QALT study of scintillating material in digital flat panels for medical imaging

QALT method (Quantitative Accelerated Life Test) is extensively used in industrial world to assess the reliability of components or systems under stresses, find major influent parameters and the laws of evolution of component or system properties. Such an approach was used in digital X-ray flat detectors for medical imaging to study the defect mechanism of scintillator under temperature and humidity. The scintillator was encapsulated as it can be in a detector to protect it from humidity. QALT experiments showed that the total quantity of light emitted by the scintillator does not decrease with aging time, so that sensitivity decrease will never be the failure mode for humid heat treatments. Structure size of material was also measured. A completely different behavior was found for the parameter controlling structure evolution depending on encapsulation type. Calculations show that the permeation coefficient of the seal used for encapsulation can modify greatly the apparent law of evolution of scintillator structure size.