Image improvement in pinhole SPECT using complete data acquisition combined with statistical image reconstruction

Pinhole single-photon emission computed tomography (SPECT) with high spatial-resolution is suitable for small-animal imaging, but has limitations associated with spatial-resolution inhomogeneity or axial blurring. We have hypothesized that this blurring is due to incompleteness of projection data acquired by a single circular pinhole orbit. And we have developed a pinhole SPECT system with two circular orbits which satisfy Tuy's condition so as to provide complete data for 3D pinhole SPECT reconstruction within the whole field-of-view (FOV); a dedicated 3D ordered subsets expectation maximization (3D-OSEM) reconstruction method for two-orbit data. This study is aimed at evaluating accuracy and impact of this system. In this system, not the camera but the object rotates and the two orbits are 90° and 45° relative to object's axis. Experiments using a multiple-disk phantom filled with ^99mTc solution and a mouse bone scan using ^99mTc-labeled HMDP agent were carried out. The Feldkamp's filtered back-projection (FBP) method and the 3D-OSEM method were applied to these data sets. The axial blurring was apparent on images reconstructed by FBP for single-orbit data, while the 3D-OSEM using two-orbit data dramatically improved the resolution homogeneity and statistical noise property, and also demonstrated considerably better image quality in the mouse scan.