JP2006110183A - Set up method of x-ray ct scan parameter, x-ray ct apparatus and helical scan method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an effective and clearly photography condition parameters such as a helical pitch and noise index independently to site and organ, respectively, to adjust/optimize recording conditions. <P>SOLUTION: The setting is carried out by displaying a scout image of subject, designating one or more area of body axis direction of the scout image by an operator, and graphically or key inputting the photography condition parameters such as the helical pitch and the noise index, independently by areas. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an X-ray CT (Computed Tomography) scan parameter setting method, an X-ray CT apparatus, and a helical scan method. More specifically, the present invention relates to an imaging condition parameter such as a helical pitch and a noise index independently for each region or organ. The present invention relates to an X-ray CT scan parameter setting method, an X-ray CT apparatus, and a helical scan method that can be set efficiently and easily.

  Conventionally, after completing input of scan parameters such as slice thickness, helical pitch, tube voltage, tube current, etc., if one reconstruction range is specified based on a scout image (scanogram image), the scan range is determined from the reconstruction range. There is known an X-ray CT apparatus that calculates and scans the scan range in a helical manner using the previously input scan parameters (see, for example, Patent Document 1).

JP-A-11-146871 ([0059] [0060] [0062])

The conventional X-ray CT apparatus has a problem that the setting operation is complicated when it is desired to set the helical pitch independently for each part or organ. In addition, there is a problem that noise index setting is not taken into consideration.
Therefore, an object of the present invention is to provide an X-ray CT scan parameter setting method, an X-ray CT apparatus, and a helical scan that can set parameters of imaging conditions such as a helical pitch and a noise index independently and efficiently for each part or organ. It is to provide a method.

In a first aspect, the present invention relates to a process of displaying a scout image of a subject, a process of an operator specifying one or more ranges in the body axis direction of the scout image, and an operator corresponding to the range. And setting a helical pitch by graphical input or key input. An X-ray CT scan parameter setting method is provided.
In the X-ray CT scan parameter setting method according to the first aspect, the operator specifies a range for each region or organ while referring to the displayed scout image, and then sets a helical pitch for the specified range. As a result, the helical pitch can be set efficiently and easily, independently for each part or organ, and the imaging conditions can be adjusted and optimized.

In a second aspect, the present invention relates to a process of displaying a scout image of a subject, a process of an operator specifying one or more ranges in the body axis direction of the scout image, and an operator corresponding to the range. And setting a noise index by graphical input or key input.
In the X-ray CT scan parameter setting method according to the second aspect, the operator designates a range for each region or organ while referring to the displayed scout image, and then sets a noise index for the designated range. As a result, the noise index can be set efficiently and easily independently for each part or organ, and the imaging conditions can be adjusted and optimized.

According to a third aspect, the present invention is the X-ray CT scan parameter setting method according to the first aspect, wherein the operator has a process of setting a noise index corresponding to the range by graphical input or key input. A characteristic X-ray CT scan parameter setting method is provided.
In the X-ray CT scan parameter setting method according to the third aspect, the operator designates a range for each part or organ while referring to the displayed scout image, and then sets a helical pitch and a noise index for the designated range. To do. Thereby, in addition to the first viewpoint, the helical pitch and the noise index can be set efficiently and easily for each part or organ independently, and the imaging conditions can be adjusted and optimized.

In a fourth aspect, the present invention provides an X-ray CT scan parameter setting method according to the first to third aspects, wherein an operator graphically inputs or inputs at least one of a tube voltage and a tube current corresponding to the range. An X-ray CT scan parameter setting method is provided.
In the X-ray CT scan parameter setting method according to the fourth aspect, the operator designates a range for each region or organ while referring to the displayed scout image, and then the helical pitch and / or noise index for the designated range. And at least one of tube voltage and tube current is set. Thereby, in addition to the first to third aspects, at least one of the tube voltage and the tube current can be set efficiently and easily independently for each part or organ, and the imaging conditions can be adjusted and optimized.

In a fifth aspect, the present invention provides an X-ray CT scan parameter setting method configured as described above, wherein an operator corresponds to the range, the slice thickness, the number of detector rows, the table speed, the number of tomographic images, the tomographic image interval, An X-ray CT scan parameter setting method comprising the step of setting at least one of table accelerations is provided.
In the X-ray CT scan parameter setting method according to the fifth aspect, in addition to the first to fourth aspects, the slice thickness, the number of detector rows, the table speed, the number of tomographic images, At least one of the tomographic image interval and table acceleration can be set, and the imaging conditions can be adjusted and optimized.

In a sixth aspect, the present invention has a process of setting one series of one or more groups in which the one range is a group in the X-ray CT scan parameter setting method of the first aspect. An X-ray CT scan parameter setting method is provided.
In the X-ray CT scan parameter setting method according to the sixth aspect, the operator defines one designated range as a group (a parameter group corresponding to one range) and a series of one or more groups. Set the chain). Thereby, in addition to the first aspect, the helical pitch can be collectively managed and the imaging conditions can be adjusted and optimized for a plurality of parts or organs.

In a seventh aspect, the present invention includes the step of setting one series of one or more groups, with the one range as one group, in the X-ray CT scan parameter setting method according to the second aspect. An X-ray CT scan parameter setting method is provided.
In the X-ray CT scan parameter setting method according to the seventh aspect, the operator defines one designated range as a group (a parameter group corresponding to one range), and a series of one or more groups. Set the chain). Thereby, in addition to the first viewpoint, the noise index can be collectively managed and the imaging conditions can be adjusted and optimized for a plurality of parts or organs.

In an eighth aspect, the present invention has a process of setting one series of one or more groups, wherein the one range is a group in the X-ray CT scan parameter setting method of the third aspect. An X-ray CT scan parameter setting method is provided.
In the X-ray CT scan parameter setting method according to the eighth aspect, the operator defines one designated range as a group (a parameter group corresponding to one range) and a series of one or more groups. Set the chain). Thereby, in addition to the third aspect, the helical pitch and the noise index can be collectively managed and the imaging conditions can be adjusted and optimized for a plurality of parts or organs.

In a ninth aspect, the present invention includes the step of setting one series of one or more groups, wherein the one range is a group in the X-ray CT scan parameter setting method of the fourth aspect. An X-ray CT scan parameter setting method is provided.
In the X-ray CT scan parameter setting method according to the ninth aspect described above, the operator designates one designated range as a group (a parameter group corresponding to one range) and a series of one or more groups. Set the chain). Thereby, in addition to the fourth viewpoint, the tube current and the tube voltage can be collectively managed for a plurality of parts or organs, and the imaging conditions can be adjusted and optimized.

In a tenth aspect, the present invention provides the X-ray CT scan parameter setting method according to the first to ninth aspects, wherein the one range is set corresponding to one organ or site. A CT scan parameter setting method is provided.
In the X-ray CT scan parameter setting method according to the tenth aspect, the operator sets one organ or part as one range. As a result, the helical pitch, noise index, tube current and tube voltage can be adjusted and optimized in organ units or site units.

In an eleventh aspect, the present invention provides an X-ray CT scan parameter setting method according to the first to tenth aspects, wherein a default value or a previous set value of at least one scan parameter is automatically set for the specified range. The present invention provides an X-ray CT scan parameter setting method characterized in that a setting value candidate is automatically set.
In the X-ray CT scan parameter setting method according to the eleventh aspect, when the operator designates one range, the default value or the previous set value corresponding to the range is automatically set as a set value candidate. Alternatively, when the previous set value is used as it is, there is an advantage that the setting work can be saved.

In a twelfth aspect, the present invention relates to the X-ray CT scan parameter setting method according to the first to eleventh aspects, wherein the X-ray CT scan is at the start or end of linear movement, during acceleration or deceleration in the middle. The present invention also provides an X-ray CT scan parameter setting method characterized by being a variable pitch helical scan or a variable speed helical scan for collecting data.
In the X-ray CT scan parameter setting method according to the twelfth aspect, the effects of the first to eleventh aspects can be obtained even in a variable pitch helical scan or a variable speed helical scan.

In a thirteenth aspect, the present invention relates to an X-ray tube, a detector, and at least one of the X-ray tube or the detector rotated around the object to be imaged, and both are linearly relative to the object to be imaged. X equipped with helical scanning means for collecting data while moving, scanning parameter setting means for an operator to set parameters for helical scanning, and image reconstruction means for reconstructing an image based on the collected data In the line CT apparatus, the parameter setting means displays a scout image of the subject, the operator designates one or more ranges in the body axis direction of the scout image, and sets a helical pitch corresponding to the range. X-ray characterized in that when graphical input or key input is performed, the input helical pitch is set as a scan parameter corresponding to the range. To provide a T devices.
In the X-ray CT apparatus according to the thirteenth aspect, the X-ray CT scan parameter setting method according to the first aspect can be suitably implemented.

In a fourteenth aspect, the present invention relates to an X-ray tube, a detector, and at least one of the X-ray tube or the detector that rotates around the object to be imaged and that both are linearly relative to the object to be imaged. X equipped with helical scanning means for collecting data while moving, scanning parameter setting means for an operator to set parameters for helical scanning, and image reconstruction means for reconstructing an image based on the collected data In the line CT apparatus, the parameter setting means displays a scout image of the subject, and the operator designates one or more ranges in the body axis direction of the scout image, and sets a noise index corresponding to the range. When graphical input or key input is performed, the input noise index is set as a scan parameter corresponding to the range. Providing that X-ray CT apparatus.
In the X-ray CT apparatus according to the fourteenth aspect, the X-ray CT scan parameter setting method according to the second aspect can be suitably implemented.

In a fifteenth aspect, the present invention provides the X-ray CT apparatus according to the thirteenth aspect, wherein the parameter setting means is configured to input noise when the operator graphically inputs or inputs a noise index corresponding to the range. An X-ray CT apparatus is provided in which an index is set as a scan parameter corresponding to the range.
In the X-ray CT apparatus according to the fifteenth aspect, the X-ray CT scan parameter setting method according to the third aspect can be suitably implemented.

In a sixteenth aspect, the present invention provides the X-ray CT apparatus according to the thirteenth to fifteenth aspects, wherein the parameter setting means graphically inputs at least one of a tube voltage and a tube current according to the range. Alternatively, the present invention provides an X-ray CT apparatus characterized by setting at least one of an input tube voltage and tube current as a scan parameter corresponding to the range when a key is input.
In the X-ray CT apparatus according to the sixteenth aspect, the X-ray CT scan parameter setting method according to the fourth aspect can be suitably implemented.

In an seventeenth aspect, the present invention provides the X-ray CT apparatus having the above-described configuration, wherein the parameter setting means is configured so that the operator corresponds to the range, the slice thickness, the number of detector rows, the table speed, the number of tomographic images, the tomographic image, When at least one of image interval and table acceleration is input, at least one of the input slice thickness, number of detector rows, table speed, number of tomographic images, tomographic image interval, and table acceleration is used as a scan parameter corresponding to the range. An X-ray CT apparatus characterized by setting is provided.
In the X-ray CT apparatus according to the seventeenth aspect, the X-ray CT scan parameter setting method according to the fifth aspect can be suitably implemented.

In an eighteenth aspect, the present invention provides the X-ray CT apparatus according to the thirteenth aspect, wherein the parameter setting means can set one series of one or more groups with the one range as one group. The helical scanning means provides an X-ray CT apparatus characterized in that, when execution of one series is instructed, helical scanning is continuously executed for groups belonging to the series.
In the X-ray CT apparatus according to the eighteenth aspect, the X-ray CT scan parameter setting method according to the sixth aspect can be suitably implemented.

In a nineteenth aspect, the present invention provides the X-ray CT apparatus according to the fourteenth aspect, wherein the parameter setting means can set one series of one or more groups, with the one range as one group. The helical scanning means provides an X-ray CT apparatus characterized in that, when execution of one series is instructed, helical scanning is continuously executed for groups belonging to the series.
In the X-ray CT apparatus according to the nineteenth aspect, the X-ray CT scan parameter setting method according to the seventh aspect can be suitably implemented.

In a twentieth aspect, the present invention provides the X-ray CT apparatus according to the fifteenth aspect, wherein the parameter setting means can set one series composed of one or more groups with the one range as one group. The helical scanning means provides an X-ray CT apparatus characterized in that, when execution of one series is instructed, helical scanning is continuously executed for groups belonging to the series.
In the X-ray CT apparatus according to the twentieth aspect, the X-ray CT scan parameter setting method according to the eighth aspect can be suitably implemented.

In a twenty-first aspect, the present invention provides the X-ray CT apparatus according to the sixteenth aspect, wherein the parameter setting means can set one series consisting of one or more groups with the one range as one group. The helical scanning means provides an X-ray CT apparatus characterized in that, when execution of one series is instructed, helical scanning is continuously executed for groups belonging to the series.
In the X-ray CT apparatus according to the twenty-first aspect, the X-ray CT scan parameter setting method according to the ninth aspect can be suitably implemented.

In a twenty-second aspect, the present invention provides the X-ray CT apparatus according to the thirteenth to twenty-first aspects, wherein the parameter setting means sets the one range corresponding to one organ or part. An X-ray CT apparatus is provided.
In the X-ray CT apparatus according to the twenty-second aspect, the X-ray CT scan parameter setting method according to the tenth aspect can be suitably implemented.

In a twenty-third aspect, the present invention provides the X-ray CT apparatus according to the thirteenth to twenty-second aspects, wherein the parameter setting means has a default value or a previous value of at least one scan parameter for the designated one range. Provided is an X-ray CT apparatus characterized by automatically setting a set value as a set value candidate.
In the X-ray CT apparatus according to the twenty-third aspect, the X-ray CT scan parameter setting method according to the eleventh aspect can be suitably implemented.

In a twenty-fourth aspect, the present invention provides the X-ray CT apparatus according to the thirteenth to twenty-third aspects, wherein the helical scanning means collects data at the start and end of linear movement and during acceleration or deceleration in the middle. An X-ray CT apparatus is provided that performs variable-pitch helical scanning or variable-speed helical scanning.
In the X-ray CT apparatus according to the twenty-fourth aspect, the X-ray CT scan parameter setting method according to the twelfth aspect can be suitably implemented.

In a twenty-fifth aspect, the present invention provides a helical scanning method characterized in that a plurality of ranges set with different helical pitches are helically scanned in order while changing the helical pitch.
In the helical scan method according to the twenty-fifth aspect, imaging can be performed with an optimal helical pitch for each part or organ.

In a twenty-sixth aspect, the present invention relates to an X-ray tube, a detector, and at least one of the X-ray tube or the detector that rotates around the object to be imaged and that both are linearly relative to the object to be imaged. X equipped with helical scanning means for collecting data while moving, scanning parameter setting means for an operator to set parameters for helical scanning, and image reconstruction means for reconstructing an image based on the collected data The X-ray CT apparatus is characterized in that the helical scanning means performs helical scanning while sequentially changing a helical pitch in a plurality of ranges in which different helical pitches are set.
In the X-ray CT apparatus according to the twenty-sixth aspect, the helical scan method according to the twenty-fifth aspect can be suitably implemented.

  According to the X-ray CT scan parameter setting method, the X-ray CT apparatus, and the helical scan method of the present invention, parameters of imaging conditions such as a helical pitch and a noise index can be set efficiently and easily for each part or organ independently. .

  Hereinafter, the present invention will be described in more detail with reference to embodiments shown in the drawings. Note that the present invention is not limited thereby.

FIG. 1 is a configuration block diagram of an X-ray CT apparatus 100 according to the first embodiment.
The X-ray CT apparatus 100 includes an operation console 1, a table apparatus 10, and a scanning gantry 20.

  The operation console 1 includes an input device 2 that receives input from an operator, a central processing unit 3 that executes image reconstruction processing, a data collection buffer 5 that collects projection data acquired by the scanning gantry 20, and a projection data. A display device 6 that displays the reconstructed tomographic image and a storage device 7 that stores programs, data, and X-ray tomographic images are provided. The display device 6 is a multi-screen display having two screens, a right screen and a left screen.

  The table device 10 includes a cradle 12 that puts a subject and puts it in and out of a bore (cavity) of the scanning gantry 20. The cradle 12 is moved up and down (y-axis direction) and linearly moved (z-axis direction) by a motor built in the table apparatus 10.

  The scanning gantry 20 includes an X-ray tube 21, an X-ray controller 22, a collimator 23, a multi-row X-ray detector 24, a DAS (Data Acquisition System) 25, and an X-ray tube around the body axis of the subject. A rotation controller 26 that rotates 21 and the like, a tilt controller 27 that performs control when the scanning gantry 20 is tilted forward or backward of the rotation axis, and a control controller 29 that exchanges control signals and the like with the operation console 1 and the bed apparatus 10. And a slip ring 30.

  The linear movement amount of the cradle 12 is counted by an encoder built in the table device 10, the controller 29 calculates the z-axis coordinate of the cradle 12 from the linear movement amount, and the z-axis coordinate is supplied to the DAS 25 via the slip ring 30. Sent.

  The projection data obtained by the multi-row X-ray detector 24 is AD-converted by the DAS 25, z-axis coordinates are added, and the data is transferred to the data acquisition buffer 5 via the slip ring 30.

  The central processing unit 3 performs preprocessing and image reconstruction processing on the projection data collected in the data collection buffer 5, generates a tomographic image, and displays the tomographic image on the display device 6.

FIG. 2 is an explanatory diagram of the X-ray tube 21 and the multi-row X-ray detector 24.
The X-ray tube 21 and the multi-row X-ray detector 24 rotate around the rotation center IC. The vertical direction is the y direction, the moving direction of the cradle 12 is the z direction, and the direction perpendicular to the y direction and the z direction is the x direction. When not tilting, the rotation plane of the X-ray tube 21 and the multi-row X-ray detector 24 is the xy plane.
The X-ray tube 21 generates an X-ray beam called an X-ray cone beam CB. When the central axis direction of the X-ray cone beam CB is parallel to the y direction, the view angle = 0 °.
The multi-row X-ray detector 24 has, for example, 64 detector rows. Each detector row has, for example, 1024 channels.

FIG. 3 is a flowchart showing an outline of the operation of the X-ray CT apparatus 100.
In step 1, a scout image of the subject is captured and displayed. The operator designates one or more ranges in the body axis direction of the scout image, and sets the scan parameters of the helical scan such as the helical pitch and noise index corresponding to the ranges by graphical input or key input. This process 1 will be described in detail later.

  In step 2, projection data is collected according to the set scan parameters. This process 2 will be described in detail later.

  In process 3, a tomographic image is reconstructed from the collected projection data, and the tomographic image is displayed on the display device 6. This process 3 will be described in detail later.

4 to 5 are flowcharts showing details of the helical scan parameter setting process (process 1).
In step A1 of FIG. 4, the central processing unit 3 displays the scan parameter setting screen shown in FIG. 6 on the right screen.
In Step A2, the operator clicks on a new patient on the scan parameter setting screen of FIG.

In step A3, the central processing unit 3 displays a patient information screen (Patient Information) and a protocol selection screen (Protocol Selection) shown in FIG. 7 on the right screen.
In step A4, the operator inputs the patient's weight and the like on the patient information screen of FIG.
In step A5, the operator clicks a portion to be photographed on the partial selection screen (Anatomical Selector) of the protocol selection screen in FIG. Here, for example, the chest is clicked.

In step A6, the central processing unit 3 pops up a protocol list screen (Protocol List) shown in FIG.
On the protocol list screen in FIG. 8, the operator clicks a desired protocol as shown in step A7, or clicks a scan type corresponding to the desired protocol as shown in step A8.

  When the operator clicks a desired protocol (for example, variable pitch (Vari-Pitch)) as shown in step A7, the central processing unit 3 deletes the protocol list screen and proceeds to step A21 in FIG.

  As shown in step A8, when the operator clicks a scan type corresponding to a desired protocol (for example, a scan type corresponding to a variable pitch (Vari-Pitch)), the process proceeds to step A9.

In step A9, the central processing unit 3 pops up a scan type setting screen (Select the desired Scan Type) shown in FIG.
On the scan type setting screen of FIG. 9, the operator selects a desired part and rotation time (Rotation Time) as shown in Step A10, or doubles the desired part as shown in Step A11. click.

  As shown in step A10, when the operator selects a desired part (for example, lung) and rotation time and is OK, the central processing unit 3 erases the scan type setting screen and returns to step A6.

When the operator double-clicks a desired part (for example, lung) as shown in step A11, the process proceeds to step A12.
In step A12, the central processing unit 3 pops up a scan parameter selection screen (Select the desired Parameters) shown in FIG. In this scan parameter selection screen, a default value or a previous set value is selected or set as a parameter value candidate.
In step A13, the operator clicks OK if the default value or the previously set value selected or set on the scan parameter selection screen in FIG. 10 is acceptable. To change the value, select or key in the desired value. For example, values are selected for slice thickness (Thickness), table speed (Speed), and helical pitch (Pitch). In addition, a noise index (Noise-Index), a start acceleration (Start Acceleration), an end acceleration (End Acceleration), and a part name (Title) are key-inputted. Then click OK. If OK is clicked, the central processing unit 3 erases the scan parameter selection screen and returns to step A9.

Each value needs to be set so that the relationship of “table speed (mm / rot)” / “actual width used in multi-row X-ray detector 24 in the slice direction (mm)” = “helical pitch” is satisfied. is there. In the above numerical example, “the actual use width (mm) of the multi-row X-ray detector 24 in the slice direction” = 64 rows × 0.625 mm: Since it is the default, 55 (mm / rot) / 40 (mm) = The relationship of 1.375 is established.
The noise index is a target value of the standard deviation (SD) of the pixel value of the tomographic image when the automatic tube current setting function (Auto mA) is used.

In step A21 shown in FIG. 5, the central processing unit 3 displays the scout scan screen shown in FIG. 12 on the right screen. In this scout scan screen, a default value or a previous set value is selected or set as a parameter value candidate.

In step A22, the operator clicks Accept if the default value or the previously set value selected or set on the slice scan screen of FIG. 12 is acceptable. If you want to change the value, select the desired item and key in the value. For example, if the lung is specified as a part, the general start location (Start Location) and end location (End Location) corresponding to the lung are set as candidates, but it ends to include the liver (Liver) Key in the position value. Then click Accept.

In step A23, the central processing unit 3 executes a scout scan. In other words, the X-ray tube 21 and the multi-row X-ray detector 24 are fixed so as to face each other in the horizontal direction (Scout Plane = 90), and the cradle 12 is linearly moved to emit X-rays, and scout data is obtained. collect. Then, a scout image (X-ray fluoroscopic image) is generated from the scout data, and the scout image is displayed on the left screen 6L of the display device 6 as shown in FIG. When, for example, a lung is designated as a part, the slice position from the general start slice position Ls to the end slice position Le corresponding to the lung is displayed on the scout image.
Further, as shown in FIG. 14, the central processing unit 3 displays a scan parameter setting screen on the right screen of the display device 6. In this scan parameter setting screen, parameters for helical scanning of a site (for example, lung) designated by the operator are displayed.

  In step A24, the operator drags and drops the display of the slice position, and sets a desired slice position as shown in FIG. In accordance with this, the central processing unit 3 recognizes the end position Le from the set start position Ls as one range. One set range is recognized as one group.

  In step A25, the operator changes the scan parameter and / or adds another range.

For example, when the value of a noise index (Noise Index) is clicked on the scan parameter setting screen of FIG. 16, for example, the central processing unit 3 pops up a tube current setting screen (mA Control) shown in FIG. In the tube current setting screen shown in FIG. 17, for example, automatic setting (Auto mA) is selected, a noise index value, for example, “10.00” is key-inputted, and OK is clicked. Then, the central processing unit 3 automatically sets the tube current based on the noise index. Then, the tube current setting screen shown in FIG. 17 is deleted, and the scan parameter setting screen shown in FIG. 16 is displayed.
For example, when the value of thickness / speed (Thick Speed) is clicked on the scan parameter setting screen of FIG. 16, for example, the central processing unit 3 selects the slice thickness etc. setting screen (Select the desired Image Thickness) shown in FIG. Is pop-up displayed, the operator sets / changes a desired value.
Further, for example, when a group preparation time (Prep Group) is clicked on the scan parameter setting screen of FIG. 17, for example, the value can be key-inputted, so the operator inputs the desired value. The group preparation time is a preparation time that is set before the scanning of the group is started. “0.0” is set as an initial value, which means that scanning of the group starts immediately without any preparation time. For example, if there is a group to be executed before a certain group and the group preparation time of the certain group is “0.0”, the scanning of the certain group is executed following the scanning of the previous group. If the group preparation time of a certain group is “1.0”, the scan of a certain group is executed after stopping for one second after the previous group scan.

  Further, when the variable pitch group addition (Add Vari-Pitch Group) is clicked on the scan parameter setting screen of FIG. 16, the central processing unit 3 returns to step A3, so that steps A3 to A24 are repeated, and FIG. Set the following range of scan parameters as shown. The variable pitch group addition is repeated, and a plurality of ranges of scan parameters are set as shown in FIG.

When the scan parameters are changed and / or another range is added, the process proceeds to step A26 in FIG. 5, and the operator performs parameter change graphic display, series name registration, and confirmation.
For example, when the parameter change display (Show Localizer) is clicked on the scan parameter setting screen of FIG. 20, the central processing unit 3 displays a scout image and main scan parameters as shown in FIG. 21 on the left screen 6L of the display device 6. Display changes.

Here, the change of the scan parameter is planned according to the following rules.
(1) Accelerate / decelerate within the range (projection data is collected even during acceleration / deceleration).
(2) When a certain range and another range partially overlap, if resolution priority is selected, the smaller helical pitch (slower linear movement speed) is prioritized. Conversely, if Low Dose is selected, priority is given to the larger helical pitch (the faster linear movement speed).
(3) Between the ranges, since the exposure is low, the linear movement is performed at the larger helical pitch (faster linear movement speed).
(4) X-ray irradiation is stopped between the ranges in order to achieve low exposure.
(5) Acceleration / deceleration is planned based on a predetermined function based on the set start acceleration.
As a result, the helical pitch and the noise index change as shown in FIG.
21 shows a case where the predetermined function of acceleration / deceleration is linear, the predetermined function may be non-linear as shown in FIG.

  When confirm is clicked on the scan parameter setting screen of FIG. 20, the central processing unit 3 displays a series registration screen (Enter the Series Name) shown in FIG. 23 on the right screen of the display device 6. Therefore, the operator inputs the series name on the series registration screen of FIG. 23 and clicks OK. Then, the central processing unit 3 registers one or more set groups as one series, and proceeds to step A27. A registered series (chain of parameter groups) can be reused by specifying the series name and calling it.

In step A27, the central processing unit 3 displays the scan progress screen shown in FIG. 24 on the right screen of the display device 6.
In step A28, the operator clicks the scan start (Scan Start) on the scan progress screen of FIG. Then, the central processing unit 3 starts a data collection process (process 2 in FIG. 3). As shown in FIG. 25, the central processing unit 3 displays the progress status of the data collection process on the scan progress screen.

FIG. 26 is a flowchart showing details of the data collection process (process 2 in FIG. 3).
In Step B1, the cradle 12 is linearly moved at a low speed to a position where the X-ray beam CB passes through the start point Z1 shown in FIG.

In step B2, the X-ray tube 21 is driven with the planned tube voltage and tube current in accordance with the current z coordinate of the cradle 12.
In step B3, the X-ray tube 21 and the multi-row X-ray tube detector 24 are rotated at the planned rotation speed according to the current z coordinate of the cradle 12.
In step B4, the cradle 12 is accelerated / constantly moved / decelerated at the planned table speed according to the current z coordinate of the cradle 12.
In step B5, projection data is collected (collected even during acceleration / deceleration).
In step B6, it is checked whether or not the last group is finished. If it is not finished, steps B2 to B5 are repeated. If finished, the process proceeds to step B7.
In step B7, the rotation of the X-ray tube 21 and the multi-row X-ray detector 24, the X-ray output, and the linear movement of the cradle 12 are stopped, and the process is terminated.

FIG. 27 is a flowchart showing details of the image reconstruction process (process 3 in FIG. 3).
In step C1, the projection data D0 (α, z, view, j, i) represented by the tilt angle α, table linear movement position z, view angle view, detector row number j, and channel number i is applied. On the other hand, preprocessing including offset correction, logarithmic conversion, X-ray dose correction, and sensitivity correction is performed to obtain projection data Din (α, z, view, j, i).
In step C2, beam hardening processing is performed on the preprocessed projection data Din (α, z, view, j, i). The beam hardening process is expressed by the following polynomial, for example. Here, B ₀ , B ₁ and B ₂ are beam hardening coefficients.
Dout (α, z, view, j, i) = Din (α, z, view, j, i) × (B ₀ (j, i) + B ₁ (j, i) × Din (α, z, view, j, i) + B ₂ (j, i) × Din (α, z, view, j, i) ² )
At this time, independent beam hardening correction can be performed for each column of the detector, so that if the tube voltage of each data acquisition system differs depending on the imaging conditions, the difference in characteristics for each column of the detector can be corrected. .

  In Step C3, a Z filter convolution process for applying a filter in the z direction (column direction) to the projection data Dout (α, z, view, j, i) subjected to beam hardening correction is performed. That is, the projection data Dcor (α, z, view, j, i) subjected to the beam hardening correction is multiplied by a column direction filter coefficient Wk (i) as shown in FIG. 28 in the column direction, for example. z, view, j, i).

The slice thickness can be controlled by the column direction filter coefficient wk (i).
As shown in FIG. 29, in the slice SL, the peripheral slice thickness is generally thicker than the reconstruction center.
Therefore, as shown in FIG. 30, a column direction filter coefficient wk (i of the center channel) having a wide width is used for the center channel, and a column direction filter coefficient wk having a large width is used for the peripheral channel. (Peripheral channel i) is used. As a result, as shown in FIG. 31, the slice SL having a slice thickness that is nearly uniform at both the reconstruction center and the periphery can be obtained.

  When the slice thickness is slightly reduced with the column direction filter coefficient wk (i), both artifact and noise are greatly improved. Thereby, the artifact improvement degree and the noise improvement degree can also be controlled. That is, the image quality of the tomographic image reconstructed by the three-dimensional image can be controlled.

  As shown in FIG. 32, a tomographic image having a thin slice thickness can also be realized by using a column-direction filter coefficient wk (i) as a deconvolution filter.

Returning to FIG. 27, in step C4, reconstruction function superimposition processing is performed. That is, the Fourier transform is performed, the reconstruction function is multiplied, and the inverse Fourier transform is performed. When the projection data after reconstruction function superimposition processing is Dr (α, z, view, j, i), the reconstruction function is Kernel (j), and the convolution operation is represented by *, the reconstruction function superimposition processing is as follows. It is expressed as
Dr (α, z, view, j, i) = Dcor (α, z, view, j, i) * Kernel (j)
Since the independent reconstruction function superimposing process can be performed using the independent reconstruction function Kernel (j) for each column of the detector, the difference in the noise characteristic and the resolution characteristic for each column of the detector can be corrected.

  In step C5, a three-dimensional backprojection process is performed on the projection data Dr (α, z, view, j, i) to obtain backprojection data D3 (x, y). This three-dimensional backprojection process will be described later with reference to FIG.

In step C6, post-processing such as image filter convolution processing and CT value conversion processing is performed on the backprojection data D3 (x, y) to obtain a tomographic image.
In the image filter superimposing process, if the data after the image filter superimposing process is D4 (x, y), the detector row number corresponding to the central pixel of the tomographic image is j, and the image filter is Filter (j),
D4 (x, y) = D3 (x, y) * Filter (j)
It becomes. That is, since independent image filter convolution processing can be performed for each slice position of the tomographic image, the difference in noise characteristics and resolution characteristics for each slice position can be corrected.

FIG. 33 is a flowchart showing details of the three-dimensional backprojection process (step C5 in FIG. 27).
In step C51, attention is paid to one view among all views necessary for image reconstruction of a tomogram (that is, a view of 360 ° or a view of “180 ° + fan angle”). Projection data Dr corresponding to each pixel is extracted.

  As shown in FIG. 34, a square reconstruction region P of 512 × 512 pixels parallel to the xy plane is used, and pixel columns L0, y = 63 of pixel columns L0, y = 63 parallel to the x axis of y = 0. Pixel column L127, pixel column L191 of y = 191, pixel column L255 of y = 255, pixel column L319 of y = 319, pixel column L383 of y = 383, pixel column L447 of y = 447, pixel column of y = 511 Taking L511 as an example, if projection data D0 on lines T0 to T511 as shown in FIG. 35 obtained by projecting these pixel rows L0 to L511 onto the surface of the multi-row X-ray detector 24 in the X-ray transmission direction is extracted. These become the projection data Dr of the pixel columns L0 to L511.

  Although the X-ray transmission direction is determined by the X-ray focal point of the X-ray tube 21 and the geometric position of each pixel and the multi-row X-ray detector 24, the projection data D0 (α, z, view, j, i) Since the z coordinate is known, the X-ray transmission direction can be accurately obtained even with projection data D0 (α, z, view, j, i) during acceleration / deceleration.

  For example, when a part of the line goes out of the plane of the multi-row X-ray detector 24, such as a line T0 in which the pixel row L0 is projected on the surface of the multi-row X-ray detector 24 in the X-ray transmission direction. The corresponding projection data Dr is set to “0”.

  Thus, as shown in FIG. 36, projection data Dr (view, x, y) corresponding to each pixel of the reconstruction area P can be extracted.

  Returning to FIG. 33, in step C52, the projection data Dr (view, x, y) is multiplied by the cone beam reconstruction weighting coefficient to create projection data D2 (view, x, y) as shown in FIG.

Here, the cone beam reconstruction weighting factors are as follows.
In the case of fan beam image reconstruction, generally, when view = βa, a straight line connecting the focal point of the X-ray tube 21 and the pixel g (x, y) on the reconstruction area P (on the xy plane) is the center of the X-ray beam. When the angle formed with respect to the axis Bc is γ and the opposite view is view = βb,
βb = βa + 180 ° -2γ
It is.
If the angles formed by the X-ray beam passing through the pixel g (x, y) on the reconstruction area P and the opposite X-ray beam to the reconstruction area P are αa and αb, the cone beam reconstruction weighting coefficient ωa depending on these angles , Ωb are multiplied and added to obtain back projection data D2 (0, x, y).
D2 (0, x, y) = ωa · D2 (0, x, y) _a + ωb · D2 (0, x, y) _b
Here, D2 (0, x, y) _a is projection data in the view βa, and D2 (0, x, y) _b is projection data in the view βb.
The sum of cone beam reconstruction weighting coefficients ωa and ωb of the X-ray beam and the opposite X-ray beam is ωa + ωb = 1.
As described above, cone angle artifacts can be reduced by multiplying and adding cone beam reconstruction weighting coefficients ωa and ωb.
For example, the cone beam reconstruction weighting coefficients ωa and ωb can be obtained by the following equations.
When f () is a function and the fan beam angle is γmax,
ga = f (π + γmax− | βa |, | tan (αa) |)
gb = f (π + γmax− | βb |, | tan (αb) |)
xa = 2 · ga ^q / (ga ^q + gb ^q )
xb = 2 · gb ^q / (ga ^q + gb ^q )
ωa = xa ²・ (3−2xa)
ωb = xb ²・ (3−2xb)
For example, f () = max (): a function that takes the larger value, and q = 1.
In the case of fan beam image reconstruction, each pixel on the reconstruction area P is further multiplied by a distance coefficient. In the distance coefficient, the distance from the focal point of the X-ray tube 21 to the detector row j and the channel i of the multi-row X-ray detector 24 corresponding to the projection data Dr is r0, and from the focal point of the X-ray tube 21 to the projection data Dr. When the distance to the pixel on the corresponding reconstruction area P is r1, (r1 / r0) ² .
The parallel beam image reconstruction is the same as the fan beam image reconstruction if βb = βa + 180 °.

In step C53, as shown in FIG. 38, the projection data D2 (view, x, y) is added to the back projection data D3 (x, y) that has been cleared in advance in correspondence with the pixels.
In step C54, steps S61 to S63 are repeated for all the views necessary for image reconstruction of the tomographic image (that is, the view of 360 ° or the view of “180 ° + fan angle”), as shown in FIG. Then, back projection data D3 (x, y) is obtained.

  As shown in FIG. 39, the reconstruction area P may be a circular area.

  According to the X-ray CT apparatus 100 of the first embodiment, scan parameters such as a helical pitch and a noise index can be set efficiently through an easy-to-understand user interface (such as a scan parameter setting screen), which is optimal for each region or organ of the subject. It is possible to obtain a tomographic image with sufficient image quality under optimum exposure conditions.

  The image reconstruction method may be a three-dimensional image reconstruction method based on a conventionally known Feldkamp method. Furthermore, JP2003-334188A, JP2004-41675A, JP2004-41474A, JP2004-73360A, JP2003-159244A, JP2004-41675A. The three-dimensional image reconstruction method proposed in (1) may be used.

  In the first embodiment, there are three groups. However, the example of more groups and the example of fewer groups are the same as those of the first embodiment.

  In the first embodiment, the settings of the field of view size, the reconstruction function, the image filter, and the like are not described. However, the image quality for each part or organ of the subject can be set by setting each group as in the first embodiment. , Exposure can be optimized.

  The X-ray CT scan parameter setting method and X-ray CT apparatus of the present invention can be used in a medical field.

1 is a block diagram showing an X-ray CT apparatus according to Embodiment 1. FIG. It is explanatory drawing which shows rotation of a X-ray tube and a multi-row X-ray detector. FIG. 3 is a flowchart showing a schematic operation of the X-ray CT apparatus according to the first embodiment. It is a flowchart which shows the detail of a helical scan parameter setting process. FIG. 5 is a flowchart subsequent to FIG. 4. It is the 1st illustration figure of a scan parameter setting screen. It is an illustration figure of a patient information screen and a protocol selection screen. It is the 1st illustration figure of a protocol list screen. It is an illustration figure of a scan type setting screen. It is an illustration figure of a scan parameter selection screen. It is a 2nd example figure of a protocol list screen. It is an illustration figure of a scout scan screen. It is a 1st illustration figure of a scout image display screen. It is the 2nd illustration figure of a scan parameter setting screen. It is a 2nd example figure of a scout image display screen. It is a 3rd illustration figure of a scan parameter setting screen. It is an illustration figure of a noise index setting screen. It is an illustration figure of a slice thickness etc. setting screen. It is a 4th illustration figure of a scan parameter setting screen. It is a 5th illustration figure of a scan parameter setting screen. It is an illustration figure of the screen which shows the change of the main scanning parameters using a scout image. It is explanatory drawing which shows the change of table speed. It is an illustration figure of a series registration screen. It is a 1st example figure of a scan progress screen. It is a 2nd example figure of a scan progress screen. It is a flowchart which shows the detail of a data collection process (process 2 of FIG. 3). It is a flowchart which shows the detail of an image reconstruction process (process 3 of FIG. 3). It is explanatory drawing which shows a column direction filter coefficient. It is explanatory drawing which shows a slice whose slice thickness is thick in the periphery from the center of a reconstruction area. It is explanatory drawing which shows the column direction filter coefficient which changes with channels. It is explanatory drawing which shows a slice with equal slice thickness at the center of a reconstruction area, and its periphery. It is explanatory drawing which shows the column direction filter coefficient for making slice thickness thin. It is a flowchart which shows the detail of a three-dimensional image reconstruction process. It is a conceptual diagram which shows the state which projects the pixel row | line on the reconstruction area | region P to a X-ray transmissive direction. It is a conceptual diagram which shows the line which projected the pixel row | line on the reconstruction area | region P on the detector surface. 7 is a conceptual diagram showing a state in which projection data Dr at a view angle view = 0 ° is projected onto a reconstruction area P. FIG. It is a conceptual diagram which shows the backprojection pixel data D2 on the reconstruction area | region P in view angle view = 0 degree. It is explanatory drawing which shows the state which obtains backprojection data D3 by adding all the views to backprojection pixel data D2 corresponding to a pixel. It is a conceptual diagram which shows the circular reconstruction area | region R. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Operation console 2 Input device 3 Central processing unit 5 Data collection buffer 6 Display device 7 Storage device 10 Table device 12 Cradle 100 X-ray CT device

Claims (26)

  A process of displaying a scout image of a subject, a process in which an operator designates one or more ranges in the body axis direction of the scout image, and an operator graphically inputs or inputs a helical pitch corresponding to the range. And setting the X-ray CT scan parameters.   The process of displaying the scout image of the subject, the process of the operator specifying a plurality of ranges in the body axis direction of the scout image, and the operator graphically or key-inputting the noise index corresponding to each of the ranges. X-ray CT scan parameter setting method characterized by comprising:   2. The X-ray CT scan parameter setting method according to claim 1, wherein the operator has a process of setting a noise index by graphical input or key input corresponding to the range. Method.   The X-ray CT scan parameter setting method according to any one of claims 1 to 3, wherein an operator sets at least one of a tube voltage and a tube current by graphical input or key input corresponding to the range. An X-ray CT scan parameter setting method comprising:   The X-ray CT scan parameter setting method according to any one of claims 1 to 4, wherein an operator corresponds to the range, the slice thickness, the number of detector rows, the table speed, the number of tomographic images, the tomographic image interval, An X-ray CT scan parameter setting method comprising a step of setting at least one of table accelerations.   2. The X-ray CT scan parameter setting method according to claim 1, wherein the X-ray CT scan includes a step of setting one series of the one range as one group and one series of one or more groups. Parameter setting method.   3. The X-ray CT scan parameter setting method according to claim 2, wherein the X-ray CT scan has a process of setting one series of the one range as one group and one series including one or more groups. Parameter setting method.   4. The X-ray CT scan parameter setting method according to claim 3, wherein the X-ray CT scan has a step of setting one series of one or more groups with the one range as one group. Parameter setting method.   5. The X-ray CT scan parameter setting method according to claim 4, wherein the X-ray CT scan has a step of setting one series of one or more groups with the one range as one group. Parameter setting method.   10. The X-ray CT scan parameter setting method according to claim 1, wherein the one range is set corresponding to one organ or part. .   The X-ray CT scan parameter setting method according to any one of claims 1 to 10, wherein a default value or a previous set value of at least one scan parameter is automatically set to a set value for the specified range. An X-ray CT scan parameter setting method characterized by being a candidate.   The X-ray CT scan parameter setting method according to any one of claims 1 to 11, wherein the X-ray CT scan collects data at the start and end of linear movement, and during acceleration or deceleration in the middle. An X-ray CT scan parameter setting method, characterized by being a variable pitch helical scan or a variable speed helical scan.   Helical scan means for collecting data while rotating at least one of the X-ray tube, the detector, and the X-ray tube or the detector around the object to be imaged and moving both of them linearly relative to the object to be imaged An X-ray CT apparatus comprising: scan parameter setting means for an operator to set helical scan parameters; and image reconstruction means for reconstructing an image based on the collected data. The means displays a scout image of the subject, and when the operator designates one or more ranges in the body axis direction of the scout image and inputs a helical pitch corresponding to the range graphically or by key input, An X-ray CT apparatus, wherein the helical pitch is set as a scan parameter corresponding to the range.   Helical scanning means for collecting data while rotating at least one of the X-ray tube, the detector, and the X-ray tube or the detector around the object to be imaged and moving both of them linearly relative to the object to be imaged An X-ray CT apparatus comprising: scan parameter setting means for an operator to set helical scan parameters; and image reconstruction means for reconstructing an image based on the collected data. The means displays a scout image of the subject, and the operator designates one or more ranges in the body axis direction of the scout image and inputs a noise index corresponding to the range by graphical input or key input. An X-ray CT apparatus, wherein the noise index is set as a scan parameter corresponding to the range.   14. The X-ray CT apparatus according to claim 13, wherein when the operator inputs a noise index graphically or key-inputs corresponding to the range, the parameter setting means sets the input noise index to a scan parameter corresponding to the range. X-ray CT apparatus characterized by setting as follows.   The X-ray CT apparatus according to any one of claims 13 to 15, wherein the parameter setting means is configured such that when an operator graphically inputs or key inputs at least one of a tube voltage and a tube current corresponding to the range, An X-ray CT apparatus, wherein at least one of an input tube voltage and tube current is set as a scan parameter corresponding to the range.   17. The X-ray CT apparatus according to claim 13, wherein the parameter setting means is configured so that an operator corresponds to the range, the slice thickness, the number of detector rows, the table speed, the number of tomographic images, the tomographic image, and the like. When at least one of image interval and table acceleration is input, at least one of the input slice thickness, number of detector rows, table speed, number of tomographic images, tomographic image interval, and table acceleration is used as a scan parameter corresponding to the range. An X-ray CT apparatus characterized by setting.   The X-ray CT apparatus according to claim 13, wherein the parameter setting unit can set one series including one or more groups with the one range as one group, and the helical scanning unit includes: An X-ray CT apparatus characterized in that, when execution of one series is instructed, helical scans for groups belonging to the series are continuously executed.   15. The X-ray CT apparatus according to claim 14, wherein the parameter setting means can set one series consisting of one or more groups with the one range as one group, and the helical scanning means includes 1 An X-ray CT apparatus characterized in that, when execution of one series is instructed, helical scans for groups belonging to the series are continuously executed.   16. The X-ray CT apparatus according to claim 15, wherein the parameter setting means can set one series including one or more groups with the one range as one group, and the helical scanning means includes 1 An X-ray CT apparatus characterized in that, when execution of one series is instructed, helical scans for groups belonging to the series are continuously executed.   17. The X-ray CT apparatus according to claim 16, wherein the parameter setting means can set one series composed of one or more groups with the one range as one group, and the helical scanning means includes 1 An X-ray CT apparatus characterized in that, when execution of one series is instructed, helical scans for groups belonging to the series are continuously executed.   The X-ray CT apparatus according to any one of claims 13 to 21, wherein the parameter setting means sets the one range in correspondence with one organ or part. .   23. The X-ray CT apparatus according to claim 13, wherein the parameter setting means automatically sets a default value or a previous set value of at least one scan parameter for the specified one range. An X-ray CT apparatus characterized in that it is a set value candidate.   The X-ray CT apparatus according to any one of claims 13 to 23, wherein the helical scanning means collects data even when linear movement starts and ends, and during acceleration or deceleration in the middle. Alternatively, an X-ray CT apparatus that performs variable-speed helical scanning.   A helical scan method, wherein a helical scan is performed while sequentially changing a helical pitch in a plurality of ranges set with different helical pitches.   Helical scan means for collecting data while rotating at least one of the X-ray tube, the detector, and the X-ray tube or the detector around the object to be imaged and moving both of them linearly relative to the object to be imaged An X-ray CT apparatus comprising: scan parameter setting means for an operator to set helical scan parameters; and image reconstruction means for reconstructing an image based on collected data. An X-ray CT apparatus characterized in that the means scans a plurality of ranges set with different helical pitches while changing the helical pitch in order.

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