The presence of RF inhomogeneity in hyperpolarized 129Xe ventilation MRI affects quantitative analysis and interpretation. These inhomogeneities are commonly corrected using the N4ITK algorithm, which retrospectively calculates a smoothly varying bias field with non-uniform intensity normalization. However, this algorithm has not been rigorously validated for functional imaging. Here we show, using flip angle maps derived directly from 3D-radial acquisitions of ventilation, that N4ITK may over-correct bias field and remove inherent physiological gradients. We illustrate this comparison by a combination of simulation, phantom, and in vivo ventilation imaging.