Digital detectors based on complementary metaloxide-semiconductors (CMOS) active pixel sensor (APS) technology have been introduced recently in many scientific applications. This work is focused on the X-ray performance evaluation of a novel CMOS APS detector in low energy medical imaging applications using monochromatic synchrotron radiation (i.e. 17-35 keV), which also allows studying how the performance varies with energy. The CMOS sensor was coupled to a Thallium-activated structured cesium iodide (CsI:Tl) scintillator and the detector's X-ray performance evaluation was carried out in terms of sensitivity, presampling modulation transfer function (pMTF), normalized noise power spectrum (NNPS) and the resulting detective quantum efficiency (DQE). A Monte Carlo simulation was used to validate the experimentally measured low frequency DQE. Finally, the effect of iodine's secondary generated K-fluorescence X-rays on pMTF and DQE results was evaluated. Good agreement (within 5%) was observed between the Monte Carlo and experimentally measured low frequency DQE results. A CMOS APS detector was characterized for the first time over a wide range of low energies covering the mammographic spectra. The detector's performance is limited mainly by the detectability of the scintillator. Finally, we show that the current data could be used to calculate the detector's pMTF, NNPS and DQE for any mammographic spectral shape within the investigated energies.
Summary.There is a clear gulf between the capabilities of modern synchrotrons to deliver high photon fluxes, and the capabilities of detectors to measure the resulting photon, electron or ion signals. While a huge investment has been made in storage ring technology, there has not to date been a commensurate investment in detector systems. With appropriate detector technology, gains in data rates could be 3 to 4 orders of magnitude in some cases. The US community working in detector technology is under-funded and fragmented and works without the long term funding commitment required for development of the most advanced detector systems. It is becoming apparent that the US is falling behind its international competitors in provision of state-of-the-art detector technology for cutting edge synchrotron radiation based experiments.There is thus an urgent need for a coordinated national program in detector research and development for synchrotron radiation research. Several new technologies are becoming available that could revolutionize the capabilities of detectors. One of the most important advances is the massive integration of parallel electronics into detectors on a pixel by pixel basis. Such detectors have the capability not only to work at very high rates, in some cases approaching 1 THz, but to include 'smart processing' of information on chip. Other important areas include the revolution in low temperature xray detectors capable of high energy resolution, and, if used in the form of arrays, potentially high counting rates. The science enabled by such detectors will be spread across the whole spectrum of synchrotron radiation research. For example, the study of the 3d structure of systems with short-range order using x-ray fluorescence holography (XFH), microsecond dynamics in polymers and magnetic systems studied using photon correlation spectroscopy, environmental chemistry studied using fluorescence yield micro-XAS, the study of chemical and electronic structure via photoemission and xray emission, and many more areas will be revolutionized by the use of advanced detectors.The principle conclusions of a national Workshop on Detectors for Synchrotron Radiation held in Washington, DC, Oct. 30 -31 st 2000, were that:•Funding of advanced detectors is the most cost effective way of increasing the effectiveness of both existing and planned future synchrotron facilities • Funding agencies should make provision for use of the most advanced present-day detectors on existing facilties; there are examples of multi-million dollar 3 rd generation beamline facilities with 1 st generation detectors.• There should be a nationally coordinated program to provide funding of long-range strategic research in a number of highlight areas.• An organization modeled after the successful BioSync dealing with biological applications of synchrotron radiation, "DetectorSync" should be formed to coordinate the area of detector research, and to represent the communities needs to funding agencies.In this document we point out general area...
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