Computed tomography (CT) is an imaging technique that uses x-ray and computers to create cross-sectional images of structures. Stereotactic CT-guided biopsy is defined as the use of a stable apparatus to direct and perform tissue biopsies under CT guidance. For the brain, the principal advantage of stereotactic CT guidance over other biopsy techniques is its high accuracy in getting a sample from deep-seated lesions. The objectives of this study were to create an inexpensive CT-guided stereotactic device adaptable to different canine head sizes and to test the accuracy of the device for needle placement in deep-seated brain targets. A biopsy device was created that consists of four main components: a CT table fixation device, a head fixture, a needle fixture , and motion control system. Accuracy was tested using 16 head and neck specimens obtained from dogs euthanitized for reasons unrelated to the brain. Deep-seated (caudate nucleus and pituitary gland) targets were identified on CT. After a 5 mm craniotomy, the biopsy needle, with CT monitoring, was progressively introduced into the target. The final needle track distance was measured on CT. The brain was removed and sliced to verify placement of the needle tip within the target and to measure the actual needle track distance. The total cost of materials and construction for the stereotactic CT-guided biopsy device was $785.00. No difference in needle placement accuracy was identified for caudate and pituitary targets. Based on assessments by 2 independent observers, the caudate target was successfully hit 75% of the time. Pituitary targets were successfully hit 96.8 % of the time. Actual needle track lengths were an average of 3.2 mm less that the track length measured on CT. This difference was most likely due to incomplete staining of the bevel part of the needle track on gross specimens. / Master of Science

Existing microstructure parameters of computed tomography (CT) are able to compute architectural properties of the bone from ex-situ and ex-vivo scans while they are highly affected by the issues of noise and low resolution when applied to clinical in-vivo imaging. A set of improvements of the standard workflow for the quantitative computation of micro-structure from clinical in-vivo scans is proposed in this thesis. Robust methods are proposed (1) for the calibration of density values, (2) the binarization into bone and marrow phase, (3) fuzzy skeletonization and (4) the calibration of the CT volumes in particular for the computation of micro-structural parameters. Furthermore, novel algorithms for the computation of rod-volume fraction with 3D rose diagrams and fractal approaches are proposed and the application of local texture operators to diffusion tensor imaging is proposed. Finally an existing computer program for the application in radiology departments, Structural Insight, was improved and largely extended. In particular the methods of the microstructural calibration, the fractal and the texture operators showed significant improvements of accuracy and precision for the prediction of fracture risk and the quantitative assessment of the progress of Alzheimer's disease, in comparison to existing state-of-the art methods. The methods were tested on artificial and in-vitro data and as well on real-world computed tomography and magnetic resonance imaging (MRI) studies. The proposed novel methods improve the computation of bone characteristics from in-vivo CT and MRI in particular if the methods are combined with each other. In consequence, this allows to assess more information from existing data or to conduct studies with less ray exposure and regarding the MRI method in shorter time than nowadays required.

The vestibular system consists of several organs that contribute to ones sense of balance. One set of organs, otoconial organs, have been shown to respond to linear acceleration (1949). Hair bundles (and hair cells), which are the mechano-electric transducers found within otoconial organs, respond to displacement of the overlying otoconial membrane (OM). Structure, position and orientation of the OM within the head may influence the stimulus of hair bundles by changing the deformation characteristics of the OM. Therefore, studying the deformation characteristics of the OM with finite element models presents a unique advantage: the ability to study how different variables may influence the deformation of the OM. Previous OM models have ignored complicated OM geometry in favor of single degree of freedom (De Vries 1951)or distributed parameter models (Grant et al. 1984; Grant and Cotton 1990; Grant et al. 1994). Additionally, OMs have been modeled considering three dimensional geometry (Benser et al. 1993; Kondrachuk 2000; 2001a), however OM layer thicknesses were assumed to be constant. Further, little research has investigated the effect of position and orientation of otoconial organs on the deformation of the OM (Curthoys et al. 1999), due to natural movement of the head. The effect of structure, position and orientation of the utricle of a red ear slider turtle on the stimulation of hair bundles in the OM is investigated here. Using confocal images, a finite element model of the utricle OM is constructed considering its full 3D geometry and varying OM layer thickness. How specific geometric variables, which are missing from other OM models, effect the deformation of the utricle OM is studied. Next, since hair bundles are part of the structure of the OM, their contribution to the deformation of the utricular OM is quantified. Then, using computed tomography of a turtle head and high speed video of turtle feeding strikes, acceleration at the utricle during natural motion is estimated. Finally, the effects of orientation of the utricle in the head on the stimulus of hair bundles within the organ is investigated. In summary, a model and methods are developed through which deformation of the turtle utricle OM through natural movements of the head may be studied. Variables that may contribute to utricle OM deformation are investigated. Utricle OM geometry, hair bundles, position and orientation all play a role in utricle OM deflection and therefore hair bundle stimulus. Their effects are quantified and their roles are discussed in this dissertation. / Ph. D.

Computed tomography (CT) is becoming more available as a diagnostic tool in the evaluation of the equine skull and brain. Objectives of this study were: 1) refine a CT protocol for evaluating the equine pituitary gland, 2.) define the CT anatomy of the pituitary region, 3.) determine a set of normal values for the pituitary dimensions (length, width, height, volume and weight), 4.) refine CT techniques for measuring pituitary size. Horses were scanned using 10x10mm, 10x5mm, 4x4mm and 4x2mm slice thickness and interval combinations. The pituitary glands were removed immediately after CT and gross measurements were performed. CT measurements were compared with gross pituitary measurements using analysis of variance (ANOVA) in a randomized block design. Accuracy percentages were also calculated using gross measurements as the known value. Mean dimensions of the histologically normal pituitary glands were: length 21.07mm, width 21.62mm, height 9.78mm and volume 2.66cm³. The weights ranged from 1.7g to 3.4g with a mean of 2.6g. Computed tomographic measurement analysis demonstrated that the 10mm slices were the most accurate way to estimate the length of the gland. The 4mm slices yielded the highest accuracy values for width, height and volume of the pituitary gland. The volume was underestimated by all interval and slice thickness combinations performed by CT. No evidence of an overlap effect was identified for any of the dimensions. Our findings indicated that contrast-enhanced CT is an accurate technique for estimating pituitary linear dimensions. Three-dimensional CT volumetry may not be an accurate method for estimating pituitary volume. / Master of Science

Reversible hyperosmotic blood-brain barrier disruption (BBBD) has been used in pharmaceutical research as well as human medicine to enhance drug delivery across the blood-brain barrier. However a technique for repeatable BBBD in the canine has not been described. This study describes a repeatable technique for BBBD in the dog and evaluates the clinical and morphological effects of BBBD. Using fluoroscopic guidance, an arterial catheter was directed into the internal carotid artery via the femoral artery in ten dogs. BBBD was achieved in 5 dogs using 25% mannitol while 5 control dogs received only saline. Following recovery, dogs were monitored for clinical signs before a second, non-survival procedure was performed 2-3 weeks later. BBBD was estimated using CT densitometry as well as Evan's blue staining on post-mortem exam. Histopathological evaluation of the brain was performed on all dogs. Seven dogs completed the study. Two treatment dogs were lost after the first infusion with deteriorating neurologic function attributed to CNS edema and increased intracranial pressure. One control dog was lost due to vessel wall damage during catheterization. The remaining dogs exhibited only transient neurologic, ocular, and vasculature injury. Successful BBBD was demonstrated in all treatment dogs as evidenced by CT and Evan's blue staining. Histopathological evaluation revealed multifocal areas of infarction in all dogs indicating refinement of the technique is needed. This study shows that repeatable disruption the BBB in the dog is possible and opens the way for further investigations of BBBD using the dog as a model. / Master of Science

No / Computed tomography (CT) arthrography of the shoulder is an imaging modality of great diagnostic accuracy with regard to glenohumeral instability and in particular labral lesions. Interpretation of the scans is made difficult by the frequent occurrence of normal anatomic variants and the complexity of injuries to the bone and soft tissues. We selected a continuous sample of 50 CT arthrograms of the shoulder and they were reported by two consultant musculoskeletal radiologists. The results were collated and analysed for the level of agreement. Hill¿Sachs showed Kappa (K) statistic to be 0.37 (fair agreement), soft tissue Bankart 0.32 (fair agreement), bony Bankart 0.61 (substantial agreement), anterior capsular laxity 0.41 (moderate agreement) and glenohumeral osteoarthritis 0.20 (slight agreement). All the results were significant with a p value of <0.05. Nine (18%) of the 50 scans were in complete agreement. The results demonstrate that there can be considerable interobserver variation (IOV) in the reports of a CT arthrogram of a shoulder. They highlight the potential difficulties in reporting such images and suggests ways in which the report could be more focussed to provide a clinically reliable report and one which matches the surgical findings accurately.

Megavoltage computed tomography (MVCT) and megavoltage cone beam computed tomography can be used for visualizing anatomical structures prior to radiation therapy treatments to assist in patient setup and target localization. These systems provide images using the same beam used for patient treatment, however their image contrast is limited by the low detective quantum efficiency (DQE) of the detectors currently available. By using higher DQE thick, segmented cadmium tungstate detectors we can improve the system contrast. This in turn would permit enhanced soft tissue visualization, allowing MVCT to be more useful. This thesis describes the evaluation of a prototype MVCT system that uses thick, segmented detectors. The system was found to be able to easily visualize a 15 mm diameter 1.5% contrast target with 2 cGy of radiation dose delivered. This system could become the basis for improved commercial MVCT systems. / Medical Physics

No description available.

Dose management in CT is an increasingly important issue as the number of CT scans per capita continues to rise. One proposed approach for enhanced dose management is to allow the spatial pattern of x-ray fluence delivered to the patient to change dynamically as the x-ray tube rotates about the patient. The changes in incident fluence could be guided using a patient model and optimization method in order to deliver user-defined image quality criteria while minimizing dose. This approach is referred to as fluence field modulated CT (FFMCT). In this work, a framework and optimization method was developed for evaluating the dose and image quality benefits of FFMCT, both in simulated and experimental data. Modulated fluence profiles were optimized for different objects and image quality criteria using a simulated annealing algorithm. Analysis involved comparing predicted image quality maps and dose outcomes to those using conventional methods. Results indicated that image quality distributions using FFMCT agreed better with prescribed image qualities than conventional techniques allow. Dose reductions ranged depending on the task and object of interest. Simulation studies using a simulated anthropomorphic phantom of the chest suggest an average dose reduction of at least 20% compared to conventional techniques is possible, where local dose reductions may be greater than 60%. Across different imaging tasks and objects, integral dose reductions ranged from 20-50% when compared to a conventional bowtie filter. The results of this study suggest that given a suitable collimator approach, FFMCT could reap significant benefits in terms of reducing dose and optimizing image quality. Though the tradeoff between image quality and imaging dose may not be eliminated, it may be better managed using an FFMCT approach.

No description available.