Brainpet

All participants completed a scanner training protocol that included the option to view videos demonstrating procedures associated with a simultaneous PET–MRI scan at the Athinoula A. Martinos Center for Biomedical Imaging and included a training scan onsite, following our published protocol [30 (link)]. We have previously obtained high-quality data using this training protocol in individuals with ASD [15 (link)]. Participants were scanned using the Siemens BrainPET, a head-only PET camera inserted inside a 3 Tesla TIM Trio MR scanner and a head-only 8-channel receive MR radiofrequency coil. A multi-echo magnetization prepared rapid acquisition gradient echo (MEMPRAGE) T1-weighted structural scan with volumetric navigator-based prospective motion correction [31 (link)] was acquired (TR = 2530 ms, TE[1–4] = 1.66 ms, 3.53 ms, 5.4 ms, 7.27 ms, FOV = 280 mm, flip angle = 7 deg, voxel size = 1 mm isotropic). [¹¹C]PBR28 PET was synthesized onsite by the Martinos Center radiopharmacy using methodology described previously [15 (link)]. A licensed nuclear medicine technologist administered ~15 mCi of [¹¹C]PBR28 to participants as a slow bolus injection through an intravenous catheter in an arm or hand vein outside of the scanner (see Table 1).

The amino acid FET was produced and applied, as described previously [33 (link),34 (link)]. All patients underwent a dynamic FET PET scan from 0 to 50 min post-injection of 3 MBq of FET per kg body weight on a high-resolution 3 T hybrid PET/MR scanner (BrainPET, Siemens Medical Systems, Inc., Erlangen, Germany) [35 (link)]. Image data were corrected for random and scatter coincidences, as well as dead time and isotope decay, before ordinary Poisson ordered subset expectation maximization (OSEM) reconstruction using software provided by the manufacturer (2 subsets, 32 iterations). The reconstructed dynamic dataset consisted of 16 time frames (5 × 1 min, 5 × 3 min, 6 × 5 min). Since the hybrid PET/MR scanner did not provide a transmission source, attenuation correction was performed by a template-based MRI approach [36 (link)].