Julie A. Horrocks

Multivariate analysis of statistically poor EDXRD spectra for the detection of concealed explosives

Energy dispersive x-ray diffraction (EDXRD) has been developed as a tool for the detection of explosives in passenger baggage. The measured spectra result from the combined diffraction from each of the materials within a scattering volume. Multivariate regression was used to identify known components within very noisy data, permitting the rapid detection of explosive materials in the presence of overlying media for security screening applications. Explosives can be positively identified in spectra containing as few as several hundred counts and the error associated with the prediction is consistent from statistically reliable data (106 integrated counts) down to spectra containing in the region of 103 counts. This analysis can be employed in any situation where qualitative information is required from poor quality spectral data.

Low angle X-ray scatter for explosives detection: A geometry optimization

Abstract A geometry has been established for a low angle X-ray scatter (LAXS) system for the detection of sheet explosive in passenger baggage. The energy dispersive diffraction profiles of two typical explosives, PE4 and Semtex, have been investigated under a wide range of geometric conditions. A scatter angle of 5° and a slit collimation arrangement with an angular resolution of 20% has been found to satisfy the required criteria of well-defined, high intensity diffraction profiles at the sufficiently high energies necessary to penetrate baggage items. An investigation of typical benign suitcase contents under the optimal geometry show in general broad low-order diffraction profiles in contrast to the highly characteristic diffraction from the explosives. Real time measurement of explosives show that characteristic diffraction profiles can be measured in times as short as 0.1 s although a large statistical uncertainty results.

Experimental validation of a radiographic simulation code using breast phantom for X-ray imaging

Computer models and simulations of X-ray imaging systems are becoming a very precious tool during the development and evaluation of new X-ray imaging techniques. To provide, however, a faithful simulation of a system, all components must be accurately modelled and tested, followed by verification through experimental measurements. This paper presents a validation study of the XRayImagingSimulator, an in-house developed X-ray imaging simulator, which is extensively used as a basic tool in carrying out complex breast imaging simulations. The approach followed compares results obtained via an experimental setup for breast phantom (CIRS 011A) imaging, using synchrotron radiation (SYRMEP beamline at ELETTRA), with those from its simulated setup under the same conditions. The study demonstrated a very good agreement between experimental and simulated images compared both in terms of subjective and objective criteria. The combination of the XRayImagingSimulator with our BreastSimulator provides a powerful tool for in silico testing of new X-ray breast imaging approaches.

X-RAY-SCATTERING SIGNATURES FOR MATERIAL IDENTIFICATION

X-ray scattering at low angles demonstrates diffraction effects that can be used to characterize materials. The effects of overlying material are shown not to affect the usefulness of the data for the identification of explosives. The important features in the scattering signature are identified.

Image quality evaluation of breast tomosynthesis with synchrotron radiation.

PURPOSEnThis study investigates the image quality of tomosynthesis slices obtained from several acquisition sets with synchrotron radiation using a breast phantom incorporating details that mimic various breast lesions, in a heterogeneous background.nnnMETHODSnA complex Breast phantom (MAMMAX) with a heterogeneous background and thickness that corresponds to 4.5 cm compressed breast with an average composition of 50% adipose and 50% glandular tissue was assembled using two commercial phantoms. Projection images using acquisition arcs of 24°, 32°, 40°, 48°, and 56° at incident energy of 17 keV were obtained from the phantom with the synchrotron radiation for medical physics beamline at ELETTRA Synchrotron Light Laboratory. The total mean glandular dose was set equal to 2.5 mGy. Tomograms were reconstructed with simple multiple projection algorithm (MPA) and filtered MPA. In the latter case, a median filter, a sinc filter, and a combination of those two filters were applied on the experimental data prior to MPA reconstruction. Visual inspection, contrast to noise ratio, contrast, and artifact spread function were the figures of merit used in the evaluation of the visualisation and detection of low- and high-contrast breast features, as a function of the reconstruction algorithm and acquisition arc. To study the benefits of using monochromatic beams, single projection images at incident energies ranging from 14 to 27 keV were acquired with the same phantom and weighted to synthesize polychromatic images at a typical incident x-ray spectrum with W target.nnnRESULTSnFilters were optimised to reconstruct features with different attenuation characteristics and dimensions. In the case of 6 mm low-contrast details, improved visual appearance as well as higher contrast to noise ratio and contrast values were observed for the two filtered MPA algorithms that exploit the sinc filter. These features are better visualized at extended arc length, as the acquisition arc of 56° with 15 projection images demonstrates the highest image reconstruction quality. For microcalcifications, filtered MPA implemented with a combination of median and sinc filters indicates better feature appearance due to efficient suppression of background tissue. The image quality of these features is less sensitive to the acquisition arc. Calcifications with size ranging from 170 to 500 μm, like the ones presently studied, are well identified and visualized for all arcs used. The comparison of single projection images obtained under different beam conditions showed that the use of monochromatic beam can produce an image with higher contrast and contrast to noise ratio compared to an image corresponding to a polychromatic beam even when the latter is acquired with double incident exposure.nnnCONCLUSIONSnFilter optimization in respect to the type of feature characteristics is important before the reconstruction. The MPA combined with median and sinc filters results in improved reconstruction of microcalcifications and low-contrast features. The latter are better visualized at extended arc length, while microcalcifications are less sensitive to this acquisition parameter. Use of monochromatic beams may result in tomographic images with higher contrast acquired at lower incident exposures.

Determination of the geometric blurring of an energy dispersive X-ray diffraction (EDXRD) system and its use in the simulation of experimentally derived diffraction profiles

Abstract A computational model has been developed to calculate the geometric blurring distribution of an energy dispersive X-ray diffraction (EDXRD) system. The scattering volume, trapezoid in the horizontal plane, is divided into typically of the order 104 elements and the blurring contribution of each element considered in an iterative procedure to build up a distribution for the entire trapezoid. The resultant distribution is asymmetric and peaks at angle below that nominally set. A correction for the focal spot intensity distribution has been included. The blurring distribution has been used as a filter to the Joint Committee on Powder Diffraction Standards (JCPDS) data for several materials to predict the experimentally derived diffraction profiles. A good agreement has been demonstrated between the simulated and measured spectra with a significant improvement on previous models assuming a Gaussian blurring distribution. The model can be used to predict the spectral blurring for any EDXRD system irrespective of the application.

Optimization of a low-angle x-ray scatter system for explosive detection

Coherent scatter measurements have been shown to be a potentially useful tool in the detection of energetic materials. The relationship between explosive volume, method of concealment, environment, and resulting threat has been considered in the design of our energy dispersive low angle x-ray scatter system. The principle application of the system is for the detection of explosives concealed within passenger luggage in sheet form. The effects of parameters such as scattering angle, beam collimation, explosive material geometry, overlying materials and counting statistics have been measured experimentally and comparison made with theoretical prediction. It has been found that: 1) scatter signature analysis dictates optimum scattering angles for different explosives, and 2) partial volume effects must be combined with scatter angles to give total system optimization.

Real time analysis of scattered x-ray spectra for sheet explosives detection

The use of multivariate calibration for the real time analysis of energy dispersive x-ray scatter profiles is being investigated. The requirements of a practical baggage scanner necessitate rapid interrogation and an analysis procedure is required that can differentiate between spectral structure in diffraction profiles in very noisy data. Multivariate analysis has been successfully used to identify sheet explosives in cases with acquisitions as low as several hundred counts. Two detector systems, a high resolution HPGe detector and a room temperature CdZnTe detector, have been used. The precision of the model predictions are highly dependent upon the detector system used producing a significantly smaller error with the high resolution detector.

Preliminary evaluation of a prototype stereoscopic a-Si : H-based X-ray imaging system for full-field digital mammography

Abstract In a pre-clinical study, we have been investigating the potential of a-Si:H active matrix, flat panel imagers for X-ray full-field digital mammography through the development of an advanced 3D X-ray imaging system and have measured a number of their important imaging characteristics. To enhance the information embodied into the digital images produced by the a-Si array, stereoscopic images, created by viewing the object under examination from two angles and recombining the images, were obtained. This method provided us with a full 3D X-ray image of the test object as well as left and right perspective 2D images all at the same time. Within this scope, images of fresh, small human breast tissue specimens—normal and diseased—were obtained at ±2°, processed and stereoscopically displayed for a pre-clinical evaluation by radiologists. It was demonstrated that the stereoscopic presentation of the images provides important additional information and has potential benefits over the more traditional 2D data.

System tuning for x-ray scatter measurements in explosive detection

The use of scattered radiation in the production of signatures for explosive detection has been studied. Signatures have been measured and the spectral analysis of these using multivariate statistics has demonstrated that explosives within realistic environments can be recognized. The problem remains of how to use this information in the time frame allowed by airport baggage security checks. To address these problems we have developed a tuned system approach. The energy-angle space diagrams have been created and the areas containing the greatest information density in the presence of an explosive have been identified. A specially designed detector (CdZnTe) array has been built to match these regions. The array has been used to identify explosives hidden within realistic case situations.