1、Designation: E 1931 09Standard Guide forX-Ray Compton Scatter Tomography1This standard is issued under the fixed designation E 1931; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses
2、 indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 PurposeThis guide covers a tutorial introduction tofamiliarize the reader with the operational capabilities andlimitations inherent in X-ray Compton Scatter
3、 Tomography(CST). Also included is a brief description of the physics andtypical hardware configuration for CST.1.2 AdvantagesX-ray Compton Scatter Tomography(CST) is a radiologic nondestructive examination method withseveral advantages that include:1.2.1 The ability to perform X-ray examination wit
4、houtaccess to the opposite side of the examination object;1.2.2 The X-ray beam need not completely penetrate theexamination object allowing thick objects to be partiallyexamined. Thick examination objects become part of theradiation shielding thereby reducing the radiation hazard;1.2.3 The ability t
5、o examine and image object subsurfacefeatures with minimal influence from surface features;1.2.4 The ability to obtain high-contrast images from lowsubject contrast materials that normally produce low-contrastimages when using traditional transmitted beam X-ray imagingmethods; and1.2.5 The ability t
6、o obtain depth information of objectfeatures thereby providing a three-dimensional examination.The ability to obtain depth information presupposes the use ofa highly collimated detector system having a narrow angle ofacceptance.1.3 ApplicationsThis guide does not specify which ex-amination objects a
7、re suitable, or unsuitable, for CST. As withmost nondestructive examination techniques, CST is highlyapplication specific thereby requiring the suitability of themethod to be first demonstrated in the application laboratory.This guide does not provide guidance in the standardizedpractice or applicat
8、ion of CST techniques. No guidance isprovided concerning the acceptance or rejection of examina-tion objects examined with CST.1.4 LimitationsAs with all nondestructive examinationmethods, CST has limitations and is complementary to otherNDE methods. Chief among the limitations is the difficulty inp
9、erforming CST on thick sections of high-Z materials. CST isbest applied to thinner sections of lower Z materials. Thefollowing provides a general idea of the range of CSTapplicability when using a 160 keV constant potential X-raysource:Material Practical Thickness RangeSteel Up to about 3 mm (18 in.
10、)Aluminum Up to about 25 mm (1 in.)Aerospace composites Up to about 50 mm (2 in.)Polyurethane Foam Up to about 300 mm (12 in.)The limitations of the technique must also consider therequired X, Y, and Z axis resolutions, the speed of imageformation, image quality and the difference in the X-rayscatte
11、ring characteristics of the parent material and the internalfeatures that are to be imaged.1.5 The values stated in both inch-pound and SI units are tobe regarded separately as the standard. The values given inparentheses are for information only.1.6 This standard does not purport to address all of
12、thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and to determine theapplicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 747 Practice for Desig
13、n, Manufacture and MaterialGrouping Classification of Wire Image Quality Indicators(IQI) Used for RadiologyE 1025 Practice for Design, Manufacture, and MaterialGrouping Classification of Hole-Type Image Quality Indi-cators (IQI) Used for RadiologyE 1255 Practice for RadioscopyE 1316 Terminology for
14、Nondestructive ExaminationsE 1441 Guide for Computed Tomography (CT) ImagingE 1453 Guide for Storage of Magnetic Tape Media thatContains Analog or Digital Radioscopic DataE 1475 Guide for Data Fields for Computerized Transfer ofDigital Radiological Examination DataE 1647 Practice for Determining Con
15、trast Sensitivity inRadiology1This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc-tive Testing and is the direct responsibility of E07.01 on Radiology (X and Gamma)Method.Current edition approved June 1, 2009. Published July 2009. Originally approvedin 1997. Last previous editio
16、n approved in 2003 as E 1931 - 97(2003).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.1Copyright ASTM Inter
17、national, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.2.2 ANSI/ASNT Standards:3SNT-TC-1A ASNT Recommended Practice for PersonnelQualification and Certification in Nondestructive TestingANSI/ASNT CP-189 Standard for Qualification and Certi-fication in Nondestru
18、ctive Testing Personnel2.3 Military Standard:MIL-STD-410 Nondestructive Testing Personnel Qualifica-tion and Certification43. Terminology3.1 Definitions:3.1.1 CST, being a radiologic examination method, usesmuch the same vocabulary as other X-ray examination meth-ods. A number of terms used in this
19、standard are defined inTerminology E 1316. It may also be helpful to read GuideE 1441.4. Summary of Guide4.1 DescriptionCompton Scatter Tomography is auniquely different nondestructive test method utilizing pen-etrating X-ray or gamma-ray radiation. Unlike computedtomography (CT), CST produces radio
20、scopic images which arenot computed images. Multiple slice images can be simulta-neously produced so that the time per slice image is in therange of a few seconds. CST can produce images that are thinwith respect to the examination object thickness (slice images)and which are at right angles to the
21、X-ray beam. Eachtwo-dimensional slice image (XY axes) is produced at anincremental distance along and orthogonal to the X-ray beam(Zaxis). A stack of CST images therefore represents a solidvolume within the examination object. Each slice imagecontains examination object information which lies predom
22、i-nantly within the desired slice. To make an analogy as to howCST works, consider a book. The examination object may belarger or smaller (in length, width and depth) then the analo-gous book. The CST slice images are the pages in the book.Paging through the slice images provides information aboutex
23、amination object features lying at different depths within theexamination object.4.2 Image FormationCST produces one or more digitalslice plane images per scan. Multiple slice images can beproduced in times ranging from a few seconds to a few minutesdepending upon the examined area, desired spatial
24、resolutionand signal-to-noise ratio. The image is digital and is typicallyassembled by computer. CST images are free from reconstruc-tion artifacts as the CST image is produced directly and is nota calculated image. Because CST images are digital, they maybe enhanced, analyzed, archived and in gener
25、al handled as anyother digital information.4.3 Calibration StandardsAs with all nondestructive ex-aminations, known standards are required for the calibrationand performance monitoring of the CST method. PracticeE 1255 calibration block standards that are representative ofthe actual examination obje
26、ct are the best means for CSTperformance monitoring. Conventional radiologic performancemeasuring devices, such as Test Method E 747 and PracticeE 1025 image quality indicators or Practice E 1647 contrastsensitivity gages are designed for transmitted X-ray beamimaging and are of little use for CST.
27、With appropriatecalibration, CST can be utilized to make three-dimensionalmeasurements of internal examination object features.5. Significance and Use5.1 Principal Advantage of Compton Scatter TomographyThe principal advantage of CST is the ability to performthree-dimensional X-ray examination witho
28、ut the requirementfor access to the back side of the examination object. CSToffers the possibility to perform X-ray examination that is notpossible by any other method. The CST sub-surface sliceimage is minimally affected by examination object featuresoutside the plane of examination. The result is
29、a radioscopicimage that contains information primarily from the slice plane.Scattered radiation limits image quality in normal radiographicand radioscopic imaging. Scatter radiation does not have thesame detrimental effect upon CST because scatter radiation isused to form the image. In fact, the mor
30、e radiation theexamination object scatters, the better the CST result. Lowsubject contrast materials that cannot be imaged well byconventional radiographic and radioscopic means are oftenexcellent candidates for CST. Very high contrast sensitivitiesand excellent spatial resolution are possible with
31、CST tomog-raphy.5.2 LimitationsAs with any nondestructive testingmethod, CST has its limitations. The technique is useful onreasonably thick sections of low-density materials. While a 25mm (1 in.) depth in aluminum or 50 mm (2 in.) in plastic isachievable, the examination depth is decreased dramatic
32、ally asthe material density increases. Proper image interpretationrequires the use of standards and examination objects withknown internal conditions or representative quality indicators(RQIs). The examination volume is typically small, on theorder of a few cubic inches and may require a few minutes
33、 toimage. Therefore, completely examining large structures withCST requires intensive re-positioning of the examinationvolume that can be time-consuming. As with other penetratingradiation methods, the radiation hazard must be properlyaddressed.6. Basis of Application6.1 Personnel Qualification is s
34、ubject to contractual agree-ment between the parties using or referencing this standard.6.1.1 If specified in the contractual agreement, personnelperforming examinations to this standard shall be qualified inaccordance with a nationally or internationally recognizedNDT personnel qualification practi
35、ce or standard such asANSI/ASNT-CP-189, SNT-TC-1A, NAS-410, or a similardocument and certified by the employer or certifying agency,as applicable. The practice or standard used and its applicablerevision shall be identified in the contractual agreement be-tween the using parties.3Available from Amer
36、ican National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.4Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http:/www.dodssp.daps.mil.E19310927. Technical Description7.1 Gen
37、eral Description of Compton Scatter TomographyTransmitted beam radiologic techniques used in radiography,radioscopy and computed tomography have dominated the useof penetrating radiation for industrial nondestructive examina-tion. The transmitted beam technique depends upon the pen-etrating radiatio
38、n attenuation mechanisms of photoelectricabsorption and Compton scattering. For low-Z materials atenergies up to about 50 keV, the photoelectric effect is thedominant attenuation mechanism. As X-ray energy increases,Compton scattering becomes the dominant attenuation mecha-nism. Pair production come
39、s into play above 1.02 MeV and canbecome the dominant effect for higher X-ray energies. Thefollowing relationships show the approximate dependence ofthe photoelectric effect and Compton scattering upon targetmaterial Z and incident X-ray energy E:Photoelectric Effect Z5/ E7/2Compton Scattering Z / E
40、Pair Production: Z2(lnE- constant)7.1.1 CST is best suited for lower Z materials such asaluminum ( Z=13 ) using a commercially available 160 keVX-ray generating system. Somewhat higher Z materials may beexamined by utilizing a higher energy X-ray generator rated at225, 320, or 450 keV.7.1.2 It is us
41、eful to envision the CST process as one wherethe X-rays that produce the CST image originate from manydiscrete points within the examined volume. Each Comptonscatter event generates a lower energy X-ray that emanatesfrom the scattering site. Singly scattered X rays that reach thedetector carry infor
42、mation about the examination object mate-rial characteristics at the site where it was generated. Thescatter radiation is also affected by the material through whichit passes on the way to the detector. The external source ofprimary penetrating radiation, that may be either X rays orgamma rays, inte
43、ract by the Compton scattering process. Theprimary radiation must have adequate energy and intensity togenerate sufficient scattered radiation at the examination site toallow detection. The examination depth is limited to that depthfrom which sufficient scattered radiation can reach the detectorto f
44、orm a usable image. The examination object is thereforeeffectively imaged from the inside out. The CST image isformed voxel (volume element) by voxel in raster fashionwhere the detectors field-of-view intersects with the centralX-ray beam at the examination site. The primary radiationbeam source and
45、 scattered radiation detector are highly colli-mated to assure collection of singly-scattered radiation from aknown small volume of the examination object. Multiplescattered radiation causes a loss of spatial resolution. Movingthe intersection of the radiation source and detector lines ofsight in a
46、systematic fashion allows a tomogram, or slice imageto be produced. Changing the distance at which the radiationsource and detector lines of sight intersect allows the tomo-gram to be produced at a selected depth below the examinationobject surface.7.2 Significant Differences in the Transmitted Beam
47、 andCompton Scattered X-Ray Imaging TechniquesThe differ-ences between conventional transmitted beam and ComptonScatter Imaging are so significant that CST must be considereda separate examination technique. For transmitted beam tech-niques, the radiation source characteristics must be carefullycont
48、rolled. The energy and intensity must be selected carefullyto fully penetrate the object and provide the required contrastsensitivity. Thick sections of high-density materials require ahigh-energy radiation source while thin sections of low-densitymaterials require a low-energy radiation source. For
49、 CSTapplications, the energy and intensity of the primary radiationbeam is relatively less important. The primary radiation beamenergy and intensity are not critical as long as they remainstable and are sufficient to generate adequate scatter radiationat the CST examination depth. Small focal spot size is criticalto transmitted beam image sharpness. The primary radiationbeam focal spot size is of much less significance for CSTtechniques. What is important is high specific activity, or thenumber of X rays or gamma rays generated per unit area (orvolume) of the primary r
