ASTM E1441-00(2005)

Standard Guide for Computed Tomography (CT) Imaging

SCOPE
1.1 Computed tomography (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. 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) 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. 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 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. Dimensionally, virtually all CT systems provide a pixel resolution of roughly 1 part in 1000 (since, at presen...

General Information

• Status: Historical
• Publication Date: 30-Nov-2005
• ICS: 35.240.80 - IT applications in health care technology
• Technical Committee: E07 - Nondestructive Testing
• Drafting Committee: E07.01 - Radiology (X and Gamma) Method

Relations

• Replaces: ASTM E1441-00 - Standard Guide for Computed Tomography (CT) Imaging
• Effective Date: 01-Dec-2005
• Replaced By: ASTM E1441-11 - Standard Guide for Computed Tomography (CT) Imaging
• Effective Date: 01-Jul-2011
• Referred By: ASTM E3166-20e1 - Standard Guide for Nondestructive Examination of Metal Additively Manufactured Aerospace Parts After Build
• Effective Date: 01-Dec-2005
• Referred By: ASTM E2767-21 - Standard Practice for Digital Imaging and Communication in Nondestructive Evaluation (DICONDE) for X-ray Computed Tomography (CT) Test Methods
• Effective Date: 01-Dec-2005
• Referred By: ASTM F3160-21 - Standard Guide for Metallurgical Characterization of Absorbable Metallic Materials for Medical Implants
• Effective Date: 01-Dec-2005
• Referred By: ASTM E543-21 - Standard Specification for Agencies Performing Nondestructive Testing
• Effective Date: 01-Dec-2005
• Referred By: ASTM D8093-19 - Standard Guide for Nondestructive Evaluation of Nuclear Grade Graphite
• Effective Date: 01-Dec-2005
• Referred By: ASTM E3327/E3327M-21 - Standard Guide for the Qualification and Control of the Assisted Defect Recognition of Digital Radiographic Test Data
• Effective Date: 01-Dec-2005
• Referred By: ASTM E1695-20e1 - Standard Test Method for Measurement of Computed Tomography (CT) System Performance
• Effective Date: 01-Dec-2005
• Referred By: ASTM E3375-23 - Standard Practice for Cone Beam Computed Tomographic (CT) Examination
• Effective Date: 01-Dec-2005
• Referred By: ASTM E1570-19 - Standard Practice for Fan Beam Computed Tomographic (CT) Examination
• Effective Date: 01-Dec-2005
• Referred By: ASTM E1672-12(2020) - Standard Guide for Computed Tomography (CT) System Selection
• Effective Date: 01-Dec-2005
• Referred By: ASTM E2533-21 - Standard Guide for Nondestructive Examination of Polymer Matrix Composites Used in Aerospace Applications
• Effective Date: 01-Dec-2005
• Referred By: ASTM E1817-08(2022) - Standard Practice for Controlling Quality of Radiological Examination by Using Representative Quality Indicators (RQIs)
• Effective Date: 01-Dec-2005
• Referred By: ASTM E1814-14(2022) - Standard Practice for Computed Tomographic (CT) Examination of Castings
• Effective Date: 01-Dec-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: E1441 – 00 (Reapproved 2005)
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.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 Department of Defense.
1. Scope examination practices are generally part and application spe-
cific, and industrial CT usage is new enough that in many
1.1 Computed tomography (CT) is a radiographic method
instances a consensus has not yet emerged. The situation is
that provides an ideal examination technique whenever the
complicated further by the fact that CT system hardware and
primary goal is to locate and size planar and volumetric detail
performance capabilities are still undergoing significant evo-
in three dimensions. Because of the relatively good penetra-
lution and improvement. Consequently, an attempt to address
bility of X-rays, as well as the sensitivity of absorption cross
generic examination procedures is eschewed in favor of
sections to atomic chemistry, CT permits the nondestructive
providing a thorough treatment of the principles by which
physical and, to a limited extent, chemical characterization of
examination methods can be developed or existing ones
the internal structure of materials. Also, since the method is
revised.
X-ray based, it applies equally well to metallic and non-
1.5 TheprincipaladvantageofCTisthatitnondestructively
metallic specimens, solid and fibrous materials, and smooth
provides quantitative densitometric (that is, density and geom-
and irregularly surfaced objects. When used in conjunction
etry) images of thin cross sections through an object. Because
with other nondestructive evaluation (NDE) methods, such as
of the absence of structural noise from detail outside the thin
ultrasound, CT data can provide evaluations of material integ-
plane of inspection, images are much easier to interpret than
rity that cannot currently be provided nondestructively by any
conventionalradiographicdata.Thenewusercanlearnquickly
other means.
(often upon first exposure to the technology) to read CT data
1.2 This guide is intended to satisfy two general needs for
because the images correspond more closely to the way the
users of industrial CT equipment: (1) the need for a tutorial
human mind visualizes three-dimensional structures than con-
guide addressing the general principles of X-ray CT as they
ventional projection radiography. Further, because CT images
applytoindustrialimaging;and(2)theneedforaconsistentset
are digital, they may be enhanced, analyzed, compressed,
of CT performance parameter definitions, including how these
archived, input as data into performance calculations, com-
performance parameters relate to CT system specifications.
pared with digital data from other NDE modalities, or trans-
Potential users and buyers, as well as experienced CT inspec-
mitted to other locations for remote viewing.Additionally, CT
tors, will find this guide a useful source of information for
images exhibit enhanced contrast discrimination over compact
determining the suitability of CT for particular examination
areas larger than 20 to 25 pixels. This capability has no
problems, for predicting CT system performance in new
classicalanalog.Contrastdiscriminationofbetterthan0.1%at
situations, and for developing and prescribing new scan pro-
three-sigma confidence levels over areas as small as one-fifth
cedures.
of one percent the size of the object of interest are common.
1.3 This guide does not specify test objects and test proce-
1.6 With proper calibration, dimensional inspections and
dures for comparing the relative performance of different CT
absolute density determinations can also be made very accu-
systems;nordoesittreatCTinspectiontechniques,suchasthe
rately. Dimensionally, virtually all CT systems provide a pixel
bestselectionofscanparameters,thepreferredimplementation
resolution of roughly 1 part in 1000 (since, at present,
of scan procedures, the analysis of image data to extract
1024 31024 images are the norm), and metrological algo-
densitometricinformation,ortheestablishmentofaccept/reject
rithms can often measure dimensions to one-tenth of one pixel
criteria for a new object.
or so with three-sigma accuracies. For small objects (less than
1.4 Standard practices and methods are not within the
4 in. in diameter), this translates into accuracies of approxi-
purview of this guide. The reader is advised, however, that
mately 0.1 mm (0.003 to 0.005 in.) at three-sigma. For much
larger objects, the corresponding figure will be p
...