Resolution recovery in pinhole SPECT based on multi-ray projections: a phantom study

Low sensitivity can become a major problem when very small pinholes are used in SPECT imaging. Although a larger pinhole aperture will improve the sensitivity, this will be at the cost of the spatial resolution. With a view to improving the resolution-sensitivity trade-off, this paper explores an iterative reconstruction algorithm that models the pinhole aperture based on multi-ray projections. This new implementation was validated using simulated data and phantom experiments. Two approaches were investigated. Firstly, the pinhole aperture was modelled in both the forward and the back projector. Secondly, the dual matrix implementation was investigated by modelling the pinhole aperture only in the forward projector. The systematic error, the full-width at half-maximum (FWHM) and the statistical error were quantified using the simulated data. Experimental phantom data were acquired for visual comparison with the reconstructions obtained from the simulated data. For a predefined number of iterations, the systematic error, the FWHM and the statistical error could be decreased when the pinhole aperture was modelled during iterative reconstruction. For a fixed, predefined statistical error of +/-10%, smaller systematic errors and smaller FWHM were obtained when modelling the pinhole opening. When the dual matrix implementation was used, equivalent results could be obtained as when modelling the pinhole opening in both the forward and the back projector. The multi-ray method to accomplish resolution recovery during the reconstruction of pinhole SPECT projection images offers a better trade-off between spatial resolution and noise compared with a reconstruction which does not model the pinhole aperture.