Reduced Afterglow Scintillator Films for High Speed Medical Imaging

DESCRIPTION (provided by applicant): While many exotic new scintillation materials are now being developed, few even come close to CsI:Tl in performance and versatility. Widely available commercially at low cost, CsI:Tl not only has superb scintillation ef ficiency, but also can readily be fabricated as large-area microcolumnar films for high-resolution imaging, making it the material of choice for a wide range of applications. Unfortunately, CsI:Tl exhibits both a strong afterglow component in its scintilla tion decay and severe hysteresis after prolonged irradiation, limiting achiev- able energy resolution and imaging quality and speed. These shortcomings effectively preclude its use in applica- tions such as radionuclide imaging and medical CT, where its lo w cost could otherwise have immense economic impact. An improved form of CsI:Tl scintillator can reduce the cost of critical life-saving medical equipment such as X-ray CT scanners, fluoroscopy systems and other devices that rely on rapid data acquisition. In systematic studies of the cooperative effects of codopants in CsI:Tl, we have identified additives that can suppress its afterglow by as much as two orders of magnitude while maintaining its extraordinary scintillation properties. We also find that sim ilar treatment can diminish hysteresis by more than a factor of ten, represent- ing a major breakthrough that has eluded researchers for decades. Moreover, we have clearly established that, through a co-evaporation technique, we can deposit thick microcolu mnar films of this modified material, which provide very high spatial resolution appropriate for such new and exciting applications as nanoSPECT and high-speed cone-beam CT using flat panel detectors. With these exceptional properties, codoped CsI:Tl is now poised for exploitation in many rapid imaging modalities from which CsI:Tl had been previously excluded. But while we have achieved all these desirable effects in melt-grown crystals, we have not yet combined them at satisfactory levels at a single fil m composition; this is the specific goal of Phase I. Having already established the feasibility of the multicomponent deposition process itself, we will reach this goal through careful and system- atic variation of deposition parameters such as source and substrate temperatures, source-substrate distances, and chemical make-up of the sources themselves. Phase I will produce material with scintillation properties at least as good as in melt-grown single crystals, thereby becoming immediately useful for comme rcial evaluation. Phase II has far more comprehensive goals than Phase I. Here we will seek to optimize the material in terms of both chemical composition and physical morphology. In addition, guided by the results of Phase I and input from substantial new theoretical support, we will seek to understand both the mechanisms responsible for the observed effects and the kinetic factors that govern the deposition process itself. Cognizant of their ultimate applications, we will grow microcolumnar films of vario us dimensions ranging from 5 x 5 cm2 to 50 x 50 cm2, and demonstrate their utility by evaluating film performance in CBCT and SPECT modes of operation. Finally, we will promote commercialization through cooperative programs with potential users of this tec hnology. PUBLIC HEALTH RELEVANCE: The widely available, low cost CsI:Tl not only has superb scintillation efficiency, but also can readily be fabricated as large-area microcolumnar films for high-resolution imaging, making it the material of choice for a w ide range of applications. Unfortunately, CsI:Tl exhibits both a strong afterglow component in its scintillation decay and severe hysteresis after prolonged irradiation, limiting achievable energy resolution and imaging quality and speed. These shortcoming s effectively preclude its use in applications such as radionuclide imaging and medical CT, where its low cost could otherwise have immense economic impact.