1、Designation: E2007 10 (Reapproved 2016)Standard Guide forComputed Radiography1This standard is issued under the fixed designation E2007; 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 parenth
2、eses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide provides general tutorial information regard-ing the fundamental and physical principles of computedradiography (CR), definitions and termino
3、logy required tounderstand the basic CR process. An introduction to some ofthe limitations that are typically encountered during the estab-lishment of techniques and basic image processing methods arealso provided. This guide does not provide specific techniquesor acceptance criteria for specific en
4、d-user inspection applica-tions. Information presented within this guide may be useful inconjunction with those standards of 1.2.1.2 CR techniques for general inspection applications maybe found in Practice E2033. Technical qualification attributesfor CR systems may be found in Practice E2445. Crite
5、ria forclassification of CR system technical performance levels maybe found in Practice E2446. Reference Images StandardsE2422, E2660, and E2669 contain digital reference acceptanceillustrations.1.3 The values stated in SI units are to be regarded as thestandard. The inch-pound units given in parent
6、heses are forinformation only.1.4 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 and health practices and determine the applica-bility of regulatory limitation
7、s prior to use.2. Referenced Documents2.1 ASTM Standards:2E94 Guide for Radiographic ExaminationE746 Practice for Determining Relative Image Quality Re-sponse of Industrial Radiographic Imaging SystemsE747 Practice for Design, Manufacture and Material Group-ing Classification of Wire Image Quality I
8、ndicators (IQI)Used for RadiologyE1025 Practice for Design, Manufacture, and MaterialGrouping Classification of Hole-Type Image Quality In-dicators (IQI) Used for RadiologyE1316 Terminology for Nondestructive ExaminationsE1453 Guide for Storage of Magnetic Tape Media thatContains Analog or Digital R
9、adioscopic DataE2002 Practice for Determining Total Image Unsharpnessand Basic Spatial Resolution in Radiography and Radios-copyE2033 Practice for Computed Radiology (PhotostimulableLuminescence Method)E2339 Practice for Digital Imaging and Communication inNondestructive Evaluation (DICONDE)E2422 Di
10、gital Reference Images for Inspection of Alumi-num CastingsE2445 Practice for Performance Evaluation and Long-TermStability of Computed Radiography SystemsE2446 Practice for Manufacturing Characterization of Com-puted Radiography SystemsE2660 Digital Reference Images for Investment Steel Cast-ings f
11、or Aerospace ApplicationsE2669 Digital Reference Images for Titanium Castings2.2 SMPTE Standard:RP-133 Specifications for Medical Diagnostic Imaging TestPattern for Television Monitors and Hard-Copy RecordingCameras33. Terminology3.1 Unless otherwise provided within this guide, terminol-ogy is in ac
12、cordance with Terminology E1316.3.2 Definitions:3.2.1 aliasingartifacts that appear in an image when thespatial frequency of the input is higher than the output iscapable of reproducing. This will often appear as jagged orstepped sections in a line or as moir patterns.3.2.2 basic spatial resolution
13、(SRb)terminology used todescribe the smallest degree of visible detail within a digitalimage that is considered the effective pixel size.1This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc-tive Testing and is the direct responsibility of Subcommittee E07.01 on Radiology(X and G
14、amma) Method.Current edition approved July 1, 2016. Published July 2016. Originally approvedin 1999. Last previous edition approved in 2010 as E2007 -10. DOI: 10.1520/E2007-10R16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org.
15、 For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from Society of Motion Picture and Television Engineers (SMPTE),3 Barker Ave, 5th Floor, White Plains, NY 10601.Copyright ASTM International, 100 Barr Harbor Drive, PO Box
16、 C700, West Conshohocken, PA 19428-2959. United States13.2.2.1 DiscussionThe concept of basic spatial resolutioninvolves the ability to separate two distinctly different imagefeatures from being perceived as a single image feature. Whentwo identical image features are determined minimally distinct,t
17、he single image feature is considered the effective pixel size.If the physical sizes of the two distinct features are known, forexample, widths of two parallel lines or bars with an includedspace equal to one line or bar, then the effective pixel size isconsidered12 of their sums. Example: A digital
18、 image isdetermined to resolve five line pairs per mm or a width of lineequivalent to five distinct lines within a millimetre. The basicspatial resolution is determined as 1/ 2 5 LP/ mm or 0.100mm.3.2.3 binary/digital pixel dataa matrix of binary (0s, 1s)values resultant from conversion of PSL from
19、each latent pixel(on the IP) to proportional (within the bit depth scanned)electrical values. Binary digital data value is proportional to theradiation dose received by each pixel.3.2.4 bit depththe number “2” increased by the exponen-tial power of the analogue-to-digital (A/D) converter resolu-tion
20、. Example 1) In a 2-bit image, there are four (22) possiblecombinations for a pixel: 00, 01, 10 and 11. If “00” representsblack and “11” represents white, then “01” equals dark grayand “10” equals light gray. The bit depth is two, but the numberof gray scales shades that can be represented is 22or 4
21、.Example 2): A 12-bit A/D converter would have 4096 (212)gray scales shades that can be represented.3.2.5 blooming or flarean undesirable condition exhibitedby some image conversion devices brought about by exceedingthe allowable input brightness for the device, causing theimage to go into saturatio
22、n, producing an image of degradedspatial resolution and gray scale rendition.3.2.6 computed radiographic systemall hardware andsoftware components necessary to produce a computed radio-graph. Essential components of a CR system consisting of: animaging plate, an imaging plate readout scanner, electr
23、onicimage display, image storage and retrieval system and interac-tive support software.3.2.7 computed radiographic system classa group of com-puted radiographic systems characterized with a standardimage quality rating. Practice E2446, Table 1, provides such aclassification system.3.2.8 computed ra
24、diographya radiological nondestructivetesting method that uses storage phosphor imaging plates(IPs), a PSL stimulating light source, PSL capturing optics,optical-to-electrical conversion devices, analogue-to-digitaldata conversion electronics, a computer and software capableof processing original di
25、gital image data and a means forelectronically displaying or printing resultant image data.3.2.9 contrast and brightnessan application of digitalimage processing used to “re-map” displayed gray scale levelsof an original gray scale data matrix using different referencelookup tables.3.2.9.1 Discussio
26、nThis mode of image processing is alsoknown as “windowing” (contrast adjustment) and “leveling”(brightness adjustment) or simply “win-level” image process-ing.3.2.10 contrast-to-noise ratio (CNR)quotient of the digi-tal image contrast (see 3.2.13) and the averaged standarddeviation of the linear pix
27、el values.3.2.10.1 DiscussionCNR is a measure of image qualitythat is dependent upon both digital image contrast and signal-to-noise ratio (SNR) components. In addition to CNR, a digitalradiograph must also possess adequate sharpness or basicspatial resolution to adequately detect desired features.3
28、.2.11 digital driving level (DDL)terminology used todescribe displayed pixel brightness of a digital image on amonitor resultant from digital mapping of various gray scalelevels within specific look-up-table(s).3.2.11.1 Discussion DDL is also known as monitor pixelintensity value; thus, may not be t
29、he PV of the original digitalimage.3.2.12 digital dynamic rangemaximum material thicknesslatitude that renders acceptable levels of specified imagequality performance within a specified pixel intensity valuerange.3.2.12.1 DiscussionDigital dynamic range should not beconfused with computer file bit d
30、epth.3.2.13 digital image contrastpixel value difference be-tween any two areas of interest within a computed radiograph.3.2.13.1 Discussiondigital contrast = PV2 PV1 wherePV2 is the pixel value of area of interest “2” and PV1 is thepixel value of area of interest “1” on a computed radiograph.Visual
31、ly displayed image contrast can be altered via digitalre-mapping (see 3.2.11) or re-assignment of specific gray scaleshades to image pixels.3.2.14 digital image noiseimaging information within acomputed radiograph that is not directly correlated with thedegree of radiation attenuation by the object
32、or feature beingexamined and/or insufficient radiation quanta absorbed withinthe detector IP.3.2.14.1 DiscussionDigital image noise results from ran-dom spatial distribution of photons absorbed within the IP andinterferes with the visibility of small or faint detail due tostatistical variations of p
33、ixel intensity value.3.2.15 digital image processingthe use of algorithms tochange original digital image data for the purpose of enhance-ment of some aspect of the image.3.2.15.1 DiscussionExamples include: contrast,brightness, pixel density change (digital enlargement), digitalfilters, gamma corre
34、ction and pseudo colors. Some digitalprocessing operations such as sharpening filters, once saved,permanently change the original binary data matrix (Fig. 1,Step 5).3.2.16 equivalent penetrameter sensitivity (EPS)thatthickness of penetrameter, expressed as a percentage of thesection thickness radiog
35、raphed, in which a 2T hole would bevisible under the same radiographic conditions. EPS is calcu-lated by: EPS% = 100/ X ( Th/2), where: h = hole diameter,T = step thickness and X= thickness of test object (see E1316,E1025, E747, and Practice E746).3.2.17 gray scalea term used to describe an image co
36、n-taining shades of gray rather than color. Gray scale is the rangeE2007 10 (2016)2of gray shades assigned to image pixels that result in visuallyperceived pixel display brightness.3.2.17.1 DiscussionThe number of shades is usually posi-tive integer values taken from the bit depth. For example: an8-
37、bit gray scale image has up to 256 total shades of gray from0 to 255, with 0 representing white image areas and 255representing black image areas with 254 shades of gray inbetween.3.2.18 image morphinga potentially degraded CR imageresultant from over processing (that is, over driving) anoriginal CR
38、 image.3.2.18.1 Discussion“Morphing” can occur following sev-eral increments of image processing where each precedingimage was “overwritten” resulting in an image that is notice-ably altered from the original.3.2.19 look up table (LUT)one or more fields of binarydigital values arbitrarily assigned t
39、o a range of reference grayscale levels (viewed on an electronic display as shades of“gray”).3.2.19.1 DiscussionA LUT is used (applied) to convertbinary digital pixel data to proportional shades of “gray” thatdefine the CR image. LUTs are key reference files that allowbinary digital pixel data to be
40、 viewed with many combinationsof pixel gray scales over the entire range of a digital image (seeFig. 5-A).3.2.20 original digital imagea digital gray scale (see3.2.17) image resultant from application of original binarydigital pixel data to a linear look-up table (see 3.2.24 and3.2.19 prior to any i
41、mage processing.3.2.20.1 DiscussionThis original gray scale image is usu-ally considered the beginning of the “computed radiograph”,since without this basic conversion (to gray scales) there wouldbe no discernable radiographic image (see Fig. 5-B).3.2.21 photostimulable luminescence (PSL)photostimul
42、able luminescence (PSL) is a physical phenom-enon in which a halogenated phosphor compound emits bluishlight when excited by a source of red spectrum light.3.2.22 pixel brightnessthe luminous (monitor) displayintensity of pixel(s) that can be controlled by means ofelectronic monitor brightness level
43、 settings or changes ofdigital driving level (see 3.2.11).3.2.23 pixel densitythe number of pixels within a digitalimage of fixed dimensions (that is, length and width).3.2.23.1 Discussionfor digital raster images, the conven-tion is to describe pixel density in terms of the number ofpixel-columns (
44、width) and number of pixel rows (height). Analternate convention is to describe the total number of pixels inthe image area (typically given as the number of mega pixels),which can be calculated by multiplying pixel-columns bypixel-rows. Another convention includes describing pixel den-sity per area
45、-unit or per length-unit such as pixels per in./mm.Resolution (see 7.1.5) of a digital image is related to pixeldensity.3.2.24 pixel value (PV)a positive integer numerical valuedirectly associated with each binary picture data element(pixel) of an original digital image where gray scale shades(see 3
46、.2.17) are assigned in linear proportion to radiationexposure dose received by that area.3.2.24.1 DiscussionComputed radiography uses grayscale shades to render visual perceptions of image contrast;thus, linear pixel value (PV) is used to measure a specific shadeFIG. 1 Basic Computed Radiography Pro
47、cessE2007 10 (2016)3of gray that corresponds to the quantity of radiation exposureabsorbed within a particular area of a part. With thisrelationship, a PV of “0” can correspond with “0” radiationdose (white image area of a negative image view) whereas aPV of “4095” can correspond with a saturated de
48、tector (blackimage area of a negative image view) for a 12 bit CR system.PV is directly related to original binary pixel data via acommon linear look-up-table (Fig. 5 A and B illustrate). Thenumber of available pixel value integers within an image isassociated with the number of available gray scale
49、 shades forthe bit depth of the image.3.2.25 PSL afterglowcontinued luminescence from a stor-age phosphor immediately following removal of an externalphotostimulating source.3.2.25.1 DiscussionAbluish luminescence continues for ashort period of time after termination of the photostimulatingsource as illustrated in Fig. 12.3.2.26 relative image quality response (RIQR)a means fordetermining the image quality performance response of a givenradiological imaging system in relative comparison to theimage quality response of another rad
