JPH03132644A - Light quantity adjusting method for lamp for photodetective sensitivity correction and photodetective sensitivity correcting method in radiation image reader - Google Patents

Abstract

PURPOSE:To find a lamp light quantity set as the reference of a device by adjusting the lamp light quantity so that a first signal obtained by which irradiates excitation light with prescribed light quantity and a second signal obtained by lighting a lamp at the same value, and storing the lamp light quantity at that time. CONSTITUTION:The photodetective sensitivity of a photomultiplier 31 is set arbitrarily, and the first signal SD1 is obtained by receiving stimulated phosphorescence light 29 emitted under a reference condition set in advance, and next, the lamp light quantity s adjusted so that the value of the second signal SD2 obtained by lighting the lamp 21 can be set at the same value as that of the first signal SD1, and the lamp light quantity is stored in a storage means in the device. In such a way, it is possible to find the lamp light quantity set as the reference of the radiation image reader 20 even when the application voltage-photodetective sensitivity characteristic of the photomultiplier 31 used in the adjustment of the lamp light quantity is unknown.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is a method for generating radiation images emitted from a stimulable phosphor sheet by irradiating excitation light onto the stimulable phosphor sheet on which the radiation image has been accumulated and recorded. The present invention relates to a radiation image reading device equipped with a photomultiplier tube (photomultiplier) that receives stimulated luminescence light to obtain an image signal, and a lamp for calibrating the light receiving sensitivity of the photomultiplier. In more detail, how to adjust the light intensity of the above lamp,
The present invention also relates to a method for determining the applied voltage-light sensitivity characteristics of the photomultiplier when the photomultiplier is replaced.

(Conventional technology) Radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.)
When irradiated with , some of this radiation energy is accumulated,
There are known stimulable phosphors (stimulable phosphors) that emit stimulated light with an amount of light corresponding to the amount of accumulated energy when irradiated with excitation light such as visible light. A radiation image of a subject such as a human body is partially photographed and recorded on a sheet of stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam to generate stimulated luminescence. The stimulated luminescent light is read photoelectrically to obtain an image signal.
The present applicant has proposed a radiation image recording and reproducing system that outputs the radiation image of the subject as a visible image to a recording material such as a photographic light-sensitive material, CRT, etc. based on this image signal (Japanese Patent Laid-Open No. 12429/1983). 56-11395
No. 55-183472, No. 56-104845, No. 55-116340, etc.).

This system has the practical advantage of being able to record images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. In other words, it is recognized that in stimulable phosphors, the amount of emitted light that is stimulated and emitted by excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range, and therefore the amount of radiation exposure varies depending on various imaging conditions. Even if the amount of stimulated luminescence light emitted from the stimulable phosphor sheet fluctuates considerably, the reading gain is set to an appropriate value and the photoelectric conversion means reads the amount of stimulated luminescence light and converts it into an electrical signal. By outputting a radiation image as a visible image to 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 the amount of radiation exposure.

Since the stimulated luminescent light emitted from the stimulable phosphor sheet has a wide dynamic range of light intensity, a photomultiplier is generally used as a receiver for receiving the stimulated luminescent light. . The photomultiplier adjusts the light receiving sensitivity (the magnitude of the output signal relative to the amount of incident light) by applying a high voltage to the photomultiplier.
is determined, and by adjusting the high voltage, a signal with a desired value can be obtained whether the amount of light is small or the amount of light is quite large.

The photomultiplier has a limited lifespan and needs to be replaced from time to time. However, even photomultipliers of the same type have different characteristics, and the problem is that it is unclear how many volts of high voltage should be applied to a newly installed photomultiplier to obtain the desired light-receiving sensitivity. .

In order to find the voltage value that gives this desired light-receiving sensitivity,
Conventionally, a stimulable phosphor sheet is irradiated with a predetermined amount of radiation that serves as a reference, and a predetermined amount of energy is accumulated in an approximately -like manner (
Hereinafter, this will be referred to as "solid exposure." ), then the stimulated luminescence light obtained by scanning at a predetermined speed with a light beam of a predetermined amount of light is received by a newly replaced photo multiplier, and the photo multiplier is applied so that an image signal of a desired value is obtained. I was looking for the voltage value of the high voltage applied to the pliers.

(Problem to be Solved by the Invention) However, in order to calibrate the light-receiving sensitivity of a photomultiplier using the above method, it is necessary to create a stimulable phosphor sheet that is exposed solidly. It takes a lot of effort to perform a good calibration, so forcing the user to perform this calibration every time they replace the photomultiplier poses a problem in terms of the accuracy of the calibration.Therefore, a simple and accurate calibration method is desired. Ta.

In order to easily perform calibration, Japanese Patent Application No. 133-22332
It is also conceivable to apply the means described in No. 4 to provide a lamp that simulates stimulated luminescence light, and to calibrate a newly replaced photomultiplier by lighting this lamp at a standard light intensity.

However, the light-receiving system that receives stimulated luminescence light differs slightly depending on each radiographic image reading device due to manufacturing errors and assembly errors of each part, so it is meaningless to determine the reference light amount for a single lamp, and each After installing a lamp in a device, it is necessary to determine the reference light amount of the lamp using the light receiving system of each device. Therefore, in a newly assembled radiation image reading device, the problem is how to determine the reference light amount of the lamp in a combination of a light receiving system including a new lamp and a new photomultiplier. In addition, in order to read the stimulated luminescence light emitted from stimulable phosphor sheets irradiated with various doses of radiation, it is necessary to set the photomultiplier to various light receiving sensitivities depending on the radiation dose, and the lamp Even if the reference light amount is determined, the problem is how to use the lamp to easily and accurately determine the applied voltage vs. light sensitivity characteristics of the new photomultiplier or the photomultiplier that has been replaced.

In view of the above circumstances, the present invention provides a radiation image reading device including a photomultiplier that receives stimulated luminescence light to obtain an image signal, and a lamp for calibrating the light reception sensitivity of the photomultiplier. The object of the present invention is to provide a new method for determining the amount of light and the applied voltage-light sensitivity characteristics of a photomultiplier.

(Means for Solving the Problems) A method for adjusting the amount of light from a stimulable phosphor sheet for calibrating light receiving sensitivity according to the present invention is to emit excitation light from a stimulable phosphor sheet on which a radiation image is accumulated and recorded. a photomultiplier having a light-receiving surface provided with a filter that cuts light in the wavelength range of the excitation light, the photomultiplier receiving the stimulated emission light representing the radiation image obtained to obtain an image signal; A method for adjusting the amount of light of the lamp in a radiation image reading apparatus comprising a lamp that emits light in the wavelength range of the stimulated luminescence light for calibrating the light receiving sensitivity of the photomultiplier tube, the method comprising: By arbitrarily setting the light-receiving sensitivity of the multiplier tube and irradiating a predetermined amount of excitation light onto a stimulable phosphor sheet that has been irradiated with a predetermined amount of radiation, the stimulated luminescence light emitted from the stimulable phosphor sheet is detected. The photomultiplier tube receives light to obtain a first signal, the lamp is turned on, and the photomultiplier tube receives light emitted from the lamp in place of the stimulated luminescence light to obtain a second signal. obtaining a signal, adjusting the light intensity of the lamp so that the value of the second signal is the same as the value of the first signal, and the value of the second signal is the same as the value of the first signal; The present invention is characterized in that the amount of light obtained when .

Further, the light reception sensitivity calibration method of the present invention includes the step of irradiating excitation light onto a stimulable phosphor sheet on which a radiation image has been accumulated and recorded, thereby generating stimulated luminescence light representing the radiation image emitted from the stimulable phosphor sheet. A photomultiplier tube (photomultiplier) whose light receiving surface is provided with a filter that cuts light in the wavelength range of the excitation light, which receives light to obtain an image signal, and for calibrating the light receiving sensitivity of the photomultiplier tube. 2. A method for adjusting the light receiving sensitivity of the photomultiplier tube in a radiation image reading device comprising a lamp that emits light in the wavelength range of the stimulated luminescence light, the light amount of the light receiving sensitivity calibrating lamp according to claim 1. lighting the lamp with the light amount stored in the storage means determined by the adjustment method; and applying the light to the photomultiplier tube so that the photomultiplier tube obtains a signal having a predetermined first value. Adjusting the voltage to obtain the first applied voltage after the adjustment, readjusting the voltage so that the photomultiplier tube obtains a signal having a predetermined second value, and determining the first applied voltage after the readjustment. The present invention is characterized in that two applied voltages are determined, and an applied voltage-photosensitivity characteristic of the photomultiplier tube is determined based on the first and second applied voltages.

(Function) The above lamp only needs to be lit when determining the applied voltage vs. light receiving sensitivity characteristics of the photomultiplier tube, so the lighting time is short;
For example, by initially lighting the lamp for a predetermined period of time to perform aging, changes in the amount of light from the lamp during use can be almost ignored. Further, for safety, a feedback circuit may be provided to maintain the reference lamp light amount once the reference lamp light amount has been determined. Therefore, the amount of light from the lamp only needs to be precisely adjusted once by the manufacturer who assembled the radiation image reading device, so even if the adjustment takes some effort, it is not a big problem. On the other hand, photomultipliers need to be replaced from time to time, and it is necessary to be able to calibrate them easily and accurately. The present invention is constructed to satisfy the above points.

The lamp light amount adjustment method of the present invention is to arbitrarily set the light receiving sensitivity of the photomultiplier, receive the stimulated luminescence light emitted under predetermined reference conditions to obtain a first signal, and then The lamp light intensity is adjusted so that the second signal obtained by lighting the lamp has the same value as the first signal, and the lamp light intensity is stored in a storage means within the device. Even if the applied voltage-light receiving sensitivity characteristic of the photomultiplier used to adjust the lamp light intensity is unknown, the lamp light intensity can be determined as a reference for the radiation image reading device. It should be noted that instead of storing the lamp light amount itself in the storage means, it is of course possible to store, for example, the voltage, power, etc. supplied to the lamp. "Store" includes storing the above-mentioned voltage, power, etc. corresponding to the amount of lamp light.

Furthermore, even if the photomultipliers are of the same type, they do not have the same light-receiving sensitivity for the same applied voltage, but the applied voltage and light-receiving sensitivity are proportional; for example, if twice the voltage is applied, the light-receiving sensitivity will be doubled. It has the property that a signal with a value of is obtained.

The light-receiving sensitivity calibration method of the present invention was made with this point in mind.The lamp is turned on at the above-mentioned standard lamp light intensity, and, for example, a newly replaced photomultiplier is set to a predetermined first value. Find the first applied voltage by adjusting the applied voltage so that a signal with a predetermined second value is obtained, then leave the lamp light intensity unchanged and adjust the applied voltage again so that a signal with a predetermined second value is obtained. The second applied voltage is determined by adjusting the applied voltage, and the applied voltage-photosensitivity characteristic of the photomultiplier is determined based on these first and second applied voltages. When the photomultiplier is replaced, etc., it is possible to easily and highly accurately determine the applied voltage vs. light sensitivity characteristics of the photomultiplier, and therefore the average radiation dose emitted from the stimulable phosphor sheet is significantly different from the standard. Even when reading stimulated luminescence light, the photomultiplier can be adjusted to an appropriate light-receiving sensitivity.

(Example) Examples of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic diagram of an example of an X-ray imaging apparatus.

X-rays 12 are emitted from the X-ray source 11 of this X-ray imaging device IO toward the subject 13, and the X-rays 1 that have passed through the subject 13
By irradiating the stimulable phosphor sheet 14 with the stimulable phosphor 2a, a transmitted X-ray image of the subject 13 is accumulated and recorded on the sheet 14.

FIG. 1 is a perspective view showing an example of an X-ray image reading device, which is an embodiment of the radiation image reading device according to the present invention.

The stimulable phosphor sheet 14 on which the X-ray image has been recorded is set at a predetermined position in the X-ray image reading device 20 .

The stimulable phosphor sheet 14 set at this predetermined position is conveyed (sub-scanned) in the direction of arrow Y by a sheet conveying means (not shown). On the other hand, the excitation light beam 24 emitted from the laser light source 23 is reflected and deflected by the rotating polygon mirror 2B which is driven by the motor 25 and rotates at high speed in the direction of the arrow. The light beam enters the sheet 14 while changing the direction of the light beam, and performs main scanning in the direction of arrow X, which is substantially perpendicular to the direction of sub-scanning (direction of arrow Y). Stimulated luminescent light 29 is emitted from the part of the sheet 14 that is irradiated with the excitation light beam 24 in an amount corresponding to the accumulated and recorded X-ray image information, and this stimulated luminescent light 29 is transmitted to the stimulable phosphor sheet. The excitation light reflected on the surface of 14 is guided by a light guide 30, and the reflected excitation light is cut by a filter 36 that cuts light in the wavelength range of the excitation light, and only the stimulated luminescence light 29 is passed through a photomultiplier ( It is photoelectrically detected by a photomultiplier tube (photomultiplier tube) 31. The light guide 30 is made by molding a light-guiding material such as an acrylic plate, and is arranged so that the linear entrance end surface 30a extends along the main scanning line on the stimulable phosphor sheet 14. The light receiving surface of the photomultiplier 31 is coupled to the annularly formed exit end surface 30b. Stimulated luminescent light 29 entering the light guide 30 from the entrance end surface 30a
travels inside the light guide 30 by repeating total reflection,
Stimulated luminescence light 29 is emitted from the exit end face 30b and received by the photomultiplier 31 via the filter 36, and is converted into an electrical signal by the photomultiplier 31, representing an X-ray image. In addition, the input end face 30 of the light guide 30
A lamp 2) that emits light in the same wavelength range as the stimulated luminescence light 29 is provided near point a at a position that does not affect the conveyance of the sheet 14. When this lamp 2) is turned on, the lamp 2)
) is also incident on the light guide 30 and detected by the photomultiplier 31.

The analog output signal S^ outputted from the photomultiplier 31 is logarithmically amplified by the logarithmic amplifier 32, and the A/D
The signal is digitized by a converter 33 to obtain a digital image signal So.

The obtained image signal So is once input manually into the computer system 40, and then transmitted to an image processing device (not shown) to undergo appropriate image processing, and then sent to an image output device (not shown) to perform processing based on the image signal S1. The visible image is reproduced and output. This computer system 40 includes a main body section 41. which has a built-in CPU and an internal memory. A drive section 42 into which a floppy disk as auxiliary memory is inserted and driven. A keyboard 43 for an operator to input necessary instructions to the computer system 40, and a CRT display 4 for displaying necessary information.
4, mainly an X-ray image reading device 20
It also plays a role when adjusting the light intensity of the lamp 2) and determining the applied voltage vs. light receiving sensitivity characteristics of the photomultiplier 31, as described below. ing.

Here, a method of adjusting the light amount of the lamp 2), which is performed during adjustment after the X-ray image reading device 20 is assembled, will be described.

FIG. 3 is a schematic diagram of an X-ray imaging apparatus similar to FIG. 2.

The entire surface of the stimulable phosphor sheet 14' is uniformly irradiated with X-rays at a reference dose (for example, 1 mR) without placing a subject.

Next, this sheet 14' is set at a predetermined position in the X-ray image reading device 20 shown in FIG. 1, and reading is performed in the same manner as the reading of the sheet 14 described above.

At this time, since the applied voltage-light sensitivity characteristics of the attached photomultiplier 31 are still unknown, it is assumed that the photomultiplier 31 has the average applied voltage-light sensitivity characteristics of the same type of photomultiplier. Then, the computer system 40 instructs the high voltage generation circuit 34 that generates the high voltage to be applied to the photomultiplier 31 so that the applied voltage matching the average characteristics is applied to the photomultiplier 31. . The first signal SDI obtained by reading the stimulated luminescence light emitted from the sheet 14' in this manner is stored in the main body 41 of the computer system 40. Here, although the entire surface of the sheet 14' is irradiated with X-rays almost uniformly (1 mR), there are variations from part to part.
For example, it is preferable to use the average value SDI of image signals obtained by reading from the central region of the sheet 14' in place of the first signal SDI. In addition, in X-ray photography, the stimulable phosphor sheet 4 is irradiated with X-rays at a dose deviated by ΔX m R from the reference dose (here, 1 mR), and the excitation light beam 24 (first beam) scans the stimulable phosphor sheet. (See Figure 1) is also scanned with a light amount that is shifted by ΔP from the reference light f8p, then these can be calculated using the formula % Formula % (1) However, a and b are corrected using correction coefficients, and the image signal after this correction is It is preferable to use S D+' instead of the first image signal SDI.

After the scanning of the sheet 14' is completed, the lamp 2) is then turned on in response to a command from the computer system 40 while applying the same voltage to the photomultiplier 31 as when reading the sheet 14'. First, the computer system 40 emits a signal Sc corresponding to the power set in advance based on past experience etc. so that the power is supplied to the lamp 2), and this signal Sc is sent via the D/A converter 35. and is input to the power supply 22. The power supply 22 supplies the lamp 2) with power corresponding to the signal Sc. In this state, the photomultiplier 31 reads the amount of lamp light and obtains a second signal 502. In the main body 41 of the computer system 40, the stored first signal SDI and the input second signal SD2 are compared, and the values of the first signal SDI and the second signal SD2 are made equal to each other. control the power supplied to lamp 2). In this way, when the value of the second signal SD2 becomes equal to the value of the first signal SDI, the signal S corresponding to the power supplied to the lamp 2) at that time
The value of c is stored within computer system 40. This completes the light amount adjustment of lamp 2).

Next, a method for determining the applied voltage-light receiving sensitivity characteristic of the photomultiplier 31 will be explained.

By means of a command signal S from the computer system 40,
A high voltage is applied to the photomultiplier 31 in consideration of the average applied voltage-photosensitivity characteristics of photomultipliers of the same type as this photomultiplier 31, and the signal SC stored as described above is applied. The light is emitted toward the power supply circuit 22, and the lamp 2) is lit with the adjusted lamp light amount as described above. In this state, the light intensity of the lamp is read to obtain the signal SD3, and this signal SD
3 is a predetermined value, for example, the image signal So is a 4-digit image signal for each sampling point in IO bits (00 in hexadecimal).
The voltage applied to the photomultiplier 3I is adjusted so that the signal SD3 has a central value of 200H when expressed as 0□ to 3FF□, that is, 1 digit per 100), and the value of the signal SD3 becomes 200H. The voltage applied to the photomultiplier 31 (the value of the command signal S) when the value of the command signal S is reached is stored in the main body 41 of the computer system 40.

Next, the analog current signal s is output from the photomultiplier 31 while maintaining the lamp light intensity as it is.
The value of A decreases by one digit (that is, the signal SD3 is 10 in hexadecimal).
The applied voltage of the photomultiplier 31 is readjusted so that the value becomes 0□, and the applied voltage at that time (the value of the command signal S) is stored in the main body 41 of the computer system 40.

The signal obtained by reading the lamp light intensity as described above is 2
The applied voltage (first applied voltage) vA that becomes 001I and 10
When the applied voltage (second applied voltage) vB that becomes 0u is found, the main body 41 calculates the sensitivity coefficient k of the photomultiplier 3I from these first and second applied voltages vA and vB based on the following formula. is required. This sensitivity coefficient k represents the applied voltage-light receiving sensitivity characteristic of this photomultiplier 31.

FIG. 4 is a diagram showing the correspondence between the applied voltage of the photomultiplier and the light receiving sensitivity. The horizontal axis is the applied voltage (logarithm), and the vertical axis is the light receiving sensitivity (logarithm).

Assuming that the light-receiving sensitivity corresponding to the first applied voltage V^ is ^^ and the light-receiving sensitivity corresponding to the second applied voltage vB is 8, the relationship between the applied voltage and the light-receiving sensitivity is on a logarithmic graph, and the slope is k
It can be expressed by straight line A.

Therefore, when obtaining an image signal SD representing a radiation image from a stimulable phosphor sheet on which a radiation image has actually been stored and recorded, the photo multiplier 31 is adjusted according to the dose of X-rays irradiated to the stimulable phosphor sheet. Although it is necessary to set the light receiving sensitivity to a certain level, the X-ray dose (1 mR) corresponding to the first applied voltage V^ is used as a reference, and a stimulable phosphor sheet that has been irradiated with a dose deviated by an order of magnitude Δ from this reference. When reading,
In order to set the photomultiplier 31 to a light receiving sensitivity shifted by Δ, the high voltage VK applied to the photomultiplier 3I is Vx "VA XLO"K (3), that is, as shown in FIG. 4. The voltage vK corresponding to KA+ΔK is determined for the straight line A, and this high voltage vK is applied to the photomultiplier 31 according to a command from the computer system 40.

(Effects of the Invention) As explained in detail above, the method for adjusting the light intensity of a lamp for light-receiving sensitivity calibration of the present invention arbitrarily sets the light-receiving sensitivity of a photomultiplier, and uses a predetermined amount of excitation light taken under predetermined conditions. irradiate to obtain the first signal, then turn on the lamp to obtain the second signal, adjust the lamp light intensity so that this second signal has the same value as the first signal, and then Since the amount of lamp light is stored, even if the applied voltage-light sensitivity characteristic of the photomultiplier used to adjust the amount of lamp light is unknown, the amount of lamp light that will serve as a reference for the radiation image reading device can be determined.

Further, in the light receiving sensitivity calibration method of the present invention, the lamp is turned on at the above-mentioned reference light intensity, the applied voltage of the photomultiplier is adjusted to obtain a signal having a predetermined first value, and then the applied voltage is again adjusted. The adjustment is made to obtain a signal having a predetermined second value, and the applied voltage-light receiving sensitivity characteristic of the photomultiplier is determined based on these first and second applied voltages. Even users can easily and accurately calibrate the photomultiplier.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of an X-ray image reading device, which is an embodiment of the radiation image reading device according to the present invention. FIG. 2 is a schematic diagram of an example of an X-ray imaging device. is a schematic diagram of an X-ray imaging apparatus similar to that shown in FIG. 2, and FIG. 4 is a diagram showing the correspondence between the applied voltage of the photomultiplier and the light-receiving sensitivity. 10, 10'...X-ray imaging device 14, 14'...Stormable phosphor sheet 20...X
Line image reading device 24...excitation light beam 29...
Stimulated luminescence light 30...Light guide 3■...Photomultiplier tube (photomultiplier) 40...Computer system Figure 2 Figure 4 Figure 4 1999 1999 Patent Application 2, Title of Invention No. Relationship with the 270゜ Incident Address of the Patented Artist 2) Nakanuma, Minamiashigara City, Kanagawa Prefecture Address Name (
520) Oshi Photo Film Co., Ltd. 4, Agent address: 5-2-1 Roppongi, Minato-ku, Tokyo, January 2, 2013 No. 42, Uraiya Pill 7M 6, ``Detailed Description of the Invention'' in the specification subject to amendment ” Column 7, Contents of amendment (1) Specification, page 13, line 20 to page 14, line 1, “has the property of being proportional” to the property of being proportional in the rlog-log domain has. ” he corrected. 5. Voluntary amendment of the date of amendment order

Claims (2)

[Claims] (1) An image signal is obtained by irradiating excitation light onto a stimulable phosphor sheet on which a radiation image has been stored and recorded, and receiving stimulated luminescence light representing the radiation image emitted from the stimulable phosphor sheet. , a photomultiplier tube having a light-receiving surface provided with a filter that cuts light in the wavelength range of the excitation light; and a photomultiplier tube that cuts light in the wavelength range of the stimulated luminescence light for calibrating the light-receiving sensitivity of the photomultiplier tube. A method for adjusting the amount of light of a radiation image reading device in a radiation image reading device comprising a lamp that emits light, the method comprising: arbitrarily setting the light receiving sensitivity of the photomultiplier tube; and a stimulable phosphor sheet irradiated with a predetermined amount of radiation. A predetermined amount of excitation light is irradiated onto the stimulable phosphor sheet, and the photomultiplier tube receives the stimulated luminescence light, thereby obtaining a first signal. A second signal is obtained by receiving light emitted from the lamp instead of the exhaustion light by the photomultiplier tube, and the value of the second signal is the same as the value of the first signal. The light amount of the lamp is adjusted to the value of the second signal, and the light amount when the value of the second signal becomes the same as the value of the first signal is stored in the storage means of the radiation image reading device. A method for adjusting the light intensity of a lamp for calibrating light receiving sensitivity in a radiation image reading device. (2) Obtaining an image signal by irradiating excitation light onto a stimulable phosphor sheet on which a radiation image has been stored and recorded, and receiving stimulated luminescence light representing the radiation image emitted from the stimulable phosphor sheet. , a photomultiplier tube having a light-receiving surface provided with a filter that cuts light in the wavelength range of the excitation light; and a photomultiplier tube that cuts light in the wavelength range of the stimulated luminescence light for calibrating the light-receiving sensitivity of the photomultiplier tube. A method for adjusting the light receiving sensitivity of the photomultiplier tube in a radiation image reading apparatus equipped with a lamp that emits light, the method comprising the steps of the lamp is turned on with the light amount determined by the amount of light, and the voltage applied to the photomultiplier tube is adjusted so that the photomultiplier tube obtains a signal having a predetermined first value; determining an applied voltage, readjusting the voltage so that a signal having a predetermined second value is obtained by the photomultiplier tube, and determining a second applied voltage after the readjustment; A method for calibrating light sensitivity in a radiation image reading apparatus, characterized in that an applied voltage-light sensitivity characteristic of the photomultiplier tube is determined based on two applied voltages.