Case for an Improved Effective-Atomic Number for the Electronic Baggage Scanning Program

Abstract

11 This document is updated from LLNL-TR-520312 with the inclusion of Reference 7, minor corrections in the calculations of Ze for several materials, and the improvement of non-substantive typographical errors and wording.

A review of automated image understanding within 3D baggage computed tomography security screening

“…Table 4: Overview of 3D object classification within baggage-CT. For each study, the target objects, the core methodology, the type and source of data, the Quantitative Evaluation (QE) measures and the main conclusions and approximate performance are provided. [93].…”

“…The most prominent recent contributions in this domain are summarised in Table 2. The reader is referred to the work of Singh [90] and Smith et al [93] for more extensive reviews of the particular role of EDS within the baggage security screening context. Single-energy CT systems produce reconstructions representative of the Linear Attenuation Coefficients (LAC) of the object under investigation.…”

“…Based on these observations, it is theoretically possible to distinguish between illicit and innocuous items by computing the effective atomic numbers and densities of the materials in a scan [83]. Traditionally, this has been achieved via a simple calibration and interpolation procedure [93] (Fig. 5).…”

“…Several more robust DECT-based techniques exist for computing the effective atomic number [111,93,88]. The majority of these rely on the decomposition of the low and highenergy data into equivalent Compton scatter and photoelectric absorption coefficients using the methods described in Section 4.2.…”

“…Dual-Energy Computed Tomography (DECT) [48], whereby objects are scanned at two distinct energies, has been shown to provide a more effective means for performing materials-based discrimination based on effective atomic numbers than do the conventional single-energy CT scanners [90,93,111]. Owing to this primary explosives detection-based objective of imaging within the aviation-security domain, DECT machines are increasingly becoming the baggage-CT scanners of choice.…”