Fig 4. Typical example of an axial view of the right lung of a patient to demonstrate the effect of the replacement of the CT-based LACs of lung tissue (μ-map CT) with the LAC from the MR-based segmentation method from the Biograph mMR (μ-map CT_MRLUNG).

To show the differences of LACs, a subtraction map is given in the upper row on the right-hand side (μ-map CT_MRLUNG—CT); as one can see, the subtraction of μ-map CT from μ-map CT_MRLUNG leads to an underestimation of LACs in the posterior regions and an overestimation in the anterior regions (given in LACs). This results in higher SUVs in PET_CTAC as compared to PET_CTAC_MRLUNG in the posterior regions, or, in other words, an underestimation of SUVs in the posterior regions of PET_CTAC_MRLUNG as shown in the subtraction image PET CTAC_MRLUNG–CTAC.