Abstract #4500

Removing bias and increasing dynamic range in DREAM flip angle mapping at 7T

Gunther Helms^1,2, Hampus Olsson¹, and Mads Andersen^2,3

¹Clinical Sciences Lund, Medical Radiation Physics, Lund University, Lund, Sweden, ²National 7T Facility, Lund University, Lund, Sweden, ³Philips Danmark A/S, Philips Healthcare, Copenhagen, Denmark

DREAM is an ultra-fast multi-slice B1+-mapping technique based on the single-shot STEAM sequence. To study noise and bias related to slice-profiles, DREAM B1+-maps at 3.75mm resolution were acquired at 7T in phantoms and in human brain with nominal flip angles (FA) between 20° and 90° of the two STEAM preparation pulses. B1+ was decreasing at actual FAs above 50°; noise became apparent at actual FAs below 20° reducing dynamic range. By varying the preparation FA, this reliable range (20°<FA<50°) is shifted over a B1+ range from 20% to 250%. The FA map is constructed from overlapping B1+ maps after thresholding.

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