1、Designation: E2007 10Standard 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 parentheses indicates the
2、 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 terminology required toun
3、derstand 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 end-user inspection
4、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. Criteria forclassificat
5、ion 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 parentheses are forinfor
6、mation 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 limitations prior to use.2.
7、Referenced Documents2.1 ASTM Standards:2E94 Guide for Radiographic ExaminationE746 Practice for Determining Relative Image QualityResponse of Industrial Radiographic Imaging SystemsE747 Practice for Design, Manufacture and MaterialGrouping Classification of Wire Image Quality Indicators(IQI) Used fo
8、r RadiologyE1025 Practice for Design, Manufacture, and MaterialGrouping Classification of Hole-Type Image Quality Indi-cators (IQI) Used for RadiologyE1316 Terminology for Nondestructive ExaminationsE1453 Guide for Storage of Magnetic Tape Media thatContains Analog or Digital Radioscopic DataE2002 P
9、ractice for Determining Total Image Unsharpnessin RadiologyE2033 Practice for Computed Radiology (PhotostimulableLuminescence Method)E2339 Practice for Digital Imaging and Communication inNondestructive Evaluation (DICONDE)E2422 Digital Reference Images for Inspection of Alumi-num CastingsE2445 Prac
10、tice for Qualification and Long-Term Stabilityof Computed Radiology SystemsE2446 Practice for Classification of Computed RadiologySystemsE2660 Digital Reference Images for Investment Steel Cast-ings for Aerospace ApplicationsE2669 Digital Reference Images for Titanium Castings2.2 SMPTE Standard:RP-1
11、33 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 accordance with Terminology E1316.3.2 Definitions:3.2.1 aliasingartifacts that appear in an image when
12、 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 (SRb)terminology used todescribe the smallest degree of visible detail within a digitalimage that is
13、 considered the effective pixel size.3.2.2.1 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,1This guide is unde
14、r the jurisdiction of ASTM Committee E07 on Nondestruc-tive Testing and is the direct responsibility of Subcommittee E07.01 on Radiology(X and Gamma) Method.Current edition approved June 1, 2010. Published July 2010. Originally approvedin 1999. Last previous edition approved in 2008 as E2007 - 08. D
15、OI: 10.1520/E2007-10.2For 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 Society of Motion Pictur
16、e and Television Engineers (SMPTE),3 Barker Ave, 5th Floor, White Plains, NY 10601.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the single image feature is considered the effective pixel size.If the physical sizes of the two disti
17、nct 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 image isdetermined to resolve five line pairs per mm or a width of lineequivalent to five distinct l
18、ines within a millimetre. The basicspatial resolution is determined as 1/ 2 3 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 each latent pixel(on the IP) to proportional (within the bit depth scanned)electrical values. Binar
19、y 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. Example 1) In a 2-bit image, there are four (22) possiblecombinations for a pixel: 00, 01, 10 and
20、 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.Example 2): A 12-bit A/D converter would have 4096 (212)gray scales shades that can be represented
21、.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 saturation, producing an image of degradedspatial resolution and gray scale rendition.3.2.6 computed radiogr
22、aphic 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, electronicimage display, image storage and retrieval system and interac-tive support software.3.2.7 compu
23、ted radiographic system classa group ofcomputed radiographic systems characterized with a standardimage quality rating. Practice E2446, Table 1, provides such aclassification system.3.2.8 computed radiographya radiological nondestructivetesting method that uses storage phosphor imaging plates(IPs),
24、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 digital image data and a means forelectronically displaying or printing resultant image data.3.2.9 cont
25、rast 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 DiscussionThis mode of image processing is alsoknown as “windowing” (contrast adjustment) and “leveling”(brigh
26、tness 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 pixel values.3.2.10.1 DiscussionCNR is a measure of image qualitythat is dependent upon both digital ima
27、ge 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.3.2.11 digital driving level (DDL)terminology used todescribe displayed pixel brightness of a digital
28、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 the PV of the original digitalimage.3.2.12 digital dynamic rangemaximum material thick-ness latitude t
29、hat 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 depth.3.2.13 digital image contrastpixel value difference be-tween any two areas of interest within
30、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.Visually displayed image contrast can be altered via digitalre-mapping (see 3.2.11) or re-assignment of s
31、pecific 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 or feature beingexamined and/or insufficient radiation quanta absorbed withinthe detector IP.3.2.14
32、.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 pixel intensity value.3.2.15 digital image processingthe use of algorithms tochange original digital
33、 image data for the purpose of enhance-ment of some aspect of the image.3.2.15.1 DiscussionExamples include: contrast, bright-ness, pixel density change (digital enlargement), digital filters,gamma correction and pseudo colors. Some digital processingoperations such as sharpening filters, once saved
34、, permanentlychange 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 radiographed, in which a 2T hole would bevisible under the same radiographic conditions. EPS is calcu-
35、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 con-taining shades of gray rather than color. Gray scale is the rangeof gray shades assigned to i
36、mage 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-bit gray scale image has up to 256 total shades of gray from0 to 255, with 0 representing white image areas and
37、 255representing black image areas with 254 shades of gray inbetween.E2007 1023.2.18 image morphinga potentially degraded CR imageresultant from over processing (that is, over driving) anoriginal CR image.3.2.18.1 Discussion“Morphing” can occur following sev-eral increments of image processing where
38、 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 to a range of reference grayscale levels (viewed on an electronic display as shades of“gray”).3.2.19.1
39、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 viewed with many combinationsof pixel gray scales over the entire range of a digital image (seeFig. 5
40、-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 image processing.3.2.20.1 DiscussionThis original gray scale image is usu-ally considered the beginning
41、 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)photostimulable luminescence (PSL) is a physical phenom-enon in which a halogenated phosphor compound emits bluis
42、hlight 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 settings or changes ofdigital driving level (see 3.2.11).3.2.23 pixel densitythe number of pixels wit
43、hin 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 (width) and number of pixel rows (height). Analternate convention is to describe the total number of pi
44、xels 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-unit or per length-unit such as pixels per in./mm.Resolution (see 7.1.5) of a digital image is relate
45、d 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 3.2.17) are assigned in linear proportion to radiationexposure dose received by that area.3.2.24.1 Disc
46、ussionComputed radiography uses grayscale shades to render visual perceptions of image contrast;thus, linear pixel value (PV) is used to measure a specific shadeof gray that corresponds to the quantity of radiation exposureabsorbed within a particular area of a part. With this relation-ship, a PV of
47、 “0” can correspond with “0” radiation dose (whiteimage area of a negative image view) whereas a PV of “4095”can correspond with a saturated detector (black image area ofa negative image view) for a 12 bit CR system. PV is directlyrelated to original binary pixel data via a common linearlook-up-tabl
48、e (Fig. 5 A and B illustrate). The number ofavailable pixel value integers within an image is associatedwith the number of available gray scale shades for the bit depthof the image.FIG. 1 Basic Computed Radiography ProcessE2007 1033.2.25 PSL afterglowcontinued luminescence from a stor-age phosphor i
49、mmediately 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 radiological imaging system.3.2.26.1 DiscussionRIQR methods are not intended as adirect measure of image quality
