Measuring B1 distributions by B1 phase encoding

Kalina V. Jordanova

doi:10.1002/mrm.26114

2016-01-17

Kalina V. Jordanova *

Dwight G. Nishimura

Adam B. Kerr

DOI：10.1002/mrm.26114

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PurposeWe propose a method to acquire B1 distribution plots by encoding in B1 instead of image space. Using this method, B1 data is acquired in a different way from traditional spatial B1 mapping, and allows for quick measurement of high dynamic range B1 data. MethodsTo encode in B1, we acquire multiple projections of a slice, each along the same direction, but using a different phase sensitivity to B1. Using a convex optimization formulation, we reconstruct histograms of the B1 distribution estimates of the slice. ResultsWe verify in vivo B1 distribution measurements by comparing measured distributions to distributions calculated from reference spatial B1 maps using the Earth Mover's Distance. Phantom measurements using a surface coil show that for increased spatial B1 variations, measured B1 distributions using the proposed method more accurately estimate the distribution than a low-resolution spatial B1 map, resulting in a 37% Earth Mover's Distance decrease while using fewer measurements. ConclusionWe propose and validate the performance of a method to acquire B1 distribution information directly without acquiring a spatial B1 map. The method may provide faster estimates of a B1 field for applications that do not require spatial B1 localization, such as the transmit gain calibration of the scanner, particularly for high dynamic B1 ranges. Magn Reson Med 77:229-236, 2017. (c) 2016 Wiley Periodicals, Inc.

Keyword:

FIELD IN-VIVO

RADIOFREQUENCY FIELD

PULSES

CALIBRATION

ACCURATE

BEAR

MRI