Sökning: "Radiofysik"

Visar resultat 1 - 5 av 99 avhandlingar innehållade ordet Radiofysik.

  1. 1. Quality assurance for magnetic resonance imaging (MRI) in radiotherapy

    Författare :Mary Adjeiwaah; Tufve Nyholm; Anders Garpebring; Joakim Jonsson; Sofie Ceberg; Umeå universitet; []
    Nyckelord :MEDICAL AND HEALTH SCIENCES; MEDICIN OCH HÄLSOVETENSKAP; MEDICIN OCH HÄLSOVETENSKAP; MEDICAL AND HEALTH SCIENCES; magnetic resonance imaging; MRI; radiotherapy; RT; geometric distortions; magnetic susceptibility; B0 maps; quality assurance; radiofysik; radiation physics;

    Sammanfattning : The use of Magnetic Resonance Imaging (MRI) in the radiotherapy (RT) treatment planning workflow is increasing. MRI offers superior soft-tissue contrast compared to Computed Tomography (CT) and therefore improves the accuracy in target volume definitions. LÄS MER

  2. 2. Ion recombination in liquid ionization chambers : development of an experimental method to quantify general recombination

    Författare :Jonas Andersson; Heikki Tölli; Lennart Johansson; Anders Ahnesjö; Umeå universitet; []
    Nyckelord :NATURAL SCIENCES; NATURVETENSKAP; MEDICAL AND HEALTH SCIENCES; MEDICIN OCH HÄLSOVETENSKAP; NATURVETENSKAP; MEDICIN OCH HÄLSOVETENSKAP; NATURAL SCIENCES; MEDICAL AND HEALTH SCIENCES; General recombination; initial recombination; liquid ionization chamber; radiation dosimetry; radiofysik; radiation physics;

    Sammanfattning : An experimental method (the two-dose-rate method) for the correction of general recombination losses in liquid ionization chambers has been developed and employed in experiments with different liquids and radiation qualities. The method is based on a disassociation of initial and general recombination, since an ionized liquid is simultaneously affected by both of these processes. LÄS MER

  3. 3. Improving accuracy of in situ gamma-ray spectrometry

    Författare :Jonas Boson; Christer Samuelsson; Umeå universitet; []
    Nyckelord :MEDICAL AND HEALTH SCIENCES; MEDICIN OCH HÄLSOVETENSKAP; MEDICIN OCH HÄLSOVETENSKAP; MEDICAL AND HEALTH SCIENCES; gamma-ray spectrometry; in situ measurement; HPGe detector; 137Cs; Monte Carlo; efficiency calibration; measurement uncertainty; Radiological physics; Radiofysik;

    Sammanfattning : Gamma-ray spectrometry measurements performed on site, or “in situ”, is a widely used and powerful method that can be employed both to identify and quantify ground deposited radionuclides. The purpose of this thesis is to improve the calibration of high purity germanium (HPGe) detectors for in situ measurements, and calculate the combined uncertainty and potential systematic effects. LÄS MER

  4. 4. Applications of statistical methods in quantitative magnetic resonance imaging

    Författare :Patrik Brynolfsson; Anders Garpebring; Tufve Nyholm; Eirik Malinen; Umeå universitet; []
    Nyckelord :MEDICAL AND HEALTH SCIENCES; MEDICIN OCH HÄLSOVETENSKAP; MEDICIN OCH HÄLSOVETENSKAP; MEDICAL AND HEALTH SCIENCES; Quantitative imaging; tumor imaging; dynamic contrast-enhanced MRI; diffusion weighted MRI; texture analysis; radiofysik; radiation physics;

    Sammanfattning : Magnetic resonance imaging, MRI, offers a vast range of imaging methods that can be employed in the characterization of tumors. MRI is generally used in a qualitative way, where radiologists interpret the images for e.g. diagnosis, follow ups, or assessment of treatment response. LÄS MER

  5. 5. Modeling Silicon Diode Dose Response in Radiotherapy Fields using Fluence Pencil Kernels

    Författare :Karin Eklund; Anders Ahnesjö; Erik Grusell; Hugo Palmans; Uppsala universitet; []
    Nyckelord :MEDICAL AND HEALTH SCIENCES; MEDICIN OCH HÄLSOVETENSKAP; MEDICIN OCH HÄLSOVETENSKAP; MEDICAL AND HEALTH SCIENCES; Radiological physics; Radiofysik; Medicinsk radiofysik; Medical Radiophysics;

    Sammanfattning : In radiotherapy, cancer is treated with ionizing radiation, most commonly bremsstrahlung photons from electrons of several MeV. Secondary electrons produced in photon-interactions results in dose deposition. The treatment response is low for low doses, raises sharply for normal treatment doses and saturates at higher doses. LÄS MER