Structural MRI methodology Sample Clauses

Structural MRI methodology. The effect of childhood abuse on brain structure was investigated in terms of regional grey matter volume and cortical thickness in cases and controls, with and without abuse exposure. This section describes the image acquisition, pre-processing of the MRI images and the statistical analyses used. 2.2.1 Acquisition of Structural MRI data All structural MRI data were acquired using a 3-Tesla GE Signa HDx MR System at the Centre of Neuroimaging Science, Institute of Psychiatry, Psychology and Neuroscience, King’s College London. For all scans an 8-channel head coil was used and head movement was limited by foam padding within the head coil. The structural scan acquired from each subject was a 3D T1-weighted, MPRAGE (magnetization-prepared rapid gradient-echo) volumetric scan in the sagittal orientation. The MPRAGE image has an image matrix size = 256x256x166, with in-plane voxel size = 1.02x1.02mm, slice thickness = 1.2 mm, echo time = 2.848ms repetition time = 6.988ms, inversion time = 650 ms, flip angle = 20°, one data average. The total acquisition time was 10 minutes. 2.2.2 Initial processing of structural images After acquisition, the images were checked for quality, movement and other artefacts using Statistical Parametric Mapping version 8 release 5263 (SPM-8-5263) (▇▇▇.▇▇▇.▇▇▇.▇▇▇.▇▇.▇▇/▇▇▇/▇▇▇▇▇▇▇▇/▇▇▇▇/), which is a widely used neuroimaging software package. The presence of artefacts was noted and used to inform subsequent analyses. The level of artefacts was graded on a scale from 1 to 3. Eight scans with a score of 2.5 or above were excluded from subsequent analyses. All images were re-oriented along the anterior and posterior commissures (AC-PC) line. The reorientation was automatically obtained and the outputs manually checked following the AC-PC line using ▇▇▇▇://▇▇▇▇▇▇▇.▇▇▇- ▇▇▇.▇▇▇.▇▇.▇▇/▇▇▇▇▇▇▇/▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇ as a guidance tool (▇▇▇▇▇://▇▇▇.▇▇▇▇▇▇▇▇.▇▇.▇▇/cgi- bin/wa.exe?A2=spm;5819d056.0810). Manual corrections of orientation were made when necessary. 2.2.3 Coding of childhood exposure for structural MRI analysis Irrespective of whether the measure of interest is either grey matter volume or cortical thickness, the power to detect structural abnormalities across groups is a function of group size (Lüders et al. 2002; ▇▇▇▇ et al. 2008; ▇▇▇▇▇▇ et al. 2010). Indeed in the presence of groups of small sample size, the power of the model decreases significantly reducing the possibility of detecting a true effect (type II error), in addition ...