Nearly Exact Discrepancy Principle for Low-Count Poisson Image Restoration.

The effectiveness of variational methods for restoring images corrupted by Poisson noise strongly depends on the suitable selection of the regularization parameter balancing the effect of the regulation term(s) and the generalized Kullback-Liebler divergence data term. One of the approaches still commonly used today for choosing the parameter is the discrepancy principle proposed by Zanella et al. in a seminal work. It relies on imposing a value of the data term approximately equal to its expected value and works well for mid- and high-count Poisson noise corruptions. However, the series truncation approximation used in the theoretical derivation of the expected value leads to poor performance for low-count Poisson noise. In this paper, we highlight the theoretical limits of the approach and then propose a nearly exact version of it based on Monte Carlo simulation and weighted least-square fitting. Several numerical experiments are presented, proving beyond doubt that in the low-count Poisson regime, the proposed modified, nearly exact discrepancy principle performs far better than the original, approximated one by Zanella et al., whereas it works similarly or slightly better in the mid- and high-count regimes.

A study on the relationship between intraglandular arterial distribution and thyroid lobe shape: implications for biotechnology of a bioartificial thyroid.

We have recently hypothesized that structural and secretory components of the adult human thyroid gland maintain constant reciprocal and geometrical relationships, even if changes occur in the three-dimensional (3D) architecture of any of these elements. This means that thyroid morphology could be studied from the point of view of a 3D topology. As a consequence, we have investigated anatomical aspects that could support this assumption. In the present study, we show that the presence of a constant relationship can be demonstrated between the vascular arrangement of the gland, including the extension of intraglandular arterial fields, arterial anastomoses and arterial calibers, and the shape as well as volume of the thyroid. Specifically, a statistically significant difference has been found between the network amplitudes of the superior and inferior thyroid arteries in relation to either a conic or an ellipsoidal geometry of the thyroid lobe. In addition, a direct relationship has been implicated between the distribution of arterial anastomoses and the behavior of the lobe as a single hemodynamic unit. Finally, a statistically significant correlation has been observed between average arterial caliber of the inferior thyroid artery and thyroid volume. On the basis of these results, we propose a model of architectural assembly between stromal and parenchymal elements of the adult thyroid that might prove useful in designing a bioartificial gland ex situ. Potential clinical applications of this principle in regenerative medicine of other endocrine organs are highlighted.

The bioartificial thyroid: a biotechnological perspective in endocrine organ engineering for transplantation replacement.

A new concept for ex situ endocrine organ bioengineering is presented, focused on the realization of a human bioartificial thyroid gland. It is based on the theoretical assumption and experimental evidence that symmetries in geometrical coordinates of the thyroid tissue remain invariant with respect to developmental, physiological or pathophysiological transformations occuring in the gland architecture. This topological arrangement is dependent upon physical connections established between cells, cell adhesion molecules and extracellular matrix, leading to the view that the thyroid parenchyma behaves like a deformable "putty", moulded onto an elastic stromal/vascular scaffold (SVS) dictating the final morphology of the gland. In particular, we have raised the idea that the geometry of the SVS per se provides pivotal epigenetic information to address the genetically-programmed, thyrocyte and endothelial/vascular proliferation and differentiation towards a functionally mature gland, making organ form a pre-requirementfor organ function. A number of experimental approaches are explored to obtain a reliable replica of a human thyroid SVS, and an informatic simulation is designed based on fractal growth of the thyroid intraparenchymal arterial tree. Various tissue-compatible and degradable synthetic or biomimetic polymers are discussed to act as a template of the thyroid SVS, onto which to co-seed autologous human thyrocyte (TPC) and endothelial/vascular (EVPC) progenitor cells. Harvest and expansion of both TPC and EVPC in primary culture are considered, with specific attention to the selection of normal thyrocytes growing at a satisfactory rate to colonize the synthetic matrix. In addition, both in vitro and in vivo techniques to authenticate TPC and EVPC lineage differentiation are reviewed, including immunocytochemistry, reverse trascriptase-polymerase chain reaction, flow cytomery and proteomics. Finally, analysis of viability of the thyroid construct following implantation in animal hosts is proposed, with the intent to obtain a bioartificial thyroid gland morphologically and functionally adequate for transplantation. We believe that the biotechnological scenario proposed herein may provide a template to construct other, more complex and clinically-relevant bioartificial endocrine organs ex situ, such as human pancreatic islets and the liver, and perhaps a new approach to brain bioengineering.

A new software for prediction of femoral neck fractures.

Femoral neck fractures are an important clinical, social and economic problem. Even if many different attempts have been carried out to improve the accuracy predicting the fracture risk, it was demonstrated in retrospective studies that the standard clinical protocol achieves an accuracy of about 65%. A new procedure was developed including for the prediction not only bone mineral density but also geometric and femoral strength information and achieving an accuracy of about 80% in a previous retrospective study. Aim of the present work was to re-engineer research-based procedures and develop a real-time software for the prediction of the risk for femoral fracture. The result was efficient, repeatable and easy to use software for the evaluation of the femoral neck fracture risk to be inserted in the daily clinical practice providing a useful tool for the improvement of fracture prediction.

Evolutionary partial differential equations for biomedical image processing.

We are presenting here a model for processing space-time image sequences and applying them to 3D echo-cardiography. The non-linear evolutionary equations filter the sequence with keeping space-time coherent structures. They have been developed using ideas of regularized Perona-Malik an-isotropic diffusion and geometrical diffusion of mean curvature flow type (Malladi-Sethian), combined with Galilean invariant movie multi-scale analysis of Alvarez et al. A discretization of space-time filtering equations by means of finite volume method is discussed in detail. Computational results in processing of 3D echo-cardiographic sequences obtained by rotational acquisition technique and by real-time 3D echo volumetrics acquisition technique are presented. Quantitative error estimation is also provided.