Advanced Diffusion Acquisition

Target Audience: Methodologically oriented scientists interested in accelerating the acquisition of diffusionweighted data using multiband/simultaneous multi-slice techniques. Outcome/Objectives: The presentation will explain how to acquire and reconstruct multiband images with diffusion weighting. The audience should understand the additional constraints imposed by performing diffusion-weighting as compared to the application of multiband acquisition for T ∗ 2 -weighted EPI, in particular with respect to limited total echo time and the effects of eddy currents and motion. Current applications of multiband DWI in the human connectome project and elsewhere will be explained. The audience should also gain insight into how to perform high resolution DWI with multiband techniques, and the possibility of reducing power deposition using PINS radio-frequency pulses. Purpose: Multiband imaging techniques offer significant reductions in acquisition time for DWI imaging. In the standard application of DW-EPI TR values in excess of 10s are often reported in applications such as DWI of the human head at high spatial resolution. Methods: Multiband imaging is implemented by modifying the RF pulses used in the DWI sequence. This is generally done by adding RF pulses, each of which has a an additional linear phase gradient corresponding to the desired frequency offset [12]. The SAR of the resultant multiband pulse is proportional to the number of superposed pulses. The peak voltage can be reduced by optimising the phase of the pulses [10], or by shifting them in time [7]. Total SAR can be reduced by the application of PINS RF pulses that periodically excite a potentially infinite number of slices [13]. The blipped version [16] of the CAIPIRINHA technique [2] makes