Near-Field Artifact Reduction using Realistic Limited-Field-of-View Coded Apertures in Planar Nuclear Medicine Imaging

Abstract

The use of coded apertures in gamma imaging has theoretical advantages over collimators. The near-field conditions of nuclear medicine, however, result in images that are corrupted by near-field artifacts. Work that was limited to ideal coded apertures has shown that near-field artifacts and ghosting can be reduced geometrically. This is achieved by placing multiple identical limited-field-of-view coded apertures side by side, in the form of a matrix. In this paper, a basic analysis extends the work towards useful coded apertures viz. apertures that are realistic in terms of thickness, transmission of the aperture material, and pinhole width. Realistic coded apertures tighten the constraints on the imaging system. Computer simulation results for a two-dimensional digital Shepp-Logan phantom are presented. The results show that realistic coded apertures introduce a new ‘tartan’ artifact, but that the technique of limiting the field-of-view controls the ‘tartan’. Near-field artifacts and ghosting are also reduced. The image is enhanced visually and in terms of a root-mean-square error measurement, which decreases from 74 to 17.