Positron Emission Tomography (PET) imaging systems used in Nuclear Medicine can suffer from loss of spatial resolution due to parallax effects, called radial elongation. A scintillation detector that allows depth-of- interaction (DOI) determination would be an important advance. Previous attempts were made to develop DOI scintillators for PET, but all of them had significant performance limitations. The goal of the proposed Phase I research is to demonstrate the feasibility of developing a novel DOI scintillator in which the decay time of the light emission varies continuously with depth. The material processing techniques will be used to form a continuous phoswich detector, which will create a structure where the decay time of the light emission varies continuously with depth. Our approach is likely applicable to a number of new scintillators that are actively under development because of their superior properties, as well as to other scintillators known to show dramatic variations in decay times with dopant concentration. A number of most likely candidates will be initially investigated. Scintillator fabrication and initial characterization will be performed at RMD, and tests pertinent to molecular imaging will be performed at our collaborator's facilities at the University of Arizona. Molecular imaging techniques are well suited for imaging radiolabeled antibodies and other substances that can be used to localize and characterize tumors, and are well suited to the development of new radiolabeled agents for diagnosing and treating diseases in humans. The development of this detector will significantly improve the resolution and sensitivity with which measurements can be made. In turn, this will encourage the development of superior drugs and technologies to diagnose, stage and treat to curtail the progression of and even cure certain cancers, diseases of the heart and disorders of the circulatory system. Outside medical imaging, the proposed development will have widespread applications in industrial radiography, nondestructive evaluations, homeland security, and advanced imaging systems. PUBLIC HEALTH RELEVANCE: Positron Emission Tomography (PET) imaging systems used in nuclear medicine can suffer from loss of spatial resolution due to parallax effects, called radial elongation. A scintillation detector that allows depth-of- interaction (DOI) determination would be an important advance. Previous attempts were made to develop DOI scintillators for PET, but all of them had significant performance limitations. The proposed research will demonstrate the feasibility of developing a novel DOI scintillator in which the decay time of the light emission varies continuously with depth. The successful completion of the research will lead to widespread applications in medical imaging, industrial radiography, nondestructive evaluations, homeland security, and advanced imaging systems. [unreadable] [unreadable] [unreadable]