ASTM E2007-00(2006)
(Guide)Standard Guide for Computed Radiology (Photostimulable Luminescence (PSL) Method)
Standard Guide for Computed Radiology (Photostimulable Luminescence (PSL) Method)
SCOPE
1.1 This guide covers practices and image quality measuring systems for the detection, display, and recording of CR data files. These data files, used in materials examination, are generated by penetrating radiation passing through the subject material and producing an image via a storage phosphor imaging plate. Although the described radiation sources are specifically X-ray and gamma-ray, the general concepts can be used for other radiation sources such as neutrons. The image detection and display techniques are nonfilm, but the use of a hard copy as a means for permanent recording of the image is not precluded.
1.2 This guide is for tutorial purposes only. It outlines the general principles of computed radiology (CR) imaging in which luminescence is emitted by a storage phosphor imaging plate, by means of photo stimulation after the detector has been penetrated by x-rays or gamma radiation.
1.3 The values stated in SI units are to be regarded as the standard. The inch-pound units given in parentheses are for information only.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific safety precautionary statements, see Section 7.
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Designation:E2007–00 (Reapproved 2006)
Standard Guide for
Computed Radiology (Photostimulable Luminescence (PSL)
Method)
This standard is issued under the fixed designation E 2007; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope (IQI) Used for Radiology
E 1025 Practice for Design, Manufacture, and Material
1.1 This guide covers practices and image quality measur-
Grouping Classification of Hole-Type Image Quality Indi-
ingsystemsforthedetection,display,andrecordingofCRdata
cators (IQI) Used for Radiology
files. These data files, used in materials examination, are
E 1817 Practice for Controlling Quality of Radiological
generated by penetrating radiation passing through the subject
Examination by Using Representative Quality Indicators
material and producing an image via a storage phosphor
(RQIs)
imaging plate. Although the described radiation sources are
2.2 Federal Standard:
specifically X-ray and gamma-ray, the general concepts can be
Fed. Std. No. 21-CFR 1020.40 Safety Requirements for
used for other radiation sources such as neutrons. The image
Cabinet X-Ray Machines
detection and display techniques are nonfilm, but the use of a
hard copy as a means for permanent recording of the image is
3. Summary of Guide
not precluded.
3.1 This guide outlines the practices for the use of CR
1.2 This guide is for tutorial purposes only. It outlines the
methods and techniques for materials examination. It is in-
general principles of computed radiology (CR) imaging in
tended to provide a basic understanding of the method and the
which luminescence is emitted by a storage phosphor imaging
techniques involved. The selection of a storage phosphor
plate,bymeansofphotostimulationafterthedetectorhasbeen
imaging plate, radiation source, and radiological techniques,
penetrated by x-rays or gamma radiation.
whicharenecessaryinachievinguserCRperformancerequire-
1.3 The values stated in SI units are to be regarded as the
ments, is described.
standard. The inch-pound units given in parentheses are for
information only.
4. Significance and Use
1.4 This standard does not purport to address all of the
4.1 This guide establishes an introduction to the theory and
safety concerns, if any, associated with its use. It is the
use of CR.The X-, gamma-ray detector discussed in this guide
responsibility of the user of this standard to establish appro-
is a storage phosphor imaging plate, hereafter referred to as
priate safety and health practices and determine the applica-
SPIP.TheSPIP,whichisthekeycomponentintheCRprocess,
bility of regulatory limitations prior to use. For specific safety
differentiates CR from other radiologic methods. This guide is
precautionary statements, see Section 7.
a tutorial standard, and therefore it does not present specified
2. Referenced Documents image quality levels as would be used to address the accep-
2 tance or rejection criteria established between two contracting
2.1 ASTM Standards:
parties, for example, NDT facility or consumer of NDT
E 142 Method for Controlling Quality of Radiographic
3 services, or both. It is not a detailed how-to procedure to be
Testing
used by the NDTfacility or consumer of NDTservice, or both.
E 747 Practice for Design, Manufacture and Material
4.2 Table 1 lists the general performance, complexity, and
Grouping Classification of Wire Image Quality Indicators
relative cost of CR systems.
5. Background
This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc-
5.1 Inspired by the success of computed tomography (CT),
tive Testing and is the direct responsibility of Subcommittee E07.01 on Radiology
new methods of radiologic imaging have been developed that
(X and Gamma) Method.
Current edition approved Dec. 1, 2006. Published January 2007. Originally utilize recent advances in electronics and computer technolo-
approved in 1999. Last previous edition approved in 2000 as E 2007 - 00.
gies to realize better image quality, and to evolve new imaging
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. Available from Standardization Documents Order Desk, Bldg. 4, Section D,
Withdrawn 700 Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2007–00 (2006)
TABLE 1 Computed Radiology (PSL Method)
Availability Good
Equipment needed Phosphor storage imaging plate, plate reader and work station
Usual readout Electronics/visual
methods
Other readout Film
methods
Practical Dependent on application and equipment
resolution
Contrast sensitivity in % Dependent on energy and material
Useful kVcp range
Min 10kV
Max 32MeV
Optimum kVcp As low as practical
Maximum field of 14[in] 3 17[in]
view
Relative
Extremely high
sensitivity to
X rays
Relative cost Low to moderate
Approximate useful
Five years or determined by handling
life
Special remarks Digital and versatile
modalities. These are generally in a category in which the 5.3 With the introduction of photostimulable luminescence
X-raysensorismainlyeithertheconventionalimageintensifier imaging systems in the early 1980’s, CR was born by the
andtelevision-cameracombinationorthelineararraysensoras combination of this highly advanced photographic technology
used in CT.The basic quality of the digital image is not limited with recent advances in computer technologies.
by digital processing but in large measure by the performance
5.4 CR can utilize various software algorithms for image
of the sensor itself in regard to spacial resolution and signal to
enhancement and optical disks for digital file storage. This
noise ratio.
advanced imaging system greatly expands the versatility of
5.2 The earliest written reference to fluorescence, the phe- radiology. Potential industrial applications include production
examination of aircraft components, welds in rocket-motor
nomenon which causes materials to emit light in response to
external stimuli, dates back to 1500 B.C. in China. This housings, castings, transistors, microcircuits, circuit-boards,
valve positions, erosion and corrosion of pipes, integrity of
phenomenon did not attract scientific interest until 1603, when
the discovery of the Bolognese stone in Italy led to investiga- pipe welds, solenoid valves, fuses, relays, tires, reinforced
plastics and automotive parts.
tion by a large number of researchers. One of these was
Becquerel, who, in his 1869 book La Lumiere, revealed that he
5.5 Limitation:
had discovered the phenomenon of stimulated luminescence in
5.5.1 Handling Characteristics—Potentially, a CR imaging
the course of his work with phosphors.
plate may be erased and reused thousands of times. The
5.2.1 Photo stimulated luminescence (PSL) is a phenom-
primary limiting factor, as is the case with lead intensifying
enon in which a phosphor that has ceased emitting light screens, is physical handling. Frequency of handling, bending
because of the removal of the stimulus once again emits light
and cleaning determines the plate’s useful lifespan.
when excited by light with a longer wavelength. The phenom-
enon is quite common since photostimulable phosphors cover
6. Interpretation and Reference Standards
a broad range of materials—compounds of elements from
6.1 Acceptance Standards—As written by other organiza-
GroupsIIBandVI(forexample,ZnS),compoundsofelements
tions for film radiography may be employed for CR inspection
from Groups 1A and VIIA, VIIB and V VIB (for example,
provided appropriate adjustments are made to accommodate
alkali halides), diamond, Groups 2A and VIIA, VIIB and V
the differences represented by the CR data files.
2+
VIB (for example, barium fluorohalides—Ba FX-EU X=Br,
6.2 ASTM Reference Standards—Reference digital image
I, etc.), oxides (for example, Zn2Si04:Mn and LaOBr:Ce, Tb),
standards, complementing existing ASTM reference film ra-
and even certain organic compounds. The materials therefore
diographic standards must be developed. Subcommittee
lend themselves to data storage because the stimulus or
E07.01 work aimed at developing such standards is underway.
primary excitation could be used to write data to the material,
the light or secondary excitation to read the data back. Storage
7. Safety Precautions
phosphor imaging plate (IP) is a name given to a two-
dimensional flexible sensor that can store a latent image 7.1 The safety procedures for the handling and use of
obtained from X rays, electron beams or other types of ionizing radiation sources must be followed. Mandatory rules
radiation, using photostimulable phosphors (P.P.), and then and regulations are published by governmental licensing agen-
sequentially reproduces them as a digital file by releasing the cies, and guidelines for control of radiation are available in
PSL with a laser beam, piping the PSL to a photomultiplier publications such as the Fed. Std. No. 21-CFR 1020.40.
tube (PMT) and then digitizing the resulting electrical signal. Careful radiation surveys should be made in accordance with
E2007–00 (2006)
regulations and codes and should be conducted in the exami- 9.3 By analyzing this flux field, we can make deductions
nation area as well as adjacent areas under all possible about the composition of the object being examined, since the
operating conditions. attenuation process depends on the number of atoms encoun-
tered by the original X-ray beam, and their atomic number.
8. Radiation Sources
9.4 The attenuation process is quite complex, since the
8.1 General:
X-ray beam is usually composed of a mixture of photons of
8.1.1 The sources of radiation for CR imaging systems
many different energies and the object may be composed of
described in this guide are X-ray machines and radioactive
atomsofmanydifferentkinds.Exactpredictionofthefluxfield
isotopes. The energy range available extends from a few kV to
falling upon the SPIP is therefore, difficult. Approximations
32 MeV. Since examination systems in general require high
can be made, since the mathematics and data are available to
dose rates, X-ray machines are the primary radiation source.
treat any single photon energy and atomic type, but in practice
The types of X-ray sources available are conventional X-ray
great reliance must be placed on the experience of the user. In
generators that extend in energy up to 420 kV. Energy sources
spite of these difficulties, successful CR SPIP’s have been
from 1 MeV and above are generally represented by linear
developed,andperformwell.Thecriteriaforchoicedependon
accelerators.
many factors, which, depending on the application, may, or
8.1.2 Usable isotope sources have energy levels from 84
may not be critical. Obviously, these criteria will include the
170 60
keV (Thulium-170, Tm ) up to 1.25 MeV (Cobalt-60, Co ).
following factors.
With high specific activities, these sources should be consid-
9.4.1 Field of View—The field of view of the SPIP and its
ered for special application where their field mobility and
resolution are interrelated. The resolution of the SPIP is fixed
operational simplicity can be of significant advantage.
by its physical characteristics, so if the X-ray image is
8.1.3 The factors to be considered in determining the
projected upon it full-size (the object and image planes in
desiredradiationsourceareenergy,focalgeometry,waveform,
contact),theresultantresolutionwillbeapproximatelyequalto
half life, and radiation output.
that of the SPIP. When SPIP resolution becomes the limiting
8.2 Selection of Sources:
factor, the object may be moved away from the SPIP, and
8.2.1 Low-Energy Sources—The radiation source selected
towards the source to enlarge the projected image and thus
for a specific examination system depends upon the material
allow smaller details to be resolved by the same SPIP. As the
beingexamined,itsmass,itsthickness,andtherequiredrateof
image is magnified, however, the detail contrast is reduced and
examination. In the energy range up to 420 kV, the X-ray units
its outlines are less distinct. (See 10.3.) It is apparent, also, that
have an adjustable energy range so that they are applicable to
when geometric magnification is used, the area of the object
a wide range of materials. Specifically, 50-kV units operate
that is imaged on the SPIP is proportionally reduced. As a
down to a few kV; 160-kVequipment operates down to 20 kV;
general rule, X-ray magnifications should not exceed 53
and 420-kV equipment operates down to about 85 kV.
except when using X-ray sources with very small (microfocus)
8.2.2 High-Energy Sources—The increased efficiency of
anodes. In such cases, magnifications in the order of 10 to 203
X-ray production at higher accelerating potentials makes
are useful. When using conventional focal-spot X-ray sources,
available a large radiation flux, and this makes possible the
magnifications from 1.2 to 1.5 provide a good compromise
examination of greater thicknesses of material. High radiation
between contrast and resolution in the magnified image.
energies in general produce lower image contrast, so that as a
9.4.2 Inherent Sensitivity—The basic sensitivity of the SPIP
guide the minimum thickness of material examined should not
may be defined as its ability to respond to small, local
be less than 2.5 half-value layers of material. The maximum
variationsinradiantenergytodisplaythefeaturesofinterestin
thickness of material can extend up to 10 half-value layers.
the object being examined. It would seem that an SPIPthat can
8.3 Source Geometry:
displayintensitychangesontheorderof1to2 %atresolutions
8.3.1 Althoughthephysicalsizeofthesourceofradiationis
approaching that of film radiography would satisfy all of the
a parameter that may vary considerably, the radiation sensor is
requirements for successful CR imaging. It is not nearly that
generally the principal source of unsharpness.
simple. Often good technique is more important than the
9. CR Storage Phosphor Imaging Plate
details of the imaging system itself. The geometry of the
system with respect to field of view, resolution and contrast is
9.1 A CR storage phosphor imaging plate (SPIP) is de-
a very important consideration as is the control of scattered
scribed as a reusable detector (flexible or rigid) that stores
radiation. Scattered X rays entering the imaging system pro-
penetrating radiation energy as a
...
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