Question Posted 03/09/17:

I'm trying to decide whether the DTI images acquired in ADNI2 will be suitable for my research. In order to qualify, I need an isotropic voxel size of 2 mm. From the protocol manuals, I see that the FOV is 35, frequency and phase are 128 each. From what I understand about MR images, voxel size = (FOV/frequency)*(FOV/phase)*slice thickness. This gives me 0.27*0.27*2.7 as the voxel size. I would like to get a confirmation if this is correct; and the images have anisotropic pixels?
Response posted 03/09/17 by ADNI MRI Core:
Thank you for your question to the ADNI MRI Core.

Your calculation is almost correct, but you are off by a factor of 10 because of a cm/mm mixup. The ADNI2 DTI resolution is 2.7x2.7x2.7mm. The resolution is isotropic, but the images were reconstructed with 1.35x1.35x2.7mm voxels (i.e. they were zero padded in x and y). If needed, the voxels can be binned into (2.7mm)^3 voxels without really losing anything.

ADNI3’s diffusion scan has isotropic 2.0 mm voxels, but it is just getting started.