This PDF file contains the front matter associated with SPIE Proceedings Volume 7450, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The europium-doped lutetium oxide (Lu₂O₃:Eu) transparent optical ceramic has excellent scintillation properties, namely very high density (9.5 g/cm³), high effective atomic number (67.3), light output comparable to thallium-doped cesium iodide (CsI:Tl), and emission wavelength (610 nm) for which silicon-based detectors have a very high quantum efficiency. If microcolumnar films of this material could be fabricated, it would find widespread use in a multitude of highspeed imaging applications. However, the high melting point of over 2400°C makes it extremely challenging to make microcolumnar films of this material. We have recently fabricated and characterized microcolumnar films of Lu₂O₃:Eu. These results are presented in this paper.

Using a many-body embedded ion method potential for La-Br system, molecular dynamics simulations have been performed to study dislocations in the UCl₃ type of LaBr₃ crystal including identification of dislocation line energy, core structure, migration mechanism, and mobility. We found that dislocations with the < 0001 > Burgers vector can move under shear stresses, but they retain perfect dislocations during the motion rather than dissociated partials as commonly seen in metal systems. Unlike the < 0001 > edge dislocations whose mobility increases with temperature, the < 0001 > screw dislocations may become sessile at high temperatures due to thermally activated dissociation of the core. Dislocations with the <1120 > Burgers vector were found to be sessile due to non-planar dissociation at the core. Because the < 0001> dislocations can only slip on the {1 1 00 } prism plane and often only the edge dislocations are operative, the stresses created during any thermal mechanical processes cannot be effectively relieved by the plastic deformation mechanism. Considering that LaBr₃ tend to cleave along the {1 1 00 } prism plane, the simulations shed some lights on why this material is so brittle and how large LaBr₃ crystals tend to fracture during growth.

While a wide variety of new scintillators are now available, new cerium-doped lanthanide halide scintillators have shown a strong potential to move beyond their familiar role in conventional gamma ray spectroscopy, toward fulfilling the needs of highly demanding applications such as radioisotope identification at room temperature, homeland security, and quantitative molecular imaging for medical diagnostics, staging and research. Despite their extraordinary advantages, however, issues related to reliable, large volume manufacturing of these high light yield materials in a rapid and economic manner have not been resolved or purposefully addressed. Also, if microcolumnar films of this material could be fabricated, it would find widespread use in a multitude of high-speed imaging/nuclear medicine applications. Here we report on synthesizing LaBr3:Ce scintillators using a thermal evaporation technique, which permits the fabrication of high spatial resolution microcolumnar films and holds a potential to synthesize large volumes of high quality material in a time efficient and cost effective manner. Performance evaluation of the fabricated films and their application for SPECT imaging are also discussed.

X-ray diffraction imaging (XDi) refers to the volumetric analysis of extended, inhomogenous objects by spatially-resolved x-ray diffraction. Following a brief description of some of the areas in which x-ray diffraction (XRD) is currently impacting on the detection of materials of interest in the security environment, the principles of energy-dispersive x-ray diffraction tomographic systems of the 1^st, 2^nd and 3^rd generation are described. The Multiple Inverse Fan Beam (MIFB) topology for 3rd Generation XDi, in which the XRD properties of a 2-D spatial array of volume elements are investigated in parallel without mechanical scanning, is described. 3rd Generation XDi is being driven among other things by technological developments taking place in the field of Multi-Focus X-ray Sources (MFXS) from which representative results are presented. MFXS source requirements for Next-Generation MIFB XDi are summarized and the potential of 3rd Generation XDi for rapid, accurate and affordable screening in the Checkpoint and Hold Baggage environments is summarized.

We have evaluated for the first time the Detective Quantum Efficiency of 2 imaging detectors which are used for Crystallography. Crystallography is the science of determining the arrangement of atoms within a crystal from the manner in which a beam of usually low energy (8-17.5 keV) monochromatic X-rays is scattered from the electrons within the crystal. There is a growing consensus in the scientific world that the Detective Quantum Efficiency (DQE) is the most suitable parameter for describing the imaging performance of an x-ray imaging device. The DQE describes the ability of the imaging system to preserve the Signal to Noise Ratio (SNR) on the way from the radiation field emerging from the very fine and practically monochrome x-ray beam through the various imaging system components up to the 3-dimensional crystal image. Normally the DQE of x-ray systems is based on the effective energy of the x-ray beam and the x-ray dose as measured with a dosimeter. Typical dosimeters are not very accurate at low x-ray energies which are used in Crystallography. We used an x-ray spectrometer to determine the x-ray photon fluence. Values of DQE at low spatial frequency were at about almost 80 % at 8 keV.

In our work with LCD monitors for medical images, we have created a computer-program simulation-suite that mimics the appearance of an LCD screen. It uses high-magnification digital-camera capture of individual monitor pixels to compose realistic the sub-pixel patterns used in the simulations. These patterns are then weighted by digital driving levels, DDL's, that correspond to the image being displayed and inserted into a digital monitor field so as to compose an image of pixels that correspond to those of a monitor. The program suite also simulates the area-capture of a screenimage by a digital camera at a selectable magnification. The research project to which we are currently applying this simulation is the reduction of near-pixel-sized fixed-pattern noise. In the actual experiment a camera is used to capture a magnified portion of the monitor. Typical magnifications are 4:1 and 8:1 CCD to LCD pixels. From this captured image, a fixed-pattern multiplicative-noise gain map is generated that is used to adjust DDL's in order to pre-compensate for that noise. In addition to the spatial characteristics of the LCD monitor and CCD camera sensor, our simulation addresses nonlinearities found in the display and capture processes. The nonlinearities become important because the captured CCD digital values, or DSL's for digital sensor levels, are converted to luminance. This conversion is necessary because we employ a subsequent local-area processing step that relies on linearity of image-spread being in energy fluxdensity. This presentation focuses specifically on the comparison of the simulation results to physical experiments.

Recent progress on a high-resolution, photon-counting gamma-ray and x-ray imager called BazookaSPECT is presented. BazookaSPECT is an example of a new class of scintillation detectors based on integrating detectors such as CCD(charge-coupled device) or CMOS(complementary metal-oxide semiconductor) sensors. BazookaSPECT is unique in that it makes use of a scintillator in close proximity to a microchannel plate-based image intensifier for up-front optical amplification of scintillation light. We discuss progress made in bringing about compact BazookaSPECT modules and in real-time processing of event data using graphics processing units (GPUs). These advances are being implemented in the design of a high-resolution rodent brain imager called FastSPECT III. A key benefit of up-front optical gain is that any CCD/CMOS sensor can now be utilized for photon counting. We discuss the benefits and feasibility of using CMOS sensors as photon-counting detectors for digital radiography, with application in mammography and computed tomography (CT). We present as an appendix a formal method for comparing various photon-counting integrating detectors using objective statistical criteria.

Color displays are increasingly used for medical imaging, replacing the traditional monochrome displays in radiology for multi-modality applications, 3D representation applications, etc. Color displays are also used increasingly because of wide spread application of Tele-Medicine, Tele-Dermatology and Digital Pathology. At this time, there is no concerted effort for calibration procedures for this diverse range of color displays in Telemedicine and in other areas of the medical field. Using a colorimeter to measure the display luminance and chrominance properties as well as some processing software we developed a first attempt to a color calibration protocol for the medical imaging field.

This presentation describes work in progress that is the result of an NIH SBIR Phase 1 project that addresses the wide- spread concern for the large number of breast-cancers and cancer victims [1,2]. The primary goal of the project is to increase the detection rate of microcalcifications as a result of the decrease of spatial noise of the LCDs used to display the mammograms [3,4]. Noise reduction is to be accomplished with the aid of a high performance CCD camera and subsequent application of local-mean equalization and error diffusion [5,6]. A second goal of the project is the actual detection of breast cancer. Contrary to the approach to mammography, where the mammograms typically have a pixel matrix of approximately 1900 x 2300 pixels, otherwise known as FFDM or Full-Field Digital Mammograms, we will only use sections of mammograms with a pixel matrix of 256 x 256 pixels. This is because at this time, reduction of spatial noise on an LCD can only be done on relatively small areas like 256 x 256 pixels. In addition, judging the efficacy for detection of breast cancer will be done using two methods: One is a conventional ROC study [7], the other is a vision model developed over several years starting at the Sarnoff Research Center and continuing at the Siemens Corporate Research in Princeton NJ [8].

Detection of X-ray radiation by digital radiographic systems (DRS) is realized using multi-element detector arrays of scintillator-photodiode (S-PD) type. Accounting for our experience in development of X-ray introscopy systems, possibilities can be found for improvement of DRS detection efficiency. Namely, a more efficient use of the dynamic range of the analog-to-digit converter by means of instrumental compensation of scatter of detector characteristics and smaller apertures of individual detection channels. However, smaller apertures lead to lower levels of useful signals, and a problem emerges of signal interference over neighboring channels, which is related to optical separation of the scintillation elements. Also, more compact arrangement of electronic components of preamplifiers is achieved. The latter problem is solved by using multi-channel (from 32 to 1024 channels) photoreceiving devices (PRD). PRD has a set of photosensitive elements formed on one crystal, as well as shift registers ensuring preliminary amplification of signals and series connection to one outlet. The work envisages creation of receiving-detecting circuit (RDC) with improved spatial resolution (ISR) with the aim of producing advanced DRS with improved characteristics: density resolution better than 0.9%, and detecting ability allowing detection of θ 0.5 mm steel wire behind 6 mm steel. The work will result in the development of RDC with ISR (800-200 microns). In combination with various ionizing radiation sources and scanning mechanisms this will allow creation of DRS for many tasks of non-destructive testing (NDT) and technical diagnostics (TD), in particular, for check-up of pipelines, objects of oil and gas industries, etc. This work was supported by the Ministry of Education and Science of Ukraine, the U.S. Civilian Research and Development Foundation (CRDF), and by the NATO Science for Peace and Security Program (Project SfP-982823).

Phase-contrast radiography (PCR) generates an image from gradients in the phase of the probing X-radiation induced by the radiographic object, and can therefore make visible features difficult or impossible to see with conventional, absorption-contrast (ACR) radiography. For any particular object, variations in either the real or imaginary parts of the index of refraction could be greater. Most practical difficulties of PCR arise from the very small deviation from unity (~10^-5-10^-6, depending of material and energy) of the real part of the index of refraction. In principal, straightforward shadowgraphy would provide a phase-contrast image, but in practice this is usually overwhelmed by the zero-order (bright field) signal. Eliminating this sets the phase-contrast signal against a dark field (as in Schlieren photography with visible light). One way to do this with X-rays is with a grating that produces a Talbot interference pattern. Minute variations in optical path lengths through the radiographic object can significantly shift the Talbot fringes, and these shifts constitute a dark-field signal separate from the zero-order wave. This technique has recently been investigated up to ~20keV [1-3]; this work addresses what sets the practical upper limit, and where that limit is. These appear to be grating fabrication, and ~60keV, respectively.