Fig. 6

A 62-year-old female patient with a 70-mm PDTC (pT3 Nx Mx) was referred for ¹⁸FDG PET/CT in November 2017 to explore a detectable serum Tg level under levothyroxine (11 ng/ml, without serum TgAb) 2 years after initial ¹³¹I treatment. Maximum intensity projection images (MIP) showed lymph node involvement of the left central compartment on both 3D-OSEM-reconstructed HN PET (a, blue arrow) and PSF_allpass-reconstructed HN PET (b, blue arrow). No abnormal ¹⁸FDG focus (score ≤ 3) was reported on 3D-OSEM-reconstructed HN PET in the left lateral compartment (at 10 min: SUVmax = 1.67, TBR = 1.19) (e). On the PSF_allpass-reconstructed HN PET data sets (f), a small focal ¹⁸FDG uptake in the left lateral compartment was scored as probably malignant (score 4) at 4–10 min (at 10 min: SUVmax = 2.43, TBR = 1.74), corresponding to a 6 × 4 mm lymph node on CT scan (c, red arrow). Left central and left lateral dissection was performed and confirmed lymph node involvement in both compartments. d The left lateral lymph node was massively invaded (black arrows). The size of the tumour deposit was 5 mm (HES staining, × 2.5)