PETRA is a Matlab software toolbox for PET and SPECT (even MRI) analysis that is being developed at the SiPBA Lab. (Signal Processing and Biomedical Applications) at the University of Granada (UGR) Spain, together with collaborating institutes and Universities worldwide. The development of PETRA was supported by funding from the Spanish Ministry of Science, the UGR, the Consejería de Innovación of Junta de Andalucía and Ingenia and currently receives support from several projects under different competitive calls. The toolbox includes algorithms for simple and advanced analysis and classification of PET, SPECT, etc. images with the aim of Alzheimer and Parkinson disease diagnosis/detection. It supports the data formats of all major functional/anatomical imaging systems (.dcm, .nii, .mat, etc.) and new formats can be added easily. Segovia-Román, Fermín, et al. "PETRA: Multivariate analyses for neuroimaging data." Proceeding of 2nd International Work-Conference on Bioinformatics and Biomedical Engineering. 2014. Changelog Added option to manually correct orientation of images (right button on the pannels) Corrected bugs.