In vivo MRI
Twelve week-old male C57BL/6 mice (Jackson Laboratories) were initially anesthetized with ketamine/xylzaine and then maintained on isofluorane for the duration of the imaging experiment.

Ex vivo MRI
Twelve week-old male C57BL/6 mice were sacrificed by an overdose of halothane (Sigma) according to procedures approved by the UCLA Animal Research Committee. The animals were intracardially perfused using a Minipuls II peristaltic pump (Gilson) at very low pressure with chilled PBS for approximately two minutes and FormaldeFresh (Fisher) for 15 minutes. The animals were decapitated, soft tissue removed, and the skulls were post-fixed in FormaldeFresh for 16 hours and then scanned.

Blockface and Histology
The brains were removed from post-fixed skulls and further post-fixed in FormaldeFresh for 16 hours. After post-fixation the brains were dipped in a mixture of india ink (Pelikan) and 5% gelatin (Sigma) to simplify segmentation of tissue from background later. The brains were cryoprotected in a solution of 20% sucrose for 16 hours to prevent freezing artifacts. The brains were then embedded in OCT compound (Sakura) at 4° C and snap-frozen at -70° C in a 2-methylbutane/dry ice bath.