Signal interferences in Actual Flip Angle Imaging (AFI) of polyvinylpyrrolidone (PVP) solutions

Motivation: Polyvinylpyrrolidone (PVP) solutions have dielectric properties similar to human tissue and therefore are widely used for validating electromagnetic simulations in phantoms. For validating the flip angle in such applications, actual flip angle imaging (AFI) is highly suitable. Goal(s): This work investigates measurement errors of AFI with PVP solutions. Approach: Different PVP/H2O ratios are investigated at 3T, with different RF-spoiling phase increments, and with NMR spectroscopy. Results: NMR spectra show the existence of off-resonant PVP signals. Integrating two isochromat ensembles with different frequencies into an EPG-simulation qualitatively explain the measured signals and resulting flip angle errors in AFI. Impact: Understanding the cause of unexpected measurement errors of actual flip angle imaging with polyvinylpyrrolidone solutions will improve their use for the validation of new B1+ mapping techniques or new transmit arrays.