ASTM E2903-13

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Designation: E2903 −13
Standard Test Method for
Measurement of the Effective Focal Spot Size of Mini and
Micro Focus X-ray Tubes
This standard is issued under the fixed designation E2903; 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.
1. Scope 2. Referenced Documents
1.1 The image quality and the resolution of X-ray images 2.1 ASTM Standards:
highly depend on the characteristics of the focal spot. The E1165 Test Method for Measurement of Focal Spots of
imaging qualities of the focal spot are based on its two Industrial X-Ray Tubes by Pinhole Imaging
dimensional intensity distribution as seen from the imaging E1255 Practice for Radioscopy
place. E1742 Practice for Radiographic Examination
E1815 Test Method for Classification of Film Systems for
1.2 This test method provides instructions for determining
Industrial Radiography
theeffectingsize(dimensions)ofminiandmicrofocalspotsof
E2002 Practice for DeterminingTotal Image Unsharpness in
industrial X-ray tubes. It is based on the European standard,
Radiology
EN 12543–5, Non-destructive testing - Characteristics of focal
E2033 Practice for Computed Radiology (Photostimulable
spots in industrial X-ray systems for use in non-destructive
Luminescence Method)
testing - Part 5: Measurement of the effective focal spot size of
E2446 Practice for Classification of Computed Radiology
mini and micro focus X-ray tubes.
Systems
1.3 Thisstandardspecifiesamethodforthemeasurementof
E2597 Practice for Manufacturing Characterization of Digi-
effective focal spot dimensions from 5 up to 300 µm of X-ray
tal Detector Arrays
systems up to and including 225 kV tube voltage, by means of
E2698 Practice for Radiological Examination Using Digital
radiographs of edges. Larger focal spots should be measured
Detector Arrays
using Test Method E1165 Standard Test Method for Measure- 3
2.2 European Standards:
ment of Focal Spots of Industrial X-Ray Tubes by Pinhole
EN 12543–5 Non-destructive testing—Characteristics of fo-
Imaging.
cal spots in industrial X-ray systems for use in non-
1.4 The same procedure can be used at higher kilovoltages
destructive testing - Part 5: Measurement of the effective
by agreement, but the accuracy of the measurement may be focal spot size of mini and micro focus X-ray tubes
poorer.
3. Terminology
1.5 The values stated in SI units are to be regarded as
3.1 Definitions of Terms Specific to This Standard:
standard. No other units of measurement are included in this
3.1.1 actual focal spot—the X-ray producing area of the
standard.
target as viewed from a position perpendicular to the target
1.6 This standard does not purport to address all of the
surface.
safety concerns, if any, associated with its use. It is the
3.1.2 effective focal spot—the X-ray producing area of the
responsibility of the user of this standard to establish appro-
target as viewed from the image plane.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This test method is under the jurisdiction of ASTM Committee E07 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Nondestructive Testing and is the direct responsibility of Subcommittee E07.01 on Standards volume information, refer to the standard’s Document Summary page on
Radiology (X and Gamma) Method. the ASTM website.
Current edition approved June 1, 2013. Published June 2013. DOI: 10.1520/ Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
E2903–13. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2903 − 13
4. Summary of Test Method 6. Apparatus
4.1 This method is based on indirect measurement of the 6.1 The following equipment is required for the measure-
focal spot size by measuring the geometric unsharpness then ment if using X-ray film:
using a geometric calculation to determine the effective focal 6.1.1 A test object as described in 6.5.
spot dimensions (see Section 8). For this purpose, edges are 6.1.2 X-ray films, without screens, of sufficient size to
imaged either on a film or by means of a radioscopic or digital image magnified test object and region around test object to
radiographic device using a relatively high geometric magni- obtain a profile as shown in Fig. 1.
fication. For a full description see reference below. 6.1.3 Film cassettes made of low absorbing material (for
example polyethylene).
5. Significance and Use 6.1.4 A film holder.
6.1.5 A film processing unit.
5.1 One of the factors affecting the image quality of a
6.1.6 A film scanner capable of reading densities greater
radiographic image is geometric unsharpness. The degree of
than 3.0 configured such that the pixel size is appropriate for
geometric unsharpness is dependent upon the focal spot size of
the measurement (refer to Section 7). The film shall be of
the radiation source, the distance between the source and the
sufficient size to image the magnified test object and region
objecttoberadiographed,thedistancebetweentheobjecttobe
around test object to obtain a profile as shown in Fig. 1.
radiographed and the image plane (film, imaging plate, Digital
6.1.7 The film system shall meet the requirements of Test
Detector Array (DDA), or radioscopic detector). This test
Method E1815 film system class I, II, or Special.
method allows the user to determine the effective focal spot
size (dimensions) of the X-ray source. This result can then be 6.2 The following equipment is required for the measure-
used to establish source to object and object to image detector
ment if using computed radiography (CR):
distances appropriate for maintaining the desired degree of
6.2.1 A test object as described in 6.5.
geometric unsharpness or maximum magnification possible, or
6.2.2 A computed radiography system, consisting of an
both, for a given radiographic imaging application. The accu-
imaging plate and scanner, configured such that the pixel size
racy of this method is dependent upon the spatial resolution of
is appropriate for the measurement (refer to Section 7). The
the imaging system, magnification, and signal-to-noise of the
imagingplateshallbeofsufficientsizetoimagetestobjectand
resultant images.
region around test object to obtain a profile as shown in Fig. 1.
6.2.3 The computed radiography system shall meet the
requirements of Practice E2446 class I, II, or Special, and
image plates shall be packed in low absorption cassettes using
no screens.
Fry,Ewert,Gollwitzer,Neuser,andSelling,“Measuringmicrofocalspotsusing
digital radiography”Materials Evaluation,, Vol 70, No.8, August 2012, p. 981.
FIG. 1 Profile of Test Object Image (Test Object: Pt wire 1 mm)
E2903 − 13
6.3 The following equipment is required for the measure-
ment if using a radioscopic or digital detector array device:
6.3.1 A test object as described in 6.5.
6.3.2 A radioscopic device, for example any image intensi-
fierwithvideoequipmentorDigitalDetectorArray,configured
such that the pixel size is appropriate for the measurement
(refer to Section 7), or
6.3.3 A Digital Detector Array system meeting the require-
ments of Practice E2597. The digital Detector Array cover
should be constructed of low X-ray absorption material and
should be free of cluster kernel pixels as defined in Practice
E2597.
6.3.4 The imaging area shall be of sufficient size to image
FIG. 2 Positioning of Test Object
magnified test object and region around test object to obtain a
profile as shown in Fig. 1.
6.4 Image processing equipment as follows:
6.4.1 An image processing device with the capability of
resultant images (See Footnote 4). If an estimate of the focal
producing linearized intensity profiles (signal is linear with
spot size, s, is available, then an optimal magnification can be
dose),integrationofprofiles,andprofileplotswithinthedigital
computed:
image in two directions perpendicular to each other, and with
M 5 111.1SNR ~P/ s ! (1)
optimal optimal
the capability to measure distances.
where:
6.5 The test object shall be either a set of wires or a sphere
SNR = unattenuated Signal-to-Noise ratio outside the object
consisting of highly absorbing material (for example tungsten,
P = pixel size
tungstenalloy,orplatinum).Thediameterofthewireorsphere
should be greater than 20 times the focal spot dimension if the 7.3.2.1 If the actual magnification is less than or equal to
focal spot is less than 40 µm to minimize edge penetration; M , then the estimated precision is:
optimal
otherwise, the diameter should be 0.8 to 1.0 mm for focal spots
2 2
Precision 5 0.71=1⁄n u1 # 1 1⁄n u2 3100% (2)
@ ~ ! @ ~ !#
estimated
greater than 40 µm. The diameter shall be known to within
61%.
where:
6.5.1 In case of using two single crossed wires they shall
n(u1) = number of pixels across the 50 to 84 % profile on
cross each other at an angle of 90° 6 3°. The wires shall be
one side (E to F in Fig. 1)
mounted across a circular aperture in a stable frame, in such a
n(u2) = numberofpixelsacrosst
...