When imaging IQI’s (Image Quality Indicators) with DDA’s (Digital Detector Arrays), image ghosting can often occur from the high attenuation difference between the IQI’s lead numbers and the surrounding material. This latent image of the lead numbers will eventually “bleed off” from the detector, but may take many seconds or even minutes for some extreme applications or for specific detectors.
To help prevent ghosting from lead numbers consider the following:
ASTM E1025 -11(IQI Design Standard Practice) now allows for alternative identification methods for plaque penetrameters.
- Material Removal Method: Numbers may be cut into the IQI in such a manner as to be clearly discernable in the image. Processes such as laser etching, chemical etching, precision stamping, EDM, etc., can be used to create the numbers within the IQI. When you consider we already use notches to identify the material group, it makes sense that we should be able to remove material to form numbers for the thickness identification.
- Material Addition Method: Numbers may be made of the same material as that of the IQI. The numbers thickness simply needs to be thick enough to make it clearly visible within the image. A good starting point would be 2-3 times the thickness of the material.
Beam Hardening Filters: When imaging low density or thin materials, a small thickness of filter material placed on the face of the tube will reduce ghosting without causing a significant reduction in image contrast.