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Abstract #4500

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

Gunther Helms1,2, Hampus Olsson1, and Mads Andersen2,3

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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