Low-Afterglow CsI:Tl microcolumnar films for small animal high-speed microCT.

Dedicated high-speed microCT systems are being developed for noninvasive screening of small animals. Such systems require scintillators with high spatial resolution, high light yield, and minimal persistence to ensure ghost free imaging. Unfortunately, the afterglow associated with conventional CsI:Tl microcolumnar films used in current high-speed systems introduces image lag, leading to substantial artifacts in reconstructed images, especially when the detector is operated at several hundreds of frames per second. At RMD, we have discovered that the addition of a second dopant, Eu(2+), to CsI:Tl crystals suppresses the afterglow by as much as a factor of 40 at 2 ms after a short excitation pulse of 20 ns, and by as much as a factor of 15 at 2 ms after a long excitation pulse of 100 ms. Our observations, supported by theoretical modeling, indicate that Eu(2+) ions introduce deep electron traps that alter the decay kinetics of the material, making it suitable for many high-speed imaging applications. Here we report on the fabrication and characterization of CsI:Tl,Eu microcolumnar films to determine if the remarkable afterglow properties of CsI:Tl,Eu crystals are preserved in the CsI:Tl,Eu microcolumnar films. Preliminary results indicate that the codoped microcolumnar films show a factor of 3.5 improvement in the afterglow compared to the standard CsI:Tl films.

Multiple doping of CsI:Tl crystals and its effect on afterglow.

Despite the acknowledged advantages of CsI:Tl in many scintillator applications, a characteristic property that undermines its use in high-speed radiographic and radionuclide imaging is the presence of a strong afterglow component in its scintillation decay. This causes pulse pileup in high count-rate applications, reduced energy resolution in radionuclide imaging, and reconstruction artifacts in computed tomography applications. The research outlined here addresses the specific issue of suppressing the afterglow in CsI:Tl crystals by modifying them with codopants. In previous work we reported that one specific codopant, Eu(2+), was particularly effective in this regard, lowering the normalized intensity of the afterglow in the time range of 10 mus - 100 ms by almost two orders of magnitude compared to conventional material. We also found, however, that the extent of the suppressive effect was significantly influenced by the presence of additional additives, some of which were inadvertently introduced by the very material that provided the primary Eu codopant itself. The effects of these secondary codopants, which include elemental iodine and various oxidic species, are addressed in the present investigation.

Depletion of high-energy carriers in YAG optical ceramic materials.

The scintillation properties of YAG:Ce transparent ceramic material prepared by a hot-pressing technique have been characterized and compared with those of a chemically identical specimen of single crystal. Each of the scintillation steps (conversion, energy transfer and luminescence) has been selectively investigated using appropriate spectroscopic techniques. The light output from the ceramic specimen was measured at approximately 1500 photons/MeV, only 10% of that from the single crystal. This drastic decrease in the ceramic reflects the inefficient transfer of energy from the excited host to the Ce ion. The inefficiency can be attributed to the presence in the ceramic material of a high population of lattice defects, as demonstrated by the UV absorption spectra. Thermoluminescence experiments show that these defects can serve as sinks for free carriers (electrons and holes), providing sites for their nonradiative recombination and preventing them from conveying their energy to the emitting centers.

Health management education partnerships: more than technology transfer.

This article presents the reflections of three faculty members from New York University based on more than two years of experience in a health management education (HME) partnership with institutions in the Republic of Albania. The most significant point to be shared with colleagues considering similar initiatives in other countries is that aiding other professionals in developing health management education programs involves much more than the transfer of technical information among professionals. Based on experience in Albania, we argue that the development of viable management and policy analysis programs will require assistance to counterparts in Central and Eastern Europe in: (1) building constituencies for these activities among influential leaders and sustaining this support through changes in government; (2) providing models of and motivations for using styles of pedagogy that vary significantly from those now common in this part of the world; and (3) reconciling conflicts between pressures for investments in the largely hospital-based activity of health management and the largely public-health-based needs of relatively poor countries.

beta-Amyloid regulates gene expression of glial trophic substance S100 beta in C6 glioma and primary astrocyte cultures.

S100 beta, a calcium-binding protein synthesized by CNS astrocytes, has trophic effects in vitro (neurite extension and glial proliferation). In Alzheimer's disease and Down's syndrome, severely afflicted brain regions exhibit up to 20-fold higher levels of S100 beta protein, and astrocytes surrounding neuritic plaques exhibit highly elevated levels of S100 beta immunostaining. A major constituent of plaques, beta-amyloid, has been reported to have neurotoxic and neurotrophic effects in vitro. In our study we examined the responses of CNS glia to beta-amyloid. C6 glioma cells and primary rat astrocyte cultures were treated with beta A(1-40) peptide at doses up to 1 microM. Weak mitogenic activity, measured by [3H]thymidine incorporation, was observed. Northern blot analysis revealed increases of S100 beta mRNA within 24 h in a dose-dependent manner. Nuclear run-off transcription assays showed that beta A(1-40) specifically induced new synthesis of S100 beta mRNA in cells maintained in serum, but under serum-free conditions, there was a general elevation of several mRNA species. Corresponding increases of S100 beta protein synthesis were observed by immunoprecipitation of 35S-labeled cellular proteins. To evaluate whether this effect of beta-amyloid was mediated via neurokinin receptors or by calcium fluxes, various agonists and antagonists were tested and found to be ineffective at stimulating S100 beta synthesis. In sum, these in vitro data suggest that in neuropathological conditions, beta-amyloid itself is an agent which may provoke chronic gliosis and the production of trophic substances by astrocytes.

Improved access to care for the uninsured poor in large cities: do public hospitals make a difference?

This study compares the volume of uncompensated care provided to the uninsured poor in cities with public hospitals to that provided in cities without a public hospital in order to determine whether public hospitals increase access to care. Multiple regression analysis is used to control for selected variables that also influence utilization of hospital care. Cities with public hospitals were found to provide between 31 and 34 uncompensated adjusted admissions per 100 uninsured poor; in cities without a public hospital, 24 such admissions were provided. In the regression analysis the coefficients for dummy variables representing three types of public hospital governance structures were all positive and statistically significant. The coefficient measuring teaching commitment among a city's hospitals was also positive and statistically significant. This analysis suggests that local tax support for public hospitals does not merely offset philanthropic or other revenue sources for voluntary hospital uncompensated care but is also likely to increase the amount of uncompensated care offered. We also find that public hospital closures may reduce access to care for the uninsured poor in large cities.

Local simulations of alternative policies for financing services to the elderly.

Because of demographic, economic, and social pressures, it is likely that public programs benefitting the elderly population will be subject to much public debate and calls for the reform in the next few years. This paper presents an analysis of two prototypical reforms that are based on alternative views of government's role in caring for the elderly. One view focuses on means-testing as a method for restricting the role of government to caring for the poor. The second view focuses on universal standards of care for the poor. The purpose of the analysis is to assess the implications of these two alternative views of the role of government as the basis for altering public support for the elderly. The authors show that either view of government results in a redistribution of public resources so that basic medical care, long-term care, and food and shelter needs of all poor elderly are met. The redistribution, however, involves a large reduction of public support for healthy, non-poor elderly.

Factors associated with variation in financial condition among voluntary hospitals.

This article uses multiple regression analysis to identify factors which affect variations in the financial condition of voluntary hospitals in New York State. Six separate ratios are used to measure financial condition and 18 independent variables are considered. The factors affecting financial conditions were found to vary among dimensions of financial health, and different causal relationships were evident among hospitals in New York City than among those in the rest of the state.

A reconsideration of long-term-care policy.

This article describes current problems in the financing and delivery of long-term care, and assesses several proposals for reform. Proposed financing changes are found to differ in their objectives, with some reforms seeking to shift from greater to lesser government support, and others seeking to replace current public efforts with expanded entitlements. Organizational reforms hold promise of more equitable allocation of public expenditures for long-term care, but are not likely to reduce such spending. Thus difficult choices cannot be avoided.

Medicaid comes to Arizona: a first-year report on AHCCCS.

In October of 1982 the State of Arizona, which had no Medicaid program, initiated an experimental program of care to the indigent that combines elements of capitation and competition. This article describes the new program, explains why key political actors in Arizona reversed their earlier stand and enacted the program, and assesses the extent to which the expectations of various groups have been met during the program's first year of operation.

Differentiation of Candida stellatoidea from C. albicans and C. tropicalis by temperature-dependent growth responses on defined media.

C. stellatoidea differs from both C. albicans and C. tropicalis in its i) much greater growth differential on minimal and amino acid enriched media and ii) unique inability to grow on minimal medium containing glycerol as carbon source at 37C. The relative responses to amino acid enrichment occur on media containing either fermentative or oxidative carbon sources, at 25C or 37C. Under any given conditions of carbon source and temperature, different assortments of individual amino acids are stimulatory for each of the three species. All assortments include one or more members of the glutamic acid family. However, sulfur amino acids stimulate only C. stellatoidea on all three carbon sources. On minimal-glycerol medium, wild type strains of C. stellatoidea grow prototrophically at 25C but are auxotrophic for amino acids at 37C; the particular auxotrophies expressed vary from strain to strain. Slow growing, mycelial mutants, prototrophic on glycerol at 37C arise spontaneously in wild type strains at frequencies indicating nuclear gene mutation. Such mutants can be induced by both transition and frame shift mutagens. The implications of these observations for the taxonomic relationships between the three Candida species and for identification of C. stellatoidea in particular are discussed.

Financial viability of community health centers.

Local public officials have become greatly concerned about the impact of the continued demand for local subsidies for outpatient programs. This article examines two basic obstacles to the fiscal viability of inner city ambulatory programs, management practices and reimbursement policies. Findings are presented with respect to the relative importance of these obstacles and options are developed for the reform of existing subsidy programs.