Figure 2.

(A) Visual instructions of the most cranial slice of manually delineated cerebellar (left) and occipital (right) reference regions. The reference regions were delineated on three consecutive transaxial T1-weighted MR images. Cerebellar reference region is shown on the left and occipital reference region on the right. (B) The diagram shows how a T1-weighted MR image of an individual’s brain is processed to produce the final reference region. The shown example is from the [¹¹C]carfentanil data set. The rectangles represent processing steps between inputs and outputs. The FreeSurfer step assigns an anatomical label to each voxel of the subject’s T1 weighted MR image. The ROI extraction step extracts a prespecified ROI from FreeSurfer’s output. The anatomical correction removes voxels that are most likely to suffer from spillover effects; for [¹¹C]carfentanil data this means voxels lateral to the lateral ventricles. In the tail-exclusion step, radioactivity distribution within the anatomically corrected reference region is estimated, and the voxels whose intensities are on the tail-ends of the distribution are excluded.