Constrained analysis of b-tensor encoding diffusion data with multiple echo times allows estimation of compartment-specific T2 relaxation times in white matter.

We used b-tensor encoding and multiple echo times to estimate the separate T2 relaxation times and apparent fractions of white matter compartments. Nineteen elderly subjects were imaged, and data were analyzed using a constrained ‘ball-and-stick’ diffusion-relaxation model. Results show that the ‘ball’ T2 relaxation time is inversely related to the fraction of ‘sticks’ in white matter lesions, and that the ‘stick’ T2 relaxation time may be sensitive to the axonal diameter. The approach could be useful to characterize white matter damage.