A variational Bayesian method for inverse problems with impulsive noise

We propose a novel numerical method for solving inverse problems subject to impulsive noises which possibly contain a large number of outliers. The approach is of Bayesian type, and it exploits a heavy-tailed t distribution for data noise to achieve robustness with respect to outliers. A hierarchical model with all hyper-parameters automatically determined from the given data is described. An algorithm of variational type by minimizing the Kullback-Leibler divergence between the true posteriori distribution and a separable approximation is developed. The numerical method is illustrated on several one- and two-dimensional linear and nonlinear inverse problems arising from heat conduction, including estimating boundary temperature, heat flux and heat transfer coefficient. The results show its robustness to outliers and the fast and steady convergence of the algorithm.Comment: 20 pages, to appear in J. Comput. Phy

Bayesian Modelling of Skull Conductivity Uncertainties in EEG Source Imaging

Knowing the correct skull conductivity is crucial for the accuracy of EEG source imaging, but unfortunately, its true value, which is inter- and intra-individually varying, is difficult to determine. In this paper, we propose a statistical method based on the Bayesian approximation error approach to compensate for source imaging errors related to erroneous skull conductivity. We demonstrate the potential of the approach by simulating EEG data of focal source activity and using the dipole scan algorithm and a sparsity promoting prior to reconstruct the underlying sources. The results suggest that the greatest improvements with the proposed method can be achieved when the focal sources are close to the skull.Comment: 4 pages, 2 figures, European Medical and Biological Engineering Conferenc

End-Users' Voice in EHR Selection : Development of a Usability Questionnaire for Demonstrations in Procurement (DPUQ)

This paper describes the development of a questionnaire for evaluating usability during EHR system procurement (DPUQ). Established usability questionnaires can be used to gather user feedback after using the systems. However, during procurement, experimenting with real system use is practical only with a limited number of system candidates. There is a need for less resource-demanding usability evaluation in the early stages of procurement in cases with several vendors. DPUQ has been designed for usability evaluation by end-users during special scenario-based vendor demonstrations. The questionnaire includes three sets of questions to be used during and after the vendor demonstration. DPUQ delivers specific usability scores and can be used to compare system candidates in procurement complementing other evaluation methods.Peer reviewe

We Need Numbers! - Heuristic Evaluation during Demonstrations (HED) for Measuring Usability in IT System Procurement

We introduce a new usability inspection method called HED (heuristic evaluation during demonstrations) for measuring and comparing usability of competing complex IT systems in public procurement. The method presented enhances traditional heuristic evaluation to include the use context, comprehensive view of the system, and reveals missing functionality by using user scenarios and demonstrations. HED also quantifies the results in a comparable way. We present findings from a real-life validation of the method in a large-scale procurement project of a healthcare and social welfare information system. We analyze and compare the performance of HED to other usability evaluation methods used in procurement. Based on the analysis HED can be used to evaluate the level of usability of an IT system during procurement correctly, comprehensively and efficiently.Peer reviewe

Regularization independent of the noise level: an analysis of quasi-optimality

The quasi-optimality criterion chooses the regularization parameter in inverse problems without taking into account the noise level. This rule works remarkably well in practice, although Bakushinskii has shown that there are always counterexamples with very poor performance. We propose an average case analysis of quasi-optimality for spectral cut-off estimators and we prove that the quasi-optimality criterion determines estimators which are rate-optimal {\em on average}. Its practical performance is illustrated with a calibration problem from mathematical finance.Comment: 18 pages, 3 figure

Quantitative photoacoustic tomography using illuminations from a single direction.

Quantitative photoacoustic tomography is an emerging imaging technique aimed at estimating optical parameters inside tissues from photoacoustic images, which are formed by combining optical information and ultrasonic propagation. This optical parameter estimation problem is ill-posed and needs to be approached within the framework of inverse problems. It has been shown that, in general, estimating the spatial distribution of more than one optical parameter is a nonunique problem unless more than one illumination pattern is used. Generally, this is overcome by illuminating the target from various directions. However, in some cases, for example when thick samples are investigated, illuminating the target from different directions may not be possible. In this work, the use of spatially modulated illumination patterns at one side of the target is investigated with simulations. The results show that the spatially modulated illumination patterns from a single direction could be used to provide multiple illuminations for quantitative photoacoustic tomography. Furthermore, the results show that the approach can be used to distinguish absorption and scattering inclusions located near the surface of the target. However, when compared to a full multidirection illumination setup, the approach cannot be used to image as deep inside tissues

Predicting functional properties of milk powder based on manufacturing data in an industrial-scale powder plant

The fundamental science relating key physical and functional properties of milk powder to plant operating conditions is complex and largely unknown. Consequently this paper takes a data-driven approach to relate the routinely measured plant conditions to one vital function property known as sediment in an industrial-scale powder plant. Data from four consecutive production seasons was examined, and linear regression models based on a chosen set of processing variables were used to predict the sediment values. The average prediction error was well within the range of the uncertainty of the laboratory test. The models could be used to predict the effect of each individual plant variable on the sediment values which could be beneficial in quality optimisation. In addition the choice of the training data set used to compute regression coefficients was studied and the resultant regression models were compared to alternative PLS models built on the same data