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Abstract #3145

Overcoming the SAR limitation of magnetization transfer pulses at 7 Tesla using parallel transmission

Bastien Guerin 1 , Jonathan R Polimeni 1 , Thomas Witzel 1 , and Lawrence L Wald 1,2

1 Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 2 Division of Health Sciences Technology, Harvard-MIT, MA, United States

Magnetization transfer (MT) pulses are useful for background reduction in time-of-flight angiography but are difficult to deploy at high fields because of their high specific absorption rate (SAR). We design MT pulses at 7 Tesla with improved saturation performance by control of SAR using parallel transmission (pTx). A first performance improvement is obtained by constraining local SAR in the pulse design using the virtual observation point concept. Saturation performance at constant SAR is further improved by irradiating multiple frequencies simultaneously. Indeed, as in Simultaneous Multi-Slice, this allows the design algorithm to better control local SAR using SAR hopping between frequencies.

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