Method and magnetic resonance apparatus to determine a B1 phase map

摘要

In a method to determine a B1 phase map for at least two excitation modes of a radio-frequency coil arrangement of a magnetic resonance apparatus, the radio-frequency coil arrangement having multiple independently controllable transmission channels, and the B1 phase map describing, with spatial resolution, the phase of radio-frequency field this is generated in a respective excitation mode relative to a common reference phase map, first magnetic resonance data describing the phase change of a basic magnetic field of the magnetic resonance apparatus between a first echo time and a second echo time are acquired, and are evaluated to determine a spatially resolved Larmor frequency value that describes the deviation from a nominal Larmor frequency of the magnetic resonance apparatus. To correct raw phase maps derived from second magnetic resonance data acquired using a respective one of the excitation modes, a correction map, determined relative to the reference phase map, is calculated and subtracted from the raw phase map under consideration of the Larmor frequency value and the echo times in the acquisition of the second magnetic resonance data.