Pet ct scanner

The effect of hair was quantified for the subject shown in Fig. 2d–f who had hair clearly visible around the head. A manual ROI was drawn on each transverse slice of the CT to carefully remove the hair without removing any of the scalp. The PET scan of this subject, acquired on the mMR, was attenuation-corrected using the CT with the hair included and alternatively using the CT with the hair cropped out of the image.
The effect of hair was also indirectly assessed on 14 subjects as part of an evaluation of a state-of-the-art atlas-based MRAC method called MaxProb [6 (link)], undertaken at our institution. MaxProb outperformed the UTE and Dixon-based segmentation methods implemented on the mMR and was one of the best performing brain attenuation correction methods reported by Ladefoged et al. [12 (link)]. The method generates a pseudo-CT image through the registration of a database of aligned MRI and CT image pairs with a T1-weighted MRI image acquired as part of the PET-MR scanning protocol. Hair is not included in the pseudo-CT image—all pixels located outside the boundary between air and the patient’s scalp are assigned an LAC value of zero. For each subject, an image was generated of the percentage difference between a static PET image attenuation-corrected using the CT-derived μ-map from a GE PET CT scanner and an image reconstructed using a pseudo-CT generated by MaxProb.

The FDG-PET scans were acquired using a PET/CT scanner (GE Healthcare, Milwaukee, WI, USA) operating in 3D mode. Prior to injection, all participants were required to fast for a period of six hours. Participants were injected with ¹⁸F-FDG of ∼459 MBq (range 367–576 MBq). After injection, all participants were placed in a dimly lit room for 30 minutes, with minimal auditory stimulation. After the 30 minutes, an 8-minute scan was performed. FDG-PET consisted of four 2-minute dynamic frames acquired from 30 to 38 minutes after injection. PET sinograms were iteratively reconstructed into a 256-mm field of view (FOV). The pixel size was 1.0 mm and the slice thickness was 3.3 mm. Standard corrections were applied. Individual-level patterns of hypometabolism were assessed using a 3D stereotactic surface projections with CortexID Suite (GE Healthcare), whereby activity at each voxel was normalized to the pons and Z-scored to an age-segmented normative database. Average medial temporal and lateral temporal Z-scores (with negative scores representing hypometabolism) were calculated and compared between the left and right hemispheres. Participants were assigned to the lpSMD or rpSDM group based on the finding of at least 0.5 differences in medial and/or lateral temporal Z-scores between the left and right hemispheres.