1、Designation: E2737 10Standard Practice forDigital Detector Array Performance Evaluation and Long-Term Stability1This standard is issued under the fixed designation E2737; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes the evaluation of DDA systemsfor industrial radiology. It is intended to ensure that theevalua
3、tion of image quality, as far as this is influenced by theDDA system, meets the needs of users, and their customers,and enables process control and long term stability of the DDAsystem.1.2 This practice specifies the fundamental parameters ofDigital Detector Array (DDA) systems to be measured todete
4、rmine baseline performance, and to track the long termstability of the DDA system.1.3 The DDA system performance tests specified in thispractice shall be completed upon acceptance of the systemfrom the manufacturer and at intervals specified in this practiceto monitor long term stability of the syst
5、em. The intent of thesetests is to monitor the system performance for degradation andto identify when an action needs to be taken when the systemdegrades by a certain level.1.4 The use of the gages provided in this standard ismandatory for each test. In the event these tests or gages arenot sufficie
6、nt, the user, in coordination with the cognizantengineering organization (CEO) may develop additional ormodified tests, test objects, gages, or image quality indicatorsto evaluate the DDA system. Acceptance levels for theseALTERNATE tests shall be determined by agreement betweenthe user, CEO and man
7、ufacturer.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 to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Re
8、ferenced Documents2.1 ASTM Standards:2E1025 Practice for Design, Manufacture, and MaterialGrouping Classification of Hole-Type Image Quality Indi-cators (IQI) Used for RadiologyE1316 Terminology for Nondestructive ExaminationsE1742 Practice for Radiographic ExaminationE2002 Practice for Determining
9、Total Image Unsharpnessin RadiologyE2445 Practice for Qualification and Long-Term Stabilityof Computed Radiology SystemsE2597 Practice for Manufacturing Characterization of Digi-tal Detector ArraysE2698 Practice for Radiological Examination Using DigitalDetector ArraysE2736 Guide for Digital Detecto
10、r Array Radiology3. Terminology3.1 Definitionsthe definition of terms relating to gammaand X-radiology, which appear in Terminology E1316, PracticeE2597, Guide E2736, and Practice E2698 shall apply to theterms used in this practice.3.2 Definitions of Terms Specific to This Standard:3.2.1 digital det
11、ector array (DDA) systeman electronicdevice 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 radiologic energy pattern impartedupon the input regio
12、n of the device. The conversion of 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 seconds perimage to many
13、 images per second, up to and in excess ofreal-time radioscopy rates (usually 30 frames per seconds).3.2.2 active DDA areathe active pixelized region of theDDA, which is recommended by the manufacturer as usable.3.2.3 signal-to-noise ratio (SNR)quotient of mean valueof the intensity (signal) and sta
14、ndard deviation of the intensity(noise). The SNR depends on the radiation dose and the DDAsystem properties.1This 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 editi
15、on approved April 15, 2010. Published June 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 AS
16、TM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.4 contrast-to-noise ratio (CNR)quotient of the differ-ence of the signal levels between two material thicknesses, andstandard deviation of the intensity (noise) of the base material.The CNR depe
17、nds on the radiation dose and the DDA systemproperties.3.2.5 contrast sensitivityrecognized contrast percentageof the material to examine. It depends on 1/CNR.3.2.6 spatial resolution (SR)the spatial resolution indi-cates the smallest geometrical detail, which can be resolvedusing the DDA with given
18、 geometrical magnification. It is thehalf of the value of the detector unsharpness divided by themagnification factor of the geometrical setup and is similar tothe effective pixel size.3.2.7 material thickness range (MTR)the wall thicknessrange within one image of a DDA, whereby the thinner wallthic
19、kness does not saturate the DDA and at the thicker wallthickness, the signal is significantly higher than the noise.3.2.8 frame ratenumber of frames acquired per second.3.2.9 lagresidual signal in the DDA that occurs shortlyafter detector read-out and erasure.3.2.10 burn-inchange in gain of the scin
20、tillator that per-sists well beyond the exposure.3.2.11 bad pixela pixel identified with a performanceoutside of the specification range for a pixel of a DDA asdefined in Practice E2597.3.2.12 five-groove wedgea continuous wedge with fivelong grooves on one side (see Fig. 1).3.2.13 phantoma part or
21、item being used to quantify DDAcharacterization metrics.FIG. 1 5-Groove-Wedge (steel) see AppendixE2737 1023.2.14 duplex plate phantomtwo plates of the same ma-terial; Plate 2 has same size in x- and half the size in v-direction of Plate 1; the thickness of Plate 1 matches theminimum thickness of th
22、e material for inspection; the thicknessof Plate 1 plus Plate 2 matches the maximum thickness of thematerial for inspection (see Fig. 2).3.2.15 DDA offset imageimage of the DDAin the absenceof x-rays providing the background signal of all pixels.3.2.16 DDA gain imageimage obtained with no structured
23、object in the x-ray beam to calibrate pixel response in a DDA.3.2.17 calibrationcorrection applied for the offset signaland the non-uniformity of response of any or all of the X-raybeam, scintillator, and the read out structure.3.2.18 gray valuethe numeric value of a pixel in the DDAimage. This is t
24、ypically interchangeable with the term pixelvalue, detector response, Analog-to-Digital unit and detectorsignal.3.2.19 saturation gray valuethe maximum possible us-able gray value of the DDA after offset correction.NOTE 1Saturation may occur because of a saturation of the pixelFIG. 2 Duplex Plate Ph
25、antom with IQIs positioned; one ASTM E1025 or E1742 Penetrameter on each plate and one ASTM E2002 DuplexWire IQI on the thinner plate. The boxes ROI 1 to ROI 4 are for evaluation of signal level and SNR.E2737 103itself, the amplifier, or digitizer, where the DDA encounters saturationgray values as a
26、 function of increasing exposure levels.3.2.20 userthe user and operating organization of theDDA system.3.2.21 customerthe company, government agency, orother authority responsible for the design, or end user, of thesystem or component for which radiologic examination isrequired, also known as the C
27、EO. In some industries, thecustomer is frequently referred to as the “Prime”.3.2.22 manufacturerDDA system manufacturer, supplierfor the user of the DDA system.4. Significance and Use4.1 This practice is intended to be used by the NDT usingorganization to measure the baseline performance of the DDAa
28、nd to monitor its performance throughout its service as anNDT imaging system.4.2 It is to be understood that the DDA has already beenselected and purchased by the user from a manufacturer basedon the inspection needs at hand. This practice is not intended tobe used as an “acceptance test” of the DDA
29、, but rather toestablish a performance baseline that will enable periodicperformance tracking while in-service.4.3 Although many of the properties listed in this standardhave similar metrics to those found in Practice E2597, datacollection methods are not identical, and comparisons amongvalues acqui
30、red with each standard should not be made.4.4 This practice defines the tests to be performed andrequired intervals. Also defined are the methods of tabulatingresults that DDA users will complete following initial baselin-ing of the DDA system. These tests will also be performedperiodically at the s
31、tated required intervals to evaluate theDDA system to determine if the system remains withinacceptable operational limits as established in this practice ordefined between user and customer (CEO).4.5 There are several factors that affect the quality of a DDAimage including the spatial resolution, ge
32、ometrical unsharp-ness, scatter, signal to noise ratio, contrast sensitivity (contrast/noise ratio), image lag, and burn in. There are several addi-tional factors and settings (for example, integration time,detector parameters or imaging software), which affect theseresults. Additionally, calibratio
33、n techniques may also have animpact on the quality of the image. This practice delineatestests for each of the properties listed herein and establishesstandard techniques for assuring repeatability throughout thelifecycle testing of the DDA.5. General Testing Procedures5.1 The tests performed herein
34、 can be completed either bythe use of the five-groove wedge phantom (see Fig. 1) or withseparate IQIs on the Duplex Plate Phantom (see Fig. 2).5.2 DDA Calibration MethodPrior to testing, the DDAshall be calibrated for offset and, or gain to generate correctedimages per manufacturers recommendation.
35、It is importantthat the calibration procedure be completed as would be donein production during routine calibration procedures, and thatthese same procedures be used throughout the periodic testingof the DDA after it is in-service.5.3 Bad Pixel Standardization for DDAsImages collectedfor testing sha
36、ll be corrected for bad pixels as would be donein production during routine bad pixel correction proceduresper manufacturers recommendation wherever required. Astandardized nomenclature is presented in Practice E2597. Theidentification and correction of bad pixels in a delivered DDAremain in the pur
37、view of agreement between the user and thesystem manufacturer. The various tests shall be completedunder similar conditions as in production. Some parameters tocontrol are listed below. If several different energies are used inproduction, the complete settings with the highest energy levelshall be u
38、sed for these tests.5.3.1 X-ray tube voltage kV5.3.2 tube current mA5.3.3 focus detector distance (FDD) mm5.3.4 object detector distance (ODD) mm5.3.5 total exposure time per image ms5.3.6 detector corrections (calibration and bad pixel substi-tution)5.3.7 detector settings5.3.8 image acquisition so
39、ftware and image processing6. Application of Baseline Tests and Test Methods6.1 DDA System Baseline Performance Tests6.1.1 The user shall accept the DDA system based onmanufacturers results of Practice E2597 on the specificdetector as provided in a data sheet for that serialized DDA orother agreed t
40、o acceptance test between the user and manufac-turer (not covered in this practice). The user baselines the DDAusing the tests defined in Table 1. Additional tests are to beTABLE 1 System Performance Tests and Process Check of the DDA SystemSystem Performance TestUnitSystem Performance Test Process
41、CheckParameterBaseLineSoftwareUpdateTubeChangeDetectorChange/RepairShortVersionLongVersionUsage ofFive-HoleWedgeDuplexPlatePhantomSpatial Resolution SR m x x x x x x xContrast Sensitivity CS % x x x x x x x xMaterial Thickness Range MTR mm x x x x x x x xSignal to Noise Ratio SNR x x x x x x x xSign
42、al Level SL x x x x x x xImage Lag Lag % x x xBurn In BI % x x x x xOffset Level OL x x x x xBad Pixel Distribution x x x x x xE2737 104defined in agreement between the CEO and the using organi-zation in terms of the specific tests to perform, how the data ispresented, and the frequency of testing.
43、This approach does thefollowing:6.1.1.1 Provides a quantitative baseline of performance,6.1.1.2 provides results in a defined form that can bereviewed by the CEO and6.1.1.3 offers a means to perform process checking ofperformance on a continuing basis.6.1.2 Acceptance values, and tolerances thereof
44、obtainedfrom these tests shall also be in agreement between the CEOand the using organization.6.1.3 Acceptance levels for individual bad pixels, bad clus-ters, relevant bad clusters, and bad lines, and their statisticaldistribution within the DDA, as well as proximity to saidanomalies is to be deter
45、mined by agreement between the userand the CEO. The user and or CEO may refer to the Guide forDDAs (E2736), Practice E2597, as well as consult with themanufacturer on how the prevalence of these anomalous pixelsmight impact a specific application. This practice does not setlimits, but does offer a m
46、eans for tracking such anomalouspixels in the table templates provided herein.6.1.4 Given that the other elements of the DDA system arewithin their tolerances including the x-ray source/generator, theimaging system, and the inspection itself (for example errorswith gain/offset mapping are controlled
47、, as is any severe x-rayscatter in the inspection), and the test produces a result belowthe “agreed to” requirements, the detector is not to be placed inservice unless it is repaired, replaced, or some other change isinstituted that will assure the quality of the inspection as statedin the agreement
48、 between contracting parties.6.1.5 The results of the initial test of the new system shall bedocumented, as delineated in Table 2 and Table 3 and taken asreference values “Result (new)” for further use.6.1.6 Maximum deviations from Result (new) as tolerancesand limits defined between contracting par
49、ties shall also bedocumented in Table 2 and Table 3 as reference values “Limit”for further use.6.1.7 If a replacement DDA is placed into service, thereference values from the acceptance test shall be updated, anda new baseline formed.6.2 User Tests After Repair, Hardware- or SoftwareUpgradeAfter modifications, such as repair or upgrade ofthe DDA system hardware, specialized tests are required toTABLE 2 Test Report of DDA SystemReport of Bad Pixels and ClustersE2737 105prove the proper performance of the DDAsystem with the newconditions.
