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Effect of number of projections on image quality of local CT

Department of Oral Radiology, Academic Center for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands

*Correspondence to: AN van Daatselaar, Department of Oral Radiology, Academic Center for Dentistry Amsterdam (ACTA), Louwesweg 1, 1066EA Amsterdam, The Netherlands; Email: a.v.daatselaar{at}acta.nl

Received 20 August 2003; revised 9 September 2004; accepted 10 September 2004

Objectives: To determine the image quality of the local CT imaging procedure, in terms of resolution, contrast, and noise as a function of the number of projections.

Methods: The contrast and resolution of the images was determined with a phantom object consisting of three rods of different materials, as well as a phantom human head embedded in soft tissue equivalent material. In addition, slices reconstructed from computed sinograms were used for comparison.

Results: Sharpness, contrast and noise were determined as a function of the number of projections. The number of projections was found to affect the contrast and the noise most, and had much less influence on resolution.

Conclusions: 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.

Keywords: tomography, X-ray computed; local CT; digital radiography; image reconstruction, image quality

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