期刊
DENTOMAXILLOFACIAL RADIOLOGY
卷 37, 期 7, 页码 365-374出版社
BRITISH INST RADIOLOGY
DOI: 10.1259/dmfr/13227258
关键词
dental; cone beam computed tomography; imaging techniques; radiographic phantoms
Objectives: As part of an ongoing programme to improve diagnosis and treatment planning relevant to implant placement, orthodontic treatment and dentomaxillofacial surgery, a study has been made of the spatial accuracy and density response of an i-CAT, a cone beam CT (CBCT) dental imaging System Supplied by Imaging Sciences International Inc. Methods: Custom-made phantoms Using acrylic Sheet and water Were used for measurements oil spatial accuracy, density response and noise. The Measurements were made over a period of several months oil a clinical machine rather than oil a machine dedicated to research. Results: Measurements on a precision grid showed the spatial accuracy to be Universally within the tolerance of +/- 1 pixel. The density response and the noise in the data were found to depend strongly on the mass in the slice being scanned. Conclusions: The density response Was Subject to two effects. The first effect changes the whole slice uniformly and linearly depends oil the total mass in the slice. The second effect exists when there is mass Outside the Field of view, dubbed the exo-mass effect. This effect lowers the measured CT number rapidly at the scan edge furthest from the exo-mass and raises it on the adjacent edge. The noise also depended quasi-linearly oil the mass in the slice. Some general performance rules were drafted to describe these effects and a preliminary correction algorithm was constructed.
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