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Kastis G.A.,Academy of Athens | Kyriakopoulou D.,Academy of Athens | Gaitanis A.,Biomedical Research Foundation of the Academy of Athens BRFAA | Fernandez Y.,Center dImatge Molecular Experimental | And 3 more authors.
Medical Physics | Year: 2014

Purpose: The spline reconstruction technique (SRT), based on the analytic formula for the inverse Radon transform, has been presented earlier in the literature. In this study, the authors present an improved formulation and numerical implementation of this algorithm and evaluate it in comparison to filtered backprojection (FBP). Methods: The SRT is based on the numerical evaluation of the Hilbert transform of the sinogram via an approximation in terms of "custom made" cubic splines. By restricting reconstruction only within object pixels and by utilizing certain mathematical symmetries, the authors achieve a reconstruction time comparable to that of FBP. The authors have implemented SRT in STIR and have evaluated this technique using simulated data from a clinical positron emission tomography (PET) system, as well as real data obtained from clinical and preclinical PET scanners. For the simulation studies, the authors have simulated sinograms of a point-source and three digital phantoms. Using these sinograms, the authors have created realizations of Poisson noise at five noise levels. In addition to visual comparisons of the reconstructed images, the authors have determined contrast and bias for different regions of the phantoms as a function of noise level. For the real-data studies, sinograms of an18F-FDG injected mouse, a NEMA NU 4-2008 image quality phantom, and a Derenzo phantom have been acquired from a commercial PET system. The authors have determined: (a) coefficient of variations (COV) and contrast from the NEMA phantom, (b) contrast for the various sections of the Derenzo phantom, and (c) line profiles for the Derenzo phantom. Furthermore, the authors have acquired sinograms from a whole-body PET scan of an 18F-FDG injected cancer patient, using the GE Discovery ST PET/CT system. SRT and FBP reconstructions of the thorax have been visually evaluated. Results: The results indicate an improvement in FWHM and FWTM in both simulated and real point-source studies. In all simulated phantoms, the SRT exhibits higher contrast and lower bias than FBP at all noise levels, by increasing the COV in the reconstructed images. Finally, in real studies, whereas the contrast of the cold chambers are similar for both algorithms, the SRT reconstructed images of the NEMA phantom exhibit slightly higher COV values than those of FBP. In the Derenzo phantom, SRT resolves the 2-mm separated holes slightly better than FBP. The small-animal and human reconstructions via SRT exhibit slightly higher resolution and contrast than the FBP reconstructions. Conclusions: The SRT provides images of higher resolution, higher contrast, and lower bias than FBP, by increasing slightly the noise in the reconstructed images. Furthermore, it eliminates streak artifacts outside the object boundary. Unlike other analytic algorithms, the reconstruction time of SRT is comparable with that of FBP. The source code for SRT will become available in a future release of STIR. © 2014 American Association of Physicists in Medicine. Source

Kastis G.A.,Pure Research | Gaitanis A.,Pure Research | Fernandez Y.,Center dImatge Molecular Experimental | Kontaxakis G.,Technical University of Madrid | And 2 more authors.
IEEE Nuclear Science Symposium Conference Record | Year: 2010

An efficient, two-dimensional, analytic, Spline Reconstruction Technique (SRT) has been presented earlier in the literature. This technique involves the Hilbert transform of the sinogram which is approximated in terms of natural cubic splines. The aim of this study is to evaluate the SRT algorithm using Monte-Carlo simulated sinograms and real PET data, in comparison with three commonly used reconstruction algorithms: FBP, MLEM and OSEM. For the simulation studies, a digital Hoffman phantom, a NEMA-like and a Derenzo phantom were employed, and Monte Carlo methods were used for the simulation of the activity distribution in the source and the resulting generation of positron-electron annihilations. No noise, scatter and absorption conditions were assumed. The phantoms were generated with different image activities. The relevant modeled system was a single-ring tomograph with 234 scintillation crystals. Image grids with an image size of 128 128 pixels were employed. For the studies of real data, PET sinograms of an FDG injected mouse and a NEMA and Derenzo phantom were acquired from an ARGUS-CT small animal PET/CT system. Both the simulated and real sinograms were reconstructed using the SRT algorithm and the reconstructed images were compared to those of FBP, MLEM and OSEM. The contrast and SNR were calculated for the simulated NEMA-like and Hofmann phantom by drawing ROIs within the images. Our results indicate that SRT and FBP give reconstructed images of comparable quality with respect to the number of counts. Striking artifacts become worse at lower total counts for both methods. SRT reconstructed images exhibit higher SNR in comparison with FBP and, in some cases, in comparison with MLEM and OSEM. SRT reconstructed images exhibit higher contrast over FBP but not over MLEM and OSEM. The reconstruction time for SRT was about 20 sec per slice, hence SRT is faster than MLEM and OSEM (for high activity images), but slower than FBP. In conclusion, SRT is a linear algorithm which can serve as a good alternative to FBP, providing images with higher contrast and SNR values. Furthermore, it has the crucial advantage that it can accommodate complicated detector geometries. © 2010 IEEE. Source

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