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A maximum likelihood expectation maximization iterative image reconstruction technique for mask/anti-mask coded aperture data

IEEE Nuclear Science Symposium Conference Record

Brubaker, Erik B.

We present a method to use mask/anti-mask coded aperture data with maximum likelihood expectation maximization (MLEM) image reconstruction. The mask/anti-mask approach eliminates 'unmodulated' data, improving image quality when backgrounds, room scatter, or noisy detectors are significant. MLEM permits complex detector response models, desirable in gamma-ray or fast neutron imaging with thick masks, near-field imaging, or tomographic reconstruction. Subtracted mask/anti-mask data is not Poisson distributed, and cannot be used with MLEM. Instead, we treat unmodulated data as generated by source terms indexed by detector pixel, so that MLEM converges to simultaneous estimates of the true image and the unmodulated event rates. © 2013 IEEE.

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TYPE Conference YEAR 2013
ScopusOSTI

Bubble masks for time-encoded imaging of fast neutrons

IEEE Nuclear Science Symposium Conference Record

Brennan, James S.; Brubaker, Erik B.; Nowack, Aaron; Steele, John T.; Sweany, Melinda; Throckmorton, Daniel J.

Time-encoded imaging is an approach to directional radiation detection that is being developed at SNL with a focus on fast neutron directional detection. In this technique, a time modulation of a detected neutron signal is induced - typically, a moving mask that attenuates neutrons with a time structure that depends on the source position. An important challenge in time-encoded imaging is to develop high-resolution two-dimensional imaging capabilities; building a mechanically moving high-resolution mask presents challenges both theoretical and technical. We have investigated an alternative to mechanical masks that replaces the solid mask with a liquid such as mineral oil. Instead of fixed blocks of solid material that move in predefined patterns, the oil is contained in tubing structures, and carefully introduced air gaps - bubbles - propagate through the tubing, generating moving patterns of oil mask elements and air apertures. Compared to current moving-mask techniques, the bubble mask is simple, since mechanical motion is replaced by gravity-driven bubble propagation; it is flexible, since arbitrary bubble patterns can be generated by a software-controlled valve actuator; and it is potentially high performance, since the tubing and bubble size can be tuned for high-resolution imaging requirements. We have built and tested various single-tube mask elements, and will present results on bubble introduction and propagation for different tube sizes and cross-sectional shapes; real-time bubble position tracking; neutron source imaging tests; and reconstruction techniques demonstrated on simple test data as well as a simulated full detector system. © 2013 IEEE.

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TYPE Conference YEAR 2013
ScopusOSTI
Results 126–150 of 174
Results 126–150 of 174