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.

主权项

1. A method to determine a B1 phase map for at least two excitation modes of a radio-frequency (RF) coil arrangement of a magnetic resonance (MR) apparatus, said RF coil arrangement comprising multiple, independently controllable transmission channels, and said B1 phase map describing, with spatial resolution, a phase of a B1 field generated in a respective excitation mode, relative to a common reference phase map, said method comprising:
operating said MR apparatus to acquire first MR data describing a phase change of a basic magnetic field of the magnetic resonance apparatus between a first echo time and a second echo time of a data acquisition sequence; providing said first MR data to a processor and, in said processor, evaluating said first MR data to determine a spatially resolved Larmor frequency value that describes a deviation from a nominal Larmor frequency of the magnetic resonance apparatus; operating the magnetic resonance apparatus to acquire second MR data with one of said at least two excitation modes; providing said second MR data to said processor and, in said processor, generating a raw phase map therefrom, and calculating a correction phase map relative to the reference phase map and subtracting the correction phase map from the raw phase map, dependent on said Larmor frequency value and the echo times in the acquisition of the second MR data in order to obtain said B1 phase map; and making said B1 phase map available in electronic form at an output of said processor.