Aim: The Institute of Clinical Denstistry, University in Oslo, has had a cone beam CT (CBCT: Promax 3D, Planmeca OY, Helsinki) for half a year to test its clinical use for maxillofacial radiology. Department of Maxillofacial Radiology has an eight slice multi detector CT (Lightspeed Ultra, GE, MI), and wanted, as a collaboration project with the Norwegian radiation protection authority, to evaluate and compare the technical performance of the two modalities in a clinical setting with respect to image quality and the radiation dose to patients examined. Material and method: The patient dose in CBCT was measured with a calibrated DAP meter (PTW, Freiburg), while the doses in MDCT was calculated by means of the CT dosimetry spreadsheet (Impact, London). The image material was gathered from one single patient who voluntarily went through examinations with both CBCT and MDCT. Results: Good agreement between the measured DAP values and the values indicated on the CBCT console after the exposure was found. The effective doses from CBCT are in the range 0,04 - 0,27 mSv for various patient sizes and field of view (FOV). MDCT protocols particularly optimised for low dose oral and maxillofacial radiology gave doses at the same range. The last version of the CBCT software gave more artefacts compared to the previous version, and did not manage to reconstruct the "lower" FOV properly. Discussion/conclusion: There seems to be some initial problems with the cone beam reconstruction algorithm with this particular machine, possibly combined with the equipment movement/raw data registration. The images based on the previous software were, however, quite good and rather similar to the CT images of the same anatomical region of jaw bone. The patient doses were also similarly low with both modalities. The measurements and quantification of noise and artefacts in CBCT will have to be evaluated further, to be able to draw fair comparisons.
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