Fig. 3.

(a) Representative image of regional gas fraction in the lung, with non-dependent (ND), middle (M), and dependent (D) regions-of-interest shown within the imaged lung field (outlined in green). (b) ¹⁸F-FDG activity within the first minute of tracer infusion: ¹⁸F-FDG is clearly visible within the right heart (RH, outlined in blue) but not yet distinguishable in the lung. (c,d) The delay required for tracer transport from the right heart to the lungs was evident in the early (<2 min) tracer kinetics, as the activity in the right heart (blue dashed lines) began to rise earlier than the activity in non-dependent (c) or dependent (d) lung regions (green lines). By accounting for tracer transport delays through inclusion of a delay of the right heart plasma function as a model parameter (t_delay), the delayed plasma function in the ROIs (red lines) coincided much more closely with the initial rise in activity of those regions