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Abstract #0576

Estimating and eliminating excitation errors in bipolar gradient composite excitations caused by RF-gradient delay: example of bipolar spokes pulses in parallel transmission

Desmond H Y Tse1, Christopher J Wiggins2, and Benedikt A Poser1

1Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Netherlands, 2Scannexus BV, Maastricht, Netherlands

Parallel transmission of spokes pulses is a promising way of mitigating flip-angle inhomogeneity in 2D imaging at ultra-high-field MRI. Bipolar slice-selective gradient is often used to minimise the overall duration of these pulses, making them more resilient to off-resonance related artefacts, but they are prone to errors caused by RF-gradient timing mismatch. In this study, we present a mathematical description for the effect of such delay on bipolar-gradient composite excitations. We demonstrate the effect with both flip-angle maps and EPI images. Finally, we propose a navigator approach to estimate the delay and show two effective ways of eliminating these errors.

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