Semiautomated Skeletonization of the Pulmonary Arterial Tree in Micro-CT Images

We present a simple and robust approach that utilizes planar images at different angular rotations combined with unfiltered back-projection to locate the central axes of the pulmonary arterial tree. Three-dimensional points are selected interactively by the user. The computer calculates a sub- volume unfiltered back-projection orthogonal to the vector connecting the two points and centered on the first point. Because more x-rays are absorbed at the thickest portion of the vessel, in the unfiltered back-projection, the darkest pixel is assumed to be the center of the vessel. The computer replaces this point with the newly computer-calculated point. A second back-projection is calculated around the original point orthogonal to a vector connecting the newly-calculated first point and user-determined second point. The darkest pixel within the reconstruction is determined. The computer then replaces the second point with the XYZ coordinates of the darkest pixel within this second reconstruction. Following a vector based on a moving average of previously determined 3- dimensional points along the vessel\u27s axis, the computer continues this skeletonization process until stopped by the user. The computer estimates the vessel diameter along the set of previously determined points using a method similar to the full width-half max algorithm. On all subsequent vessels, the process works the same way except that at each point, distances between the current point and all previously determined points along different vessels are determined. If the difference is less than the previously estimated diameter, the vessels are assumed to branch. This user/computer interaction continues until the vascular tree has been skeletonized

Spectral Analysis and Parameter Estimation in Fibre Levitated Optomechanics

In levitated optomechanics, nano-scale objects are optically trapped so that their motion can be studied. These trapped nanoparticles are held in a 3D quadratic potential and act as damped harmonic oscillators; they are thermally and mechanically decoupled from the apparatus and their position is measured interfer-ometrically to picometre accuracy. These systems are well suited to sensing and metrology applications, as any external disturbance of the particle can be observed using the scattered trapping light.When examining the motion of a levitated nanoparticle, it’s position is recorded and used to estimate a power spectral density (PSD), from which state parameters can be estimated. In this thesis an experi-mental setup is presented, optimised for maximum collection of particle position information in 1D, using a fibre-based parabolic mirror trap and heterodyne measurement system in order to produce spectra with minimal noise and unwanted artefacts.A novel application of the Middleton expansion from RF engineering is used to generate a complete power spectrum that depends on the physical parameters of the system. This method treats the particle as a stochastic harmonic oscillator, phase modulated by a Gaussian random process with known PSD. We reproduce the PSD of intensity at a detector, a quantity that is sinusoidally dependent on particle posi-tion. This technique generates a single, full PSD using modified Bessel functions, and does not depend on assumptions about the relative phases of the interfered fields, highlighting the non-linear dependence of measured signal on position. Theoretical spectra are fitted to a measured PSD and the phase modulation depth is extracted; this is used to calculate the particle oscillation amplitude and, by an equipartition ar-gument, the centre of mass temperature to mass ratio. State parameters are tracked as environmental conditions change and an increase in centre of mass temperature as a function of decreasing background gas pressure is observed

Why Do Individuals Choose Self-Employment?

This paper undertakes an analysis of the motivating factors cited by the self-employed in the UK as reasons for choosing self-employment. Very limited previous research has addressed the question of why individuals report that they have chosen self-employment. Two questions are addressed using large scale labour force survey data for the UK. The first concerns the extent to which the self-employed are self-employed out of necessity, opportunity, lifestyle decision or occupational choice. The second concerns the extent to which there is heterogeneity amongst the self-employed on the basis of the motivations that they report for choosing self-employment. Factor analysis reveals a number of different dimensions of entrepreneurship on the basis of stated motivation, but with no evidence that being 'forced' into entrepreneurship through economic necessity is a significant factor. Motivation towards entrepreneurship is therefore highly multidimensional. Multivariate regression analysis is employed using a method to control for self-selection into self-employment. This reveals significant differences between men and women, with women concerned more with lifestyle factors and less with financial gain. Market-directed 'opportunity' entrepreneurship is more strongly associated with higher educational attainment. Those joining family businesses appear not to value prior educational attainment. Public policy to promote entrepreneurship therefore needs to be tailored carefully to different groups.self-employment, entrepreneurship, motivation, occupational choice

The steps to prioritizing and undertaking action at sites threatened by climate change : incorporating a citizen science approach into heritage management in Scotland

Publisher PD

Intimate Communities. Honorific Statues and the Political Culture of the Cities of Africa Proconsularis in the First three Centuries CE

This dissertation argues that the inscriptions of honorific statues reveal a dynamic political culture in the cities of the Roman province of Africa Proconsularis in the first three centuries CE. Although the known regulations governing the public life of Roman municipia and coloniae formally restricted decision making on public matters (outside of the election of magistrates) to the ordo decurionum, the inscriptions show that the flexibility existed for the non-decurional members of the community, that is the populus, to express their opinion collectively and even, on occasion, to initiate actions. It is observed that previous studies tend to downplay or even ignore the participation of the populus in civic politics, and that they tend to present the picture of an ossified public life dominated by the decurions and leading families in the community. It is suggested that these previous studies focus too narrowly on a single dataset. In contrast, this dissertation employs a two-stage analysis. First, it studies the two political institutions of Roman cities: the ordo decurionum and the voting groups into which all adult male local citizens were distributed, the curiae. Moreover, it establishes as far as possible the formal procedures for erecting honorific statues. Second, both quantitative analyses and discourse analyses are applied to a catalogue of the 1080 published inscriptions of honorific statues from Africa Proconsularis. This second stage permits the comparison of the practices surrounding one important aspect of public life to the rules governing public life. The dissertation concludes by proposing that one important contributing factor to the dynamism of civic political culture in Africa Proconsularis was the intimacy of the communities. It is asserted that, despite the participation of the communities in the Roman Empire, people's most important political relationships remained within their community. The face-to-face nature of these small communities made it necessary for the magistrates and decurions to be responsive to the demands of the populus and to permit the populus the ability to initiate actions in the public realm, as long as those actions conformed to Roman standards of behaviour

Quasi-Exact Helical Cone Beam Reconstruction for Micro CT

A cone beam micro-CT system is set up to collect truncated helical cone beam data. This system includes a micro-focal X-ray source, a precision computer-controlled X-Y-Z-theta stage, and an image-intensifier coupled to a large format CCD detector. The helical scanning mode is implemented by rotating and translating the stage while keeping X-ray source and detector stationary. A chunk of bone and a mouse leg are scanned and quasi-exact reconstruction is performed using the approach proposed in J. Hu et al. (2001). This approach introduced the original idea of accessory paths with upper and lower virtual detectors having infinite axial extent. It has a filtered backprojection structure which is desirable in practice and possesses the advantages of being simple to implement and computationally efficient compared to other quasi-exact helical cone beam algorithms for the long object problem

Measuring the effect of airway pressure on pulmonary arterial diameter in the intact rat lung

To study the relationship between transpulomnary pressure (Ptp), intravascular pressure (Pv), and the pulmonary arterial tree structure, morphometric measurements of pulmonary arterial trees were made in intact lungs from Sprague-Dawley rats. Using cone beam micro-CT and techniques we developed for imaging small animal lungs, volumetric CT data were acquired for Ptp from 0 - 12 mmHg and Pv from 5 - 30 mmHg. The diameter, D (measured range approximately 0.08-2.0 mm), vs. pressure, P, relation can be described by D(P) = D(0)(1+ α P), where α is a distensibility coefficient. Unlike studies performed in larger animals, where changes in either Ptp or Pv had nearly identical effect on vessel distensibility, we found that there is only a small dependence of arterial diameter on Ptp in the rat. For example, using the above relation where P=Ptp and Pv is held constant at 12mmHg, alpha = 0.55±0.42(SE) %/mmHg, compared with when P=Pv and Ptp is held at 12mmHg, alpha = 2.59±0.17(SE) %/mmHg

Post-Acquisition Small-Animal Respiratory Gated Imaging Using Micro Cone-Beam CT

On many occasions, it is desirable to image lungs in vivo to perform a pulmonary physiology study. Since the lungs are moving, gating with respect to the ventilatory phase has to be performed in order to minimize motion artifacts. Gating can be done in real time, similar to cardiac imaging in clinical applications, however, there are technical problems that have lead us to investigate different approaches. The problems include breath-to-breath inconsistencies in tidal volume, which makes the precise detection of ventilatory phase difficult, and the relatively high ventilation rates seen in small animals (rats and mice have ventilation rates in the range of a hundred cycles per minute), which challenges the capture rate of many imaging systems (this is particularly true of our system which utilizes cone-beam geometry and a 2 dimensional detector). Instead of pre-capture ventilation gating we implemented a method of post-acquisition gating. We acquire a sequence of projections images at 30 frames per second for each of 360 viewing angles. During each capture sequence the rat undergoes multiple ventilation cycles. Using the sequence of projection images, an automated region of interest algorithm, based on integrated grayscale intensity, tracts the ventilatory phase of the lungs. In the processing of an image sequence, multiple projection images are identified at a particular phase and averaged to improve the signal-to-ratio. The resulting averaged projection images are input to a Feldkamp cone-beam algorithm reconstruction algorithm in order to obtain isotropic image volumes. Minimal motion artifact data sets improve qualitative and quantitative analysis techniques useful in physiologic studies of pulmonary structure and function