JPH0910191A - Radiation imaging device - Google Patents

Abstract

(57) [Abstract] [Purpose] Regardless of the size of the radiation transmittance of the subject, the detected radiation intensity is kept almost constant, and the ratio of the quantum noise to the signal is made almost the same so that for which imaging site (EN) A radiation imaging apparatus capable of obtaining imaging data of the same quality and quantitatively grasping the radiation transmittance and the like. [Structure] A total calculator 8 that integrates the outputs of the elements of the line sensor 4, and an X-ray output controller 9 that controls the output of the X-ray tube 1 so that the output of the total calculator is constant.
And a correction calculator 10 for dividing the output of each line sensor element by the output of the dosimeter 6 for measuring the X-ray intensity applied to the subject 3 from the X-ray tube. The output of the arithmetic unit is stored in the image memory 11. Since the amount of statistical fluctuation of the obtained data becomes constant regardless of the magnitude of the radiation transmittance of the subject, the obtained image has a constant accuracy at any imaging site.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image pickup apparatus for medical use and a nondestructive inspection apparatus for industrial use.

[0002]

2. Description of the Related Art In recent years, in medical X-ray imaging devices and the like, X-ray detectors made of semiconductors have been used as X-ray detection elements instead of conventional photographic film in one or more rows in a one-dimensional array. An image pickup device has been developed which obtains a two-dimensional image by accumulating the transmitted X-ray intensity data obtained by accumulating and scanning this in a direction substantially perpendicular to the parallel direction of the detection elements. FIG. 2 is a schematic diagram of a human chest imaging device. X radiated in a fan shape from the X-ray tube 21
The line 22 passes through the subject 23 and is detected by the line sensor 24. Since the line sensor 24 has a large number of X-ray detection elements arranged in the horizontal direction in the drawing, it is possible to simultaneously measure the X-ray intensity in one row. In addition, the line sensor 24 is a support 25
It is supported by and can be scanned in the direction indicated by the arrow 26. The X-ray beam 22 and the line sensor 2 whose vertical spread is limited by a limiting slit or the like.
4 is synchronously scanned in the scanning direction 26, the obtained transmitted X-ray intensity data is stored in an image memory, and the data in the image memory is displayed on a display device such as a CRT in a luminance modulation manner to display the chest of the subject. It is possible to obtain a two-dimensional transmission X-ray image of

Further, this device is characterized in that not only the chest but also the abdomen can be imaged simultaneously by enlarging the scanning range of the line sensor 24.

[0004]

However, since the X-ray transmittance of the human chest is high, but the X-rays of the abdomen are not very transparent, the radiation dose from the X-ray tube should be optimized for chest imaging. However, there is a problem in that when the abdomen is imaged, the dose becomes insufficient, and the image becomes conspicuous due to statistical fluctuation (also referred to as quantum noise). As a solution to this, a method of controlling the X-ray output according to the magnitude of the X-ray transmittance of the subject is disclosed in JP-A-61-94638.
However, the former does not disclose a method for detecting the magnitude of the X-ray transmittance of the subject. The latter discloses a method of performing preliminary imaging once before the main imaging and increasing or decreasing the X-ray output of the main imaging based on the data of the preliminary imaging. However, this method requires two imagings. There is a problem that it must be. Further, as a problem common to both, since the captured data has a strong non-linearity due to the increase / decrease in the X-ray output, even if there is no problem in displaying the image, it is inconvenient for the quantitative analysis of the data. There is a problem.

An object of the present invention is to make the detected radiation intensity substantially constant regardless of the radiation transmittance of the subject and to keep the ratio of the quantum noise to the signal substantially the same, for which imaging region. It is another object of the present invention to provide a radiation imaging apparatus which can obtain imaging data of the same quality and can quantitatively grasp the radiation transmittance and the like.

[0006]

In order to solve the above-mentioned problems, the present invention irradiates a subject with radiation from a radiation generator and uses an array type detector in which a plurality of radiation detecting elements are integrated in parallel. In a radiation imaging apparatus for measuring a transmitted radiation intensity transmitted through a specimen and storing a data obtained by scanning the array type detector in an image memory to obtain a two-dimensional image, a part of the output of the radiation detecting element. Alternatively, first calculation means for integrating all outputs, control means for controlling the output of the radiation generator based on the output of the first calculation means, and irradiation of the subject from the radiation generator An irradiation ray detecting means for measuring the radiation intensity and a second arithmetic means for correcting each output of the radiation detecting element based on the output of the irradiation ray detecting means are provided, and the second arithmetic operation is performed. The output of the stage was set to be stored in the image memory.

[0007]

The average radiation dose detected by the detector can be measured by summing the outputs of the radiation detection elements of the array type detector. By controlling the output of the radiation generator based on its size to keep the radiation intensity detected by the array-type detector almost constant, the data obtained regardless of the radiation transmittance of the subject Since the amount of statistical fluctuation becomes constant, the obtained image becomes a substantially clear image regardless of the imaged site. In addition, the amount of radiation applied to the subject is monitored by the irradiation ray detection means, and the output of the array-type detector is corrected using that value,
Even if the output of the radiation generator is increased or decreased, the radiation transmittance of the subject can be quantitatively measured.

[0008]

FIG. 1 shows an embodiment of the present invention. The X-ray tube 1 is a radiation generator, and X-rays 2 radiated in a fan shape from this
Is transmitted through an object 3 such as a human body and is detected as a linear form at once by an array type X-ray detector (line sensor) 4, and its output is read by a line sensor output circuit 5.
On the other hand, a dosimeter 6 as an irradiation ray detecting means is installed between the X-ray tube 1 and the subject 3 and is irradiated on the subject 3.
Measure the dose. The dosimeter output circuit 7 reads out the output of the dosimeter 6. Here, the line sensor 4 is formed by arranging a large number of small solid-state X-ray detection elements in one row or a plurality of rows, and the line sensor output circuit 5 amplifies signals from the individual detection elements and outputs them via a comparator / counter. It is converted into digital data. The dosimeter 5 is composed of a solid-state X-ray detection element similar to a line sensor, and the dosimeter output circuit 7 includes an amplifier, a comparator, a counter, etc., and converts the detected X-ray dose of the dosimeter 6 into digital data. To do. A two-dimensional transmitted X-ray image of the subject 3 can be obtained by scanning the line sensor 4 in a direction substantially perpendicular to the parallel direction of the X-ray detection elements and capturing data. During this scanning, a slit (not shown) that limits the spread of the X-ray in the scanning direction and the dosimeter 6 are also scanned in synchronization.

Each detecting element of the line sensor 4 used here counts the incident X-ray photons as a number. For example, assuming that 400 photons are counted per detecting element (pixel) on average when photographing a lung field (chest) of a human body, this data has a square root of 400, that is, a statistical variation of 20 counts (quantum). Noise) will be included. On the other hand, if 100 photons are counted when the abdomen is imaged with the same X-ray tube output, the quantum noise at this time is the square root of 100, that is, 10 counts. In this case, the amount of noise in the lung field is 5% of the total count value, while the amount of noise in the abdomen is 10%, so that the photographed image of the abdomen is conspicuously rough due to quantum noise.

Therefore, in this embodiment, an X-ray is calculated based on the total calculator 8 for summing the outputs from the respective detection elements included in the line sensor 4, that is, the digital outputs corresponding to the respective detection elements of the line sensor output circuit 5, and the output thereof. An X-ray output controller 9 for controlling the tube output was provided. In the above example, when the line sensor moves from the lung field to the abdomen, the output of the line sensor 4 is 400 counts to 100 counts and 4 counts.
Since it is one-half, the X-ray output controller 9 controls the output of the X-ray tube to be about four times. By doing so, the X-ray dose counted by the line sensor 4 becomes about 400 counts, and the amount of quantum noise at the time of imaging the lung field and that at the time of imaging the abdomen can be made substantially the same. That is, the X-ray controller 9 controls the output of the X-ray tube 1 by changing the tube current or the like so that the output of the total calculator 8 becomes a certain fixed value.

The X-ray dose actually applied to the subject 3 is monitored by the dosimeter 6, and the dosimeter output circuit 7 converts it into digital data. Based on the output of the dosimeter output circuit 7, the correction calculator 10 obtains the output of the line sensor output circuit 5 obtained after changing the output of the X-ray tube, a value that will be obtained when the X-ray tube output is constant. Correct so that In the above specific example, the dosimeter output circuit 7 is used when the lung field is imaged.
Outputs a relative value of 1, and outputs a relative value of 4 during abdominal imaging. On the other hand, the average output of the line sensor output circuit 5 is
Since the abdomen is 400 counts / pixel, the correction calculator 1
0 divides the output of the line sensor 4 by the output of the dosimeter output circuit 7 to obtain 400 for the lung field and 100 for the abdomen.
The count value of is output. That is, the correction calculator 1
0 indicates the output of the line sensor output circuit 5 as the dosimeter output circuit 7
Is divided by the output of (the output value relative to the reference value). The output data of the correction calculator 10 is stored in the image memory 11 as image information, and based on the data stored in the image memory 11, the transmission X is transmitted to the display device 12 such as a CRT by brightness modulation.
A line image is displayed. In the above example, the error due to the statistical fluctuation of the lung field and the abdomen is 5%, and the measured values at each site maintain a relatively correct magnitude relationship.
A quantitative consideration is always possible.

Further, the correction calculator 10 converts the counted value X using the reference value X0 and the constant A as follows: Y = -Alog (X / X0) (1) Then, the image memory 11 Data may be transferred to. If the reference value X0 is selected as the count value when the subject 3 does not exist, Y becomes a value proportional to the thickness of the subject and the transmittance per unit thickness.

The total calculator 8 may be a calculator for the outputs of all the detection elements included in the line sensor 4, or a part thereof, for example, only for the central portion covered by the subject. May be. The calculation may be a simple addition, or an average value obtained by dividing the added value by the number of pixels. Further, it may be an average value calculated with appropriate weighting according to the position of the detection element.

The dosimeter 6 may be an X-ray detector made of a semiconductor or the like which directly measures the X-ray emitted from the X-ray tube, or does not directly measure the irradiated X-ray. Alternatively, the X-ray dose may be indirectly estimated from the tube current or the like.

[0015]

In the radiation image pickup apparatus of the present invention, the outputs of the radiation detection elements of the array type detector are summed, the output of the radiation generator is controlled based on the size, and the outputs are detected by the array type detector. By keeping the radiation intensity of the subject almost constant, the amount of statistical fluctuation of the obtained data becomes constant regardless of the magnitude of the radiation transmittance of the subject, so the obtained image has a constant accuracy at any imaging site. , It is possible to take a uniform image as a whole.

Further, the amount of radiation applied to the subject is monitored by the radiation detecting means, and the output of the radiation detector is corrected using the value, so that the subject can be examined regardless of increase or decrease in radiation output. It is possible to quantitatively measure the radiation transmittance or the thickness of the subject.

Further, even if the radiation output fluctuates with time due to the drift of the device, etc., since the irradiation ray detecting means monitors it, an appropriate correction can be made and the drift can be canceled.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention.

FIG. 2 shows a conventional example of a radiation imaging apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... X-ray tube 2 ... X-ray 3 ... Subject 4 ... Line sensor 5 ... Line sensor output circuit 6 ... Dosimeter 7 ... Dosimeter output circuit 8 ... Total calculator 9 ... X-ray output controller 10 ... Correction calculator 11 ... Image memory 12 ... Display device 21 ... X-ray tube 22 ... X-ray 23 ... Subject 24 ... Line sensor 25 ... Support 26 ... Scanning direction

Claims (1)

[Claims] 1. The array-type detection is performed while irradiating a subject with radiation from a radiation generator and measuring the transmitted radiation intensity transmitted through the subject by an array-type detector in which a plurality of radiation detection elements are integrated in parallel. In a radiation imaging apparatus for storing data obtained by scanning a scanning device in an image memory to obtain a two-dimensional image, first calculation means for integrating a part or all of outputs of the radiation detection element, and Control means for controlling the output of the radiation generator based on the output of the first calculation means, irradiation line detection means for measuring the intensity of the radiation irradiated to the subject from the radiation generator, and this irradiation line detection means Second arithmetic means for correcting each output of the radiation detecting element based on the output of the second radiation detecting element, and the output of the second arithmetic means is stored in the image memory. Radiation imaging device.