High energy 3-D nuclear medicine imaging using coded apertures with a conventional gamma camera

Standard nuclear medicine imaging uses photon collimation and thus suffers from very low sensitivity, especially if high energy (>511 keV) isotopes are to be imaged. Coded aperture techniques use a coded pattern mask instead of a collimator to encode the photon source distribution, thus every photon source contributes to the signal in the whole detector area. It significantly improves the system sensitivity while retaining the spatial resolution of the reconstructed images. The authors have developed coded aperture arrays which are specifically designed for near field imaging, rather than the far field imaging appropriate to X-ray astronomy and have placed an emphasis on reducing sidelobe response in order to increase utility for images with background. The authors have used a cyclic difference set uniformly redundant array as the coded aperture pattern; have conducted imaging experiments for point sources, 2-D sources (sources in a plane with arbitrary distribution), and 3-D sources (sources in 3-D with arbitrary distribution) of 511 keV through phantoms; and have compared the experimental results with those from collimator systems. The coded aperture experiments have been conducted using a Siemens E.CAM gamma/SPECT camera. Results from the authors' experiments show significantly improved sensitivity for a coded aperture imaging system over collimator systems, while retaining reasonable resolution. The authors have demonstrated the possibility of using coded apertures and a conventional gamma camera to image gamma rays of high energy, such as 511 keV, in nuclear medicine.