The permeability of hot mix asphalt (HMA) is of special interest to engineers and researchers due to the effects that water has on asphalt pavement performance. Significant research has been done to study HMA permeability. However, most of the studies primarily focused on relating permeability to the average percent air voids in the mix. Such relationships cannot predict permeability accurately due to the different distributions of air void structures at a given average percent of air voids. Air void distribution is a function of many factors such as mix design, compaction method, and aggregate properties. Recent advances in X-ray computed tomography and image analysis techniques offer a unique opportunity to better quantify the air void structure and, consequently, predict HMA permeability. This study is focused on portraying permeability as a function of air void size distribution by using a probabilistic approach that was previously developed by Garcia Bengochea for soils. This approach expresses permeability as a function of the probability density function (pdf) of the air void size distribution. Equations are derived in this thesis to describe this relationship for laboratory specimens compacted using the linear kneading compactor (LKC) and Superave^TM gyratory compactor (SGC) as well as for field cores (labeled as MS). A good correlation exists between permeability and the pdf of the air voids that formed the flow paths (i.e. connected voids). The relationship between moisture damage, air void structure, and cohesive and adhesive bond energy is also investigated in this study. Moisture damage is evaluated by monitoring changes in mechanical properties due to moisture conditioning. The influence of air void structure on pore pressure is studied using a recently developed program at Texas A&M University that simulates fluid flow and pore pressure in a porous medium. The surface free energy of the aggregates and asphalt are calculated from laboratory measurements using the Universal Sorption Device (USD) and the Wilhelmy Plate method, respectively, in order to test the compatibility of the aggregates with the asphalt in the presence of water.

Seizures are thought to arise primarily from the cerebral cortex. However, the propagation and behavioral manifestations of seizures involve a network of both cortical and subcortical structures. The medial thalamus and upper brainstem reticular formation are crucial areas for the maintenance of normal consciousness. Bilateral involvement of these structures may be responsible for loss of consciousness during partial seizures. Therefore, we sought to investigate the role of the medial thalamus and brainstem in seizures. We performed SPECT ictal-interictal difference imaging co-registered with high-resolution MRI scans to localize regions of cerebral blood flow changes in patients undergoing inpatient monitoring for epilepsy. Ictal-interictal SPECT scans from 43 seizures in 40 patients were analyzed. The medial thalami showed SPECT difference imaging changes of >20% in 18 patients. Of patients with medial thalamic changes, the majority (13 of 18) had seizure onset in the temporal lobe, while only 1 had confirmed onset in extratemporal structures, and the remainder were non-localized. In contrast, in the 22 patients without >20% SPECT changes in the medial thalami, 6 had extratemporal onset, 6 had temporal onset, and the remainder were non-localized. In patients with temporal lobe seizures, the side of greater medial thalamic and brainstem reticular formation involvement was strongly related to SPECT injection timing such that there was a sequential pattern of ipsilateral followed by contralateral changes. Brainstem structures showed >20% SPECT changes in 27 of 43 seizures with no clear relation to temporal or extratemporal onset. We conclude that the medial thalamus is preferentially involved in seizures arising from the temporal lobes, possibly reflecting the strong connections between limbic temporal structures and the medial thalamus. Sequential involvement of ipsilateral followed by contralateral structures in the medial thalamus and upper brainstem may explain how seizures produce peri-ictal loss of consciousness despite incomplete involvement of the cerebral cortex.

Objective: To evaluate three-dimensional position of the TMJ condyle within the glenoid fossa in different types of skeletal patterns. Materials and methods: Ninety CBCT images were consecutively selected and divided into skeletal class I, class II and class III. The images were analyzed locating landmarks in the different areas of the condyle and glenoid fossa. All landmarks presented acceptable reliability. The mean results were compared using ANOVA and Bonferroni post-hoc test (p < 0.05). Results: There was a tendency for the anterior joint space to be smaller than the posterior joint space. Statistical analysis, however, evidenced no significant differences between the anterior, superior and posterior joint spaces and the different skeletal patterns or between sides. Conclusion: There was non-concentricity of the condyle for all the groups studied, and no particular direction was statistically significantly favored. It is unclear whether the differences found would be clinically significant, considering anatomical individual variations.

Coronary arteries are the blood vessels supplying oxygen-rich blood to the heart muscles. Coronary artery calcium (CAC), which is the total amount of calcium deposited in these arteries, indicates the presence or the future risk of coronary artery diseases. Quantification of CAC is done by using computed tomography (CT) scan which uses attenuation of x-ray by different tissues in the body to generate three-dimensional images. Calcium can be easily spotted in the CT images because of its higher opacity to x-ray compared to that of the surrounding tissue. However, the arteries cannot be identified easily in the CT images. Therefore, a second scan is done after injecting a patient with an x-ray opaque dye known as contrast material which makes different chambers of the heart and the coronary arteries visible in the CT scan. This procedure is known as computed tomography angiography (CTA) and is performed to assess the morphology of the arteries in order to rule out any blockage in the arteries. The CT scan done without the use of contrast material (non-contrast-enhanced CT) can be eliminated if the calcium can be quantified accurately from the CTA images. However, identification of calcium in CTA images is difficult because of the proximity of the calcium and the contrast material and their overlapping intensity range. In this dissertation first we compare the calcium quantification by using a state-of-the-art non-contrast-enhanced CT scan method to conventional methods suggesting optimal quantification parameters. Then we develop methods to accurately quantify calcium from the CTA images. The methods include novel algorithms for extracting centerline of an artery, calculating the threshold of calcium adaptively based on the intensity of contrast along the artery, calculating the amount of calcium in mixed intensity range, and segmenting the artery and the outer wall. The accuracy of the calcium quantification from CTA by using our methods is higher than the non-contrast-enhanced CT thus potentially eliminating the need of the non-contrast-enhanced CT scan. The implications are that the total time required for the CT scan procedure, and the patient's exposure to x-ray radiation are reduced.

In computed tomography (CT) there are many situations where reconstruction may need to be performed with sparse-view data. In sparse-view CT imaging, strong streak artifacts may appear in conventionally reconstructed images due to the limited sampling rate, compromising image quality. Compressed sensing (CS) algorithm has shown potential to accurately recover images from highly undersampled data. In the past few years, total variation (TV)-base compressed sensing algorithms have been proposed to suppress the streak artifact in CT image reconstruction. In this paper, we formulate the problem of CT imaging under transform sparsity and sparse-view constraints, and propose a novel compressed sensing-based algorithm for CT image reconstruction from few-view data, in which we simultaneously minimize the ℓ1 norm, total variation and a least square measure. The main feature of our algorithm is the use of two sparsity transforms: discrete wavelet transform and discrete gradient transform, both of which are proven to be powerful sparsity transforms. Experiments with simulated and real projections were performed to evaluate and validate the proposed algorithm. The reconstructions using the proposed approach have less streak artifacts and reconstruction errors than other conventional methods.

Non-invasive estimates of bone quality are of great interest as they could potentially improve the diagnosis and treatments for bone disorders, such as osteoporosis, and could aid in preoperative planning of surgical interventions, improving patient outcomes in orthopaedic trauma. Quantitative computed tomography (QCT) is currently being investigated as a method of estimating structural bone mineral content (sBMC) and, thus, bone quality. However, the reported correlations between QCT and sBMC have been variable and the relationships reported between sBMC and the apparent elastic modulus (E*) of bone have been even more variable. A series of investigations are presented, relating QCT, sBMC, apparent density and the E* of bone. These studies were performed with the ultimate objective of determining the appropriateness of QCT as a predictor of the E* of bone and whether the E* of bone could be predicted from information regarding the sBMC and apparent density. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2008-01-31 22:00:08.77 / This work was funded by the Canadian Institutes of Health Research.

The complex dose distributions delivered by modern, conformal radiation therapy techniques present a considerable challenge in dose verification. Traditional measurement tools are difficult and laborious to use, since complete verification requires that the doses be determined in three dimensions (3D). The difficulty is further complicated by a required target accuracy of ± 5% for the dose delivery. Gel dosimetry is an attractive option for realizing a tissue-equivalent, 3D dose verification tool with high resolution readout capabilities. However, much important work remains to be completed prior to its acceptance in the clinic. The careful development of easily accessible, fast optical readout tools such as cone beam optical computed tomography (CT) in combination with stable and reliable low-toxicity gel dosimeters is one key step in this process. In this thesis, the performance capabilities and limitations of the two main classes of cone beam optical CT-based absorbing and scattering gel dosimetry are characterized, and their measurement improved through careful matching of dosimeter and scanner performance. These systems are then applied to the evaluation of clinically relevant complex dose distributions. Three-dimensional quality assurance assessments of complex treatment plan dose distributions are shown to be feasible using an optically absorbing Fricke-xylenol-orange-gelatin-based gel dosimeter. Better than 95% voxel agreement is achieved between the plan and the delivery, using 3% dose difference and 3 mm spatial distance-to-agreement gamma function comparison criteria. Small field dose delivery evaluations are demonstrated to be viable using an optically scattering N-isopropylacrylamide (NIPAM)-based polymer gel, with the same comparison criteria. Full treatment process quality assurance is also possible using a NIPAM dosimeter in-phantom, but is limited in its accuracy due to the inherent difficulty of managing the effects of stray light pertubation in the optical attenuation-to-dose calibration. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2010-09-02 15:01:48.501

Objective and accurate surface measurements are important in many clinical disciplines. Non-irradiating and low cost alternatives are available but validation of these measurement tools for clinical application is variable and sparse. This thesis presents a three dimensional (3D) surface measurement method validated by gold standard Computed Tomography (CT). Forty-one 3D surface data sets were acquired by two modalities, a laser scanner and a binocular camera. The binocular camera was tested with three different texture modifiers that increased the colour variability of the imaged surface. A surface area calculation algorithm was created to process the data sets. Relative differences were calculated for each area measurement with respect to its corresponding CT measurement. The laser scanner data sets were affected by movement and specular reflection artefacts. The measurements were statistically equivalent to CT if less than 20% error were considered acceptable. The binocular camera with the slide projected texture modifier was shown to be statistically equivalent to CT gold standard with less than 5% error (p < 0.0005). The surface area measurement method can easily be expanded and customized. By following the protocol outlined by the example in this work, researchers and clinicians would also be able to objectively asses other vision systems' performance and suitability. / Thesis (Master, Computing) -- Queen's University, 2012-01-10 11:37:50.374

No description available.

No description available.