1、Designation: E2736 10Standard Guide forDigital Detector Array Radiology1This standard is issued under the fixed designation E2736; 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 i
2、ndicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This standard is a user guide, which is intended to serveas a tutorial for selection and use of various digital detectorarray systems nominally composed of th
3、e detector array and animaging system to perform digital radiography. This guide alsoserves as an in-detail reference for the following standards:Practices E2597, E2698, and E2737.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is therespo
4、nsibility 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. Referenced Documents2.1 ASTM Standards:2E94 Guide for Radiographic ExaminationE155 Reference Radiographs for Inspection of Aluminuma
5、nd Magnesium CastingsE192 Reference Radiographs of Investment Steel Castingsfor Aerospace ApplicationsE747 Practice for Design, Manufacture and MaterialGrouping Classification of Wire Image Quality Indicators(IQI) Used for RadiologyE1000 Guide for RadioscopyE1025 Practice for Design, Manufacture, an
6、d MaterialGrouping Classification of Hole-Type Image Quality Indi-cators (IQI) Used for RadiologyE1316 Terminology for Nondestructive ExaminationsE1320 Reference Radiographs for Titanium CastingsE1742 Practice for Radiographic ExaminationE1815 Test Method for Classification of Film Systems forIndust
7、rial RadiographyE1817 Practice for Controlling Quality of RadiologicalExamination by Using Representative Quality Indicators(RQIs)E2002 Practice for Determining Total Image Unsharpnessin RadiologyE2422 Digital Reference Images for Inspection of Alumi-num CastingsE2445 Practice for Qualification and
8、Long-Term Stabilityof Computed Radiology SystemsE2446 Practice for Classification of Computed RadiologySystemsE2597 Practice for Manufacturing Characterization of Digi-tal Detector ArraysE2660 Digital Reference Images for Investment Steel Cast-ings for Aerospace ApplicationsE2669 Digital Reference I
9、mages for Titanium CastingsE2698 Practice for Radiological Examination Using DigitalDetector ArraysE2737 Practice for Digital Detector Array PerformanceEvaluation and Long-Term Stability3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 digital detector array (DDA) systeman elect
10、ronicdevice that converts ionizing or penetrating radiation into adiscrete array of analog signals which are subsequently digi-tized and transferred to a computer for display as a digitalimage corresponding to the radiation energy pattern impartedupon the input region of the device. The conversion o
11、f theionizing or penetrating radiation into an electronic signal maytranspire by first converting the ionizing or penetrating radia-tion into visible light through the use of a scintillating material.These devices can range in speed from many minutes perimage to many images per second, up to and in
12、excess ofreal-time radioscopy rates (usually 30 frames per seconds).3.1.2 signal-to-noise ratio (SNR)quotient of mean valueof the intensity (signal) and standard deviation of the intensity(noise). The SNR depends on the radiation dose and the DDAsystem properties.3.1.3 normalized signal-to-noise rat
13、io (SNRn)SNR nor-malized for basic spatial resolution (see Practice E2445).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 Gamma) Method.Current edition approved April 15, 2010. Publishe
14、d July 2010.2For 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 International, 100 Barr Harbor Dr
15、ive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.4 basic spatial resolution (SRb)basic spatial resolu-tion indicates the smallest geometrical detail, which can beresolved using the DDA. It is similar to the effective pixel size.3.1.5 effciencydSNRn(see 3.1.6 of Practice E2597) d
16、i-vided by the square root of the dose (in mGy) and is used tomeasure the response of the detector at different beam energiesand qualities.3.1.6 achievable contrast sensitivity (CSa)optimum con-trast sensitivity (see Terminology E1316 for a definition ofcontrast sensitivity) obtainable using a stand
17、ard phantom withan X-ray technique that has little contribution from scatter.3.1.7 specific material thickness range (SMTR)materialthickness range within which a given image quality isachieved.3.1.8 contrast-to-noise ratio (CNR)quotient of the differ-ence of the mean signal levels between two image
18、areas and thestandard deviation of the signal levels. The CNR depends onthe radiation dose and the DDA system properties.3.1.9 lagresidual signal in the DDA that occurs shortlyafter the exposure is completed.3.1.10 burn-inchange in gain of the scintillator or photo-conductor that persists well beyon
19、d the exposure.3.1.11 internal scatter radiation (ISR)scattered radiationwithin the detector (from scintillator, photodiodes, electronics,shielding, or other detector hardware).3.1.12 bad pixela bad pixel is a pixel identified with aperformance outside of the specification for a pixel of a DDAas def
20、ined in Practice E2597.3.1.13 grooved wedgea wedge with one groove, that is5 % of the base material thickness and that is used forachievable contrast sensitivity measurement in Practice E2597.3.1.14 phantoma part or item being used to quantify DDAcharacterization metrics.4. Significance and Use4.1 T
21、his standard provides a guide for the other DDAstandards (see Practices E2597, E2698, and E2737). It is notintended for use with computed radiography apparatus. Figure1 describes how this standard is interrelated with the afore-mentioned standards.4.2 This guide is intended to assist the user to und
22、erstandthe definitions and corresponding performance parameters usedin related standards as stated in 4.1 in order to make aninformed decision on how a given DDA can be used in thetarget application.4.3 This guide is also intended to assist cognizant engineer-ing officers, prime manufacturers, and t
23、he general service andmanufacturing customer base that may rely on DDAs toprovide advanced radiological results so that these parties mayset their own acceptance criteria for use of these DDAs bysuppliers and shops to verify that their parts and structures areof sound integrity to enter into service
24、.4.4 The manufacturer characterization standard for DDA(see Practice E2597) serves as a starting point for the end userto select a DDA for the specific application at hand. DDAmanufacturers and system integrators will provide DDA per-formance data using standardized geometry, X-ray beam spec-tra, an
25、d phantoms as prescribed in Practice E2597. The enduser will look at these performance results and compare DDAmetrics from various manufacturers and will decide on a DDAthat can meet the specification required for inspection by theend user. See Sections 5 and 8 for a discussion on thecharacterizatio
26、n tests and guidelines for selection of DDAs forspecific applications.4.5 Practice E2698 is designed to assist the end user to setup the DDA with minimum requirements for radiologicalexaminations. This standard will also help the user to get therequired SNR, to set up the required magnification, and
27、provides guidance for viewing and storage of radiographs.Discussion is also added to help the user with marking andidentification of parts during radiological examinations.4.6 Practice E2737 is designed to help the end user with aset of tests so that the stability of the performance of the DDAcan be
28、 confirmed. Additional guidance is provided in thisdocument to support this standard.4.7 Figure 1 provides a summary of the interconnectivity ofthese four DDA standards.5. DDA Technology Description5.1 General Discussion:5.1.1 DDAs are seeing increased use in industries to en-hance productivity and
29、quality of nondestructive testing. DDAsare being used for in-service nondestructive testing, as adiagnostic tool in the manufacturing process, and for inlinetesting on production lines. DDAs are also being used as handheld, or scanned devices for pipeline inspections, in industrialcomputed tomograph
30、y systems, and as part of large roboticscanning systems for imaging of large or complex structures.Because of the digital nature of the data, a variety of newapplications and techniques have emerged recently, enablingquantitative inspection and automatic defect recognition.5.1.2 DDAs can be used to
31、detect various forms of electro-magnetic radiation, or particles, including gamma rays, X-rays,neutrons, or other forms of penetrating radiation. This standardfocuses on X-rays and gamma rays.5.2 DDA architecture:5.2.1 A common aspect of the different forms of thistechnology is the use of discrete s
32、ensors (position-sensitive)where, the data from each discrete location is read out into afile structure to form pixels of a digital image file. In all itssimplicity, the device has an X-ray capture material as itsprimary means for detecting X-rays, which is then coupled toa solid-state pixelized str
33、ucture, where such a structure issimilar to the imaging chips used in visible-wavelength digitalphotography and videography devices. Figure 2 shows a blockdiagram of a typical digital X-ray imaging system.5.2.2 An important difference between X-ray imaging andvisible-light imaging is the size of the
34、 read-out device. Theimagers found in cameras and for visible-light are typically onthe order of 1 to 2 cm2in area. Since X-rays are not easilyfocused, as is the case for visible light, the imaging mediummust be the size of the object. Hence, the challenge lies inmeeting the requirement of a large u
35、niform imaging areawithout loss of spatial information. This in turn requires highpixel densities of the read-out device over the object underexamination, as well a primary sensing medium that alsoretains the radiologic pattern in its structure. Therefore, eachDDA consists of a primary X-ray or gamm
36、a ray captureE2736 102medium followed by a pixelized read structure, with various means of transferring the above said captured pattern. For eachFIG. 1 Flow Diagram Representing the Connection Between the Four DDA StandardsFIG. 2 Block Diagram of a Typical Digital X-Ray Imaging SystemE2736 103of the
37、se elements, there are numerous options that can beselected in the creation of DDAs. For the primary X-rayconversion material, there are either luminescent materialssuch as scintillators or phosphors, and photoconductive mate-rials also known as direct converter semiconductors.5.2.3 For read-out str
38、uctures, the technology consists ofcharge coupled detectors (CCDs), complementary metal oxidesilicon (CMOS) based detectors, amorphous silicon thin filmtransistor diode read-out structures, and linear or area crystal-line silicon pixel diode structures. Other materials and struc-tures are also possi
39、ble, but in the end, a pixelized pattern iscaptured and transferred to a computer for review.5.2.4 Each primary conversion material can be coupled withthe various read structures mentioned through a wide range ofcoupling media, devices, or circuitry. With all of these possiblecombinations, there are
40、 many different types of DDAs thathave been produced. But all result in a digital X-ray or gammaray image that can be used for different NDT applications.5.2.5 Following the capture of the X-rays and conversioninto an analog signal on the read-out device, this signal istypically amplified and digiti
41、zed. There are numerous schemesfor each of these steps, and the reader is referred to (1, 2, 3)3for further discussion on this topic.5.3 Digitization Methods:5.3.1 Digitization techniques typically convert the analogsignal to discrete pixel values. For DDAs the digitization istypically, 8-bit (256 g
42、ray values), 12-bits (4096 gray values),14-bits (16,384 gray levels) or 16-bits (65,536 values). Thehigher the bit depth, the more finely the signal is sampled.5.3.2 The digitization does not necessarily define the graylevel range of the DDA. The useful range of performance isdefined by the ability
43、of the read device to capture signal in alinear relation to the signal generated by the primary conver-sion device. A wide linear range warrants the use of a high bitdepth digitizer. It should be noted that if digitization is not highenough to cover the information content from the read device,digit
44、ization noise might result. This can be manifested as aposterization effect, where discrete bands of gray levels areobserved in the image.5.3.3 Conversely, if digitization is selected that is signifi-cantly higher than the range of the read-out device then theadded sampling may not necessarily impro
45、ve performance.Secondly, if the digitization is completed well beyond thelinear range of the read structure, these added gray levelswould not be useable. For example, 16-bits of digitization donot necessarily indicate 65,536 levels of linear responsivity.5.3.4 The useful range of a detector is frequ
46、ently defined asthe maximum usable level, without saturation in relation to thenoise floor of the DDA, where again no useful differentiationcan be extracted from the data. This is sometimes referred to asthe detector dynamic range.5.3.5 The dynamic range is different from the specificmaterial thickn
47、ess range (SMTR) as defined in this standardand Practice E2597. That range is a true practical range of theDDA at hand, a range significantly tighter than the DDAdynamic range.5.3.6 The SMTR is one of the properties to consider in DDAselection, as it impacts the thickness range that can beinterprete
48、d in a single view. This is dependent on the charac-teristics of the read device and the digitization level. This testprovides a means of determining an effective range withoutunderstanding the subtle nuances of the detector readout, andavoids erroneous parallels between bit depth and its relation t
49、othickness range, and maximum possible signal from a device.5.4 Specific DDA componentsThere are numerous optionsin each component of the imaging chain to produce a DDA. Tounderstand the options and limitations of each category, and tobest assess which technology to pursue for a given application,the underlying technology will be discussed beginning with theimage capture medium. This is followed by the image readstructure and then the image transfer device is discussed for thevarious configurations of the read-out devices. For a moredetailed description of the archit
