Increasing robustness of radial GRASE acquisition for SAR-reduced brain imaging

Purpose: To improve a radial multi-slice 2D gradient- and spin-echo (GRASE) sequence and provide an appropriate image reconstruction technique for SAR-reduced high-resolution neuroimaging. Methods: Additional readout gradients per radio-frequency (RF) refocusing allow for a reduced number of RF pulses. In this way, a specific absorption rate (SAR) reduction is achieved and the application at high-field systems becomes more feasible. A phase insensitive image reconstruction is proposed to reduce signal dropout artifacts originating from opposite readout polarities. In addition, the image reconstruction allows for the calculation of images with varying contrast from one measurement. Results: Results obtained at 3 T and 7 T demonstrate a SAR-reduction of at least 66% for a single-slice experiment with radial GRASE. The reduced SAR is used for an increased spatial coverage without increasing the measurement time. Experiments at 3 T and 7 T showed that the visual image quality is comparable to standard TSE and GRASE sequences with the same measurement parameters. Using higher EPI factors and the presented image reconstruction, artifact-free images with a significant SAR-reduction can be achieved. Conclusion: Radial GRASE enables SAR-reduced acquisitions of high-resolution brain images with different contrasts from one measurement and is a promising sequence for high-field neuroimaging.