A new direction in nuclear medicine imaging: Pinhole tomography

We have mounted a pinhole collimator on a rotating gamma camera and used it to assess the imaging characteristics of pinhole SPECT. Phantoms consisting of point and line sources of technicium-99 m have been imaged to determine the response function of the system throughout the field of view. The images were reconstructed using a filtered-backprojection algorithm for cone-beam geometry, equivalent to the Feldkamp algorithm. The reconstructed images indicated that the system response function is quite constant in width throughout the field of view, but varies in amplitude by about 30%. Some streak artifacts are visible, particularly from activity near the edges of the field of view, and may arise because of the incomplete projection sampling. These preliminary studies will be extended by assessing the potential for improved reconstruction techniques, and assessing the performance at lower counting rates, as in potential clinical applications.