ASTM  E1165 Standard Test Method for Measurement of Focal Spots of Industrial X-Ray Tubes by Pinhole Imaging

Scope:

In this test method of ASTM  E1165, the parameters of the focus point have a significant impact on the picture quality and resolution of X-ray images. The two-dimensional intensity distribution of the focused spot as viewed from the detector plane determines the imaging characteristics of the focal spot.

It describes a technique for measuring focused spot size from 50 microns to several millimeters in X-ray sources with tube voltages ranging from 1000 kV to several thousand kV. Smaller focus points should be measured using EN 12543-5, which uses the projection of an edge to get the desired result. The values expressed in metric units (SI units) are considered the standard.

Although ASTM E1165 attempts to address all of the safety risks connected with its usage, it does not claim to do so completely. The user of this standard must develop proper safety and health procedures and identify whether or not regulatory limits are applicable before putting the standard into operation.

Procedure:

This test technique of ASTM  E1165 may also be used to detect the existence or amount of focal spot damage or degradation that may have happened due to tube age, overloading, or other factors such as those mentioned above. In this case, the fabrication of a focused spot radiograph (using the pinhole technique) and the inspection of the resulting picture for pitting, cracking, and other defects would be required.

Result:

In the result of ASTM  E1165, the geometric unsharpness of radiologic pictures is one aspect that influences the quality of radiologic images. The size of the focus point of the radiation source, the distance between the source and the item to be radiographed, and the distance between the object to be radiographed and the detector (imaging plate, Digital Detector Array (DDA), or film) all influence the degree of geometric unsharpness. 

By using this test procedure, the user may figure out the effective focal size of the X-ray source. This result is used to determine the distances between the source and the object and the distance between the object and the detector, which are necessary to maintain the desired degree of geometric unsharpness and maximum magnification for a particular radiographic imaging application. Some ASTM standards, such as E1255, E2033, and E2698, specify that this value must be used to compute the needed magnification.

Conclusion:

In this test method of ASTM  E1165, the parameters of the focus point have a significant impact on the picture quality and resolution of X-ray images. The two-dimensional intensity distribution of the focused spot as viewed from the detector plane determines the imaging characteristics of the focal spot.