JPH0638950A - Radiographic apparatus - Google Patents

Abstract

PURPOSE:To enable the monitoring of X rays transmitted from a subject itself accurately and in real time. CONSTITUTION:In a radiographic apparatus 2 which is provided with an X-ray source 1 for projecting X rays to a subject, a scintillator 23 which emits light with the entry of X rays from an X-ray source 1 as transmitted through the subject and a solid image sensor 21 to detect the light from the scintillator 23, the solid image sensor 21 has a second conductive type semiconductor substrate in which a photodetecting area is formed on the surface side thereof to convert the light from the scintillator 23 into electricity and a first conductive type impurities area on the rear side thereof. Moreover, a monitoring means is provided to detect a photocurrent output of a photodiode formed by an PN junction between the semiconductor substrate and the impurities area thereby monitoring an irradiation value of the X rays from the X-ray source. Here, the radiographic apparatus 2 also may be provided with a control means 53 to control an output of the X-ray source by the output of the monitoring means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an X using a solid-state image sensor.
The present invention relates to a line imaging device.

[0002]

2. Description of the Related Art An X-ray image pickup device using a solid-state image pickup device such as a CCD (charge coupled device) is known.
It is configured like. As shown in the figure, a subject 3 is arranged between the X-ray source 1 and the X-ray imaging apparatus 2, and the X
The rays pass through the subject 3 and enter the X-ray imaging device 2.
The X-ray image pickup apparatus 2 has a CCD element 21 as a solid-state image pickup element, and a fiber optical plate 22 and a scintillator 23 are arranged on the front surface thereof.

As shown in FIG. 5, for example, an IT (interline transfer) type CCD device 21 has a vertical charge transfer device including a light receiving region 41 including a photodiode and a vertical shift register for transferring signal charges from the light receiving region 41. It has a region 42 and a horizontal charge transfer region 43 composed of a horizontal shift register for further transferring this transfer charge.

Then, the transfer charge is output from an FDA (floating diffusion amplifier) 44.

According to this structure, the transmitted X-ray image that has been transmitted through the subject 3 is converted into an optical image by the scintillator 23, passes through the fiber optical plate 22, and passes through the CCD element 2.
1 is detected. Therefore, the X-ray image can be observed. That is, the obtained image signal has a magnitude almost proportional to the transmitted X-ray dose, and the image can be displayed on a display or the like by sequentially reading out the signal of each pixel.

A frame transfer (FT) system without storage areas is called a full frame transfer (FFT) system. However, when the FFT method is used for general purposes, it is necessary to take measures such as closing the mechanical shutter during the signal reading period or stopping the light emission of the light source. There is no problem in X-ray imaging because it is covered with a light-shielding material such as aluminum. CCD to use
May be an FT method or an FFT method in addition to the IT method.

As described above, in X-ray imaging, the image signal obtained has a size substantially proportional to the transmitted X-ray dose, and therefore the optimum conditions differ depending on the object (subject) to be imaged. Therefore, in order to obtain a good image, it is necessary to optimally set the X-ray irradiation conditions (X-ray tube voltage, tube current, irradiation time). In the medical field in particular, this condition is important because it is necessary to prevent an increase in the amount of X-ray exposure to the patient due to reimaging.

As a conventional method for monitoring the X-ray irradiation dose, there is a technique of using the output of a photodetector element such as a photodiode arranged in the vicinity of the solid-state image pickup element 21. Further, for example, as shown in FIG. 6 which is similar to the technique of Japanese Patent Laid-Open No. 63-143862 or Japanese Patent Laid-Open No. 56-123700, the output of the solid-state imaging device 21 itself provided in the X-ray imaging apparatus 2 is compared with the comparator 51. And set value circuit 52
There is a technique for monitoring the X-ray source 1 and controlling the X-ray source 1 by the X-ray source controller 53. In either method, the X-ray irradiation dose is measured from the photocurrent output, compared with the reference value set by the comparator to obtain the optimum image, and when the set value is reached, a control signal is sent to the X-ray irradiation controller. Is.

[0009]

However, in the method of monitoring the X-ray dose by using the photo-detecting elements arranged around the image pickup element, the X-ray dose can be monitored in real time, but the signal (transmission X-ray) from the subject itself is monitored. There is a problem that it lacks precision because it is not done.

In the method of monitoring the output of the image pickup device itself as shown in FIG. 6, the signal from the subject can be monitored, but it takes time to read the signal, so that it cannot be monitored in real time. By the way, as in the case of digestive system diagnosis in the medical field, when low energy X-ray irradiation is performed at any time and the flow of a positive contrast agent such as barium is observed on a TV monitor, it does not have to be a real-time monitor. Although there is no particular problem, it cannot be used as a monitor for high-energy X-ray irradiation for diagnosis.

Therefore, the present invention uses the transmission X from the subject itself.
It is an object of the present invention to provide an X-ray imaging device that can monitor a ray accurately and in real time.

[0012]

SUMMARY OF THE INVENTION The present invention is an X-ray source for projecting X-rays on an object and an X-ray from the X-ray source transmitted through the object.
In the X-ray imaging device including a scintillator that emits light upon incidence of rays, and a solid-state image sensor that detects light from the scintillator, the solid-state image sensor has a light-receiving region that photoelectrically converts light from the scintillator on the surface side, First on the back side
A semiconductor substrate of a second conductivity type having a conductivity type impurity region is formed, and a PN between the semiconductor substrate and the impurity region is formed.
It is characterized by further comprising monitor means for detecting the photocurrent output of the photodiode constituted by the junction and monitoring the irradiation amount of the X-ray from the X-ray source.

Here, the X-ray imaging apparatus may further include control means for controlling the output of the X-ray source by the output of the monitor means.

[0014]

According to the structure of the present invention, since the photodiode is formed on the back surface of the solid-state image pickup device such as CCD, the signal by the X-ray that has passed through the subject and reached the photodiode without being absorbed in the middle is directly monitored. And can be monitored in real time. Therefore, the output of the X-ray source can be accurately controlled using this monitor output.

[0015]

An embodiment of the present invention will be described below with reference to the accompanying drawings. It should be noted that the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is an overall configuration diagram of the embodiment, and FIG. 2 is a configuration diagram of essential parts. As shown in the figure, the CCD device 21 as a solid-state image sensor has a P ⁻ type semiconductor substrate 6 which is grounded, and an N type buried channel 61 is formed on the surface side thereof. Then, a positive potential is applied to the channel 61 via the N ⁺ layer 62, so that the PN junction with the semiconductor substrate 6 is reverse biased. Transfer electrodes G _{1 to} G ₃ are provided on the N-type buried channel 61 via an insulating film (not shown), and transfer clocks φ _{1 to} φ ₃ are applied to them. In addition, FT method,
In the case of the FFT method, since the light receiving area is also composed of a CCD, a PN junction is formed in the light receiving area by the buried channel similar to the above. In this light receiving area,
Of the X-rays that have passed through the subject, the light converted into visible light by the scintillator 23 is detected.

It should be noted that the CCD element 21 has a P / P ratio depending on various characteristics such as spectral sensitivity of the CCD element 21 for each purpose.
^{A +} / P ⁻ type semiconductor substrate can also be used.

On the other hand, an N ⁺ layer is formed on the back side of the CCD element 21, which is a kind of photodiode (PD) 6
It operates as 3. Here, as shown in FIG. 3, the X-rays emitted from the X-ray source also include high-energy X-rays that pass through the fiber optic plate 22. That is, when the operating voltage of the X-ray tube that is the X-ray source is increased, not only the photon energy at which the relative number of photons peaks in the output X-rays increases, but also the output spectrum thereof spreads toward the high energy side. I will have. Therefore, even when the scintillator 23 and the fiber optic plate 22 are used, high-energy X-rays pass through the fiber optic plate 22 without being converted into visible light by the scintillator 23, and thus the PD 63 according to the present embodiment. Can be used to detect carriers generated by high energy X-rays.

That is, the light converted into visible light is transferred to the CCD.
An image signal is detected on the surface side of the element 21, and carriers generated by the high-energy X-rays transmitted through the fiber optical plate 22 are detected by the PD 63 to be used as a monitor signal.
Since the PD 63 detects carriers generated by X-rays in the deep portion of the semiconductor substrate 6 and uses it as a monitor signal, the concentration of the semiconductor substrate 6 is lowered, and a bias is applied to the PD 63 in a state in which the void layer is widened. It is desirable to use.

Further, in the direct detection of X-rays, a signal in the region of X-rays of relatively low energy is detected on the front surface side of the CCD element 21 to be an image signal, and a signal by the X-rays of high energy is PD63 on the rear surface. It is possible to detect and use as a monitor signal.

That is, as shown in FIG. 1, the photocurrent output by the PD 63 formed on the back side of the P ⁻ type semiconductor substrate 6 is
It is accumulated by an ammeter and a charge amplifier (integrator) 55 and given to the comparator 51 at a constant cycle. Here, since the set voltage from the set value circuit 52 is given to the comparator 51, the output of the comparator 51 is inverted depending on the amount of X-ray irradiation, and this is given to the X-ray source controller 53.

The X-ray source controller 53 controls the start and end of X-ray imaging, but it is desirable to adjust the output of the X-ray source 1 according to the above-mentioned monitor result. In this case, it is desirable that not only the irradiation time but also the tube voltage and the tube current can be controlled. By doing so, imaging can be performed under optimum conditions according to the X-ray transparency of the subject 3.

Although an N-type buried channel is formed on the surface side of the CCD element 21 in FIG.
Even if a P-type buried channel that is P-type instead of D-type is used, the same effect as that of the above-described embodiment can be obtained. In this case, P and N in the above embodiment are all opposite.

[0024]

As described above, according to the X-ray image pickup apparatus of the present invention, the photodiode formed on the back surface side of the semiconductor substrate constituting the CCD as the solid-state image pickup element does not absorb light in the middle of the photodiode. By monitoring the signal due to the X-ray reaching the diode, it is possible to directly obtain the X-ray transmitted through the subject itself in real time. Therefore, it is accurate and has high energy X for diagnosis.
It is possible to monitor the irradiation amount in the line irradiation.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an embodiment.

FIG. 2 is a main part configuration diagram of an embodiment.

FIG. 3 is a chart showing the relationship between tube voltage and X-ray spectrum.

FIG. 4 is a configuration diagram of a general conventional device.

FIG. 5 is a plan view of a solid-state image sensor (CCD).

FIG. 6 is a configuration diagram of a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... X-ray source, 2 ... X-ray imaging device, 21 ... CCD element, 2
2 ... Fiber optic plate, 23 ... Scintillator, 3 ...
Subject, 51 ... Comparator, 52 ... Setting value circuit, 53
... X-ray source controller, 55 ... Ammeter, charge amplifier, 6 ... P-type semiconductor substrate, 61 ... N-type buried channel, 63 ... Photodiode.

Claims (2)

[Claims] 1. An X-ray source that projects X-rays onto a subject, a scintillator that emits light when incident from the X-ray source that has passed through the subject, and a solid-state image sensor that detects light from the scintillator. In the X-ray imaging device having the second conductivity type, the solid-state imaging device has a light receiving region for photoelectrically converting light from the scintillator on a front surface side, and a first conductivity type impurity region on a back surface side. A monitor configured to have a semiconductor substrate, and detecting a photocurrent output of a photodiode configured by a PN junction between the semiconductor substrate and the impurity region to monitor an X-ray irradiation amount from the X-ray source. An X-ray imaging apparatus comprising means. 2. The X-ray imaging apparatus according to claim 1, further comprising control means for controlling the output of the X-ray source by the output of the monitor means.