 |
 |
Hi Marc, If all your bvecs have the same norm "n", then the estimate of the ADC will be ADC/n^2. This means that if the norm of the bvecs is higher than 1, you will underestimate ADC (and MD, L1,2,3). It shouldn't affect FA though.. if the bvecs have different norms, then it is not easy to predict what will happen. Note that from FSL3.3 onwards, both dtifit and bedpostx automatically normalise the bvecs. Cheers, Saad. On 11 May 2009, at 16:46, Marc Dubin wrote: > Dear FSL Users, > > Does anyone know the consequences of not normalising all directions > in the bvecs file? > Mine all have magnitude 2 and I was wondering if this might have > somehow inverted the > magnitude of fractional anisotropy in the dtifit output. > > Best, > Marc > > -- > Marc Dubin, MD PhD > Clinical Research Fellow > Brain Imaging Laboratory > NYSPI & Columbia University > > Office: 212-543-6702 > Mobile: 646-831-8886 Saad Jbabdi Oxford University FMRIB Centre JR Hospital, Headington, OX3 9DU, UK +44 (0) 1865 222545 (fax 717) www.fmrib.ox.ac.uk/~saad