 DSI Studio provides the simulation function for diffusion MR images. The user needs to provide a user-defined b-table (a text file) and to assign simulation parameters, including mean diffusivity, SNR, FA, and crossing angles. The simulation function is located at "Tools"->"Diffusion MRI simulation". The simulation generates .src file, which can be loaded into Matlab for further processing or used in diffusion MR reconstruction. Simulation Model The simulation model is based on mixed Gaussian model: E(q) = S0 *( F1 * exp(-b*D1) + F2 * exp(-b*D2) + F0 * exp(-b*D0) ) where S0 is the b0 signal; F0, F1 ,and F2 are the volume fractions of the background diffusion, the first fiber, and the second fiber, respectively; D0, D1 and D2 are the corresponding diffusion tensors. Rician noise is added to simulate the image noise pattern. More detailed description can be found in the references [1]. Layout of crossing fibers in the simulation  The background region simulates the free water diffusion.B-table To generate the simulation images. DSI Studio needs a text file that records the b-values and gradient vectors. The formate of the text file is as follows.
where the first column is the b-value, and the rest of the columns stand for the gradient unit vector. Exemplary tables can be found in the attachment at the bottom of this page. Reference: [1]F-C. Yeh, V. J. Wedeen, & W-Y. I. Tseng. “Generalized Q-Sampling Imaging.” IEEE Transaction on Medical Imaging, 29:1626-1635, 2010. |