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A: A rotating modulation collimator (RMC) is a useful technique for sensing remote radiation sources. Recently, Kowash and his colleagues presented an image reconstruction algorithm to detect mid-range point sources with the RMC. However, their algorithm tends to produce undesirable artifacts in the reconstructed images. In this paper, we propose an improved image reconstruction algorithm using a regularization method. Our algorithm reduces the artifacts by increasing the sparsity during the reconstruction. We demonstrate the proposed algorithm on simulation data from RMC system model and MCNP data. K: Data processing methods; Image filtering; Inspection with gamma rays; Search for radioactive and fissile materials 1Corresponding author.

Rotating modulation collimator(RMC) is a remote sensing technique for a radiation source. This paper introduces an RMC system model and its image reconstruction algorithm based on Kowash's research. The reconstructed image can show the direction of a source. However, the distance to the source cannot be recovered. Moreover, the RMC image suffers from 180° ambiguity. In this paper, we propose a distance estimation method using two RMCs together with a solution to the ambiguity. We also demonstrate its performance using simulated RMC data.

A: A rotating modulation collimator (RMC) is an indirect imaging technique that has proven useful for remote radiation source detection. While it was initially invented for detecting sources in a far field, a recent development by Kowash has shown the feasibility of the RMC for detecting mid-range sources. However, their image reconstruction algorithm often produces spurious source estimates in pixels where no source exists. In this paper, we propose to improve the RMC image quality using a variance stabilizing transform. The transform reduces the inhomogeneous Poisson noise in the RMC data. In our simulation study, the proposed algorithm could reconstruct RMC images without misleading artifacts. K: Data processing methods; Image filtering; Search for radioactive and fissile materials; Inspection with gamma rays 1Corresponding author.

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