PurposeDiffusion spectrum imaging (DSI) has been shown to be an effective tool for noninvasively depicting the anatomical details of brain microstructure. Existing implementations of DSI sample the diffusion encoding space using a rectangular grid. Here we present a different implementation of DSI whereby a radially symmetric q‐space sampling scheme for DSI is used to improve the angular resolution and accuracy of the reconstructed orientation distribution functions.MethodsQ‐space is sampled by acquiring several q‐space samples along a number of radial lines. Each of these radial lines in q‐space is analytically connected to a value of the orientation distribution functions at the same angular location by the Fourier slice theorem.ResultsComputer simulations and in vivo brain results demonstrate that radial diffusion spectrum imaging correctly estimates the orientation distribution functions when moderately high b‐values (4000 s/mm2) and number of q‐space samples (236) are used.ConclusionThe nominal angular resolution of radial diffusion spectrum imaging depends on the number of radial lines used in the sampling scheme, and only weakly on the maximum b‐value. In addition, the radial analytical reconstruction reduces truncation artifacts which affect Cartesian reconstructions. Hence, a radial acquisition of q‐space can be favorable for DSI. Magn Reson Med 76:769–780, 2016. © 2015 Wiley Periodicals, Inc.