Exploring the relation between MR ZTE intensity and tissue density: Application to MR attenuation correction in PET/MR

One of the challenges of PET/MR is replacing CT-measured attenuation map with a MR-based, especially in the absence of bone signal in MR images. Regular MRI cannot distinguish between different tissue types based on electron density, thus, Zero Echo Time (ZTE) has been used to segment bone, air and soft tissue. In this study, we have evaluated the relationship between bone density measured in CT and signal intensity measured in ZTE on an CT-MR database of 16 patients. A linear relationship has been found on bone voxels between normalized ZTE intensity and CT density in Hounsfield Unit (HU). Using this relationship, we can derive patient-specific pseudo-CT from ZTE images.