In recent years gamma ray imagers such as the GammaCamTM and Polaris have demonstrated good imaging performance in the field. Imager performance is often summarized as “resolution”, either angular, or spatial at some distance from the imager, however the definition of resolution is not always related to the ability to image an object. It is difficult to quantitatively compare imagers without a common definition of image quality. This paper examines three categories of definition: point source; line source; and area source. It discusses the details of those definitions and which ones are more relevant for different situations. Metrics such as Full Width Half Maximum (FWHM), variations on the Rayleigh criterion, and some analogous to National Imagery Interpretability Rating Scale (NIIRS) are discussed. The performance against these metrics is evaluated for a high resolution coded aperture imager modeled using Monte Carlo N-Particle (MCNP), and for a medium resolution imager measured in the lab.
KEYWORDS: Sensors, Coded apertures, Prototyping, Signal detection, Telescopes, Imaging systems, Gamma radiation, Data acquisition, Computing systems, Control systems
We have developed a prototype of a scalable high-resolution direction and energy sensitive gamma-ray detection system
that operates in both coded aperture (CA) and Compton scatter (CS) modes to obtain optimal efficiency and angular
resolution over a wide energy range. The design consists of an active coded aperture constructed from 52 individual CZT
planar detectors each measuring 3×3×6 mm3 arranged in a MURA pattern on a 10×10 grid, with a monolithic
20×20×5 mm3 pixelated (8×8) CZT array serving as the focal plane. The combined mode is achieved by using the
aperture plane array for both Compton scattering of high-energy photons and as a coded mask for low-energy radiation.
The prototype instrument was built using two RENA-3 test systems, one each for the aperture and the focal plane,
stacked on top of each other at a distance of 130 mm. The test systems were modified to coordinate (synchronize)
readout and provide coincidence information of events within a user-adjustable 40-1,280 ns window. The measured
angular resolution of the device is <1 deg (17 mrad) in CA mode and is predicted to be approximately 3 deg (54 mrad) in
CS mode. The energy resolution of the CZT detectors is approximately 5% FWHM at 120 keV. We will present details
of the system design and initial results for the calibration and performance of the prototype.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.