JPH0833592B2 - Radiation image reading method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image reading method for obtaining an image signal by reading light representing a radiation image obtained from a recording sheet on which a radiation image of a subject is recorded. Is.

(Prior Art) It is performed in various fields to read a recorded radiation image to obtain an image signal, perform appropriate image processing on the image signal, and then reproduce and record the image. For example,
An X-ray image is recorded using an X-ray film having a low gamma value designed to be compatible with the subsequent image processing, and the X-ray image is read from the film on which the X-ray image is recorded and converted into an electric signal. By subjecting the electric signal (image signal) to image processing and reproducing it as a visible image in a copy photograph or the like, a system capable of obtaining a reproduced image having good image quality performance such as contrast, sharpness, and graininess is provided. It has been developed (see JP-B-61-5193).

In addition, the applicant of the present application, radiation (X-ray, α-ray, β-ray,
When γ-rays, electron rays, ultraviolet rays, etc.) are irradiated, a part of this radiation energy is accumulated, and when irradiation with excitation light such as visible light is subsequently performed, a stimulable luminescent material (stimulable luminescence) that emits stimulated emission according to the accumulated energy. Exhaustive phosphor) is used to temporarily record and record a radiation image of a subject such as a human body on a sheet-shaped stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as laser light to stimulate irradiation. Generates emitted light, photoelectrically reads the obtained stimulated emission light to obtain an image signal, and based on this image signal, outputs a radiation image of the subject as a visible image on a recording material such as a photographic photosensitive material or a CRT. A radiographic image recording / reproducing system has already been proposed (Japanese Patent Laid-Open No. 55-12429).
Nos. 56-11395, 55-163472, 56-104645
No. 55-116340).

This system has the practical advantage of being able to record images over a very wide radiation exposure area compared to conventional radiographic systems using silver halide photography. That is, in the stimulable phosphor, it has been recognized that the amount of emitted light stimulated by excitation after storage is proportional to the radiation exposure dose over a very wide range, and therefore the radiation exposure dose varies depending on various imaging conditions. Even if it fluctuates significantly, the amount of stimulated emission light emitted from the stimulable phosphor sheet is read by the photoelectric conversion means with the reading gain set to an appropriate value and converted into an electric signal. By using the to output a radiation image as a visible image on a recording material such as a photographic light-sensitive material or a display device such as a CRT, it is possible to obtain a radiation image that is not affected by fluctuations in radiation exposure dose.

In the above system using a recording sheet such as the X-ray film or stimulable phosphor sheet, in order to obtain an image signal by reading the radiation image recorded on the recording sheet, a radiation image reading device is usually used and Light that irradiates light and represents a radiation image obtained from the recording sheet by the irradiation of light (for example, light transmitted through the X-ray film or reflected from the X-ray film, or light emitted from the stimulable phosphor sheet). (Stimulated emission light, etc.) is received by the photodetector,
This is performed by obtaining a signal corresponding to the light amount of the light, inputting the signal to a logarithmic amplifier, and performing logarithmic compression. Further, the radiation image reading apparatus is also usually provided with a gain setting means for adjusting the magnitude of the output signal of the photodetector (the input signal of the logarithmic amplifier) with respect to the amount of light received by the photodetector.

(Problems to be Solved by the Invention) After obtaining an image signal by using the radiation image reading device as described above, the image processing device performs appropriate image processing on the image signal, The radiation image is reproduced and displayed as a visible image, and the visible image is provided for observation.

However, the light representing the radiation image obtained from the recording sheet ranges from faint light to strong light (for example, the intensity ratio of 1 :).
Very it has a wide range of light intensity width of 10 about ^40). Even with such a light amount width, if a high-performance photomultiplier tube or the like is used as the photodetector, it can be converted into an electric signal corresponding to each light amount with sufficient accuracy and sufficient speed. However, when this electric signal is input to a logarithmic amplifier for logarithmic conversion, the logarithmic amplifier usually has poor frequency response to a weak input signal, and therefore, in order to logarithmically convert a wide range of signals as described above. It was necessary to limit the reading speed of the radiation image from the recording sheet so that even the weakest signal could be logarithmically converted with sufficient accuracy. Therefore, the speed of the entire apparatus is limited, and the processing capacity per unit time is limited.

In view of the above circumstances, the present invention overcomes the condition that the frequency response of the logarithmic amplifier with respect to a weak input signal is poor,
It is an object of the present invention to provide a radiation image reading method with improved processing capacity per unit time.

(Means for Solving the Problem) A radiation image reading method of the present invention receives light representing a radiation image obtained from a recording sheet on which a radiation image of a subject is recorded, and outputs a signal corresponding to the light amount of the light. A radiation image reading apparatus including a photodetector for outputting the signal, a gain setting unit for adjusting the magnitude of the output signal of the photodetector with respect to the amount of received light, and a logarithmic amplifier for logarithmically compressing the output signal. The present invention relates to a radiation image reading method for obtaining an image signal by reading the above light using.

In order to achieve the above-mentioned object, the means used in the radiation image reading method of the present invention is such that light within each light amount range obtained by stepwise dividing the total light amount range of the light representing the radiation image is the frequency of the logarithmic amplifier. That is, the gain setting means is sequentially controlled and read for each light amount range so as to be converted into signals in the input signal range having excellent responsiveness.

(Operation) As a general property of the logarithmic amplifier, if the magnitude of the input signal is within a predetermined range, logarithmic conversion is accurately performed up to a predetermined high frequency, and if the input signal is weaker than the above predetermined range, the input signal is Has a property that the logarithmic conversion is performed with high accuracy only up to a frequency lower than the predetermined high frequency as becomes weaker. Of course, if the input signal is too large and exceeds the standard of the logarithmic amplifier, the logarithmic amplifier will not operate normally.

The present invention has a good range of frequency response of a logarithmic amplifier,
It was made by pursuing a method to overcome the fact that logarithmic conversion is narrower than the required signal range.
The above object is achieved by abandoning the reading of the required total light amount range at one time.

In the radiation image reading method of the present invention, the light within each light amount range obtained by dividing the total light amount range of the light representing the radiation image into a plurality of steps is converted into a signal within the input signal range having excellent frequency response of the logarithmic amplifier. For each light intensity range,
Since the gain setting means is controlled to perform the reading in sequence, only the range in which the frequency response of the logarithmic amplifier is good is used, and the logarithmic conversion is performed with sufficient accuracy even if the reading speed is increased. Further, in order to read the entire light amount range as described above, it is necessary to read a plurality of times, but by using only the range with good frequency response of the logarithmic amplifier, the reading speed is significantly improved. Even if the time required for reading is adjusted, the reading speed is improved and the processing capacity per unit time of the radiation image reading apparatus is improved.

(Example) Hereinafter, the Example of this invention is described with reference to drawings.

FIG. 2 is a perspective view showing an example of a radiation image reading device to which the radiation image reading device of the present invention is applied.

This radiation image reading device is a device using the above-mentioned stimulable phosphor sheet.

The stimulable phosphor sheet 11 on which the radiation image is recorded is set at a predetermined position of the radiation image reading device 100. The stimulable phosphor sheet 11 set at this predetermined position is conveyed in the direction of arrow Y (sub scanning) by the sheet conveying means 13 such as an endless belt driven by a driving means (not shown).
To be done. On the other hand, the light beam emitted from the laser light source 14
Reference numeral 15 is driven by a motor 23 and is reflected and deflected by a rotary polygon mirror 16 which rotates at a high speed in the direction of an arrow. The main scanning is performed in the arrow X direction which is substantially perpendicular to the direction (arrow Y direction). From the location of the sheet 11 irradiated with the excitation light 15, a stimulated emission light 19 of a light amount corresponding to the stored and recorded radiation image information is emitted, and the stimulated emission light 19 is guided by the light guide 20. , Photomultiplier (photomultiplier) 21 for photoelectric detection. The light guide 20 is formed by molding a light guide material such as an acrylic plate, and is arranged so that the linear incident end face 20a extends along the main scanning line on the stimulable phosphor sheet 11. The light receiving surface of the photomultiplier 21 is coupled to the emitting end surface 20b formed in a ring shape. Incident end face 20
The stimulated emission light 19 that has entered the light guide 20 from a travels through the inside of the light guide 20 by repeating total reflection, and exits the end face 20b.
Is emitted from the photomultiplier 21 and is emitted to the photomultiplier 21, and the photomultiplier 21 converts the amount of the stimulated emission light 19 representing the radiation image into an electric signal. The magnitude of the signal output from the photomultiplier 21 with respect to the amount of light input to the photomultiplier 21 is determined by the gain setting means.
Adjusted by 22.

The stimulated emission light 19 is almost proportional to the dose of the radiation applied to each part of the stimulable phosphor sheet 11 over a wide range, and in order to read the radiation image accumulated and recorded on the sheet 11 with high accuracy, The amount of exhaustive emission light is in the range of about 4 digits (The weakest intensity of the stimulated emission light to be read is 1.
When it is set to 0, it is necessary to accurately read by the photomultiplier 21 over the range in which the light having the largest light amount of the stimulated emission light to be read has the intensity of about 1.0 × 10 ⁴ .

The analog output signal S output from the photomultiplier 21 is logarithmically amplified by the logarithmic amplifier 26, and the A / D converter 2
It is digitized in 7 to obtain the image signal S _Q. The obtained image signal S _Q is once stored in the storage means 28 and then transmitted to the image processing device 200.

The image processing device 200 performs appropriate image processing on the received image signal S _Q.

The image signal S _Q subjected to the image processing is transmitted to the image reproducing device 300, and the image reproducing device 300 reproduces and records the radiation image based on the image signal S _Q.

 Here, the characteristics of the logarithmic amplifier 26 will be described.

FIG. 1 is a graph showing an example of characteristics of a logarithmic amplifier.

This logarithmic amplifier responds well up to a frequency of about 200 KHz during the two digits of the input signal (input current) of 10 ^-5 amps to 10 ^-3 amps. However, as the input signal becomes weaker than this range, the highest frequency that responds well decreases as shown in the figure.

Here, in order to logarithmically convert a 4-digit signal obtained by one reading, the gain setting means 22 shown in FIG. 2 is used to set the range of 10 ⁻⁷ to 10 ⁻³ amperes from the photomultiplier 21. Adjusted to output current. With this adjustment, a logarithmic amplifier is required to accurately logarithmically convert the signal in the range of 10 ^-7 to 10 ^-3 amps.
Since the response of 26 at 10 ^-7 amps is up to 25 KHz, the information representing the radiation image carried by the stimulated emission light 19 is
The conveying speed of the sheet 11 by the sheet conveying means 13 (speed of sub-scanning) and the rotary polygon mirror 16 so that the frequency becomes 25 KHz or less.
It is necessary to determine the rotation speed (speed of main scanning) of.

On the other hand, if the range of the signal input to the logarithmic amplifier 26 is suppressed to a two-digit range of 10 ^-5 amps to 10 ^-3 amps, the logarithmic amplifier 26 responds up to 200 KHz, so 10 ^-7 amps to 10 ^-3.
200KHz / 25K reading speed (main scanning and sub-scanning speed) compared to the case of logarithmic conversion of a signal in the 4-digit ampere range
It is possible to increase Hz = 8 times.

Therefore, first, of the stimulated emission light representing the radiation image accumulated and recorded on the sheet 11, the two digits (hereinafter referred to as the last two digits) on the weaker light side are converted into signals of 10 ^-5 to 10 ^-3 amps. The gain setting means 22 is controlled so as to be converted. The reading speed (main scanning speed and sub-scanning speed) is adjusted to such an extent that the signal includes a signal of maximum 200 KHz. By reading in this manner, logarithmic conversion of the last two digits of the signal is performed at high speed. The logarithmically converted signal is converted into the digital image signal S _Q by the A / D converter 27 as described above and stored in the storage means 28.

When the logarithmic conversion of the last two digits of the signal is completed over the entire surface of the sheet 11, the sheet 11 is quickly moved back to a position where it can be read again by the sheet conveying means 13. In addition, the gain setting means 22 is, on the side having a strong light amount, of the stimulated emission light representing the radiation image accumulated and recorded on the sheet 11 this time.
The digit (hereinafter referred to as the upper two digits) is controlled so as to be converted into a signal of 10 ⁻⁵ amperes to 10 ⁻³ amperes. In addition, the reading speed is adjusted to the same level as when reading the last two digits of the signal so that the first two digits of the signal include a maximum of 200 KHz.

By reading in this way, the logarithmic conversion of the signal of the first two digits is performed at high speed this time. The logarithmically converted signal is converted into a digital image signal S _Q by the A / D converter 27 in the same manner as the lower two digit signal and stored in the storage means 28.

Even if the stimulable phosphor sheet 11 is irradiated with the light beam 15, only a part of the energy accumulated in the sheet 11 is released, so that the amount of stimulated emission light in the second reading is the same as that in the first reading. It is slightly weaker than the case of irradiating the light beam 15 with the same light amount as in the reading of, but still a sufficient amount of stimulated emission light can be obtained. The slightly weakened amount is adjusted by the gain setting means 22. It can also be adjusted by various methods such as changing the light quantity of the light beam 15.

In this way, by separately reading the signal of the lower two digits and the signal of the upper two digits, it is necessary to read twice and it is necessary to back the sheet 11 once. Reading can be done at about three times the speed of reading four digits of signal at a time. Further, if the second reading is performed while the reading is performed backward, and the image signals are recombined when the image processing device 200 performs the image processing, the reading can be performed at a higher speed.

Although the above embodiment has described the radiation image reading method in which the reading is performed twice, the number of times is not limited to two, and the range having a good frequency response of the logarithmic amplifier and the required signal range. It is decided in consideration of.

In addition, a radiation image reading apparatus using a stimulable phosphor sheet may have a low level in advance before the image signal is obtained by reading it under optimal reading conditions according to the dose of radiation applied to the stimulable phosphor sheet. Scan the stimulable phosphor sheet with the light beam of to perform pre-reading to read the outline of the radiation image recorded on this sheet, analyze the pre-reading image signal obtained by this pre-reading, and then read the pre-reading on the sheet. There is also an apparatus configured to perform main reading by irradiating and scanning with a light beam having a higher level than the light beam at this time, and reading the radiation image under optimum reading conditions to obtain an image signal (Japanese Patent Laid-Open No. 58-58-58). 67240, 58-67241, 58-67242
No.). It goes without saying that the radiation image reading method of the present invention can also be applied to an apparatus for performing such prefetching.

Further, the present invention can be used not only in a device using a stimulable phosphor sheet but also in a device using a conventional X-ray film.

FIG. 3 is a perspective view of an embodiment of an X-ray image reading device for reading an X-ray image recorded on an X-ray film.

The X-ray film 40 on which the X-ray image is recorded and set at a predetermined position is conveyed (sub-scanned) by the film conveying means 41 in the arrow Y'direction shown in the figure.

Further, the reading light 43 emitted from the light source 42 that is long one-dimensionally is converged by the cylindrical lens 44, and X
The linear film is linearly irradiated in the X'direction substantially perpendicular to the Y'direction. Below the X-ray film 40 irradiated with the reading light 43, the X-ray film 40 is transmitted to the X-ray film 40, and the X-ray film 40 is received at the position where the reading light 43 intensity-modulated by the X-ray image recorded is received. An MO in which a large number of solid-state photoelectric conversion elements corresponding to the respective pixel intervals in the X'direction of the line image are linearly arranged
An S sensor 45 is provided. This MOS sensor 45 converts the reading light transmitted through the X-ray film 40 into X-
Light is received at a predetermined time interval corresponding to each pixel interval in the Y'direction of the line image.

FIG. 4 is a circuit diagram showing an equivalent circuit of the MOS sensor 45.

A signal due to the photocarrier generated when the reading light 43 strikes a large number of solid-state photoelectric conversion elements 46 is generated by the solid-state photoelectric conversion elements 46.
It is stored in the capacitor Ci (i = 1, 2, ... N) inside. The accumulated photocarrier signals are sequentially read out (main scanning) by sequentially opening and closing the switch unit 48 controlled by the shift register 47, whereby a time-series image signal is obtained. This image signal is then amplified by the amplifier 49 and output from its output terminal 50. The output analog image signal is logarithmically converted by the logarithmic amplifier as in the embodiment shown in FIG. In order to use only the range in which the frequency response of the logarithmic amplifier is good, the X-ray film 40 is scanned a plurality of times in the same manner as described with reference to FIG. 1, and the reading speed is improved. In this embodiment, CCD, CPD (Charge Prim) is used instead of the MOS sensor 44.
Needless to say, an ing Device) or the like can be used. Further, in the reading of the X-ray film, it is needless to say that the reading may be performed by two-dimensionally scanning with a light beam, similarly to the reading of the stimulable phosphor sheet described above. Further, in the present embodiment, the light transmitted through the X-ray film 40 is received, but it goes without saying that the light reflected from the X-ray film 40 may be received.

As described above, the radiation image reading method of the present invention can be applied to a radiation image reading apparatus generally that reads light representing a radiation image obtained from a recording sheet on which a radiation image of a subject is recorded to obtain an image signal.

(Effect of the Invention) As described in detail above, in the radiation image reading method of the present invention, the light within each light amount range obtained by stepwise dividing the total light amount range of the light representing the radiation image is the frequency of the logarithmic amplifier. The radiation setting image is read at high speed from the recording sheet because the gain setting means is sequentially controlled and read for each light amount range so as to be converted into signals in the input signal range having excellent responsiveness. The processing capability per unit time of the radiation image reading apparatus is improved.

[Brief description of drawings]

FIG. 1 is a graph showing an example of characteristics of a logarithmic amplifier, FIG. 2 is a perspective view showing an example of a radiation image reading apparatus to which the radiation image reading method of the present invention is applied, and FIG. FIG. 4 is a perspective view of an embodiment of an X-ray image reading device for reading an X-ray image recorded on a line film, and FIG. 4 is a circuit diagram showing an equivalent circuit of a MOS sensor. 11 ... Accumulative phosphor sheet, 19 ... Photostimulated emission light 21 ... Photomultiplier 22 ... Gain setting means, 26 ... Logarithmic amplifier 27 ... A / D converter, 28 ... Storage means 40 ... … X-ray film, 45 …… MOS sensor 100 …… Radiation image reading device 200 …… Image processing device, 300 …… Image reproducing device

Claims (1)

[Claims] 1. A photodetector which receives light representing a radiation image obtained from a recording sheet on which a radiation image of a subject is recorded, and outputs a signal corresponding to the amount of the light, and the photodetector. The radiation image reading apparatus is equipped with a gain setting means for adjusting the magnitude of the output signal with respect to the received light amount and a logarithmic amplifier for logarithmically compressing the output signal, and the light is read to obtain the image signal. In the radiation image reading method for obtaining the light image, the light within each light amount range obtained by stepwise dividing the total light amount range representing the radiation image into a signal within the input signal range having excellent frequency response of the logarithmic amplifier is obtained. A radiation image reading method, wherein the gain setting means is sequentially controlled to perform the reading for each light amount range so as to be converted.