JP5601674B2 - X-ray CT system - Google Patents

Description

  The present invention relates to an X-ray CT (Computed Tomography) apparatus. More specifically, the present invention can collect data in a predetermined cardiac phase range of a periodically moving heart and reduce X-ray exposure of a breast. The present invention relates to a line CT apparatus.

  2. Description of the Related Art Conventionally, an X-ray CT apparatus that detects a phase of a cardiac motion, that is, a cardiac phase, and performs X-ray irradiation for a predetermined time from a predetermined cardiac phase is known (for example, see Patent Document 1).

  On the other hand, an X-ray CT apparatus is known that lowers the X-ray irradiation output when the X-ray tube is in front of the eyeball or breast, and increases the X-ray irradiation output when not in front of the eyeball or breast (for example, patents). Reference 2).

JP 09-024405 ([0022]) Japanese Patent Laying-Open No. 2004-321587 ([0033], FIGS. 6 and 7)

The X-ray CT apparatus described in Patent Document 1 can collect data in a predetermined cardiac phase range of a periodically moving heart.
However, since X-ray irradiation is performed also in front of the breast, there is a problem that the X-ray exposure dose of the breast is not always reduced.

On the other hand, in the X-ray CT apparatus described in Patent Document 2, the amount of X-ray exposure of the breast can be reduced.
However, since it is not linked to the cardiac phase, there is a problem that data in a predetermined cardiac phase range of the heart cannot be collected.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an X-ray CT apparatus capable of collecting data in a predetermined cardiac phase range of a periodically moving heart and reducing the amount of X-ray exposure of a breast.

In a first aspect, the present invention provides an X-ray tube that irradiates a subject with X-rays while rotating around the subject, an X-ray detector that detects X-rays transmitted through the subject, and the X-rays An angle detection means for detecting the rotation angle θ of the tube, a cardiac phase detection means for detecting the cardiac phase ψ of the subject, and the rotation angle θ from the prohibition start angle Θs on the front side in the X-ray tube rotation direction from the front of the subject. X-ray irradiation is prohibited within the prohibition angle range from the front of the subject to the prohibition end angle Θe behind the X-ray tube rotation direction, and the rotational angle θ is not within the prohibition angle range and the cardiac phase ψ is Scan control means for starting the acquisition of projection data used for image reconstruction when the predetermined data acquisition start phase Ψs is reached and ending the acquisition of the projection data before the rotation angle θ enters the prohibited angle range; A CT image is generated based on the projection data To provide an X-ray CT apparatus characterized by comprising a image reconstruction means.
In the X-ray CT apparatus according to the first aspect, the rotation angle θ of the X-ray tube is from the prohibition start angle Θs on the front side in the X-ray tube rotation direction from the front of the subject to the rear side in the X-ray tube rotation direction from the front of the subject. Since X-ray irradiation within the prohibited angle range up to the prohibited end angle Θe is prohibited, the amount of X-ray exposure of the breast can be reduced. Also, when the rotation angle θ of the X-ray tube is not within the prohibited angle range and the cardiac phase ψ is the data acquisition start cardiac phase ψs, the collection of projection data used for image reconstruction is started, and the rotational angle θ falls within the prohibited angle range. Since the collection of projection data is completed before entering, projection data in a predetermined cardiac phase range can be collected from when the cardiac phase ψ is the data collection start cardiac phase ψs.

In a second aspect, the present invention relates to the X-ray CT apparatus according to the first aspect, wherein the rotation angle θ corresponding to the front of the subject is 0 degree and the angle is viewed in the X-ray tube rotation direction. The X-ray CT apparatus is characterized in that the forbidden angle range is not less than an angle range from 330 degrees to 30 degrees.
In the X-ray CT apparatus according to the second aspect, the rotation angle θ of the X-ray tube is 30 degrees on the front side in the X-ray tube rotation direction from the front of the subject to 30 degrees on the rear side in the X-ray tube rotation direction from the front of the subject. Since X-ray irradiation within a wider forbidden angle range than that is prohibited, the amount of X-ray exposure of the breast can be reduced.

In a third aspect, the present invention relates to the X-ray tube without irradiating X-rays when the angle range for collecting the projection data is W in the X-ray CT apparatus according to the first or second aspect. If the rotation angle θ is Θe <θ <Θs−W when the cardiac phase ψ becomes the data acquisition start cardiac phase ψs, X-ray irradiation is started and the projection data is collected. An X-ray CT apparatus is provided.
In the X-ray CT apparatus according to the first aspect, the collection of projection data can be reliably ended before the rotation angle θ enters the prohibited angle range.

In a fourth aspect, the present invention provides an X-ray CT apparatus according to the third aspect based on the rotational speed of the X-ray tube, the cardiac cycle of the subject, the rotational angle of the X-ray tube at a certain time, and the cardiac phase. In addition, a waiting time until the rotation angle θ becomes Θe <θ <Θs−W when the heart phase ψ becomes the data acquisition start phase ψs is calculated, and X-ray irradiation is performed when the waiting time elapses. An X-ray CT apparatus is provided that starts and collects the projection data.
In the X-ray CT apparatus according to the fourth aspect, the standby time until the X-ray irradiation and the collection of projection data are started can be known in advance.

In a fifth aspect, the present invention provides the X-ray tube without irradiating X-rays when the angle range for collecting the projection data is W in the X-ray CT apparatus according to the first or second aspect. If the rotation angle θ is Θe <θ <Θs, X-rays are emitted, and when the cardiac phase ψ becomes the data acquisition start phase ψs, the rotation angle θ becomes Θe <θ <Θs−. An X-ray CT apparatus is provided that collects the projection data if W.
In the X-ray CT apparatus according to the fifth aspect, X-ray irradiation can be started before the projection data collection is started.

In a sixth aspect, the present invention relates to the X-ray CT apparatus according to the fifth aspect, based on the rotational speed of the X-ray tube, the cardiac cycle of the subject, the rotational angle of the X-ray tube at a certain time, and the cardiac phase. In addition, a standby time until the rotation angle θ becomes Θe <θ <Θs−W when the cardiac phase ψ reaches the data acquisition start central phase ψs is calculated, and the projection data is collected when the standby time elapses. An X-ray CT apparatus is provided.
In the X-ray CT apparatus according to the sixth aspect, it is possible to know in advance the waiting time until projection data collection is started.

In a seventh aspect, the present invention is characterized in that in the X-ray CT apparatus according to the first to sixth aspects, the collection of the projection data is repeated at a plurality of imaging positions in the body axis direction of the subject. An X-ray CT apparatus is provided.
The X-ray CT apparatus according to the seventh aspect can collect three-dimensional heart data.

In an eighth aspect, the present invention provides an X-ray CT apparatus according to the seventh aspect, wherein the time from the arrival at the next imaging position to the start of collection of projection data is shortened. Provided is an X-ray CT apparatus characterized by accelerating and decelerating the rotational speed of an X-ray tube during a time of moving from one imaging position in the body axis direction to the next imaging position.
In the X-ray CT apparatus according to the eighth aspect, the time during which the subject moves from one imaging position in the body axis direction to the next imaging position (usually, there is a time corresponding to one to two cardiac cycles) is used. The timing is adjusted by accelerating / decelerating the rotational speed of the X-ray tube. Thereby, after reaching the next photographing position, the collection of projection data can be started in a short time.

In a ninth aspect, the present invention provides an X-ray tube that irradiates a subject with X-rays while rotating around the subject, an X-ray detector that detects X-rays transmitted through the subject, and the X-rays Angle detection means for detecting the rotation angle θ of the tube, cardiac phase detection means for detecting the cardiac phase ψ of the subject, and the prohibition end angle Θe on the rear side in the X-ray tube rotation direction from the front of the subject. X-ray irradiation and rotation of the X-ray tube when the X-ray tube is stopped at a position behind the X-ray tube rotation direction and the cardiac phase ψ reaches a predetermined data acquisition start phase ψs. X-ray irradiation and the collection of the projection data are started before the rotation angle θ reaches the prohibition start angle Θs on the front side in the X-ray tube rotation direction from the front of the subject. A CT image based on the scan control means for ending and the collected projection data There is provided an X-ray CT apparatus comprising an image reconstructing means.
In the X-ray CT apparatus according to the ninth aspect, the rotation angle θ of the X-ray tube is from the prohibition start angle Θs on the front side in the X-ray tube rotation direction from the front of the subject to the rear side in the X-ray tube rotation direction from the front of the subject. Since X-ray irradiation within the prohibited angle range up to the prohibited end angle Θe is prohibited, the amount of X-ray exposure of the breast can be reduced. Also, when the rotation angle θ of the X-ray tube is not within the prohibited angle range and the cardiac phase ψ is the data acquisition start cardiac phase ψs, the collection of projection data used for image reconstruction is started, and the rotational angle θ falls within the prohibited angle range. Since the collection of projection data is completed before entering, projection data in a predetermined cardiac phase range can be collected from when the cardiac phase ψ is the data collection start cardiac phase ψs.

In a tenth aspect, the present invention relates to the X-ray CT apparatus according to the ninth aspect, wherein the rotation angle θ corresponding to the front of the subject is 0 degree and the angle is viewed in the X-ray tube rotation direction. The X-ray CT apparatus is characterized in that the forbidden angle range is not less than an angle range from 330 degrees to 30 degrees.
In the X-ray CT apparatus according to the tenth aspect, the rotation angle θ of the X-ray tube is 30 degrees on the front side in the X-ray tube rotation direction from the front of the subject to 30 degrees on the rear side in the X-ray tube rotation direction from the front of the subject. X-ray irradiation within a wider prohibition angle range is prohibited until the amount of X-ray exposure of the breast can be reduced.

In an eleventh aspect, the present invention provides the X-ray CT apparatus according to the ninth or tenth aspect after the acquisition of the projection data at one imaging position in the body axis direction of the subject. The X-ray CT is characterized in that the X-ray tube is rotated to a position behind the prohibition end angle Θe in the X-ray tube rotation direction before moving to the next imaging position in the body axis direction. Providing equipment.
In the X-ray CT apparatus according to the eleventh aspect, the X-ray tube is moved in parallel with moving the X-ray tube or the subject from one imaging position in the body axis direction of the subject to the next imaging position. Since it is rotated to the irradiation start position, the preparation time can be shortened.

  According to the X-ray CT apparatus of the present invention, it is possible to collect data in a predetermined cardiac phase range of a periodically moving heart and reduce the X-ray exposure dose of the breast.

  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 device 10, a scanning gantry 20, and an electrocardiograph 40.

  The operation console 1 includes an input device 2 that receives an input from an operator, a central processing unit 3 that executes a scan control process, an image reconstruction process, and the like, and a data collection buffer 5 that collects projection data acquired by the scanning gantry 20. And a display device 6 for displaying a tomographic image reconstructed from the projection data and an image created by image creation processing, and a storage device 7 for storing programs, data and images.

  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, an X-ray detector 24, a DAS (Data Acquisition System) 25, an X-ray tube 21 around the body axis of the subject, and the like. Rotating unit controller 26 for rotating, tilt controller 27 for controlling when scanning gantry 20 is tilted forward or backward of the rotation axis, and exchange of control signals and the like with operation console 1, table device 10 and electrocardiograph 40 The controller 29 and the slip ring 30 are provided.

  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 X-ray detector 24 is AD-converted by the DAS 25, added with z-axis coordinates, and transferred to the data collection buffer 5 via the slip ring 30.

  The controller 29 sends the rotation angle θ of the X-ray tube 21 and the electrocardiographic data obtained by the electrocardiograph 40 to the central processing unit 3.

  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. Also, volume data is created from tomographic images at z-axis positions that are continuously arranged.

As shown in FIG. 2, it is assumed that the subject is lying on the cradle and the breast B is facing upward.
The angle range from the prohibition start angle Θs on the front side in the X-ray tube rotation direction from the front of the subject to the prohibition end angle Θe on the rear side in the X-ray tube rotation direction from the front of the subject is the prohibition angle range. W is an angle range for collecting projection data.
When the rotation angle θ corresponding to the front of the subject is 0 degree and the rotation angle θ is viewed in the rotation direction of the X-ray tube 21, for example, Θs = 330 degrees, Θe = 30 degrees, W = 240 degrees, Θs− W = 90 degrees. If the priority condition is W = 240 degrees, the prohibited angle range can be expanded to Θs = 360 degrees and Θe = 60 degrees.

FIG. 3 is a flowchart illustrating a procedure of exposure reduction cardiac imaging processing according to the first embodiment.
In step P1, the cradle 12 or the scanning gantry 20 is moved in the z-axis direction to image the heart at the first imaging position in the body axis direction of the subject.
In step P2, the X-ray tube 21 is rotated without irradiating the subject with X-rays. Here, in order not to irradiate the subject with X-rays, either X-rays may not be emitted from the X-ray tube 21 or X-rays may be blocked between the X-ray tube 21 and the subject with a collimator or the like. .

  In step P3, when the allowable error is ΔΨ, the process waits until the cardiac phase ψ falls within the range of Ψs−ΔΨ to Ψs + ΔΨ, and if it falls within the range, the process proceeds to step P4. Note that “when the heart phase ψ is the data acquisition start heart phase ψs” refers to a state within this range.

  In Step P4, it is checked whether the rotation angle θ is within the range of the prohibition end angle Θe to Θs-W. If not within the range, the process returns to Step P3, and if within the range, the process proceeds to Step P5. For example, as shown in FIG. 2, if the rotation angle θ is within the range of the prohibition end angle Θe to Θs−W when the cardiac phase ψ is within the range of ψs−Δψ to ψs + Δψ, the process proceeds to step P7.

In Step P7, the subject is irradiated with X-rays, and projection data is collected until the rotation angle θ changes from the current value θs to θs + W.
In Step P8, the X-ray irradiation is stopped. As a result, for example, as shown in FIG. 2, X-ray irradiation stops before the rotation angle θ enters the prohibition start angle Θs.

  In Step P9, if there is a next imaging position in the body axis direction of the subject, the process proceeds to Step P8, and if it is the last imaging position, the process proceeds to Step P21.

  In step P10, the cradle 12 or the scanning gantry 20 is moved in the z-axis direction to image the heart at the next imaging position in the body axis direction of the subject. Then, the process returns to Step P3.

In step P21, preprocessing (offset correction, logarithmic correction, X-ray dose correction, sensitivity correction) is performed on the projection data.
In Step P22, an image reconstruction process is performed on the projection data to generate a CT image.
In step P23, the CT image is post-processed so as to be suitable for display.
In step P24, a CT image is displayed. Then, the process ends.

For example, a rotation angle θ as shown in FIG. 4C is assumed with respect to the cardiac phase ψ as shown in FIG.
Since the X-ray irradiation is not started at the time t1 when the cardiac phase ψ is the data acquisition start cardiac phase ψs, it is possible to avoid the X-ray irradiation in the prohibited angle range (angle range indicated by a thick broken line).
At time t2 when the cardiac phase ψ is the data acquisition start cardiac phase ψs, X-ray irradiation is started, and projection data in the phase range h starting from the data acquisition start cardiac phase ψs is collected (angle range indicated by a very thick solid line). . However, X-ray irradiation in the prohibited angle range can be avoided.
Since the X-ray irradiation is not started at the time t3 when the cardiac phase ψ is the data acquisition start cardiac phase ψs, the X-ray irradiation in the prohibited angle range (angle range indicated by a thick broken line) can be avoided.

  According to the X-ray CT apparatus 100 of the first embodiment, the rotation angle θ of the X-ray tube 21 is after the prohibition start angle Θs on the front side in the X-ray tube rotation direction from the front of the subject and the X-ray tube rotation direction after the front of the subject. Since X-ray irradiation within the prohibition angle range up to the prohibition end angle Θe on the side is prohibited, the X-ray exposure dose of the breast B can be reduced. Further, projection data in a predetermined phase range h can be collected from the time when the cardiac phase ψ is the data collection start cardiac phase ψs.

FIG. 5 is a flowchart illustrating the procedure of exposure reduction cardiac imaging processing according to the second embodiment.
Since steps other than steps P5 and P6 are the same as those in the first embodiment, description thereof is omitted, and only steps P5 and P6 are described.

In step P5, a waiting time T until ψ = ψs and Θe <θ <Θs−W is calculated based on the correspondence between the cardiac phase ψ (t) at the current time (t) and the rotation angle θ (t).
The waiting time T is calculated as follows, for example.
(1) The rotation angle θo when ψ = ψs is detected.
(2) An angle range D that rotates in one heartbeat is detected.
(3) A rotational speed α satisfying (θo + α × D) = Θe is obtained. The left side is a fraction with respect to 360 degrees.
(4) T = α × 1 rotation time F
As a numerical example, when θo = 180 degrees, D = 360 degrees, Θe = 60 degrees, and F = 1 second,
(180 + α × 360) = 60
Therefore, if α = 2/3, the left side is (180 + 240), and the fraction with respect to 360 degrees is 60 degrees, which satisfies the equation. Therefore, the time for 2/3 rotation is the waiting time T. Some errors are allowed.

  In step P6, the X-ray tube 21 continues to rotate without irradiating X-rays until the standby time T elapses. When the standby time T elapses, the process proceeds to step P7.

FIG. 6 is a flowchart illustrating a procedure of exposure reduction cardiac imaging processing according to the third embodiment.
The procedure is basically the same as that of the first embodiment shown in FIG. 3, but the X-ray tube is rotated without irradiating X-rays (step P2), and if the rotation angle θ is not Θe <θ <Θs, X No X-ray is irradiated (steps P3a and P3b), and X-rays are irradiated if Θe <θ <Θs (steps P3a and P3c), and the rotation angle θ is set when the cardiac phase ψ becomes the data acquisition start phase ψs. If Θe <θ <Θs−W (steps P3 and P4), projection data is collected (step P7 ′).

FIG. 7 is a flowchart illustrating a procedure of exposure reduction cardiac imaging processing according to the fourth embodiment.
The procedure is basically the same as that of the second embodiment shown in FIG. 5 except that the X-ray tube is rotated without irradiating X-rays (step P2), and if the rotation angle θ is not Θe <θ <Θs, X If no radiation is irradiated (steps P3a and P3b) and Xe rays are irradiated if Θe <θ <Θs (steps P3a and P3c), and the waiting time T has elapsed (step P6), projection data is collected (steps). P7 ′).

FIG. 8 is a flowchart illustrating a procedure of exposure reduction cardiac imaging processing according to the fifth embodiment.
In step R1, the cradle 12 or the scanning gantry 20 is moved in the z-axis direction to image the heart at the first imaging position in the body axis direction of the subject.
In step R2, the X-ray tube 21 is rotated without irradiating the subject with X-rays. Here, in order not to irradiate the subject with X-rays, either X-rays may not be emitted from the X-ray tube 21 or X-rays may be blocked between the X-ray tube 21 and the subject with a collimator or the like. .

In step R3, the current cardiac phase ψ and cardiac cycle τ are measured, and A (for example, A = 10) times Ti until the cardiac phase ψ reaches the data collection start cardiac phase ψs are predicted.
Ti = τ (ψs−ψ) / 2π + i · π
(I = 0, 1, 2, ..., A)
In step R4, the current rotation angle θ is measured, and the number of rotations Nj until the rotation angle θ reaches the prohibition end angle Θe is predicted by B (for example, B = 10).
Nj = (Θe−θ) / 2π + j
(J = 0, 1, 2, ..., B)
In step R5, a plurality of average rotational speeds Vij are calculated based on the time Ti and the rotational speed Nj. However, Ti is selected to be longer than the horizontal movement time to the photographing position (movement time in the z-axis direction).
Vij = Nj / Ti
In step R6, an average speed VIJ having a minimum time Ti is selected from among the average rotational speed Vij that can be realized electrically (that is, I and J are determined).
In Step R7, a rotation speed profile is created so that the average rotation speed from the present time until the time TI elapses becomes VIJ, and the final rotation speed becomes the rotation speed at the time of photographing.
In step R8, the X-ray tube 21 is rotated by acceleration / deceleration using the created rotation speed profile.

In step R9, it waits until it reaches the photographing position, and if it reaches, it proceeds to step R10.
In step R10, the horizontal movement is stopped and the process proceeds to step R11.

In step R11, the process waits until the time TI elapses.
In step R12, the subject is irradiated with X-rays, and projection data is collected until the rotation angle θ changes from the current value θs to θs + W.
In step R13, X-ray irradiation is stopped.

  In step R14, if there is a next imaging position in the body axis direction of the subject, the process proceeds to step R15, and if it is the last imaging position, the process proceeds to step R21.

  In step R15, horizontal movement of the cradle 12 or the scanning gantry 20 is started to image the heart at the next imaging position in the body axis direction of the subject. Then, the process returns to step R3.

In step R21, preprocessing (offset correction, logarithmic correction, X-ray dose correction, sensitivity correction) is performed on the projection data.
In step R22, an image reconstruction process is performed on the projection data to generate a CT image.
In step R23, the CT image is post-processed so as to be suitable for display.
In step R24, a CT image is displayed. Then, the process ends.

FIG. 9 is a flowchart illustrating a procedure of exposure reduction cardiac imaging processing according to the sixth embodiment.
In step Q1, the cradle 12 or the scanning gantry 20 is moved in the z-axis direction to image the heart at the first imaging position in the body axis direction of the subject.
In step Q2, the X-ray tube 21 is rotated to the rotation angle θ = Θe without irradiating the subject with X-rays, and the rotation is stopped.

  In step Q3, when the allowable error is ΔΨ, the process waits until the cardiac phase ψ falls within the range of Ψs−ΔΨ to Ψs + ΔΨ, and if it falls within the range, the process proceeds to step Q4. Note that “heart phase ψ = ψs” refers to a state within this range.

In step Q4, the subject is irradiated with X-rays, the X-ray tube 21 is rotated, and projection data is collected until the rotation angle θ changes from the current value Θe to Θe + W.
In step Q5, the X-ray irradiation is stopped. As a result, X-ray irradiation stops before the rotation angle θ enters the prohibition start angle Θs.

  In step Q6, if there is a next imaging position in the body axis direction of the subject, the process proceeds to step Q7, and if it is the last imaging position, the process proceeds to step Q21.

  In step Q7, the cradle 12 or the scanning gantry 20 is moved in the z-axis direction to image the heart at the next imaging position in the body axis direction of the subject. In parallel with this, the X-ray tube 21 is rotated to the rotation angle θ = Θe, and the rotation is stopped. Then, the process returns to step Q3.

In step Q21, preprocessing (offset correction, logarithmic correction, X-ray dose correction, sensitivity correction) is performed on the projection data.
In step Q22, an image reconstruction process is performed on the projection data to generate a CT image.
In step Q23, the CT image is post-processed so as to be suitable for display.
In step Q24, a CT image is displayed. Then, the process ends.

  According to the X-ray CT apparatus of the third embodiment, the rotation angle θ of the X-ray tube 21 is the rear side in the X-ray tube rotation direction from the front of the subject from the prohibition start angle Θs on the front side in the X-ray tube rotation direction from the front of the subject. Since X-ray irradiation within the prohibited angle range up to the prohibited end angle Θe is prohibited, the amount of X-ray exposure of the breast can be reduced. In addition, projection data in a predetermined cardiac phase range can be collected from the time when the cardiac phase ψ is the data collection start cardiac phase ψs.

  The X-ray CT apparatus of the present invention can be used for imaging a heart having a predetermined cardiac phase while reducing the exposure dose to the breast.

1 is a block diagram illustrating an X-ray CT apparatus according to Embodiment 1. FIG. It is a conceptual diagram which shows the rotation angle of a X-ray tube. FIG. 6 is a flowchart showing exposure reduction cardiac imaging processing according to the first embodiment. It is a time chart which shows the timing of a cardiac phase, a rotation angle, and projection data collection. FIG. 10 is a flowchart showing an exposure reduction cardiac imaging process according to the second embodiment. FIG. 10 is a flowchart showing an exposure reduction cardiac imaging process according to the third embodiment. FIG. 10 is a flowchart showing exposure reduction cardiac imaging processing according to a fourth embodiment. FIG. 10 is a flowchart showing an exposure reduction cardiac imaging process according to the fifth embodiment. FIG. 10 is a flowchart showing an exposure reduction cardiac imaging process according to a sixth embodiment.

Explanation of symbols

1 Operation Console 2 Input Device 3 Central Processing Unit 6 Display Device 7 Storage Device 10 Table Device 20 Scanning Gantry 100 X-ray CT Device θ Rotation Angle Θs Prohibition Start Angle Θe Prohibition End Angle ψ Heart Phase ψs Data Collection Start Heart Phase W Projection Data Collect cardiac phase range

Claims (8)

An X-ray tube that irradiates the subject with X-rays while rotating around the subject;
An X-ray detector for detecting X-rays transmitted through the subject;
Angle detection means for detecting a rotation angle θ of the X-ray tube;
Cardiac phase detection means for detecting the cardiac phase ψ of the subject;
The prohibition end angle on the rear side in the X-ray tube rotation direction from the rotation start angle Θs on the front side of the subject from the prohibition start angle Θs on the front side in the X-ray tube rotation direction relative to the rotation angle corresponding to the front side of the subject. X-ray irradiation is prohibited within the prohibited angle range up to Θe, the rotation angle θ is not within the prohibited angle range, and the cardiac phase ψ is the predetermined data acquisition start phase ψs and is used for image reconstruction. When the angle range of the projection data is W, the rotation angle θ becomes Θe <when the cardiac phase ψ becomes the data acquisition start phase ψs.
Scan control means that starts collecting the projection data if θ <Θs−W, and ends the collection of the projection data before the rotation angle θ enters the forbidden angle range;
An X-ray CT apparatus comprising image reconstruction means for generating a CT image based on the collected projection data. 2. The X-ray CT apparatus according to claim 1, wherein when the rotation angle θ corresponding to the front of the subject is 0 degree and the angle is viewed in the X-ray tube rotation direction, the forbidden angle range is from 330 degrees to 30 degrees. An X-ray CT apparatus having an angle range up to degrees.
3. The X-ray CT apparatus according to claim 1, wherein the rotation angle θ is Θe <when the cardiac phase ψ becomes the data acquisition start phase ψs.
If θ <Θs−W, an X-ray CT apparatus starts X-ray irradiation that has not been irradiated before and collects the projection data.
4. The X-ray CT apparatus according to claim 3, wherein the cardiac phase ψ is the data collection based on the rotational speed of the X-ray tube, the cardiac cycle of the subject, the rotational angle of the X-ray tube at a certain time, and the cardiac phase. When the start phase Ψs is reached, the rotation angle θ is Θe <θ <.
An X-ray CT apparatus characterized by calculating a waiting time until Θs-W, starting X-ray irradiation when the waiting time elapses, and collecting the projection data.
3. The X-ray CT apparatus according to claim 1, wherein when the rotation angle θ is Θe <θ <Θs, X-rays are emitted, and when the cardiac phase ψ becomes the data collection start phase ψs. The rotation angle θ is Θe <θ <.
An X-ray CT apparatus that collects the projection data if Θs-W. 6. The X-ray CT apparatus according to claim 5, wherein the cardiac phase ψ is the data collection based on the rotational speed of the X-ray tube, the cardiac cycle of the subject, the rotational angle of the X-ray tube at a certain time, and the cardiac phase. When the start phase Ψs is reached, the rotation angle θ is Θe <θ <.
An X-ray CT apparatus that calculates a waiting time until Θs-W and collects the projection data when the waiting time elapses.
In X-ray CT apparatus according to any one of claims 6 claim 1, X-ray CT apparatus characterized by repeating the collection of the projection data at a plurality of photographing positions in the body axis direction of the subject.
  8. The X-ray CT apparatus according to claim 7, wherein the next imaging position from the imaging position in the body axis direction of the subject is shortened so that the time from the arrival at the next imaging position to the start of collection of projection data is shortened. An X-ray CT apparatus characterized by accelerating or decelerating the rotational speed of an X-ray tube during the time of moving to an imaging position.

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