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master's thesis
10
0
Simulation of a detector system for positron emission tomography
Julio Car (2017)
University of Zagreb
Faculty of Science
Department of Physics
Cite this item:
https://urn.nsk.hr/urn:nbn:hr:217:737933
Metadata
Title
Simulacija detektorskog sustava za pozitronsku emisijsku tomografiju
Author
Julio Car
Mentor(s)
Mihael Makek
(thesis advisor)
Abstract
Pozitronska emisijska tomografija (PET) je moćna neinvazivna dijagnostička metoda nuklearne medicine koja se bazira na koincidentnoj detekciji dvaju kolinearnih γ fotona čiji izvor je u anihilaciji pozitrona i elektrona. Temeljno svojstvo PET sustava je osjetljivost, koja se definira kao omjer opaženih koincidentnih događaja i ukupnog broja anihilacijskih događaja koje proizvodi izvor, a ovisi o efikasnosti detektora i prostornoj akceptanciji. Razvoj geometrije realnih PET sustava temeljen je na simulacijama provedenim na 8 jednostavnih modela u programskom paketu GATE. Jednostavni modeli poslužili su za precizne interpretacije prostornih raspodjela i udjela različitih mehanizama interakcije γ zračenja i scintilacijskih materijala. Za odabrane LSO i LFS materijale pokazalo se da prostorni raspored interakcija γ fotona u kristalu ima maksimum na prednjoj strani što je u skladu sa atenuacijskim ponašanjem γ zračenja. Od interakcija dominiraju one u kojima je deponirana ukupna energija anihilacijskog gama zračenja od 511 keV sa 48 % udjela, dok je 46 % događaja u kojima je depozicija energije gama čestica u intervalu od 50–400 keV, što odgovara Comptonovim raspršenjima, dok se Rayleighovo raspršenje dograda u 6 % događaja. U simulacijskom sučelju GATE konstruirane su dvije realne PET geometrije: jedna manja sa 4 prstena radijusa 0.135 m sa po 48 detektorskih modula unutar prstena, a druga veća sa 16 prstenova radijusa 0.630 m sa po 200 detektorskih modula unutar prstena. Detektorski moduli su dimenzija 20x16x16 mm3 za malu odnosno 20x20x25 mm3 za veliku geometriju i sastoje se od 4x4 scintilacijska kristala dimenzija 20x3x3 mm3. Simulacija sa točkastim izvorom u središtu geometrije pokazala je da je osjetljivost 5.55 % za manju geometriju odnosno 2.48 % za veću geometriju, uz uvjet da se opažaju samo anihilacijski fotoni koji u detektorima deponiraju svu energiju u prozoru 0.4–0.6 MeV, što je usporedivo sa standardnim PET sustavima. Ispitan je utjecaj atenuirajućeg materijala (fantoma), kao i utjecaj konačne veličine pozitronskog izvora na osjetljivost PET sustava. Konačno određena je gornja granica osjetljivosti konstruiranih PET sustava, kao ona u kojoj bi se uzimali u obzir svi koincidentni događaji u kojima je depozicija energije gama čestica u puno širem energijskom prozoru 0.05–0.65 MeV. Dobiveni rezultati pokazuju da su gornje granice osjetljivosti PET sustava 55.75 % za manju odnosno 23.51 % za veću geometriju.
Keywords
PET
coincidence
detection efficiency
sensitivity
scintillation crystals
Parallel title (English)
Simulation of a detector system for positron emission tomography
Committee Members
Mihael Makek
(committee chairperson)
Matko Milin
(committee member)
Ivica Smolić
(committee member)
Nils Paar
(committee member)
Nikola Poljak
(committee member)
Granter
University of Zagreb
Faculty of Science
Lower level organizational units
Department of Physics
Place
Zagreb
State
Croatia
Scientific field, discipline, subdiscipline
NATURAL SCIENCES
Physics
Study programme type
university
Study level
integrated undergraduate and graduate
Study programme
Physics; specializations in: Research
Study specialization
Research
Academic title abbreviation
mag. phys.
Genre
master's thesis
Language
Croatian
Defense date
2017-09-26
Parallel abstract (English)
Positron emission tomography (PET) is powerful non-invasive diagnostic technique of nuclear medicine based on detecting coincidence events of two colinear γ photons emerging from positron-electron annihilation events. Basic property which characterizes PET system is sensitivity for coincidences which is defined as a ratio of detected coincidence events and all annihilation events which emerge from the source. Sensitivity depends on detection efficiency and solid angle of PET system. Development of geometries for modern PET systems made in software package GATE was based on tests conducted on 8 simple models. Models were used in order to understand mechanism of γ radiation interaction with scintillation materials precisely and for understanding of spatial distribution of interactions. For LSO and LFS scintillation crystals it was shown that spatial distribution of interactions has maximum in front part of the crystal which is consistent with attenuation of γ radiation. Considering types of interactions of γ photons with crystals, the biggest energy deposition of 511 keV γ photons comes above 400 keV in 48 % of events while interactions due to Compton scattering in energy interval 50–400 keV contribute in 46 % of events and finally Rayleigh scattering in 6 % of events. Two real PET geometries were constructed using simulation interface GATE: one smaller consisting of 4 detection rings with radius 0.135 m with 48 detector modules per ring and second bigger with 16 detection rings with radius 0.630 m with 200 detector modules per ring. Dimensions of detector modules were 20x16x16 mm3 for small geometry and 20x20x25 mm3 for big geometry and they consisted of 4x4 scintillation crystals sized 20x3x3 mm3. Simulation with pointlike source in the center of geometry gave sensitivity of 5.55 % for smaller and 2.48 % for bigger geometry with condition that detected photons had deposited energy in interval 0.4–0.6 MeV similar to standard PET systems. Furthermore, attenuation material (phantom) was introduced as well as volume distribution of positron source in order to investigate their influence on PET sensitivity. Eventually, the upper limit of sensitivity of developed PET system was determined by using all coincidence events in which deposited energy of γ photons was in wider window 0.05–0.65 MeV. Results showed that upper limits for sensitivity were 55.75 % for smaller and 23.51 % for bigger geometry.
Parallel keywords (Croatian)
PET
koincidencija
efikasnost
osjetljivost
scintilacijski kristal
Resource type
text
Access condition
Embargo period 2019-09-26
Terms of use
URN:NBN
https://urn.nsk.hr/urn:nbn:hr:217:737933
Committer
Iva Čizmin