ASTM E2446-05(2010)

Standard Practice for Classification of Computed Radiology Systems

SIGNIFICANCE AND USE
There are several factors affecting the quality of a CR image including the spatial resolution of the IP system, geometrical unsharpness, scatter and contrast sensitivity (signal-to-noise ratio), as well as software. There are several additional factors (for example, scanning parameters), which affect the accurate reading of images on exposed IPs using an optical scanner.
This practice is to be used to establish a classification of CR system classes on the basis of a normalized SNR. Due to the difference between the methods, it is required to specify the CR system classes with spatial resolution values. The CR system classes in this document do not refer to any particular manufacturers’ imaging plates. A CR system class results from the use of a particular imaging plate together with the exposure conditions, particularly total exposure, the scanner type and software and the scanning parameters. This classification system provides a means to compare differing CR technologies, as is common practice with film systems, which guides the user to the appropriate configuration, IP and technique for the application at hand. The class selected may not match the imaging performance of a corresponding film class due to the difference in the spatial resolution and scatter sensitivity. Therefore, the practice should always use IQIs for proof of contrast sensitivity and spatial resolution.
The quality factors can be determined most accurately by the tests described in this practice. Some of the system tests require special tools, which may not be available in user laboratories. Simpler tests are described for quality assurance in Practice E2445, which are designed for a fast test of the quality of CR systems and long-term stability and are recommended as practical user tests, should the user not have the special tools available as needed for the tests in this practice.
Manufacturers of industrial CR systems will use this practice. Users of industrial CR systems may also perf...
SCOPE
1.1 This practice describes the evaluation and classification of a computed radiography (CR) system, a particular phosphor imaging plate (IP), system scanner and software, in combination with specified metal screens for industrial radiography. It is intended to ensure that the evaluation of image quality, as far as this is influenced by the scanner/IP system, meets the needs of users.
1.2 The practice defines system tests to be used to classify the systems of different suppliers and make them comparable for users.
1.3 The CR system performance is described by signal and noise parameters. For film systems, the signal is represented by gradient and the noise by granularity. The signal-to-noise ratio is normalized by the basic spatial resolution of the system and is part of classification. The normalization is given by the scanning aperture of 100 µm diameter for the micro-photometer, which is defined in Test Method E1815 for film system classification. This practice describes how the parameters shall be measured for CR systems.
1.4 The values stated in SI are to be regarded as the standard.
1.5 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 to determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-May-2010
• ICS: 19.100 - Non-destructive testing
• Technical Committee: E07 - Nondestructive Testing
• Drafting Committee: E07.01 - Radiology (X and Gamma) Method

Relations

• Replaces: ASTM E2446-05 - Standard Practice for Classification of Computed Radiology Systems
• Effective Date: 01-Jun-2010
• Referred By: ASTM E2736-17(2022) - Standard Guide for Digital Detector Array Radiography
• Effective Date: 01-Jun-2010
• Referred By: ASTM E2737-23 - Standard Practice for Digital Detector Array Performance Evaluation and Long-Term Stability
• Effective Date: 01-Jun-2010
• Referred By: ASTM E2033-17 - Standard Practice for Radiographic Examination Using Computed Radiography (Photostimulable Luminescence Method)
• Effective Date: 01-Jun-2010
• Referred By: ASTM E2597/E2597M-22 - Standard Practice for Manufacturing Characterization of Digital Detector Arrays
• Effective Date: 01-Jun-2010
• Referred By: ASTM E2533-21 - Standard Guide for Nondestructive Examination of Polymer Matrix Composites Used in Aerospace Applications
• Effective Date: 01-Jun-2010
• Referred By: ASTM E2445/E2445M-20 - Standard Practice for Performance Evaluation and Long-Term Stability of Computed Radiography Systems
• Effective Date: 01-Jun-2010
• Referred By: ASTM E3166-20e1 - Standard Guide for Nondestructive Examination of Metal Additively Manufactured Aerospace Parts After Build
• Effective Date: 01-Jun-2010
• Referred By: ASTM E2662-15(2022) - Standard Practice for Radiographic Examination of Flat Panel Composites and Sandwich Core Materials Used in Aerospace Applications
• Effective Date: 01-Jun-2010
• Referred By: ASTM E2982-21 - Standard Guide for Nondestructive Examination of Thin-Walled Metallic Liners in Filament-Wound Pressure Vessels Used in Aerospace Applications
• Effective Date: 01-Jun-2010
• Referred By: ASTM E2903-18 - Standard Test Method for Measurement of the Effective Focal Spot Size of Mini and Micro Focus X-ray Tubes
• Effective Date: 01-Jun-2010
• Referred By: ASTM E1475-13(2023) - Standard Guide for Data Fields for Computerized Transfer of Digital Radiological Examination Data
• Effective Date: 01-Jun-2010
• Referred By: ASTM E94/E94M-22 - Standard Guide for Radiographic Examination Using Industrial Radiographic Film
• Effective Date: 01-Jun-2010
• Referred By: ASTM E2007-10(2023) - Standard Guide for Computed Radiography
• Effective Date: 01-Jun-2010
• Referred By: ASTM E746-18 - Standard Practice for Determining Relative Image Quality Response of Industrial Radiographic Imaging Systems
• Effective Date: 01-Jun-2010

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:E2446 −05(Reapproved 2010)
Standard Practice for
Classification of Computed Radiology Systems
This standard is issued under the fixed designation E2446; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E2002PracticeforDeterminingTotalImageUnsharpnessin
Radiology
1.1 This practice describes the evaluation and classification
E2007Guide for Computed Radiography
of a computed radiography (CR) system, a particular phosphor
E2033Practice for Computed Radiology (Photostimulable
imaging plate (IP), system scanner and software, in combina-
Luminescence Method)
tion with specified metal screens for industrial radiography. It
E2445Practice for Performance Evaluation and Long-Term
isintendedtoensurethattheevaluationofimagequality,asfar
Stability of Computed Radiography Systems
as this is influenced by the scanner/IPsystem, meets the needs
of users.
3. Terminology
1.2 The practice defines system tests to be used to classify
3.1 Definitions—Thedefinitionoftermsrelatingtogamma-
the systems of different suppliers and make them comparable
and X-radiology, which appear in Terminology E1316, Guide
for users.
E2007,andPracticeE2033,shallapplytothetermsusedinthis
1.3 The CR system performance is described by signal and
practice.
noiseparameters.Forfilmsystems,thesignalisrepresentedby
3.2 Definitions of Terms Specific to This Standard:
gradient and the noise by granularity. The signal-to-noise ratio
3.2.1 computed radiology system (CR system)—Acomplete
is normalized by the basic spatial resolution of the system and
systemofastoragephosphorimagingplate(IP),acorrespond-
is part of classification. The normalization is given by the
ing read out unit (scanner or reader) and software, which
scanning aperture of 100 µm diameter for the micro-
convertstheinformationoftheIPintoadigitalimage(seealso
photometer, which is defined in Test Method E1815 for film
Guide E2007).
system classification. This practice describes how the param-
3.2.2 computed radiology system class—A particular group
eters shall be measured for CR systems.
of storage phosphor imaging plate systems, which is charac-
1.4 The values stated in SI are to be regarded as the
terized by a SNR (signal-to-noise ratio) range shown in Table
standard.
1 and by a certain unsharpness range in a specified exposure
1.5 This standard does not purport to address all of the
range.
safety concerns, if any, associated with its use. It is the
3.2.3 ISO speed S —DefinesthespeedofaCRsystemand
IPx
responsibility of the user of this standard to establish appro-
is calculated from the reciprocal dose value, measured in gray,
priate safety and health practices and to determine the
whichisnecessarytoobtainaspecifiedminimumSNRofaCR
applicability of regulatory limitations prior to use.
system.
2. Referenced Documents
3.2.4 signal-to-noise ratio (SNR)—Quotient of mean value
of the linearized signal intensity and standard deviation of the
2.1 ASTM Standards:
noise (intensity distribution) at this signal intensity. The SNR
E1316Terminology for Nondestructive Examinations
depends on the radiation dose and the CR system properties.
E1815Test Method for Classification of Film Systems for
Industrial Radiography
3.2.5 modulation transfer function (MTF)—The normalized
magnitude of the Fourier-transform (FT) of the differentiated
edge spread function (ESF) of the linearized PSL (photo
This practice is under the jurisdiction of ASTM Committee E07 on Nonde-
stimulated luminescence) intensity, measured perpendicular to
structive Testing and is the direct responsibility of Subcommittee E07.01 on
Radiology (X and Gamma) Method.
a sharp edge. MTF describes the contrast transmission as a
Current edition approved June 1, 2010. Published August 2010 Originally
function of the object size. In this practice, the MTF charac-
approved in 2005. Last previous edition approved in 2005 as E2446–05. DOI:
terizes the unsharpness of the CR system. This depends on the
10.1520/E2446-05R10.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or scanning system itself and IP-type and cassette employed.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
3.2.6 gain/amplification—Opto-electrical gain setting of the
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. scanning system.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2446−05 (2010)
TABLE 1 CR System Classification
guides the user to the appropriate configuration, IP and
CR System Minimum technique for the application at hand. The class selected may
Classification Signal-Noise Ratio
not match the imaging performance of a corresponding film
ASTM IP Special/Y 130
class due to the difference in the spatial resolution and scatter
ASTM IP I/Y 65
ASTM IP II/Y 52 sensitivity. Therefore, the practice should always use IQIs for
ASTM IP III/Y 43
proof of contrast sensitivity and spatial resolution.
4.3 The quality factors can be determined most accurately
bythetestsdescribedinthispractice.Someofthesystemtests
3.2.7 linearized signal intensity—a numerical signal value
require special tools, which may not be available in user
of a picture element (pixel) of the digital image, which is
laboratories. Simpler tests are described for quality assurance
proportional to the radiation dose. The linearized signal inten-
in Practice E2445, which are designed for a fast test of the
sity is zero, if the radiation dose is zero.
quality of CR systems and long-term stability and are recom-
3.2.8 basic spatial resolution—the read-out value of un-
mended as practical user tests, should the user not have the
sharpness measured with duplex wire IQI in accordance with
special tools available as needed for the tests in this practice.
Practice E2002 divided by 2 as effective pixel size of the CR
4.4 Manufacturers of industrial CR systems will use this
system.
practice. Users of industrial CR systems may also perform the
tests and measurements outlined in this practice, provided that
4. Significance and Use
the required test equipment is used and the methodology is
4.1 There are several factors affecting the quality of a CR
strictly followed. Any alternative methods may be applied if
image including the spatial resolution of the IP system,
equivalence to the methods of this practice is proven to the
geometrical unsharpness, scatter and contrast sensitivity
appropriate Cognizant Engineering Organization.
(signal-to-noise ratio), as well as software. There are several
4.5 The publication of CR system classes will enable
additional factors (for example, scanning parameters), which
affect the accurate reading of images on exposed IPs using an specifying bodies and contracting parties to agree to particular
system class, as a first step in arriving at the appropriate
optical scanner.
settingsofasystem,ortheselectionofasystem.Confirmation
4.2 Thispracticeistobeusedtoestablishaclassificationof
of necessary image quality shall be achieved by using Practice
CR system classes on the basis of a normalized SNR. Due to
E2033.
thedifferencebetweenthemethods,itisrequiredtospecifythe
CR system classes with spatial resolution values. The CR
5. Apparatus
system classes in this document do not refer to any particular
manufacturers’imaging plates.ACR system class results from 5.1 CR system evaluation depends on the combined prop-
theuseofaparticularimagingplatetogetherwiththeexposure erties of the phosphor imaging plate (IP) type, the scanner and
conditions, particularly total exposure, the scanner type and software used, and the selected scan parameters. Therefore,
software and the scanning parameters. This classification documentation for each test shall include the IP type, scanner,
system provides a means to compare differing CR software and scan parameters, and the results shall be calcu-
technologies, as is common practice with film systems, which lated and tabulated prior to arriving at a class assignment. The
FIG. 1Scheme of Experimental Arrangement for the Step Exposure Method
E2446−05 (2010)
applied test equipment for SNR measurement (Fig. 1) and shall be carried out with 0.3 mm lead screens in front and
algorithm 6.1.1 correspond toTest Method E1815.The recom- behindtheIP.Also8mmCushallbeusedforpre-filtering(see
mended thickness for aperture test object (diaphragm) is
Fig. 1).
10.2-mm(0.4in.)ofPb.TheSDDshallbeatleast1m(39in.).
6.1.1.5 The scanner shall read with a dynamic range of ≥12
Donotuseanymaterial(forexample,lead)behindthecassette
bit and operate at its highest spatial resolution or a spatial
and leave a free space of at least 1 m (39 in.) behind the
resolution for which the classification shall be carried out.
cassette.
Background and anti-shading correction may be used before
5.2 The step wedge method (Fig. 2) describes a simpler the analysis of data, if it relates to the standard measurement
procedure for SNR measurement than described in Test
procedureforallmeasurements.Theprocedureshallbecarried
Method E1815, which permits obtaining similar results with
out and documented for all sensitivity and latitude ranges and
less expense, and less accuracy.
all read-out pixel sizes if any of these parameters change the
SNR-analysis.
6. Procedure for quantitative measurement of image
6.1.1.6 IPsareexposedinasimilarwaytofilmradiography
quality parameters
and under the conditions described: signal and noise (σ )or
PSL
6.1 Measurement of the Normalized Signal-to-Noise Ratio
SNR over dose curve shall be measured. It is especially
(SNR)
important that the exposure of the IP for the SNR measure-
6.1.1 Step Exposure Method—FormeasurementoftheSNR,
ments be spatially uniform. Any nonuniformities in X-ray
the following steps are taken (see also Test Method E1815):
transmissionofthecassettefront,ordefectsinthePbfoilorin
6.1.1.1 The IP, with front and back lead screens of 0.1 mm
the phosphor itself could influence the SNR measurement. No
(0.004 in.) thickness in the typical exposure cassette, shall be
major scratches or dust shall be visible in the measurement
positionedinfrontofanX-raytubewithtungstenanode.Make
area. Therefore, exercise considerable care in selection and
theexposureswithan8mm(0.32in.)copperfilterattheX-ray
placement of the aperture, and selection and maintenance of
tube and the kilovoltage set such that the half value layer in
the cassette, the lead screens and the phosphor screen. To
copper is 3.5 mm (0.14 in.). The kilovoltage setting will be
achieve a uniform region of interest on to the IP, the following
approximately 220 kV.
standard protocol is recommended. Other approaches may be
6.1.1.2 Determine the required exact kilovoltage setting by
used as long as a uniform exposure is created.At least twelve
making an exposure (or an exposure rate) measurement with
2 2
areas (test areas) of ≥400 mm (0.62 in. ) are evenly exposed
the detector placed at a distance of at least 750 mm (29.5 in.)
on the same IPover the full working range of dose. Due to the
from the tube target and an 8 mm (0.32 in.) copper filter at the
different construction principles of scanners, the measurement
tube. Then make a second measurement with a total of 11.5
shall be performed for all possible pixel sizes, if the results
mm (0.45 in.) of copper at the tube. These filters should be
change.Thedigitalread-outintensityvalues(grayvalues)shall
made of 99.9% pure copper.
becalibratedinsuchaway,thattheyarelinearinrelationtothe
6.1.1.3 Calculatetheratioofthefirstandsecondreadings.If
radiation dose, which corresponds to the photo stimulated
this ratio is not 2, adjust the kilovoltage up or down and repeat
luminescence (PSL) intensity of the exposed IPs. These cali-
the measurements until a ratio of 2 (within 5%) is obtained.
bratedgrayvaluesshallbeusedforthecalculationoftheSNR.
Record the setting of kilovoltage for use with the further IP
In order to get a reliable result at least six measurements shall
tests.
6.1.1.4 The sensitive layer of the IP shall face the X-ray be made on different samples, and the results are to be
source.ForgammaradiographywithIr-192,themeasurements averaged for each of the twelve or more dose levels measured.
FIG. 2Scheme for the Measurement of the SNR by the Step Wedge Method
E2446−05 (2010)
6.1.1.7 The signal (intensity I ) and noise (standard cover a range of two or more orders of magnitude of the
meas
deviation σ ) shall be computed from a region without radiation dose at least two suitable and different exposures,
PSL
shading or artifacts. Sample SNR values shall be taken in with adequate exposure time or tube current (mA), shall be
different regions of the image area under test to ensure that made. The distance between step wedge and IP shall be ≥500
SNR values are within 10% stable. The size of the ROI used mm(19.69in.)toreducetheinfluenceofscatteredradiation.A
tomeasurethemeansignalandnoiseshallbeatleast20by55 magnification of 2× is recommended.Abeam collimator shall
pixels and it should be an area ROI.An example technique for be used. X-ray voltage and filtering shall be selected in
assuring reliable signal-to-noise measurements is described accordance with 6.1.1.1.
below.Thiscanbeachievedusingacommonlyavailableimage
NOTE 3—X-ray penetration through Cu-steps of different thickness is
processing tool. The signal and noise shall be calculated from
distorted by beam hardening and suitable adjustment of exposure is
a data set of 1100 values or more per exposed area. The
required.
unfiltereddatasetissubdividedinto55groupsormorewith20
6.1.2.2 The projected area of each step shall be about 20 by
valuespergroup.Foreachgroupwithindex i,thevalueI 2
meas_i
20 mm (≥400 mm ). No values of at least two times the
iscalculatedasthemeanoftheunfilteredgroupvaluesandthe
geometric unsharpness shall be taken from areas near the step
value σ is calculated from the same group values. An
PSLi
edges.
increased number of groups yields a better (lower) uncertainty
6.1.2.3 All details for the measurement of the SNR shall
of the result. Due to the filtering effect of this grouping
correspond to 6.1.1.2 – 6.1.1.5.The graphical analysis shall be
procedure, the σ -values shall be corrected by the following
PSLi
based on the plot of SNR = f(log (Exposure) – µ ·w ),
Cu Cu
equation:
where µ is the absorption coefficient, w is the wall
Cu Cu
σ 51.0179·σ (1) thickness of the corresponding step of the step wedge and the
PSLi_corr P
...