ASTM E94/E94M-22

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: E94/E94M − 17 E94/E94M − 22
Standard Guide for
Radiographic Examination Using Industrial Radiographic
Film
This standard is issued under the fixed designation E94/E94M; 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 Scope*
1.1 This guide covers satisfactory X-ray and gamma-ray radiographic examination as applied to industrial radiographic film
recording. It includes statements about preferred practice without discussing the technical background which justifies the
preference. A bibliography of several textbooks and standard documents of other societies is included for additional information
on the subject.
1.2 This guide covers types of materials to be examined; radiographic examination techniques and production methods;
radiographic film selection, processing, viewing, and storage; maintenance of inspection records; and a list of available reference
radiograph documents.
NOTE 1—Further information is contained in Guide E999, Practice E1025, Test Methods Practice E1030E1030/E1030M, and Practice E1032.
1.3 The use of digital radiography has expanded and follows many of the same general principles of film based radiography but
with many important differences. The user is referred to standards for digital radiography [E2597, E2698, E2736, and E2737 for
digital detector array (DDA) radiography and E2007, E2033, E2445/E2445M, and E2446 for computed radiography(CR)] if
considering the use of digital radiography.
1.4 Interpretation and Acceptance Standards—Interpretation and acceptance standards are not covered by this guide, beyond
listing the available reference radiograph documents for castings and welds. Designation of accept - reject standards is recognized
to be within the cognizance of product specifications and generally a matter of contractual agreement between producer and
purchaser.
1.5 Safety Practices—Problems of personnel protection against X rays and gamma rays X-rays and gamma-rays are not covered
by this document.guide. For information on this important aspect of radiography, reference should be made to the current document
of the National Committee on Radiation Protection and Measurement, Federal Register, U.S. Energy Research and Development
Administration, National Bureau of Standards, and to state and local regulations, if such exist. For specific radiation safety
information, refer to NIST Handbook ANSI 43.3, 21 CFR 1020.40, and 29 CFR 1910.1096 or state regulations for agreement
states.
This guide is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.01 on Radiology (X and
Gamma) Method.
Current edition approved June 1, 2017Dec. 1, 2022. Published August 2017December 2022. Originally approved in 1952. Last previous edition approved in 20102017
as E94 - 04E94/E94M – 17.(2010). DOI: 10.1520/E0094_E0094M-17.10.1520/E0094_E0094M-22.
For ASME Boiler and Pressure Vessel Code applications, see related Guide SE-94 in Section V of that Code.
*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
E94/E94M − 22
1.6 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in
each system may not be exact equivalents; therefore, each system should be used independently of the other. Combining values
from the two systems may result in non-conformance with the standard.
1.7 If an NDT agency is used, the agency should be qualified in accordance with Specification E543.
1.8 Personnel Qualification—If specified in the contractual agreement, personnel performing examinations to this guide should
be qualified in accordance with a nationally or internationally recognized NDT personnel qualification practice or standard and
certified by the employer or certifying agency, as applicable.
1.9 This standard does not purport to address all of the safety problems, 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. (See 1.5.)
1.10 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.
2. Referenced Documents
2.1 ASTM Standards:
E543 Specification for Agencies Performing Nondestructive Testing
E746 Practice for Determining Relative Image Quality Response of Industrial Radiographic Imaging Systems
E747 Practice for Design, Manufacture and Material Grouping Classification of Wire Image Quality Indicators (IQI) Used for
Radiology
E801 Practice for Controlling Quality of Radiographic Examination of Electronic Devices
E999 Guide for Controlling the Quality of Industrial Radiographic Film Processing
E1000 Guide for Radioscopy
E1025 Practice for Design, Manufacture, and Material Grouping Classification of Hole-Type Image Quality Indicators (IQI)
Used for Radiography
E1030E1030/E1030M Practice for Radiographic Examination of Metallic Castings
E1032 Practice for Radiographic Examination of Weldments Using Industrial X-Ray Film
E1079 Practice for Calibration of Transmission Densitometers
E1165 Test Method for Measurement of Focal Spots of Industrial X-Ray Tubes by Pinhole Imaging
E1254 Guide for Storage of Radiographs and Unexposed Industrial Radiographic Films
E1316 Terminology for Nondestructive Examinations
E1390 Specification for Illuminators Used for Viewing Industrial Radiographs
E1453 Guide for Storage of Magnetic Tape Media that Contains Analog or Digital Radioscopic Data
E1475 Guide for Data Fields for Computerized Transfer of Digital Radiological Examination Data
E1735 Practice for Determining Relative Image Quality Response of Industrial Radiographic Imaging Systems from 4 to 25
MeV
E1742E1742/E1742M Practice for Radiographic Examination
E1815 Test Method for Classification of Film Systems for Industrial Radiography
E1817 Practice for Controlling Quality of Radiological Examination by Using Representative Quality Indicators (RQIs)
E1936 Reference Radiograph for Evaluating the Performance of Radiographic Digitization Systems
E2007 Guide for Computed Radiography
E2033 Practice for Radiographic Examination Using Computed Radiography (Photostimulable Luminescence Method)
E2339 Practice for Digital Imaging and Communication in Nondestructive Evaluation (DICONDE)
E2445/E2445M Practice for Performance Evaluation and Long-Term Stability of Computed Radiography Systems
E2446 Practice for Manufacturing Characterization of Computed Radiography Systems
E2597 Practice for Manufacturing Characterization of Digital Detector Arrays
E2698 Practice for Radiographic Examination Using Digital Detector Arrays
E2736 Guide for Digital Detector Array Radiography
E2737 Practice for Digital Detector Array Performance Evaluation and Long-Term Stability
E2903 Test Method for Measurement of the Effective Focal Spot Size of Mini and Micro Focus X-ray Tubes
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
E94/E94M − 22
E3169 Guide for Digital Imaging and Communication in Nondestructive Evaluation (DICONDE)
2.2 ANSI Standards:Standard:
PH1.41 Specifications for Photographic Film Archival Records, Silver Type
PH2.22ANSI/I3A/PIMA IT 2.26 Photography (Sensitometry)—Determination Determination of Safelight Conditions
T9.1 Imaging Media (Film)—Silver-Gelatin Type Specifications for Stability
T9.2 Imaging Media—Photographic Processed Films, Plates, and Paper Filing Enclosures and Storage Containers
2.3 Federal Standards:
Title 21, Code of Federal Regulations (CFR) 1020.40, Safety Requirements of Cabinet X-Ray Systems
Title 29, Code of Federal Regulations (CFR) 1910.96, Ionizing Radiation (X-Rays, RF, etc.)
2.4 ISO Standards:
ISO 14096-2 Non-destructive Testing — Qualification of Radiographic Film Digitization Systems — Part 2: Minimum
Requirements
ISO 18901 Imaging Materials — Processed Silver-Gelatin-type Black-and-white Films — Specifications for Stability
ISO 18902 Imaging Materials — Processed Imaging Materials — Albums, Framing and Storage Materials
ISO 18917 Photography—Determination of Residual Thiosulphate and Other Related Chemicals in Processed Photographic
Materials—Methods Using Iodine-amylose, Methylene Blue and Silver Sulfide
2.5 Other Document:
ISO 18917 Photography—Determination of residual thiosulphate and other related chemicals in processed photographic
materials—Methods using iodine-amylose, methylene blue and silver sulfide
NBS Handbook ANSI N43.3 General Radiation Safety Installations Using NonMedical X-Ray and Sealed Gamma-Ray Sources
up to 10 MeV
3. Terminology
3.1 Definitions—For definitions of terms used in this guide, refer to Terminology E1316.
4. Significance and Use
4.1 Within the present state of the radiographic art, this guide is generally applicable to available materials, processes, and
techniques where industrial radiographic films are used as the recording media.
4.2 Limitations—This guide does not take into consideration the benefits and limitations of nonfilm radiography such as
fluoroscopy,radioscopy, digital detector arrays, or computed radiography. Refer to Guides E1000, E2736, and E2007.
4.3 Although reference is made to documents that may be used in the identification and grading, where applicable, of
representative discontinuities in common metal castings and welds, no attempt has been made to set standards of acceptance for
any material or production process.
4.4 Radiography will be consistent in image quality (contrast sensitivity and definition) only if all details of techniques, such as
geometry, film, filtration, viewing, etc., are obtained and maintained.
5. Equipment and Configuration
5.1 To obtain quality radiographs, it is necessary to consider as a minimum the following list of items. Detailed information on
each item is further described in this guide.
5.1.1 Radiation source (X-ray or gamma),
5.1.2 Energy selection,
5.1.3 Source size (X-ray focal spot dimension or gamma source size),
5.1.4 Ways and means to eliminate scattered radiation,
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https://www.iso.org.
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5.1.5 Film system class,
5.1.6 Source-to-film and object-to-film distance,
5.1.7 Image quality indicators (IQIs),
5.1.8 Screens and filters,
5.1.9 Geometry of part or component configuration,
5.1.10 Identification and location markers, and
5.1.11 Radiographic quality level.
6. Radiographic Quality Level
6.1 Image Quality Indicators (IQIs) are devices placed within a radiographic set-up to indicate that a certain contrast sensitivity
and definition has been achieved. IQIs demonstrating the required sensitivity level do not guarantee that a similar size flaw in a
part will be detected but indicate that the radiographic quality has been met. Information on the design and manufacture of image
quality indicators (IQIs) can be found in Practices E747, E801, E1025, and E1742E1742/E1742M.
6.2 Radiographic quality level is usually expressed in percent of part thickness and diameter of feature to be detected. If a single
percent number is given, the feature diameter is assumed to be twice the given percent thickness of the part. For example, if 2%
is given for one inch [25.4 mm] thick part, the feature diameter is 2 × 0.02 × 1 in. [25.4 mm] or 0.04 in. [1.016 mm]. Image quality
levels using hole-type IQIs (see Practice E1025) are designated by a two part expression X-YT. The first part of the expression X
refers to the IQI thickness expressed as a percentage of the specimen thickness. The second part of the expression YT refers to the
diameter of the hole and is expressed as a multiple of the IQI thickness, T. The image quality level 2-2T means that the IQI
thickness T is 2% of the specimen thickness and that the diameter of the IQI imaged hole is 2 times the IQI thickness. If using
wire IQIs, the wire set and wire number are designated. Correspondence between hole-type and wire-type IQIs is given in Practice
E747. Hole- and wire-type IQIs are the major types used for industrial radiography. Other types may also be used (for example,
see Practice E1817). The quality level usually required for radiography is 2 % (2-2T when using hole type IQI) unless a higher
or lower quality is agreed upon between the purchaser and the supplier. The level of inspection specified should be based on the
service requirements of the product. Great care should be taken in specifying quality levels 2-1T, 1-1T, and 1-2T by first
determining that these quality levels can be maintained in production radiography.
6.3 If IQIs of material radiographically similar to that being examined are not available, IQIs of the required dimensions but of
a lower-absorption material may be used.
6.4 The quality level required using wire IQIs should be equivalent to the 2-2T level of Practice E1025 unless a higher or lower
quality level is agreed upon between purchaser and supplier. Table 4 of Practice E747 provides a list of various hole-type IQIs and
the corresponding diameter of the wires to achieve the Equivalent Penetrameter Sensitivity (EPS) with the applicable 1T, 2T, and
4T holes in the plaque IQI. Appendix X1 of Practice E747 gives the equation for calculating other equivalencies, if needed.
7. Energy Selection
7.1 X-ray energy affects image quality. In general, the lower the energy of the source utilized the higher the achievable
radiographic contrast, however, other variables such as excessive dose geometry and scatter conditions may override the potential
advantage of higher contrast. For a particular energy, a range of thicknesses which are a multiple of the half value layer, may be
radiographed to an acceptable quality level utilizing a particular X-ray machine or gamma ray source. In all cases, the specified
IQI (penetrameter) quality level must be shown on the radiograph. In general, satisfactory results can normally be obtained for
X-ray energies between 100 kV to 500 kV in a range between 2.5 to 10 half value layers (HVL) of material thickness (see Table
1). This range may be extended by as much as a factor of 2 in some situations for X-ray energies in the 1 to 25 MV range primarily
because of reduced scatter.
8. Radiographic Equivalence Factors
8.1 The radiographic equivalence factor of a material is that factor by which the thickness of the material must be multiplied to
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TABLE 1 Typical Steel HVL Thickness in Inches [mm] for
Common Energies
Thickness,
kV/MV
Inches [mm]
120 kV 0.10 [2.5]
150 kV 0.14 [3.6]
200 kV 0.20 [5.1]
250 kV 0.25 [6.4]
400 kV (Ir 192) 0.35 [8.9]
400 kV (Se 75) 0.35 [8.9]
750 kV (Ir 192) 0.51 [12.5]
1 MV 0.57 [14.5]
2 MV (Co 60) 0.80 [20.3]
4 MV 1.00 [25.4]
6 MV 1.15 [29.2]
10 MV 1.25 [31.8]
16 MV and higher 1.30 [33.0]
give the thickness of a “standard” material (often steel) which has the same absorption. Radiographic equivalence factors of several
of the more common metals are given in Table 2, with steel arbitrarily assigned a factor of 1.0.
Example: To radiograph 1.0 in. [25.4 mm] of aluminum at 220 kV, multiply 1.0 by the 0.18 (equivalence factor for aluminum at
220 kV) and this indicates that 1.0 in. [25.4 mm] of aluminum is equivalent to 0.18 in. [4.57 mm] of steel when using 220 kV.
The factors may be used:
8.1.1 To determine the practical thickness limits for radiation sources for materials other than steel, and
8.1.2 To determine exposure for one metal from exposure techniques for other metals.
9. Film
9.1 Various industrial radiographic films are available to meet the needs of production radiographic work. However, definite rules
on the selection of film are difficult to formulate because the choice depends on individual user requirements. Some user
requirements are as follows: radiographic quality levels, exposure times, and various cost factors. Several methods are available
for assessing image quality levels (see Practices E746, E747, and E801). Information about specific products can be obtained from
the manufacturers.
9.2 Various industrial radiographic films are manufactured to meet quality level and production needs. Test Method E1815
provides a method for film manufacturer classification of film systems. A film system consistconsists of the film and associated
film processing system. Users may obtain a classification table from the film manufacturer for the film system used in production
radiography. A choice of film class can be made as provided in Test Method E1815. Additional specific details regarding
classification of film systems isare provided in Test Method E1815. ANSI Standards PH1.41, ISO 417, T9.1, and T9.2 ISO 18901,
ISO 18902, and ISO 18917 provide specific details and requirements for film manufacturing.
TABLE 2 Approximate Radiographic Equivalence Factors for Several Metals (Relative to Steel)
kVMVkV / MV
Metal
192 60 75
100 kV 150 kV 220 kV 250 kV 400 kV 1 MV 2 MV 4 to 25 MV Ir Co Se
Magnesium 0.05 0.05 0.08
Aluminum 0.08 0.12 0.18 0.35 0.35 0.5
Aluminum alloy 0.10 0.14 0.18 0.35 0.35 0.5
Titanium 0.54 0.54 0.71 0.9 0.9 0.9 0.9 0.9 0.6
Iron/all steels 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
Copper 1.5 1.6 1.4 1.4 1.4 1.1 1.1 1.2 1.1 1.1 1.4
Copper 1.5 1.5 1.4 1.4 1.4 1.1 1.1 1.2 1.1 1.1 1.4
Zinc 1.4 1.3 1.3 1.2 1.1 1.0 1.2
Brass 1.4 1.3 1.3 1.2 1.1 1.0 1.1 1.0 1.3
Inconel X 1.4 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.3
Monel 1.7 1.2 1.1
Zirconium 2.4 2.3 2.0 1.7 1.5 1.0 1.0 1.0 1.2 1.0 1.6
Lead 14.0 14.0 12.0 5.0 2.5 2.7 4.0 2.3 8.0
Hafnium 14.0 12.0 9.0 3.0 11.0
Uranium 20.0 16.0 12.0 4.0 3.9 12.6 3.4 14.0
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10. Filters
10.1 Definition—Filters are uniform layers of material placed between the radiation source and the film.
10.2 Purpose—The purpose of filters is to absorb the softer components of the primary radiation, thus resulting in one or several
of the following practical advantages:
10.2.1 Decreasing scattered radiation, thus increasing contrast.
10.2.2 Decreasing undercutting, thus increasing contrast.
10.2.3 Decreasing contrast of parts of varying thickness, thereby increasing radiographic latitude.
10.3 Location—Usually the filter will be placed in one of the following two locations:
10.3.1 As close as possible to the radiation source, which minimizes the size of the filter and also the contribution of the filter itself
to scattered radiation to the film.
10.3.2 Between the specimen and the film in order to absorb preferentially the scattered radiation from the specimen. It should
be noted that lead foil and other metallic screens (see 13.1) fulfill this function.
10.4 Thickness and Filter Material—The thickness and material of the filter will vary depending upon the following:
10.4.1 The material radiographed.
10.4.2 Thickness of the material radiographed.
10.4.3 Variation of thickness of the material radiographed.
10.4.4 Energy spectrum of the radiation used.
10.4.5 The improvement desired (increasing or decreasing contrast). Filter thickness and material can be calculated or determined
empirically.
11. Masking and Collimation
11.1 Masking or blocking (surrounding specimens or covering thin sections with an absorptive material) is helpful in reducing
scattered radiation. Such a material can also be used to equalize the absorption of different sections, but the loss of detail may be
high in the thinner sections.
11.2 Collimating the beam by restricting its size with heavy metal beam blockers to only that area needed to expose the area of
interest is helpful in restricting scatter from areas in the part outside the area of interest and the surrounding environment, including
air scatter. Collimators are usually placed close to the source to minimize size and weight; however, collimators may be placed
anywhere in the beam to help with scatter control.
12. Back-Scatter Protection
12.1 Effects of back-scattered radiation can be reduced by confining the radiation beam to the smallest practical cross section and
by placing lead behind the film. In some cases, either or both the back lead screen and the lead contained in the back of the cassette
or film holder will furnish adequate protection against back-scattered radiation. In other instances, this shallshould be
supplemented by additional lead shielding behind the cassette or film holder.
12.2 If there is any question about the adequacy of protection from back-scattered radiation, a characteristic symbol (frequently
a ⁄8-in. [3.2-mm] thick letter B) should be attached to the back of the cassette or film holder, and a radiograph made in the normal
manner. If the image of this symbol appears on the radiograph aswith a lighter lower optical density than background, it is an
indication that protection against back-scattered radiation is insufficient and that additional precautions shallshould be taken.
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13. Screens
13.1 Metallic Foil Screens:
13.1.1 Lead foil screens are commonly used in direct contact with the films, and, depending upon their thickness, and composition
of the specimen material, will exhibit an intensifying action at as low as 90 kV. In addition, any screen used in front of the film
acts as a filter (Section 10) to preferentially absorb scattered radiation arising from the specimen, thus improving radiographic
quality. The selection of lead screen thickness, or for that matter, any metallic screen thickness, is subject to the same
considerations as outlined in 10.4. Lead screens lessen the scatter reaching the film regardless of whether the screens permit a
decrease or necessitate an increase in the radiographic exposure. To avoid image unsharpness due to screens, there should be
intimate contact between the lead screen and the film during exposure.
13.1.2 Lead foil screens of appropriate thickness should be used whenever they improve radiographic quality or penetrameter
sensitivity, or both. The thickness of the front lead screens should be selected with care to avoid excessive filtration in the
radiography of thin or light alloy materials, particularly at the lower kilovoltages. In general, there is no exposure advantage to
the use of 0.005 in. [0.13 mm] in front and back lead screens below 125 kV in the radiography of ⁄4-in. [6.35-mm] or lesser
thickness steel. As the kilovoltage is increased to penetrate thicker sections of steel, however, there is a significant exposure
advantage. In addition to intensifying action, the back lead screens are used as protection against back-scattered radiation (see
Section 12) and their thickness is only important for this function. As exposure energy is increased to penetrate greater thicknesses
of a given subject material, it is customary to increase lead screen thickness. For radiography using radioactive sources, the
minimum thickness of the front lead screen should be 0.005 in. [0.13 mm] for iridium-192, and 0.010 in. [0.25 mm] for cobalt-60.
13.2 Other Metallic Screen Materials:
13.2.1 Lead oxide screens perform in a similar manner to lead foil screens except that their equivalence in lead foil thickness
approximates 0.0005 in. (0.013 mm).[0.013 mm].
13.2.2 Copper screens have somewhat less absorption and intensification than lead screens, but may provide somewhat better
radiographic sensitivity with higher energy above 1 MV.
13.2.3 Gold, tantalum, or other heavy metal screens may be used in cases where lead cannot be used.
13.3 Fluorescent Screens—Fluorescent screens may be used as required providing the required image quality is achieved. Proper
selection of the fluorescent screen is required to minimize image unsharpness. Technical information about specific fluorescent
screen products can be obtained from the manufacturers. Good film-screen contact and screen cleanliness are required for
successful use of fluorescent screens. Additional information on the use of fluorescent screens is provided in Appendix X1.
13.4 Screen Care—All screens should be handled carefully to avoid dents and scratches, dirt, or grease on active surfaces. Grease
and lint may be removed from lead screens with a solvent. Fluorescent screens should be cleaned in accordance with the
recommendations of the manufacturer. Screens showing evidence of physical damage should be discarded.
14. Radiographic Image Quality
14.1 Radiographic image qualityImage Quality is a qualitative term used to describe the capability of a radiograph to show flaws
in the area under examination. There are three fundamental components of radiographic image quality as shown in Fig. 1. Each
component is an important attribute when considering a specific radiographic technique or application and will be briefly discussed
below.
14.2 Radiographic contrastContrast between two areas of a radiograph is the difference between the filmoptical densities of those
areas. The degree of radiographic contrast is dependent upon both subject contrast and film contrast as illustrated in Fig. 1.
14.2.1 Subject contrastContrast is the ratio of X-ray or gamma-ray intensities transmitted by two selected portions of a specimen.
Subject contrast is dependent upon the nature of the specimen (material type and thickness), the energy (spectral composition,
hardness, or wavelengths) of the radiation used and the intensity and distribution of scattered radiation. It is independent of time,
milliamperage or source strength (curies), source distance and the characteristics of the film system.
14.2.2 Film contrastContrast refers to the slope (steepness) of the film system characteristic curve. Film contrast is dependent
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Radiographic Image Quality
Radiographic Contrast Radiographic Definition
Film System
Subject Film Inherent Geometric
Granularity
Contrast Contrast Unsharpness Unsharpness
Affected by: Affected by: • Grain size and distribution within Affected by: Affected by:
• Absorption differences in • Type of film the film emulsion • Degree of screen-film contact • Focal spot or source
specimen (thickness, • Degree of development (type of • Processing conditions (type and • Total film thickness physical size
composition, density) developer, time, temperature and activity of developer, temperature of • Single or • Source-to-film distance
• Radiation wavelength activity of developer, degree of developer, etc.) double emulsion coatings • Specimen-to-film
• Scattered radiation agitation) • Type of screens (that is, • Radiation quality distance
• Optical density (that is, the fluorescent, lead or none) • Type and thickness of screens • Abruptness of thick-
greater the optical density, the • Radiation quality (that is, energy (fluorescent, lead or none) ness changes in
greater the resultant contrast) level, filtration, etc. specimen
• Type of screens (that is, • Exposure quanta (that is, • Motion of specimen or
fluorescent, lead or none) intensity, dose, etc.) radiation source
•The contract increases approxi- •The granularity increases approxi-
mately linearly with the new optical mately with the square root of the
density net optical density
Affected by: Affected by: • Grain size and distribution within Affected by: Affected by:
• Absorption differences in • Type of film the film emulsion • Degree of screen-film contact • Focal spot or source
specimen (thickness, • Degree of development (type of • Processing conditions (type and • Total film thickness physical size
composition, density) developer, time, temperature and activity of developer, temperature of • Single or • Source-to-film distance
• Radiation wavelength activity of developer, degree of developer, etc.) double emulsion coatings • Specimen-to-film
• Scattered radiation agitation) • Type of screens (that is, • Radiation quality distance
• Optical density (that is, the fluorescent, metal, or none) • Type and thickness of screens • Abruptness of thick-
greater the optical density, the • Radiation quality (that is, energy (fluorescent, metal, or none) ness changes in
greater the resultant contrast) level, filtration, etc.) specimen
• Type of screens (that is, • Exposure quanta (that is, • Motion of specimen or
fluorescent, lead or none) intensity, dose, etc.) radiation source
•The contrast increases approxi- •The granularity increases approxi-
mately linearly with the optical den- mately with the square root of the
sity above fog and base optical density above fog and base
Reduced or enhanced by:
• Masks and diaphragms
• Filters
• Lead screens
• Potter-Bucky diaphragms
FIG. 1 Variables of Radiographic Image Quality
upon the type of film, the processing it receives, and the amount of optical density. It also depends upon whether the film was
exposed with lead screens (or without) or with fluorescent screens. Film contrast is independent, for most practical purposes, of
the wavelength and distribution of the radiation reaching the film and, hence is independent of subject contrast. For further
information, consult Test Method E1815.
14.3 Film system granularitySystem Granularity is the objective measurement of the local density variations variation in optical
density that produce the sensation of graininess on the radiographic film (for example, measured with a densitometer with a small
aperture of ≤ 0.0039 in. [0.1 mm]). Graininess is the subjective perception of a mottled pattern apparent to a viewer who sees small
local optical density variations in an area of overall uniform optical density (that is, the visual impression of irregularity of silver
deposit in a processed radiograph). The degree of granularity will not affect the overall spatial radiographic resolution (expressed
in line pairs per mm, etc.) of the resultant image and is usually independent of exposure geometry arrangements. Granularity is
affected by the applied screens, screen-film contact, and film processing conditions. For further information on detailed
perceptibility, consult Test Method E1815.
14.4 Radiographic definitionDefinition refers to the sharpness of the image (both the image outline as well as image detail).
Radiographic definition is dependent upon the inherent unsharpness of the film system and the geometry of the radiographic
exposure arrangement (geometric unsharpness) as illustrated in Fig. 1.
14.4.1 Inherent unsharpnessUnsharpness (U ) is the degree of visible detail resulting from geometrical aspects within the
i
film-screen system, that is, screen-film contact, screen thickness, total thickness of the film emulsions, whether single or
double-coated emulsions, quality of radiation used (wavelengths, etc.) and the type of screen. Inherent unsharpness is independent
of exposure geometry arrangements.
14.4.2 Geometric unsharpnessUnsharpness (U ) determin
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