Summary of current challenges for DT imaging

	Current Challenges	Current Solutions	Future Directions
Acquisition	Low resolution		Higher static/gradient field
			PROPELLER
			Parallel acquisition
	Distortions by EPI	Postprocessing corrections	PROPELLER
			Parallel acquisition
	Cardiac/CSF pulsation	Cardiac triggering	Cardiac triggering in routine practice
	Robust estimate of the DT	More averages	Higher static field
			Optimized sequence parameters
			Increased number of DW directions
Postprocessing and analysis	Subjectivity of the ROI approach	Training of the neurologist	Registration to standard space
		Histogram analysis
	Correlations of DT derived metrics with clinical histopathology	ROI and histogram analysis of MD and FA maps	Include analysis of eigenvalues
			Focus on systems that have a functional significance (ie, specific fiber tracts)
			Voxel based assessment after normalization to standard space to avoid a priori hypotheses
Acquisition and analysis	Crossing/merging fibers		Multicompartment models
			Q-space formalism
			High angular resolution

Note:—PROPELLER indicates periodically rotated overlapping parallel lines with enhanced reconstruction; EPI, echo-planar imaging; DT, diffusion tensor; DW, diffusion-weighted; ROI, region of interest; MD, mean diffusivity; FA, fractional anisotropy.