ASTM E2007-2008 Standard Guide for Computed Radiography.pdf

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1、Designation: E 2007 08Standard Guide forComputed Radiography1This standard is issued under the fixed designation E 2007; 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 t

2、he 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 to

3、understand 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 inspectio

4、n applica-tions. Information presented within this guide may be useful inconjunction with those standards of section 1.2.1.2 CR techniques for general inspection applications maybe found in Practice E 2033. Technical qualification attributesfor CR systems may be found in Practice E 2445. Criteria fo

5、rclassification of CR system technical performance levels maybe found in Practice E 2446. Reference Images StandardE 2422 contains digital reference acceptance illustrations.1.3 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconve

6、rsions to SI units that are provided for information onlyand are not considered standard.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 practice

7、s and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E94 Guide for Radiographic ExaminationE 746 Practice for Determining Relative Image QualityResponse of Industrial Radiographic Imaging SystemsE 747 Practice for Design, Manufacture an

8、d 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 1316 Terminology for Nondestructive ExaminationsE 1453 Guide for Sto

9、rage of Media that Contains Analog orDigital Radioscopic DataE 2002 Practice for Determining Total Image Unsharpnessin RadiologyE 2033 Practice for Computed Radiology (PhotostimulableLuminescence Method)E 2339 Practice for Digital Imaging and Communication inNondestructive Evaluation (DICONDE)E 2422

10、 Digital Reference Images for Inspection of Alumi-num CastingsE 2445 Practice for Qualification and Long-Term Stabilityof Computed Radiology SystemsE 2446 Practice for Classification of Computed RadiologySystems2.2 SMPTE Standard:RP133 Specifications for Medical Diagnostic Imaging TestPattern for Te

11、levision Monitors and Hard-Copy RecordingCameras33. Terminology3.1 Unless otherwise provided within this standard guide,terminology is in accordance with Terminology E 1316.3.2 Definitions:3.2.1 aliasingartifacts that appear in an image when thespatial frequency of the input is higher than the outpu

12、t 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)the read-out value ofunsharpness divided by 2 as effective pixel size of the CRsystem (Practices E 2445 and E 2446).3.2.3 binary/digital pixel dataa matri

13、x 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. Binary digital data value is proportional to theradiation dose received by each pixel.3.2.4 bit depththe number “2” increased by the exponen-

14、tial power of the analogue-to-digital (A/D) converter resolu-tion. Example 1): in a 2 bit image, there are four (22) possible1This 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 Gamma) Method

15、.Current edition approved July 1, 2008. Published August 2008. Originallyapproved in 1999. Last previous edition approved in 2006 as E 2007 - 00(2006).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStan

16、dards 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 10601.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, P

17、A 19428-2959, United Sbinations 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 levels that can be represented is 22or 4. Example 2): a12 bit A/D converter would have

18、4096 (212) gray levels thatcan 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 saturation, producing an image of degradedspatial resolution an

19、d 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, electronicimage display, image storage and retrieval system

20、and interac-tive support software.3.2.7 computed radiographic system classa group ofcomputed radiographic systems characterized with a standardimage quality rating. Practice E 2446, Table 1, provides such aclassification system.3.2.8 computed radiographya radiological nondestructivetesting method th

21、at 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 raw digital image data and a means for electroni-cally displaying

22、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 DiscussionThis mode of image processing is alsoknown as “windowing”

23、 (contrast adjustment) and “leveling”(brightness adjustment) or simply “win-level” image process-ing.3.2.10 contrast-to-noise ratio (CNR)terminology used todescribe image quality associated with a quotient of contrastand noise level within the image.3.2.11 detector signal-to-noise ratio (SNRD)quotie

24、nt ofmean pixel value and standard deviation of pixel value noise(and intensity distribution) for a defined detector area-of-interest and ISO exposure dose (see Practice E 2446).3.2.11.1 DiscussionNotwithstanding extraneous sourcesof digital image noise, SNRDwill normally increase as ISOexposure dos

25、e is increased over the useful exposure range ofthe detector. SNRDis intended for evaluation of detectorperformance without influence of absorbing materials.3.2.12 digital driving level (DDL)terminology used todescribe displayed pixel brightness of a digital image on amonitor resultant from digital

26、mapping of various gray scalelevels within specific look-up-table/s.3.2.12.1 DiscussionDDL is also known as monitor pixelintensity value; thus, may not be the PV of the original digitalimage.3.2.13 digital dynamic rangemaximum material thick-ness latitude that renders acceptable levels of specified

27、imagequality performance within a specified pixel intensity valuerange.3.2.13.1 DiscussionDigital dynamic range should not beconfused with computer file bit depth.3.2.14 digital image contrastpixel intensity value differ-ence between any two areas of interest within a computedradiograph.3.2.14.1 Dis

28、cussiondigital 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.3.2.15 digital image noiseimaging information within acomputed radiograph that is not directly correlated with thedegree of radiation atten

29、uation by the object or feature beingexamined, or insufficient radiation quanta absorbed within thedetector IP, or both.3.2.15.1 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 to

30、statistical variations of pixel intensity value.3.2.16 digital image processingthe use of algorithms tochange original digital image data for the purpose of enhance-ment of some aspect of the image.3.2.16.1 DiscussionExamples include: contrast, bright-ness, pixel density change (digital enlargement)

31、, digital filters,gamma correction and pseudo colors. Some digital processingoperations such as sharpening filters, once saved, permanentlychange the original binary data matrix (Fig. 1, Step 5).3.2.17 equivalent penetrameter sensitivity (EPS)thatthickness of penetrameter, expressed as a percentage

32、of thesection thickness radiographed, 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 E 1316,E 1025, E 747, and Practice E 746).3.2.18 gray scale

33、a term used to describe an image con-taining shades of gray rather than color. Gray scale is the rangeof shades of gray assigned to pixel values that determines pixeldisplay brightness.3.2.18.1 DiscussionThe number of shades is usually posi-tive integer values taken from the bit depth. For example:

34、an8-bit gray scale image has up to 256 total levels of gray from0 to 255, with 0 being white and 255 being black with 254 graylevels in between.3.2.19 image morphinga potentially degraded CR imageresultant from over processing (that is, over driving) anoriginal CR image.3.2.19.1 Discussion“Morphing”

35、 can occur following sev-eral increments of image processing/file save cycles whereeach preceding image was “overwritten” resulting in an imagethat is noticeably altered from the original.3.2.20 look up table (LUT)one or more fields of binarydigital values arbitrarily assigned to a range of referenc

36、e grayscale levels (viewed on an electronic display as shades of“gray”).3.2.20.1 DiscussionA LUT is used (applied) to convertbinary digital pixel data to proportional shades of “gray” thatE2007082define the CR image. LUTs are key reference files that allowbinary digital pixel data to be viewed with

37、many combinationsof pixel gray scales over the entire range of a digital image (seeFig. 2A).3.2.21 measured unsharpnessa term used to describe anattribute of image quality associated with blurring within aradiographic image. Discussion:3.2.21.1 DiscussionMeasured unsharpness is describedwith a numer

38、ical value corresponding with a measure ofresolution taken from a line pair gauge (line pairs per mm) orfrom a duplex wire gauge (width of wires just merged).Measured unsharpness is the total of geometrical and inherentunsharpness within an image.3.2.22 normalized signal-to-noise ratio (SNRN)detecto

39、rsignal-to-noise ratio (SNRDpixel statistics) mathematicallycombined with a measure of detector basic spatial resolution(SRb) on the same radiographic image.3.2.22.1 DiscussionSNRNis calculated by: Imeas/ sPsl3(BSR/88.6) and is used to classify digital detector systemperformance (see Practice E 2446

40、). SNRNis highly influencedby quantity of exposure dose.3.2.23 original digital imagea digital gray scale imageresultant from application of original binary digital pixel datato a look-up table prior to any image processing.3.2.23.1 Discussionthis gray scale image is usually con-sidered the beginnin

41、g of the “computed radiograph”, sinceFIG. 1 Basic Computed Radiography ProcessFIG. 2 (A) Sample 12 bit Look-up Table (B) Graph Version of Applied LUTE2007083without this basic conversion (to gray scales) there would be nodiscernable radiographic image (see Fig. 2B).3.2.24 photostimulable luminescenc

42、e (PSL)photo stimu-lated luminescence (PSL) is a physical phenomenon in whicha phosphor that has ceased emitting light because of removal ofthe stimulus once again emits light when excited by light witha longer wavelength than the emission wavelength.3.2.25 pixel brightnessthe luminous (monitor) dis

43、playintensity of pixel/s that can be controlled by means ofelectronic monitor brightness level settings or changes ofdigital driving level (see 3.2.12).3.2.26 pixel densitythe number of pixels within a digitalimage of fixed dimensions (that is, length and width).3.2.26.1 DiscussionFor digital raster

44、 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 pixels inthe image area (typically given as the number of mega pixels),which can be calculated by multiply

45、ing 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 7.1.6) of a digital image is related to pixeldensity.3.2.27 pixel value (PV, also known as gray value)apositive integer numerical value wit

46、hin the gray scale values ofa picture data element (pixel) directly proportional with binarypixel data values of a digital image.3.2.27.1 DiscussionPV is directly related to binary pixeldata via a look-up-table (Fig. 2 illustrates). The number ofavailable PVs is associated with gray scale bit depth

47、of digitalimage.3.2.28 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.3.2.28.1 DiscussionRIQR methods are not intended

48、 as adirect measure of image quality for a specific radiographictechnique application. Practice E 746 provides a standardRIQR method.3.2.29 storage phosphor imaging plate (IP)a photostimu-lable luminescent material that is capable of storing a latentradiographic image of a material being examined an

49、d, uponstimulation by light of appropriate wavelength, will generateluminescence (PSL) proportional to radiation absorbed.3.2.29.1 DiscussionWhen performing computed radiog-raphy, an IP is used instead of a film. When establishingtechniques related to source focal geometries, the IP is referredto as a detector (that is, source-to detector-distance or SDD).4. Significance and Use4.1 This guide is intended as a source of tutorial andreference information that can be used during establishment ofcomputed radiography techniques