ASTM E2736-10
(Guide)Standard Guide for Digital Detector Array Radiology
Standard Guide for Digital Detector Array Radiology
SIGNIFICANCE AND USE
This standard provides a guide for the other DDA standards (see Practices E2597, , and E2737). It is not intended for use with computed radiography apparatus. Figure 1 describes how this standard is interrelated with the aforementioned standards.
This guide is intended to assist the user to understand the definitions and corresponding performance parameters used in related standards as stated in 4.1 in order to make an informed decision on how a given DDA can be used in the target application.
This guide is also intended to assist cognizant engineering officers, prime manufacturers, and the general service and manufacturing customer base that may rely on DDAs to provide advanced radiological results so that these parties may set their own acceptance criteria for use of these DDAs by suppliers and shops to verify that their parts and structures are of sound integrity to enter into service.
The manufacturer characterization standard for DDA (see Practice E2597) serves as a starting point for the end user to select a DDA for the specific application at hand. DDA manufacturers and system integrators will provide DDA performance data using standardized geometry, X-ray beam spectra, and phantoms as prescribed in Practice E2597. The end user will look at these performance results and compare DDA metrics from various manufacturers and will decide on a DDA that can meet the specification required for inspection by the end user. See Sections 5 and 8 for a discussion on the characterization tests and guidelines for selection of DDAs for specific applications.
Practice is designed to assist the end user to set up the DDA with minimum requirements for radiological examinations. This standard will also help the user to get the required SNR, to set up the required magnification, and provides guidance for viewing and storage of radiographs. Discussion is also added to help the user with marking and identification of parts during radiological examinations.
Practice E2737 ...
SCOPE
1.1 This standard is a user guide, which is intended to serve as a tutorial for selection and use of various digital detector array systems nominally composed of the detector array and an imaging system to perform digital radiography. This guide also serves as an in-detail reference for the following standards: Practices E2597, , and E2737.
1.2 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 determine the applicability of regulatory limitations prior to use.
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Designation: E2736 − 10
Standard Guide for
Digital Detector Array Radiology
This standard is issued under the fixed designation E2736; 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 standard is a user guide, which is intended to serve
E2422Digital Reference Images for Inspection of Alumi-
as a tutorial for selection and use of various digital detector
num Castings
arraysystemsnominallycomposedofthedetectorarrayandan
E2445Practice for Performance Evaluation and Long-Term
imagingsystemtoperformdigitalradiography.Thisguidealso
Stability of Computed Radiography Systems
serves as an in-detail reference for the following standards:
E2446Practice for Classification of Computed Radiology
Practices E2597, E2698, and E2737.
Systems
1.2 This standard does not purport to address all of the
E2597Practice for Manufacturing Characterization of Digi-
safety concerns, if any, associated with its use. It is the
tal Detector Arrays
responsibility of the user of this standard to establish appro-
E2660Digital Reference Images for Investment Steel Cast-
priate safety and health practices and determine the applica-
ings for Aerospace Applications
bility of regulatory limitations prior to use.
E2669Digital Reference Images for Titanium Castings
2. Referenced Documents
E2698Practice for Radiological Examination Using Digital
Detector Arrays
2.1 ASTM Standards:
E2737Practice for Digital Detector Array Performance
E94Guide for Radiographic Examination
Evaluation and Long-Term Stability
E155Reference Radiographs for Inspection of Aluminum
and Magnesium Castings
3. Terminology
E192Reference Radiographs of Investment Steel Castings
for Aerospace Applications
3.1 Definitions of Terms Specific to This Standard:
E747Practice for Design, Manufacture and Material Group-
3.1.1 digital detector array (DDA) system—an electronic
ing Classification of Wire Image Quality Indicators (IQI)
device that converts ionizing or penetrating radiation into a
Used for Radiology
discrete array of analog signals which are subsequently digi-
E1000Guide for Radioscopy
tized and transferred to a computer for display as a digital
E1025 Practice for Design, Manufacture, and Material
image corresponding to the radiation energy pattern imparted
Grouping Classification of Hole-Type Image Quality In-
upon the input region of the device. The conversion of the
dicators (IQI) Used for Radiology
ionizing or penetrating radiation into an electronic signal may
E1316Terminology for Nondestructive Examinations
transpire by first converting the ionizing or penetrating radia-
E1320Reference Radiographs for Titanium Castings
tionintovisiblelightthroughtheuseofascintillatingmaterial.
E1742Practice for Radiographic Examination
These devices can range in speed from many minutes per
E1815Test Method for Classification of Film Systems for
image to many images per second, up to and in excess of
Industrial Radiography
real-time radioscopy rates (usually 30 frames per seconds).
E1817Practice for Controlling Quality of Radiological Ex-
amination by Using Representative Quality Indicators
3.1.2 signal-to-noise ratio (SNR)—quotient of mean value
(RQIs)
of the intensity (signal) and standard deviation of the intensity
(noise). The SNR depends on the radiation dose and the DDA
system properties.
This guide is under the jurisdiction ofASTM Committee E07 on Nondestruc-
tive Testing and is the direct responsibility of Subcommittee E07.01 on Radiology
3.1.3 normalized signal-to-noise ratio (SNR )—SNR nor-
n
(X and Gamma) Method.
malized for basic spatial resolution (see Practice E2445).
Current edition approved April 15, 2010. Published July 2010.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.1.4 basic spatial resolution (SRb)—basic spatial resolu-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
tion indicates the smallest geometrical detail, which can be
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. resolvedusingtheDDA.Itissimilartotheeffectivepixelsize.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2736 − 10
3.1.5 effıciency—dSNR (see 3.1.6 of Practice E2597) di- end user will look at these performance results and compare
n
vided by the square root of the dose (in mGy) and is used to DDAmetrics from various manufacturers and will decide on a
measuretheresponseofthedetectoratdifferentbeamenergies DDAthat can meet the specification required for inspection by
and qualities. the end user. See Sections 5 and 8 for a discussion on the
characterization tests and guidelines for selection of DDAs for
3.1.6 achievable contrast sensitivity (CSa)—optimum con-
specific applications.
trast sensitivity (see Terminology E1316 for a definition of
contrast sensitivity) obtainable using a standard phantom with
4.5 Practice E2698 is designed to assist the end user to set
an X-ray technique that has little contribution from scatter.
up the DDA with minimum requirements for radiological
examinations. This standard will also help the user to get the
3.1.7 specific material thickness range (SMTR)—material
required SNR, to set up the required magnification, and
thickness range within which a given image quality is
provides guidance for viewing and storage of radiographs.
achieved.
Discussion is also added to help the user with marking and
3.1.8 contrast-to-noise ratio (CNR)—quotient of the differ-
identification of parts during radiological examinations.
enceofthemeansignallevelsbetweentwoimageareasandthe
4.6 Practice E2737 is designed to help the end user with a
standard deviation of the signal levels. The CNR depends on
set of tests so that the stability of the performance of the DDA
the radiation dose and the DDA system properties.
can be confirmed. Additional guidance is provided in this
3.1.9 lag—residual signal in the DDA that occurs shortly
document to support this standard.
after the exposure is completed.
4.7 Figure 1 provides a summary of the interconnectivity of
3.1.10 burn-in—change in gain of the scintillator or photo-
these four DDA standards.
conductor that persists well beyond the exposure.
3.1.11 internal scatter radiation (ISR)—scattered radiation
5. DDA Technology Description
within the detector (from scintillator, photodiodes, electronics,
5.1 General Discussion:
shielding, or other detector hardware).
5.1.1 DDAs are seeing increased use in industries to en-
3.1.12 bad pixel—a bad pixel is a pixel identified with a
hanceproductivityandqualityofnondestructivetesting.DDAs
performance outside of the specification for a pixel of a DDA
are being used for in-service nondestructive testing, as a
as defined in Practice E2597.
diagnostic tool in the manufacturing process, and for inline
3.1.13 grooved wedge—a wedge with one groove, that is
testing on production lines. DDAs are also being used as hand
5% of the base material thickness and that is used for
held, or scanned devices for pipeline inspections, in industrial
achievablecontrastsensitivitymeasurementinPracticeE2597.
computed tomography systems, and as part of large robotic
3.1.14 phantom—apartoritembeingusedtoquantifyDDA
scanning systems for imaging of large or complex structures.
characterization metrics.
Because of the digital nature of the data, a variety of new
applications and techniques have emerged recently, enabling
4. Significance and Use quantitative inspection and automatic defect recognition.
5.1.2 DDAs can be used to detect various forms of electro-
4.1 This standard provides a guide for the other DDA
magneticradiation,orparticles,includinggammarays,X-rays,
standards (see Practices E2597, E2698, and E2737). It is not
neutrons,orotherformsofpenetratingradiation.Thisstandard
intended for use with computed radiography apparatus. Figure
focuses on X-rays and gamma rays.
1 describes how this standard is interrelated with the afore-
mentioned standards.
5.2 DDA architecture:
5.2.1 A common aspect of the different forms of this
4.2 This guide is intended to assist the user to understand
technology is the use of discrete sensors (position-sensitive)
thedefinitionsandcorrespondingperformanceparametersused
where, the data from each discrete location is read out into a
in related standards as stated in 4.1 in order to make an
file structure to form pixels of a digital image file. In all its
informed decision on how a given DDA can be used in the
simplicity, the device has an X-ray capture material as its
target application.
primary means for detecting X-rays, which is then coupled to
4.3 This guide is also intended to assist cognizant engineer-
a solid-state pixelized structure, where such a structure is
ing officers, prime manufacturers, and the general service and
similar to the imaging chips used in visible-wavelength digital
manufacturing customer base that may rely on DDAs to
photography and videography devices. Figure 2 shows a block
provide advanced radiological results so that these parties may
diagram of a typical digital X-ray imaging system.
set their own acceptance criteria for use of these DDAs by
5.2.2 An important difference between X-ray imaging and
suppliers and shops to verify that their parts and structures are
visible-light imaging is the size of the read-out device. The
of sound integrity to enter into service.
imagers found in cameras and for visible-light are typically on
4.4 The manufacturer characterization standard for DDA the order of 1 to 2 cm in area. Since X-rays are not easily
(see Practice E2597) serves as a starting point for the end user focused, as is the case for visible light, the imaging medium
to select a DDA for the specific application at hand. DDA must be the size of the object. Hence, the challenge lies in
manufacturers and system integrators will provide DDA per- meeting the requirement of a large uniform imaging area
formance data using standardized geometry, X-ray beam without loss of spatial information. This in turn requires high
spectra, and phantoms as prescribed in Practice E2597. The pixel densities of the read-out device over the object under
E2736 − 10
FIG. 1 Flow Diagram Representing the Connection Between the Four DDA Standards
FIG. 2 Block Diagram of a Typical Digital X-Ray Imaging System
E2736 − 10
examination, as well a primary sensing medium that also canbeextractedfromthedata.Thisissometimesreferredtoas
retains the radiologic pattern in its structure. Therefore, each the detector dynamic range.
DDA consists of a primary X-ray or gamma ray capture
5.3.5 The dynamic range is different from the specific
medium followed by a pixelized read structure, with various
material thickness range (SMTR) as defined in this standard
meansoftransferringtheabovesaidcapturedpattern.Foreach
and Practice E2597. That range is a true practical range of the
of these elements, there are numerous options that can be
DDA at hand, a range significantly tighter than the DDA
selected in the creation of DDAs. For the primary X-ray
dynamic range.
conversion material, there are either luminescent materials
5.3.6 TheSMTRisoneofthepropertiestoconsiderinDDA
such as scintillators or phosphors, and photoconductive mate-
selection, as it impacts the thickness range that can be
rials also known as direct converter semiconductors.
interpreted in a single view. This is dependent on the charac-
5.2.3 For read-out structures, the technology consists of
teristics of the read device and the digitization level. This test
charge coupled detectors (CCDs), complementary metal oxide
provides a means of determining an effective range without
silicon (CMOS) based detectors, amorphous silicon thin film
understanding the subtle nuances of the detector readout, and
transistor diode read-out structures, and linear or area crystal-
avoids erroneous parallels between bit depth and its relation to
line silicon pixel diode structures. Other materials and struc-
thickness range, and maximum possible signal from a device.
tures are also possible, but in the end, a pixelized pattern is
5.4 Specific DDA components—Therearenumerousoptions
captured and transferred to a computer for review.
ineachcomponentoftheimagingchaintoproduceaDDA.To
5.2.4 Eachprimaryconversionmaterialcanbecoupledwith
understand the options and limitations of each category, and to
the various read structures mentioned through a wide range of
bestassesswhichtechnologytopursueforagivenapplication,
couplingmedia,devices,orcircuitry.Withallofthesepossible
theunderlyingtechnologywillbediscussedbeginningwiththe
combinations, there are many different types of DDAs that
image capture medium. This is followed by the image read
have been produced. But all result in a digital X-ray or gamma
structureandthentheimagetransferdeviceisdiscussedforthe
ray image that can be used for different NDT applications.
various configurations of the read-out devices. For a more
5.2.5 Following the capture of the X-rays and conversion
detailed description of the architectures of these devices, the
into an analog signal on the read-out device, this signal is
reader is referred to Ref. (2).
typically amplified and digitized.There are numerous schemes
3 5.4.1 X-ray Capture—Scintillators (phosphors)—
for each of these steps, and the reader is referred to (1, 2, 3)
Scintillators are materials that convert X-ray or gamma ray
for further discussion on this topic.
photons into visible-light photons, which are then converted to
5.3 Digitization Methods:
a digital signal using technologies such as amorphous silicon
5.3.1 Digitization techniques typically convert the analog
(a-Si) arrays, CCDs or CMOS devices together with an
signal to discrete pixel values. For DDAs the digitization is
analog-to-digital converter. This will facilitate real time acqui-
typically, 8-bit (256 gray values), 12-bits (4096 gray values),
sition of images without the need for offline processing. Since
14-bits (16,384 gray levels) or 16-bits (65,536 values). The
therearevariousstagesofconversioninvolvedinrecordingthe
higher the bit depth, the more finely the signal is sampled.
digital image, it is very important to ensure that minimum
5.3.2 The digitization does not necessarily define the gray
information is lost during conversion in the scintillator. The
level range of the DDA. The useful range of performance is
propertiesdesirableofid
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