3D image reconstruction using complete data in pinhole SPECT

Inhomogeneous spatial resolution or axial blurring is a major problem in conventional pinhole SPECT, which is largely attributed to the incompleteness of the acquired projection data sets. In this study we have developed new system that provides 3D images without the axial blurring. The complete projection data sets were acquired using a pinhole collimator fitted to a conventional gamma camera with different two circular orbits (i.e. the 90 degrees and 45 degrees tilted angles to axis of rotation). Data sets from these orbits satisfied the Tuy's condition (Tuy, 1983), to which the 3D-OSEM algorithm was applied. The present system was first evaluated by a cylindrical phantom that had several disk areas of 0.5 mm thickness filled with Tc-99m solution separated by a 10 mm gap. The reconstructed imaged with two orbital data sets demonstrated no axial blurring and better image quality than the image reconstructed with only one orbit. This study suggested that accurate reconstruction without axial blurring could be obtained by acquiring complete data set in pinhole SPECT. This system will be useful for quantitative analysis of bio-physiological functions in small animals.