Europium-doped strontium and barium iodide are found to be readily growable by the Bridgman method and to produce high scintillation light yields. Sr12(Eu) emits into the Eu2+ band, centered at 435 nm, with a decay time of 1.2 ps and a light yield of -90 000 photons/MeV. It offers energy resolution better than 4% full width at half maximum at 662 keV, and exhibits excellent light yield proportionality. BaIz(Eu) produces >30 000 photons/MeV into the Eu2+ band at 420 nm (< 1 ps decay). An additional broad impurity-mediated recombination band is present at 550 nm (>3 ps decay), unless high-purity feedstock is used.

We explore dual-ended read out of LSO arrays with two position sensitive avalanche photodiodes (PSAPDs) as a high resolution, high efficiency depth-encoding detector for PET applications. Flood histograms, energy resolution and depth of interaction (DOI) resolution were measured for unpolished LSO arrays with individual crystal sizes of 1.0, 1.3 and 1.5 mm, and for a polished LSO array with 1.3 mm pixels. The thickness of the crystal arrays was 20 mm. Good flood histograms were obtained for all four arrays, and crystals in all four arrays can be clearly resolved. Although the amplitude of each PSAPD signal decreases as the interaction depth moves further from the PSAPD, the sum of the two PSAPD signals is essentially constant with irradiation depth for all four arrays. The energy resolutions were similar for all four arrays, ranging from 14.7% to 15.4%. A DOI resolution of 3-4 mm (including the width of the irradiation band which is approximately 2 mm) was obtained for all the unpolished arrays. The best DOI resolution was achieved with the unpolished 1 mm array (average 3.5 mm). The DOI resolution for the 1.3 mm and 1.5 mm unpolished arrays was 3.7 and 4.0 mm respectively. For the polished array, the DOI resolution was only 16.5 mm. Summing the DOI profiles across all crystals for the 1 mm array only degraded the DOI resolution from 3.5 mm to 3.9 mm, indicating that it may not be necessary to calibrate the DOI response separately for each crystal within an array. The DOI response of individual crystals in the array confirms this finding. These results provide a detailed characterization of the DOI response of these PSAPD-based PET detectors which will be important in the design and calibration of a PET scanner making use of this detector approach.

Articles you may be interested inScintillator high-gain avalanche rushing photoconductor active-matrix flat panel imager: Zero-spatial frequency xray imaging properties of the solid-state SHARP sensor structure Med. Phys. 39, 7102 (2012); 10.1118/1.4760989 2 ∕ 3 in. ultrahigh-sensitivity image sensor with active-matrix high-efficiency electron emission device J. Vac. Sci. Technol. B 28, C2D11 (2010); 10.1116/1.3271163 High dynamic range active pixel sensor arrays for digital x-ray imaging using a -Si : H J. Vac. Sci. Technol. A 24, 850 (2006); 10.1116/1.2192526 X-ray detection by direct modulation of an optical probe beam-Radsensor: Progress on development for imaging applications Rev. Sci. Instrum. 75, 3995 (2004); 10.1063/1.1790055X-ray-induced recombination effects in a-Se-based x-ray photoconductors used in direct conversion x-ray sensors J.The factors determining the x-ray sensitivity of HgI 2 and PbI 2 as direct detector materials for large area matrix addressed x-ray image sensors are described, along with a model to explain their different properties. The imaging studies are made on test arrays with 512ϫ512 pixels of size 100 m. The x-ray sensitivity and spatial resolution are reported, along with measurements of the various mechanisms that influence the sensitivity, such as charge collection, x-ray absorption, fill factor, and image lag. The spatial resolution of PbI 2 decreases with increasing film thickness, but this effect is not observed in HgI 2 . The x-ray response data are used to compare the sensitivity to the theoretical values for the ionization energy and to identify the various loss mechanisms. We find that the sensitivity of HgI 2 can be explained by a few small and well characterized loss factors. This material exhibits good spatial resolution, high fill factor, and high charge collection. PbI 2 films exhibit lower sensitivity, principally attributable to a very large image lag. We propose that the x-ray response of the two materials is distinguished by their different depletion layer properties, and present a model that accounts for the sensitivity, image lag, and spatial resolution of PbI 2 .

A theoretical investigation of factors limiting the detective quantum efficiency (DQE) of active matrix flat-panel imagers (AMFPIs), and of methods to overcome these limitations, is reported. At the higher exposure levels associated with radiography, the present generation of AMFPIs is capable of exhibiting DQE performance equivalent, or superior, to that of existing film-screen and computed radiography systems. However, at exposure levels commonly encountered in fluoroscopy, AMFPIs exhibit significantly reduced DQE and this problem is accentuated at higher spatial frequencies. The problem applies both to AMFPIs that rely on indirect detection as well as direct detection of the incident radiation. This reduced performance derives from the relatively large magnitude of the square of the total additive noise compared to the system gain for existing AMFPIs. In order to circumvent these restrictions, a variety of strategies to decrease additive noise and enhance system gain are proposed. Additive noise could be reduced through improved preamplifier, pixel and array design, including the incorporation of compensation lines to sample external line noise. System gain could be enhanced through the use of continuous photodiodes, pixel amplifiers, or higher gain x-ray converters such as lead iodide. The feasibility of these and other strategies is discussed and potential improvements to DQE performance are quantified through a theoretical investigation of a variety of hypothetical 200 microm pitch designs. At low exposures, such improvements could greatly increase the magnitude of the low spatial frequency component of the DQE, rendering it practically independent of exposure while simultaneously reducing the falloff in DQE at higher spatial frequencies. Furthermore, such noise reduction and gain enhancement could lead to the development of AMFPIs with high DQE performance which are capable of providing both high resolution radiographic images, at approximately 100 microm pixel resolution, as well as variable resolution fluoroscopic images at 30 fps.

is the most promising. SrI 2 (Eu) emits into the Eu 2+ band, centered at 435 nm, with a decay time of 1.2 µs and a light yield of up to 115,000 photons/MeV. It offers energy resolution better than 3% FWHM at 662 keV, and exhibits excellent light yield proportionality. Transparent ceramics fabrication allows production of Gadolinium-and Terbium-based garnets which are not growable by melt techniques due to phase instabilities. While scintillation light yields of Cerium-doped ceramic garnets are high, light yield non-proportionality and slow decay components appear to limit their prospects for high energy resolution.We are developing an understanding of the mechanisms underlying energy dependent scintillation light yield non-proportionality and how it affects energy resolution. We have also identified aspects of optical design that can be optimized to enhance energy resolution.