Development and Application of PET-enabled Dual-Energy CT Imaging

University Of California At Davis, Davis CA

Investigators

Abstract

PROJECT SUMMARY Molecular imaging with hybrid positron emission tomography (PET) and x-ray computed tomography (CT) has been widely used in clinical applications. CT in PET/CT is typically operated with a single x-ray energy to provide anatomic localization and attenuation correction for PET. A major limitation of single-energy CT is its limited ability to characterize tissue compositions quantitatively. Dual-energy CT (DECT) fills this gap by employing two different x-ray energies to allow quantitative material decomposition. Combining DECT with PET may enable PET/CT for several applications that have been hitherto impossible or less feasible due to the lack of tissue composition information, for example, (i) for simultaneous PET and contrast-enhanced CT imaging where the presence of contrast media may compromise attenuation correction, and (ii) for PET imaging of bone marrow where neglecting the trabecular bone volume may underestimate tracer uptake in true bone marrow. Despite all the clinical potential, integration of DECT with PET/CT would require either a costly scanner hardware upgrade or a significant increase in radiation dose and scan cost. As a result, application of combined PET and DECT imaging has been largely hampered in molecular imaging with PET/CT. The PI and team have proposed a PET- enabled DECT imaging method. This method does not require a change of existing PET/CT scanner hardware or increase the radiation dose but exploits the inherent annihilation-photon attenuation property of a radiotracer to derive a 511 keV high-energy gamma-ray CT (gCT) image from a standard time-of-flight PET/CT emission scan. The enabling technique is the simultaneous reconstruction of the gCT image from the existing PET emission data, and the combination with low-energy x-ray CT (usually ≤140 keV) to form dual-energy imaging. Our preliminary work has demonstrated the feasibility of this PET-enabled DECT method for quantitative material decomposition using computer simulation and physical phantom studies. The goal of this R01 grant proposal is to further develop, validate, and translate this method in the context of PET/CT molecular imaging. We propose three specific aims to fulfill this goal: (1) Develop the technical approaches for gCT imaging with PET; (2) Evaluate the PET-enabled DECT method for material decomposition in human subjects; (3) Apply the method for metabolic PET quantification of bone marrow. Successful completion of these specific aims will establish an innovative PET-enabled DECT imaging method with broad applicability. The enabled or enhanced ability for quantitative material decomposition on PET/CT will open new avenues to improve molecular imaging. This project would make a significant impact in numerous clinical applications where the characterization of tissue composition matters, such as for bone-marrow PET/CT imaging or contrast-enhanced PET/CT in cancer, heart disease, and aging.