Feedback system with warm air

MRI was performed on a 7T Bruker (Billerica, MA) system with a 4-channel receive-only cryogen-cooled surface coil and a volume transmit coil (Bruker, Billerica, MA). T2-weighted images were acquired with a multi-spin echo sequence: TR 5100 ms, TE 10, 20, 30, 40, 50, 60, 70, 80ms, 56 contiguous axial slices of 0.3 mm thickness, FOV 19.2 mm x 19.2 mm, matrix size 256 3 128, 1 average, with a scan time of 11 min/mouse. During imaging, anesthesia for mouse was maintained at 1.5% isoflurane and rectal temperature was maintained at 37 ± 1 C using a feedback system with warm air (SA Instruments, Stony Brook, NY). Only female animals were used for this time point (11 months). The regional and voxel differences in the brain structure were evaluated by registration-based region of interest (ROI) analysis. In brief, multiple echo images were averaged and corrected for field inhomogeneity to maximize the contrast to noise ratio and the images were analyzed based on a 20-region pre-defined in-vivo mouse atlas (http://brainatlas.mbi.ufl.edu/) that was co-registered to a study template and warped to individual mouse datasets. All the co-registration steps were performed in SPM8 (Wellcome Trust Centre for Neuroimaging, UCL, UK). The ROI volumes were normalized to whole brain volumes to minimize any genotype differences associated with size of the animals.

Longitudinal MRI study was performed on Tau-P301S and nonTg female mice (n=10 each group) by imaging animals at 6, 9 and 12 months of age using a 9.4T Varian/Agilent (Agilent Technologies) system with a 30 mm inner-diameter transmit/receive volume coil. The animals were anesthetized using 3% isoflurane and placed in a custom-built head holder with a tooth bar. During imaging, anesthesia was maintained at 1.5% isoflurane. Rectal temperature was monitored and maintained at 37 ± 1 C using a feedback system with warm air (SA Instruments). T2-weighted images were acquired using a multi-spin echo sequence with TR=6000 ms, TE ranged from 10 -80 ms for 8 echoes with a spacing of 10 ms, 56 axial slices of 0.3 mm, FOV 19.2 mm x 19.2 mm, matrix size 128 x 96 (zero-filled to 128 x 128), 2 signal averages, with a scan time of 19 min.