1、Designation: E 2007 00 (Reapproved 2006)Standard Guide forComputed Radiology (Photostimulable Luminescence (PSL)Method)1This standard is issued under the fixed designation E 2007; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 year of last 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 guide covers practices and image quality measur-ing systems for the detection, display, and recording o
3、f CR datafiles. These data files, used in materials examination, aregenerated by penetrating radiation passing through the subjectmaterial and producing an image via a storage phosphorimaging plate. Although the described radiation sources arespecifically X-ray and gamma-ray, the general concepts ca
4、n beused for other radiation sources such as neutrons. The imagedetection and display techniques are nonfilm, but the use of ahard copy as a means for permanent recording of the image isnot precluded.1.2 This guide is for tutorial purposes only. It outlines thegeneral principles of computed radiolog
5、y (CR) imaging inwhich luminescence is emitted by a storage phosphor imagingplate, by means of photo stimulation after the detector has beenpenetrated by x-rays or gamma radiation.1.3 The values stated in SI units are to be regarded as thestandard. The inch-pound units given in parentheses are forin
6、formation only.1.4 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.
7、 For specific safetyprecautionary statements, see Section 7.2. Referenced Documents2.1 ASTM Standards:2E 142 Method for Controlling Quality of RadiographicTesting3E 747 Practice for Design, Manufacture and MaterialGrouping Classification of Wire Image Quality Indicators(IQI) Used for RadiologyE 1025
8、 Practice for Design, Manufacture, and MaterialGrouping Classification of Hole-Type Image Quality Indi-cators (IQI) Used for RadiologyE 1817 Practice for Controlling Quality of RadiologicalExamination by Using Representative Quality Indicators(RQIs)2.2 Federal Standard:Fed. Std. No. 21-CFR 1020.40 S
9、afety Requirements forCabinet X-Ray Machines43. Summary of Guide3.1 This guide outlines the practices for the use of CRmethods and techniques for materials examination. It is in-tended to provide a basic understanding of the method and thetechniques involved. The selection of a storage phosphorimagi
10、ng plate, radiation source, and radiological techniques,which are necessary in achieving user CR performance require-ments, is described.4. Significance and Use4.1 This guide establishes an introduction to the theory anduse of CR. The X-, gamma-ray detector discussed in this guideis a storage phosph
11、or imaging plate, hereafter referred to asSPIP. The SPIP, which is the key component in the CR process,differentiates CR from other radiologic methods. This guide isa tutorial standard, and therefore it does not present specifiedimage quality levels as would be used to address the accep-tance or rej
12、ection criteria established between two contractingparties, for example, NDT facility or consumer of NDTservices, or both. It is not a detailed how-to procedure to beused by the NDT facility or consumer of NDT service, or both.4.2 Table 1 lists the general performance, complexity, andrelative cost o
13、f CR systems.5. Background5.1 Inspired by the success of computed tomography (CT),new methods of radiologic imaging have been developed thatutilize recent advances in electronics and computer technolo-gies to realize better image quality, and to evolve new imaging1This guide is under the jurisdictio
14、n 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 Dec. 1, 2006. Published January 2007. Originallyapproved in 1999. Last previous edition approved in 2000 as E 2007 - 00.2For referenced
15、 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.3Withdrawn4Available from Standardization Documents Order Desk, Bldg. 4, Sec
16、tion D,700 Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.modalities. These are generally in a category in which theX-ray sensor is mainly either the conventional image intensif
17、ierand television-camera combination or the linear array sensor asused in CT. The basic quality of the digital image is not limitedby digital processing but in large measure by the performanceof the sensor itself in regard to spacial resolution and signal tonoise ratio.5.2 The earliest written refer
18、ence to fluorescence, the phe-nomenon which causes materials to emit light in response toexternal stimuli, dates back to 1500 B.C. in China. Thisphenomenon did not attract scientific interest until 1603, whenthe discovery of the Bolognese stone in Italy led to investiga-tion by a large number of res
19、earchers. One of these wasBecquerel, who, in his 1869 book La Lumiere, revealed that hehad discovered the phenomenon of stimulated luminescence inthe course of his work with phosphors.5.2.1 Photo stimulated luminescence (PSL) is a phenom-enon in which a phosphor that has ceased emitting lightbecause
20、 of the removal of the stimulus once again emits lightwhen excited by light with a longer wavelength. The phenom-enon is quite common since photostimulable phosphors covera broad range of materialscompounds of elements fromGroups IIB and VI (for example, ZnS), compounds of elementsfrom Groups 1A and
21、 VIIA, VIIB and V VIB (for example,alkali halides), diamond, Groups 2A and VIIA, VIIB and VVIB (for example, barium fluorohalidesBa FX-EU2+X=Br,I, etc.), oxides (for example, Zn2Si04:Mn and LaOBr:Ce, Tb),and even certain organic compounds. The materials thereforelend themselves to data storage becau
22、se the stimulus orprimary excitation could be used to write data to the material,the light or secondary excitation to read the data back. Storagephosphor imaging plate (IP) is a name given to a two-dimensional flexible sensor that can store a latent imageobtained from X rays, electron beams or other
23、 types ofradiation, using photostimulable phosphors (P.P.), and thensequentially reproduces them as a digital file by releasing thePSL with a laser beam, piping the PSL to a photomultipliertube (PMT) and then digitizing the resulting electrical signal.5.3 With the introduction of photostimulable lum
24、inescenceimaging systems in the early 1980s, CR was born by thecombination of this highly advanced photographic technologywith recent advances in computer technologies.5.4 CR can utilize various software algorithms for imageenhancement and optical disks for digital file storage. Thisadvanced imaging
25、 system greatly expands the versatility ofradiology. Potential industrial applications include productionexamination of aircraft components, welds in rocket-motorhousings, castings, transistors, microcircuits, circuit-boards,valve positions, erosion and corrosion of pipes, integrity ofpipe welds, so
26、lenoid valves, fuses, relays, tires, reinforcedplastics and automotive parts.5.5 Limitation:5.5.1 Handling CharacteristicsPotentially, a CR imagingplate may be erased and reused thousands of times. Theprimary limiting factor, as is the case with lead intensifyingscreens, is physical handling. Freque
27、ncy of handling, bendingand cleaning determines the plates useful lifespan.6. Interpretation and Reference Standards6.1 Acceptance StandardsAs written by other organiza-tions for film radiography may be employed for CR inspectionprovided appropriate adjustments are made to accommodatethe differences
28、 represented by the CR data files.6.2 ASTM Reference StandardsReference digital imagestandards, complementing existing ASTM reference film ra-diographic standards must be developed. SubcommitteeE07.01 work aimed at developing such standards is underway.7. Safety Precautions7.1 The safety procedures
29、for the handling and use ofionizing radiation sources must be followed. Mandatory rulesand regulations are published by governmental licensing agen-cies, and guidelines for control of radiation are available inpublications such as the Fed. Std. No. 21-CFR 1020.40.Careful radiation surveys should be
30、made in accordance withTABLE 1 Computed Radiology (PSL Method)Availability GoodEquipment needed Phosphor storage imaging plate, plate reader and work stationUsual readoutmethodsElectronics/visualOther readoutmethodsFilmPracticalresolutionDependent on application and equipmentContrast sensitivity in
31、% Dependent on energy and materialUseful kVcp rangeMin 10kVMax 32MeVOptimum kVcp As low as practicalMaximum field ofview14in 3 17inRelativesensitivity toX raysExtremely highRelative cost Low to moderateApproximate usefullifeFive years or determined by handlingSpecial remarks Digital and versatileE 2
32、007 00 (2006)2regulations and codes and should be conducted in the exami-nation area as well as adjacent areas under all possibleoperating conditions.8. Radiation Sources8.1 General:8.1.1 The sources of radiation for CR imaging systemsdescribed in this guide are X-ray machines and radioactiveisotope
33、s. The energy range available extends from a few kV to32 MeV. Since examination systems in general require highdose rates, X-ray machines are the primary radiation source.The types of X-ray sources available are conventional X-raygenerators that extend in energy up to 420 kV. Energy sourcesfrom 1 Me
34、V and above are generally represented by linearaccelerators.8.1.2 Usable isotope sources have energy levels from 84keV (Thulium-170, Tm170) up to 1.25 MeV (Cobalt-60, Co60).With high specific activities, these sources should be consid-ered for special application where their field mobility andoperat
35、ional simplicity can be of significant advantage.8.1.3 The factors to be considered in determining thedesired radiation source are energy, focal geometry, wave form,half life, and radiation output.8.2 Selection of Sources:8.2.1 Low-Energy SourcesThe radiation source selectedfor a specific examinatio
36、n system depends upon the materialbeing examined, its mass, its thickness, and the required rate ofexamination. In the energy range up to 420 kV, the X-ray unitshave an adjustable energy range so that they are applicable toa wide range of materials. Specifically, 50-kV units operatedown to a few kV;
37、 160-kV equipment operates down to 20 kV;and 420-kV equipment operates down to about 85 kV.8.2.2 High-Energy SourcesThe increased efficiency ofX-ray production at higher accelerating potentials makesavailable a large radiation flux, and this makes possible theexamination of greater thicknesses of ma
38、terial. High radiationenergies in general produce lower image contrast, so that as aguide the minimum thickness of material examined should notbe less than 2.5 half-value layers of material. The maximumthickness of material can extend up to 10 half-value layers.8.3 Source Geometry:8.3.1 Although the
39、 physical size of the source of radiation isa parameter that may vary considerably, the radiation sensor isgenerally the principal source of unsharpness.9. CR Storage Phosphor Imaging Plate9.1 A CR storage phosphor imaging plate (SPIP) is de-scribed as a reusable detector (flexible or rigid) that st
40、orespenetrating radiation energy as a latent image.9.2 When X-ray photons pass through an object, they areattenuated. At low-to-medium energies this attenuation iscaused primarily by photoelectric absorption, or Comptonscattering. At high energies, scattering is by pair production(over 1 MeV) and ph
41、oton photonuclear processes (at about11.5 MeV). As a result of attenuation, the character of the fluxfield in a cross-section of the X-ray beam is changed. Varia-tions in photon flux density and energy are most commonlyencountered, and are caused by photoelectric absorption andCompton scattering.9.3
42、 By analyzing this flux field, we can make deductionsabout the composition of the object being examined, since theattenuation process depends on the number of atoms encoun-tered by the original X-ray beam, and their atomic number.9.4 The attenuation process is quite complex, since theX-ray beam is u
43、sually composed of a mixture of photons ofmany different energies and the object may be composed ofatoms of many different kinds. Exact prediction of the flux fieldfalling upon the SPIP is therefore, difficult. Approximationscan be made, since the mathematics and data are available totreat any singl
44、e photon energy and atomic type, but in practicegreat reliance must be placed on the experience of the user. Inspite of these difficulties, successful CR SPIPs have beendeveloped, and perform well. The criteria for choice depend onmany factors, which, depending on the application, may, ormay not be
45、critical. Obviously, these criteria will include thefollowing factors.9.4.1 Field of ViewThe field of view of the SPIP and itsresolution are interrelated. The resolution of the SPIP is fixedby its physical characteristics, so if the X-ray image isprojected upon it full-size (the object and image pla
46、nes incontact), the resultant resolution will be approximately equal tothat of the SPIP. When SPIP resolution becomes the limitingfactor, the object may be moved away from the SPIP, andtowards the source to enlarge the projected image and thusallow smaller details to be resolved by the same SPIP. As
47、 theimage is magnified, however, the detail contrast is reduced andits outlines are less distinct. (See 10.3.) It is apparent, also, thatwhen geometric magnification is used, the area of the objectthat is imaged on the SPIP is proportionally reduced. As ageneral rule, X-ray magnifications should not
48、 exceed 53except when using X-ray sources with very small (microfocus)anodes. In such cases, magnifications in the order of 10 to 203are useful. When using conventional focal-spot X-ray sources,magnifications from 1.2 to 1.5 provide a good compromisebetween contrast and resolution in the magnified i
49、mage.9.4.2 Inherent SensitivityThe basic sensitivity of the SPIPmay be defined as its ability to respond to small, localvariations in radiant energy to display the features of interest inthe object being examined. It would seem that an SPIP that candisplay intensity changes on the order of 1 to 2 % at resolutionsapproaching that of film radiography would satisfy all of therequirements for successful CR imaging. It is not nearly thatsimple. Often good technique is more important than thedetails of the imaging system itself. The geometry of thesystem with respect to field
