Phase retrieval is required for achieving artifact-free x-ray phase-sensitive 3D imaging. A phase-retrieval approach based on the phase-attenuation duality with high energy x-rays can greatly facilitate for phase sensitive imaging by allowing phase retrieval from only one single projection image. The previously derived phase retrieval formula is valid only for small Fresnel propagator phases corresponding to common clinical imaging tasks. In this work we presented a new duality-based phase retrieval formula that can be applied for cases with large Fresnel propagator phases corresponding to high spatial resolution imaging. The computer simulation demonstrated superiority of this new formula over the previous phase retrieval formula in reconstructing the high frequency components of imaged objects. A modified Tikhonov regularization technique has been devised for phase retrieval in cases of very high resolution and large object-detector distance such that some Fresnel propagator phases may be close or greater than π. This new phase retrieval formula lays the foundation for implementing high-resolution phase-sensitive 3D imaging of soft tissue objects. © 2009 Optical Society of America.