Affiliations: [a] Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB, Canada | [b] CancerCare Manitoba, Winnipeg, MB, Canada | [c] Department of Radiology, University of Manitoba, Winnipeg, MB, Canada
Abstract: The availability of high resolution, energy discriminating photon counting
detectors should make it possible to use Compton scattered photons to
improve the diagnostic capability of computed tomography (CT). With high,
spatial and energy resolution detectors Compton scatter tomography (CST)
images of adequate quality can be obtained with a single projection. In
practice, the limitations of realistic detectors require multiple
projections for good quality images. The relationship between the number of
projections used for reconstruction and the reconstructed image quality
obtained for conventional CT does not necessarily apply to multi-projection
Compton scatter tomography (MPCST). The purpose of this work was to
investigate the dependence of the reconstructed image quality on the number
of projections for MPCST. Analytical simulations and reconstructions were
used to evaluate the contrast and spatial resolution for images
reconstructed with one to 720 projections. Contrast-to-noise ratios (CNR)
and the modulation transfer functions (MTF) demonstrated that the contrast
increases monotonically with the number of projections while spatial
resolution was independent of the number of projections. The contrast
initially increases rapidly with projection number, becoming more gradual as
the number of projections increase, with the rate of change being a function
of fluence. The number of projections required to asymptotically approach
the maximum contrast decreases as the fluence increases, with no indication
of an optimal value for the range of fluences and projections investigated.
For the projections considered, an increase in the number of projections
increases the CNR even though the number of photons per projection
decreases.
Keywords: Compton scatter tomography, number of projections
