The diffusion weighting followed an optimized scheme [21]
where the diffusion weightings were isotropically distributed along 54
directions. With the diffusion parameters d and D equal to 34 and 40ms
respectively, the b-value was 1150 , the optimum for white
matter DTI measurements. 6 diffusion-weighted volumes were acquired
with b-value 300
, and 6 volumes were acquired with no
diffusion weighting. Each volume covered the whole brain with 60
slices of 2.3 mm slice thickness, field of view
. An imaging matrix of 96 x 96 was used, giving isotropic voxels
of
and the images were reconstructed
on a
matrix, giving a final resolution of
. An optimized cardiac gating scheme
[21] was used to minimize artifacts arising from
cerebrospinal fluid pulsatile flow. The total scan time for the DTI
protocol was approximately (depending on heart rate) 20 minutes.
The high resolution T1 weighted scan was obtained with a 3D inversion
recovery prepared spoiled gradient echo (IR-SPGR). Parameters for the
acquisition were: FOV =
; matrix size =
; in-plane
resolution =
; 156 slices of 1.2mm slice thickness;
inversion time = 450ms; repetition time = 2s; echo time = 53ms.