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Optimum exposure ranges for computed dental radiography
Y Hayakawa1, A G Farman, W C Scarfe
1Division of Radiology and Imaging Sciences, School of Dentistry, University of Louisville, Kentucky, USA.
Objective:
Computed dental radiography (CDR; Schick Technologies Inc, Lond Island City, NY, USA) can be used with any dental X-ray generator. The optimum exposure at various tube voltage settings was studied.
Methods:
Images were made of a dental QA jaw phantom and a standard aluminium stepwedge. Exposures were made between 50 and 90 kVp at 10 kVp intervals. Two contrast indices were calculated from the bone stepwedge pixel values: CI(1), the ratio between the highest and lowest pixel values, and CI(2), the difference between them.
Results:
Contrast indices were greatest at low kVp. The gradual decrease in CI(1) with increased exposure demonstrated that the optimum exposure range was always relatively wide. Maximum CI(2) values were found at exposures of 27, 17, 15, 11 and 9microC kg-1 at 50, 60, 70, 80 and 90 kVp, respectively, at the centre of the optimum exposure range. Pixel values for each aluminium step increased both with increased exposure and with increased kVp. The longest contrast scale was obtained at 11.0, 9.6, 8.7, 7.2 and 7.0 microC kg-1 at 50, 60, 70, 80 and 90 kVp. The steepest slopes were obtained either with thin aluminium steps or at low kVp.
Conclusions:
CDR is a fast CCD-based system and is capable of operating at a wide range of kVp settings.