k-TE Generalized Autocalibrating Partially Parallel Acquisition (GRAPPA) for accelerated Multiple Gradient-Recalled Echo (MGRE) R₂* mapping in the abdomen

Multiple gradient-recalled echo (MGRE) methods are commonly used for abdominal R₂* mapping. Accelerated MGRE acquisitions would offer the potential to shorten requisite breathhold times and/or increase spatial resolution and coverage. In both phantom and normal volunteer studies, view-sharing (VS) methods, generalized autocalibrating partially parallel acquisition (GRAPPA) methods, and newly proposed k-echo time (k-TE) GRAPPA methods were compared for the purpose of accelerating MGRE acquisitions. Utilization of water-selective spatial spectral excitation pulses reduced artifact levels for both VS and k-TE GRAPPA approaches. VS approaches were found to be highly sensitive to off-resonance effects, particularly at increasing acceleration rates. k-TE GRAPPA significantly reduced residual artifact levels compared to GRAPPA approaches while improving the accuracy of accelerated abdominal R₂* measurements. These initial feasibility studies demonstrate that k-TE GRAPPA is an effective method to reduce scan times during abdominal R₂*-mapping procedures.