JP4240199B2 - Operation console, X-ray CT apparatus, and control method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an operation console, an X-ray CT apparatus, and a control method thereof.
[0002]
[Prior art]
Conventionally, in fields such as CT and MRI, there is an inspection method for inspecting blood flow by injecting a contrast medium into an inspection site of a subject and obtaining tomographic images of the inspection site in time series. For example, in CT, one position to perform scanning (processing to irradiate X-rays and obtain projection data of an irradiation target) is determined at an examination site (a site where a contrast medium is injected and blood flow is examined). A process (scan) for irradiating the scan position with X-rays and obtaining an X-ray tomographic image at the one scan position is performed a plurality of times (such a test for performing a plurality of scans at one scan position). (Hereinafter referred to as perfusion CT). As a result, the projection data of the one scan position can be obtained in time series. By referring to the X-ray tomogram generated based on these projection data, the flow of the contrast medium can be referred to as the blood flow as it is in time series. I can do it.
[0003]
In general, a technique for optimizing the X-ray dose has been proposed previously (see, for example, Patent Document 1).
[0004]
[Patent Document 1]
JP 2001-43993 A
[0005]
[Problems to be solved by the invention]
Since the perfusion CT repeatedly scans the same scan position, the amount of exposure with respect to this scan position is large. Therefore, it is preferable that the X-ray dose is as small as possible. However, if the X-ray dose is too small, the resulting X-ray tomogram contains a lot of noise. Therefore, it is preferable to optimize the X-ray dose used for the scan in this case.
[0006]
The present invention has been made in view of such a problem, and an object thereof is to optimize the X-ray dose used when scanning the same scan position a plurality of times.
[0007]
[Means for Solving the Problems]
In order to achieve the object of the present invention, for example, an operation console of the present invention comprises the following arrangement.
[0008]
That is, an operation console that transmits an instruction to perform scanning to a gantry device that scans a subject, and receives projection data at a plurality of scan positions of the subject obtained by the gantry device based on the instruction,
Image reconstruction means for generating an X-ray tomographic image for each scan position by performing image reconstruction processing on the received projection data for each scan position;
Instructing means for indicating a target scan position to be inspected among the plurality of scan positions;
A control value for controlling the amount of X-rays used for scanning at the target scan position when the target scan position of the subject instructed by the instruction unit is continuously scanned a plurality of times. Calculating means for obtaining using an X-ray tomographic image generated by the image reconstruction means based on projection data at a scan position of interest;
An instruction to perform a scan performed by irradiating the target scan position with an amount of X-rays based on a control value obtained by the calculation means is transmitted to the gantry apparatus.
[0009]
In order to achieve the object of the present invention, for example, an X-ray CT apparatus of the present invention comprises the following arrangement.
[0010]
That is, a gantry device that scans a subject,
An X-ray CT apparatus comprising an operation console that transmits an instruction to cause the gantry apparatus to perform scanning and receives projection data at a plurality of scan positions of the subject obtained by the gantry apparatus based on the instruction. And
Image reconstruction means for generating an X-ray tomographic image for each scan position by performing image reconstruction processing on the received projection data for each scan position;
Instructing means for indicating a target scan position to be inspected among the plurality of scan positions;
A control value for controlling the amount of X-rays used for scanning at the target scan position when the target scan position of the subject instructed by the instruction unit is continuously scanned a plurality of times. Calculating means for obtaining using an X-ray tomographic image generated by the image reconstruction means based on projection data at a scan position of interest;
An instruction to perform a scan performed by irradiating the target scan position with an amount of X-rays based on a control value obtained by the calculation means is transmitted to the gantry apparatus.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail according to preferred embodiments with reference to the accompanying drawings.
[0012]
FIG. 1 is a block diagram of the X-ray CT system of this embodiment. As shown in the figure, the present system includes a gantry apparatus 100 that integrally attaches an X-ray irradiation to a subject and an X-ray detection mechanism for detecting X-rays transmitted through the subject, and various operations on the gantry apparatus 100. The operation console 200 is configured to perform setting and reconstruct and display an X-ray tomogram based on data output from the gantry apparatus 100.
[0013]
The gantry apparatus 100 has the following configuration including the main controller 1 that controls the entire system.
[0014]
2 is an interface for communicating with the operation console 200, and 3 has a cavity for transporting a subject (patient) lying on the table 12 (hereinafter also referred to as z-axis in a direction perpendicular to the drawing). The gantry includes an X-ray tube 4 as an X-ray generation source driven and controlled by the X-ray tube controller 5, a collimator 6 having a slit for defining an X-ray irradiation range, and an X-ray of the collimator 6. A motor 7a that is a motor for adjusting the slit width that defines the irradiation range is provided. The driving of the motor 7a is controlled by the collimator controller 7.
[0015]
The gantry 3 also includes an X-ray detector 8 that detects X-rays that have passed through the subject, and a data collector 9 that collects projection data obtained from the transmitted X-rays obtained by the X-ray detector 8. The X-ray tube 4 and the collimator 6 and the X-ray detection unit 8 are provided at positions facing each other with the cavity portion sandwiched therebetween, that is, with the subject sandwiched therebetween, and rotate around the gantry 3 while maintaining the relationship therebetween. It comes to move. This rotation is performed by the rotary motor 10 driven by a drive signal from the motor controller 11. The table 12 on which the subject is placed is transported in the z-axis direction, and is driven by the table motor 13. The driving of the table motor 13 is controlled by the table motor controller 14.
[0016]
The main controller 1 analyzes various commands received via the interface 2, and based on the analysis, the X-ray tube controller 5, collimator controller 7, motor controller 11, table motor controller 14, and data collection unit 9 On the other hand, various control signals are output. The main controller 1 also performs a process of sending the projection data collected by the data collection unit 9 to the operation console 200 via the interface 2.
[0017]
The operation console 200 is a so-called workstation, and includes a CPU 51 that controls the entire apparatus, a ROM 52 that stores a boot program, and a RAM 53 that functions as a main storage device as shown in the figure.
[0018]
The HDD 54 is a hard disk device for giving various instructions to the gantry apparatus 100 in addition to the OS and scan control program, and for reconstructing an X-ray tomogram based on data received from the gantry apparatus 100. An image reconstruction program is stored. The VRAM 55 is a memory for developing image data to be displayed, and can be displayed on the CRT 56 by developing the image data or the like here. Reference numerals 57 and 58 denote a keyboard and a mouse for performing various settings. Reference numeral 59 denotes an interface for communicating with the gantry apparatus 100.
[0019]
Using the X-ray CT system having the above-described configuration, when the examination site is the head of the subject, one scan position (examination scan position) is determined on the head, and the scan position is continuously detected. In the following, a process for controlling the amount of X-rays irradiated by the X-ray tube 4 when performing a process of performing multiple scans (perfusion CT) will be described.
[0020]
First, before performing perfusion CT, as is well known, in order to determine the inspection scan position on the head, it is necessary to perform a scan (pre-scan) at each scan position on the head using the gantry device 100. is there. Therefore, pre-scanning is performed by a known method using the gantry apparatus 100, and projection data at each scanning position is collected.
[0021]
The collected projection data at each scan position is sent from the data collection unit 9 to the operation console 200 via the data input I / F 60. The CPU 51 of the operation console 200 executes an image reconstruction program loaded from the HDD 54 to the RAM 53, performs image reconstruction processing on the projection data sent at each scan position, and generates an X-ray tomogram at each scan position. To do. The generated X-ray tomographic image at each scan position is sent to the VRAM 55 and displayed on the display screen of the CRT 56. Each generated X-ray tomogram is also held in the RAM 53.
[0022]
An operator of the operation console 200 determines a scan position to be inspected with reference to the plurality of X-ray tomographic images displayed on the display screen of the CRT 56, that is, the inspection scan position. This inspection scan position is a scan position for obtaining an X-ray tomographic image to be viewed in order to inject a contrast medium into the head and inspect blood flow in the head.
[0023]
Then, an instruction to perform perfusion CT at the determined inspection scan position is transmitted to the gantry apparatus 100 using the keyboard 57 and the mouse 58, and the operation console 200 further irradiates from the X-ray tube 4 when performing this perfusion CT. A control value for controlling the X-ray dose is determined.
[0024]
The X-ray dose irradiated from the X-ray tube 4 is controlled by a current flowing through the X-ray tube 4 (hereinafter referred to as tube current or mA), and an auto mA function (automatic tube current control function) is used as a function for controlling the tube current. The X-ray CT system is conventionally equipped as a standard.
[0025]
Conventionally, this auto mA function irradiates a subject with X-rays at a predetermined X-ray dose from a predetermined direction, for example, by fixing the gantry angle to 0 degree and scanning the subject. The optimum tube current value is obtained using the obtained projection data and the projection data obtained by scanning the subject with the angle of the gantry fixed at 90 degrees.
[0026]
In the present embodiment, the auto mA function is performed using a control value for controlling the X-ray dose emitted from the X-ray tube 4 when performing perfusion CT using the X-ray tomogram obtained by the pre-scan, that is, the tube current. Apply to desired process. Hereinafter, the auto mA function performed by the X-ray CT system of the present embodiment will be described below.
[0027]
FIG. 2 is a diagram illustrating a process for determining a tube current using an X-ray tomographic image at an inspection scan position. First, the operation console 200 obtains a result (graph) 210 obtained by adding the CT value corresponding to each pixel constituting the X-ray tomographic image at the inspection scan position for each row, and holds it in the RAM 53. In the graph 210, the vertical axis represents the total CT value for each row, and the horizontal axis represents the number (row number) assigned to each row.
[0028]
Similarly, a result (graph) 220 obtained by adding CT values for each column is obtained and stored in the RAM 53. In the graph 220, the vertical axis represents the total CT value for each column, and the horizontal axis represents the number (row number) assigned to each column.
[0029]
In addition, before the CT value is added for each row and column, in order to make all the CT values positive, a minimum value of -1000, which is the minimum CT value, is added in advance to all the CT values. Keep it.
[0030]
Here, the area S of one of the regions 201 and 202 is obtained. In other words, this is obtained by adding CT values corresponding to the pixels constituting the X-ray tomographic image to all the pixels. Therefore, since the area of the region 201 and the area of the region 202 are the same, one of the areas is obtained and this is set as S.
[0031]
Next, when the cross section of the head is regarded as an ellipse (in FIG. 2, it is regarded as an ellipse having a major axis in the row direction and a minor axis in the column direction), the ratio R (that is, the ellipticity) of the major axis and minor axis of this ellipse is Ask. This is equivalent to obtaining the ratio of the total CT value r1 of the columns near the major axis of the ellipse and the total r2 of the CT values of the rows near the minor axis in the graphs 210 and 220.
[0032]
Here, as a method for obtaining r1, for example, as shown in FIG. 3, the sum of the CT values of 49 columns on the left and 50 columns on the right (100 columns in total) with the center column as the center is added. Ask for. Note that it may be 50 columns left and 49 columns right centered on the center column.
[0033]
Similarly, for example, as shown in FIG. 3, the method of obtaining r2 is obtained by adding all the sums of CT values of 49 columns left and 50 columns right (100 columns in total) with the center column as the center. . Note that it may be 50 columns left and 49 columns right centered on the center column.
[0034]
As a result, r1 and r2 can be obtained, and the ellipticity R can be obtained as R = r1 / r2.
[0035]
Next, a method for calculating the tube current using the above S and R will be described below. The tube current can be calculated based on the ratio between the image SD and the target SD (image quality level required for the X-ray tomogram).
[0036]
In general, image noise in an X-ray CT system is expressed as CT value variation (image SD) when a homogeneous material is imaged. The smaller the value of the image SD, the higher the quality of the tomographic image, and the larger the value of the image SD. First, a method for obtaining the image SD will be described.
[0037]
The image SD varies depending on the area S and the ellipticity R. Therefore, the image SD can be obtained by using the area S and the ellipticity R obtained above. The image SD (σ _px ) of the area having the area S can be obtained according to the following equation.
[0038]
ρ _px = α + β × S + γ × S ²
Here, α, β, and γ are predetermined constants. Further, the SD ratio k of the region having the ellipticity R can be obtained by the following equation.
[0039]
k = A + B × R ²
Here, A and B are constants obtained in advance. Using the above ρ _px and k, an image SD (ρ ′ _px ) for a region having an area S and an ellipticity R is obtained as follows.
[0040]
ρ ' _px = ρ _px × k
Next, a method for obtaining the target SD will be described. The target SD is determined based on the slice thickness at the time of performing perfusion CT and the examination site (head in this embodiment). Specifically, it is determined with reference to the table shown in FIG. FIG. 4 is a diagram showing an example of a table used when setting the target SD. The table is stored in the HDD 54 and loaded into the RAM 53 as necessary.
[0041]
For example, before performing perfusion CT, the operator uses the keyboard 57 and the mouse 58 to set IQ as a recommended mode when the examination site is the head, the slice thickness is 10 mm, and the mode is high quality. Then, the CPU 51 refers to the table shown in the figure and determines the set value of the target SD as 2.0. In the present embodiment, the slice thickness and mode used in the perfusion CT are the slice thickness and mode set when pre-scanning is performed. If the determined target SD is ρ _target , the finally obtained tube current value can be obtained based on the following equation.
[0042]
mA = (mA _reference × tf) / (ρ ′ _px / ρ _target ) ² Here, mA _reference is the tube current passed through the X-ray tube 4 during the pre-scan, and tf is 10 / (slice thickness) ) Is the calculated value.
[0043]
With the above processing, the tube current that flows through the X-ray tube 4 when performing perfusion CT can be obtained. The obtained tube current value is transmitted to the main controller 1 of the gantry apparatus 100 via the I / F 59 and I / F 2 together with the scan plan (slice thickness, setting items such as mode) for performing the perfusion CT. The main controller 1 of the gantry apparatus 100 sends the received tube current value to the X-ray tube controller 5, and the X-ray tube controller 5 passes the tube current according to the received tube current value to the X-ray tube 4. As a result, an optimized amount of X-rays is emitted from the X-ray tube 4, and the amount of exposure to the subject can be suppressed while suppressing noise in the obtained X-ray tomographic image.
[0044]
FIGS. 5 and 6 are flowcharts of the processing for determining the tube current value and obtaining the X-ray tomographic image based on the calculated tube current as described above.
[0045]
FIG. 5 is a flowchart of main processing performed by each of the operation console 200 and the gantry apparatus 100 when performing perfusion CT. 5, first, an input of a pre-scan plan using the keyboard 57 and the mouse 58 is received from the operator of the operation console 200 (step S701). This pre-scan plan includes the examination site, tube current, slice thickness, etc. of the subject to be pre-scanned. Next, the inputted pre-can plan is transmitted to the gantry apparatus 100 (step S702). The gantry apparatus 100 receives the pre-scan plan transmitted from the operation console 200 (step S751), performs pre-scan based on the received pre-can plan, collects projection data at each slice position, and transmits it to the operation console 200. (Step S752). The operation console 200 receives the projection data at each scan position transmitted from the gantry apparatus 100 (step S703), and generates an X-ray tomogram at each scan position by image reconstruction processing (step S704).
[0046]
Then, an input of the inspection scan position using the keyboard 57 and the mouse 58 is received from the operator (step S705). Next, the tube current value calculation process is performed (step S706). FIG. 6 is a flowchart showing details of the processing in step S706.
[0047]
In FIG. 6, first, the sum of CT values corresponding to the pixels constituting the X-ray tomographic image at the examination scan position held in the RAM 53 is obtained as the area S (step S801). Next, when the cross section of the head is regarded as an ellipse, the sum r1 of the CT values of the columns near the major axis and the sum r2 of the CT values of the rows near the minor axis are obtained (step S802). Then, the ellipticity R is obtained using the obtained r1 and r2 (step S803).
[0048]
Next, an image SD (ρ _px ) of the region having the area S is obtained using the area S (step S804), and further, the SD ratio (k) of the region having the ellipticity R is obtained using the ellipticity R (step S804). S805).
[0049]
Then, using the image SD (ρ _px ) obtained in step S804 and the SD ratio (k) obtained in step S805, an image SD (ρ ′ _px ) of an area having an area S and an ellipticity R is obtained (step S806). ). Next, the target SD is specified by referring to the examination site, slice thickness, mode, and the table shown in FIG. 4 which are the inputs of the pre-scan plan (step S807). The process in step S807 may be performed when the pre-scan plan in step S701 is input.
[0050]
Next, a tube current value (mA) is obtained using the image SD (ρ ′ _px ) obtained in step S806 and the target SD (ρ _target ) specified in step S807 (step S808).
[0051]
Returning to FIG. 7, a scan plan for perfusion CT is input using the keyboard 57 and mouse 58 (step S707), and the scan includes the inspection scan position input in step S705 and the tube current value calculated in step S706. The plan is transmitted to the gantry apparatus 100 (step S708). The gantry apparatus 100 receives the scan plan transmitted from the operation console 200 (step S753), and performs a perfusion CT scan based on the received scan plan (step S754). At this time, the gantry apparatus 100 sends the tube current value included in the received scan plan to the X-ray controller 5 and controls the tube current based on the tube current value to flow through the X-ray tube 4. As a result, the X-ray tube 4 emits X-rays based on the controlled tube current.
[0052]
In step S754, the gantry apparatus 100 transmits projection data to the operation console 200 while scanning the inspection scan position. The operation console 200 receives the projection data transmitted from the gantry apparatus 100 (step S709). Then, the operation console 200 generates an X-ray tomogram from the received projection data by performing image reconstruction, and displays it on the CRT 56 (step S710).
[0053]
Another object of the present invention is to supply a storage medium (or recording medium) in which a program code of software that realizes the functions of the above-described embodiments is recorded to a system or apparatus, and to perform a computer (or CPU or CPU) of the system or apparatus. (MPU) can also be realized by reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read out by the computer (operation console), not only the functions of the above-described embodiments are realized, but also an operating system running on the computer based on the instruction of the program code ( OS) etc. perform part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.
[0054]
When the present invention is applied to the above-described storage medium, the storage medium stores program codes corresponding to the parts described above (part or all of the flowcharts shown in FIGS. 5 and / or 6). Become.
[0055]
As a storage medium for storing such a program code, for example, a floppy (registered trademark) disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used. Furthermore, it may be downloaded via a medium called a network (for example, the Internet).
[0056]
【The invention's effect】
As described above, according to the present invention, it is possible to optimize the X-ray dose used when the same scan position is scanned a plurality of times.
[Brief description of the drawings]
FIG. 1 is a block diagram of an X-ray CT system in an embodiment of the present invention.
FIG. 2 is a diagram illustrating a process for determining a tube current using an X-ray tomographic image at an inspection scan position.
FIG. 3 is a diagram illustrating a process for obtaining the sum of CT values near the major axis or the sum of CT values near the minor axis.
FIG. 4 is a diagram illustrating an example of a table used when setting a target SD.
FIG. 5 is a flowchart of processing performed by each of the operation console 200 and the gantry apparatus 100 when performing perfusion CT.
FIG. 6 is a flowchart showing details of processing in step S706.

Claims (7)

Transmitting means for transmitting an instruction to cause the gantry apparatus for scanning the subject to perform scanning, receiving means for receiving projection data of the object obtained by scanning by the gantry apparatus based on the instruction, and the received projection An operation console including an image reconstruction unit that performs image reconstruction processing on data and generates an X-ray tomogram,
The transmission means includes an inspection scan instruction means for instructing a plurality of consecutive scans for the target scan position, a pre-scan instruction means for instructing a pre-scan performed before the plurality of consecutive scans for the target scan position, Including
The operation console gives a tube current value for controlling the amount of X-rays used for a plurality of consecutive scans with respect to the target scan position, instructed by the examination scan instruction means, to the projection data obtained by the pre-scan. Calculation obtained by an automatic tube current control mechanism using the result of adding CT values corresponding to each pixel of the X-ray tomographic image at the target scan position obtained in the image reconstruction process for each row and the result of adding for each column An operation console, further comprising means. The calculation means adds the CT value corresponding to each pixel of the X-ray tomographic image at the scan position of interest to the tube current value for each row, the result of adding for each column, and the X-ray tomographic image A first value representing a variation in CT value when imaging a homogeneous substance is obtained based on the area of
The ratio between the first value and the second value representing the image quality level required for the X-ray tomographic image determined by the slice thickness and the examination site of the examination scan and the X used for the pre-scan. 2. The operation console according to claim 1, wherein the operation console is obtained by using a tube current value for controlling the amount of the line. The plurality of consecutive scans with respect to the target scan position are scans for examining blood flow by obtaining a time series of X-ray tomographic images of the subject into which a contrast agent has been injected. Or the operation console of 2. 4. The pre-scan is a scan for determining the target scan position, and obtains projection data of a plurality of scan positions including the target scan position. The operation console described in the section. A gantry device for scanning a subject;
An X-ray CT apparatus comprising the operation console according to any one of claims 1 to 4. A program that causes a computer to function as the operation console according to claim 1 by being read by a computer. A computer-readable storage medium storing the program according to claim 6.

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