ZTE-based attenuation correction in head and neck PET/MR

Accurate attenuation correction (AC) is needed for PET/MR in head and neck cancer. Dixon-based AC is used in the clinical routine ignoring racial and vertebral bones. ZTE MRI, previously used to segment skull in brain applications, is used here to detect bone in MRI in 7 patients. To account for fat in the neck, a combined ZTE and Dixon-based AC map is considered as fat and water are separated on the Dixon fat and water MRI. CT acquired on the same patients and registered to ZTE image formed an AC gold-standard. PET images reconstructed with Dixon, ZTE and ZTE-Dixon AC maps are compared to CTAC PET image. SUVmean and SUVmax were compared in volumes of interest (VOI) drawn on physiological uptake in the PET images. Results showed that ZTE-AC and ZTE-Dixon AC performed similarly in regions located in bones such as mandible and maxilla. ZTE-Dixon AC showed a decreased error in regions with interface: mastoid process, pterygoid muscles and airways. However, ZTE-based AC methods still showed an error higher than Dixon AC in nasal cavities due to partial volume effect. Consequently, the hybrid ZTE and Dixon AC map showed promising results for head and neck PET/MR especially in regions surrounding bones.