Phase Gradient Mapping (PGM) for Positive Contrast Generation

Introduction: Detecting paramagnetic contrast agent in vivo can be used in many applications such as cell tracking. Traditional T2-weighted sequence generates a signal loss appearing as a dark spot, referred to as negative contrast, at the site of paramagnetic contrast agent. Recently, there have been many efforts [1,2] to generate a positive contrast image by modifying pulse sequences. Liu et al [3] proposed a post-processing method referred to as the SGM (Susceptibility Gradient Mapping) without pulse sequence manipulation. In this study, a new post-processing method, referred to as PGM (Phase Gradient Mapping), is proposed to obtain a positive contrast image. The proposed method is different from the SGM in that the SGM measures a susceptibility induced echo-shift in the k-space, whereas the PGM does so in the image space by measuring the derivative of a phase map.