1、Designation: E 2597 07e1Standard Practice forManufacturing Characterization of Digital Detector Arrays1This standard is issued under the fixed designation E 2597; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last rev
2、ision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEEditorial corrections were made throughout in April 2008.1. Scope1.1 This practice describes the evaluation of Digital Detec-tor Ar
3、rays (DDAs), and assures that one common standardexists for quantitative comparison of DDAs so that an appro-priate DDA is selected to meet NDT requirements.1.2 This practice is intended for use by manufacturers orintegrators of DDAs to provide quantitative results of DDAcharacteristics for NDT user
4、 or purchaser consumption. Someof these tests require specialized test phantoms to assureconsistency among results among suppliers or manufacturers.These tests are not intended for users to complete, nor are theyintended for long term stability tracking and lifetime measure-ments. However, they may
5、be used for this purpose, if sodesired.1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the
6、 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:2E 1316 Terminology for Nondestructive ExaminationsE 1647 Practice for Determining Contrast Sensitivity inRad
7、iologyE 1742 Practice for Radiographic ExaminationE 1815 Test Method for Classification of Film Systems forIndustrial RadiographyE 2002 Practice for Determining Total Image Unsharpnessin RadiologyE 2445 Practice for Qualification and Long-Term Stabilityof Computed Radiology SystemsE 2446 Practice fo
8、r Classification of Computed RadiologySystems2.2 Other Standards:ISO 7004 PhotographyIndustrial Radiographic FilmsDetermination of ISO Speed, ISO Average Gradient andISO Gradients G2 and G4 When Exposed to X- andGamma-Radiation3IEC 62220-1 Medical Electrical Equipment Characteristicsof Digital X-ray
9、 Imaging Devices Part 1: Determination ofthe Detective Quantum Efficiency43. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 digital detector array (DDA) systeman electronicdevice that converts ionizing or penetrating radiation into adiscrete array of analog signals which are sub
10、sequently digi-tized and transferred to a computer for display as a digitalimage corresponding to the radiologic energy pattern impartedupon the input region of the device. The conversion of theionizing or penetrating radiation into an electronic signal maytranspire by first converting the ionizing
11、or penetrating radia-tion into visible light through the use of a scintillating material.These devices can range in speed from many seconds perimage to many images per second, up to and in excess ofreal-time radioscopy rates (usually 30 frames per seconds).3.1.2 active DDA areathe size and location
12、of the DDA,which is recommended by the manufacturer as usable.3.1.3 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.3.1.4 contrast-to-noise ratio (CNR)quotien
13、t of the differ-ence of the mean signal levels between two image areas and thestandard deviation of the signal levels.As applied here, the twoimage areas are the step-wedge groove and base material. The1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is t
14、he direct responsibility of Subcommittee E07.01 onRadiology (X and Gamma) Method.Current edition approved Dec. 1, 2007. Published January 2008.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards vo
15、lume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.4Available from International Electrotechnical Commission (IEC), 3 rue deVaremb, Case posta
16、le 131, CH-1211, Geneva 20, Switzerland, http:/www.iec.ch.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.standard deviation of the intensity of the base material is ameasure of the noise. The CNR depends on the radiation doseand the
17、 DDA system properties.3.1.5 basic spatial resolution (SRb)the basic spatial reso-lution indicates the smallest geometrical detail, which can beresolved using the DDA. It is similar to the effective pixel size.3.1.6 detector signal-to-noise rationormalized (dSNRn)the SNR is normalized for basic spat
18、ial resolution SRb asmeasured directly on the detector without any object other thanbeam filters in the beam path.3.1.7 internal scatter radiation (ISR)scattered radiationwithin the detector.3.1.8 effciencydSNRn (see 3.1.6) divided by the squareroot of the dose (in mGy) and is used to measure the re
19、sponseof the detector at different beam energies and qualities.3.1.9 achievable contrast sensitivity (CSa)optimum con-trast sensitivity (see Terminology E 1316 for a definition ofcontrast sensitivity) obtainable using a standard phantom withan x-ray technique that has little contribution from scatte
20、r.3.1.10 specific material thickness range (SMTR)the ma-terial thickness range within which a given image quality isachieved. As applied here, the wall thickness range of a DDA,whereby the thinner wall thickness is limited by 80 % of themaximum gray value of the DDA and the thicker wallthickness by
21、a SNR of 130:1 for 2 % contrast sensitivity andSNR of 250:1 for 1 % contrast sensitivity. Note that SNRvalues of 130:1 and 250:1 do not guarantee that 2 % and 1 %contrast sensitivity values will be achieved, but are being usedto designate a moderate quality image, and a higher qualityimage respectiv
22、ely.3.1.11 frame ratenumber of frames acquired per second.3.1.12 lagresidual signal in the DDA that occurs shortlyafter the exposure is completed.3.1.13 burn-inchange in gain of the scintillator that per-sists well beyond the exposure.3.1.14 GlobalLag1f (global lag 1st frame)the ratio ofmean signal
23、value of the first frame of the DDA where thex-rays are completely off to the mean signal value of an imagewhere the x-rays are fully on. This parameter is specifically forthe integration time used during data acquisition.3.1.15 GlobalLag1s (global lag 1 s)the projected value ofGlobalLag1f for an in
24、tegration time of 1 second.3.1.16 GlobalLag60s (global lag 60 s)the ratio betweenmean gray value of an image acquired with the DDA after 60s where the x-rays are completely off, to same of an imagewhere the x-rays are fully on.3.1.17 bad pixela pixel identified with a performanceoutside of the speci
25、fication range for a pixel of a DDA asdefined in 6.2.3.1.18 step-wedgea stepped block of a single metallicalloy with a thickness range that is to be manufactured inaccordance with 5.2.3.1.19 phantoma part or item being used to quantify DDAcharacterization metrics.3.1.20 DDA offset imageimage of the
26、DDAin the absenceof x-rays providing the background signal of all pixels.3.1.21 DDA gain imageimage obtained with no structuredobject in the x-ray beam to calibrate pixel response in a DDA.3.1.22 calibrationcorrection applied for the offset signal,and the non-uniformity of response of any or all of
27、the x-raybeam, scintillator and the read out structure.3.1.23 gray valuethe numeric value of a pixel in a DDAimage. This is typically interchangeable with the term pixelvalue, detector response, Analog-to-Digital Unit, and detectorsignal.3.1.24 pixel valuethe numeric value of a pixel in a DDAimage.
28、This is typically interchangeable with the term grayvalue.3.1.25 saturation gray valuethe maximum possible grayvalue of the DDA after offset correction.4. Significance and Use4.1 This practice provides a means to compare DDAs on acommon set of technical measurements, realizing that inpractice adjust
29、ments can be made to achieve similar resultseven with disparate DDAs given geometric magnification, orother industrial radiologic settings that may compensate forone shortcoming of a device.4.2 A user must understand the definitions and correspond-ing performance parameters used in this practice in
30、order tomake an informed decision on how a given DDA can be usedin the target application.4.3 The factors that will be evaluated for each DDA are:basic spatial resolution (SRb), efficiency (Detector SNR-normalized (dSNRn) at 1 mGy, for different energies and beamqualities), achievable contrast sensi
31、tivity (CSa), specific mate-rial thickness range (SMTR), image lag, burn-in, bad pixels andinternal scatter radiation (ISR).5. Apparatus5.1 Duplex Wire Image Quality Indicator for SRbTheduplex wire quality indicator corresponds to the design speci-fied in Practice E 2002 for the measurement of SRb a
32、nd notunsharpness.5.2 Step-Wedge Image Quality IndicatorThe wedge hassix steps in accordance with the drawing provided in Fig. 1.The wedge may be formed with built-in masking to avoidX-ray scatter and undercut. In lieu of built-in masking, thestep-wedge may be inserted into a lead frame. The Pb fram
33、ecan then extend another 25.4 mm (1 in.) about the perimeter ofthe step-wedge, beyond the support. The slight overlap of thePb support with the edges of the step-wedge (no more than 6mm (0.25 in.) assures a significantly reduced number ofX-rays to leak-through under the step-wedge that will contami-
34、nate the data acquired on each step. The step-wedges shall beformed of three different materials Aluminum6061,TitaniumTi-6Al-4V, and Inconel 718 with a center groove ineach step, as shown in Fig. 1. The dimensions of the wedges forthe different materials are shown in Table 1.5.3 Filters for Measurin
35、g Effciency of the DDAThefollowing filter thicknesses (5.3.1-5.3.7) and alloys (5.3.8)shall be used to obtain different radiation beam qualities andare to be placed at the output of the beam. The tolerance forthese thicknesses shall be 60.1 mm (60.004 in.).5.3.1 No external filter (50 kV).5.3.2 30 m
36、m (1.2 in.) Al (90 kV).5.3.3 40 mm (1.6 in.) Al (120 kV).E259707e125.3.4 3 mm (0.12 in.) Cu (120 kV).5.3.5 10 mm (0.4 in.) Fe (160 kV).5.3.6 8 mm (0.3 in.) Cu (220 kV).5.3.7 16 mm (0.6 in.) Cu (420 kV).5.3.8 The filters shall be placed directly at the tube window.The aluminum filter shall be compose
37、d of Aluminum 6061.The Copper shall be composed of 99.9 % purity or better. TheIron filter shall be composed of Stainless steel 304.NOTE 1Radiation qualities in 5.3.2 and 5.3.3 are in accordance withDQE standard IEC 62220-1, and radiation quality in 5.3.4 and 5.3.5 are inaccordance with ISO 7004. Ra
38、diation quality in 5.3.6 is used also in TestMethod E 1815, Practice E 2445, and Practice E 2446.5.4 Filters for Measuring, Burn-In and Internal ScatterRadiationThe filters for measuring burn-in and ISR shallconsist of a minimum 16 mm (0.6 in.) thick Cu plate (5.3.7)100 by 75 mm (4 by 3 in.) with a
39、minimum of one sharp edge.If the DDA is smaller than 15 by 15 cm (5.9 by 5.9 in.) use aplate that is dimensionally 25 % of the active DDA area.6. Calibration and Bad Pixel Standardization6.1 DDA Calibration MethodPrior to qualification testingthe DDA shall be calibrated for offset and, or gain (see
40、3.1.20and 3.1.21) to generate corrected images per manufacturersrecommendation. It is important that the calibration procedurebe completed as would be done in practice during routineFIG. 1 Step-Wedge Drawing (dimensions are listed in Table 1)E259707e13calibration procedures. This is to assure that d
41、ata collected bymanufacturers will closely match that collected when thesystem is entered into service.6.2 Bad Pixel Standardization for DDAsManufacturerstypically have different methods for correcting bad pixels.Images collected for qualification testing shall be corrected forbad pixels as per manu
42、facturers bad pixel correction proce-dure wherever required. In this section a standardized nomen-clature is presented. The following definitions enable classifi-cation of pixels in a DDA as bad or good types. Themanufacturers are to use these definitions on a statistical set ofdetectors in a given
43、detector type to arrive at “typical” resultsfor bad pixels for that model. The identification and correctionof bad pixels in a delivered DDA remains in the purview ofagreement between the purchaser and the supplier.6.2.1 Definition and Test of Bad Pixels:6.2.1.1 Dead PixelPixels that have no respons
44、e, or thatgive a constant response independent of radiation dose on thedetector.6.2.1.2 Over Responding PixelPixels whose gray valuesare greater than 1.3 times the median gray value of an area ofa minimum of 21321 pixels. This test is done on an offsetcorrected image.6.2.1.3 Under Responding PixelPi
45、xels whose gray valuesare less than 0.6 times the median gray value of an area of ina minimum of 21321 pixels. This test is done on an offsetcorrected image.6.2.1.4 Noisy PixelPixels whose standard deviation in asequence of 30 to 100 images without radiation is more than 6times the median pixel stan
46、dard deviation for the completeDDA.6.2.1.5 Non-Uniform PixelPixel whose value exceeds adeviation of more than 61 % of the median value of its 939neighbor pixel. The test should be performed on an imagewhere the average gray value is at or above 75 % of the DDAslinear range. This test is done on an o
47、ffset and gain correctedimage.6.2.1.6 Persistence/Lag PixelPixel whose value exceeds adeviation of more than a factor of 2 of the median value of its939 neighbors in the first image after X-ray shut down (referto 7.11.1).6.2.1.7 Bad Neighborhood PixelPixel, where all 8 neigh-boring pixels are bad pi
48、xels, is also considered a bad pixel.6.2.2 Types or Groups of Bad Pixels:6.2.2.1 Single Bad PixelA single bad pixel is a bad pixelwith only good neighborhood pixels.TABLE 1 Dimension of the Three Step-Wedges for Three Different Materials Used as Image Quality Indicators in this PracticeMaterial Unit
49、 A B1 B2 B3 B4 B5 B6 C D EStep-wedge (Inconel 718) mm 35.0 1.25 2.5 5.0 7.5 10.0 12.5 175.0 70.0 35.0Tolerance (6) microns 200 25 25 38 38 38 38 200 200 2005 % Groove microns 63 125 250 375 500 625Tolerance (6) microns 10 10 10 10 10 10Material Unit A B1 B2 B3 B4 B5 B6 C D EStep-wedge (Ti-6Al-4V) mm 35.0 2.5 5.0 7.5 10.0 20.0 30.0 175.0 70.0 35.0Tolerance (6) microns 200 50 50 50 50 50 50 200 200 2005 % Groove microns 125 250 375 500 1000 1500Tolerance (6) microns 10 10 10 10 10 10Material Unit A B1 B2 B3 B4 B5 B6 C D EStep-wedge (
