Monte Carlo comparison study of the radiation absorption of scintillators for use in Diagnostic Radiology and Nuclear Medicine Applications
Monte Carlo comparison study of the radiationabsorption of scintillators for use in DiagnosticRadiology and Nuclear Medicine Applications.Authors:T. J. Sevvosa, A. A. Fotopoulosa, E. M.Vlamakisa, X. A.Argyrioua,N. N. Chatzisavvasa,A. Efdaimona, K. Vagennasa,P. H. Yannakopoulosa, I. Valaisb, I. Kandarakisb and D. Nikolopoulosa.TEI of Pireaus b.TEI of AthensTeam:env-hum-comp-res.teipir.gr
AIMX-ray absorption and x-ray fluorescenceproperties of medical imaging scintillatingscreens via Monte Carlo methods.
IntroductionScintillators are materials which are used asradiation sensors in medical representation.Scintillators which were studied: Scintillator Density (g cm3)Gd2SiO (GSO) 4.15YAlO3 (YAP) 7.40LuSiO5 (LSO) 6.71LuAlO3 (LuAP) 7.34
Materials and Methods 1Adequate EGSnrcMP codes were generatedtogether with other self-developed and validatedMonte-Carlo software.Parameters studied were (a) scintillator materialand (b) energy of exposure. Energy value studiedwas 511 keV. This is the characteristic energy forpositron emission tomography(PET).
Materials and Methods 2EGSThe EGS (Electron–Gamma–Shower) platform isa general purpose package for the Monte Carlosimulation of the coupled transport of electronsand photons in an arbitrary geometry for particleswith energies above a few keV up to severalhundreds of GeV.
Materials and Methods 3Phenomena for EGS simulations: ● Compton scattering● Coherent (Rayleigh) scattering● Multiple scattering of charged particles● Møller and Bhabha scattering● Continuous energy loss of charged particle tracks between discrete interactions● Pair production● Bremsstrahlung production● Positron annihilation in flight and at rest● Relaxation of excited atoms after vacancies are created
Materials and Methods 4 PEGS4 code Generation of mortran codes (Fortran pre processor) for the input of simulation parameters● pegs4dat:definition if the charasteristics of the material(name,structure etc)● egsinp:definition of the parameters for how the simulation is going to be.
Materials and Methods 5The scintillators were modelled as blocks of variousthickness values. A series of thickness values rangingfrom 0 to 50 mm were investigated.Modeled scintillators were considered to be exposed tox-ray initiating from a point source located at the centralaxis of the entrance area of the scintillator block at pencilbeam geometry. z
Materials and Methods 6 Parameters were studied from simulations:● Quantum Detection Efficiency (QDE) from every block of scintillator● Energy Absorption Efficiency(EAE) from every block of scintillator● Efficiency of Absorption of Incident Energy (EAIE)
Results and Discussion 1 For the LSO, GSO and LuAP crystals: Overall Absorbed-EAIE increases with increasing crystal thickness tending to form a plateau above at 40 mm thickness. For these crystals this EAIE at the 10 mm thickness had the values of 44.8%, 36.9% and 45.7% respectively and 96.4%, 93.2% and 96.9% at the 50 mm thickness. For the YAP crystals:Overall absorbed-EAIE at 511 keV for the Overall Absorbed-EAIEfour scintillators under study. increases continuously in the whole of the examined thickness range. The Overall Absorbed- EAIE of the YAP crystals presented the values of 16.8% at the 10 mm crystal thickness and 68.1 % at the 50 mm thickness respectively.
Results and Discussion 2 The Scatter and Reabsorbed-EAIE increases with crystal thickness. 30 Scatter and Reabsorbed-EAIE: For LSO crystals: 12.8% 10 mm thickness 20 LSO 59.9% 50 mm thickness GSO 57-59% plateau area (40mm)(%) YAP 10 For the GSO crystals: LuAP 22.3% 10 mm thickness 63.5% 50 mm thickness 0 59-63% plateau area (40mm) 0 10 20 30 40 50 For the YAP crystals: Thickness (mm) 15.2% 10 mm thickness 26.2% 50 mm thicknessScatter and Reabsorbed-EAIE at 511keV for 52-63% plateau area (40mm)the four scintillators under study For the LuAP crystals: 62.9% 10 mm thickness 61.6% 50 mm thickness 58-61% plateau area (40mm)
Results and Discussion 3 For the LSO, GSO, YAP and LuAP: QDE was found to be: 10mm LSO:54.9% GSO:48.8% YAP:37.4% LuAP:56.8% 50mmQDE at 511 keV for the four LSO:96.4%scintillators under study. GSO:95.4% YAP:89.9% LuAP:96.9%
Results and Discussion 4The shapes of the QDE curves presented similarities tothe corresponding curves of the overall absorbed-EAIEbut they are shifted up to higher values.This was more strongly observed for the YAP scintillator.
Results and Discussion 5● Results indicated that x-ray absorption and x-ray fluorescence are affected by the incident photon energy and the thickness.● X-ray absorption and fluorescence was found to exhibit very intense changes near the corresponding K-edge of the heaviest element in the scintillator.● Thicker scintillators exhibited higher x-ray absorption and x-ray fluorescence.● A significant fraction of the generated x-ray fluorescent quanta was found to escape from the studied scintillators.This increased with increase in thickness.
Results and Discussion 6● Most of the incident photons were found to be absorbed via one-hit photoelectric effect.● Differences in x-ray absorption and x-ray fluorescence were found among the various scintillators studied.● LSO scintillator was found to be the most attractive material for use in many applications, exhibiting the best absorption properties in the largest part of the energy studied.● Y based scintillators were also found of significant absorption performance within the low energy ranges.
References● Comparative study using Monte Carlo methods of the radiation detection efficiency of LSO, LuAP, GSO and YAP scintillators for use in positron emission imaging (PET) ,Dimitrios Nikolopoulos, Ioannis Kandarakis, Xenophon Tsantilas, Ioannis Valais, Dionisios Cavouras, Anna Louizi● Monte Carlo study of the Detection Efficiency of various scintillators for use in positron emission imaging (PET) ,D. Nikolopoulos, I. Valais, P.Gonias, N. Bertsekas, S. David, C. Michail D. Cavouras, G.S. Panayiotakis, I. Kandarakis● J.M. Boone, J.A. Seibert, J.M. Sabol, M. Tecotzky, Med. Phys. 26 (6) (1999) 905.● I. Kandarakis, D. Cavouras, Eur. Radiol. 11 (2001) 1083.● J.M. Bonne, V.N. Cooper, Med. Phys. 27 (8) (2000) 1818.● J.M. Boone, X-ray production, interaction, and detection in diagnostic imaging, in: J. Beutel, H.L. Kundel, R.L. Van Metter (Eds.), Handbook of Medical Imaging, Physics and Psycophysics, vol. 1, SPIE Press, Bellingham, 2000, p. 40.