[en] Data acquisition using more than one energy window has been proposed principally for scatter correction in positron emission tomography (PET). However, prior to scatter correction, such data must be corrected for various distortions including detector efficiency and spectral non-uniformities. The aim of this work is to describe and validate a normalization technique that can minimize these undesirable effects. The method has been validated using data with different degrees of spatial and spectral distortion, and has been found to be capable of restoring the greatest spectral asymmetric acquisition possible with our animal PET system. (author)