The removal of scattered radiation is recognised as one of the major goals to be achieved in SPECT. In this work three scatter removal techniques were investigated. These were dual window scatter subtraction, deconvolution using a Wiener filter and energy weighted acquisition (EWA) using a weighted acquisition module (WAM). In addition to this, the effects of simple background subtraction on SPECT images was also investigated. The techniques were investigated in both a semi-quantitative manner, in terms of the effects of each technique on the cold lesion contrast and image mottle, and qualitatively, in terms of the ability of observers to perform a detection task. This was done using Relative Operating Characteristic (ROC) experiments. Each technique is investigated individually to discover the parameters needed to optimise performance. The results showed that the optimum parameters for each scatter reduction technique was dependent on the measure of image quality used for optimisation and showed that all of the techniques investigated produced better results than those produced using the standard 20&'37 photopeak acquisition approach, however, in general no significant difference could be found between the techniques. The image noise produced by each technique was also evaluated by calculating the noise power spectra (NPS) produced by each technique. The calculated NPS showed the spatial content of the noise produced by each technique was different for each scatter reduction technique. The results in this work showed that empirically defined measures of image quality are poor predictors of observer performance.

Vertebral body deformities resulting from osteoporosis are commonly observed in lateral spine radiographs. Clinically, these deformities are judged rather subjectively, both in their classification and in the assessment of the extent of deformity. In order to objectify clinical observation, morphometric measurements are a means for classifying and quantifying the presence and extent of vertebral body deformities. Drawing on the morphometric systems of Minne et al. (1988) and Smith-Bindman et al. (1991), we propose a total vertebral deformity index (TVDI) which provides a single, clinically meaningful number indicative of the extent of deformity in a vertebral column. Each of the three deformity types (wedge, biconcave, and compression) is classified and measured independently, using ratios relating measurements of anterior, mid, and posterior heights, and inferior width. Expected measurements are determined for each vertebral level, and the sum of the deviations from the measured to the expected values generates a vertebral deformity index. This proposed index addresses issues in vertebral body morphometry, including vertebral level specificity, body size differences, multiple compression effects, and multiple deformity types. Inherent in the practical use of morphometric quantification are issues of accuracy and reproducibility of the measurements, .and of the time involved in making these measurements. Digital image processing algorithms are developed to attempt automated detection and measurement of the vertebral body boundary, using Computed Radiography images of the lateral spine. Three different methods yield varying results. In addition to the characteristics of lateral spine images (such as high intensity vertebral ridges) which are used to advantage by the algorithms, all three methods must deal with problematic anatomical characteristics such as the presence of the high intensity ribs and ilium. The first method is a series of image enhancement and thresholding steps applied to each vertebra, in order to delineate its vertebral boundary in a hi-level image. This method is fairly effective, but suffers from its dependence on thresholding. The second method uses the cross-correlation measure to detect the vertebrae, given a starting vertebra, and then uses edge-gradient tracking to trace the vertebral boundary. Results of this method are promising. There remains a weakness in the cross-correlation detector, which fails to accurately locate vertebrae that are further away from the starting vertebra. The third method is an active contouring technique called Snakes, in which the vertebral boundary is represented by a deformable spline which seeks to minimize an energy functional consisting of curvature, continuity, and image energy terms. Present results display minimal convergence onto the vertebral boundaries. Future work should refine the customization of the energy functional to produce better results. At present, all three methods require some kind of user interaction. Further development may prove fruitful in reducing user interaction to achieve a truly automated system. / Thesis / Master of Engineering (ME)

No description available.

Die moderne multimodale Computertomografie (CT) beinhaltet das Schichtröntgen des Gehirns (native CT), die Darstellung der hirnversorgenden Arterien (CT-Angiografie) und die Messung der Hirndurchblutung (CT-Perfusion). Mit Hilfe dieser Untersuchungstechnik kann bei Patienten mit akutem Schlaganfall rasch die Ursache der plötzlich eingesetzten Symptome beleuchtet werden: Liegt eine Gefäßobstruktion oder eine Blutung in das Gehirn vor? Wie ausgedehnt ist die Durchblutungsstörung und wie viel Hirngewebe ist bereits beschädigt bzw. vom Untergang bedroht? Anhand dieser Informationen kann sofort eine spezifische Therapie eingeleitet werden, die es ermöglicht, die Patienten vor dauerhafter schwerer Behinderung zu bewahren bzw. die Prognose schon früh abzuschätzen. / Computed tomography (CT), including CT perfusion imaging and CT angiography, has the capacity to assess stroke pathology on a functional and morphological level and can thus provide important information about patients with acute stroke. It excludes brain haemorrhage, assesses the extent of perfusion deficit, the extent of ischemic damage, and the site and type of arterial obstruction. Ischemic brain tissue below the blood flow level of structural integrity takes up water immediately and causes a decrease in x-ray attenuation. Computed tomography thus has the specific advantage of being able to identify the brain tissue which is irreversibly injured. If CT can exclude major ischemic damage in acute stroke patients, reperfusion strategies may rescue brain function and prevent disability.

Diss. (sammanfattning) Göteborg : Göteborgs universitet, 2009. / Härtill 5 uppsatser.

No description available.

A New Zealand Qualified Health Physicist (QHP) is required, under the Radiation Protection Act of 1965 and the Radiation Protection Regulations 1982, to perform auditing compliance tests on x-ray equipment at regular intervals to ensure that this equipment conforms to the Code of Safe Practice with the use of x-rays. The protocol for these tests must be approved by the National Radiation Laboratory (NRL). One of these test protocols sets out the requirements for the functionality testing of the x-ray machine Automatic Exposure Control (AEC). The current NRL protocol for AEC testing is based on the radiographic film environment (NRL C5 1994). This protocol was tested to determine its applicability to the digital computed radiography (CR) imaging systems which are replacing screen-film systems. To begin this process a comparison of the different exposure indexes for each image medium was required. This proved to be achievable using a system of exposure dose comparison. The AEC test process for both image modalities follows identical requirements but differ slightly in the test methods used to achieve these. The most significant finding throughout this stage was not the differences between protocols but was the requirement to achieve consistent exposure index values over the clinical kVp range for each image medium. This requirement, applicable to any x-ray image medium, became the focus of this thesis. The thesis has explored through experimentation, the effect of optimisation of AEC kVp compensation for the variable kVp response of an image medium, on image consistency. At Christchurch Hospital where this investigation took place the work has shown that the performance of AEC devices can be optimised to improve image consistency, indicated by a more consistent exposure index over the clinical kVp range. The optimisation process also achieves a more consistent dose response to the image plate. A dose variation of 8.3% from the average was achieved compared to 26% in the unoptimised version. No clinically significant changes to image quality were apparent in test images. Under these conditions it was found that AEC functionality could be assessed solely by the measurement of AEC dose to the image plate (IP). Use of this test method provides quantifiable time management benefits for the Medical Physicist and for the radiology departments in which they work. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1369625 / Thesis (M.Sc.(Med.Physics)) - University of Adelaide, School of Chemistry and Physics, 2009

Diss. (sammanfattning) Uppsala : Univ., 2003. / Härtill 5 uppsatser.

Diss. (sammanfattning) Uppsala : Univ., 2001. / Härtill 6 uppsatser.

Cachexia occurs commonly and is a significant cause of morbidity and up to 20% mortality in patients with cancer. Loss of muscle mass occurs as part of the cachexia wasting process and low muscle mass is a key element of the most recent consensus cachexia definition. Measuring muscle mass and changes in skeletal muscle is important to phenotype cachectic individuals and to monitor response to anti-cachectic treatments. This thesis investigates minimally invasive or burdensome methods of measuring muscle mass and muscle protein kinetics for use in a clinical or research setting. Quantification of muscle area on routine diagnostic cross-sectional imaging offers a novel and relatively non-invasive method of assessing both regional (and by extrapolation) whole body muscle mass. The need for such a direct measurement of muscle mass was demonstrated by showing that simple anthropometric formulae are unable to predict muscularity accurately (within 25%) when compared with estimates derived from patients diagnostic CT scans. It may be that qualitative changes in muscle may be more sensitive indices of the wasting process rather than qualitative change. Myosteatosis (infiltration of muscle by fat) is known to occur in both cachexia and age related sarcopenia and can be quantified using the Hounsfield spectrum observed on routine diagnostic CT scans. However, not all patients undergo routine CT scanning and there is a need for a biomarker derived from urine or blood. Consequently, cross sectional imaging was used to phenotype patients in a proteomic analysis of urine with the aim of identifying protein or peptide biomarkers associated with myosteatosis in cancer cachexia. A biomarker model for myosteatosis was developed with good sensitivity (97%) but poor specificity (71%). Many of the potential protein / peptide markers identified had poor associations with known mechanisms of muscle wasting and further study of the identified peptides in an extended cohort would help determine the validity of the present findings. However, two proteins with potential roles in muscle repair or neuromuscular function (Agarin and Cathepsin C) were identified and these may warrant targeted investigation with evaluation against sequential measures of muscle mass to determine their value in defining muscle loss over time. As different regional measures of muscularity are available, trunk (L3 CT) and limb muscle (quadriceps MRI) cross sectional measurements were compared with functional assessments to determine the optimal site for measurement. Neither measure proved superior to the other but appeared to reflect different aspects of function. Quadriceps muscle area correlated with quadriceps strength and power whilst truncal muscle area correlated more with complex movements such as the timed-up-and-go test. Changes in regional muscle area in patients with upper gastrointestinal cancer were assessed by upper and lower limb MRI before and after surgery and by L3 CT cross sectional area before and after neo-adjuvant chemotherapy. No change in limb muscularity was seen at 220 days post operatively compared with pre-op measurements. During neo-adjuvant chemotherapy a significant loss of truncal muscle occurred in the absence of significant weight loss suggesting that sequential cross sectional imaging is capable of detecting changes in body composition that may not be apparent clinically. Whilst sequential scans may document changes in muscularity, they do not describe the underlying levels of muscle synthesis or degradation that may regulate muscle volume. The final section of this thesis describes the development of a novel tracer method to measure skeletal muscle synthesis and its application in a study of patients with cancer and healthy volunteers. This novel method was able to measure skeletal muscle fractional synthetic rate (FSR) over a longer time-period than previous methods (weeks rather than hours) and reduced the burden on the patient by the use of a single oral tracer dose and single muscle biopsy. Comparison of synthesis rates in quadriceps and rectus abdominis showed higher rates in quadriceps, 0.067% per hour vs 0.058% per hour respectively. Despite a net loss of muscle as measured by serial CT scans, skeletal muscle FSR appeared to be marginally increased in weight losing patients with cancer compared with weight stable patients and healthy controls. When FSR was combined with measures of muscle mass it was demonstrated that only small differences between synthesis and degradation are required to see the levels of muscle wasting seen in patients with cancer. In summary, routine cross sectional imaging provides a useful and unique measure of muscularity that is associated with function in patients with cancer Sequential scans can provide additional information about changes in body composition even in the absence of weight loss. There are significant regional variations in both muscle wasting and skeletal muscle fractional synthetic rate. The combination of sequential estimates of muscle mass from diagnostic CT scans along with estimates of FSR allow assessment of the contribution of altered synthesis and degradation to muscle loss. In patients with upper GI cancer it would appear that increased degradation may be more important that altered synthesis. The relative change in either process to account for absolute loss of muscle mass is small. Such findings have implications for the targeted therapy of muscle wasting in cancer patients.