Figure 5. Problems with accurate delineation of target volumes as a result of differences in the state of respiration between emission and transmission maps (note changes in the tumour in the mediastinum as well as the artefact areas). Left: attenuation correction using a respiration average transmission map with radioactive rod sources. Centre: attenuation correction using a CT map acquired at end inspiration. Right: attenuation correction using a CT map acquired at end expiration or under free breathing. Adapted from: Visvikis D, Costa DC, Croasdale I, et al. CT-based attenuation correction in the calculation of semi-quantitative indices of [18F]FDG uptake in PET. Eur J Nucl Med Mol Imaging. 2003;30:344–53. Reprinted with kind permission of Springer Science and Business Media.