JP2004130147A - Computerized tomographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suitably realize interruption control of helical scanning. <P>SOLUTION: The subject computerized tomographic apparatus is provided with a helical scanning means having an X-ray tube 53 for exposing X-rays, and an X-ray detector 54 for detecting X-rays transmitted through a subject at a rotating part 52 and carrying out helical scanning of the subject; a reconstruction processing part 62 for reconstructing image data based on projection data collected by helical scanning whenever collecting the projection data in an angle range required to reconstruct image data; a display device 64 for displaying the image data reconstructed by the reconstruction processing part 62; a switch 67 for instructing interruption; and a system control part 66 for controlling to perform image reconstruction processing and image display operation abreast with the scanning operation of helical scanning, and performing interruption control of helical scanning based on the interruption instruction from the switch 67. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a computed tomography apparatus (hereinafter abbreviated as CT), and more particularly to a CT capable of continuously performing a scanning operation.

Generally, in CT, three processes of scan, image reconstruction, and image display are performed in time series. The multi-directional projection data collected by the rotation of the X-ray tube or the integrated rotation of the X-ray tube and the detector array is digitized and subjected to pre-processing such as calibration, and then becomes raw data such as a magnetic disk. Is temporarily stored in the large-capacity storage device.

At the time of reconstruction, raw data is read from the magnetic disk and sent to the reconstruction unit via the memory. The tomographic image data reconstructed by the reconstructing unit is stored on a magnetic disk and transferred to a CRT monitor as a video signal via a display memory and displayed.

By the way, continuous scanning became possible by introducing a slip ring. By this continuous scanning, a plurality of projection data in a plurality of directions regarding the same or a plurality of slices can be collected in time series. These multidirectional projection data are read out to the reconstructing unit at an arbitrary timing via the magnetic disk as described above, and are used for reconstructing. The time required for the reconstruction process is longer than the scan time, and the storage and access time of the magnetic disk is long. Therefore, it has not been possible to continuously display a tomographic image in real time like a cine image while performing continuous scanning.

In recent years, high-speed reconstruction processing has been studied, and is approaching the level of practical use. This is expected to continuously display tomographic images in real time like a cine image while performing continuous scanning, but the long storage and access time of the magnetic disk is an obstacle, and it is not practical. Not reached. Furthermore, since the waiting time when storing and accessing the magnetic disk occurs irregularly, the time interval from the scanning operation to the display of the tomographic image becomes irregular, and the actual movement of the subject can be reproduced. Could not.

他 In addition, when real-time X-ray CT is used in a clinical setting, the following various problems occur. The first problem is that the operator manually adjusts the slice position by manually sliding the tabletop while watching the cross light projected on the subject from the projector, but this operation requires a long time. The second problem is that, in a scan involving a top plate movement such as a helical scan or a multi-slice scan, if the scan is temporarily interrupted, it takes a long time to resume the scan. This is because, at the time of resuming, it is necessary to manually return the top plate to the slice position of the display image at the time of interruption.

目的 It is an object of the present invention to suitably interrupt a helical scan.

The present invention has an X-ray tube for irradiating X-rays and an X-ray detector for detecting X-rays transmitted through a subject in a rotating section, helical scanning means for helically scanning the subject, and image data. Every time projection data in an angle range necessary for reconstruction is acquired, image reconstruction means for reconstructing the image data based on the projection data acquired by the helical scan, and reconstruction by the image reconstruction means. Display means for displaying the configured image data, instruction means for instructing interruption, and, in parallel with the scan operation of the helical scan, the reconstruction processing by the image reconstruction means and the display operation by the display means. And control means for performing interruption control of the helical scan based on an interruption instruction from the instruction means.

According to the present invention, the helical scan can be suitably stopped.

Hereinafter, an embodiment of a computed tomography apparatus according to the present invention will be described with reference to the drawings.
(1st Embodiment)
FIG. 2 is a schematic diagram showing the configuration of the first embodiment. The computer tomography apparatus according to the present embodiment includes a gantry 1, a bed 2, and a console 3. An opening 4 into which the subject is inserted is provided in the center of the gantry 1. A bed 2 is arranged on the front of the gantry 1. The couch 2 is configured to be electrically adjustable in height. A top plate 5 on which a subject is placed is provided on the upper surface of the bed 2, and the top plate 5 is configured to be electrically slidable from the upper surface of the bed 2 toward the gantry 1. Although not shown, a caster or the like is attached to a lower portion of the gantry 1 so that the gantry 1 can be manually slid toward the bed 2. This is because CT fluoroscopy may be used in combination with surgery, and in this case, it is preferable from the viewpoint of safety to change the slice position by moving the gantry 1 rather than by moving the top 5. . Of course, the slice position can be changed by sliding the top plate 5. In the photographing mode, the slice position is generally changed only by sliding the top 5.

A keyboard (may include a mouse) 6 and a CRT monitor 7 are arranged on the console 3, and a control unit is housed in the console 3. This control unit is connected to both the gantry 1 and the bed 2.

As shown in FIG. 3, the gantry 1 includes an X-ray tube 12 that irradiates a fan-shaped X-ray beam to a subject 10 mounted on a table 5, and a focus on the X-ray tube 12. A plurality of detectors are arranged in an arc shape, and a detector array 16 for detecting X-rays transmitted through the subject 10 in multiple channels is integrally formed around the subject 10 while facing each other with the subject 10 interposed therebetween. Are supported by a rotating part so that the can be continuously rotated. Further, the X-ray tube 12 and the detector array 16 are electrically connected to a fixed portion via a slip ring. Thereby, while the X-ray tube 12 and the detector array 16 continuously rotate around the subject 10, multidirectional projection data on the subject 10 required for reconstruction of one tomographic image is continuously collected. When rotating continuously at the same slice position, for example, so-called dynamic scan that tracks a change in tomographic image due to inflow and outflow of a contrast agent becomes possible, and when changing a slice position in synchronization with rotation, , So-called helical scan becomes possible. This type of CT is called a third generation (R / R system). The gantry 1 is not limited to this type, and may be a so-called fourth generation (R / S type) in which detectors are arranged around the subject over 360 ° and only the X-ray tube 12 rotates, In addition to the detector, the X-ray tube 12 may be a so-called fifth generation (S / S type), which is arranged around the subject over 360 °.

An X-ray generator 14 that supplies a tube current and a tube voltage to the X-ray tube 12 in a continuous or pulsed manner to generate X-rays is installed on a fixed portion of the gantry 1, and the X-ray is generated via a slip ring. Connected to tube 12. This X-ray generator 14 can also be mounted on the rotating part of the gantry 1. A data acquisition system (DAS: Data Acquisition System) 18 is installed on the rotating part of the gantry 1 and connected to the detector array 16. The data acquisition system 18 includes an integrator for temporally integrating output signals from the detectors of the detector array 16, a multiplexer for taking in the output of the integrator in a channel unit at high speed and serially, and the multiplexer. And an analog-to-digital converter for converting the output signal of the X-ray into digital data, and collects and outputs projection data reflected on the X-ray transmittance for each X-ray path.

FIG. 4 is a block diagram of the control unit 20 in the console 3. A CPU 22 is provided as a host controller, and a control bus 24 and a data bus 26 are connected to the CPU 22. The CPU 22 has a built-in clock circuit 42, manages the operation and time of each unit using a clock from the clock circuit 42, and supplies this clock to each unit in the control unit 20 as a common clock. To the control bus 24, a pre-processing unit 28, a disk interface (disk I / F) 30, a reconfiguration unit 32, and a display memory 34 are connected. The keyboard 6 and the X-ray generator 14 described above are connected to the control bus 24. The data bus 26 is connected to a pre-processing unit 28, a disk I / F 30, a reconfiguration unit 32, a display memory 34, and a memory 36. A magnetic disk device 38 as a mass storage device is connected to the disk I / F 30. The data collection system 18 is connected to the preprocessing unit 28. The projection data from the data collection system 18 is subjected to pre-processing such as calibration in the pre-processing unit 28, and is once written as raw data to a memory 36 such as a readable and writable DRAM via the data bus 26. It is read from here and sent to the reconstruction unit 32. The reconstructing unit 32 reconstructs tomographic image data based on multidirectional projection data. The tomographic image data is temporarily written into a display memory 34 such as a readable and writable DRAM, and is read out from this to the CRT monitor 7 and displayed as a tomographic image. The tomographic image data is read from the display memory 34 and stored in the magnetic disk device 38 via the disk I / F 30.

Next, the operation of the present embodiment will be described. FIG. 1 is a flowchart of the fluoroscopy mode. FIG. 5 is a diagram showing a schematic flow from scanning in the fluoroscopic mode to display. . In the present embodiment, as described above, the operation mode includes the fluoroscopic mode and the photographing mode, and one of the modes is selectively set by an operator's instruction input via the keyboard 6.
When the operation is started, continuous rotation of the X-ray tube 12 and the detector array 16 is started in step # 10, and continuous scanning is started. The continuous scan is defined by repeating a scan operation continuously. The scanning operation is defined by collecting projection data in multiple directions required to reconstruct one tomographic image while the X-ray tube 12 and the detector array 16 rotate. During successive scans, the slice position may be fixed or may change. As will be described later, according to the present embodiment, data collection, image reconstruction, and display are performed at high speed as a series of operations, and a scan operation time for collecting one sheet of projection data is passed through reconstruction processing. Since the time interval (time difference) until the display of the tomographic image is constant for all the scanning operations, the time interval from the scanning operation to the display of the tomographic image is waited for writing and reading to and from the memories 34 and 36. The tomographic image can be displayed almost in real time like a cine image without causing irregularities due to the presence or absence of time and making it impossible to reproduce the actual movement of the subject 10 in real time. This fluoroscopic mode is performed, for example, to confirm the arrival of the tip of the puncture needle to the tumor portion during puncture treatment by continuous display of tomographic images while performing continuous scanning. In this case, the slice position during the continuous scan is fixed. In addition, it can be used for positioning a slice position where normal imaging is performed, but in this case, it is considered that the slice position needs to be freely changed. The change of the slice position may be performed by sliding the top 5. However, when the fluoroscopic mode is used during the operation, it is not preferable to move the patient to which various tubes and instruments are attached. It is desirable to change the slice position. In this case, it is preferable that the gantry 1 is provided with a power assist mechanism so that the doctor can easily move manually. Further, the change of the slice position in the fluoroscopic mode does not need to be at a constant speed as in a normal helical scan, but may be stopped and moved irregularly or the speed may be changed irregularly.

During the scanning operation, the projection data collected and output by the data collection device 18 is subjected to pre-processing such as calibration in the pre-processing unit 28, and is then sequentially written to the memory 36 as raw data. For example, the rotation speed of the X-ray tube 12 and the detector array 16 is 1 second / 1 rotation, and one continuous scan determines a period (50 seconds) in which the X-ray tube 12 and the detector array 16 rotate 50 times. This period is set so as not to exceed an allowable time determined from the viewpoint of the heat resistance of the X-ray tube 12 and the safety of the subject 10 against exposure. Assuming that 2 MB of raw data is collected in one rotation, the memory 36 has a storage capacity of about 100 MB so that all the raw data for one continuous scan can be stored. Further, the display memory 34 has a storage capacity capable of storing a plurality of tomographic image data obtained by one continuous scan.

In step # 12, the CPU 22 determines whether or not raw data necessary to reconstruct one piece of tomographic image data has been collected. If collected, the raw data is transferred from the memory 36 to the reconstruction unit 32 in step # 14. Note that the scanning operation is continuously performed. Since the raw data is sent from the data collection device 18 to the reconstructing unit 32 via the memory 36, the time from the scanning operation to the start of the reconstructing process is remarkably reduced as compared with the case of using a magnetic disk having a long access time. It became possible to do. In the past, all raw data was stored once on a magnetic disk, and then read out and reconstructed at an empty time. Could not get.

The processing time of the reconstruction unit 32 is high-speed processing shorter than the scanning operation (data collection time). As a result, the time lag of the completion of the reconstruction of the tomographic image with respect to the scanning operation, specifically, the reconstruction using the data from the time when the collection of the projection data necessary to reconstruct one tomographic image is completed It is possible to avoid that the time difference until the completion is cumulatively increased each time the scanning operation is repeated. In the high-speed processing, the reconstruction unit 32 connects a plurality of processors in parallel, divides the raw data for each view, or for each channel (one detector generally corresponds to one channel) and reconstructs the raw data. Processing proceeds in parallel. The processing speed can be increased by increasing the number of parallel processes. Further, the processing speed can be increased by increasing the clock speed.

In order to realize the high-speed processing of {reconstruction}, in the present embodiment, it is also adopted to further reduce (thinning out or bundling) the number of views per 360 (1 rotation). For example, at the time of normal photographing, projection data of 900 views / 1 rotation is collected. That is, data collection is repeated at 900 cycles by the data collection device 18 during one rotation. Repeat data collection in one revolution. In this case, the spatial resolution of the tomographic image is reduced, but the purpose of the fluoroscopic mode by the continuous scan is to immediately see the movement of the subject 10 in a state close to real time, and tomographic images with a high spatial resolution are taken. Since the photographing is performed in the mode, there is no problem that the ripples are caused by the deterioration of the spatial resolution. Further, in order to shorten the reconstruction time, the number of pixels (the number of pixels) at the time of reconstruction may be reduced. In a normal imaging mode, one tomographic image is reconstructed with a size of 512 × 512 pixels and displayed at that size. In a fluoroscopic mode, the image is reconstructed with a size of 256 × 256 pixels. The time can be reduced by increasing the number of pixels to 512 × 512 pixels by interpolation at the time of display.

Further, in a continuous scan, a tomographic image is repeatedly reconstructed. It is assumed that one tomographic image is reconstructed in one rotation, and the next one tomographic image is reconstructed in the next one rotation. If the rotation speed of the X-ray tube 12 and the detector array 16 is 1 second / 1 rotation, the tomographic image is reconstructed at a rate of 1/1 second. In the present embodiment, the technique described in Japanese Patent Application Laid-Open No. 4-266744 may be employed to increase the reconstruction rate. That is, each time the X-ray tube 12 and the detector array 16 rotate by a small angle α ° (for example, α = 10 °), partial images are successively reconstructed from projection data for 10 °. Then, one complete tomographic image for 360 ° is created by adding the 36 partial images for 360 °. Further, once one tomographic image is created, the process of adding the latest partial image to this tomographic image and subtracting the oldest partial image from the tomographic image are repeated. As a result, new tomographic images are generated one after another every 10 ° rotation, and tomographic images can be continuously acquired at a high reconstruction rate. Further, in order to increase the reconstruction rate, the technique disclosed in Japanese Patent Application No. 1-2136 may be adopted. With this technique, reconstructed image information is obtained from a group of projection data for one image by back projection. Then, the difference data between the latest projection data obtained immediately after the group of projection data and the projection data in the group corresponding to the projection data immediately after this group of data is further backed up to the reconstructed image information. Projection. As a result, the next reconstructed image information shifted in time can be created at high speed. In any of the techniques, the idea of sequentially updating the reconstructed tomographic images is present at the root thereof, and another technique spreading from this idea may be used to increase the reconstruction rate.

When the reconstruction is completed, the tomographic image data is written to the display memory 34 in step # 16. Until the next tomographic image is reconstructed and displayed, the current tomographic image data is repeatedly read out from the display memory 34 at a constant period so that the current tomographic image is displayed in a frozen state on the CRT monitor 7. The read data is transferred to the CRT monitor 7. Such a display method is the same as the cine display in the X-ray imaging apparatus. Note that if the next tomographic image data is written while the display memory 34 is being read, the information will be different between the upper and lower parts of the image. Therefore, it is necessary to wait for the writing during the reading.

In step # 18, the CPU 22 determines whether or not one continuous scan has been completed, that is, whether or not 50 seconds have elapsed since the start of the scan. If no, the process returns to step # 12, and waits until the collection of data necessary for reconstruction of the next one tomographic image is completed. When one continuous scan is completed, the raw data in the memory 36 is stored on the magnetic disk 38 in step # 20. If there is no need to save the raw data, step # 20 may be omitted. In step # 22, it is determined whether or not to perform the next continuous scan. If so, the process returns to step # 10. If not, the process ends.

Since the raw data for at least the last one continuous scan is stored in the memory 36, if the tomographic image is to be displayed again after the continuous scan, the raw data read from the memory 36 may be reconstructed. Good. As described above, in the fluoroscopy mode, a tomographic image can be observed almost in real time, so that it may be used as a surgical support image during an operation such as puncture. However, the surgeon often cannot observe the monitor during the operation, and gives various instructions to the surgeon (doctor) while the assistant looks at the monitor. However, the doctor sometimes wants to see the progress of the puncture after the end of one continuous scan, and after the end of the continuous scan, freezes the last tomographic image and reads it from the memory 36 when the doctor gives an instruction. It can be viewed by reconstructing the raw data and displaying the images frame by frame.

Next, the operation from data collection to display of one piece of tomographic image data will be described in detail. FIG. 6 is a time chart showing this operation. While the X-ray tube 12 and the detector array 16 rotate around the subject 10, projection data is output from the data acquisition system 18 at each minute angle. The projection data is sequentially written into the memory 36 as raw data via the preprocessing unit 28. After all projection data for all angles (0 ° to 360 °) necessary for reconstructing one tomographic image is written to the memory 36, the projection data is read out from the memory 36, and the reconstruction unit 32 Will be forwarded to In the reconstruction unit 32, the tomographic image data is reconstructed at a high speed, that is, in a shorter time than the data collection time, and written into the display memory 34. During this time, access to the magnetic disk 38 is not performed. The tomographic image data is read from the display memory 34 and sent to the CRT monitor 7 for display. As described above, the reading of the tomographic image data from the display memory 34 is repeated until the next tomographic image is displayed.

Here, what is important for real-time cine display (moving image display) is that in addition to shortening the time from the scanning operation to displaying the tomographic image, there is a case where the speed of the movement is faithfully reproduced. For example, switching between two tomographic images collected at one-second intervals and displaying them at 1.1-second intervals does not reproduce actual movement. In the present embodiment, as shown in FIG. 7A, the time difference Δt from the completion of the scanning operation for one tomographic image (the completion of data collection) to the start of display of the tomographic image is calculated for all the tomographic images. By making the images I1, I2, I3... Constant, in other words, as shown in FIG. 7B, the tomographic images I1, I2 are displayed at intervals equal to the interval Δt1 between the respective scanning operations, and I2 and I3 are displayed at intervals equal to the interval .DELTA.t2 between the scanning operations, and thereafter, the tomographic images are sequentially switched and displayed in the same manner with a time difference equal to the interval between the scanning operations, so that the time scale of the scanning operation and the display are equalized. To achieve a faithful reproduction of the actual movement. In general, the time △ t ′ from the scanning operation to the end of the writing of the tomographic image data to the display memory 34 may be long depending on the load on the CPU 22, for example, longer during scanning and shorter when not scanning. ,fluctuate. Therefore, if the reading is started immediately after the writing of the tomographic image data to the display memory 34 is completed, the actual movement cannot be reproduced. In the present embodiment, the time difference from the scanning operation to the start of tomographic image data reading (start of display) is fixed to at least the time (longest time) when the CPU 22 is under the maximum load, and the actual movement is reproduced. To achieve. This time control can be realized by a well-known technique. As shown in FIG. 4, the operation of each unit 28, 32, 34, 36 may be comprehensively controlled by the CPU 22, as shown in FIG. The clocks of the reconfiguration unit 32 and the display memory 34 may be shared, and although not shown, a timer circuit is provided in the preprocessing unit 28 and the display memory 34 so that the preprocessing unit 28 May be notified of the time at which one piece of projection data has arrived, and the tomographic image data may be read from the display memory 34 at a time after a lapse of a predetermined time from this time.

As described above, according to the present embodiment, it is possible to observe the movement of a target almost in real time like a cine image while continuously scanning. Therefore, it is possible to support a biopsy or the like by observing a blood flow (flow of a contrast medium), executing imaging at an optimal timing under the fluoroscopy, and observing a movement of a catheter and a change in a blood type.

In addition, as a modification example of increasing the data collection speed, in the case of a third-generation CT apparatus, a multi-tube (for example, three-tube) X-ray tube is used, the rotation speed of X-rays is increased, This can be achieved by using a fifth generation CT apparatus. The fifth-generation CT apparatus can be operated at high speed by arranging a large number of X-ray tubes around the subject or scanning the electron beam using a bell-shaped X-ray tube having an annular cathode surrounding the subject. Realize rotation.

Further, as a modified example for increasing the data collection speed and the reconstruction time, a so-called half which performs reconstruction from projection data of less than 360 °, for example, 180 °, instead of reconstruction from 360 ° of projection data. A scan reconstruction method is adopted.

変 形 Further, as a modification for preventing an increase in the exposure dose due to the continuous scan, an X-ray generator capable of generating X-rays with a low tube current and an X-ray generator capable of generating pulsed X-rays are employed. The X-ray dose greatly depends on mAs which is a product of the tube current mA and the exposure time t (second). Therefore, the tube current may be reduced to reduce the dose. However, since a normal CT apparatus is designed to output X-rays with a tube current of several hundred mA, a method of controlling the tube voltage and the tube current so that X-rays can be output even at a low tube current of several tens mA. change.

In order to reduce the exposure dose, there is a method in which pulsed X-rays are used instead of continuous X-rays which are currently mainstream in CT devices. For example, as shown in FIG. 9, when a pulse X-ray having a duty ratio of 50% (X-rays are emitted only for half of the total time) is used, the dose is reduced to て compared to continuous X-rays. can do. Further, a circuit for controlling on / off of X-ray irradiation at a high speed is provided in a control unit in the console 3 so that the rotation of the X-ray tube 12 and the detector array 16 can be continued and the preheating state of the X-ray tube 12 can be controlled. The X-rays may be turned on and off at a high speed when the operator intends, while continuing. As a result, frequent X-ray on / off operations can be easily performed at high speed, and the amount of exposure of the subject can be reduced.

Further, as shown in FIG. 10, by providing a filter 40 made of aluminum or copper near the X-ray exit of the X-ray tube 12 or near the upper slit 42, the exposure dose of the subject can be reduced. Examples of the material of the filter 40 include Teflon and molybdenum. In addition, by making the thickness of the filter 40 and the wedge 43 variable during imaging, the amount of exposure can be adjusted during imaging.

Furthermore, in the above description, the tomographic image data is not stored on the magnetic disk 38, but the tomographic image displayed on the CRT monitor 7 may be stored using a video recorder as needed. After the scan is completed, the tomographic image is reproduced and displayed from the video recorder, thereby making it possible to perform frame-by-frame and reverse feed, thereby facilitating diagnosis. Further, the reconstructed image data and supplementary information may be recorded as they are in a digital format. When displaying the recorded data, the data is transferred to the CRT monitor 7 via the display 34. When recorded as digital data, post-processing such as deletion can be easily performed.

(2nd Embodiment)
FIG. 11 shows the configuration of a computer tomography apparatus according to the second embodiment. Here, a third-generation (R / R) computed tomography apparatus in which the X-ray tube and the X-ray detector rotate around the subject as a unit will be described. It may be a fourth generation (R / S) computed tomography apparatus in which the X-ray detector is fixed.

Inside the gantry 51, the X-ray tube 53 and the multi-channel type X-ray detector 54 are supported by the rotating unit 52 in a state where they face each other with the subject interposed therebetween. The gantry control unit 57 controls the rotation of the rotating unit 52 by supplying driving power to a driving device such as an electric motor that drives the rotation of the rotating unit 52. The X-ray tube 53 and the multi-channel X-ray detector 54 are each connected to a high voltage generator on a fixed part side via a slip ring (not shown) so that projection data at an angle of 360 ° or more can be continuously collected. 55 and the data collection unit 60 are electrically connected. From the focal point of the X-ray tube 53 supplied with power from the high voltage generator 55, X-rays are emitted in a fan shape. The multi-channel X-ray detector 54 is composed of a plurality of detection elements arranged in an arc around the focal point of the X-ray tube 53. At the center of the gantry 51, an opening (not shown) capable of accommodating the subject is provided. The gantry 51 is installed on the floor via a tilt table so as to be tiltable with respect to the vertical axis. A bed (not shown) is arranged on the front of the gantry 51. A top plate on which the subject is placed is provided on the upper surface of the bed. The top plate is supported so as to be slidable along a longitudinal direction from the bed to the gantry 51 and slidable along a width direction orthogonal to the longitudinal direction in a horizontal plane. The top plate is independently and electrically slid in each direction by a driving device such as a motor. The couch control unit 56 controls the position in the longitudinal direction (the slice position of the subject) and the position in the width direction of the tabletop by supplying a control signal to the driving device.

The data collection unit 60 collects projection data corresponding to the X-ray transmittance based on the output of the multi-channel X-ray detector 54. The projection data from the data collection unit 60 is sent to the scanogram memory 61 during scanogram imaging, and sent to the reconstruction processing unit 62 during scanning. The scanogram is an X-ray projection image of the subject viewed from one direction, and is captured while sliding the top while the rotating unit 52 is stopped. At the time of CT fluoroscopy, scanogram data is repeatedly read out from the scanogram memory 61 at regular intervals, is combined with the line cursor data from the system control unit 8 by the adder 63, and then reconstructed by the reconstruction processing unit 62. The data is sent to the image display device 64 together with the constituted tomographic image data. At the time of CT fluoroscopy, a scanogram and a tomographic image are simultaneously displayed on one screen in the image display device 64. An operation unit 59 such as a trackball or a joystick is connected to the system control unit 8. When the operation unit 59 is operated by the operator, the line cursor moves on the scanogram accordingly. The position of this line cursor on the scanogram corresponds to the slice position of the subject for which data acquisition is actually being performed. When the line cursor is moved on the scanogram, the system control unit 8 controls the bed control unit 56 to move the tabletop so that the slice position corresponds to this position.

Next, the operation of the present embodiment will be described. FIG. 12 shows an example of a display screen during CT fluoroscopy. Since the CT fluoroscopy has been described in the first embodiment, it is omitted here. Before actually starting CT fluoroscopy, a scanogram is taken. The X-ray exposure and data collection are repeated with the rotating unit 2 fixed at an angle of, for example, 0 °. During this time, the top plate is moved continuously or intermittently. The X-ray exposure and the data collection may be repeated while rotating the rotating unit 2 only at an angle of, for example, 0 °. Based on the output of the multi-channel X-ray detector 54, the data collection unit 60 repeats the collection of projection data in synchronization with the X-ray exposure. The projection data is sent to the scanogram memory 11 and stored. As described above, the scanogram is an X-ray projection image, and the projection data collected by the data collection unit 60 is used as it is as scanogram data.

Next, CT fluoroscopy is actually started. Here, a single slice CT fluoroscopy will be described. In CT fluoroscopy, X-ray exposure and data acquisition are repeated while the rotating unit 52 rotates continuously, and projection data is continuously acquired over an angle of 360 ° or more. Each time projection data necessary for reconstructing one piece of tomographic image data is collected, the reconstruction processing unit 62 continuously reconstructs the tomographic image data and sequentially transmits the tomographic image data to the image display device 64. Can be Further, the scanogram data is read from the scanogram memory 61, added with the line cursor data via the adder 63, and sent to the image display device 64. In the image display device 64, as shown in FIG. 12, the tomographic image is combined with the scanogram on one screen and displayed simultaneously. The line cursor on the scanogram indicates the current slice position.

When the operator wants to change the slice position (diagnosis site), he operates the operation unit 59 to move the line cursor on the scanogram along the body axis direction. The system control unit 8 controls the bed control unit 56 in accordance with the movement of the line cursor on the scanogram to move the couchtop in the longitudinal direction. As a result, the tabletop moves following the movement of the line cursor, a slice position corresponding to the position of the line cursor on the scanogram is set, and the slice position can be scanned. Actually, it is considered that the line cursor is roughly moved to a desired position on the scanogram, and thereafter, the position of the line cursor is finely adjusted while observing a tomographic image displayed in real time. .

ラ イ ン Further, the line cursor is moved along the width direction orthogonal to the body axis on the scanogram by operating the operation unit 59. The system control unit 8 controls the bed control unit 56 to move the tabletop in the width direction according to the movement of the line cursor on the scanogram. This makes it possible to correct the displacement between the reconstruction area and the subject so that the desired part is included in the tomographic image.

ス ラ イ ス By moving the line cursor on the scanogram in this manner, the change of the slice position can be completed easily and in a short time.

While the tabletop is sliding, and while the gantry 51 is tilted as shown in FIG. 14, the gantry control section 57 is controlled by the system control section 58 to rotate the gantry control section 57 as shown in FIG. The rotation of 52 is continued, and the high voltage generator 55 temporarily stops the power supply to the X-ray tube 53 to stop the X-ray exposure. Since the rotation of the rotating unit 52 is continued as described above, after the slide of the top plate 65 is completed and a desired slice position is set, the power supply from the high voltage generator 55 to the X-ray tube 53 is performed. By restarting, the data collection can be restarted immediately and CT fluoroscopy can be started. This is because, if the rotation of the rotating unit 52 is stopped while the top plate 65 is sliding, the waiting time until the rotating unit 52 reaches the rotation at a constant angular velocity after the sliding of the top plate 65 is unnecessary. Because it becomes. Further, while the top plate 65 is sliding, the exposure of X-rays is stopped, so that unnecessary exposure can be prevented.

(Third embodiment)
Next, a third embodiment will be described. FIG. 15 is a diagram showing the overall configuration of the X-ray CT according to the third embodiment. The same parts as those in FIG. Here, a helical scan in which the X-ray tube 53 moves along a spiral trajectory as viewed from the subject as shown in FIG. Scan is employed. Here, a helical scan will be described as an example. The helical scan is performed by repeating the data collection while the rotating unit 52 continuously rotates and the top plate slides in one direction at a constant speed. The projection data is represented by D (CH, ψ, Z). CH is the channel, ψ is the angle of the rotating part 52, and Z is the top position in the longitudinal direction (body axis direction). In the helical scan, since the top plate slides continuously, Z changes according to ψ. In order to reconstruct one tomographic image, it is necessary to use 360 ° projection data with the same Z. Since the projection data actually obtained by the helical scan changes Z according to 応 じ, as shown in FIG. 16B, the projection data for 720 ° actually collected by the distance interpolation processing is 720 °. The projection data is converted into 360-degree projection data unified to the center Zc (Zc = (Z1-Zn) / 2) of the Z range (Z1 -Zn) of the projection data for -degree. The slice position of the helical scan tomographic image is defined by Zc.

When the support of “interruption” is input through the operation unit 67 while performing CT fluoroscopy by helical scan, the system control unit 66 stops the top plate, stops X-ray exposure, and collects data. Interrupted. However, continuing the rotation of the rotating unit 52 as in the second embodiment is preferable for prompt restart of CT fluoroscopy. There is a certain time lag between the data collection and the display of the tomographic image because the time required for the distance interpolation processing and the reconstruction processing is required. Due to the existence of the time lag and the principle of the distance interpolation, when the interruption is supported, the slice position of the tomographic image displayed on the image display device 64 does not necessarily coincide with the current position of the top board.

When the CT fluoroscopy is interrupted, the top panel is slid in the opposite direction until the CT fluoroscopy is resumed, and the tomographic image displayed on the image display device 64 when the instruction to interrupt is given. The image is returned to the slice position of the latest tomographic image. When an instruction to restart CT fluoroscopy is input via the operation unit 67, the system control unit 66 controls the bed control unit 56 to restart sliding of the top board, and restarts CT fluoroscopy. In the interrupted CT fluoroscopy, the rotation of the rotating unit 52 is continued, and the top plate is returned to the slice position of the latest tomographic image displayed on the image display device 64 when the interruption instruction is given. Since it is in a standby state in a state in which the X-ray is irradiated, it can be quickly resumed only by restarting the X-ray exposure.

By designating an arbitrary one of a plurality of reconstructed tomographic image data, it is possible to automatically return the top plate to the specified slice position of the tomographic image data. By designating any two of the reconstructed tomographic image data, CT fluoroscopy can be performed while reciprocating in the range of the slice positions of both images. Further, in the case where the helical scan is executed while changing the tilt angle of the gantry 51, the tilt angle is stored in correspondence with the position of the tabletop, so that the image display device 64 is supported when the interruption is supported. Can be returned to the tilt angle at the time of collecting the tomographic image data displayed in FIG.

The present invention is not limited to the above-described embodiment, and can be implemented with various modifications.

5 is a flowchart illustrating an operation in a fluoroscopic mode according to the first embodiment. FIG. 2 is an external view of an X-ray CT. FIG. 3 is a structural view of the inside of the gantry of FIG. FIG. 3 is a block diagram of a control unit. The figure which shows the process progress of the fluoroscopy mode. FIG. 6 is a diagram showing a processing procedure from data collection to display of one tomographic image. FIG. 4 is a diagram showing timings of data collection and display in a continuous scan. FIG. 5 is a modified view of FIG. 4. The figure which shows the pulse X-ray used for exposure dose reduction. The figure which shows the filter used for exposure dose reduction. FIG. 9 is a configuration diagram of an X-ray CT according to a second embodiment. The figure which shows an example of a display screen. 9 is a time chart showing operations related to a rotating part and X-ray exposure at the time of a top slide or a gantry tilt. The figure which shows a gantry tilt. FIG. 9 is a configuration diagram of a third embodiment. The figure which shows the trajectory of the X-ray tube in a helical scan.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... stand, 2 ... bed, 3 ... operation console, 4 ... opening part, 5 ... top plate, 6 ... keyboard, 7 ... CRT monitor, 10 ... subject, 12 ... X-ray tube, 14 ... X-ray generator, 16 detector array, 18 data acquisition system, 20 control unit, 22 CPU, 24 control bus, 26 data bus, 28 preprocessing unit, 30 disk interface, 32 reconfiguration unit, 34 Display memory, 36 memory, 38 magnetic disk device, 42 clock circuit.

Claims (9)

A helical scanning unit that has an X-ray tube that emits X-rays and an X-ray detector that detects X-rays transmitted through the subject in a rotating unit, and that performs helical scanning of the subject;
Image reconstruction means for reconstructing the image data based on the projection data collected by the helical scan, each time the projection data of the angle range necessary to reconstruct the image data is collected,
Display means for displaying image data reconstructed by the image reconstructing means;
Instruction means for instructing interruption,
In parallel with the scan operation of the helical scan, control is performed so that reconstruction processing by the image reconstruction unit and display operation by the display unit are performed, and interruption of the helical scan is performed based on an interruption instruction from the instruction unit. A computer tomography apparatus, comprising: control means for performing control. 2. The computed tomography apparatus according to claim 1, wherein the control unit performs control for stopping X-ray irradiation from the X-ray tube based on the interruption instruction. The computer tomography apparatus according to claim 1, wherein the control unit performs control for interrupting acquisition of projection data by the helical scan based on the interruption instruction. 4. The computed tomography apparatus according to claim 1, wherein the control unit continues the rotation of the X-ray tube in the helical scan even if the interruption instruction is issued. 2. The apparatus according to claim 1, wherein the control unit returns the scan position to a position where projection data necessary for reconstructing the latest image data displayed on the display unit is collected when the interruption instruction is issued. The computer tomography apparatus according to any one of claims 1 to 4. Further comprising a designation unit for designating the image data reconstructed by the reconstruction unit,
5. The apparatus according to claim 1, wherein the control unit moves a scan position to a position where projection data necessary for reconstructing image data specified by the specifying unit is collected. Computer tomography equipment. 5. The control device according to claim 1, wherein the control unit repeats scanning between two positions at which projection data necessary for reconstructing the two pieces of image data specified by the specifying unit is collected. 6. A computer tomography apparatus according to any one of the preceding claims. When the interruption instruction is issued, the control unit sets the X-ray tube and the X-ray detector to a tilt angle at which projection data necessary for reconstruction of the latest image data displayed on the display unit is collected. 2. The computed tomography apparatus according to claim 1, wherein the gantry is returned. The control means reconstructs the image data in a shorter time than the time required for the scanning operation for collecting the projection data in the angle range in the image reconstructing means, and repeats the next to successively generate a series of image data one after another. 9. The display device according to claim 1, wherein the display means controls the display so that the successively reconstructed image data is displayed after a predetermined time from the corresponding scanning operation. The computed tomography apparatus according to any one of the preceding claims.

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