Imaging Glossary

• B-value – Indicative of the timing/strength of gradients in diffusion MRI scans; higher b-values capture more information about diffusion at the cost of a higher signal-to-noise ratio; two b-vals (b1000 and b2000) are required for DKI

• dicom – the format in which MRI data is stored initially after acquisition

• Diffusion metrics

  • FA – fractional anisotropy; describes the degree to which diffusion within a voxel is isotropic (free diffusion in all directions) or anisotropic (highly aligned structures driving diffusion in a specific direction); 0 = completely isotropic, 1 = complete anisotropic

  • MD – mean diffusivity; describes the magnitude of diffusion

  • RD – radial diffusivity; describes the magnitude of diffusion perpendicular to a fiber tract

  • AD – axial diffusivity; describes the magnitude of diffusion parallel to a fiber tract

• Hyperintensity/hypointensity – a cluster of voxels at a markedly higher/lower intensity (appearing brighter) than those around it

• Intensity – the measure of tissues as reflected in the brightness or darkness of each voxel

• Kurtosis metrics - describe non-Gaussianity

  • MK (mean kurtosis)

  • AK (axial kurtosis)

  • RK (radial kurtosis)

• nifti – an MRI data format that compiles all dicoms in a sequence into a viewable 3D image

• Normalization – The process of warping an image or many images into a common space.

  • This may involve warping all images into an average space or, more often, warping all images into a standard space (such as MNI space)

• Preprocessing – the process of removing image artifacts and performing necessary corrections to raw MRI data; types of corrections performed during preprocessing

  • Denoising

  • Unringing

  • EPI Distortion Correction

• ROI - Region of interest; a specific part of the brain of interest to a specific analysis pipeline

• Registration – The process of spatially aligning 2+ images

• Sequence – The specific type of scan that was performed when the patient/participant was in the MRI scanner; eg. Diffusion weighted (DKI, DTI, FBI, etc), T1MPRAGE, T2 FLAIR, proton density (PD), MR spectroscopy (MRS), etc.

• T1 Weighted (T1W/MPRAGE) – high res anatomical image included is basically every scan ; white matter appears more light, grey matter appears more mid-ranged grey, CSF appears dark grey or black

• T2 Weighted (T2W/FLAIR)