JPH0696000B2 - CT device - Google Patents

Description

The present invention relates to a CT apparatus, and more particularly to a CT apparatus that scans a subject with radiation and obtains a tomographic image of the subject.

(Prior Art) A typical CT apparatus is an X-ray CT apparatus. This X-ray CT apparatus has an X-ray generator and an X-ray detector, which are arranged to face each other and in which a subject is arranged, and an X-ray generator and an X-ray detector centering on the subject. Is rotated to scan the subject with X-rays, collect data output from the X-ray detector, and form a CT image of the subject.

In order to obtain a CT image of good image quality with less noise by the X-ray CT apparatus, the X-ray dose should be increased. However, when the X-ray dose is increased, there are problems such as cooling of the X-ray tube and exposure of the patient. Therefore, it is necessary to determine the irradiation condition so that the image quality and the dose are well balanced. Therefore, conventional X-ray CT
When starting CT imaging with the device, first,
That is, the irradiation conditions such as the scan time, the tube voltage and the tube current as shown in the table below are determined by the experience and intuition of the operator in consideration of the size of the patient, the imaging region, the slice thickness, etc. It is set in the X-ray CT system via the operation keys. After the irradiation conditions are set, the CT scan is started.

(Problems to be Solved by the Invention) According to the conventional CT apparatus, the irradiation condition is determined according to the state of the subject based on the experience and intuition of the operator before starting the CT scan as described above, and the irradiation condition is set. Must be set in the CT device. With such operator's experience and intuition, it is very difficult to obtain a CT image of appropriate image quality, and the accuracy of diagnosis by the CT image may be significantly impaired.

Therefore, an object of the present invention is to provide a CT apparatus that can automatically set irradiation conditions according to the state of the subject.

[Structure of the Invention] (Means for Solving the Problems) Scanning is performed a plurality of times in an angular range necessary to reconstruct a tomographic image of a subject by radiation, and data corresponding to the radiation passing through the subject is obtained. Scanning means that occur,
By the data collecting means for collecting the data output from the scanning means, the reconstructing means for inputting the data from the data collecting means and reconstructing the image data for each scan, and the reconstructing means, By addition means for adding the image data obtained for each scan, and scan control means for detecting the data output from the scanning means and repeating the scanning operation of the scanning means until the transmitted radiation reaches a predetermined amount. A configured CT device is provided.

(Function) Since the scan control circuit detects the radiation transmission dose based on the data output from the scanner and the scanner continues to scan the subject until the transmission dose reaches a predetermined level, irradiation conditions such as the number of scans Is automatically set, and CT images of appropriate quality are always obtained.

(Embodiment) According to the embodiment shown in FIG. 1, a CT scanner 10 includes a radiation generator, that is, an X-ray generator 11 including an X-ray tube and the X-ray generator.
11 and an X-ray detector 12 arranged so as to face each other. The subject 13 is arranged between the X-ray generator 11 and the X-ray detector 12, and the subject is exposed to X-rays by rotating the X-ray generator 11 and the X-ray detector 12 about the subject. To be scanned.

The X-ray detector 12 of the scanner 10 is coupled to the data acquisition unit 14. The data collection unit 14 collects the X-ray detection data output from the X-ray detector 12, and outputs the collected data to the reconstruction circuit 15. The reconstruction circuit 15 reconstructs the collected data into an image by a known method, and outputs the image data to the monitor 16. The monitor 16 displays the image data as a reconstructed image, that is, a tomographic image of the subject.

On the other hand, for example, several central channels of the X-ray detector 12, that is, several central X-ray detecting elements are connected to the integrating circuit 17. The integration circuit 17 integrates the detection signal obtained from the central X-ray tube detection element and outputs the integration result to the comparator 18. This comparator
18 compares the integration result with the set value sent from the condition setting circuit 19. The output terminal of the comparator 18 is connected to the input terminal of the scan control circuit 20. This scan control circuit 20 is a comparator
The scanner 10 is driven and controlled in response to the output signal from 18. That is, the scanner 10 is continuously driven until the integrated output of the integrating circuit 17 reaches the set value.

The condition setting circuit 19 is configured to output a set value for obtaining an appropriate image quality in a CT image. By the way, in order to obtain good image quality, the S / N ratio may be improved, but this S / N ratio is proportional to the dose, that is, the tube current (mA) × scan time (sec). Therefore, theoretically, the image quality improves with increasing dose. However, when the dose is increased, the amount of exposure to the patient is increased, the heating of the X-ray tube becomes remarkable, and accordingly, sufficient cooling is required, and further, the life of the X-ray tube is shortened. is there. Therefore, the CT apparatus according to the present invention is configured to drive the scanner so that an appropriate image quality can be obtained by defining the upper limit of the dose to a certain value and controlling the number of scans. Therefore, the condition setting circuit 19 has a set value corresponding to the dose that can obtain an appropriate image quality, and the scan control circuit 20 performs each scan at the dose set in consideration of the exposure dose, cooling, and life. Is configured to control the scanner 10.

In this embodiment, the dose set in the scan control circuit 20 is, for example, 100 mAS (mass) (where mAS represents tube current (mA) × scan time (Sec)). This value is a suitable dose for pediatric abdomen imaging, 300 mAS for normal adult abdomen, and 400 mAS for the same head. In this way, the required dose differs depending on the type of patient or the region to be imaged, and the set value corresponding to these required doses is the condition setting circuit.
It is set to 19. Therefore, if an adult abdomen is scanned with a dose of 100 mAS, the subject will be scanned three times to obtain the data equivalent to the required dose of 300 mAS,
The image data obtained thereby is added.

Next, the operation of the embodiment of the present invention will be described.

A patient is placed between the X-ray generator 11 and the X-ray detector 12 of the scanner 10. First, the condition setting circuit 19 sets a condition according to the type and site of the patient, for example, an adult abdominal imaging mode. After this, when the scanner 10 is instructed, the X-ray generator
The subject 13 is scanned by the X-rays generated from 11. By this scan, an X-ray detection signal is output from the X-ray detector 12 and input to the data acquisition circuit 14. The data collection circuit 14 collects X-ray detection signals, that is, X-ray detection data, and outputs the collected data to the reconstruction circuit 15. Reconstruction circuit
15 reconstructs the collected data into image data.

On the other hand, the X-ray detection signal detected by the central detection element 12c of the X-ray detector 12 is input to the integration circuit 17 and integrated.
The integrated signal is input to the comparator 18 and compared with the set value of the condition setting circuit 19, that is, the set value corresponding to the dose 300 mAS required for adult abdominal imaging. The scanner 10 has a linear flow rate as described above.
Since the subject 13 is set to scan with 100 mAS, the dose is insufficient in the first scan, and the output of the comparator 18 does not change. Therefore, the scan control circuit 20 controls the scanner 10 again to perform the second scan. As a result, the scanner 10 starts the second scan. The collected data obtained by this second scan is reconstructed into image data by the reconstruction circuit 15. At this time, this second image data is added to the first image data obtained by the first scan.

In the second scan, the integration value obtained by the integration circuit 17 is less than the set value, so the scan control circuit 20 controls the scanner 10 to perform the third scan. The third image data obtained by this third scan is added to the previous added image data. That is, the reconstruction circuit 15 generates image data obtained by adding the three image data. This added image data is input to the monitor 16 and displayed as a tomographic image. At this time, the integrated value of the integrating circuit 17 becomes equal to or larger than the setting value of the condition setting circuit 19, and the comparator 18 outputs the output signal to the scan control circuit 20. Scan control circuit
20 stops the scanner 10 and resets the integrating circuit 17 in response to this output signal.

As described above, according to the present invention, the dose transmitted through the subject is detected, the detection signal is integrated, and the scan is performed several times until the integrated value becomes a constant value. As a result, it is not necessary to select and set the tube current, the tube voltage, the scan time, and the like at the start of scanning, and it is possible to obtain appropriate image quality regardless of the condition of the subject. Especially continuous rotation possible
In the CT device, the scan can be easily repeated, so that a greater effect can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a CT apparatus according to an embodiment of the present invention. 10 ... Scanner, 11 ... X-ray generator, 12 ... X-ray detector, 14 ... Data acquisition circuit, 15 ... Reconstruction circuit, 17 ...
Integrator circuit, 18 …… Comparator, 19 …… Condition setting circuit, 20 ……
Scan control circuit.

Claims (1)

[Claims] 1. A scanning unit that scans an angular range required to reconstruct a tomographic image of a subject by radiation a plurality of times to generate data corresponding to the radiation transmitted through the subject, and the scanning unit. Data collecting means for collecting data output from the device, reconstructing means for reconstructing image data for each scan by inputting the data from the data collecting means, and for each scan by the reconstructing means. It is composed of adding means for adding the obtained image data, and scan control means for detecting the data output from the scanning means and repeating the scanning operation of the scanning means until the transmitted radiation reaches a predetermined amount.
CT device.