Airway remodeling and accompanying changes in wall thickness are known to be a major symptom of chronic obstructive pulmonary disease (COPD), associated with reduced lung function in diseased individuals. Further investigation of this disease as well as monitoring of disease progression and treatment effect demand for accurate and reproducible assessment of airway wall thickness in CT datasets. With wall thicknesses in the sub-millimeter range, this task remains challenging even with today's high resolution CT datasets. To provide accurate measurements, taking partial volume effects into account is mandatory. The Full-Width-at-Half-Maximum (FWHM) method has been shown to be inappropriate for small airways<sup>1,2</sup> and several improved algorithms for objective quantification of airway wall thickness have been proposed.<sup>1-8</sup> In this paper, we describe an algorithm based on a closed form solution proposed by Weinheimer et al.<sup>7</sup> We locally estimate the lung density parameter required for the closed form solution to account for possible variations of parenchyma density between different lung regions, inspiration states and contrast agent concentrations. The general accuracy of the algorithm is evaluated using basic tubular software and hardware phantoms. Furthermore, we present results on the reproducibility of the algorithm with respect to clinical CT scans, varying reconstruction kernels, and repeated acquisitions, which is crucial for longitudinal observations.
Tridirectional Phase-Contrast (PC)-MRI sequences provide spatially and temporally resolved measurements of
blood flow velocity vectors in the human body. Analyzing flow conditions based on these datasets requires
prior segmentation of the vessels of interest. In view of decreased quality of morphology images in PC-MRI
sequences, the flow data provides valuable information to support reliable segmentation. This work presents a
semi-automatic approach for segmenting the large arteries utilizing both morphology and flow information. It
consists of two parts, the extraction of a simplified vessel model based on vessel centerlines and diameters, and a
following refinement of the resulting surface for each time frame. Vessel centerlines and diameters are extracted
using an offset adaptive medialness function that estimates a voxel's likelihood of belonging to a vessel centerline.
The resulting centerline model is manually post-processed to select the appropriate centerlines and link possible
gaps. The surface described by the final centerline model is used to initialize a 3D level set segmentation of each
time frame. Deformation velocities that depend on both morphology and flow information are proposed and a
new approach to account for the curved shape of vessels is introduced. The described segmentation system has
been successfully applied on a total of 22 datasets of the thoracic aorta and the pulmonary arteries. Resulting
segmentations have been assessed by an expert radiologist and were considered to be very satisfactory.
The photoluminescence (PL) and PL excitation (PLE) spectra of quantum wells (QWs) formed by CdSe insertions in ZnSe matrix reveal the states of heavy and light excitons localized in CdSe-rich islands, and the energy <i>E</i><sub>ME</sub> which is associated with the percolation threshold over the entire lateral plane of QW. The model calculations are performed which result in evaluation of the island mean size and composition of ZnCdSe solid solution within and outside of islands.
The occupied and unoccupied electronic structure of high quality single crystals of the copper- free layered perovskite superconductor Sr<SUB>2</SUB>RuO<SUB>4</SUB> has been measured for the first time. Angle-resolved photoemission spectroscopy with high energy and angle resolution determined band dispersions along the principle directions of the projected Brillouin zone of the (001) surface. The highlight of these spectra is the observation and characterization of an extended van Hove singularity. The singularity is located 17 meV below the Fermi level and extends around the M point for around 0.2 angstrom<SUP>-1</SUP> along both (Gamma) -M-Gamma and X-M-X. Dispersions of the near-Fermi level states in Sr<SUB>2</SUB>RuO<SUB>4</SUB> reveal 3 bands which cross the Fermi level giving rise to 3 Fermi surfaces; 1 electron-like Fermi surface around the (Gamma) point and 2 hole-like surfaces encircling the X point. The topology of the empirically determined Fermi surfaces is found to be in qualitative agreement with local density approximation band structure calculations. Photoemission of the full valence band of Sr<SUB>2</SUB>RuO<SUB>4</SUB> are also presented. The total valence band width is approximately 9 eV, the density of states at the Fermi level derived from photoemission is 1.3 states/(eV cell) and has an 80%/20% mix of metal to ligand character. Polarization-dependent O1s NEXAFS performed on Sr<SUB>2</SUB>RuO<SUB>4</SUB> demonstrate mainly hole states at the Fermi level in orbitals in the RuO<SUB>2</SUB> planes. Electron correlations among Ru 4d levels in Sr<SUB>2</SUB>RuO<SUB>4</SUB> are argued to have a lesser impact than that of 3d levels in the cuprates.