Fingerprinting Orientation Diffusion Functions in Diffusion MRI detects smaller crossing angles

Vancouver Convention Centre 

Higher Angular Resolution Diffusion Imaging (HARDI) methods, such as Diffusion Spectrum Imaging (DSI[1]) and multishell Q-ball imaging[2] are robust tools for studying in vivo white matter architecture. These methods capture the complex intravoxel crossings [1] in Orientation Distribution Functions (ODFs). To use these ODFs in tractography algorithms the fiber directions in each voxel must be identified. Limited angular resolution and intrinsic ODF peak width [3] make it however difficult to correctly estimate fiber directions when the relative angle between the bundles is small [4,5]. Most methods fail to detect crossing angles less than 40° [4,5]. Even after deconvolving the ODFs with a Fiber Response Function, it remains difficult to reliably detect crossing angles smaller than 30°[6].
Here we propose a new approach inspired by key concepts first introduced in MR Fingerprinting [7,8]. Instead of a dictionary with spin evolutions at different T1 and T2 relaxation times, we generate a library of ODF-fingerprints and identify the fiber directions of ODFs by assessing the similarity between the measured data and the elements in our library (Fig 1a). We demonstrate this method on both simulated and in vivo measured ODFs.