In brachytherapy, radiation therapy is performed by placing the radiation source into or very close to the tumour. When calculating the absorbed dose, water is often used as the radiation transport and dose scoring medium for soft tissues and this leads to inaccuracies. The iterative reconstruction algorithm DIRA is under development at the Center for Medical Imaging Science and Visualization, Linköping University. DIRA uses dual-energy CT to decompose tissues into different doublets and triplets of base components for a better absorbed dose estimation. To accurately determine mass fractions of these base components for different tissues, the tissues needs to be identified in the image. The aims of this master thesis are: (i) Find an automated segmentation algorithm in CT that best segments the male pelvis. (ii) Implement a segmentation algorithm that can be used in DIRA. (iii) Implement a fully automatic segmentation algorithm. Seven segmentation methods were tested in Matlab using images obtained from Linköping University Hospital. The methods were: active contours, atlas based registration, graph cuts, level set, region growing, thresholding and watershed. Four segmentation algorithms were selected for further analysis: phase based atlas registration, region growing, thresholding and active contours without edges. The four algorithms were combined and supplemented with other image analysis methods to form a fully automated segmentation algorithm that was implemented in DIRA. The newly developed algorithm (named MK2014) was sufficiently stable for pelvic image segmentation with a mean computational time of 45.3 s and a mean Dice similarity coefficient of 0.925 per 512×512 image. The performance of MK2014 tested on a simplified anthropomorphic phantom in DIRA gave promising result. Additional tests with more realistic phantoms are needed to confirm the general applicability of MK2014 in DIRA.

Automatic segmentation of human organs allows more accurate calculation of organ doses in radiationtreatment planning, as it adds prior information about the material composition of imaged tissues. For instance, the separation of tissues into bone, adipose tissue and remaining soft tissues allows to use tabulated material compositions of those tissues. This approximation is not perfect because of variability of tissue composition among patients, but is still better than no approximation at all. Another use for automated tissue segmentationis in model based iterative reconstruction algorithms. An example of such an algorithm is DIRA, which is developed at the Medical Radiation Physics and the Center for Medical Imaging Science and Visualization(CMIV) at Linköpings University. DIRA uses dual-energy computed tomography (DECT) data to decompose patient tissues into two or three base components. So far DIRA has used the MK2014 algorithm which segments human pelvis into bones, adipose tissue, gluteus maximus muscles and the prostate. One problem was that MK2014 was limited to 2D and it was not very robust. Aim: The aim of this thesis work was to extend the MK2014 to 3D as well as to improve it. The task was structured to the following activities: selection of suitable segmentation algorithms, evaluation of their results and combining of those to an automated segmentation algorithm. Of special interest was image registration usingthe Morphon. Methods: Several different algorithms were tested.  For instance: Otsu's method followed by threshold segmentation; histogram matching followed by threshold segmentation, region growing and hole-filling; affine phase-based registration and the Morphon. The best-performing algorithms were combined into the newly developed JJ2016. Results: For the segmentation of adipose tissue and the bones in the eight investigated data sets, the JJ2016 algorithm gave better results than the MK2014. The better results of the JJ2016 were achieved by: (i) a new segmentation algorithm for adipose tissue which was not affected by the amount of air surrounding the patient and segmented smaller regions of adipose tissue and (ii) a new filling algorithm for connecting segments of compact bone. The JJ2016 algorithm also estimates a likely position for the prostate and the rectum by combining linear and non-linear phase-based registration for atlas based segmentation. The estimated position (center point) was in most cases close to the true position of the organs. Several deficiencies of the MK2014 algorithm were removed but the improved version (MK2014v2) did not perform as well as the JJ2016. Conclusions: JJ2016 performed well for all data sets. The JJ2016 algorithm is usable for the intended application, but is (without further improvements) too slow for interactive usage. Additionally, a validation of the algorithm for clinical use should be performed on a larger number of data sets, covering the variability of patients in shape and size.

Thesis (MSc)-- University of Stellenbosch, 1954 / Published in the Annals of the University of Stellenbosch, Volume 31, Section A, No.1 (1955) / ENGLISH ABSTRACT: The pelvic girdles of the two anuran genera Ascaphus and Leiopelma of the family Ascaphidae are very similar. Attached to them by cartilage (or connective tissue in some Ascaphus specimens) is a cartilaginous, in Leiopelmu somewhat ossified, epibubis. In Ascaphu8, as in Xenopus, the epipubis originates from two Anlages, and its muscles are also paired in the Ascaphidae, while in Xenopus only one is present, although this also appears to originate (rom two muscles. The cloaca extends behind the pelvic girdle in both sexes in Al:lcaphus, and it is supported by two rods consisting of strong connective tissue (Faserknochen?). These rods are attached to the ventral surface of the pelvic girdle, in the female closely, in the male by means of tendons. Between the rods and the epipubis a broad tendinous band extends, which is thick in the male; in the latter the mm. compressores cloacae have their origins posteriorly on the rods, while in the female the rods are completely imbedded in these muscles posteriorly. In the female particularly there are transverse muscle fibres which are not striped although probably derived from the mm. compressorcs cloacae. Behind the pelvic girdle there is cavernous tissue in both layers of the tunica muscularis, and ventrally it covers the mm. eompressores cloacae. The circular and longitudinal muscle layers are poste riorly separated by gliding planes. The cloaca is supplied by branches of the a. mcsenterica posterior and the au. pudendae anteriores, and is drained by the vv. pudendae and a small medial v. eaudalis. The cloaca is innervated dorsally by the plexus ischio·coccygeus and ventrally by a branch of the n.ischiadicus (the n. pudendus). The cloaca of the male serves as a copulatory organ. There is internal fertilization. / No Afrikaans abstract available. / The copy we received from the author were pages individually scanned in as JPEG images.