JPS63279825A - Television tomographic imaging apparatus - Google Patents

Abstract

PURPOSE:To always take the photograph of an object to be examined with the optimum quantity of beam, by controlling a quantity-of-beam controller according to the quantity-of-beam table stored in a quantity-of-beam table memory part. CONSTITUTION:Prior to the photographing in this examination, an X-ray condition is lowered as compared wit that at the time of said photographing to perform test photographing and the change characteristic of the quantity of the beam from an X-ray tube bulb at every projection position is calculated to a preliminarily form a quantity-of-beam table which is, in turn, stored in a quantity-of-beam memory part 14. At the time of the photographing of an object 2 to be examined in this examination, a quantity-of-beam controller 15 is controlled according to the quantity-of-beam table stored in the quantity-of- beam table memory part 14 at each time when the X-ray tube bulb 1 moves to each projection position to control the quantity of the beam incident to a television camera 4.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method of irradiating a subject with X-rays from an X-ray tube, and photographing and displaying a tomographic image of an arbitrary tomographic plane within the subject using a television camera. Regarding the television tomography apparatus, in particular, it is possible to take images with an optimal view at each projection position of the X-ray tube, and
The present invention relates to a television tomography apparatus that can effectively use the dynamic range of a television camera.

[Conventional technology]

The conventional TV tomography apparatus, as shown in FIG.
A ray tube 1, a detector 3 that is arranged opposite to the X-ray tube 1 with the subject 2 in between and converts the transmitted X-rays into visible light, and a television camera 4 that photographs the output optical image. A scanning device that changes the positional relationship between the X-ray tube 1 and the detector 3, an A/D converter 5 that converts the output signal of the television camera 4 into a digital quantity, and a storage device that stores this digital signal. frame memories 6a, 6b, . . . , 6n, an arithmetic device 7 that reads data from these frame memories 68 to 6n and processes it, and a D/A converter that converts the processed digital signal into an analog signal. 8 and a display device consisting of a monitor 9 for displaying its analog signal. In addition, in Figure 3,
Reference numeral 10 is a top plate on which the subject 2 is placed. Then, the two-dimensional transmission or absorption distribution of X-rays of the subject 2 is determined by the mutual positional relationship between the X-ray tube 1 and the detector 3 indicated by arrow A
, B, and perform calculations on a set of data passing through one plane within the subject 2 from these multiple images to obtain an arbitrary tomographic plane within the subject 2. It calculated and displayed tomographic images of

[Problems to be solved by the invention] □ However, in such a conventional television tomography apparatus, as shown in FIG. Since X-rays are emitted, the thickness through which they pass through the subject 2 (hereinafter referred to as the "exposed area") changes sequentially depending on the projection position, and the exposed area d1 is the maximum when emitted at the maximum exposure angle at position 1a. Therefore, when irradiating at the minimum exposure angle at position 1b, the exposure area d2 was the minimum. Since the conditions for the X-rays emitted from the X-ray tube 1 are constant, the X-rays are
When the radiation is emitted, it is transmitted to the television camera 4 through the detector 3a.
When the exposure part d2 emits X-rays from the minimum position 1b, the amount of light that enters the television camera 4 via the detector 3b becomes the maximum, and the amount of light that enters the X-ray tube 1 becomes the minimum. The amount of light incident on the television camera 4 at each projection position varied sequentially. Therefore, the X-ray tube 1
It was difficult to always photograph the subject 2 with the optimum light intensity at each projection position.

Here, if the X-ray conditions of the X-ray tube 1 are adjusted to provide the optimum light amount for the smallest exposed area d2 of the subject 2, then
For parts of the irradiation area that are larger than this, the amount of light may be insufficient, or the dynamic range of the television camera 4 may not be used effectively to its maximum, resulting in a reduction in the quality of the photographed image. Furthermore, if the X-ray conditions of the X-ray tube 1 are adjusted to provide the optimum light intensity for the maximum exposure area di, the light intensity will be excessive for the minimum exposure area d2, resulting in halation in the photographed image. There was something that happened.

In this case, the subject 2 has to be photographed again, which increases the X-ray exposure dose to the subject 2.

Therefore, an object of the present invention is to provide a television tomography apparatus that can solve these problems.

[Means for solving problems]

Means of the present invention for solving the above problems includes an X-ray tube,
The X-ray tube is placed opposite the X-ray tube with the subject in between.
A detector that converts radiation into visible light, a television camera that captures the output optical image, a scanning bag that changes the positional relationship between the X-ray tube and the detector, and converts the output signal of the television camera into a digital quantity. an A/D converter that converts the digital signal into an analog signal, a storage device that stores this digital signal, an arithmetic device that reads data from this storage device and processes it, and converts the processed digital signal into an analog signal and displays it. In the TV tomography apparatus, which has a display device that calculates and displays a tomographic image of an arbitrary tomographic plane within the subject, the control unit of the calculation device includes a A light intensity table storage unit that stores a light intensity table created by performing test imaging with lowered X-ray conditions and determining light intensity change characteristics from the imaging data for each projection position of the X-ray tube is connected, and the above detector and TV are connected. A television tomography apparatus is connected to the camera and is equipped with a light amount controller that controls the amount of light that enters the television camera from the detector for each projection position according to the data in the light amount table mentioned above during imaging for the main examination.

[For production]

The television tomography apparatus configured in this manner stores, in the light intensity table storage unit, the imaging data for each projection position of the X-ray tube, which is obtained by performing test imaging with lowered X-ray conditions compared to that at the time of imaging, before imaging for the main examination. The amount of light incident on the TV camera from the detector is controlled by storing a light amount table created by determining the change characteristics of light amount from the detector, and operating the light amount controller according to the data in the light amount table when photographing the main examination of the subject. Control is performed for each projection position of the X-ray tube.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a television tomography apparatus according to the present invention. This television tomography device irradiates a subject with X-rays from an X-ray tube, and photographs and displays tomographic images of arbitrary tomographic planes within the subject using a television camera.
Ray tube 1, detector 3, television camera 4, scanning device, A/D converter 5, storage device (6a to 6n), arithmetic device 7, display device (8, 9), have. The X-ray tube 1 irradiates the subject 2 with X-rays. The detector 3 converts the transmitted X-rays of the subject 2 into visible light, and is composed of, for example, an image intensifier, and is arranged opposite to the X-ray tube 1 with the subject 2 in between. There is. The television camera 4 photographs the output optical image of the detector 3 and converts it into an electrical signal. The scanning device changes the positional relationship between the X-ray tube 1 and the detector 3 as shown by arrows A and B, and is not shown in the drawings.
It consists of the scanning trajectory of the X-ray tube 1, the scanning trajectory of the detector 3, their driving devices, etc. The A/D converter 5 converts the output signal of the television camera 4 into a digital quantity. The storage device stores signals converted into digital quantities by the A/D converter 5, and is composed of separate frame memories 6a, 6b, . . . 6n for each projection image. The arithmetic unit 7 includes each of the frame memories 6a to 6n.
It reads data stored in the computer and performs arithmetic processing on it. The display device converts the digital signal processed by the arithmetic device 7 into an analog signal and displays it, and is composed of a D/A converter 8 and a monitor 9.

In FIG. 1, numeral 10 is a top plate on which the subject 2 is placed, numeral 11 is a logarithmic converter for logarithmically converting the digital signal from the A/D converter 5, and numeral 12 is a top plate on which the subject 2 is placed. This is an enhancement circuit that enhances the contrast of images from the memories 6a to 6n. Reference numeral 13 is a control unit that controls each component, and X
Controlling the irradiation of X-rays from the ray tube 1, controlling the control signal S2
controls the capture of images by scanning the television camera 4, controls the arithmetic unit 7 using the control signal S3, controls where in the frame memories 68 to 6n the captured image data is stored, and further controls The arithmetic unit 7 is controlled by the signal S4, and each frame memory 6a to 6n
The image data is controlled so that necessary arithmetic processing is performed on the image data.

Then, the television camera 4 scans the X-ray irradiation from the X-ray tube 1, and the two-dimensional X-ray of the subject 2 is scanned.
The transmission or absorption distribution of the rays is measured multiple times while changing the mutual positional relationship between the X-ray tube 1 and the detector 3 as shown by arrows A and B, and from these multiple images, the inside of the subject 2 is determined. Computation is performed on a set of data passing through one plane, and a tomographic image of an arbitrary tomographic plane substantially parallel to the plane of the detector 3 within the subject 2 is computed and displayed. At this time, the arithmetic unit 7 shifts the data of each projection image read out from each frame memory 6a to 6n by an appropriate shift amount, adds and averages the data, and reconstructs the image.

Here, in the present invention, the control section 1 of the arithmetic device 7
A light amount table storage section 14 is connected to 3, and a light amount controller 15 is provided between the detector 3 and the television camera 4.

The light intensity table storage unit 14 is used to correct changes in the amount of light incident on the television camera 4 for each projection position due to the movement of the X-ray tube 1, and is used to correct changes in the amount of light incident on the television camera 4 for each projection position as the X-ray tube 1 moves. A test image of the subject 2 is taken under lower X-ray conditions than in the past, and a light amount table created by determining the change characteristics of the light amount from the image data for each projection position of the X-ray tube 1 is now stored. For example, it consists of RAM (random read/write memory). Further, the light amount controller 15 controls the amount of light that enters the television camera 4 from the detector 3 for each projection position according to the data of the light amount table stored in the light amount table storage section 14 when photographing the subject 2 for the main examination. , to enable shooting with the optimum amount of light, such as optical apertures that limit the range of light beams, polarizing plates that use polarized light to adjust the amount of light passing through, and liquid crystals that utilize the optical anisotropy of liquid crystals. Consists of shutters, etc.

Next, creation of the light amount table to be stored in the light amount table storage section 14 will be explained with reference to FIG. 2 and Table 1. First, before imaging the main examination for subject 2, the X-ray conditions are lowered compared to the time of imaging, that is, the emitted X-ray amount is reduced, instantaneous pulse radiation is used, or fluoroscopic imaging is performed. As shown in Figure 2, while moving the X-ray tube 1 to a, b, c,...i, move the detector 3 to a', b', c',...i'. Move around and take test shots. Then, in FIG. 1, the X-rays emitted from the X-ray tube 1 and transmitted through the subject 2 enter the detector 3 and are converted into visible light, and this output optical image is transmitted to the next television camera 4. was photographed,
converted into an electrical signal. At this time, the amount of control of the amount of incident light by the light amount controller 15 provided between the detector 3 and the television camera 4 is fixed at a standard neutral state. Then, each projection position a of the X-ray tube 1 =
The change characteristics of the light amount (actually, the value digitized by the A/D converter 5) is determined from the photographic data for each i. An example of the measurement and calculation results is shown in Table 1.

In this table, "photographing light amount" is the change in light amount when the values measured at each projection position a to i are taken as 100% with the value at projection position a as a reference.

Here, the maximum imaging light amount is 115% at the projection position e where the exposed thickness of the subject 2 is the minimum. Next, the "converted light amount" is the change in the light amount when the maximum photographing light amount at the projection position e is set as 100%. The value of this converted light amount provides a characteristic in which the amount of transmitted light changes at each projection position a=i. Next, the [control amount] is as follows, since the actual shooting starts from projection position a.
The light amount control amount at the projection position a when the light amount is controlled to be the optimum light amount at the projection position a is the standard 0%
The ratio (%) of the light amount control amount at each projection position b=i with respect to this reference value is calculated. In other words, this indicates that the light amount is controlled to reduce the light amount by 2% at position a relative to position a. Further, at position C, it is shown that the light amount is controlled so as to reduce the light amount by 4% compared to position a. Further, at position i, the light amount is controlled so as to increase the light amount by 2% relative to position a = 12-. Next, the "control amount difference" indicates how much the control amount at each projection position a-i changes between adjacent positions, expressed as a percentage difference in the control amount. In this way, the change characteristics of the amount of light are determined from the photographic data for each projection position a-i, the control amount values for each projection position a-i are determined, and these data are tabulated. As a result, a light amount table is created for correcting changes in the amount of light incident on the television camera 4 for each of the projection positions a to i.

Next, the operation of photographing the subject 2 for the main examination using the light amount table created in advance in this way will be described. First, in Fig. 1, an X-ray tube 1 and a detector 3
Arrow A indicates the mutual positional relationship between the two.

X-rays are emitted to the subject 2 and photographed while being varied in the B direction by a scanning device. At this time, first, a trial image is taken at the projection position a shown in FIG.
That is, the amount of light that allows the maximum use of the dynamic range of the television camera 4 is determined, and imaging is started under the X-ray conditions. Next, after actually photographing at this projection position a, while moving to the next projection position, the light amount is reduced by 2% for the projection position a based on the value of "control amount" in Table 1. Control to reduce. At this time, in FIG.
3 reads out the light amount table stored in the light amount table storage unit 14, and sends the light amount control signal S5 containing control amount data for each projection position a-i to the light amount controller 15.
Send to. Then, the light amount controller 15 controls the amount of light that enters the television camera 4 from the detector 3 by narrowing down the optical aperture by 2%, for example, based on the input of the light amount control signal S5. As a result, images can be taken with the optimum amount of light even at the projection position. Next, while moving to the projection position C, in the same manner as above, the light amount controller 15 is controlled to reduce the amount of light by 4% with respect to the projection position a, and the light is incident from the detector 3 to the television camera 4. Control the amount of light. As a result, even at the projection position C, the image is photographed with the optimum amount of light. Thereafter, in the same manner, each time the X-ray tube 1 moves to each projection position a - i, the light amount controller 15 is controlled according to the data in the light amount table in the light amount table storage section 14 to adjust the amount of light incident on the television camera 4. By controlling the X-ray tube 1, the subject 2 can always be imaged with the optimum light intensity at each projection position a-i of the X-ray tube 1.

1 and 2, the X-ray tube 1 is mainly shown as moving on a linear trajectory, but the present invention is not limited to this, and the X-ray tube 1 is moved on a circular or elliptical trajectory. Alternatively, the same can be applied to the case of moving on a thinly wound orbit.

〔Effect of the invention〕

Since the present invention is configured as described above, a test image is taken with the X-ray conditions lowered compared to that at the time of the actual examination, and
A light amount table is created in advance by determining the change characteristics of the light amount for each projection position a - i of the X-ray tube 1, and when imaging the main examination of the subject 2, the X-ray tube 1 is set at each projection position. a-1
Each time the light amount controller 1 moves, the light amount controller 1
5 and the amount of light incident on the television camera 4, the subject 2 can always be photographed with the optimum amount of light at each projection position a-i of the X-ray tube 1. Therefore, the dynamic range of the television camera 4 can be effectively used to its maximum at each projection position a to i of the X-ray tube 1°, and the quality of the captured image can be improved. Furthermore, the X-ray exposure dose to the subject 2 increases because the photographed image does not undergo halation due to changes in the irradiation thickness of the subject 2, and it is possible to prevent re-imaging due to a failure in radiography. can be prevented. In addition to changes in the irradiation thickness of the subject 2, halation has conventionally been caused when gas or air accumulates in a specific part of the subject 2, but according to the present invention, this can be prevented. Even in such cases, halation can be prevented from occurring.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the television tomography apparatus according to the present invention, and Fig. 2 shows the
An explanatory diagram showing the state of X-ray radiation from each projection position of the ray tube. Fig. 3 is a block diagram showing a conventional TV tomography device. Fig. 4 shows the state of X-ray radiation from each projection position of the X-ray tube. It is an explanatory view showing a state where radiation thickness changes. DESCRIPTION OF SYMBOLS 1... X-ray tube, 2... Subject, 3... Detector, 4... Television camera, 5... A/D converter, 6a-6n... Frame memory (storage device) ),
7... Arithmetic device, 8... D/A converter, 9.
...Monitor, 10...Top plate, 13...Control unit,
14... Light amount table storage unit, 15... Light amount controller.

Claims (1)

[Claims] An X-ray tube, a detector arranged opposite to the X-ray tube with a subject in between and converting the transmitted X-rays into visible light, a television camera that photographs the output optical image, and the X-ray tube. a scanning device that changes the positional relationship between the sphere and the detector; an A/D converter that converts the output signal of the television camera into a digital quantity; a storage device that stores this digital signal; and a storage device that reads data from this storage device. an arithmetic device that performs arithmetic processing;
A television tomography apparatus that has a display device that converts the processed digital signal into an analog signal and displays it, and that calculates and displays a tomographic image of an arbitrary tomographic plane within the subject; The control unit has a control unit that performs test radiography with lower X-ray conditions compared to the time of radiography before the main examination.
A light intensity table storage unit that stores a light intensity table created by determining the change characteristics of light intensity from the photographic data for each projection position of the tube is connected, and between the detector and the television camera, there is a A television tomography apparatus characterized in that a light amount controller is provided for controlling the amount of light incident on the television camera from the detector for each projection position in accordance with the data in the light amount table.