ASTM E1441-19
(Guide)Standard Guide for Computed Tomography (CT)
Standard Guide for Computed Tomography (CT)
SIGNIFICANCE AND USE
5.1 Computed tomography (CT) is a radiographic reconstruction method that provides a sensitive technique whenever the primary goal is to locate and size planar and volumetric detail in three dimensions.
5.2 CT provides quantitative volume images as a function of density and element number (attenuation coefficient) by means of computer-processed combinations of many X-ray measurements taken from different angles to produce cross-sectional images of specific areas of a scanned object, allowing the user to see inside the object without cutting. CT is considered much easier to interpret than conventional radiographic data due to the elimination of overlapping structures. The new user can learn quickly to read CT data because the images correspond more closely to the way the human mind visualizes three-dimensional structures than conventional projection radiography. Further, because CT slices and volumes are digital, they may be enhanced, analyzed, compressed, archived, input as data into performance calculations, compared with digital data from other NDE modalities, or transmitted to other locations for remote viewing.
SCOPE
1.1 CT is a radiographic examination technique that generates digital images in three dimensions of an object, including the interior structure. Because of the relatively good penetrability of X-rays, CT permits the nondestructive physical and, to a limited extent, chemical characterization of the internal structure of materials. Also, since the method is X-ray based, it applies equally well to metallic and non-metallic specimens, solid and fibrous materials, and smooth and irregularly surfaced objects.
1.2 This guide is intended to satisfy two general needs for users of industrial CT equipment: (1) the need for a tutorial guide addressing the general principles of X-ray CT as they apply to industrial imaging; and (2) the need for a consistent set of CT performance parameter definitions, including how these performance parameters relate to CT system specifications.
1.3 This guide does not specify CT examination techniques, such as the best selection of scan parameters, the preferred implementation of scan procedures, or the establishment of accept/reject criteria for a new object.
1.4 Units—No units are mentioned in this document. However, for CT, values are typically stated in SI units and are regarded as 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1441 − 19
Standard Guide for
1
Computed Tomography (CT)
This standard is issued under the fixed designation E1441; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 2. Referenced Documents
2
2.1 ASTM Standards:
1.1 CT is a radiographic examination technique that gener-
ates digital images in three dimensions of an object, including E746Practice for Determining Relative Image Quality Re-
sponse of Industrial Radiographic Imaging Systems
the interior structure. Because of the relatively good penetra-
bilityofX-rays,CTpermitsthenondestructivephysicaland,to E1316Terminology for Nondestructive Examinations
a limited extent, chemical characterization of the internal E1570Practice for Fan Beam Computed Tomographic (CT)
structureofmaterials.Also,sincethemethodisX-raybased,it Examination
applies equally well to metallic and non-metallic specimens, E1695Test Method for Measurement of Computed Tomog-
solid and fibrous materials, and smooth and irregularly sur- raphy (CT) System Performance
faced objects. E1935Test Method for Calibrating and Measuring CT
Density
1.2 This guide is intended to satisfy two general needs for
E2698Practice for Radiographic Examination Using Digital
users of industrial CT equipment: (1) the need for a tutorial
Detector Arrays
guide addressing the general principles of X-ray CT as they
E2736Guide for Digital Detector Array Radiography
applytoindustrialimaging;and(2)theneedforaconsistentset
3
2.2 ISO Standards:
of CT performance parameter definitions, including how these
ISO 15708-1:2017-02 International Standard for Non-
performance parameters relate to CT system specifications.
destructive Testing - Radiation Methods for Computed
1.3 ThisguidedoesnotspecifyCTexaminationtechniques,
Tomography - Part 1: Terminology
such as the best selection of scan parameters, the preferred
ISO 15708-2:2017-02 International Standard for Non-
implementation of scan procedures, or the establishment of
destructive Testing - Radiation Methods for Computed
accept/reject criteria for a new object.
Tomography - Part 2: Principles, Equipment and Samples
ISO 15708-3:2017-02 International Standard for Non-
1.4 Units—No units are mentioned in this document.
However,forCT,valuesaretypicallystatedinSIunitsandare destructive Testing - Radiation Methods for Computed
Tomography - Part 3: Operation and Interpretation
regarded as standard.
ISO 15708-4:2017-02 International Standard for Non-
1.5 This standard does not purport to address all of the
destructive Testing - Radiation Methods for Computed
safety concerns, if any, associated with its use. It is the
Tomography - Part 4: Qualification
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3. Terminology
mine the applicability of regulatory limitations prior to use.
3.1 Definitions—In addition to terms defined in Terminol-
1.6 This international standard was developed in accor-
ogy E1316, the following terms are specific to this standard.
dance with internationally recognized principles on standard-
3.1.1 Throughout this guide, the term “X-ray” is used to
ization established in the Decision on Principles for the
denote penetrating electromagnetic radiation; however, elec-
Development of International Standards, Guides and Recom-
tromagnetic radiation may be either X-rays or gamma rays.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
3.2 Definitions of Terms Specific to This Standard:
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
1
This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc- contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
tive Testing and is the direct responsibility of Subcommittee E07.01 on Radiology Standards volume information, refer to the standard’s Document Summary page on
(X and Gamma) Method. the ASTM website.
3
Current edition approved July 1, 2019. Published August 2019. Originally Available from International Organization for Standardization (ISO), ISO
approved in 1991. Last previous edition approved in 2011 as E1441–11. DOI: Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
10.1520/E1441-19. Geneva, Switzerland, http://www.iso.org.
*A Summary of Changes section appears at the
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E1441 − 11 E1441 − 19
Standard Guide for
1
Computed Tomography (CT) Imaging
This standard is issued under the fixed designation E1441; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 Computed tomography (CT) CT is a radiographic method that provides an ideal examination technique whenever the
primary goal is to locate and size planar and volumetric detail in three dimensions. examination technique that generates digital
images in three dimensions of an object, including the interior structure. Because of the relatively good penetrability of X-rays,
as well as the sensitivity of absorption cross sections to atomic chemistry, CT permits the nondestructive physical and, to a limited
extent, chemical characterization of the internal structure of materials. Also, since the method is X-ray based, it applies equally
well to metallic and non-metallic specimens, solid and fibrous materials, and smooth and irregularly surfaced objects. When used
in conjunction with other nondestructive evaluation (NDE) methods, such as ultrasound, CT data can provide evaluations of
material integrity that cannot currently be provided nondestructively by any other means.
1.2 This guide is intended to satisfy two general needs for users of industrial CT equipment: ((1)1) the need for a tutorial guide
addressing the general principles of X-ray CT as they apply to industrial imaging; and ((2)2) the need for a consistent set of CT
performance parameter definitions, including how these performance parameters relate to CT system specifications. Potential users
and buyers, as well as experienced CT inspectors, will find this guide a useful source of information for determining the suitability
of CT for particular examination problems, for predicting CT system performance in new situations, and for developing and
prescribing new scan procedures.
1.3 This guide does not specify test objects and test procedures for comparing the relative performance of different CT systems;
nor does it treat CT inspection CT examination techniques, such as the best selection of scan parameters, the preferred
implementation of scan procedures, the analysis of image data to extract densitometric information, or the establishment of
accept/reject criteria for a new object.
1.4 Standard practices and methods are not within the purview of this guide. The reader is advised, however, that examination
practices are generally part and application specific, and industrial CT usage is new enough that in many instances a consensus
has not yet emerged. The situation is complicated further by the fact that CT system hardware and performance capabilities are
still undergoing significant evolution and improvement. Consequently, an attempt to address generic examination procedures is
eschewed in favor of providing a thorough treatment of the principles by which examination methods can be developed or existing
ones revised.
1.5 The principal advantage of CT is that it nondestructively provides quantitative densitometric (that is, density and geometry)
images of thin cross sections through an object. Because of the absence of structural noise from detail outside the thin plane of
inspection, images are much easier to interpret than conventional radiographic data. The new user can learn quickly (often upon
first exposure to the technology) to read CT data because the images correspond more closely to the way the human mind visualizes
three-dimensional structures than conventional projection radiography. Further, because CT images are digital, they may be
enhanced, analyzed, compressed, archived, input as data into performance calculations, compared with digital data from other NDE
modalities, or transmitted to other locations for remote viewing. Additionally, CT images exhibit enhanced contrast discrimination
over compact areas larger than 20 to 25 pixels. This capability has no classical analog. Contrast discrimination of better than 0.1 %
at three-sigma confidence levels over areas as small as one-fifth of one percent the size of the object of interest are common.
1.6 With proper calibration, dimensional inspections and absolute density determinations can also be made very accurately.
Dimensio
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