Images acquired with variable nominal flip angle (VFA) can be combined with a map of the transmit field efficiency and a signal model to estimate the longitudinal relaxation rate, R1. However, if motion occurs between the acquisition of the VFA volumes the inherent assumptions of consistent receive field modulation and transmit field efficiency can be violated causing substantial errors in R1. Through in vivo experiment and simulation we show that the differential receive field modulation introduces the largest amount of error. We further show that the majority of the error can be mitigated with a simple, time efficient correction.
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