JP2013111272A - Radiation tomograph and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately evaluate the exposure of a subject and the image quality of an image when performing radiation output modulation to reduce a radiation output to be smaller than that in a normal case by a predetermined view angle range in order to reduce the exposure of a high radiation-sensitive region near the body surface of the subject in scanning with a radiation tomograph.SOLUTION: Two ranges are displayed. The one range is a desired first range DR that is designated in the body axial direction of a subject. The other range is a second range ER that is different from the first range DR and is supposed to be substantially affected by the effect of radiation output modulation when the radiation output modulation is performed thereby to irradiate the first range DR with a radiation that receives the radiation output modulation and also the radiation output modulation is performed in accordance with the condition of the radiation output modulation determined in consideration of scan characteristics. Consequently, the unintended exposure reduction is recognized.

Description

  The present invention relates to a radiation tomography apparatus that performs radiation output modulation for reducing a radiation output level in a predetermined view angle range, and a program therefor.

  2. Description of the Related Art A radiation tomography apparatus that performs radiation output modulation that makes a radiation output level smaller than a normal level by a predetermined view angle range in at least a part of a scan of a subject is known (see Patent Document 1, Abstract, etc.) ).

  According to such a radiation tomography apparatus, it is possible to locally reduce the exposure of a radiation sensitive part near the body surface of the subject.

JP 2004-321587 A

  When performing radiation output modulation, the operator normally designates a desired range for which exposure reduction is desired in the body axis direction of the subject, and the radiation subjected to radiation output modulation falls within this designated desired range. Radiation output modulation conditions are set so that irradiation is performed.

  An exposure reduction effect is produced in a range irradiated with radiation that has undergone radiation output modulation, but as a side effect, image quality degradation also occurs.

  Therefore, it is ideal that the radiation output modulation condition is set so that the radiation that has undergone the radiation output modulation is irradiated only to a specified desired range.

  However, in practice, there are cases where the radiation output modulation condition cannot be set ideally due to restrictions imposed by the characteristics of the scan to be performed.

  For example, when the scan to be performed is an axial scan, the radiation output modulation can only be performed in units of axial scan. Therefore, when it is desired to prioritize the setting of the initial radiation beam width, the range irradiated with the radiation output modulated radiation is limited to the axial scan range unit, and is within the specified desired range. Difficult to match.

  For example, when the scan to be performed is a helical scan, radiation having a predetermined width in the body axis direction of the subject continuously moves while spirally rotating in the body axis direction. To do. For this reason, if the radiation output modulation is performed on all the radiation irradiated to the specified desired range, the range irradiated with the radiation that has been subjected to the radiation output modulation is expanded more than the desired range. Become.

  As described above, the range in which the effect of the radiation output modulation actually reaches may be different from the one intended by the operator due to the limitation due to the scan characteristics. In this case, if the situation is unknown, the exposure evaluation of the subject and the image quality evaluation of the image cannot be performed properly.

  Under such circumstances, there is a demand for a technique that can appropriately perform exposure evaluation of an object and image quality evaluation of an image when performing radiation output modulation in scanning.

The invention of the first aspect
In at least a part of the scan on the subject, the radiation output level when the radiation source is located in the first view angle range is located in a second view angle range different from the first view angle range. A radiation tomography apparatus that performs radiation output modulation to be smaller than when
Determined based on the desired first range specified in the body axis direction of the subject, the radiation subjected to the radiation output modulation to the first range, and the characteristics of the scan When the radiation output modulation is performed in accordance with the radiation output modulation conditions, the second range different from the first range, which is expected to substantially reach the effect of the radiation output modulation, is simultaneously applied. Provided is a radiation tomography apparatus including display control means for controlling display means to display.

  Note that “the effect of the radiation output modulation substantially reaches” includes that the effect of the radiation output modulation actually reaches or is effective.

The invention of the second aspect is
The scan is one or more axial scans;
Among the one or more axial scans, the radiation output modulation is applied to a range having both ends at the outermost two ends of the axial scan range in one or more axial scans corresponding to the first range. A radiation tomography apparatus according to the first aspect of the present invention, further comprising a determining means for determining the condition so that the irradiated radiation is irradiated.

The invention of the third aspect is
The scan is a plurality of axial scans in which an axial scan range is continuously arranged in the body axis direction,
Determination means for determining the condition by determining an axial scan position and a radiation beam width in one or a plurality of axial scans for performing the radiation output modulation, wherein the radiation beam width is selected from candidates. A radiation tomography apparatus according to the first aspect, further comprising means is provided.

The invention of the fourth aspect is
The radiation tomography apparatus according to the third aspect, wherein the determining unit selects the radiation beam width to be equal to or smaller than a desired width specified as a scan condition of the scan.

The invention of the fifth aspect is
The radiation tomography apparatus according to the third aspect or the fourth aspect, wherein the determination unit selects the radiation beam width so that the number of axial scans for performing the radiation output modulation is minimized.

The invention of the sixth aspect is
The scan is a helical scan, and an error occurs in the control of the scan position of the subject.
Radiation at the center in the body axis direction of the radiation beam subjected to the radiation output modulation is irradiated to a range including the first range and having a width obtained by adding a predetermined length to the width of the first range. Thus, the radiation tomography apparatus according to the first aspect, further comprising a determination unit that determines the condition is provided.

The invention of the seventh aspect
The radiation tomography apparatus according to the sixth aspect, wherein the predetermined length is 1 mm or more and 10 mm or less.

The invention of the eighth aspect
The scan is a helical scan;
The center of the radiation beam that has been subjected to the radiation output modulation in the direction of the body axis is expanded to a range that is half the distance of the desired radiation beam width specified as the scanning condition at both ends of the first range. The radiation tomography apparatus according to the first aspect of the present invention further includes a determination unit that determines the condition so that the radiation is irradiated.

The invention of the ninth aspect is
The radiation tomography apparatus according to any one of the first to eighth aspects, wherein the display control unit controls the first and second ranges to be displayed on an image representing the subject. I will provide a.

The invention of the tenth aspect is
A program for causing a computer to function as display control means in the radiation tomography apparatus according to any one of the first to ninth aspects is provided.

  Here, the “view angle” defines the rotational angle position of the radiation source and is also referred to as a gantry angle.

  The “radiation output modulation condition” is, for example, the position or range of the radiation source in the body axis direction of the subject, and the radiation output modulation is performed when scanning is performed with the radiation source positioned at this position or range. can do.

  The “axial scan range” is a range in which radiation is irradiated by axial scan on the rotation axis of the radiation source, that is, the iso-center axis.

  The “radiation beam width” is the width of the radiation beam on the isocenter axis. When the scan is an axial scan, the width of the axial scan range is equal to the radiation beam width.

  The “axial scan” includes a cine scan and the like, and the “helical scan” includes a variable pitch helical scan and a shuttle scan.

  According to the invention of the above aspect, when performing radiation output modulation in at least a part of the scan on the subject, when the desired first range designated for exposure reduction and actually performing radiation output modulation Since the second range different from the first range, which is expected to have the effect of the radiation output modulation, is displayed together, the unintended exposure reduction range can be known, and the exposure evaluation of the subject and the image Image quality evaluation can be performed appropriately.

1 is a diagram schematically showing a configuration of an X-ray CT apparatus according to an embodiment of the invention. It is a functional block (block) figure of the part which concerns on execution of the scan in the X-ray CT apparatus by this embodiment. It is a figure which shows the example of a setting of the scanning range and exposure reduction desired range in a 1st example. It is a figure which shows the scanning conditions and X-ray output modulation conditions in a 1st example. It is a figure which shows the example of a display of the exposure reduction desired range in the 1st example, and an exposure reduction expected range. It is a figure which shows the example of a setting of the scanning range and exposure reduction desired range in a 2nd example. It is a figure which shows the initial scanning conditions in a 2nd example. It is a figure which shows the scanning conditions and X-ray output modulation conditions after recombination in a 2nd example. It is a figure which shows the example of a display of the exposure reduction desired range in the 2nd example, and an exposure reduction expected range. It is a figure which shows the example of a setting of the scanning range and exposure reduction desired range in a 3rd example. It is a figure which shows the scanning conditions and X-ray output modulation conditions in a 3rd example. It is a figure which shows the example of a display of the exposure reduction desired range in the 3rd example, and an exposure reduction expected range. It is a figure which shows the example of a setting of the scanning range and exposure reduction desired range in a 4th example. It is a figure which shows the scanning conditions and X-ray output modulation conditions in a 4th example. It is a figure which shows the example of a display of the exposure reduction desired range in 4th example, and an exposure reduction expected range.

  Embodiments of the invention will be described below.

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

  The operation console 1 includes an input device 2 that receives input from an operator, and a central processing device 3 that performs control of each unit for imaging a subject, data processing for generating or reconstructing an image, and the like. And a data collection buffer (buffer) 5 for collecting data acquired by the scanning gantry 20, a monitor 6 for displaying an image, and a storage device 7 for storing programs and data.

  The imaging table 10 includes a cradle 12 on which the subject 40 is placed and conveyed to the opening of the scanning gantry 20. The cradle 12 is moved up and down and horizontally moved by a motor built in the imaging table 10. Here, the body axis direction of the subject 40, that is, the horizontal linear movement direction of the cradle 12 is the z direction, the vertical direction is the y direction, and the horizontal direction perpendicular to the z direction and the y direction is the x direction.

  The scanning gantry 20 includes a rotating unit 15 and a main body 20a that rotatably supports the rotating unit 15. The rotating unit 15 includes an X-ray tube 21, an X-ray controller 22 that controls the X-ray tube 21, and an X-ray beam 81 generated from the X-ray tube 21 by collimating the X-ray beam width. A collimator 23 that changes the X-ray, an X-ray detector 24 that detects an X-ray beam 81 that has passed through the subject 40, and a data collection device that converts the output of the X-ray detector 24 into projection data and collects the projection data ( A DAS (Data Acquisition System) 25 and an X-ray controller 22, a collimator 23, and a rotating unit controller 26 for controlling the DAS 25 are mounted. The main body 20 a includes a controller 29 that communicates control signals and the like with the operation console 1 and the imaging table 10. The rotating part 15 and the main body part 20 a are electrically connected via a slip ring 30.

  FIG. 2 is a functional block diagram of a portion related to scan planning processing in the X-ray CT apparatus according to the present embodiment. As shown in FIG. 2, the X-ray CT apparatus according to the present embodiment includes a scan condition setting unit 101, an exposure reduction desired range specifying unit 102, an X-ray output modulation condition determining unit (determining means) 103, and a display control unit (display). Control means) 104.

  The scan condition setting unit 101 sets scan conditions for one examination in accordance with the operation of the operator. In this example, the posture of the subject, the imaging region, the scan range in the z direction, the X-ray beam width, the scan mode, etc. are set as the scan conditions.

  The “subject's posture” is set by selecting from supine, lying down, right sideways, left sideways, etc. The “imaging region” is set by selecting from the head, chest, abdomen, waist, and the like. The scan mode is set by selecting an axial mode or a helical mode. The scan range is set graphically on the scout image of the subject 40.

  In this example, when “subject posture” and “imaging region” are set, the type and position of the region to be subjected to exposure reduction are predicted, and the X-ray output is set to a level lower than the normal level in the X-ray output modulation. The view angle range VR to be reduced and the X-ray output reduction rate k at this time are automatically determined. For example, when the “subject posture” is “backward” and the “imaging region” is “chest”, the view angle range VR is ±± The range is 90 degrees (for 180 degrees on the front side of the subject), and the X-ray output reduction rate k is 50%.

  The X-ray output reduction rate k is a tube current reduction rate under a constant tube voltage. When the modulation curve of the X-ray output is obtained by the CT automatic exposure mechanism, the X-ray output along the modulation curve becomes a normal level. As the X-ray output reduction rate k, a desired reduction rate may be set according to the operation of the operator.

  The exposure reduction desired range designating unit 102 designates a desired exposure reduction desired range (first range) for which exposure reduction is required in the z direction in accordance with the operation of the operator. For example, the operator graphically inputs a desired range on the scout image of the subject 40 on the screen of the monitor 6 and designates the input range as the exposure reduction desired range DR.

  The X-ray output modulation condition determining unit 103 performs X-ray output modulation so that X-rays subjected to X-ray output modulation are irradiated to the designated exposure reduction desired range DR and considering the scanning characteristics. Determine the conditions. Here, X-ray output modulation is performed when the X-ray focal point is located at a predetermined position or range in the z direction, and this predetermined position or range is determined as the X-ray output modulation condition.

  When the display control unit 104 performs the X-ray output modulation with the designated exposure reduction desired range DR and the determined X-ray output modulation condition, the effect of the X-ray output modulation is actually substantially or The monitor 6 is controlled so that the exposure reduction expected range ER different from the exposure reduction desired range DR, which is expected to be effective, is displayed together. For example, the exposure reduction desired range DR and the exposure reduction expected range ER are simultaneously displayed on the scout image of the subject 40.

  Hereinafter, an operation example by each of these units will be described.

(First example)
In this example, the scan mode is an axial mode. That is, the scan for one inspection is one or a plurality of axial scans.

  In the present example, the X-ray output modulation condition determination unit 103 determines the end of the axial scan range in one or more axial scans corresponding to the exposure reduction desired range DR among the one or more axial scans as one examination. The X-ray output modulation conditions are determined so that X-rays subjected to X-ray output modulation are irradiated in a range having the two outermost ends as both ends.

  3 and 4 show setting examples of the scan range and the exposure reduction desired range in this example. The Z axis (IC) in FIG. 4 is an isocenter axis.

  In this example, the imaging region is the chest of the subject 40. As the scan range, a first scan range from coordinates Z1 to Z2 and a second scan range from coordinates Z3 to Z4 are set on the scout image 41. In addition, these two scan ranges are set to be scanned by two axial scans A1 and A2 in which the axial scan ranges are arranged in the z direction. The X-ray beam widths d of the axial scans A1 and A2 are a first width d1 (160 mm) and a second width d2 (120 mm), respectively.

  The exposure reduction desired range DR is set so as to cover the breast (mammary gland) which is a highly radiation-sensitive part. In this example, the exposure reduction desired range DR is included in the first scan range.

  Both ends of the exposure reduction desired range DR do not coincide with any two ends of the axial scan ranges in the axial scans A1 and A2. However, here, it is assumed that the setting of the X-ray beam width d has priority and is not changed. In this case, X-ray output modulation can only be performed in one of the axial scans A1 and A2.

  Therefore, the X-ray output modulation condition determining unit 103 determines the X-ray output modulation condition so that the X-ray output modulation is performed in the axial scan A1 in which the axial scan range is closest to the exposure reduction desired range DR.

  In this case, the exposure reduction expected range ER that is expected to have the effect of the X-ray output modulation coincides with the axial scan range of the axial scan A1, as shown in FIG.

  FIG. 5 shows a display example of the exposure reduction desired range DR and the exposure reduction expected range ER in this example. Here, an exposure reduction desired area DS that represents the exposure reduction desired range DR by the width in the z direction, and a difference area FS that represents the difference FR between the exposure reduction expected range ER and the exposure reduction desired range DR by the width in the z direction are displayed. I try to let them. In this way, the exposure reduction desired range DR, the exposure reduction expected range ER, and the difference FR thereof are clear and easy to understand. Further, these displays are preferably performed using blue-green colors while avoiding red-yellow colors so as not to give an impression of high exposure.

(Second example)
In this example, the scan mode is an axial mode. The scan for one examination is a plurality of axial scans in which the axial scan range is continuously arranged in the z direction.

  In this example, the X-ray output modulation condition determining unit 103 determines the axial scan position and the X-ray beam width in one or more axial scans that perform X-ray output modulation so as to substantially cover the exposure reduction desired range DR. To do. However, the X-ray beam width d of each axial scan is determined by selecting each from a plurality of predetermined candidates. The plurality of candidates include, for example, a first width d1 (160 mm), a second width d2 (120 mm), a third width d3 (80 mm), a fourth width d4 (40 mm), and a fifth width d5 ( 20 mm). Here, in order to balance the imaging time and the image quality, the X-ray beam width d of each axial scan is determined to be equal to or smaller than the X-ray beam width set as the scan condition, and the axial scan position and the X-ray beam are determined. The width is determined such that the number of axial scan positions, that is, the number of axial scans is minimized. Here, the X-ray beam width set as the scan condition is the third width d3 (80 mm).

  6 and 7 show setting examples of the scan range and the exposure reduction desired range in this example.

  In this example, the imaging region is the chest of the subject 40. The scan range is set on the scout image 41 from the coordinate Z1 to the coordinate Z4. In addition, the scan range is initially set to be scanned by four axial scans A1 to A4 in which the axial scan range is continuously arranged in the z direction. The X-ray beam widths d of the axial scans A1 to A4 are all the same, and each has a third width d3 (80 mm).

  The exposure reduction desired range DR is set so as to cover the breast (mammary gland) which is a highly radiation-sensitive part. In this example, the exposure reduction desired range DR straddles the boundary between the axial scan ranges of the axial scans A1 and A2. The width of the exposure reduction desired range DR is about 90 mm.

  As shown in FIG. 7, both ends of the exposure reduction desired range DR do not coincide with any two ends of the axial scan ranges in the axial scans A1 to A4. However, here, as described above, the setting of the scan position of the axial scan and the X-ray beam width d can be changed. However, it is assumed that the X-ray beam width d can be selected only from predetermined candidates. ing. In this case, the axial scan position of the axial scan that performs the X-ray output modulation and the X-ray beam width selected from the candidates are set so that the X-ray output modulated X-ray is irradiated to the exposure reduction desired range DR. There is no choice but to decide.

  Therefore, the X-ray output modulation condition determination unit 103 first sets any two of the ends of the axial scan range in one or a plurality of axial scans performed on the scan range to approach both ends of the exposure reduction desired range DR. The axial scan position and X-ray beam width of each axial scan are recomposed. At this time, the X-ray beam width d is selected from the candidates as many as possible within the third width d3 (80 mm), which is the set desired X-ray beam width, as much as possible. . That is, the X-ray beam width is selected so that the number increases as much as possible in the order of the third width (80 mm), the fourth width (40 mm), and the fifth width (20 mm). Then, an X-ray output modulation condition is determined so that X-ray output modulation is performed on the reconfigured axial scan corresponding to the exposure reduction desired range DR.

  FIG. 8 shows a setting example of each axial scan after reassembly. In this example, axial scans A1 ′ to A6 ′ are set for the scan range. The axial scans corresponding to the exposure reduction desired range DR are the axial scans A2 ′ and A3 ′, and X-ray output modulation is performed in these axial scans.

  Since the X-ray beam width d of each axial scan can only be selected from the determined candidates, the outermost 2 of the ends of the exposure scan reduction desired range DR and the axial scan range of the axial scan that performs X-ray output modulation. In many cases, the range having two ends is not completely coincident. Also in this example, the width of the exposure reduction desired range DR is about 90 mm, and selectable X-ray beam widths are the third width (80 mm), the fourth width (40 mm), and the fifth width (20 mm). Therefore, they do not match completely.

  In this example, the expected exposure reduction range ER that is expected to have the effect of X-ray output modulation coincides with the range obtained by adding the respective axial scan ranges of the axial scans A2 'and A3' as shown in FIG. Will do.

  FIG. 9 shows a display example of the exposure reduction desired range DR and the exposure reduction expected range ER in this example.

(Third example)
In this example, the scan mode is a helical mode. Here, the range in which the effect of the X-ray output modulation is effectively reached is the range of the position of the X-ray focal point when the X-ray output modulation is performed, and this range is set as the exposure reduction expected range ER. In the helical scan, it is assumed that the cradle 12 slightly slides with respect to the drive system when moving due to the load of the subject 40 and an error occurs in the control of the scan position.

  10 and 11 show setting examples of the scan range and the exposure reduction desired range in this example.

  In this example, the imaging region is the chest of the subject 40. The scan range is set on the scout image 41 from the coordinate Z1 to the coordinate Z4. The scan range is set so that a helical scan H1 for irradiating X-rays is performed when the X-ray focal point of the X-ray tube 21 is located in the scan range. The X-ray beam width d of the helical scan H1 is the first width d3 (80 mm). The helical pitch hp is 1.

  The exposure reduction desired range DR is set so as to cover the breast (mammary gland) which is a highly radiation-sensitive part.

  In this example, the X-ray output modulation condition determining unit 103 determines that the X-ray beam at the center in the z direction of the X-ray beam subjected to the X-ray output modulation is exposed when the scan position control includes no error. Basically, the X-ray output modulation condition is determined so that the desired reduction range DR is irradiated. That is, it is considered that the X-ray output modulation is performed when the X-ray focal point of the X-ray tube 21 is located in the exposure reduction desired range DR.

  However, in practice, there is a slight error in the control of the scan position. Accordingly, the X-ray output modulation condition determining unit 103 takes into account that an error occurs in the control of the scan position, and as shown in FIG. 11, the X-ray output modulation condition determining unit 103 is in a range slightly expanded from the exposure reduction desired range DR. When X is positioned, an X-ray output modulation condition is set so that X-ray output modulation is performed. For example, X-ray output modulation is performed when the X-ray focal point is located in a range including the exposure reduction desired range DR and having a width obtained by adding a predetermined length to the width of the exposure reduction desired range DR. Thus, the X-ray output modulation condition is determined.

  Here, considering the slip of the cradle when the subject 40 is accelerated due to the weight of the subject 40, the end of the exposure reduction desired range DR that is irradiated with the X-rays later is set to a predetermined length da. The expanded range is the range of the position of the X-ray focal point where X-ray output modulation is performed. The predetermined length da is, for example, 1 mm or more and 10 mm or less, and a more realistic length is about 4 to 5 mm.

  In this case, as shown in FIG. 11, the exposure reduction expected range ER is a range expanded by a predetermined length da from the exposure reduction desired range DR.

  FIG. 12 shows a display example of the exposure reduction desired range DR and the exposure reduction expected range ER in this example.

(4th example)
In this example, the scan mode is a helical mode. Here, the range in which the effect of the X-ray output modulation is effectively reached is the range of the position of the X-ray focal point when the X-ray output modulation is performed, and this range is set as the exposure reduction expected range ER.

  13 and 14 show setting examples of the scan range and the exposure reduction desired range in this example.

  In this example, the imaging region is the chest. As the scan range, the range from the coordinate Z1 to the coordinate Z4 on the scout image 41 is set. The scan range is set so that a helical scan H1 for irradiating X-rays is performed when the X-ray focal point of the X-ray tube 21 is located in the scan range. The X-ray beam width d of the helical scan H1 is the third width d3 (80 mm). The helical pitch hp is 1.

  The exposure reduction desired range DR is set so as to cover the breast (mammary gland) which is a highly radiation-sensitive part.

  In this example, the X-ray output modulation condition determination unit 103 determines the X-ray output modulation condition so that all X-rays irradiated to the exposure reduction desired range DR are subjected to X-ray output modulation. In other words, the X-ray beam at the center in the z direction of the X-ray beam subjected to the X-ray output modulation is expanded to a range expanded by a distance half the set X-ray beam width to both ends of the exposure reduction desired range DR. The X-ray output modulation condition is determined so that the line is irradiated. This is equivalent to performing X-ray output modulation when the X-ray focal point is located in the range.

  Here, since the third width d3 (80 mm) is set as the X-ray beam width d, as shown in FIG. 14, each is expanded by d3 / 2 (40 mm) from both ends of the exposure reduction desired range DR. When the X-ray focal point of the X-ray tube 21 is located within the range, the X-ray output modulation condition is determined so as to perform the X-ray output modulation.

  In this case, the expected exposure reduction range ER is a range expanded by d3 / 2 (40 mm) from the desired exposure reduction range DR, as shown in FIG.

  FIG. 15 shows a display example of the exposure reduction desired range DR and the exposure reduction expected range ER in this example.

  As described above, according to the present embodiment, when X-ray output modulation is performed in at least a part of the scan on the subject, the desired exposure reduction desired range DR designated for exposure reduction and the scan characteristics are used. When the X-ray output modulation is performed according to the X-ray output modulation condition determined under the restriction, the effect of the X-ray output modulation is expected to be actually, substantially, or effectively expected. Since the exposure reduction expected range ER different from the range DR is displayed together, the unintended exposure reduction range can be known, and the exposure evaluation of the subject 40 and the image quality evaluation of the image can be appropriately performed.

  The embodiment of the invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the invention.

  For example, a program for causing a computer to function as the display control unit 104 is also an embodiment of the invention.

DESCRIPTION OF SYMBOLS 1 Operation console 2 Input device 3 Central processing unit 5 Data collection buffer 6 Monitor (display means)
DESCRIPTION OF SYMBOLS 7 Memory | storage device 10 Imaging table 12 Cradle 15 Rotating part 20 Scanning gantry 21 X-ray tube 22 X-ray controller 23 Collimator 24 X-ray detector 25 Data acquisition device 26 Rotating part controller 29 Control controller 30 Slip ring 40 Subject 41 Scout image 81 X-ray 100 X-ray CT apparatus 101 Scan condition setting unit 102 Exposure reduction desired range specifying unit 103 X-ray modulation condition determining unit (determining means)
104 Display control unit (display control means)

Claims (10)

In at least a part of the scan on the subject, the radiation output level when the radiation source is located in the first view angle range is located in a second view angle range different from the first view angle range. A radiation tomography apparatus that performs radiation output modulation to be smaller than when
Determined based on the desired first range specified in the body axis direction of the subject, the radiation subjected to the radiation output modulation to the first range, and the characteristics of the scan When the radiation output modulation is performed in accordance with the radiation output modulation conditions, the second range different from the first range, which is expected to substantially reach the effect of the radiation output modulation, is simultaneously applied. A radiation tomography apparatus comprising display control means for controlling display means to display. The scan is one or more axial scans;
Among the one or more axial scans, the radiation output modulation is applied to a range having both ends at the outermost two ends of the axial scan range in one or more axial scans corresponding to the first range. The radiation tomography apparatus according to claim 1, further comprising a determining unit that determines the condition so that the irradiated radiation is irradiated. The scan is a plurality of axial scans in which an axial scan range is continuously arranged in the body axis direction,
Determination means for determining the condition by determining an axial scan position and a radiation beam width in one or a plurality of axial scans for performing the radiation output modulation, wherein the radiation beam width is selected from candidates. The radiation tomography apparatus according to claim 1, further comprising means.   The radiation tomography apparatus according to claim 3, wherein the determination unit selects the radiation beam width to be equal to or less than a desired width specified as a scan condition of the scan.   The radiation tomography apparatus according to claim 3, wherein the determination unit selects the radiation beam width so that the number of axial scans for performing the radiation output modulation is minimized. The scan is a helical scan, and an error occurs in the control of the scan position of the subject.
Radiation at the center in the body axis direction of the radiation beam subjected to the radiation output modulation is irradiated to a range including the first range and having a width obtained by adding a predetermined length to the width of the first range. The radiation tomography apparatus according to claim 1, further comprising a determining unit that determines the condition.   The radiation tomography apparatus according to claim 6, wherein the predetermined length is 1 mm or more and 10 mm or less. The scan is a helical scan;
The center of the radiation beam that has been subjected to the radiation output modulation in the direction of the body axis is expanded to a range that is half the distance of the desired radiation beam width specified as the scanning condition at both ends of the first range. The radiation tomography apparatus according to claim 1, further comprising a determination unit that determines the condition so that radiation is irradiated.   The radiation tomography apparatus according to any one of claims 1 to 8, wherein the display control unit controls the first and second ranges to be displayed on an image representing the subject.   The program for functioning a computer as a display control means in the radiation tomography apparatus as described in any one of Claims 1-9.

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