1. A method for correcting a positron emission tomography (PET) image, said method comprising: obtaining a magnetic resonance (MR) image dataset; classifying at least one object in the MR image as a bone; identifying a reference bone voxel in the MR image dataset; counting a number and distribution of neighbor bone voxels for the reference bone voxel; generating a MR-derived PET attenuation correction factor scaling for the reference bone voxel based on the number and distribution of neighbor bone voxels; and attenuation correcting a plurality of PET emission data using the MR-derived PET attenuation correction factors.