Degree) is a means for reading. Scout result (0
Degree) Scou read by the reading means 1101
The t result (0 degree) is sent to the projected area calculation means 1102, and the projected area (0 degree) is calculated based on Expression 2.

Of the Scout result (0 degree) read by the Scout result (0 degree) reading means 1101, the data of the central 100 channel is sent to the long axis / short axis ratio calculating means 1105, and based on the equation (4). Then, the projected central area (0 degree) is calculated.

Reference numeral 1104 denotes a Scout result (90 degrees) reading means, which is a means for reading the Scout result (90 degrees) out of the basic data extracted by the Scout extraction means 1001. Scout result (90 degrees) Scout result (90 degrees) read by the reading means 1104
Of the central 100 channels, the data of the central 100 channel is sent to the major axis / minor axis ratio calculation means 1105, and the central area under projection (90 degrees) is calculated based on Equation 5. Furthermore, from the above-mentioned projected central area (0 degree) and projected central area (90 degrees),
The long axis / short axis ratio is calculated using Equation 6.

1103 is a projected area calculation means 1102.
This is a means for obtaining the Image SD by using the equation 9 based on the projected area calculated in (1) and the long axis / short axis ratio calculated by the long axis / short axis ratio calculating means 1105.

Reference numeral 1106 denotes Target SD selecting means 1
A Target SD reading means for reading the Target SD selected in 002.
Targ read by the D reading means 1106
et SD is sent to the tube current calculation means 1107.

In the tube current calculation means 1107, the Image
Image SD calculated by SD calculation means 1103
And Target SD read by Target SD reading means, and slice thickness, mAs
_The tube current is calculated using Equation 10 based on the _reference . The tube current is calculated for each position in the Z-axis direction.

FIG. 12 is a diagram showing a list of Target SDs in the X-ray CT system according to the first embodiment of the present invention.

Reference numeral 1201 indicates an inspection site, 1203 indicates a slice thickness, and 1202 indicates an inspection purpose. Also, 1204 is each inspection site 1201, slice thickness 1203, inspection purpose 1
Target SD corresponding to 202 is shown. The reason why the Target SD is changed for each examination site is that the difference in the X-ray absorption rate of the human tissue is different for each examination site.
The reason why the Target SD is changed for each slice thickness is that the contrast of the peripheral portion of the reconstructed tomographic image tends to decrease as the slice thickness increases.

As a result, for example, when the examination site is the chest and the slice thickness is 10 mm, the Target SD for examination for the purpose of lung cancer examination is 5.6.

The item "Other" in the bottom line of the inspection purpose 1202 is an item to be selected when it does not correspond to any of the inspection purposes described above it, and can be changed as necessary. Is.

FIG. 13 is a flow chart showing details of the Target SD selection means 1002 in the X-ray CT system according to the first embodiment of the present invention.

The inspection region is recognized in step S1301, and the slice thickness is recognized in step S1302. Furthermore, in step S1303, the inspection purpose is recognized. If the recognized inspection purpose is one in step S1303, the process proceeds to step S1305 in step S1304, and the Target SD corresponding to the item recognized in steps S1301 to S1303 is stored in a table (see FIG. 1).
Extract from 2) and set to Target SD.

On the other hand, when there are a plurality of inspection purposes recognized in step S1303, step S1304 executes step S1304.
Proceed to 1306, Tar corresponding to each inspection purpose
Get SD is extracted from the table (FIG. 12). In step S1307, the smallest one (the one with the highest target image quality level) is selected from the plurality of Target SDs extracted in step S1307, and the value is selected as Target.
Set to t SD.

From the above, the optimum Tar for each inspection purpose is obtained.
It is possible to set the get SD, and even if multiple tests or diagnoses can be performed in one test, the optimum T
The target SD can be set. (Second Embodiment) In the first embodiment, T
I decided to have one table for the target SD,
It is also possible to prepare multiple types for each country or region. For example, it is possible to have tables in Asia, Europe, and the United States. In addition to different body types for each region, the required level of image quality is different for each region even if the inspection purpose is the same. Therefore, with the increase in the number of tables, it is possible to further reduce the exposure dose to the subject.

[0077]

As described above, according to the present invention,
It is possible to realize an X-ray CT system capable of setting a tube current in accordance with not only the examination site and slice thickness but also the examination purpose, and it is possible to reduce the radiation dose of the subject.

[Brief description of drawings]

FIG. 1 is a functional block diagram of an auto mA function in a conventional X-ray CT system.

FIG. 2 Target SD of a conventional X-ray CT system
It is a figure which shows the table used when selecting Target SD in a selection means.

FIG. 3 is a diagram for explaining a Scout function of a general X-ray CT system.

FIG. 4 is a diagram for explaining a Scout function of a general X-ray CT system.

FIG. 5 is a diagram showing a projected area calculated in a general X-ray CT system.

FIG. 6 is a diagram showing a central area under projection calculated in a general X-ray CT system.

FIG. 7 is a diagram showing a relationship between an imaged area under projection and an Image SD experimentally obtained in a general X-ray CT system.

FIG. 8 is a diagram showing a relationship between an experimentally obtained major axis / minor axis ratio and SD ratio in a general X-ray CT system.

FIG. 9 is a system configuration diagram of an X-ray CT system according to the first embodiment of the present invention.

FIG. 10 is a functional block diagram in the X-ray CT system according to the first embodiment of the present invention.

FIG. 11 is a diagram showing in further detail the function of the tube current calculation means in the X-ray CT system according to the first embodiment of the present invention.

FIG. 12 is a diagram showing a list of Target SDs in the X-ray CT system according to the first embodiment of the present invention.

FIG. 13 is a flowchart showing details of Target SD selection means in the X-ray CT system according to the first embodiment of the present invention.

Continued front page    (72) Inventor Tetsuya Horiuchi             127, 4-7 Asahigaoka, Hino City, Tokyo             GE Yokogawa Medical System Co., Ltd.             Within F-term (reference) 4C093 AA22 CA34 EA02 FA18 FA55

Claims (8)

[Claims] 1. An X-ray CT system for reconstructing a tomographic image of a subject by irradiating the subject with X-rays from an X-ray tube and detecting transmitted X-rays, wherein an examination site of the subject is set. First setting means for setting, second setting means for setting slice thickness, third setting means for setting an inspection purpose, and re-setting based on the contents set by the first to third setting means. Selecting means for selecting a target image quality level of the tomographic image to be constructed, wherein the X-ray irradiation dose is controlled by the tube current calculated based on the target image quality level selected by the selecting means. X-ray CT system to do. 2. The selecting means selects the highest target image quality level from a plurality of corresponding target image quality levels when there are a plurality of inspection purposes set by the third setting means. The X-ray CT system according to claim 1. 3. The X-ray CT system according to claim 2, wherein the target image quality level selected by the selection means is different for each region. 4. A control method in an X-ray CT system for reconstructing a tomographic image of a subject by irradiating the subject with X-rays from an X-ray tube and detecting transmitted X-rays. The first setting step for setting the inspection site of the, the second setting step for setting the slice thickness, the third setting step for setting the inspection purpose, and the first to third setting steps A step of selecting a target image quality level of the tomographic image to be reconstructed based on the contents, and controlling the X-ray irradiation dose by the tube current calculated based on the target image quality level selected in the selecting step. A method of controlling in an X-ray CT system, comprising: 5. The selecting step, when there are a plurality of inspection purposes set in the third setting step, selects the highest target image quality level from the corresponding plurality of target image quality levels. The control method in the X-ray CT system according to claim 4. 6. The control method in an X-ray CT system according to claim 5, wherein the target image quality level selected in the selection step is different for each region. 7. A storage medium storing a control program for realizing the control method according to claim 4 by a computer. 8. A control program for causing a computer to implement the control method according to claim 4.