JP3660670B2 - Computed tomography equipment - Google Patents

Description

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

  In general, in CT, three processes of scanning, image reconstruction, and image display are performed in time series. 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, subjected to preprocessing such as calibration, and then as raw data such as a magnetic disk Are once stored in the mass 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 in the magnetic disk and transferred to the CRT monitor as a video signal via the display memory and displayed.

  By the way, the introduction of the slip ring has enabled continuous scanning. With this continuous scanning, a plurality of multidirectional projection data relating to the same or a plurality of slices can be collected in time series. These multi-directional projection data are read to the reconstruction unit at an arbitrary timing via the magnetic disk as described above and are used for reconstruction. The time required for this reconstruction process is longer than the scan time, and the magnetic disk has a longer storage and access time. Therefore, it was impossible to continuously display the tomographic image like a cine video in real time while executing the continuous scan.

  In recent years, high-speed processing of reconstruction has been studied, and is about to reach a practical range. As a result, it is expected that tomographic images will be displayed continuously like cine video in real time while executing continuous scanning. Not reached. Furthermore, since the waiting time for storage and access to 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 is reproduced. I could not.

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

  An object of the present invention is to suitably interrupt a helical scan.

The present invention has an X-ray tube for exposing X-rays and an X-ray detector for detecting X-rays transmitted through the subject in a rotating part, helical scanning means for helically scanning the subject, and image data An image reconstruction unit that reconstructs the image data based on the projection data collected by the helical scan each time the projection data in the angular range necessary for reconstruction is collected, and the image reconstruction unit reconstructs the image data. Display means for displaying the configured image data, instruction means for an operator to instruct interruption, and reconstruction processing by the image reconstruction means and the display means in parallel with the scanning operation of the helical scan controls to perform the display operation, on the basis of the interruption instruction from the instruction means to stop the X-ray radiation from the X-ray tube, the in the helical scan Also the rotation of the line pipe is made the interruption instruction, characterized by comprising a control means for controlling said helical scanning means to continue.

  According to the present invention, helical scanning can be suitably interrupted.

Embodiments of a computer tomography apparatus according to the present invention will be described below with reference to the drawings.
(First embodiment)
FIG. 2 is a schematic diagram showing the configuration of the first embodiment. The computed tomography apparatus according to this embodiment includes a gantry 1, a bed 2, and a console 3. An opening 4 into which the subject is inserted is provided at the center of the gantry 1. A bed 2 is arranged on the front surface of the gantry 1. The bed 2 is configured to be electrically adjustable in height. A couchtop 5 on which a subject is placed is provided on the upper surface of the couch 2, and the couchtop 5 is configured to be slidable electrically from the upper surface of the couch 2 toward the gantry 1. Although not shown, a caster or the like is attached to the 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 moving the top plate 5. . Of course, the slice position can be changed by sliding the top plate 5. In the photographing mode, it is common to change the slice position only by sliding the top plate 5.

A keyboard (which 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.

  In the gantry 1, as shown in FIG. 3, an X-ray tube 12 that exposes a fan-shaped X-ray beam to a subject 10 placed on the top 5, and a focal point of the X-ray tube 12. A plurality of detectors are arranged in a circular arc shape, and a detector array 16 that detects X-rays transmitted through the subject 10 in multiple channels is integrated around the subject 10 while facing the subject 10 therebetween. Is supported by the rotating part so that it can be continuously rotated. Further, the X-ray tube 12 and the detector array 16 are electrically connected to the fixed portion via a slip ring. Thereby, the X-ray tube 12 and the detector array 16 continuously rotate around the subject 10 and continuously collect multidirectional projection data related to the subject 10 required for reconstruction of one tomographic image. If it rotates continuously at the same slice position, for example, so-called dynamic scan that tracks changes in tomographic images due to inflow and outflow of contrast agent is possible, and if the slice position is changed in synchronization with rotation So-called helical scan is possible. This type of CT is referred to as a so-called third generation (R / R method). The gantry 1 is not limited to this type, and may be a so-called fourth generation (R / S system) 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 also be a so-called fifth generation (S / S system) arranged around the subject over 360 °.

  An X-ray generator 14 that supplies tube current and tube voltage to the X-ray tube 12 in a continuous or pulsed manner to generate X-rays is installed in the fixed portion of the gantry 1, and X-rays are supplied via slip rings. Connected to tube 12. The X-ray generator 14 can also be mounted on the rotating part of the gantry 1. In addition, a data acquisition system (DAS) 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 that temporally integrates an output signal from each detector of the detector array 16, a multiplexer for capturing the output of the integrator in a channel unit at high speed, and the multiplexer The analog-digital converter or the like that converts the output signal into digital is collected, and projection data reflected in the X-ray transmittance for each X-ray path is collected and output.

  FIG. 4 is a block diagram of the control unit 20 in the console 3. A CPU 22 as a host controller is provided, 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 the clock from the clock circuit 42, and supplies this clock to each unit in the control unit 20 as a common clock. A pre-processing unit 28, a disk interface (disk I / F) 30, a reconstruction unit 32, and a display memory 34 are connected to the control bus 24. The keyboard 6 and the X-ray generator 14 are connected to the control bus 24. To the data bus 26, a preprocessing unit 28, a disk I / F 30, a reconstruction unit 32, a display memory 34, and a memory 36 are connected. A magnetic disk device 38 as a mass storage device is connected to the disk I / F 30. A data collection system 18 is connected to the preprocessing unit 28. The projection data from the data collection system 18 is subjected to preprocessing such as calibration in the preprocessing unit 28, and then temporarily written as raw data into a readable / writable memory 36 such as a DRAM via the data bus 26. It is read from here and sent to the reconstruction unit 32. The reconstruction unit 32 reconstructs tomographic image data based on multidirectional projection data. This tomographic image data is temporarily written in a display memory 34 such as a readable / writable DRAM, and is further read from here 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 this embodiment will be described. FIG. 1 is a flowchart of the fluoroscopic mode. FIG. 5 is a diagram showing a schematic flow from scanning to display in the fluoroscopic mode. . In the present embodiment, as described above, there are a fluoroscopic mode and a photographing mode as operation modes, and one mode is selectively set according to 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. A continuous scan is defined by continuously repeating a scanning operation. The scanning operation is defined by collecting multi-directional projection data 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 a high speed as a series of operations, and a reconstruction process is performed from a scan operation time for collecting projection data for one sheet. Since the time interval (time difference) until the tomographic image is displayed is constant for all scanning operations, the time interval from the scanning operation to the display of the tomographic image is waiting for writing to and reading from the memories 34 and 36. The tomographic image can be displayed almost like a cine video in real time without becoming irregular due to the presence of time or the like and being unable to reproduce the actual movement of the subject 10 in real time. This fluoroscopic mode is performed, for example, in order to confirm the arrival of the tip of the puncture needle at the tumor part during continuous puncture treatment by continuous display of tomographic images while continuously scanning. In this case, the slice position during the continuous scan is fixed. Further, it can be used for positioning of a slice position for performing normal photographing, but in this case, it is considered that the slice position needs to be freely changed. The slice position may be changed by sliding the top plate 5, but when using the fluoroscopic mode during the operation, it is not preferable to move the patient to which various tubes and equipment 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 it manually. Further, the change in the slice position in the fluoroscopic mode does not need to be a constant speed as in a normal helical scan, and may stop and move irregularly, or change the speed.

  During the scanning operation, the projection data collected and output by the data collection device 18 are sequentially written as raw data in the memory 36 after undergoing preprocessing such as calibration by the preprocessing unit 28. For example, the rotation speed of the X-ray tube 12 and the detector array 16 is 1 second / rotation, and a period of time during which the X-ray tube 12 and the detector array 16 rotate 50 times (50 seconds) is determined for one continuous scan. This period is set so as not to exceed the 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. The memory 36 has a storage capacity of about 100 MB, assuming that 2 MB of raw data is collected in one rotation 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. The scanning operation is continued continuously. Since the raw data is sent from the data collection device 18 to the reconstruction unit 32 via the memory 36, the time from the scanning operation to the start of the reconstruction process is significantly shortened compared to 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 the magnetic disk and then read and reconstructed at a free time, so it took a long time from the scan operation to the start of the reconstruction process, and real-time performance Could not get.

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

  In order to realize high-speed processing of reconstruction, the present embodiment further employs reducing (thinning out or bundling) the number of views per 360 ° (one rotation). For example, during normal imaging, projection data of 900 views / revolution is collected, that is, data collection is repeated in 900 cycles in the data collection device 18 during one revolution, but 450 views / return in the perspective mode. Repeat data collection in one rotation. In this way, although the spatial resolution of the tomographic image is reduced, the purpose of the fluoroscopic mode by continuous scanning is to immediately see the movement of the subject 10 in a state close to real time, and the tomographic image with high spatial resolution is taken. Since it is only necessary to shoot in the mode, there will be no problem spreading from the drop in spatial resolution. Further, in order to shorten the reconstruction time, the number of pixels (number of pixels) at the time of reconstruction may be reduced. In the normal imaging mode, one tomographic image is reconstructed with a size of 512 × 512 pixels and displayed in that size, but in the fluoroscopic mode, it is reconstructed with a size of 256 × 256 pixels, The time can be shortened by increasing the number of pixels to 512 × 512 pixels by interpolation at the time of display.

  Furthermore, in the continuous scan, the tomographic image is reconstructed repeatedly. With this, one tomographic image is reconstructed by one rotation, and the next tomographic image is reconstructed by the next one rotation. If the rotational speeds of the X-ray tube 12 and the detector array 16 are 1 second / rotation, the tomographic image is reconstructed at a rate of 1 / second. In this embodiment, in order to increase the reconstruction rate, the technique described in Japanese Patent Laid-Open No. 4-266744 may be employed. This reconstructs partial images one after another from 10 ° projection data each time the X-ray tube 12 and the detector array 16 rotate by a minute angle α ° (for example, α ° = 10 °). Then, by adding 36 partial images for 360 °, one complete tomographic image for 360 ° is created. Furthermore, once a tomographic image is created, the latest partial image is added to the tomographic image, and the oldest partial image is subtracted from the tomographic image. As a result, new tomographic images are created one after another every 10 ° rotation, and the tomographic images can be continuously acquired at a high reconstruction rate. In order to increase the reconstruction rate, the technique disclosed in Japanese Patent Application No. 1-23136 may be employed. With this technique, reconstructed image information is obtained from back-projection from a group of projection data for one image. 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 position of the projection data immediately after the group is further backed up against the reconstructed image information. Project. This makes it possible to create the next reconstructed image information shifted in time at high speed. Each technique has the idea of sequentially updating the tomographic images once reconstructed, and the reconstruction rate may be increased by adopting another technique that spreads from this concept.

  When the reconstruction is completed, the tomographic image data is written into the display memory 34 at step # 16. Until the timing when the next tomographic image is reconstructed and displayed, the current tomographic image data is repeatedly read from the display memory 34 at a constant cycle 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 during reading of the display memory 34, the information differs between the top and bottom of the image, so it is necessary to wait for writing during reading.

  In step # 18, the CPU 22 determines whether or not one continuous scan is completed, that is, whether or not 50 seconds have elapsed since the start of the scan. If not, 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 in the magnetic disk 38 in step # 20. If there is no need to store the raw data, step # 20 may be omitted. In step # 22, it is determined whether or not the next continuous scan is performed. If so, the process returns to step # 10, and if not, the process ends.

  Since the raw data for at least the last continuous scan is stored in the memory 36, if the tomographic image is to be displayed again after the continuous scan is completed, the raw data read from the memory 36 can be reconstructed. Good. As described above, in the fluoroscopic mode, a tomographic image can be observed almost in real time, so that it may be used as an operation support image during an operation such as puncture. However, the surgeon often cannot observe the monitor during the operation, and the assistant (the doctor) gives various instructions while watching the assistant. However, the doctor may want to see the puncture process after the end of one continuous scan. After the end of the continuous scan, the last tomographic image is frozen and read from the memory 36 when the doctor gives an instruction. It can be viewed by reconstructing the raw data and displaying the 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 every minute angle. The projection data is successively written in the memory 36 as raw data via the preprocessing unit 28. After all projection data for all angles (0 ° to 360 °) necessary to reconstruct one tomographic image are written in the memory 36, the projection data is read from the memory 36 and reconstructed by the reconstruction unit 32. Forwarded to In the reconstruction unit 32, the tomographic image data is reconstructed at a high speed, that is, in a time shorter than the data collection time, and written in 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 to faithfully reproduce the speed of movement in addition to shortening the time from scanning operation to tomographic image display. For example, switching between two tomographic images collected at 1-second intervals and displaying them at 1.1-second intervals does not reproduce actual motion. In the present embodiment, as shown in FIG. 7A, the time difference Δt from the time when the scanning operation for one tomographic image is completed (data collection completion time) to the start of tomographic image display 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 of each scanning operation. I2 and I3 are displayed at intervals equal to the interval Δt2 of each scanning operation, and thereafter the tomographic images are sequentially switched and displayed with a time difference equal to the scanning operation interval, thereby equalizing the time scale of the scanning operation and display. Realizing the actual movement faithfully. In general, the time Δt ′ from the scanning operation to the end of the writing of tomographic image data to the display memory 34 is, for example, longer during scanning and shorter when not scanning depending on the load on the CPU 22. ,fluctuate. Therefore, if the reading is started immediately after the tomographic image data has been written to the display memory 34, 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 (display start) is fixed to at least the time (maximum time) when the CPU 22 receives the maximum load, and the actual movement is reproduced. Is realized. This time control can be realized by a well-known technique. As shown in FIG. 4, the CPU 22 may control the operations of the units 28, 32, 34, and 36 as a whole, or as shown in FIG. Although the clocks of the reconstruction unit 32 and the display memory 34 may be shared, and although not shown, the preprocessing unit 28 and the display memory 34 are equipped with a timer circuit, the preprocessing unit 28 can display the display memory 34. It is also possible to notify the controller of the time when the projection data for one sheet has arrived and read out the tomographic image data from the display memory 34 at the time when a fixed time has elapsed from this time.

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

  As a modification to increase the data collection speed, in the case of the third generation CT apparatus, a multi-tube (for example, 3-tube) X-ray tube is used, the X-ray rotation speed is increased, This can be achieved by using a fifth generation CT apparatus. The fifth-generation CT apparatus is a high-speed scanner that scans an electron beam using a bell-shaped X-ray tube having a large number of X-ray tubes arranged around the subject or having an annular cathode surrounding the subject. Realize rotation.

  Further, as a modified example of increasing the data collection speed and reconstruction time, the reconstruction is not performed from 360 ° projection data but is performed from projection data less than 360 °, for example, 180 ° projection data, so-called half. Adopt scan reconstruction method.

  Further, as a modified example for preventing an increase in exposure dose due to continuous scanning, 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 the product of the tube current mA and the exposure time t (seconds). Therefore, the tube current may be lowered 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 for controlling tube voltage and tube current so that X-rays can be output with a tube current as low as several tens of mA. change.

  Further, in order to reduce the exposure dose, there is a method of using pulsed X-rays instead of continuous X-rays that are currently mainstream in CT apparatuses. For example, as shown in FIG. 9, when using pulsed X-rays with a duty ratio of 50% (exposing X-rays for ½ of the total time), the dose is halved compared to continuous X-rays. can do. In addition, the control unit in the console 3 is provided with a circuit for controlling on / off of X-ray exposure at high speed, and the rotation of the X-ray tube 12 and the detector array 16 and the preheat state of the X-ray tube 12 are controlled. The X-ray may be turned on or off when the operator intends at high speed while continuing. Thereby, frequent on / off of X-rays can be easily performed at high speed, and the exposure dose of the subject can be reduced.

  Furthermore, as shown in FIG. 10, the exposure dose of the subject can be reduced 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. Examples of the material of the filter 40 include Teflon and molybdenum. Further, by adopting a configuration in which the thickness of the filter 40 and the wedge 43 can be varied during photographing, the exposure dose can be adjusted during photographing.

  Further, 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 necessary. By reproducing and displaying a tomographic image from the video recorder after the scan is completed, frame advance and reverse feed are possible, and diagnosis is facilitated. Further, the reconstructed image data and incidental information may be recorded in the digital format as they are. When displaying the recorded data, it is transferred to the CRT monitor 7 via the display 34. When recording as digital data, post-processing such as deletion can be easily performed.

(Second Embodiment)
FIG. 11 shows the configuration of the computed tomography apparatus of the second embodiment. Here, the X-ray tube and the X-ray detector will be described as a third generation (R / R) computed tomography apparatus in which the X-ray tube and the X-ray detector rotate together, but only the X-ray tube rotates and rotates once. It may be a fourth generation (R / S) computed tomography apparatus in which the minute X-ray detector is fixed.

  Inside the gantry 51, the X-ray tube 53 and the multi-channel 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 each have a high voltage generator on the fixed part side via a slip ring (not shown) so that projection data of 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 includes a plurality of detection elements arranged in an arc shape with the focal point of the X-ray tube 53 as the center. An opening (not shown) that can accommodate the subject is provided in the central portion of the gantry 51. The gantry 51 is installed on the floor via a tilt table so as to be tiltable with respect to the vertical axis. On the front surface of the gantry 51, a bed (not shown) is arranged. A top plate for placing a subject is provided on the upper surface of the bed. The top plate is supported so as to be slidable along the longitudinal direction from the bed toward the pedestal 51 and to be slidable along a width direction orthogonal to the longitudinal direction in the horizontal plane. The top plate is electrically slid independently in each direction by a driving device such as an electric motor. The couch controller 56 controls the position in the longitudinal direction (slice position of the subject) and the position in the width direction of the top board 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. Projection data from the data collection unit 60 is sent to the scanogram memory 61 at the time of scanogram imaging, and sent to the reconstruction processing unit 62 at the time of scanning. A scanogram is an X-ray projection image of a subject viewed from one direction, and is imaged while sliding the top plate with the rotating unit 52 stopped. The scanogram data is repeatedly read from the scanogram memory 61 at a predetermined period during CT fluoroscopy, and 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. It is sent to the image display device 64 together with the constructed tomographic image data. The image display device 64 simultaneously displays a scanogram and a tomographic image in one screen during CT fluoroscopy. 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 the line cursor on the scanogram corresponds to the slice position of the subject that is actually collecting data. When the line cursor is moved on the scanogram, the system control unit 8 controls the bed control unit 56 so that the slice position corresponds to this position, and moves the top board.

  Next, the operation of this embodiment will be described. FIG. 12 shows an example of a display screen during CT fluoroscopy. Since CT fluoroscopy has been described in the first embodiment, it is omitted here. Prior to actually starting CT fluoroscopy, a scanogram is taken. X-ray irradiation 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. Note that X-ray irradiation and data collection may be repeated while rotating the rotating unit 2 only at an angle of 0 °, for example. 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 and stored in the scanogram memory 11. 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, the description will be made as a single slice CT fluoroscopy. In CT fluoroscopy, X-ray irradiation and data collection are repeated while the rotating unit 52 continuously rotates, and projection data is continuously collected over an angle of 360 ° or more. Each time projection data necessary for reconstructing one piece of tomographic image data is collected, the tomographic image data is continuously reconstructed by the reconstruction processing unit 62 and sequentially sent to the image display device 64. It is done. Further, scanogram data is read from the scanogram memory 61, and line cursor data is added via the adder 63, and then 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 (diagnostic site), he / she operates the operation unit 59 to move the line cursor along the body axis direction on the scanogram. The system control unit 8 controls the bed control unit 56 according to the movement of the line cursor on the scanogram to move the top board along the longitudinal direction. As a result, the top board 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 then the position of the line cursor is finely adjusted while observing the tomographic image displayed in real time. .

  Further, the operation of the operation unit 59 moves the line cursor along the width direction orthogonal to the body axis on the scanogram. The system control unit 8 controls the bed control unit 56 according to the movement of the line cursor on the scanogram to move the top board along the width direction. Thereby, the shift | offset | difference of a reconstruction area | region and a test object can be corrected so that a desired site | part may be included in a tomographic image.

  Thus, by moving the line cursor on the scanogram, the change of the slice position can be easily completed in a short time.

  While the top plate is slid, and while the gantry 51 is tilted as shown in FIG. 14, the gantry controller 57 is rotated by the control of the system controller 58 as shown in FIG. The high voltage generator 55 temporarily stops the power supply to the X-ray tube 53 and stops the X-ray exposure. Since the rotation of the rotating unit 52 is continued in this way, after the slide of the top board 65 is finished and a desired slice position is set, power supply from the high voltage generator 55 to the X-ray tube 53 is performed. By resuming, data collection can be resumed 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, there is no need to wait for the rotating unit 52 to reach a constant angular speed after the top plate 65 has finished sliding. Because it becomes. Further, since the X-ray exposure is stopped while the top plate 65 is sliding, 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, as shown in FIG. 16A, the X-ray tube 53 moves along a spiral trajectory as viewed from the subject, and a helical scan that collects data and a multi-slice that repeats a single scan at a plurality of discrete slice positions. Scan is adopted. Here, a helical scan will be described as an example. The helical scan is performed by repeating 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 plate position in the longitudinal direction (body axis direction). In the helical scan, since the top plate slides continuously, Z changes according to ψ. To reconstruct one tomographic image, projection data for 360 ° having the same Z is required. Since Z in the projection data actually obtained by the helical scan changes according to ψ, as shown in FIG. 16B, the projection data for 720 ° actually collected by the distance interpolation processing is 720. The projection data for 360 ° is converted into projection data for 360 ° unified at the center Zc (Zc = (Z1−Zn) / 2) of the Z range (Z1 to Zn). The slice position of the tomographic image of the helical scan is defined by this Zc.

  When support for “interrupt” is input via the operation unit 67 while performing CT fluoroscopy with a helical scan, the system control unit 66 stops the top plate, stops X-ray exposure, and collects data. Interrupted. However, as in the second embodiment, it is preferable to continue the rotation of the rotating unit 52 in order to quickly resume CT fluoroscopy. There is a certain time lag from the data collection to the display of the tomographic image because the time required for the distance interpolation process and the reconstruction process is required. Due to the existence of the time lag and the principle of distance interpolation, when the suspension is supported, the slice position of the tomographic image displayed on the image display device 64 and the current position of the top board inevitably do not coincide.

  When the CT fluoroscopy is interrupted, the system controller 66 slides the top plate in the reverse direction until the CT fluoroscopy is resumed, and the tomographic image displayed on the image display device 64 when the interrupt instruction is given. The image is returned to the slice position of the latest tomographic image. When an instruction to resume CT fluoroscopy is input via the operation unit 67, the system control unit 66 controls the bed control unit 56 to resume sliding the top plate and resume CT fluoroscopy. In the CT fluoroscopy that has been interrupted, 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 an instruction to interrupt is given. Therefore, it can be resumed quickly only by resuming X-ray irradiation.

  Note that it is possible to automatically return the top plate to the slice position of the designated tomographic image data by designating any one of the plurality of reconstructed tomographic image data. Also, by designating any two of the reconstructed tomographic image data, CT fluoroscopy can be executed while reciprocating the range of slice positions of both images. Further, when a helical scan is executed while changing the tilt angle of the gantry 51, the tilt angle is stored corresponding to the top plate position, so that the image display device 64 is supported when the suspension is supported. It is possible to return to the tilt angle when the tomographic image data displayed in is collected.

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

The flowchart which shows operation | movement of fluoroscopic mode in 1st Embodiment. External view of X-ray CT. FIG. 3 is a structural diagram inside the gantry of FIG. 2. The block diagram of a control part. The figure which shows process progress of fluoroscopic mode. The figure which shows the process sequence from the data collection regarding one tomographic image to a display. The figure which shows the timing of the data collection and display in a continuous scan. The deformation | transformation figure of FIG. The figure which shows the pulse X-ray used for exposure dose reduction. The figure which shows the filter used for exposure dose reduction. The block diagram of X-ray CT of 2nd Embodiment. The figure which shows an example of a display screen. The time chart which shows the operation | movement relevant to a rotation part at the time of a top-plate slide or a frame tilt, and X-ray irradiation. The figure which shows mount stand tilt. The block diagram of 3rd Embodiment. The figure which shows the track | orbit of the X-ray tube in a helical scan.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Stand, 2 ... Bed, 3 ... Console, 4 ... Opening part, 5 ... Top plate, 6 ... Keyboard, 7 ... CRT monitor, 10 ... Subject, 12 ... X-ray tube, 14 ... X-ray generator, DESCRIPTION OF SYMBOLS 16 ... Detector array, 18 ... Data acquisition system, 20 ... Control part, 22 ... CPU, 24 ... Control bus, 26 ... Data bus, 28 ... Pre-processing part, 30 ... Disk interface, 32 ... Reconstruction part, 34 ... Display memory 36... Memory 38. Magnetic disk device 42. Clock circuit.

Claims (7)

An X-ray tube for exposing X-rays and an X-ray detector for detecting X-rays transmitted through the subject in a rotating part, and helical scanning means for helically scanning the subject;
Image reconstructing means for reconstructing the image data based on the projection data collected by the helical scan each time the projection data in the angular range necessary to reconstruct the image data is collected;
Display means for displaying the image data reconstructed by the image reconstruction means;
Instruction means for the operator to instruct interruption;
In parallel with the scanning operation of the helical scan, control is performed so as to perform reconstruction processing by the image reconstruction unit and display operation by the display unit, and from the X-ray tube based on an interruption instruction from the instruction unit And a control means for controlling the helical scan means so as to stop the X-ray exposure and continue the rotation of the X-ray tube in the helical scan even if the interruption instruction is given. Computer tomography device.   The computer tomography apparatus according to claim 1, wherein the control unit performs control for interrupting collection of projection data by the helical scan based on the interruption instruction. Wherein, when an instruction of the interruption has been made, according to claim 1, characterized in that to return the scanning position at a position to collect projection data necessary for reconstruction of the latest image data to be displayed on said display means The computed tomography apparatus of description. Further comprising designation means for designating the image data reconstructed by the reconstruction means;
The control means according to claim 1 computer tomography apparatus, wherein the moving the scanning position at a position to collect projection data necessary for reconstruction of the image data specified by the specifying means. 2. The computed tomography according to claim 1 , wherein the control unit repeats scanning between two positions where projection data necessary for reconstruction of two pieces of image data designated by the designation unit are collected. apparatus.   The control means sets the X-ray tube and the X-ray detector at a tilt angle obtained by collecting projection data necessary for reconstructing the latest image data displayed on the display means when the interruption instruction is given. The computed tomography apparatus according to claim 1, wherein the gantry to be accommodated is returned. The control means reconstructs the image data in a time shorter than the time required for the scanning operation for collecting the projection data in the angle range in the image reconstruction means, and repeats this to repeat a series of image data one after another. and give, in the above display unit, the successively computed tomography apparatus according to claim 1, wherein the controller controls to display after a certain time the reconstructed image data from each corresponding scan operation.

Images