ASTM E2446-05

Standard Practice for Classification of Computed Radiology Systems

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 m diameter for the micro-photometer, which is defined in Test Method E 1815 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-2005
• ICS: 19.100 - Non-destructive testing
• Technical Committee: E07 - Nondestructive Testing
• Drafting Committee: E07.01 - Radiography (X and Gamma) Method

Relations

• Replaced By: ASTM E2446-05(2010) - Standard Practice for Classification of Computed Radiology Systems
• 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-2005
• 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-2005
• Referred By: ASTM E1475-13(2023) - Standard Guide for Data Fields for Computerized Transfer of Digital Radiological Examination Data
• Effective Date: 01-Jun-2005
• Referred By: ASTM E746-18 - Standard Practice for Determining Relative Image Quality Response of Industrial Radiographic Imaging Systems
• Effective Date: 01-Jun-2005
• Referred By: ASTM E1735-19 - Standard Practice for Determining Relative Image Quality Response of Industrial Radiographic Imaging Systems from 4 to 25 MeV
• Effective Date: 01-Jun-2005
• 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-2005
• Referred By: ASTM E94/E94M-22 - Standard Guide for Radiographic Examination Using Industrial Radiographic Film
• Effective Date: 01-Jun-2005
• 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-2005
• Referred By: ASTM E2007-10(2023) - Standard Guide for Computed Radiography
• Effective Date: 01-Jun-2005
• Referred By: ASTM E2533-21 - Standard Guide for Nondestructive Examination of Polymer Matrix Composites Used in Aerospace Applications
• Effective Date: 01-Jun-2005
• Referred By: ASTM E2597/E2597M-22 - Standard Practice for Manufacturing Characterization of Digital Detector Arrays
• Effective Date: 01-Jun-2005
• Referred By: ASTM E2033-17 - Standard Practice for Radiographic Examination Using Computed Radiography (Photostimulable Luminescence Method)
• Effective Date: 01-Jun-2005
• Referred By: ASTM E2736-17(2022) - Standard Guide for Digital Detector Array Radiography
• Effective Date: 01-Jun-2005
• Referred By: ASTM E2737-23 - Standard Practice for Digital Detector Array Performance Evaluation and Long-Term Stability
• Effective Date: 01-Jun-2005

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
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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E2007 Guide for Computed Radiography
E2033 Practice for Computed Radiology (Photostimulable
1.1 This practice describes the evaluation and classification
Luminescence Method)
of a computed radiography (CR) system, a particular phosphor
E2445 Practice for Qualification and Long-Term Stability
imaging plate (IP), system scanner and software, in combina-
of Computed Radiology Systems
tion with specified metal screens for industrial radiography. It
isintendedtoensurethattheevaluationofimagequality,asfar
3. Terminology
as this is influenced by the scanner/IP system, meets the needs
3.1 Definitions—The definition of terms relating to gamma-
of users.
and X-radiology, which appear in Terminology E1316, Guide
1.2 The practice defines system tests to be used to classify
E2007,andPracticeE2033,shallapplytothetermsusedinthis
the systems of different suppliers and make them comparable
practice.
for users.
3.2 Definitions of Terms Specific to This Standard:
1.3 The CR system performance is described by signal and
3.2.1 computed radiology system (CR system)—Acomplete
noiseparameters.Forfilmsystems,thesignalisrepresentedby
system of a storage phosphor imaging plate (IP), a correspond-
gradient and the noise by granularity. The signal-to-noise ratio
ing read out unit (scanner or reader) and software, which
is normalized by the basic spatial resolution of the system and
converts the information of the IPinto a digital image (see also
is part of classification. The normalization is given by the
Guide E2007).
scanning aperture of 100 µm diameter for the micro-
3.2.2 computed radiology system class—A particular group
photometer, which is defined in Test Method E1815 for film
of storage phosphor imaging plate systems, which is charac-
system classification. This practice describes how the param-
terized by a SNR (signal-to-noise ratio) range shown in Table
eters shall be measured for CR systems.
1 and by a certain unsharpness range in a specified exposure
1.4 The values stated in SI are to be regarded as the
range.
standard.
3.2.3 ISO speed S —DefinesthespeedofaCRsystemand
IPx
1.5 This standard does not purport to address all of the
is calculated from the reciprocal dose value, measured in gray,
safety concerns, if any, associated with its use. It is the
whichisnecessarytoobtainaspecifiedminimumSNRofaCR
responsibility of the user of this standard to establish appro-
system.
priate safety and health practices and to determine the
3.2.4 signal-to-noise ratio (SNR)—Quotient of mean value
applicability of regulatory limitations prior to use.
of the linearized signal intensity and standard deviation of the
2. Referenced Documents noise (intensity distribution) at this signal intensity. The SNR
2 depends on the radiation dose and the CR system properties.
2.1 ASTM Standards:
3.2.5 modulation transfer function (MTF)—The normalized
E1316 Terminology for Nondestructive Examinations
magnitude of the Fourier-transform (FT) of the differentiated
E1815 Test Method for Classification of Film Systems for
edge spread function (ESF) of the linearized PSL (photo
Industrial Radiography
stimulated luminescence) intensity, measured perpendicular to
E2002 Practice for Determining Total Image Unsharpness
a sharp edge. MTF describes the contrast transmission as a
in Radiology
function of the object size. In this practice, the MTF charac-
terizes the unsharpness of the CR system. This depends on the
This practice is under the jurisdiction of ASTM Committee E07 on Nonde-
scanning system itself and IP-type and cassette employed.
structive Testing and is the direct responsibility of Subcommittee E07.01 on
3.2.6 gain/amplification—Opto-electrical gain setting of the
Radiology (X and Gamma) Method.
scanning system.
Current edition approved June 1, 2005. Published June 2005. DOI: 10.1520/
E2446-05.
3.2.7 linearized signal intensity—a numerical signal value
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
of a picture element (pixel) of the digital image, which is
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
proportional to the radiation dose. The linearized signal inten-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. sity is zero, if the radiation dose is zero.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2446 – 05
TABLE 1 CR System Classification
Therefore, the practice should always use IQIs for proof of
CR System Minimum contrast sensitivity and spatial resolution.
Classification Signal-Noise Ratio
4.3 The quality factors can be determined most accurately
ASTM IP Special/Y 130
by the tests described in this practice. Some of the system tests
ASTM IP I/Y 65
require special tools, which may not be available in user
ASTM IP II/Y 52
ASTM IP III/Y 43
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 recom-
mended as practical user tests, should the user not have the
3.2.8 basic spatial resolution—the read-out value of un-
special tools available as needed for the tests in this practice.
sharpness measured with duplex wire IQI in accordance with
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
specifying bodies and contracting parties to agree to particular
affect the accurate reading of images on exposed IPs using an
system class, as a first step in arriving at the appropriate
optical scanner.
settings of a system, or the selection of a system. Confirmation
4.2 This practice is to be used to establish a classification of
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
5.1 CR system evaluation depends on the combined prop-
manufacturers’imaging plates.ACR system class results from
erties of the phosphor imaging plate (IP) type, the scanner and
the use of a particular imaging plate together with the exposure
software used, and the selected scan parameters. Therefore,
conditions, particularly total exposure, the scanner type and
software and the scanning parameters. This classification documentation for each test shall include the IP type, scanner,
software and scan parameters, and the results shall be calcu-
system provides a means to compare differing CR technolo-
gies, as is common practice with film systems, which guides lated and tabulated prior to arriving at a class assignment. The
the user to the appropriate configuration, IP and technique for applied test equipment for SNR measurement (Fig. 1) and
the application at hand. The class selected may not match the algorithm 6.1.1 correspond to Test Method E1815. The recom-
imaging performance of a corresponding film class due to the mended thickness for aperture test object (diaphragm) is
difference in the spatial resolution and scatter sensitivity. 10.2-mm(0.4in.)ofPb.TheSDDshallbeatleast1m(39in.).
FIG. 1 Scheme of Experimental Arrangement for the Step Exposure Method
E2446 – 05
Do not use any material (for example, lead) behind the cassette 6.1.1.5 The scanner shall read with a dynamic range of$12
and leave a free space of at least 1 m (39 in.) behind the bit and operate at its highest spatial resolution or a spatial
cassette. resolution for which the classification shall be carried out.
5.2 The step wedge method (Fig. 2) describes a simpler Background and anti-shading correction may be used before
procedure for SNR measurement than described in Test the analysis of data, if it relates to the standard measurement
Method E1815, which permits obtaining similar results with procedure for all measurements.The procedure shall be carried
less expense, and less accuracy. out and documented for all sensitivity and latitude ranges and
all read-out pixel sizes if any of these parameters change the
6. Procedure for quantitative measurement of image
SNR-analysis.
quality parameters
6.1.1.6 IPs are exposed in a similar way to film radiography
and under the conditions described: signal and noise (s )or
6.1 Measurement of the Normalized Signal-to-Noise Ratio
PSL
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—For measurement of the
ments be spatially uniform. Any nonuniformities in X-ray
SNR, the following steps are taken (see also Test Method
E1815): transmission of the cassette front, or defects in the Pb foil or in
the phosphor itself could influence the SNR measurement. No
6.1.1.1 The IP, with front and back lead screens of 0.1 mm
(0.004 in.) thickness in the typical exposure cassette, shall be major scratches or dust shall be visible in the measurement
area. Therefore, exercise considerable care in selection and
positioned in front ofanX-raytubewithtungstenanode.Make
theexposureswithan8mm(0.32in.)copperfilterattheX-ray placement of the aperture, and selection and maintenance of
the cassette, the lead screens and the phosphor screen. To
tube and the kilovoltage set such that the half value layer in
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
standard protocol is recommended. Other approaches may be
approximately 220 kV.
used as long as a uniform exposure is created. At least twelve
6.1.1.2 Determine the required exact kilovoltage setting by
2 2
areas (test areas) of$400 mm (0.62 in. ) are evenly exposed
making an exposure (or an exposure rate) measurement with
on the same IPover the full working range of dose. Due to the
the detector placed at a distance of at least 750 mm (29.5 in.)
different construction principles of scanners, the measurement
from the tube target and an 8 mm (0.32 in.) copper filter at the
shall be performed for all possible pixel sizes, if the results
tube. Then make a second measurement with a total of 11.5
change.Thedigitalread-outintensityvalues(grayvalues)shall
mm (0.45 in.) of copper at the tube. These filters should be
becalibratedinsuchaway,thattheyarelinearinrelationtothe
made of 99.9 % pure copper.
radiation dose, which corresponds to the photo stimulated
6.1.1.3 Calculatetheratioofthefirstandsecondreadings.If
luminescence (PSL) intensity of the exposed IPs. These cali-
this ratio is not 2, adjust the kilovoltage up or down and repeat
brated gray values shall be used for the calculation of the SNR.
the measurements until a ratio of 2 (within 5 %) is obtained.
In order to get a reliable result at least six measurements shall
Record the setting of kilovoltage for use with the further IP
tests. be made on different samples, and the results are to be
averaged for each of the twelve or more dose levels measured.
6.1.1.4 The sensitive layer of the IP shall face the X-ray
source. For gamma radiography with Ir-192, the measurements 6.1.1.7 The signal (intensity I ) and noise (standard
meas
shall be carried out with 0.3 mm lead screens in front and deviation s ) shall be computed from a region without
PSL
behind the IP.Also 8 mm Cu shall be used for pre-filtering (see shading or artifacts. Sample SNR values shall be taken in
Fig. 1). different regions of the image area under test to ensure that
FIG. 2 Scheme for the Measurement of the SNR by the Step Wedge Method
E2446 – 05
SNR values are within 10 % stable. The size of the ROI used with adequate exposure time or tube current (mA), shall be
to measure the mean signal and noise shall be at least 20 by 55 made. The distance between step wedge and IP shall be$500
pixels and it should be an area ROI.An example technique for mm (19.69 in.) to reduce the influence of scattered radiation.A
assuring reliable signal-to-noise measurements is described magnification of 23 is recommended.Abeam collimator shall
below.Thiscanbeachievedusingacommonlyavailableimage be used. X-ray voltage and filtering shall be selected in
processing tool. The signal and noise shall be calculated from accordance with 6.1.1.1.
a data set of 1100 values or more per exposed area. The
NOTE 3—X-ray penetration through Cu-steps of different thickness is
unfiltereddatasetissubdividedinto55groupsormorewith20
distorted by beam hardening and suitable adjustment of exposure is
valuespergroup.Foreachgroupwithindex i,thevalueI
meas_i
required.
is calculated as the mean of the unfiltered group values and the
6.1.2.2 The projected area of each step shall be about 20 by
value s is calculated from the same group values. An
PSLi
20 mm ($400 mm ). No values of at least two times the
increased number of groups yields a better (lower) uncertainty
geometric unsharpness shall be taken from areas near the step
of the result. Due to the filtering effect of this grouping
edges.
procedure, the s -values shall be corrected by the following
PSLi
6.1.2.3 All details for the measurement of the SNR shall
equation:
correspond to 6.1.1.2-6.1.1.5. The graphical analysis shall be
s 5 1.0179 · s (1)
PSLi_corr PSLi
basedontheplotofSNR=f(log(Exposure)–µ ·w ),where
Cu Cu
NOTE 1—The values s are multiplied with 1.0179 to correct for the
PSLi µ is the absorption coefficient, w is the wall thickness of
Cu Cu
following median unbiased esti
...