ASTM E1672-12(2020)
(Guide)Standard Guide for Computed Tomography (CT) System Selection
Standard Guide for Computed Tomography (CT) System Selection
SIGNIFICANCE AND USE
5.1 This guide will aid the purchaser in generating a CT system specification. This guide covers the conversion of purchaser's requirements to system components that must occur for a useful CT system specification to be prepared.
5.2 Additional information can be gained in discussions with potential suppliers or with independent consultants.
5.3 This guide is applicable to purchasers seeking scan services.
5.4 This guide is applicable to purchasers needing to procure a CT system for a specific examination application.
SCOPE
1.1 This guide covers guidelines for translating application requirements into computed tomography (CT) system requirements/specifications and establishes a common terminology to guide both purchaser and supplier in the CT system selection process. This guide is applicable to the purchaser of both CT systems and scan services. Computed tomography systems are complex instruments, consisting of many components that must correctly interact in order to yield images that repeatedly reproduce satisfactory examination results. Computed tomography system purchasers are generally concerned with application requirements. Computed tomography system suppliers are generally concerned with the system component selection to meet the purchaser's performance requirements. This guide is not intended to be limiting or restrictive, but rather to address the relationships between application requirements and performance specifications that must be understood and considered for proper CT system selection.
1.2 Computed tomography (CT) may be used for new applications or in place of radiography or radioscopy, provided that the capability to disclose physical features or indications that form the acceptance/rejection criteria is fully documented and available for review. In general, CT has lower spatial resolution than film radiography and is of comparable spatial resolution with digital radiography or radioscopy unless magnification is used. Magnification can be used in CT or radiography/radioscopy to increase spatial resolution but concurrently with loss of field of view.
1.3 Computed tomography (CT) systems use a set of transmission measurements made along a set of paths projected through the object from many different directions. Each of the transmission measurements within these views is digitized and stored in a computer, where they are subsequently conditioned (for example, normalized and corrected) and reconstructed, typically into slices of the object normal to the set of projection paths by one of a variety of techniques. If many slices are reconstructed, a three dimensional representation of the object is obtained. An in-depth treatment of CT principles is given in Guide E1441.
1.4 Computed tomography (CT), as with conventional radiography and radioscopic examinations, is broadly applicable to any material or object through which a beam of penetrating radiation may be passed and detected, including metals, plastics, ceramics, metallic/nonmetallic composite material and assemblies. The principal advantage of CT is that it has the potential to provide densitometric (that is, radiological density and geometry) images of thin cross sections through an object. In many newer systems the cross-sections are now combined into 3D data volumes for additional interpretation. Because of the absence of structural superposition, images may be much easier to interpret than conventional radiological images. The new purchaser can quickly learn to read CT data because images correspond more closely to the way the human mind visualizes 3D structures than conventional projection radiology. Further, because CT images are digital, the images may be enhanced, analyzed, compressed, archived, input as data into performance calculations, compared with digital data from other nondestructive evaluation modalities, or transmitted to other locations for remote viewing. 3D data sets can be rendered ...
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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: E1672 − 12 (Reapproved 2020)
Standard Guide for
Computed Tomography (CT) System Selection
This standard is issued under the fixed designation E1672; 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* paths by one of a variety of techniques. If many slices are
reconstructed, a three dimensional representation of the object
1.1 This guide covers guidelines for translating application
is obtained.An in-depth treatment of CT principles is given in
requirements into computed tomography (CT) system
Guide E1441.
requirements/specifications and establishes a common termi-
nology to guide both purchaser and supplier in the CT system
1.4 Computed tomography (CT), as with conventional radi-
selection process. This guide is applicable to the purchaser of
ographyandradioscopicexaminations,isbroadlyapplicableto
both CT systems and scan services. Computed tomography
any material or object through which a beam of penetrating
systems are complex instruments, consisting of many compo-
radiation may be passed and detected, including metals,
nents that must correctly interact in order to yield images that
plastics, ceramics, metallic/nonmetallic composite material
repeatedly reproduce satisfactory examination results. Com-
and assemblies.The principal advantage of CTis that it has the
puted tomography system purchasers are generally concerned
potential to provide densitometric (that is, radiological density
with application requirements. Computed tomography system
and geometry) images of thin cross sections through an object.
suppliers are generally concerned with the system component
In many newer systems the cross-sections are now combined
selection to meet the purchaser’s performance requirements.
into 3D data volumes for additional interpretation. Because of
This guide is not intended to be limiting or restrictive, but
the absence of structural superposition, images may be much
rather to address the relationships between application require-
easier to interpret than conventional radiological images. The
ments and performance specifications that must be understood
new purchaser can quickly learn to read CT data because
and considered for proper CT system selection.
images correspond more closely to the way the human mind
1.2 Computed tomography (CT) may be used for new visualizes 3D structures than conventional projection radiol-
applications or in place of radiography or radioscopy, provided ogy.Further,becauseCTimagesaredigital,theimagesmaybe
that the capability to disclose physical features or indications
enhanced, analyzed, compressed, archived, input as data into
that form the acceptance/rejection criteria is fully documented performance calculations, compared with digital data from
and available for review. In general, CT has lower spatial
other nondestructive evaluation modalities, or transmitted to
resolution than film radiography and is of comparable spatial other locations for remote viewing. 3D data sets can be
resolution with digital radiography or radioscopy unless mag-
rendered by computer graphics into solid models. The solid
nification is used. Magnification can be used in CT or
models can be sliced or segmented to reveal 3D internal
radiography/radioscopy to increase spatial resolution but con-
information or output as CAD files. While many of the details
currently with loss of field of view.
are generic in nature, this guide implicitly assumes the use of
penetrating radiation, specifically X rays and gamma rays.
1.3 Computed tomography (CT) systems use a set of trans-
mission measurements made along a set of paths projected
1.5 Units—The values stated in SI units are to be regarded
through the object from many different directions. Each of the
as standard. The values given in parentheses are mathematical
transmission measurements within these views is digitized and
conversions to inch-pound units that are provided for informa-
stored in a computer, where they are subsequently conditioned
tion only and are not considered standard.
(for example, normalized and corrected) and reconstructed,
1.6 This standard does not purport to address all of the
typicallyintoslicesoftheobjectnormaltothesetofprojection
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc-
mine the applicability of regulatory limitations prior to use.
tive Testing and is the direct responsibility of Subcommittee E07.01 on Radiology
(X and Gamma) Method.
1.7 This international standard was developed in accor-
Current edition approved Dec. 1, 2020. Published December 2020. Originally
dance with internationally recognized principles on standard-
approved in 1995. Last previous edition approved in 2012 as E1672 – 12. DOI:
10.1520/E1672-12R20. ization established in the Decision on Principles for the
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1672 − 12 (2020)
Development of International Standards, Guides and Recom- 4.2 Section 7 identifies typical purchaser’s examination
mendations issued by the World Trade Organization Technical requirements that must be met. These purchaser requirements
Barriers to Trade (TBT) Committee. factorintothesystemdesign,sincethesystemcomponentsthat
are selected for the CT system will have to meet the purchas-
2. Referenced Documents
er’s requirements. Some of the purchaser’s requirements are:
the ability to support the object under examination, that is, size
2.1 ASTM Standards:
and weight; detection capability for size of defects and flaws,
E1316 Terminology for Nondestructive Examinations
orboth,(spatialresolutionandcontrastdiscrimination);dimen-
E1441 Guide for Computed Tomography (CT)
sioning precision; artifact level; throughput; ease of use;
E1570 Practice for Fan Beam Computed Tomographic (CT)
archival procedures. Section 7 also describes the trade-offs
Examination
between the CT performance as required by the purchaser and
E2339 Practice for Digital Imaging and Communication in
the choice of system components and subsystems.
Nondestructive Evaluation (DICONDE)
E2767 Practice for Digital Imaging and Communication in
4.3 Section 8 covers some management cost considerations
Nondestructive Evaluation (DICONDE) for X-ray Com-
in CT system procurements.
puted Tomography (CT) Test Methods
4.4 Section 9 provides some recommendations for the
procurement of CT systems.
3. Terminology
3.1 Definitions—For definitions of terms used in this guide,
5. Significance and Use
refer to Terminology E1316 and Guide E1441, Appendix X1.
5.1 This guide will aid the purchaser in generating a CT
3.2 Definitions of Terms Specific to This Standard:
system specification. This guide covers the conversion of
3.2.1 purchaser—purchaser or customer of CT system or
purchaser’s requirements to system components that must
scan service.
occur for a useful CT system specification to be prepared.
3.2.2 scan service—use of a CT system, on a contract basis,
5.2 Additional information can be gained in discussions
for a specific examination application. A scan service acquisi-
with potential suppliers or with independent consultants.
tionrequiresthematchingofaspecificexaminationapplication
to an existing CT machine, resulting in the procurement of CT
5.3 This guide is applicable to purchasers seeking scan
system time to perform the examination. Results of scan services.
service are contractually determined but typically include
5.4 This guide is applicable to purchasers needing to pro-
some, all, or more than the following: meetings, reports,
cure a CT system for a specific examination application.
images, pictures, and data.
3.2.3 subsystem—one or more system components inte-
6. Basis of Application
grated together that make up a functional entity.
6.1 The following items should be agreed upon by the
3.2.4 supplier—suppliers/owners/builders of CT systems.
purchaser and supplier.
3.2.5 system component—generic term for a unit of equip-
6.1.1 Requirements—General system requirements are cov-
ment or hardware on the system.
ered in Section 7.
3.2.6 throughput—number of CT scans performed in a
given time frame. 7. Subsystems Capabilities and Limitations
7.1 Thissectiondescribeshowvariousexaminationrequire-
4. Summary of Guide
ments affect the CT system components and subsystems.
4.1 This guide provides guidelines for the translation of
Trade-offs between requirements and hardware are cited. Table
examination requirements to system components and specifi-
1 is a summary of these issues. Many different CT system
cations. Understanding the CT purchaser’s perspective as well
configurations are possible due to the wide range of system
as the CT equipment supplier’s perspective is critical to the
components available for integration into a single system. It is
successful acquisition of new CT hardware or implementation,
important to understand the capability and limitations of
or both, of a specific application on existing equipment. An
utilizing one system component over another as well as its role
understanding of the performance capabilities of the system
in the overall subsystem. Fig. 1 is a functional block diagram
components making up the CT system is needed in order for a
for a generic CT system.
CT system purchaser to prepare a CT system specification. A
7.1.1 Pencil-Beam, Fan-Beam and Cone-Beam Type Sys-
specification is required for acquisition of either CT system
tems:
hardware or scan services for a specific examination applica-
7.1.1.1 Pencil Beam Systems—Thex-raybeamiscollimated
tion.
to a pencil and the effective pixel size becomes the size of the
beam on the detector area. The beam is translated over the
object and the object rotated after each pass of the beam over
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
the object or the beam and detector are translated and rotated
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
around the object to build up linear slice profiles. If a three
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. dimensional data set is desired the object or beam/detector
E1672 − 12 (2020)
TABLE 1 Computed Tomography (CT) System Examination
faster scan times than pencil-beam systems and some scatter
Requirements and Their Major Ramifications
rejection with the primary disadvantage being long scan times
Components/Subsystems
for 3D data.
Requirement Reference
Affected
7.1.1.3 Cone-Beam Systems—The x-ray beam is usually
Object, size and weight Mechanical handling equipment 7.2
collimated to the entire or a selected portion of the active area
Object radiation Dynamic range 7.3
penetrability
of a two dimensional detector array and full 2D images are
Radiation source 7.3.1
captured as the object or beam/detector rotates. In this manner
Detectability 7.4
multiple slices are generated without needing to elevate. The
Spatial resolution Detector size/aperture 7.4.1.1
Source size/source spot size 7.4.1.2 primary advantage of this technique is speed or acquiring 3D
Mechanical handling equipment 7.4.1.5
data,withtheprimarydisadvantagebeingincreasedscatterdue
Contrast discrimination Strength/energy of radiation 7.4.2
to larger field of view.
source
Detector size/source spot size 7.4.2.1
7.2 Object, Size and Weight—The most basic consideration
Artifact level Mechanical handling equipment 7.4.3
Throughput/speed of CT process 7.5 for selecting a CT system is the examination object’s physical
Scan time (Spatial resolution) 7.5.1
dimensions and characteristics, such as size, weight, and
(Contrast discrimination)
material. The physical dimensions, weight, and attenuation of
Image matrix size (number of Number/configuration of 7.5.2
pixels in image) detectors the object dictate the size of the mechanical subsystem that
Amount of data acquired
handlestheexaminationobjectandthetypeofradiationsource
Computer/hardware resources
and detectors, or both, needed. To select a system for scan
Slice thickness range Detector configuration/collimators 7.5.3
System dynamic range
services, the issues of CT system size, object size and weight,
Operator interface 7.6
and radiation energy must be addressed first. Considerations
Operator console 7.6.1
like detectability and throughput cannot be addressed until
Computer resources 7.6.2
Ease of use 7.6.3 these have been satisfactorily resolved. Price-performance
Trade-offs 7.6.4
tradeoffs must be examined to guard against needless costs.
7.2.1 The maximum height and diameter of an object that
can be examined on a CT system defines the equipment
examination envelope. Data must be captured over the entire
width of the object for each view. If the projected x-ray beam
through the object does not provide complete coverage, the
object or beam/detector must translate. Some specialized
algorithms may allow the reduction of this requirement but
detectability and scan time may be affected. The weight of the
object and any associated fixturing must be within the manipu-
lation system capability. For example, a very different me-
chanical sub-system will be required to support and accurately
move a large, heavy object than to move a small, light object.
Similarly, the logistics and fixturing for handling a large
number of similar items will be a much different problem than
for handling a one-of-a-kind item.
7.2.2 Two Most Common Types of Scan Motion
Geometries—Bothgeometriesareapplicableto2Dfanbeamor
3D cone beam systems.
7.2.2.1 Translate-Rotate Motion—The object or detector is
translated in a direction perpendicular to the direction and
parallel to the plane of the X-ray beam. Full data sets are
FIG. 1 Functional Block Diagram for a Generic CT System
obtained by rotating the article between translations by the fan
angle of the beam and again translating the object until a
minimum of 180° of data have been acquired. The advantage
of this design is simplicity, good view-to-view detector
must elevate so that multiple slices are generated. T
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