18F-Choline PET imaging studies

One monkey (M6) and all three human PD patients underwent ¹⁸F-Choline PET imaging once BBB opening was confirmed on T1w-Gd images. Subjects were transferred to a hybrid PET-MRI scanner (mMR Biograph; Siemens, Erlangen) for PET acquisition, which started immediately following the intravenous injection of FCH radiotracer (~2 mCi in the monkey and ~5 mCi in humans). On average, ¹⁸F-Choline PET acquisition was started around 1 hour after finalizing the BBB procedure. Forty minutes of PET was acquired in list mode. PET emission data were reconstructed with an ordered subset-expectation maximization algorithm and corrected for attenuation using subject-specific multicompartment MR-based maps (58). PET activity between 10 and 40 min was reconstructed in a single frame and converted to standardized uptake value ratios (SUVr) taking a cerebellar mask as a reference region. Subsequently, several spherical regions of interest (ROIs) were drawn on a high-resolution T1w-Gd MRI showing enhanced contrast in the areas where the BBB was opened. For patients, ROIs were placed on the posterior putamen (radius, 5 mm), anterior caudate nucleus (radius, 5 mm), and substantia nigra (radius, 4 mm) bilaterally. For the monkey (M6), the defined ROIs were placed on the posterior putamen (radius 4 mm) and substantia nigra (radius 3 mm). SUVr were averaged in all ROIs, and ¹⁸F-Choline SUVr were normalized to contralateral (control) regions. In the case of bilateral targeting (HP02), ¹⁸F-Choline SUVr were normalized to the ipsilateral caudate region.