IEC 62945:2018 pdf download – Radiation protection instrumentation – Measuring the imaging performance of X-ray computed tomography (CT) security-screening systems

03-05-2022 comment

IEC 62945:2018 pdf download – Radiation protection instrumentation – Measuring the imaging performance of X-ray computed tomography (CT) security-screening systems.
Security screening systems are generally used to scan parcels, including luggage, for the presence of ilicit items such as explosives, drugs, or other contraband. Many of the screening systems currently used, particularly in transportation security applications, are based on CT imaging technology. Generally, as the parcel is transported through the system, the system collects a CT image of the parcel. These data are then subjected to automated analysis to determine whether a threat may be present or the parcel is considered clear. If the automated analysis determines a threat may be present, the image is often presented to a system operator who can override the automated decision, clearing the parcel, or referring it for further processing such as opening it and manually searching for threats. Historically, government regulators have established evaluation procedures to determine whether a system’s automated detection performance is adequate for use in applications within their borders. Typically, a vendor submits a copy of their product, including their software to the regulator’s facility. The regulator runs a wide variety of parcels with threats inside through the system as well as parcels without threats that represent the typical stream of commerce. Detection and false alarm rates are determined and compared against performance criteria. If the criteria are met, the system is approved for use. This testing ensures that the system is capable of meeting the required criteria, but how does one ensure that all copies of the system meet the criteria? Normal manufacturing variability, quality control issues, or aging of the equipment may degrade performance versus what was observed on the article tested by the regulator. Replicating the original test on each machine in question is impractical. Transporting the regulator’s threat set to a factory site or to locations where the machines are in use presents significant security and in some cases safety concerns.
System components and adjustments should be as for the standard commercial product in normal security screening operation mode; any deviations shall be noted by the evaluators in the manually recorded data. If the system is approved to operate under more than one configuration, the user may want to request the test be carried out at all appropriate settings. Evaluation is to be based on images or other data normally used in standard mode of operation. The exposure time and level shall be chosen as that used when the CT system is operated for the intended use in the security screening application. A calibration of the CT system shall be carried out prior to any testing. Any recalibration of the CT system shall be allowed according to the standard operation of the system. In order to ensure that the system is using a configuration approved by the appropriate regulatory agency, the user may wish to request that the vendor provide the specific settings used during the evaluation such as: tube voltage(s),amperage, voxel size, belt speed, etc. Changes in CT image reconstruction software should be followed by gathering a new baseline measurement set. Alternatively, new baseline results may be recomputed offline if the data are available.
The test articles (see 4.2) shall be presented to the system in a controlled position and orientation. The main axis of each test article should be parallel to the conveyor belt motion direction and the front of the article shall enter the system first (front designated via labeling). The test method described in 6.3 determines the angle of rotation and side to side offset of the test articles relative to the centerline of the system conveyor. Results for rotations more than 2 degrees off parallel from conveyor centerline shall be rejected. This document requires that the test articles be measured at the center of the belt, directly on the belt, within 士2 cm of the conveyor centerline. If the user decides to also run the test articles off centerline, the parallel requirement shall still be met, and the data shall be segregated and treated separately.

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