JPH08196532A - X-ray computer tomograph - Google Patents

Abstract

PURPOSE: To shorten latency until image display is started after restarting the exposure of an X-ray and the collection of data by starting the reconfiguration of an image based on projection data of prescribed angle before interruption and the one after restart when the collection of the projection data is restarted after it is interrupted. CONSTITUTION: An X-ray tube 2 and a one-dimensional array type X-ray detector 3 collect the projection data repeatedly as rotating successively around an examinee, and a rotary driving control part 6 drives and controls the rotation of the X-ray tube 2 and the one-dimensional array type X-ray detector 3. The projection data outputted from a data collection unit 4 is sent to a control/data bus 7, and a reconfiguration processing part 8 generates a tomographic image with a division system. The reconfiguration processing part 8 starts the reconfiguration of the image based on the projection data of prescribed angle before interruption and the projection data after restart when the exposure of the X-ray is interrupted while CT radiographing is continued and the collection of the projection data is restarted after it is interrupted accordingly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray computed tomography apparatus capable of so-called CT fluoroscopy.

[0002]

2. Description of the Related Art CT fluoroscopy is a recently developed technique capable of simultaneously scanning a subject, image reconstruction and image display. CT fluoroscopy is based on speeding up the image reconstruction process, and it is necessary to reconstruct one image in order to avoid a cumulative time delay between scanning and image display. It is basically necessary to complete the reconstruction process of one image in a time shorter than the time of collecting projection data for one minute, and to display the image with a certain time delay from the scan in order to faithfully obtain time reproducibility. It is defined. This CT fluoroscopy technique is expected to support the same applications as X-ray fluoroscopy, such as supporting catheterization and neurosurgery, and further improving diagnostic throughput.

There are various problems to be solved in this CT fluoroscopy technique. One of them is that X-ray exposure is temporarily interrupted during CT fluoroscopy accidentally or intentionally. This is the establishment of a technique for preferably coping with the situation that the collection of projection data is also interrupted. It should be noted that such a situation is intentionally interrupted by a doctor (operator) in order to avoid unnecessary exposure, accidentally interrupted by a discharge phenomenon of a high-voltage power source, and a doctor (operator) operates an X-ray by an operation error. It is considered to be caused by releasing the ON switch or pressing the interruption switch.

When such a situation occurs, in the current apparatus, it takes the data acquisition time and the image reconstruction time for one image before the image display is started after the restart of the X-ray exposure and the data acquisition. There is a problem of waiting time.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to address the above-mentioned circumstances, and its purpose is to temporarily or accidentally expose X-rays during CT fluoroscopy. An object of the present invention is to provide an X-ray computed tomography apparatus capable of shortening the waiting time until the image display is started after the restart of X-ray exposure and data acquisition even in the case of interruption.

[0006]

SUMMARY OF THE INVENTION According to the present invention, the projection data is repeatedly collected while the projection direction changes periodically, and the images are reconstructed sequentially every time projection data for a predetermined angle is collected. In the X-ray computed tomography apparatus, when the projection data acquisition is restarted after the projection data acquisition is interrupted, the image is reconstructed based on the projection data before the interruption for the predetermined angle and the projection data after the restart. It is characterized by comprising a reconfiguring means for starting the configuration.

[0007]

According to the present invention, after interruption of the acquisition of projection data,
When the collection of projection data is restarted, image reconstruction is started based on the projection data before the interruption for the predetermined angle and the projection data after the restart, so the projection data for the predetermined angle collected after the restart. After the resumption, the waiting time until the image display is started is shortened as compared with the conventional method in which the image reconstruction is started based on.

[0008]

Embodiments of the X-ray computed tomography apparatus according to the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram of a main portion of the first embodiment. The scanner 1 is a main structure for repeating the collection of projection data regarding a subject while changing the projection direction periodically, and includes an X-ray tube 2 and a one-dimensional array type X-ray detector 3.
And are rotatably housed around the subject while facing each other with the subject sandwiched therebetween. The X-ray tube 2 receives a high voltage applied from the X-ray generation controller 5 and emits a fan-shaped X-ray beam. The one-dimensional array type X-ray detection unit 3 is formed by arranging a plurality of X-ray detectors in an arc shape with the focal point of the X-ray tube 2 as the center. The data acquisition unit (DAS) 4 provided in the one-dimensional array type X-ray detector 3 receives a weak current signal detected by the one-dimensional array type X-ray detector 3, and performs high-speed amplification processing and digital processing for each channel. Conversion processing and integration processing for each extremely short time. The X-ray tube 2, the X-ray generation controller 5, the data acquisition unit 4, and the computer system outside the scanner are electrically connected to each other via a slip ring mechanism, and the X-ray tube 2 and the one-dimensional array type X It is realized that the line detector 3 continuously collects projection data while continuously rotating around the subject. The rotation drive control unit 6 drives and controls the rotation of the X-ray tube 2 and the one-dimensional array type X-ray detector 3. The X-ray tube 2 and the one-dimensional array type X-ray detector 3 rotate around the subject, which is a so-called third generation R / R system, but the present invention is not limited to this system. Other schemes,
For example, a so-called fourth-generation R / S system in which a large number of X-ray detectors are circumferentially fixed around the subject and the X-ray tube is rotated may be used. Many X
The so-called fifth in which the X-ray detector and the X-ray tube are fixedly arranged.
It may be a generational S / S system.

The projection data output from the data collection unit 4 via the slip ring mechanism is sent to the control / data bus 7. The control / data bus 7 is connected to the reconstruction processing unit 8, the storage unit 9, and the display unit 10. The reconstruction processing unit 8 creates a tomographic image (referred to as a main image) by the division method. The division method divides the predetermined angle range of 360 ° or 180 ° + fan angle (half scan method) required to create one main image into n parts,
Every time the ray tube 2 rotates by the partial angle range (predetermined angle range / n), the partial image is repeatedly reconstructed from the projection data for the partial angle range, and the latest n partial images are added to obtain 1 One main image is created, each time a partial image is reconstructed, the latest main image is added to the latest main image, and the main image is converted into the latest partial image. This is one of the speed-up techniques for reconstruction of creating a main image at high speed with high time resolution by subtracting partial images of the same angle.

The reconstruction processing unit 8 is
When the X-ray exposure is interrupted and the projection data acquisition is interrupted accordingly, a process (specifically described later) is appropriately performed. In order for the reconstruction processing unit 8 to recognize interruption of X-ray exposure, a signal indicating ON / OFF of X-rays is fetched from the X-ray generation control unit 5 to the reconstruction processing unit 8. However, the recognition method is not necessarily limited to such a recognition method, and another method such as recognition from the voltage change of the cable for applying the high voltage from the X-ray generation control unit 5 to the X-ray tube 2 may be used. Further, in order for the reconstruction processing unit 8 to recognize the rotation angle of the X-ray tube 2, a signal indicating the rotation angle of the X-ray tube 2 is fetched from the rotation drive control unit 6 to the reconstruction processing unit 8. However, the recognition method is not necessarily limited to such a recognition method, and another method such as recognizing a rotation angle via an angle detection sensor such as a rotary encoder may be used.

The storage unit 9 is configured to always store the latest data of at least n partial images and the latest data of at least one main image. The created main image is sent to the display unit 10 and displayed.

Next, the operation of this embodiment will be described. Here, the predetermined angle range required to create one main image is 360 ° for one rotation, and n = 6 (partial angle range = 60 °), that is, the X-ray tube 2 is 60 °. It is assumed that partial images are reconstructed one after another from the projection data each time the image is rotated.

FIG. 2 is an explanatory diagram of the division method. In FIG. 2, the main image is described by I and the partial image is I ′.
It is described in. Further, the main image is defined as I1, I2, I3, ... In addition, the partial image shows the number of rotations of the X-ray tube 2 when the projection data used for the reconstruction is collected, and the partial angle range 0 ° to 60 °, 60 ° to 120 °, 120 °. ~ 1
80 °, 180 ° ~ 240 °, 240 ° ~ 300 °, 300 ° ~ 360
° Code each to 1, 2, 3, 4, 5, 6
Insert two pieces of information about which partial angle range the projection data used for reconstruction corresponds to,
It is defined as I '(1,1), I' (1,2), I '(1,3) ... For example, the partial image I '(3,5) is 240 ° in the third rotation.
It shows that it was reconstructed from the projection data collected in the partial angle range of ~ 300 °.

After the scan is started (the X-ray tube 2 starts rotating from 0 °), the reconstruction processing unit 8 causes the partial image to be I '(1,1) every time the X-ray tube 2 rotates by 60 °. ), I '(1,2), I'
(1,3) ... and so on. At the time when the reconstruction of the six partial images I ′ (1,1) to I ′ (1,6) reaching the predetermined angle range required to create one main image is completed, the reconstruction processing unit 8 creates the first main image I1 by adding the latest six partial images I '(1,1) to I' (1,6) at this point in time between frames. This main image I1 is sent to the display unit 10 and displayed. Further, when the X-ray tube 2 reaches 60 ° in the second rotation, the partial image I ′ (2,1) is reconstructed. The second main image I2 is the latest main image I1 at this time and the latest partial image I '(2,
1) is added, and the partial image I ′ (1,1) having the same partial angle range as the latest partial image I ′ (2,1) is subtracted. The second main image I2 is displayed on the display unit 10.
And is displayed by switching from the main image I1.
In this way, each time the X-ray tube 2 is rotated by 60 °, a main image is sequentially created.

FIG. 3 is an explanatory diagram of the processing when the X-ray exposure is interrupted during the continuation of CT fluoroscopy and the projection data acquisition is interrupted accordingly. The reason for the interruption has been described in the prior art, so refer to it if necessary. Here, when the X-ray exposure is interrupted, the X-ray tube 2
It is assumed that the rotation occurs at α ° (60 ° <α ° <120 °) and continues to β ° at the mth rotation (300 ° <β ° <0 ° (= 360 °)). When interrupted, the storage unit 9 stores in the storage unit 9 the latest six partial images I ′ (m-1,21) to I ′ (m, 1),
And the latest 6 partial images I '(m-1,21) to I' (m, 1)
At least the latest data of the main image In has been stored at the time of interruption based on.

After the X-ray exposure is restarted and the projection data acquisition is restarted, the partial image I '(m, 6) is first reconstructed. The reconstruction processing unit 8 adds the partial image I ′ (m, 6) to the main image In, and the partial image I ′ (in the same partial angle range as the partial image I ′ (m, 6) from the main image In. (m-1,1) is subtracted to obtain the first main image In + 1 after restart.
Create

Thereafter, each time the X-ray tube 2 is rotated by 60 °,
By adding the latest partial image to the latest main image and subtracting from this main image In, the partial image one rotation before in the same partial angle range as this latest partial image, the main images are successively added. Create it.

According to the processing of the present embodiment, the collection of projection data is interrupted and then resumed,
The waiting time until the main image is created and displayed, ignoring the data transfer rate, etc., causes the X-ray tube 2 to reach the starting point (300 ° in Fig. 3) of the partial angular range, and 60 ° from there.
It is the total of the time required to rotate, the time required to reconstruct one partial image, and the time required to subtract and add a partial image from the main image. On the other hand, in the past,
After the restart, the same processing as when a new scan is started is performed, so this waiting time reaches the starting point (300 ° in FIG. 3) of the partial angle range of the X-ray tube 2 and then 360 seconds from that point. ° This is the total of the time required to rotate, the time required to reconstruct one partial image, and the time required to add a partial image to the main image. Therefore,
It will be appreciated that the waiting time is greatly reduced in this embodiment. (Second Embodiment) FIG. 4 is a block diagram of the main part of the second embodiment. 4, the same parts as those in FIG. 1 are designated by the same reference numerals.

As described in the first embodiment, the data acquisition unit 4 receives the weak current signal detected by the one-dimensional array type X-ray detector 3 and performs high-speed amplification processing for each channel.
The digitization process and the integration process are repeatedly executed every very short time. That is, the projection data is repeatedly collected at every rotation angle p ° at which the X-ray tube 2 rotates within this extremely short time.

The reconstruction processing unit 12 updates the latest 360 ° including the projection data every time new projection data is collected.
A main image is repeatedly created based on minute projection data. Actually, it is currently difficult to realize real-time CT fluoroscopy on the condition that the main image is reconstructed from projection data of 360 ° within the time when the X-ray tube 2 rotates by the rotation angle p °. Conceivable. Therefore, it can be said that it is preferable to adopt the back projection processing method as the reconstruction processing. The back projection processing method means that once the first main image is reconstructed from the projection data of 360 °, the X-ray tube 2 is rotated by the rotation angle p ° and the newly obtained projection data is generated. When collected,
For the main image, the back projection process is executed with the newly obtained projection data, and the back projection process is executed in the reverse direction with the oldest projection data. Real-time CT requires less calculation than reconstructing the main image from projection data
It achieves a speedup sufficient to realize fluoroscopy.

The storage unit 11 is constructed so that the latest projection data for at least one rotation and the latest main image are always stored. The created main image is the display unit 10.
Sent to and displayed.

Next, the operation of this embodiment will be described. In addition, here, it is assumed that one main image is created based on projection data for one 360 ° rotation. Figure 5
FIG. 6 is an explanatory diagram of a process when X-ray exposure is interrupted during continuation of CT fluoroscopy, and projection data acquisition is interrupted accordingly. The reason for the interruption has been described in the prior art, so refer to it if necessary. Here, X
The X-ray tube 2 is interrupted at α ° (60 °
Occurs at <α ° <120 °) and β ° at the mth rotation (300 ° <
It is assumed that it continues to β ° <0 ° (= 360 °). In FIG. 5, the main image is described by I and the projection data is described by D. Further, the main image is defined as I1, I2, I3, ... Further, the projection data is obtained by inserting two pieces of information, which is the number of rotations of the X-ray tube 2 when the projection data is collected and the rotation angle of the X-ray tube 2 when the data is collected, and D (1, 0), D (1, p), I (1,2p) ... For example, the projection data D (m-1, β) is X
It shows that the ray tube 2 was collected at β ° of the m−1th rotation.

When the X-ray exposure is interrupted, the projection data D (m-1, α + p) to D (m,
The main image In is reconstructed from α). The projection data D (m-1, α + p) to D (m,
At least α) and the data of the main image In are stored.

From the time when the X-ray exposure is restarted, the X-ray tube 2 rotates by p °, and the projection data D (m, β) is first acquired. The reconstruction processing unit 12 receives the main image In
Back projection processing is performed in the forward direction on the projection data D (m, β), and the projection data has the same rotation angle as the projection data D (m, β) and is used to create the main image In. By executing the back projection process in the reverse direction with D (m-1, β), the first main image In + 1 is created after the restart. That is, the main image In + 1 is the projection data D (m-1, α + p) to D (m-1, β-p), D before the interruption.
(m-1, β + p) ~ D (m, α) and projection data D after restart
It can be said that it is equivalent to the main image reconstructed from (m, β).

Thereafter, each time the X-ray tube 2 is rotated by p °,
The same process is executed to create main images one after another. According to the process of the present embodiment, the waiting time from the time when the collection of projection data is interrupted and then resumed until the main image is created and displayed is X when the data transfer speed is ignored. It is the total time of the time required for the tube 2 to rotate by p ° and the time required to perform the back projection process in the forward and backward directions on the main image, which is shorter than that of the first embodiment. Will be understood. Further, in the first embodiment, the projection data collected by the X-ray tube 2 immediately before the interruption from the end point of the partial angular range (240 ° in FIG. 3) to α ° at the interruption point, and the X-ray after the restart. Origin of partial angle range from tube 2 to β ° (300 ° in Fig. 3)
There is a problem that the projection data collected until the time reaches is not used, that is, it is not reflected in the main image, but this problem is solved in the present embodiment.

The present invention is not limited to the above-mentioned embodiments, but can be modified in various ways. For example, when a doctor (operator) intentionally interrupts to reduce radiation exposure, the interruption period may be extremely long,
In such a case, there is a risk of misunderstanding the doctor that the main image after resumption is created from projection data collected when the images are very temporally separated. In order to avoid this, when the interruption period is a long time period that exceeds a certain fixed time, all the data before the interruption is cleared from the storage unit, and similarly after restarting, a new scan is started. It is conceivable to give the reconstruction processing unit the function of creating the main image after waiting for the projection data for one rotation to be collected. It can be said that the fixed time is preferably 3 seconds.

Further, after the operator gives an instruction to start scanning, the 360 ° necessary for reconstructing one main image is displayed.
(Or 180 ° + fan angle) 360 ° necessary to reconstruct at least one main image even if an operation error such as stopping the scan is made before the projection data is collected. Continue scanning until (or 180 ° + fan angle) projection data collection is completed,
After that, adding a function of stopping the scan to each of the above-described embodiments is effective in compensating such an erroneous operation. It can be said that this function is preferably stored in the scan control unit that integrally controls the scan-related parts such as the X-ray generation control unit 5, the data acquisition unit 4, and the rotation drive control unit 6.

[0028]

According to the present invention, the X-ray computer which repeatedly collects the projection data regarding the subject while the projection direction changes periodically and reconstructs the image sequentially every time the projection data for the predetermined angle is collected. In the tomographic apparatus, when the projection data collection is restarted after the projection data collection is interrupted, image reconstruction is started based on the projection data before the interruption for the predetermined angle and the projection data after the restart. It is characterized by comprising a reconstructing means. When the projection data collection is resumed after the projection data collection is interrupted, the reconstruction of the image is started based on the projection data before the interruption and the projection data after the restart for the predetermined angle. The waiting time until the image display is started after the restart is shortened compared to the conventional case where the image reconstruction is started based on the projection data for the predetermined angle.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of an X-ray computed tomography apparatus according to a first embodiment.

FIG. 2 is an explanatory diagram of a division method of the reconstruction processing unit in FIG.

FIG. 3 is an explanatory diagram of a process according to the first embodiment when X-ray exposure is interrupted while CT fluoroscopy is continued, and projection data acquisition is interrupted accordingly.

FIG. 4 is a configuration diagram of a main part of an X-ray computed tomography apparatus according to a second embodiment.

FIG. 5 is an explanatory diagram of a process according to the second embodiment when the X-ray exposure is interrupted during the continuation of CT fluoroscopy and the projection data acquisition is interrupted accordingly.

[Explanation of symbols]

1 ... Scanner, 2 ... X-ray tube,
3 ... One-dimensional array type X-ray detection unit, 4 ... Data acquisition unit, 5 ... X-ray generation control unit,
6 ... Rotation drive control unit, 7 ... Control / data bus,
8 ... Reconstruction processing unit, 9 ... Storage unit,
10 ... Display section.

Claims (4)

[Claims] 1. An X-ray computed tomography apparatus for reconstructing an image every time projection data for a subject is repeatedly collected while the projection direction changes periodically and projection data for a predetermined angle is collected. Reconstructing means for starting image reconstruction based on the projection data before the interruption and the projection data after the resumption of the predetermined angle when the collection of the projection data is restarted after the interruption of the projection data acquisition. An X-ray computed tomography apparatus, comprising: 2. The reconstructing means reconstructs the partial images sequentially every time the projection direction changes by the predetermined angle / n °, and adds the latest n partial images to form one image. After reconstruction, X-ray exposure is restarted and projection data collection is restarted, then image reconstruction is started from n-1 partial images before interruption and the first partial image after restarting. The X-ray computed tomography apparatus according to claim 1, wherein 3. The reconstructing means first collects the latest image reconstructed at the time of resuming after the resumption of X-ray exposure and the collection of projection data. The image is obtained by performing back projection processing on projection data, and performing back projection processing on the latest image in the reverse direction with projection data in the same projection direction as the projection data initially acquired. The X-ray computed tomography apparatus according to claim 1, characterized in that the reconstruction is started. 4. The X-ray computed tomography according to claim 1, wherein when the interruption exceeds a predetermined time, image reconstruction is started based on the projection data for the predetermined angle collected after the restart. Imaging device.