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The International Atomic Energy Agency (IAEA) has recently approved passivegamma emission tomography (PGET) as a method for inspecting spent nuclear fuelassemblies (SFAs), an important aspect of international nuclear safeguardswhich aim at preventing the proliferation of nuclear weapons. The PGETinstrument is essentially a single photon emission computed tomography (SPECT)system that allows the reconstruction of axial cross-sections of the emissionmap of the SFA. The fuel material heavily self-attenuates its gamma-rayemissions, so that correctly accounting for the attenuation is a criticalfactor in producing accurate images. Due to the nature of the inspections, itis desirable to use as little a priori information as possible about the fuel,including the attenuation map, in the reconstruction process. Currentreconstruction methods either do not correct for attenuation, assume a uniformattenuation throughout the fuel assembly, or assume an attenuation map based onan initial filtered back projection (FBP) reconstruction. Here, we propose amethod to simultaneously reconstruct the emission and attenuation maps byformulating the reconstruction as a constrained minimization problem with aleast squares data fidelity term and regularization terms. Using simulateddata, we compare the proposed method to FBP, showing that our approach producessignificantly better reconstructions by various numerical metrics and a muchbetter classification of spent, missing, and fresh fuel rods.

Simultaneous Reconstruction of Emission and Attenuation in Passive Gamma Emission Tomography of Spent Nuclear Fuel