Sökning: "scatter reduction"

Visar resultat 1 - 5 av 22 avhandlingar innehållade orden scatter reduction.

1. 1. Characterisation and application of a laser-based hard x-ray source

   Författare :Matthias Grätz; Atomfysik; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; X-ray spectroscopy; radiography; medical imaging; differential imaging; time-gated imaging; scatter reduction; Monte Carlo simulation; Atomic and molecular physics; computed tomography; Fysicumarkivet A:1998:Grätz; laser-produced plasma; Atom- och molekylärfysik; X-ray sources;

   Sammanfattning : Hard X-rays are generated by focusing 110 fs laser pulses with intensities of about 1017 W·cm-2 onto solid metal targets. Characteristic properties of this X-ray source are the small source size, the short pulse duration and the high peak flux. LÄS MER

3. 2. Calculation of scatter in cone beam CT : Steps towards a virtual tomograph

   Författare :Alexandr Malusek; Michael Sandborg; Gudrun Alm Carlsson; Michael Ljungberg; Linköpings universitet; []
   Nyckelord :MEDICIN OCH HÄLSOVETENSKAP; MEDICAL AND HEALTH SCIENCES; Radiology; Radiologi;

   Sammanfattning : Scattered photons—shortly scatter—are generated by interaction processes when photon beams interact with matter. In diagnostic radiology, they deteriorate image quality since they add an undesirable signal that lowers the contrast in projection radiography and causes cupping and streak artefacts in computed tomography (CT). LÄS MER

4. 3. Energy and intensity modulated radiation therapy with electrons

   Författare :Lennart Olofsson; Mikael Karlsson; Magnus Karlsson; Björn Zackrisson; Erik Traneus; Umeå universitet; []
   Nyckelord :MEDICIN OCH HÄLSOVETENSKAP; MEDICAL AND HEALTH SCIENCES; Radiation sciences; Radiation therapy; Conformal therapy; IMRT; Electrons; Electron treatment head; Electron MLC; Bremsstrahlung reduction; Integral dose; Penumbra; Output factor; Strålningsvetenskap; Radiation biology; Strålningsbiologi; radiofysik; radiation physics;

   Sammanfattning : In recent years intensity modulated radiation therapy with photons (xIMRT) has gained attention due to its ability to reduce the dose in the tissues close to the tumour volume. However, this technique also results in a large low dose volume. LÄS MER

5. 4. Evaluation of absorbed dose and image quality in mammography

   Författare :Bengt Hemdal; Malmö Medicinsk strålningsfysik; []
   Nyckelord :MEDICIN OCH HÄLSOVETENSKAP; MEDICAL AND HEALTH SCIENCES; optically stimulated luminescence; radioluminescence; in vivo dosimetry; dose reduction; dose protocol; average glandular dose; absorbed dose; Breast cancer; mammography; Monte Carlo; image quality; image quality criteria; contrast-detail phantom;

   Sammanfattning : Mammography refers to the X-ray examination of the human breast, and is considered the single most important diagnostic tool in the early detection of breast cancer, which is by far the most common cancer among women. There is good evidence from clinical trials, that mammographic screening can reduce the breast cancer mortality with about 30%. LÄS MER

7. 5. Effective use of X rays in diagnostic radiology : Guidance for the optimisation of image quality and absorbed dose in the patient by use of a Monte Carlo computational model of the imaging chain

   Författare :Michael Sandborg; Heang-Ping Chan; Linköpings universitet; []
   Nyckelord :MEDICINE; MEDICIN;

   Sammanfattning : The primary objective of this thesis is to give guidance for the reduction of absorbed dose in the patient and the improvement of image quality by the optimisation of the various parameters which control the performance of the radiological imaging system. The optimisation means that image quality (contrast in screen-film imaging and signal-to-noise ratio in digital imaging) is kept constant and combinations of operating parameters which yields the lowest mean absorbed dose in the patient is determined. LÄS MER