JP2011080971A - Ct equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a CT equipment capable of readily setting the tube voltage and tube current. <P>SOLUTION: The CT equipment with a reconfiguration section 9f for reconfiguring the cross-sectional-image of an object 5 to be inspected from transmission images detected at a plurality of rotation positions includes an X-ray control unit 8 for controlling the tube voltage and the tube current of an X-ray tube 1 at set values; a shift mechanism 7 for changing the distance between the X-ray tube 1 and an X-ray detector 3 to set; and a photographic condition setting section 9d for setting, when a plurality of combinations of respective references of the tube voltage, the tube current, and the distance are stored and a single combination of the plurality of combinations of a tube voltage Vj, a tube current Ij, and a distance FDDj is selected and a distance FDD is set, the tube voltage V at a tube voltage Vj to change to set the tube current I from the tube current Ij to a value which corresponds to the distance FDDj and the distance FDD set. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a computed tomography apparatus (hereinafter referred to as a CT (Computed Tomography) apparatus) that captures a cross-sectional image of a subject.

  A so-called RR (Rotate Rotate) (third generation) CT apparatus that performs only rotation irradiates a subject with radiation (X-rays) generated from a radiation source, and the subject is in the direction of the optical axis of the radiation. A radiation detector having a plurality of one-dimensional or two-dimensional detection channels that rotate relative to the radiation at a rotation axis that intersects with respect to the radiation and transmits the radiation transmitted from the subject at each predetermined rotational position during one rotation. Detection is performed, and a cross-sectional image or three-dimensional data of the subject is obtained (tomographic imaging) from the detector output.

  FIG. 4 shows a configuration of a CT apparatus described in Patent Document 1 as a conventional example (front view). An X-ray tube 101 and an X-ray detector 103 that detects a pyramid-shaped X-ray beam 102 generated from the X-ray tube 101 with a two-dimensional resolution are arranged to face each other, and are placed on a table 104 so as to enter the X-ray beam 102. A transmission image (transmission data) of the placed subject 105 is obtained.

  The table 104 is disposed on the rotation / elevation mechanism 106, and when taking a cross-sectional image of the subject 105, transmission images are displayed in a number of directions while the table 104 is rotated once by the rotation / elevation mechanism 106 with respect to the rotation axis RA. Get (referred to as scanning). The multiple transmission images are processed by the control processing unit 107 to obtain cross-sectional images (one or many) of the subject 105.

  Further, the rotation axis RA and the X-ray detector 103 can be moved closer to or away from (shifted to) the X-ray focal point F of the X-ray tube 101 by the shift mechanism 108, and the imaging distance FCD (Focus to rotation Center Distance) and the detection distance. The imaging magnification (= FDD / FCD) can be changed according to the purpose by changing FDD (Focus to Detector Distance).

  Further, the tube voltage and tube current of the X-ray tube 101 can be freely set according to the subject 105 by the X-ray control unit 109, the tube voltage that sufficiently passes through the subject, and the maximum output (air) of the X-ray detector 103. The tube current that does not saturate the output is set.

JP 2002-62268 A

  In the conventional CT apparatus, the imaging condition setting before imaging is performed as follows.

  First, the subject 105 is placed on the table 104, X-rays are emitted, and a transmission image output from the X-ray detector is displayed on the control processing unit 107 in real time. The transmitted tube voltage and the tube current that does not saturate the brightness are set so that the transmitted image can be seen well. Next, the FCD and FDD are adjusted so that a desired portion of the subject 105 is within the field of view of the X-ray detector 103 at a desired imaging magnification.

  In the above-described imaging condition setting, the first problem of the conventional CT apparatus is that in tube voltage setting, both the tube voltage and the tube current must be adjusted while viewing the transmission image.

  The second problem is that in adjusting the photographing magnification, the brightness of the transmitted image changes with the change of the FDD and becomes too dark or saturated, so that the transmitted image can be visually observed while adjusting the tube current. It is necessary to adjust the FCD and FDD, and the operation is troublesome.

  An object of the present invention is to provide a CT apparatus that facilitates the setting of tube voltage and tube current.

  In order to achieve the above object, a CT apparatus according to claim 1 of the present invention detects an X-ray source that emits X-rays toward a subject, and detects X-rays transmitted through the subject as a transmission image. X-ray detection means for outputting, rotation means for rotating the subject and the X-ray relatively with respect to a rotation axis intersecting with the X-ray, and the transmission images detected at a plurality of rotation positions. In a CT apparatus having reconstruction means for reconstructing a cross-sectional image of a subject, X-ray control means for controlling the tube voltage and tube current of the X-ray source to set values, the X-ray source, and the X-ray A shift mechanism for changing and setting the distance to the detection means, and a plurality of combinations of reference values of the tube voltage, the tube current, and the distance are stored, and a tube voltage Vj that is one of the plurality of sets is stored. , Tube current Ij, distance FDDj are selected and the distance FDD is X-ray condition setting means for setting the tube voltage V to the tube voltage Vj and changing the tube current I from the tube current Ij according to the distance FDDj and the set distance FDD. The gist is to have.

  With this configuration, in setting the tube voltage V, the tube voltage V and the tube current I are automatically set only by selecting the reference value Vj, and manual setting of the tube current I is unnecessary.

  Further, according to this configuration, in the adjustment of the photographing magnification (FCD and FDD), the tube current I is automatically changed from Ij to FDDj and the set FDD in response to the change in FDD. The maximum output of the line detection means can be kept constant and adjustment is easy.

  A CT apparatus according to a second aspect of the present invention includes an X-ray source that emits X-rays toward the subject, and an X-ray detection unit that detects the X-rays that have passed through the subject and outputs them as a transmission image. , A rotating means for rotating the subject and the X-ray relative to a rotation axis intersecting the X-ray, and a cross-sectional image of the subject is reproduced from a plurality of transmission images detected at the rotational positions. In a CT apparatus having a reconfiguring means to configure, the X-ray control means for controlling the tube voltage and tube current of the X-ray source to set values, and the distance between the X-ray source and the X-ray detection means is changed. The tube voltage, the tube current, and the distance are set to the initial values of the tube voltage Vj, the tube current Ij, and the distance FDDj, respectively, and the distance FDDj is set after the initial values are set. When the distance FDD is changed, the tube voltage V is changed to the tube voltage. Set vj, is summarized in that with the X-ray condition setting means for setting and change according to the tube current I from the tube current Ij distance FDDj and the changed distance FDD.

  With this configuration, after setting the initial values (Vj, Ij, FDDj) of the tube voltage, tube current, and FDD, the tube current I is automatically adjusted with respect to changes in FDD in the adjustment of the photographing magnification (FCD and FDD). , Ij is changed according to FDDj and the set FDD, so that the maximum output of the X-ray detection means can be kept constant, and adjustment is easy.

A CT apparatus according to a third aspect of the present invention is the CT apparatus according to the first or second aspect, wherein the X-ray condition setting means calculates the tube current I by the formula 1, I = Ij · (FDD / FDDj) The gist is to change and set the value obtained in ² .

With this configuration, the tube current I is automatically changed and set according to Formula 1 in response to changes in FDD, so that the maximum output of the X-ray detection means can be kept constant. Since the output of the X-ray detection means is proportional to I / FDD ² , if I is changed in proportion to FDD ² as in Equation 1, the output becomes constant.

A CT apparatus according to a fourth aspect of the present invention is the CT apparatus according to the third aspect, wherein the X-ray condition setting means stores a lower limit value of the tube current at the tube voltage, and at the tube voltage Vj. When the tube current I obtained by the equation 1 is smaller than the tube current lower limit value IjL using the tube current lower limit value IjL, the tube voltage V is expressed by the equation 2, V = Vj · (I / IjL) ^{1 / γ} The gist is to set the tube current I to the tube current lower limit value at the tube voltage V obtained by the equation (2).

The CT apparatus according to claim 5 of the present invention is the CT apparatus according to claim 3, wherein the X-ray condition setting means stores an upper limit value of the tube current at the tube voltage, and at the tube voltage Vj. When the tube current I obtained by the above equation 1 using the tube current upper limit value IjU is larger than the tube current upper limit value IjU, the tube voltage V is expressed by the equation 3, V = Vj · (I / IjU) ^{1 / γ} The gist is to set the tube current I to the tube current upper limit value at the tube voltage V obtained by Equation 3.

According to the configurations of claims 4 and 5, when the tube current to be automatically set is lower than the lower limit or higher than the upper limit in the adjustment of the photographing magnification (FCD and FDD), the tube voltage V is automatically set to the formula 2 or By changing and setting using Equation 3, the maximum output of the X-ray detection means can be kept constant and adjustment is easy. Since the output of the X-ray detection means is proportional to I · V ^γ , the output becomes constant if V is changed in proportion to (1 / I) ^{1 / γ} as in Equations 2 and 3.

  ADVANTAGE OF THE INVENTION According to this invention, the CT apparatus which made easy the setting of a tube voltage and a tube current can be provided.

The schematic diagram (front view) which showed the structure of CT apparatus concerning 1st embodiment of this invention. FIG. 3 is a flowchart of shooting condition setting (preset mode) in the first embodiment. FIG. 5 is a flowchart of shooting condition setting (manual mode) in the first embodiment. The schematic diagram (front view) which showed the structure of the conventional CT apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Configuration of the first embodiment of the present invention)
The configuration of the first embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a schematic view (front view) showing the configuration of a CT apparatus according to the first embodiment of the present invention.

  An X-ray tube (X-ray source) 1 and a pyramid-shaped X-ray beam (X-ray) 2 that is a part of the X-ray emitted from the X-ray focal point F of the X-ray tube 1 are detected with two-dimensional resolution. An X-ray detector (X-ray detection means) 3 is arranged to face the X-ray beam 2 that has passed through the subject 5 placed on the table 4 so as to enter the X-ray beam 2. Detected by the device 3 and output as a transmission image (transmission data).

  The table 4 is disposed on a rotation / elevation mechanism (rotation means) 6 and is rotated by a rotation / elevation mechanism 6 with respect to a rotation axis RA perpendicular to the central X-ray optical axis L of the X-ray beam 2. The z is moved (lifted / lowered) in the z direction parallel to the rotation axis RA.

  Further, the shift mechanism 7 positions the rotation axis RA and the X-ray detector 3, sets an imaging distance FCD (Focus to rotation Center Distance) and a detection distance FDD (Focus to Detector Distance) (distance), and rotates the rotation axis RA. Then, the X-ray detector 3 is moved closer to or away from the X-ray tube 1 to change the imaging distance FCD and the detection distance FDD.

  Here, the shift mechanism 7 is used to change the imaging magnification (= FDD / FCD) according to the purpose, and the z movement (up / down) of the rotation / lifting mechanism 6 moves the target portion of the subject 5 to the X-ray beam 2. Used to adjust to the height of The rotation of the rotation / lifting mechanism 6 is used to obtain a transmission image in a number of directions by rotating the subject 5 with respect to the X-ray beam 2 when taking a cross-sectional image.

  The shift mechanism 7 measures and outputs FCD and FDD by an encoder (not shown), and the rotation / lifting mechanism 6 similarly measures and outputs the rotation angle φ and the lifting position z by an encoder (not shown).

  The X-ray control unit (X-ray control means) 8 applies the set tube voltage and tube current to the X-ray tube 1 and controls the X-ray tube 1 to emit the X-ray beam 2.

  As other components, each control unit (rotation / lifting mechanism 6 and shift mechanism 7) is controlled, and a control processing unit 9 for processing transmission data from the X-ray detector 3 and processing results are displayed. There is a display unit 9a and the like.

  The control processing unit 9 is a normal computer and includes a CPU, a memory, a disk (nonvolatile memory), a display unit 9a, an input unit (keyboard, mouse, etc.) 9b, a mechanism control board, an interface, and the like.

  The control processing unit 9 receives the operation position signals (FCD, FDD, φ, z) output from the mechanism units 6 and 7 by the mechanism control board, and controls the mechanism units 6 and 7 to position the subject. In addition to performing alignment, scanning (tomographic scanning), etc., a transmission image collection command pulse or the like is sent (controlled) to the X-ray detector 3.

  The control processing unit 9 captures a transmission image from the X-ray detector 3 at the time of imaging condition setting and displays it on the display unit 9a in real time, and collects a transmission image from the X-ray detector 3 at the time of tomography. It memorize | stores and reconstructs, produces the cross-sectional image of a test object, and displays it on the display part 9a.

  Further, the control processing unit 9 issues a command to the X-ray control unit 8 to set a tube voltage and a tube current, and to instruct X-ray emission and stop. The tube voltage and tube current can be changed according to the subject. The control processing unit 9 stores a settable tube voltage, a tube current lower limit value and a tube current upper limit value for all settable tube voltages, and does not set a value exceeding this range.

  As shown in FIG. 1, the control processing unit 9 reads the software as a functional block for the CPU to function as a calibration control unit 9c that calibrates the standard tube voltage / tube current in advance, and the tube voltage / tube current before tomography. A cross-sectional image is created from transmission data obtained by scanning and an imaging condition setting unit (X-ray condition setting unit) 9d for setting a geometric condition and a scan control unit (scan control unit) 9e for scanning tomography A reconstruction unit (reconstruction means) 9f is provided.

(Operation of the first embodiment)
The operation will be described with reference to FIGS.

The action is
1. 1. Calibration of tube voltage and tube current reference values Shooting condition setting (preset mode or manual mode)
3. Perform in order of tomography. Here, calibration of 1 may be performed once in advance, but setting of 2 is performed every time tomography is performed.

<Calibration of tube voltage and tube current reference values>
In this calibration, the calibration control unit 9c stores combinations Vj, Ij, and FDDj of preset values (reference values) of the tube voltage, tube current, and detection distance for J sets (j = 1, 2,..., J). Calibration. Here, Vj is arbitrarily set so as to increase as j increases. J is an arbitrary value of 3 or more.

The j-th preset value is calibrated as follows.
First, the operator sets the tube voltage to Vj and the detection distance to an arbitrary value FDDj in the absence of the subject, emits X-rays, and displays a transmission image. The transmission image is digital data. The brighter the image (the larger the X-ray dose), the larger the value, and the value from 0 to the saturation value (the maximum value of AD conversion). The operator, for example, averages the maximum value portion (usually the central portion) of the transmitted image (air image) so that the value of the transmitted image (air image) does not saturate with a margin and becomes as large as possible. Is adjusted to 90% of the saturation value, and the tube current is set as Ij, and Vj, Ij, and FDDj are stored in the control processing unit 9. Here, FDDj needs to be set so that the tube current Ij is between the settable tube current lower limit value IjL and the tube current upper limit value IjU at Vj.
Thereafter, the calibration is similarly performed with j = 1, 2,. <> End

  Next, the operator selects one of the preset mode and the manual mode when setting the shooting conditions.

<Shooting condition setting (preset mode)>
FIG. 2 is a flowchart of photographing condition setting (preset mode) in the first embodiment. This setting is performed by the photographing condition setting unit 9d.

  In step S1, the operator places the subject 5 on the table 4 and selects an arbitrary j-th preset value Vj, Ij, FDDj.

  In step S2, the operator sets an appropriate detection distance FDD and inputs a command to start shooting condition setting.

In step S3, the imaging condition setting unit 9d sets the tube voltage V to Vj and sets the tube current I as a preset value according to the FDD.
I = Ij · (FDD / FDDj) ² (1)
Change from Ij and set.

In step S4, when the tube current I is smaller than the tube current lower limit value IjL in the tube voltage Vj, the imaging condition setting unit 9d determines the tube voltage V as
V = VJ · (I / IjL) ^{1 / γ} (2)
Is corrected and set, and the tube current I is set to the tube current lower limit value at V obtained. Here, γ uses a value of 2.0 to 2.4, for example, 2.2. The optimum value of γ varies depending on the conditions (thickness and material) of the X-ray filter.

In step S5, when the tube current I is larger than the tube current upper limit value IjU in the tube voltage Vj, the imaging condition setting unit 9d sets the tube voltage V to the equation:
V = Vj · (I / IjU) ^{1 / γ} (3)
Is calculated and corrected, and the tube current I is set to the obtained tube current upper limit value at V.

  In step S6, the imaging condition setting unit 9d emits the X-ray beam 2 with the set V and I.

  In step S7, the imaging condition setting unit 9d takes the transmission image output from the X-ray detector 3 and displays it on the display unit 9a in real time.

  In step S8, when the operator visually checks the displayed transmission image and determines that this is acceptable, the operator inputs the end of setting. Does the imaging condition setting unit 9d have a setting end command from the operator? If not, the process proceeds to step S9.

  In step S9, the operator changes the preset number j, FCD, FDD (, φ, z) if necessary. Here, j, FCD, FDD (, φ, z) set appropriately can be changed while viewing the transmission image. When it is desired to increase the transmittance of the transmission image, j is increased, FCD and FDD are changed, the imaging magnification is changed, φ is changed to change the fluoroscopic direction, z is changed, and the target portion of the subject 5 is moved to the X-ray beam 2. Fit to height.

  Further, steps S3 to S7 are repeated with j, FCD, FDD (, φ, z) corrected in step S9, and the photographing conditions V, I, FCD, FDD (, φ, z) are changed and set. A transmission image under the shooting conditions is displayed.

  If there is a setting end command from the operator in step S8, the shooting condition setting unit 9d stores the shooting conditions V, I, FCD, FDD (, z) at that time as the final shooting conditions, and the shooting conditions. Exit settings (preset mode).

  In the above flow, unless an end command is input, the loop created by steps S3 to S9 is repeated at high speed (even if there is no change in the shooting conditions in step S9). Accordingly, when the shooting condition is changed, the transmitted image displayed in real time changes accordingly, so that the shooting condition can be set while viewing this. <> End

<Shooting condition setting (manual mode)>
The manual mode is used when the preset value Vj of the tube voltage does not have an appropriate value and it is desired to set another tube voltage in the preset mode.

  FIG. 3 is a flowchart of shooting condition setting (manual mode) in the first embodiment. This setting is performed by the photographing condition setting unit 9d.

  When the operator places the subject 5 on the table 4, in step T1, the operator sets appropriate arbitrary initial values Vj, Ij, and FDDj.

  In step T2, the imaging condition setting unit 9d radiates the X-ray beam 2 with the set Vj and Ij.

  In step T3, the imaging condition setting unit 9d takes the transmission image output from the X-ray detector 3 and displays it on the display unit 9a in real time.

  In step T4, when the operator visually checks the displayed transmission image and determines that this is acceptable, the operator inputs an end of initial setting. Does the imaging condition setting unit 9d have an initial setting end command from the operator? If not, the process proceeds to step T1, and steps T1 to T3 are repeated.

  In step T4, if there is a command to end the initial setting from the operator, the imaging condition setting unit 9d proceeds to step T5 using the imaging conditions Vj, Ij, and FDDj at that time as initial imaging conditions.

  In step T5, the operator changes FCD, FDD (, φ, z). Here, FCD and FDD (, φ, z) set appropriately can be changed while viewing the transmission image. The imaging magnification is changed by changing FCD and FDD, the fluoroscopic direction is changed by changing φ, and z is changed to adjust the target portion of the subject 5 to the height of the X-ray beam 2.

  In step T6, the imaging condition setting unit 9d sets the tube voltage V to Vj, and sets the tube current I by changing it from Ij in Expression (1) according to the initial value and the set FDD.

  In step T7, when the tube current I is smaller than the tube current lower limit value IjL in the tube voltage Vj, the imaging condition setting unit 9d corrects and sets the tube voltage V by calculating equation (2). It sets to the tube current lower limit in V calculated | required by Formula (2).

  In step T8, when the tube current I is larger than the tube current upper limit value IjU in the tube voltage Vj, the imaging condition setting unit 9d corrects and sets the tube voltage V by calculating the equation (3). It sets to the tube current upper limit in V calculated | required by Formula (3).

  In step T9, the imaging condition setting unit 9d emits the X-ray beam 2 with the set V and I.

  In step T10, the imaging condition setting unit 9d takes the transmission image output from the X-ray detector 3 and displays it on the display unit 9a in real time.

  In step T11, when the operator visually observes the displayed transmission image and determines that this is acceptable, the operator inputs the end of setting. Does the imaging condition setting unit 9d have a setting end command from the operator? If not, the process proceeds to step T5, and steps T5 to T10 are repeated.

  If there is a setting end command from the operator in step T11, the shooting condition setting unit 9d stores the shooting conditions V, I, FCD, FDD (, z) at that time as the final shooting conditions, and the shooting conditions. Exit the setting (manual mode).

  In the above flow, unless an initial setting end command is input, the loop created by step T1 to step T4 is repeated at high speed (even if the initial value is not changed in step T1). Accordingly, when the initial value is changed, the transmitted image displayed in real time changes accordingly, so that the initial value can be set while viewing this.

  Further, unless an imaging condition setting end command is input, the loop created by steps T5 to T11 is repeated at high speed (even if FCD and FDD are not changed in step T5). Accordingly, when the FCD and FDD are changed, the transmitted image displayed in real time changes accordingly, so that the FCD and FDD can be set while viewing this. <> End

<Tomography>
When the imaging condition setting is completed and the operator inputs tomographic imaging start, the scan control unit 9e emits the X-ray beam 2 with the set tube voltage V and tube current I, and the table 4 is rotated by the rotation / lifting mechanism 6. , The transmission image is captured from the X-ray detector 3 and stored at every constant rotation angle over one rotation.

  Subsequently, the reconstruction unit 9f performs a known reconstruction process from the acquired transmission image for one rotation, reconstructs one or more cross-sectional images of the subject 5, and stores and displays them. . <> End

(Effects of the first embodiment)
According to the first embodiment (preset mode), when the tube voltage V is set, the preset maximum output value of the X-ray detector 3 (air of the transmission image) is automatically selected only by selecting the preset value Vj. The tube current Ij is set so that the value of the portion does not saturate with a margin and becomes as large as possible, for example, about 90% of the saturation value. That is, there is no need for two-dimensional adjustment of the tube voltage and tube current as in the prior art, and only one-dimensional adjustment of the tube voltage is required, and tube voltage setting is easy. That is, the first problem described above is solved.

Further, according to the first embodiment (preset mode and manual mode), in the adjustment of the photographing magnification (FCD and FDD), the tube current I is automatically calculated with respect to the change of FDD, and the FDD of Formula (1) is calculated. Since it changes in proportion to the square, the maximum output of the X-ray detector 3 (the output of the air portion) can be kept constant. This can be derived from the fact that since the output of the X-ray detector 3 is proportional to I / FDD ² , the output becomes constant if I is changed in proportion to FDD ² . That is, when adjusting the imaging magnification (FCD and FDD), the tube current I is automatically set so as to keep the maximum output (the output of the air portion) of the X-ray detector 3 constant, so that the adjustment is easy. That is, the second problem described above is solved.

Furthermore, according to the first embodiment (preset mode and manual mode), in the adjustment of the photographing magnification (FCD and FDD), the tube voltage V is set when the automatically set tube current is lower than the lower limit or higher than the upper limit. The maximum output of the X-ray detector 3 (the output of the air portion) can be kept constant by adjusting the expression (2) or (3). This can be derived from the fact that since the output of the X-ray detector 3 is proportional to I · V ^γ , the output becomes constant if V is changed in proportion to (1 / I) ^{1 / γ} . Accordingly, in adjusting the imaging magnification (FCD and FDD), even when the tube current I exceeds the upper limit or the lower limit, the tube voltage V and the tube are maintained so that the maximum output (output of the air portion) of the X-ray detector 3 is kept constant. Adjustment is easy because the voltage I is automatically set.

(Modification of the first embodiment)
In addition, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

  For example, in the first embodiment, the subject 5 is rotated with respect to the X-ray beam 2, but conversely, the subject 5 may be fixed and the X-ray beam 2 may be rotated with respect to the rotation axis RA. . In this case, the X-ray tube 1 and the X-ray detector 3 are fixed to a frame that rotates about the rotation axis RA. Then, the X-ray tube 1 and the X-ray detector 3 are moved toward and away from the rotating frame to change the FCD and FDD. Even in such a case, the operations and effects of the first embodiment can be applied as they are.

  In the first embodiment, one rotation scan is performed. However, a half scan that rotates more than 180 ° + fan angle or a helical scan that rotates while moving the subject up and down along the rotation axis are performed. May be. Further, a table movement (translation) mechanism in a direction orthogonal to the X-ray optical axis L and the rotation axis RA may be provided to perform a so-called TR (Translate Rotate) method (second generation method) scan.

  In the first embodiment, the rotation axis RA intersects the X-ray optical axis L perpendicularly, but a so-called tilted CT apparatus in which the rotation axis is inclined from the vertical can also be used.

DESCRIPTION OF SYMBOLS 1 ... X-ray tube, 2 ... X-ray beam, 3 ... X-ray detector, 4 ... Table, 5 ... Subject, 6 ... Rotation / lifting mechanism, 7 ... Shift mechanism, 8 ... X-ray control part, 9 ... Control Processing unit, 9a ... Display unit, 9b ... Input unit, 9c ... Calibration control unit, 9d ... Imaging condition setting unit, 9e ... Scan control unit, 9f ... Reconstruction unit,
DESCRIPTION OF SYMBOLS 101 ... X-ray tube, 102 ... X-ray beam, 103 ... X-ray detector, 104 ... Table, 105 ... Subject, 106 ... Rotation / lifting mechanism, 107 ... Control processing part, 108 ... Shift mechanism, 109 ... X-ray Control unit

Claims (5)

An X-ray source that emits X-rays toward the subject, X-ray detection means for detecting the X-rays transmitted through the subject and outputting them as a transmission image, and the rotation axis intersecting the X-rays In a CT apparatus comprising: a rotating unit that relatively rotates a specimen and the X-ray; and a reconstructing unit that reconstructs a cross-sectional image of the subject from a plurality of transmission images detected at the rotation positions.
X-ray control means for controlling the tube voltage and tube current of the X-ray source to set values;
A shift mechanism that changes and sets the distance between the X-ray source and the X-ray detection means;
A plurality of combinations of reference values of the tube voltage, the tube current, and the distance are stored, and a tube voltage Vj, a tube current Ij, a distance FDDj, which is one of the plurality of sets, are selected, and the distance FDD is selected. Is set, the tube voltage V is set to the tube voltage Vj, and the tube current I is set by changing the tube current Ij from the tube current Ij according to the distance FDDj and the set distance FDD. Means,
CT apparatus characterized by having. An X-ray source that emits X-rays toward the subject, X-ray detection means for detecting the X-rays transmitted through the subject and outputting them as a transmission image, and the rotation axis intersecting the X-rays In a CT apparatus comprising: a rotating unit that relatively rotates a specimen and the X-ray; and a reconstructing unit that reconstructs a cross-sectional image of the subject from a plurality of transmission images detected at the rotation positions.
X-ray control means for controlling the tube voltage and tube current of the X-ray source to set values;
A shift mechanism that changes and sets the distance between the X-ray source and the X-ray detection means;
When the tube voltage, the tube current, and the distance are set to the initial values of the tube voltage Vj, the tube current Ij, and the distance FDDj, and the distance FDDj is changed to the distance FDD after the initial values are set. X-ray condition setting means for setting the tube voltage V to the tube voltage Vj and changing the tube current I from the tube current Ij according to the distance FDDj and the changed distance FDD;
CT apparatus characterized by having. The CT apparatus according to claim 1 or 2,
The X-ray condition setting means sets the tube current I to Equation 1,
I = Ij · (FDD / FDDj) ²
A CT apparatus characterized in that it is set by changing to the value obtained in (1). The CT apparatus according to claim 3.
The X-ray condition setting means stores the lower limit value of the tube current at the tube voltage, and the tube current I obtained by the equation 1 using the tube current lower limit value IjL at the tube voltage Vj is the tube current lower limit value. When the value is less than IjL, the tube voltage V is expressed by Equation 2,
V = Vj · (I / IjL) ^{1 / γ}
A CT apparatus characterized in that the tube current I is set to the tube current lower limit value at the tube voltage V obtained by the equation (2). The CT apparatus according to claim 3,
The X-ray condition setting means stores an upper limit value of the tube current at the tube voltage, and the tube current I obtained by the equation 1 is calculated as the tube current upper limit value using the tube current upper limit value IjU at the tube voltage Vj. If it is greater than the value IjU, then the tube voltage V is
V = Vj · (I / IjU) ^{1 / γ}
A CT apparatus characterized in that the tube current I is set to the tube current upper limit value at the tube voltage V obtained by the equation (3).

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