Coded apertures derived from the fresnel zone plate

Mertz and Young introduced the idea of using a Fresnel zone plate as a shadow-casting reticle, or coded aperture, in x-ray astronomy. More recently, considerable progress has been made toward using the zone-plate aperture for gamma-ray imaging in nuclear medicine. The most successful configuration has used an off-axis section of a zone plate in conjunction with a halftone screen. In this paper, we discuss a variety of closely related coded apertures, including an annulus, an inverted zone plate, a spiral zone plate and the Girard grill. In most cases, the technique of grid-coded subtraction is used to suppress the zero-order (DC) background light usually associated with zone-plate imaging. The first application of this technique, reported by Stoner et al., used a sequence of two to four on-axis zone plates. In the present paper it is shown that the method can be extended to other apertures and is also very useful in synthesizing the spatial filters for optical decoding.