An investigation of coded aperture imaging for small animal SPECT

Coded apertures provide a substantial gain in detection efficiency compared with conventional collimation and are well suited to imaging small volumes. Here, the authors investigated several aspects of coded aperture design for a small animal SPECT system, including aperture/detector configuration, sampling requirements, and susceptibility to scatter. They simulated various source distributions and detection systems which included one, two, and four stationary detectors placed around the object, each with a pinhole array or a Fresnel zone plate in front of the detector. Image volumes were reconstructed using an iterative successive over-relaxation algorithm with a penalized weighted least squares cost function. Multiple pinhole arrays performed better than Fresnel zone plates in terms of reconstructed mean squared error and signal-to-noise. The authors´ design goals of <2 mm spatial resolution (full width at half maximum) and >1% detection efficiency can be achieved with a four-detector system with arrays of 100 pinholes per detector and the scatter fraction for a 2-cm diameter object is <5%. It is concluded that a coded aperture design shows great promise for small animal SPECT