1、Designation: F792 171Standard Practice forEvaluating the Imaging Performance of Security X-RaySystems1This standard is issued under the fixed designation F792; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revisi
2、on.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon () indicates an editorial change since the last revision or reapproval.1NOTEEditorially corrected adjunct number in 2.2 in September 2017.1. Scope1.1 This practice applies to all X-ray-based screening sys-tems with t
3、unnel apertures up to1mwide1mhigh, whetherthey are conventional X-ray systems or explosives detectionsystems, that provide a projection or projection/scatter image.1.2 This practice applies to X-ray systems used for thescreening for prohibited items such as weapons, explosives,and explosive devices
4、in baggage, packages, cargo, or mail.1.3 This practice establishes quantitative and qualitativemethods for evaluating the systems. This practice does notestablish minimum performance requirements for any particu-lar application.1.4 This practice relies upon the use of three differentstandard test ob
5、jects: ASTM X-ray test object HP, for evalu-ating human perception based performance parameters;ASTMX-ray test object RT, for routine testing to assess operation;andASTM X-ray test object OE, for objective evaluation andscoring of the technical capability of the system. The specifictest objects are
6、subsequently described and referred to in thispractice as the HP test object, RT test object, and OE testobject.1.4.1 Part RTThis part considers only the methods forroutine and periodic verification of system operation andfunction, and therefore requires use of ASTM X-ray testobject RT.1.4.2 Part HP
7、This part considers only the methods for,and use of, the ASTM X-ray test object HP.1.4.3 Part OEThis part considers only the methods forobjective evaluation of the technical capabilities of a system,and therefore requires use of theASTM X-ray test object OE.1.5 The values stated in SI units are to b
8、e regarded asstandard. No other units of measurement are included in thisstandard.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health and environmental
9、practices and deter-mine the applicability of regulatory limitations prior to use.1.7 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guide
10、s and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2B258 Specification for Standard Nominal Diameters andCross-Sectional Areas of AWG Sizes of Solid RoundWires Used as Electrical ConductorsD6100 Specifica
11、tion for Extruded, Compression Molded andInjection Molded Polyoxymethylene Shapes (POM)2.2 ASTM Adjuncts:Adjunct to F0792 Drawings for Test Piece32.3 Other Documents:IEC 60317-1:2010-03 Specification for Particular Types ofWinding Wires Part 1: Polyvinyl Acetal EnamelledRound Copper Wire, Class 1054
12、ANSI/NEMA MW 1000-2014 American National Standard,Magnet Wire (MW 80-C)5ISO 12233-2000 Photography Electronic Still-PictureCameras Resolution Measurements, Section 6.3 andAn-nex C1This practice is under the jurisdiction of ASTM Committee F12 on SecuritySystems and Equipment and is the direct respons
13、ibility of Subcommittee F12.60 onControlled Access Security, Search, and Screening Equipment.Current edition approved April 1, 2017. Published August 2017. Originallyapproved in 1982. Last previous edition approved in 2008 as F792 08 which waswithdrawn January 2017 and reinstated in April 2017. DOI:
14、 10.1520/F0792-17E01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from ASTM International Headq
15、uarters. Order Adjunct No.ADJF079217-E-PDF. Original adjunct produced in 2017.4Available from International Electrotechnical Commission (IEC), 3, rue deVaremb, 1st Floor, P.O. Box 131, CH-1211, Geneva 20, Switzerland, http:/www.iec.ch.5Available from American National Standards Institute (ANSI), 25
16、W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization establi
17、shed in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 blocking materiala thickness of mate
18、rial used toobscure the view of an object in an X-ray image by attenuatingthe X-ray beam used to form the image.3.1.2 boundary signal-to-noise ratio (BSNR)a metric formeasuring the detectability of a boundary; the BSNR iscomputed by comparing the average pixel value betweenregions of interest on eit
19、her side of the boundary; the signifi-cance of the difference in the pixel value is determined bymeasuring the consistency for repeated measurements fordifferent images; see A3.1 for a complete technical definition.3.1.3 contrast sensitivitya measure of the minimumchange in an object that produces a
20、 perceptible brightnesschange in the image on a display.3.1.4 effective atomic number (Zeff)the atomic number of asingle hypothetical element that, for a particular x-rayspectrum, would exhibit essentially identical X-ray attenuationcharacteristics as the material under consideration.3.1.5 huea prop
21、erty of a color that reflects the degree towhich it can be classified as red, green, and blue; this propertycan be considered independently of the lightness of the color,for example, a red color and a pink color may have the samehue but different lightness and saturation.3.1.6 image quality metric (
22、Part HP)a quantitative assess-ment of a capability of an imaging system; nine image qualitymetrics are defined in this practice along with the standard testobject and methods necessary for their measurement.3.1.6.1 test 1: wire displaythe ability of an X-ray systemto display images that can be used
23、by an operator to identifymetal wires.3.1.6.2 test 2: useful penetrationthe ability of an X-raysystem to produce an image that allows for the detection, by anoperator or algorithm, of wires that are hidden by differentthicknesses of blocking material.3.1.6.3 test 3: spatial resolutionthe ability of
24、an X-raysystem to display closely spaced, high-contrast items as sepa-rate.3.1.6.4 test 4: simple penetrationthe ability of an X-raysystem to display images that can be used by an operator toidentify lead numerals that would otherwise be hidden by steelblocking material.3.1.6.5 test 5: thin organic
25、imagingthe ability of an X-raysystem to display images that can be used by an operator toidentify thin pieces of organic material.3.1.6.6 test 6: steel contrast sensitivitythe ability of anX-ray system to display images that can be used by an operatorto identify shallow circular recesses in steel.3.
26、1.6.7 test 7: materials discriminationthe ability of anX-ray system to display images that can be used by an operatorto discriminate between materials with different effectiveatomic numbers.3.1.6.8 test 8: materials classificationthe ability of anX-ray system to display images that can be used by an
27、 operatorto consistently identify a particular material over a range ofdifferent thicknesses.3.1.6.9 test 9: organic differentiationthe ability of anX-ray system to display images that can be used by an operatorto differentiate between organic materials of different effectiveatomic numbers.3.1.7 ima
28、ge quality metric (Part OE)a quantitative assess-ment of a capability of an imaging system; six image qualitymetrics are defined in this part of the practice along with thestandard test pieces and methods necessary for their measure-ment.3.1.7.1 test 1: steel differentiationthe ability of an X-raysy
29、stem to provide an image that can be used to detect, using anobjective algorithm, boundaries between different thicknessesof steel.3.1.7.2 test 2: useful penetrationthe ability of an X-raysystem to produce an image that allows for the detection, by anoperator or algorithm, of wires that are hidden b
30、y differentthicknesses of blocking material.3.1.7.3 test 3: organic boundary signal-to-noise ratioameasure of the ability of an X-ray system to detect thicknesschanges in thin pieces of low atomic-number material.3.1.7.4 test 4: spatial resolutionthe ability of an X-raysystem to display closely spac
31、ed, high-contrast items as sepa-rate.3.1.7.5 test 5: dynamic rangethe ratio between the largestand smallest usable grayscale values.3.1.7.6 test 6: noise equivalent quanta (NEQ)a spatial-frequency-dependent measure of the detection ability of animaging system that is quantified in terms of the numbe
32、r ofphotons, or quanta, that would be required to achieve the samedetection ability for an ideal imaging system; the NEQ iscomputed from measurements of the modulation transferfunction, the noise power spectrum, and the average pixelvalue of uniformly illuminated noise images.3.1.8 modulation transf
33、er function (MTF)a spatial-frequency-dependent measure of contrast reduction used tocharacterize an imaging systems spatial resolution, that is herederived from the systems edge-spread function.3.1.9 noise power spectrum (NPS)a spatial-frequency-dependent function that characterizes the noise proper
34、ties of animage, computed using the Fourier transform of uniformlyilluminated noise images.3.1.10 Nyquist frequencya frequency that is half the spa-tial sampling frequency; in units of cycles per pixel, it alwayshas a value of 0.5 but in this practice it should be expressed inunits of cycles per mm.
35、3.1.11 operatorthe person operating the X-ray imagingdevice.3.1.12 region of interest (ROI)an area on the image of aspecified size and position; an ROI is usually selected in orderto compute some statistical quantity over the pixels it contains(for example, the mean value or the standard deviation).
36、F792 17123.1.13 test imagea grayscale digital X-ray image of theASTM X-ray test object-OE to which the objective algorithmsare applied.3.1.14 test objectthe physical object required to test asystem using this practice; the test object includes various testpieces, the mounting board, a protective cas
37、e, paddingmaterial, and fasteners.3.1.15 test piecea part of the test object that is used tomeasure the value of an image quality metric in this practice;for example, the POM step wedge used to evaluate the thinorganic imaging test (test 5 of part OE).3.1.16 useful penetrationthe ability of an X-ray
38、 system toproduce an image that allows for the detection, by an operatoror objective algorithm, of wires that would otherwise be hiddenby different thickness of blocking material.4. Part RT4.1 Significance and Use:4.1.1 This practice applies to and establishes methods tomeasure the imaging performan
39、ce of X-ray systems used forsecurity screening. Such systems are typically used to screenfor prohibited items such as weapons, explosives, and explo-sive devices in baggage, packages, cargo, or mail.4.1.2 The most significant attributes of this practice are thedesign of test object and standard meth
40、ods for determining theperformance levels of the system.4.1.3 In screening objects with X-ray systems, still imagesare the primary inputs provided to operators. It is assumed thatthe better the quality of these images, the better will be thepotential performance of the operator.4.1.4 This practice i
41、s intended to provide the ability toroutinely assess the performance of a cabinet X-ray system.This routine assessment can be used to ensure that: the cabinetX-ray system is operational; the imaging performance nomi-nally meets expectation; and any changes in imaging perfor-mance are tracked.4.1.5 T
42、his practice is not intended to be used as the basis forsystem qualification or validation.4.2 Test Object:4.2.1 Images of the RT test object are shown in Fig. 1.Mechanical drawings for the test object that shall be used withthis practice are given in A1.1.1.4.2.2 The RT is fragile because of the po
43、lycarbonate sub-strate on which the wires and step wedge are mounted.Consequently, the RT shall be contained and scanned within acase with the following specifications:Interior dimensions: at least (19.5 cm 12.5 cm5cm)0.5cmWall, top and bottom (largest surfaces of case):Material: ABS plasticThicknes
44、s: between 1.5 mm and 3 mmConstruction: single piece of ABS Plastic. No joints, fasteners, or foreignobjects, other than fill material, shall be between the case and theRT test object. These surfaces shall be nominally flat (this is, exhibit aradius of curvature greater than about 10 m) over a nomin
45、ally central areaof at least 17 cm 11 cm.Fill:Material: polyethylene foamThickness: sufficient to hold RT firmly in place and nominally centered withinthe case.4.3 Test Procedures:4.3.1 Obtain an image of the test object in its case using thestandard operating procedure (for example, by placing the
46、testobject on the conveyor belt so that it is run through thescanning area). The location and orientation of the RT testobject on the conveyor belt of the cabinet X-ray system is notcritical. However, to maximize the accuracy and usefulness ofimage performance tracking, the position and orientation
47、of theRT test object should be nominally the same each time it isused for this purpose, and this orientation and location shall berecorded. More than one location and orientation may be used,in which case each orientation and location pairing of the RTshall be recorded. Any image enhancement feature
48、s providedby the cabinet X-ray system may be used, and the setting forthese features shall be recorded.4.4 Evaluation Considerations:4.4.1 GeneralUse of this practice does not guarantee thatthe X-ray system is operating properly. It is not intended toreplace the X-ray systems diagnostics. If problem
49、s are expe-rienced with the X-ray system they must be resolved prior tooperation.4.4.2 Training RequirementsTo effectively conduct theevaluation of an X-ray system, it is recommended that theevaluator be trained to operate the X-ray system under test.FIG. 1 An Image of the Front and Back of the Practice F792 RT Test ObjectF792 17134.4.3 Result Interpretation and SignificanceA wire notunder aluminum is considered to be seen if more than half ofit is visible in the X-ray image. A wire under a particular stepi
