The aim of this retrospective study was to determine, by dynamic acquisition
, the optimal scan time of 18
in patients with recurrent medullary thyroid carcinoma (MTC).
Twenty-one patients with suspected recurrent MTC underwent dynamic 18
(lasting 45 minutes) followed by whole-body scan. Three different time intervals of dynamic acquisition
were evaluated: ultra-early phase (2–5 minutes), early phase (5–10 minutes), and late phase (40–45 minutes). The number and SUVmax of all detected lesions among the 3 dynamic acquisition
phases were compared on qualitative and semiquantitative analyses. Time-activity curves, SUVmax washout rate between ultra-early or early phase and late phase, and signal-to-noise ratio (SNR) between lesion and background activity were also calculated.
At dynamic acquisition
, 15 of 21 patients were classified as PET-positive and 6 of 21 as PET-negative, with overall 21 detected lesions. Ultra-early and early imaging provided a better lesion visualization than late phase in more than 70% of cases, as also reflected by SNR (mean SNR reduction between 2 and 45 minutes, −45% ± 19%). Time-activity curves showed a rapid tracer accumulation in MTC lesions, with an average maximum uptake at 2 minutes after injection. Mean lesion SUVmax was 2-fold higher in ultra-early frames compared with last frames (mean washout rate, −44% ± 33%). Finally, compared with whole-body imaging in the same field of view, dynamic acquisition
identified 1 additional positive patient and 3 additional lesions in 2 patients.
Our study, showing a very fast 18
F-DOPA uptake in MTC lesions, suggests the utility to obtain early PET/CT
images, already at 2 to 5 minutes after tracer injection, when maximum lesion tracer uptake is reached.