Autocalibrated multiband CAIPIRINHA with through‐time encoding: Proof of principle and application to cardiac tissue phase mapping

PURPOSE: In conventional multiband (MB) CAIPIRINHA, additional reference scans are acquired to allow the separation of the excited slices. In this study, an acquisition-reconstruction technique that makes use of the MB data to calculate these reference data is presented. The method was integrated into a 2D time-resolved phase-contrast MR sequence used to assess velocities of the myocardium. METHODS: The RF phases of the MB pulse are cycled through time so that consecutive cardiac phases can be grouped to form reference scans at a lower temporal resolution. These reference data are subsequently used to separate the original slices at the original, high temporal resolution using slice/split-slice GRAPPA algorithms. Slice separation performances are evaluated and compared with conventional methods at 3 T, and 3 different strategies for the calibration of the kernels are proposed and compared. Finally, 6 subjects were scanned to assess velocities of the myocardium. RESULTS: Because the acquisition of external references is not needed, no additional breath-holds are required and the full MB acceleration could be exploited. Because the reference and MB data have the same resolution and phase structure, better slice separation was achieved when comparing the proposed technique to conventional workflows. Finally, time-resolved velocities of the myocardial tissue were successfully quantified from MB data, showing good agreement with single-band measurements. CONCLUSION: Our built-in reference method allows the full exploitation of the MB acceleration and it limits the number of breath-holds.