Patent ID: 7342242

Claim:
A method for estimating sensitivity change in a photomultiplier used in a radiation image reading unit in which a radiation image recorded on a storage phosphor sheet through the exposure of the radiation carrying the image is read out by irradiating excitation light on the storage phosphor sheet to produce stimulated luminescence light, and obtaining image signals that correspond to the radiation image through photoelectrical detection of the stimulated luminescence light emitted from the storage phosphor sheet using the photomultiplier, wherein information that indicates the sensitivity change in the photomultiplier is obtained by the steps of: obtaining exposure conditions which were set when the radiation image was recorded on the storage phosphor sheet; calculating an estimated amount of radiation irradiated on the storage phosphor sheet based on the exposure conditions obtained; cumulatively adding the estimated amount of radiation for each radiation image read out by the radiation image reading unit; and obtaining the cumulative value of the estimated amounts as the information that indicates the sensitivity change in the photomultiplier.