Scintillation camera compensation for shifting the center channel of the energy spectrum due to photomultiplier gain change

Claim 1

A scintillation camera apparatus comprising: scintillation camera means, having a two-dimensional radiation detector, for detecting gamma rays radiated from the interior of an object to be examined, into which a radio isotope is injected, to produce X and Y position signals representing a detection position of gamma rays and a Z signal representing the intensity of gamma rays for each detection position; image memory means, coupled to said scintillation camera means, for storing data indicating a detection frequency of gamma rays exceeding a predetermined energy level at a memory location addressed by the X and Y position signals when the Z signal exceeds the predetermined energy level and for providing image data representing a distribution of the radio isotope in the object; first compensation table means for storing compensation data for compensating for nonlinearity of the X and Y position signals, said first compensation table means being accessed by the X and Y position signals from said scintillation camera means to read out corresponding X and Y compensation data therefrom; second compensation table means for storing energy compensation data corresponding to an energy detection response for gamma rays of said scintillation camera means, said second compensation table means being accessed by the Z signal from said scintillation camera means to read out corresponding Z compensation data therefrom; compensation means coupled between said scintillation camera means and said image memory means, and responsive to the X, Y, Z compensation data from said first and second compensation tables for compensating the X and Y position signals and the Z signal to be supplied from said scintillation camera means to said image memory means; energy spectrum data memory means, coupled to said scintillation camera means, for storing an energy spectrum of gamma rays; energy spectrum peak detecting means, coupled to said energy spectrum data memory means, for detecting the peak value of the energy spectrum distribution; and rewriting means, coupled to said energy spectrum data memory means and said second compensation table means, for, when a current peak value position detected by said energy spectrum peak detecting means is shifted from a previously detected peak value position, forming energy compensation data in accordance with a shifting amount between said peak value positions, and rewriting said second compensation table means in accordance with the energy compensation data.