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

Abstract

Standard nuclear medicine imaging uses photon collimation and thus suffer 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. We 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.We 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 gammdSPECT camera. Results from our experiments show significantly improved sensitivity for a coded aperture imaging system over collimator systems, while retaining reasonable resolution. We have demonstrated the possibility of using coded apertures and a conventional gamma camera to image gamma rays of high energy, such as 5 11 KeV, in nuclear medicine.

Aperture collimation correction and maximum-likelihood image reconstruction for near-field coded aperture imaging of single photon emission computerized tomography

“…Fig. 5(c) shows the same image further corrected for the collimation effect by the expressed in (18). As shown in Fig.…”

“…A complete representation of the collimation effect is an average of all possible incident rays passing through the mask expressed as (18) Notice that above is an average of all possible rays with the implicit assumption that all possible rays exist and are of equal intensity. However, this is not always true.…”

“…For instance, in the case of a point source, at any point on the detector plane only one possible ray exists. Therefore, (18) is accurate only when the source distribution is homogeneous. For SPECT imaging, the radioactivity distribution within the targeted object is quite smooth (slow varying).…”

“…1). It was suggested that the slice of a 3-D object can be reconstructed [17], [18] by (23) where is the decoding mask corresponding to . Consequently, a stack of image slices can be reconstructed by choosing different .…”

A novel three‐dimensional image reconstruction method for near‐field coded aperture single photon emission computerized tomography

“…Results of partial 3D reconstruction from a single coded aperture projection have been reported previously by others. [16][17][18][19] However, these methods produced low quality images with poor resolution along the depth direction. Meikle et al reported their studies on coded aperture SPECT for small animal imaging and provided useful perspectives on numerous system designs.…”