JP2005091815A - Radiation image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a radiation image reader preventing deterioration in image quality by artifact or the like caused by the compensation of afterglow in the case of photographing a corpulent subject. <P>SOLUTION: Since a photodetecting means 4 has a dynamic range of 4.3 figures, the graininess of a plate 3 is not changed, and a situation that output from the photodetecting means 4 is saturated exceeding an upper limit and the compensation of the afterglow using an afterglow compensation means 7 performed at a subsequent step is improperly performed is prevented, and further the image quality of the radiation image reproduced by an image reproducing device 9 is prevented from being deteriorated by the artifact or the like not only in the case of a subject having standard bodily shape but also in the case of the corpulent subject. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a radiographic image reading apparatus that removes afterglow components from the photostimulated luminescence of a photostimulable phosphor plate in which radiographic image information is stored, and acquires accurate photostimulated luminescence information.

  A so-called X-ray transmitted through a subject is irradiated onto a fluorescent screen (phosphor layer) to generate visible light proportional to the transmitted dose, and this visible light is exposed to a film similar to a commercially available silver salt photograph and developed. Radiographs are often used as radiographic images for disease diagnosis.

  However, in recent years, image information of a subject is read directly from a phosphor layer without using a silver salt photograph. According to this, the X-ray transmitted through the subject is absorbed by the stimulable phosphor, and then the stimulable phosphor is excited by the excitation light, and the X-ray absorbed and accumulated in the stimulable phosphor. The line energy and the image information are stimulated to emit light as fluorescence, and this stimulated emission is photoelectrically converted by the light detection means to acquire image information.

  By the way, the photostimulable phosphor emits photostimulated light by excitation light, and this stimulated light emission remains as a so-called afterglow during the response time inherent to the photostimulable phosphor after the end of the excitation light irradiation. Continue to emit light. Therefore, when the plate-like photostimulable phosphor plate is scanned with excitation light, the excitation light is sequentially emitted to sequentially read the excitation light emitted by the excitation light and acquire image information in units of pixels. In addition to the stimulated light emission from the scanning point, the afterglow component from the scanning point where the irradiation of the excitation light is completed is stored as image information of the pixel located at the scanning point where the excitation light is irradiated. . As a result, the image information is not completely separated for each scanning point, and the contrast resolution is lowered or the sharpness of the displayed image information is lowered.

Therefore, the acquired image information is corrected based on empirical or theoretically determined afterglow information to remove the afterglow component (see, for example, Patent Documents 1 and 2). .
Japanese Patent Laid-Open No. 2-15154 Japanese Patent Laid-Open No. Sho 62-18536

  However, according to the background art, afterglow correction is not performed correctly when the subject is obese. That is, in an obese subject, the amount of X-rays irradiated is greatly attenuated in the subject, and the X-ray dose reaching the photostimulable phosphor plate is reduced when the same dose of radiation source is used. On the other hand, it is known that the granularity of the phosphor layer deteriorates as the X-ray dose that arrives decreases.

  For these reasons, in obese subjects, the irradiated X-ray dose is set to be larger than usual to prevent the granularity of the phosphor layer from deteriorating. On the other hand, as the X-ray irradiation dose increases, a large dynamic range, which is a ratio between the maximum value and the minimum value of the optical signal handled by the light detection means, is required. However, when using the conventional light detection means, a saturation phenomenon occurs in the output of the light detection means when a light amount exceeding the dynamic range is generated.

  When this saturation phenomenon occurs, the output of the light detection means does not accurately reflect the light quantity of the stimulated light emission, and therefore, even when the afterglow is corrected, it cannot be corrected accurately.

  For these reasons, when photographing an obese subject, it is important how to realize a radiation image reading apparatus that prevents image quality deterioration such as artifacts caused by afterglow correction.

  The present invention has been made to solve the above-described problems of the prior art, and provides a radiographic image reading apparatus that prevents image quality deterioration such as artifacts caused by afterglow correction when an obese subject is photographed. For the purpose.

  In order to solve the above-described problems and achieve the object, the radiation image reading apparatus according to the first aspect of the present invention is a scanning that scans the stimulable phosphor plate in which the radiation image information is stored with excitation light. From the means, the photodetection means having a dynamic range of 4.3 digits or more for detecting the stimulated light emission caused by the excitation light for each scanning point constituting the scan, and the detected light emission information, And an afterglow correcting unit that removes and corrects afterglow from a scanning point different from the scanning point where the stimulated light emission occurs.

  In the first aspect of the present invention, the stimulable phosphor plate in which the radiation image information is stored is scanned with the excitation light by the scanning means, and the light detecting means having a dynamic range of 4.3 digits or more is used. For each scanning point constituting the scan, the photostimulated luminescence generated by the excitation light is detected, and the afterglow from the scanning point different from the scanning point where the photostimulated luminescence is generated from the detected photostimulated luminescence information by the afterglow correcting means. Therefore, even when an obese subject is photographed, the light detection means does not saturate, and the afterglow is corrected accurately.

  According to a second aspect of the present invention, there is provided a radiographic image reading apparatus comprising: scanning means for scanning a stimulable phosphor plate in which radiographic image information is stored with excitation light; and each scanning point constituting the scan. A photodetection means for detecting the photostimulated luminescence generated by the excitation light, and an afterglow for removing and correcting afterglow from a scanning point different from the scanning point at which the photostimulated luminescence occurs from the detected photostimulated luminescence information A radiological image reading apparatus comprising: a correction unit, wherein the afterglow correction unit determines whether the light detection unit is saturated for each scanning point while performing the correction, and the saturation is A saturation sequential determination means is provided for stopping the correction when it occurs, and continuing the correction when the saturation does not occur.

  In the second aspect of the invention, the afterglow correcting means determines whether or not the light detecting means is saturated for each scanning point while performing correction by the saturation sequential determining means, and this saturation has occurred. In this case, the correction is stopped, and when this saturation does not occur, the correction is continued, so that erroneous afterglow correction is prevented when there is a scanning point where the photostimulated light emission information is saturated. As a result, the read image has a high quality with few artifacts.

  According to a third aspect of the present invention, there is provided a radiographic image reading apparatus comprising: a scanning unit that scans a stimulable phosphor plate in which radiographic image information is stored with excitation light; and a scanning point that constitutes the scanning. A photodetection means for detecting the photostimulated luminescence generated by the excitation light, and an afterglow for removing and correcting afterglow from a scanning point different from the scanning point at which the photostimulated luminescence occurs from the detected photostimulated luminescence information A correction unit, and the afterglow correction unit collectively determines whether the light detection unit is saturated at all the scanning points before performing the correction, Based on the collective determination, a saturation collective determination unit is provided that stops the correction when the saturation occurs and performs the correction when the saturation does not occur.

  In the invention according to the third aspect, the afterglow correcting means collectively determines whether or not the light detecting means is saturated at all scanning points before performing the correction by the saturation batch determining means. Based on the judgment, when the saturation occurs, the correction is stopped, and when the saturation does not occur, the correction is performed. Therefore, there is a scanning point where the photostimulated light emission information is saturated. This prevents erroneous afterglow correction when the image is read, and as a result, the read image has a high quality with few artifacts.

  According to a fourth aspect of the present invention, there is provided a radiographic image reading apparatus comprising: scanning means for scanning a stimulable phosphor plate in which radiographic image information is stored with excitation light; and each scanning point constituting the scan. A light detecting means for detecting the stimulated light emission caused by the excitation light, and a residual light for removing and correcting afterglow from a scanning point different from the scanning point where the stimulated light emission has occurred, from the detected stimulated light emission information. It comprises light correction means and bit reduction means for reducing the number of bits of the corrected stimulated light emission information.

  In this invention, the stimulable phosphor plate in which the radiation image information is accumulated is scanned with excitation light by the scanning means, and excitation is performed for each scanning point constituting the scan by the light detection means. Detects the photostimulated luminescence caused by the light, and corrects the afterglow correcting means by removing and correcting the afterglow from the scanning point different from the scanning point where the photostimulated luminescence is generated from the detected photostimulated luminescence information. Therefore, the number of bits of the corrected stimulated light emission information is reduced, so that even when an obese subject is imaged, a conventionally used dynamic range 4.0 digit image processing apparatus or image reproduction is used. Use equipment.

  According to a fifth aspect of the present invention, there is provided a radiographic image reading apparatus comprising: scanning means for scanning a stimulable phosphor plate in which radiographic image information is stored with excitation light; and each scanning point constituting the scan. A light detecting means for detecting the stimulated emission generated by the excitation light, a linearity recovery means for recovering the linearity of the stimulated emission information based on a non-linear reading characteristic of the light detecting means, and the detected And afterglow correcting means for removing and correcting afterglow from a scanning point different from the scanning point where the stimulated light emission has occurred.

  In the invention according to claim 5, the stimulable phosphor plate in which the radiation image information is accumulated is scanned with the excitation light by the scanning means, and the scanning point is constituted by the light detecting means for each scanning point constituting the scan. The stimulated luminescence generated by the excitation light is detected, the linearity recovery means recovers the linearity of the stimulated luminescence information based on the non-linear reading characteristics of the light detection means, and the afterglow correction means detects the detected luminescence. Since the afterglow from the scanning point different from the scanning point where the stimulated light emission has occurred is removed from the exhausted light information and corrected, the stimulated light emitting information on the obese subject shows the nonlinear characteristic of the light detection means. Even within the range, the photostimulated luminescence information is linearized and correct afterglow correction is performed.

  According to a sixth aspect of the present invention, there is provided a radiographic image reading apparatus comprising: scanning means for scanning a stimulable phosphor plate in which radiographic image information is stored with excitation light; and each scanning point constituting the scan. A light detecting means for detecting the stimulated light emission caused by the excitation light, and a residual light for removing and correcting afterglow from a scanning point different from the scanning point where the stimulated light emission has occurred, from the detected stimulated light emission information. A radiation image reading apparatus comprising: a light correction means, wherein the afterglow correction means recovers the linearity of the photostimulated luminescence information based on a nonlinear reading characteristic of the light detection means. It is characterized by providing.

  In the invention according to claim 6, the afterglow correcting means recovers the linearity of the photostimulated luminescence information based on the non-linear reading characteristic of the light detecting means by the linearity recovering means. Even if the photostimulated luminescence information is within the range having the non-linear characteristics of the light detection means, the photostimulated luminescence information is linearized and correct afterglow correction is performed.

  As described above, according to the first aspect of the present invention, the stimulable phosphor plate in which the radiation image information is accumulated is scanned with the excitation light by the scanning means, and the dynamic range of 4.3 digits or more is obtained. The photodetection means that detects the stimulated light emission caused by the excitation light at each scanning point constituting the scan, and the afterglow correction means detects the stimulated light emission from the detected light emission information. Since afterglow from different scanning points is removed and corrected, even when an obese subject is photographed, the photodetection means is not saturated and the afterglow can be corrected accurately.

  According to the second aspect of the present invention, the afterglow correcting means determines whether or not the light detecting means is saturated for each scanning point while performing correction by the saturation sequential determining means, and this saturation occurs. When this happens, the correction is stopped and the correction is continued when this saturation does not occur.Therefore, an incorrect afterglow correction is performed when there is a scanning point where the photostimulated light emission information is saturated. Therefore, the read image can be made high quality with few artifacts.

  According to the third aspect of the present invention, the afterglow correcting means collectively determines whether or not the light detecting means is saturated at all scanning points before performing the correction by the saturation batch determining means. Based on the collective determination, correction is stopped when saturation occurs, and correction is performed when saturation does not occur. It is possible to prevent erroneous afterglow correction when present, and thus to make the read image high quality with few artifacts.

  According to the invention described in claim 4, the stimulable phosphor plate in which the radiation image information is stored is scanned with the excitation light by the scanning means, and the scanning point is configured by the light detection means for each scanning point. Detects the photostimulated luminescence caused by the excitation light, and the afterglow correction means removes and corrects the afterglow from the scanning point that is different from the scanning point where the photostimulated luminescence is detected from the detected photostimulated luminescence information. Since the number of bits of the corrected light emission information is reduced by the means, the image processing apparatus or image having a dynamic range of 4.0 digits conventionally used even when imaging an obese subject is used. A playback device or the like can be used.

  According to the fifth aspect of the present invention, the stimulable phosphor plate in which the radiation image information is accumulated is scanned with the excitation light by the scanning means, and each scanning point constituting this scan is scanned by the light detecting means. The photoluminescence generated by the excitation light is detected, and the linearity recovery means recovers the linearity of the photoluminescence information based on the non-linear reading characteristics of the light detection means, and is detected by the afterglow correction means. Since the afterglow from the scanning point that is different from the scanning point where the stimulated light emission is removed is corrected from the stimulated light emission information, the stimulated light emission information is the non-linear characteristic of the light detection means in an obese subject. Even within the range having the light emission, it is possible to correct the afterglow correction by linearizing the photostimulated luminescence information.

  According to the sixth aspect of the present invention, the afterglow correcting means recovers the linearity of the photostimulated luminescence information based on the non-linear reading characteristic of the light detecting means by the linearity recovering means. Even in an obese subject, even if the photostimulated luminescence information is within a range having the nonlinear characteristics of the light detection means, the photostimulated luminescence information can be linearized and correct afterglow correction can be performed.

The best mode for carrying out the radiation image reading apparatus according to the present invention will be described below with reference to the accompanying drawings. Note that the present invention is not limited thereby.
(Embodiment 1)
First, an overall configuration of a radiation imaging apparatus including a radiation image reading apparatus (hereinafter referred to as a reading apparatus) 20 according to the present embodiment will be described. FIG. 1 is a diagram showing an overall configuration of a radiation imaging apparatus according to the present invention. The radiation imaging apparatus includes a radiation generator 1, a subject 2, a stimulable phosphor plate (hereinafter abbreviated as a plate) 3, a reading device 20, an image processing device 8, and an image reproducing device 9. The reading device 20 includes a scanning unit 10, a light detection unit 4, a logarithmic conversion circuit 5, an A / D converter 6, and an afterglow correction unit 7.

  The radiation generation apparatus 1 includes an X-ray tube that generates X-rays, and bombards the subject 2 with X-rays. The plate 3 is a flat plate made of a photostimulable phosphor and absorbs X-rays transmitted through the subject 2 and accumulates transmission image information of the subject 2. The plate 3 uses, for example, those disclosed in JP-A-61-72091 or JP-A-59-75200 as the material of the stimulable phosphor to be used. Those disclosed in US Pat. No. 4,769,549 or US Pat. No. 5,023,461 are used.

  The scanning means 10 irradiates the plate 3 with semiconductor laser light that forms excitation light. In this irradiation, spot-like excitation light scans on the plate 3 by means such as rotation of a polygon mirror that reflects the semiconductor laser light or movement of the plate 3 itself. Further, at each scanning point on the plate 3, when emitted, stimulated light emission including transmission image information occurs.

  The light detection means 4 photoelectrically reads the stimulated emission at each scanning point. FIG. 2 shows the configuration of the light detection means 4. The light detection means 4 includes a condenser 21, a filter 22, and a photoelectric converter 23 including a photomultiplier tube 24 and a peripheral circuit 25. The condensing body 21 is composed of an assembly of optical fibers or the like, and guides the stimulated light emission on the plate 3 to the light receiving portion of the photoelectric converter 23. The filter 22 is provided in the light receiving part of the photoelectric converter 23 and removes the excitation light component mixed in the stimulated light emission. The photoelectric converter 23 receives the stimulated light emission and converts it into a current signal.

  The logarithmic conversion circuit 5 converts the current signal output from the light detection means 4 into a voltage signal, and the A / D converter 6 successively converts this voltage signal into a digital signal. The afterglow correcting means 7 performs afterglow correction on this digital signal and removes afterglow components from the photostimulated luminescence information.

  The image processing device 8 performs image processing such as gradation processing on the digital signal after the afterglow correction, and sequentially transmits the digital signal to the image reproduction device 9. The image reproducing device 9 stores or displays this digital signal. In this storage or display, an image memory for recording image information, a graphic display such as an LCD, or an imager for recording image information on a photosensitive film is used. Further, using these devices connected to the image processing apparatus 8 via a network, storage or display can be similarly performed.

  Next, the photoelectric converter 23 of the light detection unit 4 according to the first embodiment will be described in more detail. FIG. 3 is a diagram illustrating a configuration of the photoelectric converter 23. The photoelectric converter 23 includes a photomultiplier tube 24 and a peripheral circuit 25. The photomultiplier tube 24 photoelectrically converts the photostimulated light photons input through the light receiving surface into photoelectrons by the cathode 11 and collects the photoelectrons in the dynode unit 13 by the focusing unit 12.

  The photoelectrons collected in the dynode section 13 are exponentially multistage amplified by a plurality of dynodes to which the voltage generated by the high-voltage power supply 14 is applied via the bleeder circuit 16, and the amplified photoelectrons 15 is output as an anode output current.

  The photoelectron current from the cathode 11 is the cathode current Ik, the sum of the resistance values of the bleeder circuit 16 is the bleeder resistance R, the power consumed by the bleeder circuit 16 is Wb, the anode output current from the anode 15 is Ip, and the high voltage power supply If the voltage of 14 is HV, the following relationship is established.

Ip = G × Ik ――――――― (1)
HV = Ib × R ――――――― (2)
HWmax = (HVmax) ² / R ――― (3)
Here, G is a proportional constant representing the current multiplication factor, HVmax is the maximum value of the voltage of the high-voltage power supply 14, and HWmax is the maximum value of power consumed by the bleeder resistance.

  The light detection means 4 has a 4.3 digit dynamic range. Here, the relationship between the dynamic range that is the signal range that can be handled by the light detection means 4 and the subject will be described. First, radiation image information has a wide dynamic range, and requires a light detection means capable of reading a wide range of light quantity, and a circuit having a large number of bits for ensuring high signal resolution. For this reason, the configuration of the apparatus becomes complicated, the cost increases, and at the same time, the apparatus becomes large and is not preferable. Therefore, only the minimum necessary dynamic range is ensured in the light detection means and the peripheral circuit. On the other hand, in adults of standard body type, the dynamic range of the transmitted radiation dose required for each imaging site is different, and in the lumbar portion where the maximum dynamic range is required, a dynamic range of approximately 3.5 digits is required. Is done. Further, in consideration of dose fluctuations due to differences in imaging conditions, a 4.0-digit dynamic range that allows for a 0.5-digit margin is required in the light detection means and its peripheral circuits.

Further, it has been empirically known that obese adults can ensure the same level of plate granularity as that of an adult with a standard figure by doubling the X-ray irradiation dose. From these facts, if the dynamic range of an adult with a standard figure is 4.0 digits,
10 ^4.3 = 10 ^0.3 × 10 ^4.0 ≒ 2 × 10 ^4.0
Therefore, the dynamic range is approximately 4.3 digits, and the post-detection means for processing this transmitted radiation requires a 4.3 digit dynamic range.

  Next, the configuration of the light detection means 4 having a 4.3-digit dynamic range will be described with reference to FIG. The amount of radiation that reaches the plate 3 varies depending on imaging conditions, for example, whether the subject is a standard body shape or an obese subject. The current multiplication factor G of the photomultiplier tube 24 shown in the equation (1) is in a proportional relationship with the high voltage applied voltage HV in a range that is normally used, and changes in the amount of radiation reaching the plate 3, and hence from the plate 3. The change in the amount of stimulated emission is output as an appropriate anode output current Ip by increasing or decreasing the voltage HV applied to the photomultiplier tube 24. Here, the variable range of the applied voltage HV is a range in which the current multiplication factor G can be adjusted in the range of 20,000 to 200,000 times.

  The logarithmic conversion circuit 5 is connected to the anode 15 of the photomultiplier tube 24, and outputs a voltage value that is logarithmically proportional to the current value output from the photodetecting means 4, and the gain of the output voltage from the logarithmic amplifier. And an analog multiplier for adjusting the offset. The logarithmic amplifier and the analog multiplier are configured using an operational amplifier, a transistor, or the like. In the logarithmic conversion circuit, an input current range in which an optimum S / N ratio and frequency characteristics are obtained with a dynamic range of 4.0 digits is exemplified to be 100 nA to 1 mA (for example, Japanese Patent Laid-Open No. 2002-277593). reference). In the logarithmic conversion circuit 5 according to the present invention, 100 nA to 2 mA is used as an input current range in which an optimum S / N ratio and frequency characteristics that guarantee a dynamic range of 4.3 digits are obtained.

  Here, when the cathode current Ik of the photomultiplier tube 24 is maximized, the current multiplication factor G is 20,000 times, and the anode output current Ip is 2 mA, the cathode current Ik is 100 nA from the equation (1). . Therefore, the amount of radiation reaching the cathode 11 and the cathode current Ik are set to be linear up to a cathode current Ik of at least 100 nA.

  Further, the bleeder current Ib of the photomultiplier tube 24 needs to supply a sufficient current to the dynode unit 13 even when the anode output current Ip is maximum, and to ensure the linearity of the anode output current Ip. Therefore, the bleeder current Ib is supplied with 10 mA, which is at least five times the maximum value of the anode output current Ip. On the other hand, it is desirable that the bleeder current Ib is as small as possible in order to reduce the amount of heat generated by the bleeder circuit 16 and reduce the power supply capacity of the high voltage power supply 14. Therefore, the bleeder current Ib of the bleeder circuit 16 is set to 10 mA.

  Further, if the voltage HV of the high-voltage power supply 14 is too low, it is difficult to ensure the bleeder current Ib. That is, even when the minimum voltage HV is 500 V, the bleeder current Ib is 10 mA when the bleeder resistance R is 50 kΩ according to the equation (2). From the above, the bleeder resistance is set to 50 kΩ or less. Note that the lower limit of the bleeder resistance R is not preferably an extremely small value in terms of the amount of heat generated by the bleeder resistance R and the power supply capacity of the high voltage power supply 14. In this embodiment, the bleeder resistance R is set to 50 kΩ.

  When the voltage HV is high, the high-voltage power supply 14 requires high power consumption by the bleeder circuit and requires a large power supply capacity. Therefore, the maximum voltage HVmax of the high voltage power supply 14 is 1400V. At this HVmax = 1400V, the maximum power HWmax consumed by the bleeder circuit is 39.2 W from Equation (3). Therefore, the power supply capacity of the high voltage power supply 14 is required to be at least 39.2 W. In the high voltage power supply 14 according to the present embodiment, a power supply capacity of approximately 40 W is used.

  The photomultiplier tube 24 has a current multiplication factor G of 20,000 or less when the voltage HV of the high voltage power supply 14 is 500 V, and a current multiplication factor G of 200,000 when the voltage HV is 1400 V. It is necessary to be above. However, the sensitivity of the photomultiplier tube 24 varies, and even with the same type of photomultiplier tube, the same current multiplication factor is not always obtained with the same voltage HV. Therefore, the photomultiplier tube 24 is of a type that can obtain many photomultiplier tubes that satisfy the above-described conditions.

  Next, the operation of the light detection means 4 according to the present embodiment is shown in FIG. FIG. 4 is a diagram showing the characteristics of the light detection means 4 with the horizontal axis representing the amount of radiation reaching the plate 3 and the vertical axis representing the anode output current Ip. The horizontal axis and the vertical axis indicate logarithm of the displayed quantity, the vertical axis is A (ampere) which is a unit of current, and the horizontal axis is R (radiogram) which is a unit of radiation dose. is there.

  FIG. 4 shows that the relationship between the anode output current Ip and the radiation dose reaching the plate is linear up to a radiation dose reaching the plate of at least 500 mR. Therefore, even for an obese subject, the correct radiation amount reaching the plate can be known without the anode output current Ip being saturated.

  It should be noted that a gap can be provided between the photostimulable phosphor layer constituting the plate 3 and the sealing film to improve the image quality of the plate (see, for example, JP-A-11-249243). In this case, the light detection means 4 optimizes the setting of the current multiplication factor G to prevent saturation of the anode output current Ip, and to obtain an appropriate plate reaching radiation dose without changing the above-described configuration. Can be output.

  That is, the current multiplication factor G is optimized by adjusting the voltage HV applied to the photomultiplier tube 24, and image information without saturation is acquired. Here, the current multiplication factor G is proportional to the anode output current Ip and the cathode current Ik and is set in the range of 20,000 to 200,000 times, as expressed by the equation (1).

  Here, the photostimulable luminescence information is transmitted from the light detection means 4 to the logarithmic conversion circuit 5 as a current signal over a wide dynamic range, and then converted into current and voltage at the same time as logarithmic conversion, and the band-compressed voltage. The signal is transmitted to the A / D converter 6 as a signal.

  The A / D converter 6 includes an A / D converter that converts an input voltage signal into a digital signal, and a digital filter that changes the sampling interval and the number of quantization bits of the digital signal from the A / D converter. The A / D converter 6 quantizes the voltage signal input from the logarithmic conversion circuit 5 with a resolution of 1024 steps per digit at a predetermined sampling interval synchronized with the scanning of the laser beam. That is, a voltage signal having a dynamic range of 4.3 digits is assigned to a digital value from 0 to 4403.

  A voltage signal exceeding the upper limit of the 4.3 digit dynamic range is assigned to a digital value of 4403, and a voltage signal lower than the lower limit of the 4.3 digit dynamic range is assigned to a digital value of 0. Then, the photostimulable light emission information converted into 13-bit digital information is transmitted as an image signal to the afterglow correction means 7 at the subsequent stage. The range of the voltage signal is not limited to the above-described example. For example, a voltage signal corresponding to a 5-digit dynamic range can be assigned to a digital value from 0 to 5119. Further, the number of quantization bits is not limited to 13 bits, and may be 16 bits, for example.

  Here, before explaining the afterglow correcting means 7, afterglow light afterglow correction will be described. The afterglow component associated with the photostimulable emission causes deterioration of the image quality, and is thus removed digitally using an electrical or theoretical formula. For example, there is an image reading method in which the afterglow in the photostimulable phosphor is approximated by one exponential function, assuming that the afterglow decays exponentially from the highest intensity level at the time of excitation, and the image signal is corrected according to this approximate characteristic. It is known (see, for example, Patent Document 1). According to this, the attenuation coefficient f (x) of the afterglow generated in the pixel on an arbitrary scanning point is approximated by the following expression (4) as a function of the moving distance x of the scanning point.

In this formula (4), α is the scanning speed, τ is the emission lifetime (the time until the intensity of the stimulated emission becomes 1 / e after the irradiation of the excitation light is completed), and a is a constant.

  Also known is an image reading method that approximates the afterglow characteristics of a photostimulable phosphor to the sum of two or more exponential functions and corrects the image signal according to the approximate characteristics (see, for example, Patent Document 2). According to this, the attenuation coefficient f (x) of the afterglow of a pixel generated in a pixel on an arbitrary scanning point is expressed as a function of the moving distance x of the scanning point by, for example, the sum of three exponential functions. (5)

In this equation (5), α is the scanning speed, τ, τ ′, τ ″ are all emission lifetimes, and a, b, and c are constants.

  According to the equations (4) and (5) described above, a corrected linear image in which the influence of afterglow is correctly corrected from an image signal (hereinafter referred to as a linear image signal) L (x) proportional to the amount of stimulated emission light. In order to obtain a signal (hereinafter referred to as a corrected linear image signal) L (x) ′, in addition to the linear image signal L (x) at the scanning point x, already scanned positions x−1, x−2 ,... Also require linear image signals L (x−1), L (x−2),.

  Next, FIG. 5 shows a configuration of the afterglow correcting means 7. The afterglow correction unit 7 includes an inverse logarithm conversion unit 31, a calculation unit 32, and a logarithm conversion unit 33. Assuming that the image signal sequentially input from the A / D converter 6 is S (x), S (x) is sequentially subjected to inverse logarithmic conversion by the inverse logarithmic conversion means 31 to be a linear image signal L (x).

  The afterglow of the linear image signal L (x) is corrected by the computing means 32 using the afterglow attenuation coefficient calculated from the equation (4) based on the values of τ and a. The corrected linear image signal L (x) ′ is sequentially logarithmically converted by the logarithmic conversion means 33 to become data (hereinafter referred to as a corrected image signal) S (x) ′ representing the corrected image signal. Thereafter, the corrected image signal S (x) ′ is sequentially transmitted to the image processing device 8.

  The inverse logarithmic conversion means 31 and the logarithmic conversion means 33 may be configured to store the result in advance in a conversion table and refer to this table as appropriate, for example, in order to reduce calculation addition and improve the calculation speed. .

  Next, the afterglow correction by the calculation means 32 will be described in detail. First, in the plate 3 using the plate disclosed in Patent Document 6, the decay characteristic of afterglow generated in a pixel on an arbitrary scanning point is approximated by the following equation (8). Further, when the relationship between the linear image signal L (x) and the corrected linear image signal L (x) ′ is discretely expressed by using the afterglow attenuation coefficient f (x) of Expression (4), Equation (9) is obtained.

Here, xn and xi are distances from the scanning start point proportional to the number of pixels n and i, respectively, and α represents the scanning speed. Δx is a sampling pitch.

  Then, in order to reduce the amount of calculation, the second term on the right side of the equation (9) that expresses afterglow is extracted and approximated to a recurrence equation that expresses the afterglow Z (n) of the nth pixel. 10).

Here, when the parameters B and D of the equation (10) representing the afterglow characteristic of the plate 3 are experimentally obtained, B = 9.3471 × 10 ⁻⁵ and D = 9.99819 × 10 ⁻¹ . For example, reading of the plate 3 is started, and the linear image signal L (x1) of the first pixel, which is the first scanning point on the scanning line, is input to the calculation unit 32. Since there is no pixel scanned before the first pixel, the corrected linear image signal L (x1) ′ of the first pixel is equal to L (x1). Further, corrected linear image signals L (x2) ′, L (x3) ′,..., L (xn) ′ after the second pixel are sequentially obtained as shown in Table 1 below.

  Note that the afterglow attenuation coefficient is not limited to that approximated by Equation (4), and the afterglow attenuation coefficient can also be approximated by three exponential functions as in Equation (5). For example, in the plates disclosed in Japanese Patent Application Laid-Open Nos. 2002-020742 and 2002-006092, an afterglow coefficient generated in a pixel on an arbitrary scanning line is approximated by the following equation (11).

  Similarly to equation (10), the second term on the right side of equation (9) representing afterglow is extracted for the purpose of reducing the amount of computation, and a recurrence equation representing afterglow Z (n) of the nth pixel. Is approximated to the above equation (12).

  Here, when parameters B1, D1, B2, D2, B3, and D3 of the equation (12) representing the afterglow characteristic of the plate 3 are experimentally obtained, B1 = 1.00 × 10 −6, D1 = 9.99. X10-1, B2 = 2.00x10-6, D2 = 9.97x10-1, B3 = 5.00x10-6 and D3 = 9.92x10-1. Using these constants, corrected linear image signals L (x) ′ are sequentially obtained as shown in Table 2 below.

As described above, in the first embodiment, since the light detection means 4 has a 4.3-digit dynamic range, the plate 3 is used not only for a standard-shaped subject but also for an obese subject. The afterglow correction using the afterglow correction unit 7 performed in the subsequent stage is prevented from being inappropriately performed without changing the graininess of the light, and the output of the light detection unit 4 is saturated exceeding the upper limit. As a result, it is possible to prevent the radiation image reproduced by the image reproducing device 9 from being deteriorated in image quality due to artifacts or the like.
(Embodiment 2)
By the way, in the first embodiment, the light detection means 4 has a 4.3-digit dynamic range so that proper afterglow correction can be performed even in the case of an obese subject. 4 is left in the 4.0 digit dynamic range for a standard subject, and when output is saturated in an obese subject, the afterglow correction is stopped and image quality deterioration due to inappropriate afterglow correction is prevented. You can also Therefore, in the second embodiment, it is determined whether or not the output of the light detection means 4 is in a saturated state and the afterglow correction is controlled.

  Here, in the reading device 20, the light detection unit 4 has a dynamic range of 4.0 digits for a standard-shaped subject, and an afterglow correction unit 71 is used instead of the afterglow correction unit 7. Other configurations are the same as those shown in FIG.

  FIG. 6 is a diagram showing a configuration of the afterglow correction unit 71. The afterglow correction unit 71 is an input buffer that temporarily stores all image signals in addition to the inverse logarithmic conversion unit 31, the calculation unit 32, and the logarithmic conversion unit 33 that constitute the afterglow correction unit 7 shown in FIG. 34. A saturation sequential determination means 35 for sequentially determining saturation of pixels in the image signal and an output buffer 36 for temporarily storing the image signal S after the afterglow correction.

  Note that the saturation mentioned here was obtained because the amount of radiation reaching the plate 3 exceeded the upper limit of the detection region over the dynamic range of 4.0 digits of the light detection means 4 in the pixel on the scanning point x. This is a case where the image signal value S (x) is aligned with 4403 which is the maximum value that the number of 13-bit quantization bits can take.

  Subsequently, afterglow correction using the afterglow correcting means 71 will be described. First, image signals sequentially input from the A / D converter 6 are stored in the input buffer 34. The saturation sequential determination means 35 takes out only one pixel of the image information in the input buffer 34 in the order. Then, it is determined whether or not the extracted image signal S (x) satisfies the following expression (13).

S (x) = 4403 ――――― (13)
Here, when the image signal S (x) does not satisfy the expression (13), the image signal S (x) is not saturated, so that the image signal S (x) is sent to the inverse logarithmic conversion means 31 in the subsequent stage. Send sequentially. The image signal S (x) is corrected for afterglow and stored in the output buffer 36 as in the first embodiment. Thereafter, the next pixel is taken out from the input buffer 34 and the above-described procedure is repeated. Further, after all image signals are taken out from the input buffer 34 and correction is completed, they are stored in the output buffer 36. The image signal whose afterglow is corrected is sent to the subsequent image processing apparatus 8 at a time.

  When the image signal S (x) satisfies the expression (13), the image signal S (x) is saturated, so the contents of the output buffer 36 are erased and remain in the input buffer 34. Uncorrected image signals are sent to the subsequent image processing apparatus 8 at a time.

As described above, in the second embodiment, the afterglow correcting unit 71 sequentially determines whether or not the image signal S (x) is saturated during the afterglow correction, and the saturated image signal S (x ), The correction is canceled and all uncorrected image signals are sent to the subsequent device, so that the influence of afterglow is corrected by mistake, resulting in artifacts and preventing adverse effects on diagnosis and the like. .
(Embodiment 3)
In the second embodiment, the saturation is sequentially determined during the afterglow correction. However, the saturation can also be determined collectively. Therefore, in the third embodiment, a case where saturation determination is collectively performed and then an uncorrected image signal is transmitted to the subsequent stage will be described.

  Here, in the reading device 20, the light detection unit 4 has a dynamic range of 4.0 digits for a standard-shaped subject, and an afterglow correction unit 72 is used instead of the afterglow correction unit 7. Other configurations are the same as those shown in FIG.

  FIG. 7 is a diagram showing a configuration of the afterglow correcting means 72. The afterglow correction unit 72 is an input buffer that temporarily stores all image signals in addition to the inverse logarithmic conversion unit 31, the calculation unit 32, and the logarithmic conversion unit 33 constituting the afterglow correction unit 7 shown in FIG. 34 and a saturation batch determination means 37 for detecting the presence or absence of an image signal saturated in all the image signals.

  Subsequently, afterglow correction using the afterglow correcting means 72 will be described. Image signals sequentially input from the A / D converter 6 are stored in the input buffer 34. The saturation batch determination unit 37 extracts the image information of the input buffer 34 by one pixel in the order. Then, it is determined whether or not the extracted image signal S (x) satisfies Expression (13) shown in the second embodiment.

  Here, when the image signal S (x) does not satisfy the expression (13), the image signal S (x) is not saturated. After the determination of all the image information is completed, the image signal is sequentially transmitted from the input buffer 34 to the inverse logarithmic conversion means 31, and afterglow is corrected in the same manner as in the first embodiment. Sequentially transmitted to the image processing device 8.

  If the image signal S (x) satisfies the expression (13), the image signal S (x) is saturated. The uncorrected image signal remaining in the buffer 34 is transmitted to the subsequent image processing apparatus 8 at a time.

As described above, in the third embodiment, the afterglow correction unit 72 determines whether or not there is a saturated image signal in all image signals before correction, and the saturated image signal S (x) If there is, an uncorrected image signal is transmitted to the subsequent device without starting correction, so that the influence of afterglow is erroneously corrected to prevent artifacts and prevent adverse effects on diagnosis, etc. .
(Embodiment 4)
By the way, in Embodiment 1 described above, the output of the afterglow correction means 7 that is also the output of the reading device 20 uses a signal range of 4.3 digits in the dynamic range as a 4403-stage signal with a quantization bit number of 13 bits. . On the other hand, the image processing device 8 and the image reproducing device 9 can also be adapted to the output, but the signal range having a dynamic range of 4.0 digits conventionally used is quantized with 1024 steps per digit. It is also possible to use the image processing device 8 and the image reproduction device 9 corresponding to an image signal having a quantization bit number of 12 bits. Therefore, in the fourth embodiment, a bit number reducing means for reducing the number of bits of data representing an image signal is provided between the afterglow correcting means 7 and the image processing apparatus 8, and the conventional image processing apparatus 8 and the quantum processing means 8 are coupled with each other. Let us show the case where the number of bits is equalized.

  This bit number reduction means considers that the image signal output from the afterglow correction means 7 represents a signal range of 4.3 digits in the dynamic range in 4403 stages with a quantization bit number of 13 bits. While maintaining the resolution of 1024 steps per digit, the optimum 4.0 digit image signal is cut out from the signal range of 4.3 digits of dynamic range, and is associated with 4096 steps, which is the number of quantization bits of 12 bits. Is called.

  FIG. 8 shows the configuration of the bit number reduction means 73. The bit number reduction means 73 includes a buffer 38, an image range determination means 39, an image range cutout means 40, a flag 81, a calculation means 32, and a logarithmic conversion means 33. The bit number reduction means 73 is provided between the output of the afterglow correction means 7 and the input of the image processing apparatus 8.

The bit number reduction unit 73 stores in the buffer 38 an image signal having a quantization bit number of 13 bits sequentially input from the afterglow correction unit 7. A 12-bit image signal is represented by S ₁₂ (x) and a 13-bit image signal is represented by S ₁₃ (x). The flag 81 indicates whether or not an image signal exists in a range of 0 to 0.3 digits when the flag is low. The initial value is off, and the flag height is from 4.0 digits to 4.3 digits. This is a flag indicating whether or not an image signal exists in a digit range, and the initial value is also turned off.

  The image range determination means 39 extracts an image signal having a quantization bit number of 13 bits from the buffer 38 one pixel at a time, and determines whether this image signal satisfies the following expressions (14) and (15). To do.

Here, when the image signal satisfies the equation (14), the image signal S ₁₃ (x) includes the image signal in the range of 0 digit to 0.3 digit, so that the flag low of the flag 81 is turned on. To do. If the image signal satisfies Expression (15), the image signal S ₁₃ (x) includes image information in the range of 4.0 digits to 4.3 digits. To. Then, the above-described determination is repeated until all the image information is finished.

Thereafter, the image range cutout unit 40 refers to the flag 81. Here, when the flag low is off and the flag high is on, the entire image signal does not include an image signal in the range of 0 digit to 0.3 digit, and 4.0 digit to 4.3 digit. The image signal of the range is included. Therefore, the image signal is taken out from the buffer 38 pixel by pixel, and the image signal S ₁₃ (x) is substituted into the equation (16), and the range from 0.3 digit to 4.3 digit is changed from 0 digit to 4.0 digit. And a 12-bit image signal is sequentially transmitted to the image processing device 8. Then, the above-described clipping is repeated until clipping is completed for all image signals.

  Further, it is considered that most pixels having an image signal in the range of 4.0 digits to 4.3 digits are directly irradiated with radiation, and such pixels contain almost no subject information. Accordingly, an image signal in the range of 4.0 digits to 4.3 digits is less likely to contain information necessary for diagnosis than an image signal in the range of 0 digits to 0.3 digits.

Here, when the flag low of the flag 81 is ON, the entire image signal includes an image signal in the range of 0 digit to 0.3 digit. Therefore, there is a high possibility that the information necessary for diagnosis is included. The image signal is cut out so as to include a range of 0.3 digits from. That is, an image signal is taken out from the buffer 38 pixel by pixel, and this image signal S ₁₃ (x) is substituted into the equation (17) to cut out an image range from 0 digit to 4.0 digit, and a corresponding 12-bit image is obtained. The image signal is transmitted to the subsequent image processing apparatus 8. Then, the above operation is repeated until all the image signals are cut out.

  When both the flag high and flag low of the flag 81 are off, the image range of 0 digit to 4.0 digit is cut out and transmitted to the image processing device 8 in the same manner as when the flag low is on.

As described above, in the fourth embodiment, the bit number reduction unit 73 uses a quantum range corresponding to a dynamic range of 4.0 digits, which is considered useful for diagnosis, from an image signal having a quantization bit number of 13 bits. Since the image signal having the quantization bit number of 12 bits is taken out and output, the commercially available image processing device 8 and the image reproducing device 9 corresponding to the quantization bit number of 12 bits that are conventionally used can be used. Can be advantageous in terms of cost.
(Embodiment 5)
By the way, in the first to fourth embodiments, the voltage signal output with respect to the incident light amount is linear in the light detection means 4. However, in an obese subject, the incident light amount has a dynamic range of 4.3 digits. The voltage signal output with respect to the incident light quantity is nonlinear. Then, the processes performed in the subsequent image processing apparatus 8 and image reproduction apparatus 9 are not properly performed. Therefore, in the fifth embodiment, the output of the light detection unit 4 is linear with respect to the amount of incident light by signal processing so that the processing performed in the subsequent stage is performed appropriately.

  FIG. 9 shows a block diagram of a reading device 91 according to the fifth embodiment. The reading device 91 includes a light detection means 94, a logarithmic conversion circuit 95, an A / D converter 96, a reference means 42, a linearity recovery table 41, and an afterglow correction means 97.

  In the light detection means 94, the output current signal is nonlinear and has a one-to-one relationship when the incident light quantity is in the dynamic range of 4.3 to 4.5 digits, and the current signal in the range of 2 mA to 2.5 mA is output. Output. The logarithmic conversion circuit 95 has an input range of 100 nA to 2.5 mA, and the A / D converter 96 converts a voltage signal having a dynamic range of 4.5 digits into a digital value of 0 to 4607. .

  The reference means 42 refers to the linearity recovery table 41 with respect to the output data of the A / D converter 96, generates new linear data, and outputs it to the afterglow correction means 97. The linearity recovery table 41 is a LUT (Look Up Table) that converts a nonlinear digital value of the amount of incident light into a linear digital value based on the nonlinear characteristic of the light detection means 94. FIG. 10 shows an example of the linearity recovery table 41. The horizontal axis represents the input digital value from the A / D converter 96, and the vertical axis represents the output digital value output to the afterglow correction means 97. The linearity recovery table 41 is determined so as to cancel out the nonlinear characteristic of the light detection means 94 obtained experimentally.

  Here, the non-linear digital information of the incident light quantity sequentially input from the A / D converter 6 is converted into linear digital information by using the linearity recovery table 41 by the reference means 42, and then the afterglow correction means. 97 is output.

  As described above, in the fifth embodiment, the reference unit 42 converts the non-linear digital value of the incident light quantity into a linear digital value and outputs it to the afterglow correction unit 97. Even after shooting, the afterglow can be corrected appropriately.

  In the fifth embodiment, the reference unit 42 and the linearity recovery table 41 are arranged between the A / D converter 96 and the afterglow correcting unit 97. 97.

  FIG. 11 is an example of the afterglow correction unit 98 including the functions of the reference unit 42 and the linearity recovery table 41. The other configuration of the reading device 91 is the same as that shown in FIG. The afterglow correction unit 98 includes a reference unit 44, a conversion table 43, a calculation unit 32, and a logarithmic conversion unit 33. The calculation means and logarithmic conversion means 33 are the same as those of the afterglow correction means 7 shown in FIG.

  The conversion table 43 has the functions of the linearity recovery table 41 in FIG. 9 and the inverse logarithmic conversion unit 31 in FIG. 5, and a non-linear digital value with respect to the amount of incident light is based on the non-linear characteristic of the light detection unit 94. Thus, the image signal is converted into a linear digital value image signal, and at the same time, the image signal is inversely log-transformed into a linear image signal.

  The reference unit 44 refers to the conversion table 43 and sets the input non-linear digital value as a linear image signal proportional to the amount of incident light. This linear image signal is corrected for afterglow by the calculation means 32 and logarithmic conversion means 33 shown in FIG. 5, and is sequentially transmitted to the image processing apparatus 8 at the subsequent stage. Thereby, the same thing as Embodiment 5 is realizable with a simple structure.

It is a figure which shows the whole structure of a reader. FIG. 3 is a block diagram illustrating a configuration of a light detection unit according to the first embodiment. 2 is a diagram showing a photomultiplier tube and a peripheral circuit according to Embodiment 1. FIG. FIG. 4 is a diagram illustrating input / output characteristics of the light detection unit according to the first embodiment. FIG. 3 is a block diagram showing a configuration of afterglow correcting means 7 of the first embodiment. FIG. 10 is a block diagram showing a configuration of afterglow correcting means 71 of the second embodiment. FIG. 10 is a block diagram showing a configuration of afterglow correcting means 72 according to Embodiment 3. FIG. 10 is a block diagram illustrating a configuration of a bit number reduction unit 73 according to the fourth embodiment. FIG. 10 is a block diagram illustrating a configuration of a reading device 91 according to a fifth embodiment. It is a figure which shows the content of the linearity recovery table of Embodiment 5. FIG. 10 is a block diagram showing a configuration of afterglow correcting means 98 of the fifth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radiation generator 2 Subject 3 Plate 4, 94 Light detection means 5, 95 Logarithmic conversion circuit 6, 96 A / D converter 7, 71, 72, 97, 98 Afterglow correction means 8 Image processing apparatus 9 Image reproduction apparatus 10 Scanning means 11 Cathode 12 Converging part 13 Dynode part 14 High voltage power supply 15 Anode 16 Bleeder circuit 20, 91 Reading device 21 Condensing body 22 Filter 23 Photoelectric converter 24 Photomultiplier tube 25 Peripheral circuit 31 Inverse logarithmic conversion means 32 Computing means 33 logarithmic conversion means 34 input buffer 35 saturation sequential determination means 36 output buffer 37 saturation batch determination means 38 buffer 39 image range determination means 40 image range cutout means 41 linearity recovery tables 42 and 44 reference means 43 conversion table 73 bit number reduction means 81 flag

Claims (6)

Scanning means for scanning the stimulable phosphor plate in which the radiation image information is accumulated, with excitation light;
Photodetection means having a dynamic range of 4.3 digits or more for detecting stimulated luminescence generated by the excitation light for each scanning point constituting the scan;
Afterglow correction means for removing and correcting afterglow from a scanning point different from the scanning point where the stimulated light emission occurs from the detected photostimulated light emission information,
A radiation image reading apparatus comprising: Scanning means for scanning the stimulable phosphor plate in which the radiation image information is accumulated, with excitation light;
For each scanning point constituting the scanning, a light detecting means for detecting stimulated light emission generated by the excitation light, and
Afterglow correction means for removing and correcting afterglow from a scanning point different from the scanning point where the stimulated light emission occurs from the detected photostimulated light emission information,
A radiation image reading apparatus comprising:
The afterglow correction unit determines whether the light detection unit is saturated for each scanning point while performing the correction. When the saturation occurs, the correction is stopped, and the saturation is performed. A radiological image reading apparatus, comprising: a saturation sequential determination unit that continues the correction when the error does not occur. Scanning means for scanning the stimulable phosphor plate in which the radiation image information is accumulated, with excitation light;
For each scanning point constituting the scanning, a light detecting means for detecting stimulated light emission generated by the excitation light, and
Afterglow correction means for removing and correcting afterglow from a scanning point different from the scanning point where the stimulated light emission occurs from the detected photostimulated light emission information,
A radiation image reading apparatus comprising:
The afterglow correction unit collectively determines whether the light detection unit is saturated at all the scanning points before performing the correction, and when the saturation occurs based on the batch determination. The radiographic image reading apparatus further comprises a saturation batch determination unit that stops the correction and performs the correction when the saturation does not occur. Scanning means for scanning the stimulable phosphor plate in which the radiation image information is accumulated, with excitation light;
For each scanning point constituting the scanning, a light detecting means for detecting stimulated light emission generated by the excitation light, and
Afterglow correction means for removing and correcting afterglow from a scanning point different from the scanning point where the stimulated light emission has occurred, from the detected light emission information.
Bit reduction means for reducing the number of bits of the corrected stimulated light emission information;
A radiation image reading apparatus comprising: Scanning means for scanning the stimulable phosphor plate in which the radiation image information is accumulated, with excitation light;
For each scanning point constituting the scanning, a light detecting means for detecting stimulated light emission generated by the excitation light, and
Linearity recovery means for recovering the linearity of the photostimulated luminescence information based on the non-linear reading characteristics of the light detection means;
Afterglow correction means for removing and correcting afterglow from a scanning point different from the scanning point where the stimulated light emission has occurred, from the detected light emission information.
A radiation image reading apparatus comprising: Scanning means for scanning the stimulable phosphor plate in which the radiation image information is accumulated, with excitation light;
For each scanning point constituting the scanning, a light detecting means for detecting stimulated light emission generated by the excitation light, and
Afterglow correction means for removing and correcting afterglow from a scanning point different from the scanning point where the stimulated light emission has occurred, from the detected light emission information.
A radiation image reading apparatus comprising:
The afterglow correcting means includes a linearity recovery means for recovering the linearity of the photostimulated luminescence information based on a non-linear reading characteristic of the light detecting means.

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