Real time depth-of-interaction correction for coded-aperture, gamma-ray images

The size of the image pixels in a coded-aperture image is a function of the mask hole size, the focal length (mask-to-detector spacing), and the distance to the scene being imaged. Gamma-ray imaging instruments designed for field use can have a focal length that is comparable to the thickness of the detector, resulting in radially blurred images because a range of image pixel sizes contributes to the image. If so equipped, one can use a detector’s depth-of-interaction resolution to eliminate this blurring by binning images formed from different depths within the detector to a common image scale. However, binning to a common image scale requires handling a number of issues including spatially dependent energy weighting, spatially varying offset corrections, and spatially correlated uncertainties. This paper explores these issues and provides effective solutions that have been implemented for online use in a field-portable instrument.