HL-case:  PET-FDG.   Reconstruction artefact due to the Gross motion between timepoints #34 and #36.  It appears that at T#35 the reconstruction has combined the head signal from several grossly distant positions, resulting in blurred image and halo (well visible on left-top corner T#35).
This timepoint is too blurred to be motion corrected but result is reasonable. Everything else is motion corrected quite well.

HL - T#34 (2440 sec)

HL-T#35 (2740 sec)

HL- T#36 (3040 sec)