Activity concentration Arctangent Article Austria Bearing Bivariate gaussian distributions Cartesians Close range Dosimetry Extended Kalman filters Gaussian Gaussian distribution Gaussian noise (electronic) Gaussians Humans Kalman filter Liver phantom Mathematical transformations Metrological quality Monte Carlo Method Monte Carlo method Non-linear transformations PDF Phantoms, Imaging Polar transformations Probability density function Reproducibility of Results SIRT SPECT quantification State-variables