-Recently suggested non-negative matrix factorization (NMF) seems to overcome fundamental limitations of factor analysis at least in theoretical aspect. NMF cost function uses Poisson statistics as a noise model, rather than the Gaussian statistics, and provides a simple learning rule, in contrast to the tricky optimization in factor analysis. To study the feasibility of NMF for the analysis of...

Segmentation is an important task in all kinds of image analysis. In medical image analysis segmentation has a great clinical value since the aim could be to localize organs or pathologies in order to raise the quality of diagnoses. This thesis consists of three papers where different segmentation techniques have been applied to different imaging modalities. In the first paper a full computer a...

Introduction: One of the major problems of lymphoscintigraphy is the time of patient presence in the nuclear medicine wards. The operating room schedule can be compromised if the patients stay longer than usual in the nuclear medicine departments. However, too early imaging can be falsely negative for sentinel node visualization and delayed imaging may be required. The aim of t...

Annually, many people are irradiated for diagnostic and therapeutic purposes. Assessment of radiation dose and its related risks to patients are important issues in radiation protection dosimetry. The complex mathematical calculations of the absorbed and effective doses are now done with computers. The calculations are performed with the help of anthropomorphic computational models of human bod...

introduction: occupational exposure to ionizing radiation due to medical activities (both diagnostic and therapeutic procedures) has increased sharply in recent years. among the occupationally exposed workers in these fields, those most affected by this increased exposure to ionizing radiation are nuclear medicine workers. in this study, annual average effective dose, annual collective effectiv...

background: annual patient effective dose equivalent can be considered as a quantitative physical parameter describing the activities performed in each nuclear medicine department. annual staff dose equivalent could be also considered as a parameter describing the amount of radiation risk for performing the activities. we calculated the staff to patient dose equivalent ratio to be used as a phy...

the production and application of pet tracers has been a unique step in the progress of nuclear medicine in last two decades. the most important pet tracers include f-18, c-11 and n-13 radioisotopes and many nuclear medicine centers throughout the globe are using them. however some new tracers are under their way to the mass administration, currently being in the clinical trials or preliminary ...

thyroid nodules are common, occurring in almost two-thirds of some populations; among these only about 7% are malignant. the most important question with any new discovered thyroid nodule is, “is this malignant?” the main arbiter of malignancy or benignity remains fine needle aspiration and the mainstay of treatment surgery. but given the resources involved, doing an fnac or surgery in every di...

background: various variance reduction techniques such as forced detection (fd) have been implemented in monte carlo (mc) simulation of nuclear medicine in an effort to decrease the simulation time while keeping accuracy. however most of these techniques still result in very long mc simulation times for being implemented into routine use. materials and methods: convolution-based forced detectio...