Investigation of the influence of B0 drift on the performance of the PLANET method and an algorithm for drift correction.

PURPOSE: The PLANET method was designed to simultaneously reconstruct maps of T1 and T2 , the off-resonance, the RF phase, and the banding free signal magnitude. The method requires a stationary B0 field over the course of a phase-cycled balanced SSFP acquisition. In this work we investigated the influence of B0 drift on the performance of the PLANET method for single-component and two-component signal models, and we propose a strategy for drift correction. METHODS: The complex phase-cycled balanced SSFP signal was modeled with and without frequency drift. The behavior of the signal influenced by drift was mathematically interpreted as a sum of drift-dependent displacement of the data points along an ellipse and drift-dependent rotation around the origin. The influence of drift on parameter estimates was investigated experimentally on a phantom and on the brain of healthy volunteers and was verified by numerical simulations. A drift correction algorithm was proposed and tested on a phantom and in vivo. RESULTS: Drift can be assumed to be linear over the typical duration of a PLANET acquisition. In a phantom (a single-component signal model), drift induced errors of 4% and 8% in the estimated T1 and T2 values. In the brain, where multiple components are present, drift only had a minor effect. For both single-component and two-component signal models, drift-induced errors were successfully corrected by applying the proposed drift correction algorithm. CONCLUSION: We have demonstrated theoretically and experimentally the sensitivity of the PLANET method to B0 drift and have proposed a drift correction method.