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90Y-Scintigraphy of small animals A study of imaging parameters

Joo, Melinda (2003)
Medical Physics Programme
Abstract (Swedish)
Yttrium-90 is a pure β-emitting radionuclide with a high energy (Emax = 2.28 MeV) and a short half-life (T½ = 64.1 h). It has shown to be a promising isotope to use in radio-immunotherapy. In the absence of direct photon emission scintillation camera imaging can be obtained by acquiring events from bremsstrahlung photons created at or near the decay site of the radionuclide. It is, however, not evident how the energy window has to be defined, because the photon energy spectrum from the interacting β-particles extends from zero to the maximum energy of the β-particle. The aim of this master’s work was to examine the imaging parameters of the gamma camera (energy window, collimator) to achieve information in order to determine the optimum... (More)
Yttrium-90 is a pure β-emitting radionuclide with a high energy (Emax = 2.28 MeV) and a short half-life (T½ = 64.1 h). It has shown to be a promising isotope to use in radio-immunotherapy. In the absence of direct photon emission scintillation camera imaging can be obtained by acquiring events from bremsstrahlung photons created at or near the decay site of the radionuclide. It is, however, not evident how the energy window has to be defined, because the photon energy spectrum from the interacting β-particles extends from zero to the maximum energy of the β-particle. The aim of this master’s work was to examine the imaging parameters of the gamma camera (energy window, collimator) to achieve information in order to determine the optimum conditions for bremsstrahlung imaging. Methods: A Siemens DIACAM scintillation camera and a water phantom simulating a rat were used for the experimental studies. Spheres, filled with 90Y, simulated tumours. Three collimators denoted LEAP (Low-Energy All Purpose), HE (High-Energy) and UHE (Ultra High Energy) were investigated for various settings of the energy window. The system sensitivity [cps/MBq] and the primary-to-total radiation ratio were compared for the three collimators and the different energy window settings. In addition, Monte Carlo simulations using the SIMIND code were made to demonstrate how the image quality degrades as function of physical parameters. The simulations were setup in such a way that the components in the images from geometrical penetrating and scatter events were separated. Results: The LEAP collimator showed the highest sensitivity as expected, but also the lowest image quality because of the septum penetration. The UHE collimator has, generally, lower sensitivity and lower ratio of primary-to-total radiation than the LEAP collimator but the septal penetration was less than the LEGP. The HE collimator with an energy window between 86-254 keV was selected as optimal acquisition setting with consideration of both the sensitivity and primary-to-total ratio. The lower limit of 86 keV for the energy windows was chosen to eliminate the characteristic K X-ray photons, with energies 74.97 keV (46.2%), 72.81 keV (27.7%), 84.94 keV (10.7%) and 84.45 keV (5.58%). Results from the simulations also showed that a large fraction of the recorded events when using the LEAP collimator originates from photons that have penetrated the septal walls. As the energy window decreased the ratio primary-to-total increased which means that fewer scattering and penetrating events are registered. The simulations also show that the penetration is a significant problem for the LEAP collimator, while the UHE collimator shows the smallest penetration fraction. LUJI-RADFYS-EX-4/2003 (Less)
Please use this url to cite or link to this publication:
author
Joo, Melinda
supervisor
organization
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Nukleärmedicin
language
English
id
2156929
date added to LUP
2011-09-13 15:22:40
date last changed
2011-09-13 15:22:40
@misc{2156929,
  abstract     = {Yttrium-90 is a pure β-emitting radionuclide with a high energy (Emax = 2.28 MeV) and a short half-life (T½ = 64.1 h). It has shown to be a promising isotope to use in radio-immunotherapy. In the absence of direct photon emission scintillation camera imaging can be obtained by acquiring events from bremsstrahlung photons created at or near the decay site of the radionuclide. It is, however, not evident how the energy window has to be defined, because the photon energy spectrum from the interacting β-particles extends from zero to the maximum energy of the β-particle. The aim of this master’s work was to examine the imaging parameters of the gamma camera (energy window, collimator) to achieve information in order to determine the optimum conditions for bremsstrahlung imaging. Methods: A Siemens DIACAM scintillation camera and a water phantom simulating a rat were used for the experimental studies. Spheres, filled with 90Y, simulated tumours. Three collimators denoted LEAP (Low-Energy All Purpose), HE (High-Energy) and UHE (Ultra High Energy) were investigated for various settings of the energy window. The system sensitivity [cps/MBq] and the primary-to-total radiation ratio were compared for the three collimators and the different energy window settings. In addition, Monte Carlo simulations using the SIMIND code were made to demonstrate how the image quality degrades as function of physical parameters. The simulations were setup in such a way that the components in the images from geometrical penetrating and scatter events were separated. Results: The LEAP collimator showed the highest sensitivity as expected, but also the lowest image quality because of the septum penetration. The UHE collimator has, generally, lower sensitivity and lower ratio of primary-to-total radiation than the LEAP collimator but the septal penetration was less than the LEGP. The HE collimator with an energy window between 86-254 keV was selected as optimal acquisition setting with consideration of both the sensitivity and primary-to-total ratio. The lower limit of 86 keV for the energy windows was chosen to eliminate the characteristic K X-ray photons, with energies 74.97 keV (46.2%), 72.81 keV (27.7%), 84.94 keV (10.7%) and 84.45 keV (5.58%). Results from the simulations also showed that a large fraction of the recorded events when using the LEAP collimator originates from photons that have penetrated the septal walls. As the energy window decreased the ratio primary-to-total increased which means that fewer scattering and penetrating events are registered. The simulations also show that the penetration is a significant problem for the LEAP collimator, while the UHE collimator shows the smallest penetration fraction. LUJI-RADFYS-EX-4/2003},
  author       = {Joo, Melinda},
  keyword      = {Nukleärmedicin},
  language     = {eng},
  note         = {Student Paper},
  title        = {90Y-Scintigraphy of small animals A study of imaging parameters},
  year         = {2003},
}