Intera quasar scanner

The participants were scanned using a 3-T Intera Quasar scanner initially, followed by a 3-T Achieva Quasar Dual scanner, both manufactured by Philips Medical Systems, Best, The Netherlands. There was no alteration in acquisition parameters for T1-weighted sequences for both the scanners: TR = 6.39 ms, TE = 2.9 ms, flip angle = 8°, matrix size = 256 × 256, FOV = 256 × 256 × 190, and slice thickness = 1 mm with no gap between; yielding 1 × 1 × 1 mm³ isotropic voxels. The use of different scanners was due to reasons beyond investigator’s control and any systematic bias arising from the scanner change is unlikely given that participant recruitment was random. In fact, there were no significant differences in cortical features found between the two scanners in the Sydney MAS cohort (18 (link)). Even though there were some cohort differences across the two scanners (at age scan: scanner 1 = 77.9, scanner 2 = 79.0, p = 0.003; years of education: scanner 1 = 11.4, scanner 2 = 12.2, p = 0.013; male/female ratio: scanner 1 = 125/160, scanner 2 = 120/137, p = ns; the final selection of subjects in Section 2.2 are part of this larger cohort), previous studies have suggested that when vendor, field strength, and acquisition parameters remained unchanged, data collected during scanner upgrades could be pooled (19 (link)).