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The effects of LPBF parameter variation on preliminary test samples were investigated by nano-focus Computed Tomography ( CT ) and Optical microscopy to clarify the internal structure and defects for further LPBF process optimization .
 LPBF, variation, samples, Computed Tomography, CT, Optical microscopy, internal structure, defects, LPBF, optimization
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 LPBF, variation, samples, Computed Tomography, CT, Optical microscopy, internal structure, defects, LPBF, optimization