Signal fading, erasure, and rescan in storage phosphor imaging

This paper addresses three problems in storage phosphor imaging: natural fading of latent image signals, proper erasure of the exposed plates, and re-scanning for a second readout. Signal and signal-to-noise ratios were measured as a function of time, erasure power/time, or number of pre-scans to study these problems. The latent image signals were found to decay very rapidly during the first several minutes and stabilize after several hours. The fading effect results in a variable signal gain (signal per unit exposure), which may affect the system calibration and quantitative use of the image data. Complete erasure of the latent image signals is necessary to ensure that no residual image signals are present when the plate is exposed again. It was found that plates used in high exposure applications (GI, therapeutic imaging) may require an excessively long erasure time to prepare them for use in low exposure applications (chest imaging). Although the latent image is partially erased during the readout process, it may sometimes become necessary to re-scan the plate for a second or third readout. It was found that because a large number of energy traps are generated for each X-ray photon, a significant portion of the X-ray information remains intact for reuse after the first or second scans. Measurement of the signals and signal-to-noise ratios are presented to demonstrate and discuss the aforementioned problems or effects.