Judging from the images of the phantom head and the numerical data, it seems that the minimum number of projections needed to obtain images of useful quality in the geometry used is about 33. Improved image quality (at any number of projections) can best be achieved through noise suppression.
Vertically reformatted CT slices obtained with local CT performed significantly better than conventional 2D digital radiographs in visually detecting caries. Axial slices did not perform better than conventional radiographs. When vertically reformatted slices are used, local CT is a promising tool for the detection of interproximal caries.
We conclude that the number of CT projections used can be reduced at least to 20 with the diagnostic performance still markedly better than that of conventional film, provided that the observer can make use of both axial and vertical stacks of CT slices.
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