Medical & Biological Engineering & Computing

The aim of our work is to investigate whether the optical flow algorithm applied to video recordings can be used to detect movement during sleep in pediatric patients with epilepsy. The optical flow algorithm allocates intensities to pixels proportional to their involvement in movement of an object. The average of a percentage of the highest movement vectors was plotted as a function of time (R(t)). The used dataset contains video data acquired at the University Hospital of Leuven consisting of normal sleep movement and seizure movement. We investigated R(t), to make a distinction between movement and non-movement. We used the acquisition parameters (320 × 240 at 12.5 fps), derived from a previous study (Cuppens et al., Proceedings of the 4th European congress of the international federation for medical and biological engineering (MBEC 2008), ECIFBME 2008, Antwerp, Belgium, IFMBE Proceedings, vol 22, pp 784–789, 2008). Two experiments were concluded, one with global thresholds of R(t) in all datasets and one with a variable threshold in each dataset. The latter is obtained by inspecting a non-movement epoch and calculating the mean and standard deviations of R(t) over time. The variable threshold on R(t) was then obtained for each dataset by adding to the mean a fixed multiple of the standard deviation. Optimal thresholds were derived based on a three-fold cross-validation. The best result was achieved when using a variable threshold, which resulted in a sensitivity of one in all the test sets and a PPV of 1, 0.821, and 1, respectively, for the three test sets.

This study addressed layer-specific differences in the biomechanical response of ascending aortic aneusysms, obtained from patients during graft replacement. Tensile tests were conducted on pairs of (orthogonally directed) intimal, medial, and adventitial strips from the anterior, posterior, and two lateral quadrants. The experimental data were reduced by the Fung-type model, affording appropriate characterization of the material properties. Testing of individual layers beyond rupture disclosed their failure properties, namely their capacity to bear varying deformation and stress levels. Material parameters $$ c_{\theta \theta } $$ and $$ c_{zz} $$ , specifying circumferential and longitudinal stiffness, received the highest values in the adventitia or intima and the smallest in the media, with $$ c_{\theta \theta } $$  >  $$ c_{zz} $$ in every layer but the intima. Similar extensibility at failure was found among layers, whereas the adventitia was the strongest of all. Circumferentially and longitudinally directed strips from each layer did not show uniform material parameters and failure properties among regions, but most differences did not reach significance. Medial and adventitial but not intimal layers were stronger circumferentially than longitudinally. This is the first study to place emphasis on the biomechanical properties of the distinct layers of human aneurysmal aorta that may be expected to shed light into the mechanisms promoting aneurysm dissection and rupture.

A novel high-resolution electro-encephalographic (EEG) procedure is proposed, including high spatial sampling (128 channels), a realistic magnetic resonance-constructed subject head model, a multi-dipole cortical source model and regularised weighted minimum-norm linear inverse source estimation (WMN). As an innovation, EEG potentials (two healthy subjects; median-nerve, short-latency somatosensory-evoked potentials (SEPs)) are preliminarily Laplacian-transformed (LT) to remove brain electrical activity generated by subcortical sources (i.e. not represented in the source model). LT-WMN estimates are mathematically evaluated by figures of merit (WMN estimates as a reference). Results show higher dipole identifiability (0.69;0.88), lower dipole localisation error (0.6 mm; 7.8mm) and lower spatial dispersion (8.6 mm; 24mm) in LT-WMN than in WMN estimates (Bonferroni corrected p<0.001). These estimates are presented on the subject modelled cortical surface to highlight the increased spatial information content in LT-WMN compared with WMN estimates. The proposed high-resolution EEG technique is useful for the study of somatosensory functions in basic research and clinical applications.

Finite-element modelling is used to simulate the response of atherosclerotic arteries to a balloon angioplasty procedure. Material properties for the normal wall are derived from experimental data, and the properties of the plaque are varied over a wide range. Comparison with experimental data shows that the normal aterial wall can be appropriately modelled using a hyperelastic material definition. Large-strain, nonlinear analysis was used to simulate the dilatation of three typical plaque configurations by an angioplasty balloon. Stress contour plots are presented for each configuration. Results show good agreement with previous histologic studies.

L'appareil de culture décrit réalisein vitro des conditions d'oxygénation, de nutrition et d'élimination de déchets proches de celles du milieu intérieur. Tout en reposant sur un principle simple, il offre de nouvelles possibilités d'analyse fonctionnelle et quantitative d'organesin vitro.

The purpose of the research is to determine how the pacing rate affects the strength-interval curve in cardiac tissue. Computer simulations are used to calculate the cathodal and anodal strength-interval curves. The tissue is represented by the bidomain model with Beeler-Reuter membrane properties. The strength-interval curves shift to shorter intervals as the pacing rate increases. However, the shape of the strength-interval curve, including the separation into ‘make’ and ‘break’ sections and the presence of a ‘dip’, is insensitive to pacing rate.