Susceptibility Weighted Imaging (SWI) has many applications. One crucial step of SWI is background phase error removal that typically involves smoothing either before or after phase unwrapping. Both approaches may have to face difficulties when large isolated phase loops (around poles or singularities) are present in the image. In this work, background correction with phase diffusor (BACOPSOR) is introduced. It is straightforward to implement and has a desirable immunity to phase loops. Application of BACOPSOR to SWI has been demonstrated with in vivo data.