In a method of annealing a storage phosphor screen comprising a photostimulable phosphor by adding energy in form of heat and/or radiation, said method is applied during a time and in relative humidity conditions such that said phosphor shows peaks in an electron paramagnetic resonance (EPR) spectrum measured at a frequency of 34 GHz, at flux densities of magnetic fields of 880 mT, 1380 mT and 1420 mT, wherein said peaks exceed normalized signal intensity percentages of at least 45% and even of at least 55%, wherein a central peak height in the said EPR-spectrum, measured at a magnetic flux density of 1220 mT, is calculated to have a normalized value of 100%.