Abstract: The disclosure provides phase-sensitive methods of radio frequency field mapping (e.g., B1 mapping), in which flip angle is encoded in the phase of a transverse magnetization produced by a series of RF pulses. The phase-sensitive methods can measure flip angle over a wider range than other methods such as double-angle methods. In one aspect, a phase-sensitive method of radio frequency mapping includes acquiring a first transverse magnetization phase measurement using an RF excitation pulse with flip angle 2? and acquiring a second transverse magnetization phase measurement using an RF excitation pulse with flip angle ?2?. The method also includes computing a phase difference between the two phase measurements and generating a radio frequency map based on the phase difference. The radio frequency map may be used, for example, to correct an image for variation in image intensity caused by B1 field inhomogeneity and correct T1 measurements for variations caused by B1 field inhomogeneity.

Abstract: The disclosure provides phase-sensitive methods of radio frequency field mapping (e.g., B1 mapping), in which flip angle is encoded in the phase of a transverse magnetization produced by a series of RF pulses. The phase-sensitive methods can measure flip angle over a wider range than other methods such as double-angle methods. In one aspect, a phase-sensitive method of radio frequency mapping includes acquiring a first transverse magnetization phase measurement using an RF excitation pulse with flip angle 2? and acquiring a second transverse magnetization phase measurement using an RF excitation pulse with flip angle ?2?. The method also includes computing a phase difference between the two phase measurements and generating a radio frequency map based on the phase difference. The radio frequency map may be used, for example, to correct an image for variation in image intensity caused by B1 field inhomogeneity and correct T1 measurements for variations caused by B1 field inhomogeneity.