1、Designation: E 2445 05Standard Practice forQualification and Long-Term Stability of ComputedRadiology Systems1This standard is issued under the fixed designation E 2445; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of l
2、ast revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice specifies the fundamental parameters ofcomputed radiography systems to assure satisfactory andrepeatable
3、 results for nondestructive testing.1.2 This practice describes the evaluation of ComputedRadiology (CR) systems for industrial radiography. It isintended to ensure that the evaluation of image quality, as faras this is influenced by the scanner/IP system, meets the needsof users and enables the tes
4、t of long-term stability.1.3 Each of the tests described may be performed withindividual gages specified. The user shall decide which testsshall be used for system control using individual test objects orthe CR test phantom2(Appendix X1). The computed radio-logical tests, specified as “user tests” i
5、n this practice, may beutilized at appropriate intervals determined by the user, basedon the application of the examination operations. The testsshall be appropriate for the materials and range of use of thesystem. Fading, uniformity, and erasure tests shall also be partof the control system. All ot
6、her tests for qualification andcapability are to be performed and certified by the CRequipment manufacturer.1.4 The values stated in SI units are to be regarded as thestandard. Values in inch-pound units are for informationpurposes.1.5 This standard does not purport to address all of thesafety conce
7、rns, 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. Referenced Documents2.1 ASTM Standards:3E 1316 Terminology for Nondestructive Te
8、stingE 1647 Practice for Determining Contrast Sensitivity inRadioscopyE 2002 Practice for Determining Total Image Unsharpnessin RadiologyE 2007 Guide for Computed Radiology (PSL Method)E 2033 Practice for Computed Radiology (PSL Method)E 2446 Practice for Classification of Computed Radiogra-phy Syst
9、ems3. Terminology3.1 DefinitionsThe definition of terms relating to gamma-and X-radiology, which appear in Terminology E 1316, GuideE 2007, and Practice E 2033 shall apply to the terms used inthis practice.3.2 Definitions of Terms Specific to This Standard:3.2.1 aliasingpre-sampled high spatial freq
10、uency signalsbeyond the Nyquist frequency (given by the pixel distance)reflected back into the image at lower spatial frequencies.3.2.2 computed radiology system (CR system)a completesystem of a storage phosphor imaging plate (IP) and corre-sponding read out unit (scanner or reader), which converts
11、theinformation of the IP into a digital image (see also GuideE 2007).3.2.3 computed radiology system classa particular groupof storage phosphor imaging plate systems, which is charac-terized by a SNR (Signal-to-Noise Ratio) range shown inTable 1 and by a certain unsharpness range (for example,MTF20-
12、value) in a specified exposure range.3.2.4 CR phantoma device containing an arrangement oftest targets to evaluate the quality of a CR system, as well asmonitoring the quality of the chosen system.1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the di
13、rect responsibility of Subcommittee E07.01 onRadiology (X and Gamma) Method.Current edition approved June 1, 2005. Published June 2005.2The sole source of supply of the apparatus known to the committee at this timeis Nuclear Associates, A Division of Cardinal Health, 120 Andrews Road,Hicksville, NY
14、11801, Phone: 1-888-466-8257, Catalog Number: 07-605-2435. Ifyou are aware of alternative suppliers, please provide this information to ASTMInternational Headquarters. Your comments will receive careful consideration at ameeting of the responsible technical committee,1which you may attend.3For refer
15、enced 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 Drive, PO Box C700, West
16、 Conshohocken, PA 19428-2959, United States.3.2.5 gain/amplificationopto-electrical gain setting of thescanning system.3.2.6 ISO speed SIPxdefines the speed of a CR system andis calculated from the reciprocal dose value, measured in Gray,which is necessary to obtain a specified minimum SNR of a CRsy
17、stem.3.2.7 laser beam jittera lack of smooth movement of theimaging plate/laser scanning device, which results in lines ofthe image, which consist of a series of steps.3.2.8 linearized signal intensitya numerical signal valueof a picture element (pixel) of the digital image, which isproportional to
18、the radiation dose. The linearized signal inten-sity is zero, if the radiation dose is zero.3.2.9 long-term stabilityperformance measurements of aCR system over the life-cycle of the devices, used to evaluaterelative system performance over time.3.2.10 scanner slippagethe slipping of an IP in a scan
19、nertransport system resulting in fluctuation of intensity of hori-zontal image lines.3.2.11 signal-to-noise ratio (SNR)quotient of mean valueof the linearized signal intensity and standard deviation of thenoise (intensity distribution) at this signal intensity. The SNRdepends on the radiation dose a
20、nd the CR system properties.4. Significance and Use4.1 There are several factors affecting the quality of a CRimage including the spatial resolution of the IP system,geometrical unsharpness, scatter and contrast sensitivity(signal/noise ratio). There are several additional factors (forexample, scann
21、ing parameters), which affect the accuratereading of images on exposed IPs using an optical scanner.4.2 The quality factors can be determined most accuratelyby the CR equipment manufacturer tests as described inPractice E 2446. Individual test targets, which are recom-mended for practical user tests
22、, are described for qualityassurance. These tests can be carried out either separately or bythe use of the CR phantom (Appendix X1). This CR phantomincorporates many of the basic quality assessment methods andthose associated with the correct functioning of a CR system,including the scanner, for rea
23、ding exposed plates and incor-rectly erasing IPs for future use of each plate.4.3 This practice is for users of industrial CR systems. Thispractice defines the tests to be performed, by users of CRsystems, periodically to evaluate the CR systems to proveproper performance over the life-cycle of the
24、system.4.4 Application of Various Tests and Test Methods4.4.1 Tests after Repair, Upgrade or the Use of Another IPType:Since modifications, such as repair or upgrade of the CRscanner and improved IP may improve the functionality of thesystem, specialized tests are required to prove the properperform
25、ance of the CR system.4.4.1.1 User Tests for Long-term StabilityQuality assur-ance in test laboratories requires periodical tests of the CRsystem to prove the proper performance of the system. Thetime interval depends on the degree of usage of the system andshall be defined by the user and considera
26、tion of the CRequipment manufacturers information.4.4.1.2 The tests described in 6.2.1 through 6.2.6 requireusage of quality indicators of 5.1 or the CR test phantom shallbe used regularly at user-defined intervals to test the basicperformance. The documentation shall contain:(1) Spatial resolution
27、(by duplex-wire method, optionalconverging line pairs),(2) Contrast (recognized contrast percentage of the materialto examine),(3) Slipping (yes/no),(4) Jitter (yes/no),(5) Shading (percentage at selected distance),(6) Radiation parameters of the performed tests, and(7) Date and operator name.4.4.1.
28、3 Fading tests should be performed only if the scanneror IP-brand is changed without data from the CR equipmentmanufacturer, or the system is used under extreme (beyondmanufacturers recommendation) temperature conditions. Thefading should be less than 50 % in the expected period betweenexposure and
29、scan.4.4.1.4 The IPs shall be checked for artifacts (6.2.7) andproper erasure (6.2.6).4.4.1.5 Degradation of IPs or photo multipliers in thescanner may reduce the system sensitivity after extensiveusage. For this reason, the SNR should be measured at longerintervals (for example, annual period) by t
30、he user or servicepersonnel. The SNR shall not be less than 90 % of the originalvalue. The increase of the SNR can be accepted without limits,if the system unsharpness is not increased.5. ApparatusCR Quality Indicators5.1 Description of CR Quality Indicators for User TestsThe following is a descript
31、ion of CR quality indicators, whichwill be identified by reference to this practice.5.1.1 Contrast Sensitivity Quality Indicator:5.1.1.1 The description of the contrast sensitivity targetcorresponds to Practice E 1647. For use with this practice,three targets are made from aluminum (Material Group 0
32、2),copper (Material Group 4) and stainless steel (Material Group1). The target thickness is 12.5 mm (0.50 in.) aluminum, 6.3mm (0.25 in.) copper and stainless steel. Each target containsa contrast area for 1, 2, 3, and 4 % wall-thickness contrastsensitivity.5.1.2 Duplex Wire Quality Indicator:5.1.2.
33、1 The description of the duplex wire quality indicatorcorresponds to Practice E 2002. The gage shall be oriented at a5 angle to the direction of the scanned lines (fast-scandirection) or the perpendicular direction (slow-scan-direction).5.1.3 Converging Line Pair Quality Indicator:5.1.3.1 The target
34、 consists of five converging strips of lead(0.03 mm (0.001 in.) thickness), which can be used for a spatialresolution test by reading the limit of recognizable line pairs. Itshall cover a range from 1.5 to 20 line pairs per mm (lp/mm).Two quality indicators shall be used, one in parallel with thesca
35、nned lines and the other one oriented in the perpendiculardirection.5.1.4 Linearity Quality Indicators:5.1.4.1 Rulers of high-absorbing materials are located onthe perimeter of the scanned range. Two quality indicators shallbe used, one parallel with the scanned lines and the other oneE2445052orient
36、ed in the perpendicular direction. The scaling should beat least in mm or tenths of inches.5.1.5 T-target:5.1.5.1 This CR quality indicator consists of a thin plate ofbrass or copper (#0.5 mm (#0.02 in. ) thick) with sharp edges.This plate is manufactured in a T-shape with 0.5 mm (0.2 in.)wide segme
37、nts. The T should have a size of at least 50 by 70mm (2 by 234 in.). It shall be aligned perpendicular and parallelto the direction of the scanned lines and is used to check forlaser jitter and may be used to measure a modulation transferfunction of the complete system (see Fig. X1.1).5.1.6 Scanner
38、Slipping Quality Indicator:5.1.6.1 The quality indicator consists of a homogeneousstrip of aluminum 0.5 mm (0.02 in.) in thickness. The qualityindicator has the shape of a rectangle (see Fig. X1.1) and shallbe aligned perpendicular and parallel to the direction of thescanned lines.5.1.7 Shading Qual
39、ity Indicator:5.1.7.1 Different shading quality indicators may be used.One type is based on the homogeneous exposure of an imagingplate (IP) with a thin Al-plate 0.5 to 1.0 mm (0.06 to 0.04 in.)above the IP. The exposure shall be made with low-energyradiation (50 to 100 keV).5.1.7.2 Another type is
40、the shading quality indicator of theCR test phantom (see X1.1).5.1.8 Central Beam Alignment Quality Indicator (BAM-snail):5.1.8.1 The alignment quality indicator consists of a roll 1.5to 2.0 mm high (0.06 to 0.08 in.) of thin lead foil separated bya spacer of 0.1 to 0.2 mm (0.004 to 0.008 in.) of lo
41、w-absorbingmaterial (see X1.2).5.2 Application Procedures for CR Quality IndicatorsTheCR quality indicators provide an evaluation of the quality of aCR system as well as for a periodical quality control. Arrange-ment of the CR quality indicators shall be in accordance withthis practice, or as specif
42、ied by the cognizant engineeringorganization.5.2.1 Exposure of CR Quality Indicators (User Test):5.2.1.1 The CR quality indicators can be applied separatelyor all together in the CR phantom. The selected set of CRquality indicators or the CR phantom is placed on the cassette,which contains an imagin
43、g plate. The radiation source is set ata distance of 1 m (39 in.) or greater and the beam is alignedwith the center of the plate.Above radiation energy of 100 keV,a lead screen of 0.1 mm (0.004 in.) shall be applied betweenCR quality indicators or CR phantom and the IP to reducescattered radiation.
44、Test exposures are made and the radiationand CR system functions are optimized. The final image forevaluation is to be agreed among contracting parties.5.2.1.2 The exposure time and the parameter setting of theCR scanning unit determine the image quality as well as thetype of imaging plate to use. T
45、hese values, the X-ray settings,and the type of IP have to be documented and agreed, as wellas the radiation energy (keV, gamma-source type), dose (forexample, in mAs) and quality (prefilters, tube type and tubewindow).NOTE 1High exposure time and low gain settings yield high contrastresolution and
46、SNR. Furthermore, the contrast sensitivity is higher forlarge pixel size settings (high unsharpness) than for small pixel size setting(low unsharpness).5.2.2 Initial Assessment of CR Quality Indicators:5.2.2.1 For initial quality assessment, examine the radio-graphic image(s) of the CR phantom or th
47、e separated qualityindicators on the monitor (or hard copy) for the featuresdescribed in 5.1.1 to 5.1.8 and 6.2.1 to 6.2.8. The results canprovide the basis of agreement between contracting parties.5.3 Periodical Control:5.3.1 The CR quality indicators of 5.1.1 through 5.1.7(alignment by 5.1.8) or t
48、he CR phantom shall be exposed andthe results examined at any interval agreed between thecontracting parties. For periodical control, ensure that theagreed quality values of the tests 6.1.3 and 6.2.1 to 6.2.8 areachieved.5.4 Imaging Plate Fading:5.4.1 The intensity of the stored image in the imaging
49、 platewill decrease over time (called “fading”). The measurement offading characteristic shall be done by performing the followingsteps:5.4.1.1 Expose a plate homogeneously using typical expo-sure conditions. For documentation, the following parametersshall be recorded: kV, mAs, SDD, pre-filter and plate material,and thickness. The exposed image shall have an intensitybetween 70 and 90 % of the maximum possible intensity of theCR reader at lowest gain and under linearized condition.5.4.1.2 Readout the imaging plate five minutes after expo-sure.5.4.1.3 Set the linear
copyright@ 2008-2019 麦多课文库（www.mydoc123.com）网站版权所有
备案/许可证编号：苏ICP备17064731号-1