A medical X-ray CT scanner was used as a non-destructive inspection method for the detection of selected non-metallic materials embedded in various fluids and food materials. The X-ray absorption characteristics of tested materials were expressedas X-ray CT numbers. It was found that the CT number of a foreign object was affected by a systemic error (a point spread function), even if its size was greater than 1 pixel in the video image provided by the scanner Within the interface region betweenthe foreign object and its surrounding matrix, CT numbers were found to vary smoothly between characteristic values for the object and the matrix thus pointing to important effects to consider when developing X-ray CT techniques for the detection andidentification of foreign materials in foods. Specific threshold values for CT numbers of selected foodstuffs were defined for successful detection of foreign materials. This study also pointed out the limitation of using X-ray linear absorptioncoefficients from typical CT systems to detect certain combination of foreign materials and foodstuffs.
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