This paper presents a new method to match a twodimensional image to a translated, rotated, and scaled reference image. The approach consists of two steps: the calculation of a Fourier-Mellin invariant (FMI) descriptor for each image to be matched, and the matching of the FMI descriptors. The FMI descriptor is translation invariant, and represents rotation and scaling as translations in parameter space. The matching of the FMI descriptors is achieved using a symmetric phase-only matched filtering (SPOMF).The performance of the FMI-SPOMF algorithm is the same or similar to that of the phase-only matched filtering when dealing with image translations. The significant advantage of the new technique is its capability to match rotated and scaled images accurately and efficiently. The innovation is the application of the SPOMF to the FMI descriptors, which guarantees a high discriminating power and an excellent robustness in the presence of noise. This paper describes the principle of the new method and its discrete implementation for either image detection problems or image registration problems. Practical results are presented for various applications in medical imaging, remote sensing, fingerprint recognition, and multiobject identification.

Pinhole single-photon emission tomography (SPET) has been proposed to improve the trade-off between sensitivity and resolution for small organs located in close proximity to the pinhole aperture. This technique is hampered by artefacts in the non-central slices. These artefacts are caused by truncation and by the fact that the pinhole SPET data collected in a circular orbit do not contain sufficient information for exact reconstruction. The ordered subsets expectation maximization (OS-EM) algorithm is a potential solution to these problems. In this study a three-dimensional OS-EM algorithm was implemented for data acquired on a single-head gamma camera equipped with a pinhole collimator (PH OS-EM). The aim of this study was to compare the PH OS-EM algorithm with the filtered back-projection algorithm of Feldkamp, Davis and Kress (FDK) and with the conventional parallel-hole geometry as a whole, using a line source phantom, Picker's thyroid phantom and a phantom mimicking the human cervical column. Correction for the angular dependency of the sensitivity in the pinhole geometry was based on a uniform flood acquisition. The projection data were shifted according to the measured centre of rotation. No correction was made for attenuation, scatter or distance-dependent camera resolution. The resolution measured with the line source phantom showed a significant improvement with PH OS-EM as compared with FDK, especially in the axial direction. Using Picker's thyroid phantom, one iteration with eight subsets was sufficient to obtain images with similar noise levels in uniform regions of interest to those obtained with the FDK algorithm. With these parameters the reconstruction time was 2.5 times longer than for the FDK method. Furthermore, there was a reduction in the artefacts caused by the circular orbit SPET acquisition. The images obtained from the phantom mimicking the human cervical column indicated that the improvement in image quality with PH OS-EM is relevant for future clinical use and that the improvements obtained using the OS-EM algorithm are more significant for the pinhole geometry than for the conventional parallel-hole geometry. We conclude that PH OS-EM is a practical and promising alternative for pinhole SPET reconstruction.

The authors have derived an approximate expression for the variance at the centre of a uniform spherical source reconstructed using the 3D filtered backprojection technique. The derivation is based on the assumption that the projection data are affected only by Poisson noise, and that the projection is sufficiently finely and uniformly sampled to ensure the validity of the filtered backprojection approach. The expression for the voxel variance in a 3D reconstruction is similar to the usual 2D expression, but contains a factor dependent on the aperture of the cylindrical detector. This factor has been calculated for two different reconstruction filters and in both cases, the influence of the detector aperture on the voxel variance is small. Thus, for an isotropic source such as the uniform sphere, Poisson noise is propagated similarly by both the 2D and 3D filtered backprojection algorithms.

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Abstract. The ANIMMA conferences offer a unique opportunity to discover research carried out in all fields of nuclear measurements and instrumentation with applications extending from fundamental physics to fission and fusion reactors, medical imaging, environmental protection and homeland security. After four successful editions of the Conference, it was decided to prepare a review based to a large extent but not exclusively on the papers presented during the first four editions of the conference. This review is organized according to the measurement methodologies: neutronic, photonic, thermal, acoustic and optical measurements, as well as medical imaging and specific challenges linked to data acquisition and electronic hardening. The paper describes the main challenges justifying research in these different areas, and summarizes the recent progress reported. It offers researchers and engineers a way to quickly and efficiently access knowledge in highly specialized areas.