Figure 1.

Technical considerations in region-of-interest (ROI) delineation. On diagnostic CT, auto-segmented ROIs should closely match lung parenchyma margins (A). Our SPECT/CT ROI technique requires the inclusion of a very thin sliver of pleura within its margins (blue arrows), but this has a tendency to over-include the left mediastinal border (red triangles) (B). Due to differences in CT scan technique, diagnostic CT (C) and SPECT/CT (D) of the same patient performed a week apart show dependent atelectasis on SPECT/CT (D, blue arrows) but not on diagnostic CT (C).