| dc.description.abstract | On a general level it is known that several hormones have effects on both body composition and risk factors related to morbidity and mortality. The aims of this thesis were to examine changes in body composition during treatment of patients with Cushing's syndrome, acromegaly, growth hormone (GH) deficiency and hyperthyroidism (paper I-IV). Other aims were to examine conditions for dose reduction when using CT for body composition purposes and to compare tissue volumes obtained with CT and MRI (paper V-VI).A 22 scan CT technique was used to determine the areas of subcutaneous and visceral adipose tissue (AT), muscle plus skin (M) and visceral organs (V) (I-III). Corresponding tissue volumes were calculated from tissue areas and the distances between scans. Previous studies have demonstrated a high reproducibility and validity with this technique. In paper IV tissue areas were determined in 4 CT scans and body composition was also evaluated with dual energy X-ray absorptiometry (DXA). Paper V utilizes measurements in vivo and on phantoms with two different CT scanners. Uncertainties at different radiation doses were analysed. Comparisons were made with simulated and theoretical data. In paper VI, MRI imaging was performed with a spoiled gradient echo technique using the lower human leg as a simple model and CT as a reference technique. Various histogram techniques were compared with a commercially available MRI 3D program.The increased total and visceral AT in patients with Cushing's syndrome was reduced after treatment (I). Similarly, abdominal subcutaneous AT and, in particular, visceral AT were reduced during treatment of adult onset GH deficient patients, while skeletal muscles were increased (III). The opposite changes were seen during treatment of patients with acromegaly (II). During treatment of patients with hyperthyroidism skeletal muscles and visceral AT had almost recovered after 3 months while subcutaneous AT was unchanged. After 12 months of euthyroidism subcutaneous AT was also increased (IV). If the radiation dose is reduced the image noise is increased. It is shown that AT and msucle tissue area determination with CT can tolerate up to 40 HU of image noise. This corresponds to a dose reduction of at least one order of magnitude but an area error of less than 5 % of total area. The effective dose in this case was 13.5µSv per trunk slice (paper V). Study VI demonstrated that MRI values of total lower leg volume was in agreement with CT measurements when using histogram techniques. As compared to CT, MRI overestimated AT slightly and muscles markedly while bone was several-fold underestimated. If joint regions were excluded agreement was achieved between CT and MRI with respect to AT. The operator influenced 3D volume rendering technique underestimated muscle as well as bone markedly.Cortisol increases total and visceral AT while high concentrations of thyroxin decreases AT as well as muscles. GH has marked and discordant effects on muscles (increase) and adipose tissue (decrease) and also influences the adipose tissue distribution (visceral AT reduced). Thus, from a metabolic point of view it seems warranted to avoid low GH levels and high cortisol levels. The early replenishment of visceral AT on the expense of subcutaneous AT during treatment of hyperthyroidism may have a biological message which is currently difficult to interpret. The CT technology permits considerable reductions of radiation dose when used for body composition purposes and perhaps also when utilized for other applications. MRI needs further methodological development until it can be used for multicompartmentalisation of the human body. | en |
