JPH03107940A - Method and device for reading radiograph information - Google Patents

Abstract

PURPOSE:To execute preliminary read precisely and at a high speed extending over a wide dynamic range almost simultaneously with the radiation of X-rays by making an X-ray image visible with the aid of a fluorescent screen which is arranged to closely contact with the back surface of an accumulating phosphor plate or sheet and picking up the image of the visible image with the aid of plural image pickup devices. CONSTITUTION:By arranging the fluorescent screen 1-2 so that it closely contacts with the back surface of the accumulating phosphor plate or sheet 1-1, X-ray image information transmitted through an object such as a human body is accumulated and recorded on the accumulating phosphor plate or sheet 1-1 at the time of exposuring the X-rays. Then, the X-ray image information transmitted through the accumulating phosphor plate or sheet 1-1 is made visible by the fluorescent screen 1-2. Besides, the image of the visible image is picked up by the image pickup devices such as two-dimensional semiconductor image pickup elements 1-6 and 1-7 and converted to an electric signal. Thus, the preliminary read of the radiograph information accumulated and recorded on the accumulating phosphor plate or sheet 1-1 can be precisely executed extending over the wide dynamic range almost simultaneously with the radiation exposure. As the result, the read is shortened and the setting accuracy of normal read condition is improved.

Description

[Detailed Description of the Invention] [Summary] An object of the present invention is to provide a radiation image information reading method and device that can perform pre-reading over a wide dynamic range accurately and at high speed, regarding a radiation image information reading device for X-ray photography. , By scanning an excitation light beam on a stimulable phosphor plate or sheet that has accumulated radiation image information, stimulated luminescent light corresponding to the radiation image information is generated, and the stimulated luminescent light is photoelectrically converted to generate electricity. In a radiation image information reading device that reads radiation image information as a signal, fluorescence from a phosphor plate disposed close to the stimulable phosphor plate or sheet;
Alternatively, a two-dimensional image corresponding to radiation image information formed by instantaneous light emitted by a stimulable phosphor plate or sheet is divided into two or more images having different intensity, and each image is transmitted to a plurality of imaging devices. By taking an image with the stimulable phosphor plate or sheet, the outline of the radiation image information accumulated and recorded on the stimulable phosphor plate or sheet is read in advance, and readout conditions for later reading out the image information as an electrical signal are determined based on the readout. Configure.

[Industrial application field]

The present invention visualizes an X-ray image using a phosphor plate placed close to the back of a stimulable phosphor plate or sheet that stores radiation image information, and captures this visible image using a plurality of imaging devices. Pre-reading is performed accurately and at high speed in a wide dynamic range almost simultaneously with X-ray irradiation.

[Conventional technology]

2. Description of the Related Art Radiological images such as X-ray images have been widely used for disease diagnosis and the like. As a means for obtaining an X-ray image, a radiograph in which a phosphor layer (phosphor screen) is irradiated with X-rays transmitted through an object and developed is conventionally used.

On the other hand, as a high-sensitivity, high-resolution X-ray imaging system, a stimulable phosphor is used instead of the conventional method of recording two-dimensional images of indirect or direct radiation on a film coated with a sheet of silver salt photosensitizer. method is beginning to be used. Regarding this method, as a basic system, US Patent No. 3.8
No. 59.527.

The phosphor used in this system is a so-called stimulable phosphor that stores energy in its phosphor crystal when it receives radiation energy such as X-rays, and this storage state is relatively stable and can last for a long time. Retained for a long time. When the phosphor in this state is irradiated with the first light that acts as excitation light, stimulated luminescence light with an intensity corresponding to the stored energy is emitted as second light. In this case, the first light is not limited to visible light, but has a wide range of wavelengths from infrared to ultraviolet. However, the selection differs depending on the phosphor material used. There are various kinds of second light, ranging from infrared light to ultraviolet light, and the difference depends on the phosphor material used.

Using the characteristics of this stimulable phosphor, an X-ray imaging system has been put into practical use in which radiation is transmitted through an object such as a human body, irradiated onto the stimulable phosphor, and recorded, thereby obtaining radiographic image information. Specifically, a stimulable phosphor plate or sheet that stores and records the X-ray information of the subject is scanned with excitation light such as a laser beam to emit stimulated luminescence light, which is then collected and received to produce photovoltaic electricity. By converting it into an electrical signal using a converter, an electrical signal proportional to the intensity of the accumulated radiation is obtained. Thereafter, this electric signal is subjected to image processing and printed on a silver halide film or displayed on a CRT to obtain a visualized radiation image.

In this case, in order to determine readout conditions for obtaining radiographic image information, it is important to know the outline of the stored image information before reading it out, in order to improve the gradation, etc. of the obtained radiographic image. It is important for

[Problem to be solved by the invention]

As described above, a method for reading out the outline of image information (hereinafter referred to as optical reading) prior to reading out (hereinafter referred to as main reading) to obtain radiographic image information is disclosed in Japanese Patent Application Laid-Open No. 185944/1983.
As described in JP-A No. 60-280163, prior to the actual reading, the stimulable phosphor sheet is scanned with excitation light at a lower level than the excitation light used for the actual reading,
There is a method of measuring the amount of stimulated luminescence emitted from the sheet and determining the readout conditions for main reading based on the histogram, but this method requires two excitation light scans for optical reading and main reading. However, there were problems in that it took a long time to read out, and that even with low-level excitation light, part of the information stored in the optically read portion was lost.

As another method, as described in JP-A-55-50180 and JP-A-56-11348, the instantaneous light emitted when the stimulable phosphor sheet is irradiated with X-rays is There is a method of receiving light with a large number of photoelectric conversion elements such as photodiodes arranged on the back side of a phosphor sheet to obtain optically read information. This method utilizes the property that the intensity of the instantaneous emitted light is proportional to the intensity of stimulated emitted light during actual reading.

The intensity range of the instantaneous light emitted above, which corresponds to the X-ray intensity, has a wide dynamic range of more than four orders of magnitude, and the intensity of the instantaneous light emitted is weak overall, so the sensitivity of the photodiode is not very good. With such semiconductor photoelectric conversion elements, only a strong part of the intensity range of instantaneous emitted light can be measured. Therefore, the maximum and minimum values of the radiation image information recorded on the stimulable phosphor sheet are detected by optical reading.
When trying to determine the readout conditions for the main reading, there is a problem that if the intensity difference between the maximum value and the minimum value exceeds the dynamic range of the semiconductor photoelectric conversion element, it will be impossible to detect it. there were.

SUMMARY OF THE INVENTION An object of the present invention is to provide a radiation image information reading device that can perform optical reading over a wide dynamic range accurately and at high speed.

[Means to solve the problem]

The first aspect of the present invention is to scan an excitation light beam on a stimulable phosphor plate or sheet that stores radiation image information.
generating stimulated luminescence light corresponding to the radiation image information;
A radiation image information reading method for photoelectrically converting the stimulated luminescence light and reading it as an electric signal to obtain radiation image information, the method comprising: a method for reading radiation image information by photoelectrically converting the stimulated luminescent light and reading it as an electric signal, the method comprising: fluorescence from a phosphor plate disposed close to the stimulable phosphor plate or sheet; splitting a two-dimensional image corresponding to radiation image information formed by instantaneous light emitted from a phosphor plate or sheet into two or more images having a difference in intensity;
By capturing each image with a plurality of imaging devices, the outline of the radiation image information accumulated and recorded on the stimulable phosphor plate or sheet is optically read, and the image information is later read out as an electrical signal based on the pre-reading. Further, the second aspect of the present invention is characterized in that it includes an excitation light source that generates an excitation light beam, and an excitation light beam that is directed onto a phosphor plate or sheet storing radiographic image information. a main scanning means for scanning; a sub-scanning means for moving the phosphor or sheet in a direction approximately perpendicular to the main scanning direction; In a radiation image information reading device comprising an optical guide for condensing stimulated luminescence light and guiding it to a photoelectric converter, and a photoelectric converter for converting the concentrated stimulated luminescence light into an electrical signal, the stimulable fluorescence A fluorescent screen disposed close to the body plate or sheet, and a branching means for branching a two-dimensional image appearing on the fluorescent screen when irradiated with radiation into two or more two-dimensional images with different brightness;
The present invention is characterized by having a radiation image information pre-reading means consisting of a plurality of imaging devices for photographing each of the branched images.

[Effect]

The radiation image information reading device according to the present invention visualizes an X-ray image using a fluorescent plate placed close to the back of a stimulable phosphor plate or sheet, and captures this visible image using a plurality of imaging devices. , optical reading is performed accurately and at high speed over a wide dynamic range almost simultaneously with X-ray irradiation.

Specifically, by placing a fluorescent plate close to the back of the stimulable phosphor plate or sheet, information on the X-ray image transmitted through a subject such as a human body when irradiated with X-rays can be collected from the stimulable phosphor plate or sheet. At the same time, the X-ray image information transmitted through the stimulable phosphor plate or sheet is visualized by a phosphor plate, and the visible image is captured by an imaging device such as a two-dimensional semiconductor image sensor and converted into an electrical signal.

Fluorescent screens generally have a property that the higher the X-ray fluorescence conversion efficiency (sensitization rate), the lower the spatial resolution, but in advance reading, it is sufficient to know the rough distribution of image information, and high resolution is not necessary. do not have. Therefore, it is possible to use a fluorescent plate with high X-ray fluorescence conversion efficiency as the fluorescent plate used in the present invention, which is about 10 to 100 times more efficient than when using instantaneous light emission as shown in the conventional example. A bright visual increase is obtained. Furthermore, the wavelength of the instantaneous emitted light in the conventional example is the same wavelength as the stimulated fluorescence generated during the subsequent main reading, so it cannot be freely selected, and the spectral sensitivity characteristics of the imaging device used for the pre-reading If the peak does not match the wavelength of the instantaneous emitted light, the imaging sensitivity will further decrease.

According to the method of the present invention, the wavelength of the fluorescence emitted by the fluorescent screen can be selected independently of the wavelength of stimulated fluorescence generated during the subsequent main reading, so the fluorescent screen It is now possible to match the wavelength of the fluorescence emitted by
A bright visible image of approximately 0x is obtained.

Next is a method of capturing the visible image on the fluorescent screen obtained by the above method, but in order to capture an image over a wide dynamic range, it is necessary to sense even very weak light.

A method for sensing weak light is to use an accumulation-type imaging device to accumulate all photons generated from a fluorescent screen by X-ray irradiation as electric charge in each pixel of the imaging device for a certain period of time.
A reading method is then used. According to this method, it is possible to measure even the very weak light within the wide dynamic range of fluorescence generated from the fluorescent screen, which has a wide dynamic range of more than four orders of magnitude. However, when the dynamic range of the imaging device is two to three orders of magnitude, A problem arises in that the accumulated charge in pixels that are hit by strong fluorescence becomes saturated, making it impossible to measure them.

Therefore, in the present invention, a plurality of such imaging devices are used, this visible image is split by a half mirror having a reflectance according to the dynamic range of the imaging device, and each branched visible image is photographed separately. We propose a method that captures images with a device and later synthesizes them using image processing.

For example, if the dynamic range of fluorescence generated from a fluorescent screen is 4 digits, and the dynamic range of the imaging device is 2 digits, and if this visible light is split by a /%-humirror with a transmittance of 1%, then Imaging device A, which is used to photograph the intensities transmitted through the half mirror, obtains an image signal of the first two digits of the fluorescence generated from the fluorescent screen, and imaging device B, which is used to image the intensities reflected by the half mirror, obtains an image signal of the first two digits of the fluorescence generated from the fluorescent screen. Obtain image signals of the last two digits of fluorescence. After that, by image processing, pixels with valid signals are selected from each imaging device, and the signals are combined with intensity correction according to the reflectance of the half mirror, thereby creating a pre-read image with a wide dynamic range. You can get information.

In this example, by using two imaging devices with a two-digit dynamic range, a four-digit dynamic range can be obtained as a whole.

That is, in the present invention, (1) a visible image is obtained by arranging a phosphor plate with high X-ray fluorescence conversion efficiency (sensitization rate) close to the back side of a stimulable phosphor plate or sheet;

■Using a half mirror to split the visible image into multiple images with different brightness; ■By capturing images using multiple imaging devices,
It is possible to perform pre-reading accurately and at high speed over a wide dynamic range, and it is possible to determine reading conditions for main reading with high precision.

〔Example〕

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

FIG. 1 is a configuration diagram of an embodiment of the present invention. In the figure, 1 is an X-ray imaging and pre-reading section according to the present invention, and 2 is a main reading section. 1.1 is a stimulable phosphor plate, which is used to store and record information about X-rays that have passed through the human body. 1.2
is a fluorescent screen, for example, CaWO4Cd2O. S:T
A phosphor such as B is used, and it emits fluorescence due to the X-rays that pass through the human body and the stimulable phosphor plate, forming a two-dimensional image whose brightness corresponds to the difference in X-ray absorption of the human body. The lead glass 1.3 absorbs X-rays, eliminates backscatter of X-rays, and serves to prevent other equipment from being exposed to X-rays.

The two-dimensional image on the phosphor 1.2 is transmitted through the lead glass 1.3,
An image is formed on an imaging device 1.6.1.7 by an optical system 1.4. At this time, 71-humirrer 1°5 with a transmittance of 0.1%
The optical image is divided into two parts. That is, the imaging device 1.6 captures a two-dimensional image with a luminance of 1/1000, and the imaging device 1.7 captures a two-dimensional image with a luminance of 999/1000.

FIG. 2 shows the output signal of each imaging device with respect to the intensity of a two-dimensional image when a two-dimensional semiconductor imaging device such as a MOS or CCD is used as an imaging device.

Normally, the dynamic range of these semiconductor image sensors is about 3 digits, whereas the intensity of the two-dimensional image on the fluorescent screen varies by 4 digits depending on the X-ray irradiation conditions, the size and size of the human body, and the narrowing of the irradiation field. It has a dynamic range of more than an order of magnitude.

On the other hand, according to the method of the present invention, as shown in FIG.
A six-digit dynamic range can be obtained by using two imaging devices with a three-digit dynamic range. Here, 1.8 is a signal processing unit that synthesizes signals from each imaging device. First, after A/D converting the image signal from each imaging device, a pixel that has reached the saturation voltage is detected from among the image digital signals from the imaging device 1.7, and the imaging device 1.6 for that pixel is The value obtained by multiplying the digital value by 999 is adopted as the true value of the saturated pixel. In this way, the image signals from the two imaging devices are combined into one image signal, a histogram is obtained by the histogram analysis section 1.9 and the reading condition determining section, reading conditions are determined from the histogram, and the main reading is started. The information is transmitted to the reading section 2 that performs the reading. The reading conditions can be determined by, for example, determining the first moment of the histogram and reading out only the image signal within a predetermined range around that value, or by using unnecessary information in the histogram (such as by narrowing the irradiation field). There is a method of determining the readout intensity range by excluding the histogram of the area where the X-rays did not hit when the image was taken, or the area where the X-rays passed through without passing through the subject, etc., but this is not the gist of the present invention, so the explanation will be omitted. do. On the other hand, the stimulable phosphor plate 1.1 on which X-ray image information has been stored and recorded is transported to the reading section 2 by a transport mechanism (not shown), and main reading is performed under the determined reading conditions.

FIG. 3 is a detailed view of the book reading section 3.3 of FIG.

A semiconductor laser with a wavelength of 780 nm is used as the excitation light source 3.4, and the laser beam is scanned in the main scanning direction by a galvanometer 3.5. Further, by moving the stimulable phosphor plate 3.1 in a direction perpendicular to the main scanning direction using the precision fine movement table 3.7, the excitation light can be scanned over the entire surface of the stimulable phosphor plate. Stimulated luminescent light generated by one scan of the laser beam is focused by a light guide path made up of a large number of optical fibers 3.1, and then passed through a photomultiplier 3.1.
2.

At this time, the light guide path 3.1 and the photomultiplier 3.1.
Between 2 and 2, there is a filter (not shown) that does not transmit the wavelength of the excitation laser but transmits the wavelength of the stimulated emission light.
Place. The stimulated luminescent light selectively extracted by this filter is converted into an electrical signal by a photomultiplier 3.2, and then is transferred to an A/D converter 3 by a first stage amplifier 3.8.
．． 9 is amplified to the optimal signal level. At this time, the photomultiplier of the photomultiplier 3.2 and the first stage amplifier 3
．． The amplification conditions and the like of No. 8 are set according to the reading conditions determined by the optical reading. Image data converted into digital signals by A/D converter 3.9 is an image memo! J 3.10
After that, the image is processed and output to screen 1.6 or hard copy.

In still other embodiments, a half mirror for branching and three or more two-dimensional semiconductor image sensors may be used to further widen the dynamic range, or an imaging section or the like may be used in place of the two-dimensional semiconductor image sensor. Further, the transmittance of the half mirror may also be other than the above, and may be determined based on the dynamic range of the imaging device used and the required pre-reading.

Furthermore, cooling the individual two-dimensional semiconductor image sensors used to reduce noise due to dark current is also effective in expanding the dynamic range of pre-reading.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to accurately pre-read radiation image information accumulated and recorded on a stimulable phosphor plate or sheet almost simultaneously with radiation irradiation over a wide dynamic range. It is possible to shorten the time and improve the setting accuracy of the main reading conditions, which greatly contributes to speeding up reading and improving the quality of the obtained image.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the main part of an embodiment of the radiation image reading device of the present invention, FIG. 2 is an explanatory diagram of the dynamic range of the pre-reading section of the present invention, and FIG. 3 is a main part of the image reading section of the present invention. It is a partial configuration perspective view. (Explanation of symbols) 1... Pre-reading section, 2... Main reading section, 1.1... Stimulable phosphor plate or sheet, 1.2...
Fluorescent screen, 1.3... Lead glass, 1.4... Imaging lens, 1.5... Half mirror 1 1, 6, 1, 7... Two-dimensional semiconductor image sensor, 1.8...
...Signal processing unit, 1.9...Histogram analysis unit/reading determination unit, 3.1
...Light guide path, 3.2...Photoelectric converter, 3.4...Excitation light source, 3.5...Galvanometer, 3.6...Fθ lens, 3.7...Precision Fine movement table, 3.8... First stage amplifier, 3.9... A/D converter, 3.10... Image memory.

Claims (1)

[Claims] 1. By scanning an excitation light beam on a stimulable phosphor plate or sheet that has accumulated radiation image information, stimulated luminescence light corresponding to the radiation image information is generated, and the stimulated luminescence In a radiation image information reading method for obtaining radiation image information by photoelectrically converting light and reading it out as an electrical signal, fluorescence from a phosphor screen disposed close to the stimulable phosphor plate or sheet, or the stimulable phosphor plate or sheet By splitting a two-dimensional image corresponding to radiographic image information formed by emitted instantaneous light emitted into two or more images having a difference in intensity, and capturing each image with a plurality of imaging devices, the accumulation property can be reduced. A radiation image information reading method characterized in that the outline of radiation image information stored and recorded on a phosphor plate or sheet is read in advance, and readout conditions for later reading out the image information as an electrical signal are determined based on the preliminary reading. . 2. An excitation light source that generates an excitation light beam; a main scanning unit that scans the excitation light beam onto a phosphor plate or sheet storing radiation image information; or a sub-scanning means for moving the sheet, and an optical guide for condensing stimulated luminescence light for one scanning line generated from the phosphor plate or sheet by scanning the excitation light beam and guiding it to a photoelectric converter. , in a radiation image information reading device comprising a photoelectric converter that converts focused stimulated luminescence light into an electrical signal, a phosphor plate disposed close to the stimulable phosphor plate or sheet, and when irradiated with radiation. a branching means for branching a two-dimensional image appearing on the fluorescent screen into two or more two-dimensional images having different luminance; and a radiation image information destination comprising a plurality of imaging devices for photographing each of the branched images. A radiation image information reading device characterized by having a reading means.