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Significance and Use
One of the factors affecting the quality of radiologic images is the geometric unsharpness. The degree of geometric unsharpness is dependent on the focal spot size of the radiation source, the distance between the source and the object to be radiographed, and the distance between the object to be radiographed and the detector (imaging plate, Digital Detector Array (DDA) or film). This test method allows the user to determine the effective focal size of the X-ray source. This result may then be used to establish source to object and object to detector distances appropriate for maintaining the desired degree of geometric unsharpness and/or maximum magnification for a given radiographic imaging application. Some ASTM standards require this value for calculation of a required magnification, for example, E1255, E2033, and E2698.
1.1 The image quality and the resolution of X-ray images highly depend on the characteristics of the focal spot. The imaging qualities of the focal spot are based on its two dimensional intensity distribution as seen from the detector plane.
1.2 This test method provides instructions for determining the effective size (dimensions) of standard and mini focal spots of industrial x-ray tubes. This determination is based on the measurement of an image of a focal spot that has been radiographically recorded with a “pinhole” technique.
1.3 This standard specifies a method for the measurement of focal spot dimensions from 50 μm up to several mm of X-ray sources up to 1000 kV tube voltage. Smaller focal spots should be measured using EN 12543-5 using the projection of an edge.
1.4 This test method may also be used to determine the presence or extent of focal spot damage or deterioration that may have occurred due to tube age, tube overloading, and the like. This would entail the production of a focal spot radiograph (with the pinhole method) and an evaluation of the resultant image for pitting, cracking, and the like.
1.5 Values stated in SI units are to be regarded as the standard.
1.6 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.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
PapersKlaus Bavendiek, Uwe Heike, Uwe Zscherpel, Uwe Ewe New measurement methods of focal spot size and shape of X-ray tubes in digital radiological applications in comparison to current standards, WC-NDT 2012, Durban, South Africa
European StandardsEN 12543-5 Non-destructive testing--Characteristics of focal spots in industrial X-ray systems for use in non-destructive testing--Part 5: Measurement of the effective focal spot size of mini and micro focus X-ray tubes
E1000 Guide for Radioscopy
E1255 Practice for Radioscopy
E2002 Practice for Determining Total Image Unsharpness in Radiology
E2033 Practice for Computed Radiology (Photostimulable Luminescence Method)
E2698 Practice for Radiological Examination Using Digital Detector Arrays
ICS Number Code 19.100 (Non-destructive testing)
ASTM E1165-12, Standard Test Method for Measurement of Focal Spots of Industrial X-Ray Tubes by Pinhole Imaging, ASTM International, West Conshohocken, PA, 2012, www.astm.orgBack to Top