1、Designation: E2597/E2597M 14Standard Practice forManufacturing Characterization of Digital Detector Arrays1This standard is issued under the fixed designation E2597/E2597M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year o
2、f last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes the evaluation of Digital Detec-tor Arrays (DDAs), and assures that one common standardexist
3、s 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 or purchaser consumption. Someof these tests require
4、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 be used for this purpose, if sodesired.1.3 The results
5、 reported based on this standard should bebased on a group of at least three individual detectors for aparticular model number.1.4 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefor
6、e, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.5 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 t
7、o establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E1316 Terminology for Nondestructive ExaminationsE1815 Test Method for Classification of Film Systems forIndustrial RadiographyE2002
8、 Practice for Determining Total Image Unsharpness inRadiologyE2445 Practice for Qualification and Long-Term Stability ofComputed Radiology SystemsE2446 Practice for Classification of Computed RadiologySystems2.2 Other Standards:ISO 7004 PhotographyIndustrial Radiographic FilmsDetermination of ISO Sp
9、eed, ISO Average Gradient andISO Gradients G2 and G4 When Exposed to X- andGamma-Radiation3IEC 62220-1 Medical Electrical Equipment Characteristicsof Digital X-ray Imaging Devices Part 1: Determination ofthe Detective Quantum Efficiency43. Terminology3.1 Definitions of Terms Specific to This Standar
10、d:3.1.1 achievable contrast sensitivity (CSa)optimum con-trast sensitivity (see Terminology E1316 for a definition ofcontrast sensitivity) obtainable using a standard phantom withan X-ray technique that has little contribution from scatter.3.1.2 active DDA areathe size and location of the DDA,which
11、is recommended by the manufacturer as usable.3.1.3 bad pixela pixel identified with a performanceoutside of the specification range for a pixel of a DDA asdefined in 6.2.3.1.4 burn-inchange in gain of the scintillator that persistswell beyond the exposure.3.1.5 calibrationcorrection applied for the
12、offset signal,and the non-uniformity of response of any or all of the X-raybeam, scintillator and the read-out structure.3.1.6 contrast-to-noise ratio (CNR)quotient of the differ-ence of the mean signal levels between two image areas and thestandard deviation of the signal levels.As applied here, th
13、e 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 the direct responsibility of Subcommittee E07.01 onRadiology (X and Gamma) Method.Current edition approved Jan. 1, 2014. Published Februar
14、y 2014. Originallyapproved in 2007. Last previous edition approved in 2007 as E2597- 071. DOI:10.1520/E2597_E2597M-14.2For 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 t
15、o 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 postale 131, CH-1211, Geneva 2
16、0, Switzerland, http:/www.iec.ch.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1standard deviation of the intensity of the base material is ameasure of the noise. The CNR depends on the radiation doseand the DDA system properties.3.1
17、.7 detector signal-to-noise rationormalized (dSNRn)the SNR is normalized for basic spatial resolution SRb asmeasured directly on the detector without any object other thanbeam filters in the beam path.3.1.8 digital detector array (DDA) systeman electronicdevice that converts ionizing or penetrating
18、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 radiologic energy pattern impartedupon the input region of the device. The conversion of theionizing or penetrating radiation into an el
19、ectronic 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 seconds perimage to many images per second, up to and in excess ofreal-time radioscopy rates (usually 30 f
20、rames per seconds).3.1.9 DDA gain imageimage obtained with no structuredobject in the X-ray beam to calibrate pixel response in a DDA.3.1.10 DDA offset imageimage of the DDAin the absenceof X-rays providing the background signal of all pixels.3.1.11 effciencydSNRn (see 3.1.7) divided by the squarero
21、ot of the dose (in mGy) and is used to measure the responseof the detector at different beam energies and qualities.3.1.12 frame ratenumber of frames acquired per second.3.1.13 GlobalLag1f (global lag 1st frame)the ratio ofmean signal value of the first frame of the DDA where theX-rays are completel
22、y 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.3.1.14 GlobalLag1s (global lag 1 s)the projected value ofGlobalLag1f for an integration time of 1 se.3.1.15 GlobalLag60s (global lag 60 s)the r
23、atio 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.3.1.16 gray valuethe numeric value of a pixel in a DDAimage. This is typically interchangeable with the terms pixelvalue, detector response, A
24、nalog-to-Digital Unit, and detectorsignal.3.1.17 internal scatter radiation (ISR)scattered radiationwithin the detector.3.1.18 iSRbdetectorthe interpolated basic spatial resolutionof the detector indicates the smallest geometric detail, whichcan be resolved spatially using a digital detector array w
25、ith nogeometric magnification.NOTE 1It is equal to 12 of the measured detector unsharpness and itis determined from a digital image of the duplex wire IQI (PracticeE2002), directly placed on the DDA without object. The iSRbdetectorvalueis determined from the interpolated or approximated modulation d
26、epth oftwo, or several, neighbor wire pairs at 20 % modulation depth.3.1.19 lagresidual signal in the DDA that occurs shortlyafter the exposure is completed.3.1.20 phantoma part or item being used to quantify DDAcharacterization metrics.3.1.21 pixel valuethe numeric value of a pixel in a DDAimage. T
27、his is typically interchangeable with the term grayvalue.3.1.22 saturation gray valuethe maximum possible grayvalue of the DDA after offset correction.3.1.23 signal-to-noise ratio (SNR)quotient of mean valueof the intensity (signal) and standard deviation of the intensity(noise). The SNR depends on
28、the radiation dose and the DDAsystem properties.3.1.24 specific material thickness range (SMTR)the mate-rial 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 valu
29、e of the DDA and the thicker wallthickness by 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 qual
30、ity image, and a higher qualityimage respectively.3.1.25 step-wedgea stepped block of a single metallicalloy with a thickness range that is to be manufactured inaccordance with 5.2.4. Significance and Use4.1 This practice provides a means to compare DDAs on acommon set of technical measurements, rea
31、lizing that inpractice, adjustments 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 param
32、eters used in this practice in 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:interpolated basic spatial resolution (iSRbdetector), efficiency(Detector SNR-normalized (dSNRn) at 1 mGy, for differentene
33、rgies and beam qualities), achievable contrast sensitivity(CSa), specific material thickness range (SMTR), image lag,burn-in, bad pixels and internal scatter radiation (ISR).5. Apparatus5.1 Duplex Wire Image Quality Indicator for iSRbdetectorThe duplex wire quality indicator corresponds to the desig
34、nspecified in Practice E2002 for the measurement of iSRbdetectorand not unsharpness.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 mas
35、king, thestep-wedge may be inserted into a lead frame. The lead framecan then extend another 25.4 mm 1 in. about the perimeter ofthe step-wedge, beyond the support. The slight overlap of theE2597/E2597M 142lead support with the edges of the step-wedge (no more than 6mm 0.25 in. assures a significant
36、ly reduced number ofX-rays to leak-through under the step-wedge that will contami-nate the data acquired on each step. The step-wedges shall beformed of three different materials: Aluminum 6061, TitaniumTi-6Al-4V, and Inconel 718 with a center groove in each step,as shown in Fig. 1. The dimensions o
37、f the wedges for thedifferent materials are shown in Table 1.5.3 Filters for Measuring 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
38、thicknesses shall be 60.1 mm 60.004 in.5.3.1 No external filter (50 kV).5.3.2 30 mm 1.2 in. aluminum (90 kV).5.3.3 40 mm 1.6 in. aluminum (120 kV).5.3.4 3 mm 0.12 in. copper (120 kV).5.3.5 10 mm 0.4 in. iron (160 kV).5.3.6 8 mm 0.3 in. copper (220 kV).5.3.7 16 mm 0.6 in. copper (420 kV.5.3.8 The fil
39、ters shall be placed directly at the tube window.The aluminum filter shall be composed of aAluminum 6061.The copper shall be composed of 99.9 % purity or better. Theiron filter shall be composed of Stainless Steel 304.NOTE 2Radiation qualities in 5.3.2 and 5.3.3 are in accordance withDQE standard IE
40、C62220-1, and radiation quality in 5.3.4 and 5.3.5 are inaccordance with ISO 7004. Radiation quality in 5.3.6 is used also in TestMethod E1815, Practice E2445, and Practice E2446.5.4 Filters for Measuring, Burn-In and Internal ScatterRadiationThe filters for measuring burn-in and ISR shallconsist of
41、 a minimum 16 mm 0.6 in. thick copper plate (5.3.7)100 by 75 mm 4 by 3 in. with a 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 t
42、o qualification testingthe DDA shall be calibrated for offset, or gain, or both, (see3.1.10 and 3.1.9) to generate corrected images per manufac-turers recommendation. It is important that the calibrationprocedure be completed as would be done in practice duringroutine calibration procedures. This is
43、 to assure that datacollected by manufacturers will closely match that collectedwhen the system 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 p
44、ixels as per manufacturers 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 ofdete
45、ctors in a given 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 tha
46、t have no response, 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 2121 pixels. This test is done on an offsetcorrected image.6.2.1.3 Under Re
47、sponding PixelPixels whose gray valuesare less than 0.6 times the median gray value of an area of aminimum of 2121 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 thansix times the med
48、ian pixel standard 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 99neighbor 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
49、 done on an offset and gain correctedimage.6.2.1.6 Persistence/Lag PixelPixel whose value exceeds adeviation of more than a factor of two of the median value ofits 99 neighbors in the first image after X-ray shut down andare exceeds six times the median noise value in the dark image(refer to 7.11.1).FIG. 1 Step-Wedge Drawing (dimensions are listed in Table 1)E2597/E2597M 1436.2.1.7 Bad Neighborhood PixelPixel, where all eightneighboring pixels are bad pixels, is also considered a badpixel.6.2.2 Typ
