For any quantitative PET work you have to make sure that the right input data units are specified if the data is not read from DICOM, ECAT or the database. Activity concentration values are always converted to the internal representation of kBq/cc during a read operation. If the data is saved again, the values after conversion will be stored. Additionally, the acquisition times must also be specified. There is a facility for saving/retrieving timing protocols in all tools which load image data.