A nodule in the lower lung sits just under the diaphragm, and the team wants a time-activity curve from it while the patient breathes shallowly but unevenly. Counts are limited, so image noise should stay low and the data must stay re-sortable after the scan. Which PET acquisition setup preserves the framing, gating and noise advantages this study needs?

List-mode acquisition preserves event timing, allowing the data to be reframed into a time-activity curve after the scan; recording the breathing signal permits retrospective respiratory sorting, which is useful when breathing is shallow or irregular; and time-of-flight (TOF) information improves localization and noise performance when counts are limited. Short fixed frames with TOF and a recorded trace are a familiar dynamic protocol, but event data have already been grouped into frames, so they cannot be freely re-sorted at the event level after acquisition. List mode with retrospective respiratory gating retains the desired timing and gating flexibility, but omitting TOF gives up a useful noise-reduction advantage in this low-count study. Retrospective data-driven respiratory estimation is also used in PET, but it does not meet the stated requirement to record the breathing signal; moreover, estimating motion from sparse events may be less dependable. Exam caveat: list mode alone does not guarantee a useful curve—frame duration and respiratory-bin choices must balance temporal resolution against counts per bin. Practical check: confirm that the scanner stores list-mode events, the respiratory trace is synchronized and retained, and TOF is enabled in the reconstruction protocol.