1. Impact of detector thickness on imaging
characteristics of the Siemens Biograph
DUO PET/CT with GATE
N. N. Chatzisavvasd, T. J. Sevvosd, Em. M. Vlamakisd, A. A.
Fotopoulos d, X. A. Argyriou d X. Tsantilasb, S. Kottoub ,
P.H.Yannakopoulosd, A. Louizib , I. Kandarakisc, J. Malamitsib and
D. Nikolopoulosa
a Department of Physics, Chemistry and Material Science, Technological Educational
Institute (TEI) of Piraeus, Petrou Ralli & Thivon 250, 122 44,Aigaleo,Athens,Greece
b Medical Physics Department, Medical School, University of Athens, Mikras Asias 75,
11527, Athens, Greece
c Department of Medical Instruments Technology, Technological Educational Institution
of Athens, Ag. Spyridonos, Aigaleo, 122 10 Athens, Greece
d Department of Engineering of Electronic and Computer Systems,Technological
Educational Institute (TEI) of Piraeus, Petrou Ralli & Thivon 250, 122
44,Aigaleo,Athens,Greece
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2. AIM
The present paper is a Monte Carlo study of a
Siemens Biograph DUO PET/CT with GATE,with
emphasis given on PET imaging and, especially,
to changes caused by changing the thickness of
the LSO detector of a PET/CT.
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3. Introduction 1/3
Positron emission tomography - computed
tomography PET-CT is a medical imaging technique
using a device which combines system both a
Positron Emission Tomography (PET) and an x-ray
Computed Tomography.
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4. Introduction 2/3
Scintillation is a process of emitted
characteristic light spectrum when a
scintillator is absorbing ionising radiation.
LSO Scintillator :
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5. Introduction 3/3
GATE is an advanced open
source software , combines
the advantages of the
GEANT4 simulation toolkit,
dedicated to numerical
simulations in medical
imaging and radiotherapy
written in C/C++
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6. Materials and Methods
 Simulation with Gate-Geant of the PET/CT Siemens Biograph DUO
 GATE codes for (building the simulation):
 (a) the entire PET detector arrangement
 (b) the light guides, photomultiplier tubes and related
electronics
 (c) the digitizer
 (d) the shielding between PET and CT
 (e) the coincidence circuits and processors
 (f) the time-delay of PET
 (g) the data processing systems
 (h) the examination bed
 (i) the PET and CT gantry
 (j) the PET motions (gantry, bed)
 (k) the shielding of the room
 (l) the CT image reconstruction chain .
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7. Materials and Methods
 Software phantoms (inside the simulation):
 (a) a cylindrical source phantom of radius 1 mm and height 15
cm filled with F-18 FDG
 (b) human body phantom :
◦ (b-i) an ellipsoid of 8 cm minimum and 15 cm maximum radius mimicking
the human main body.
◦ (b-ii) two cylinders of radius 5 cm and height 30 cm mimicking the human
hands.
◦ (b-iii) a sphere of 14 cm radius mimicking the human head.
◦ (b-iii) A cylindrical F-18 FDG source of 0.5 cm radius and 5 cm height .
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8. Materials and Methods
 Interaction phenomena :
 i) Crystal energy blurring: resolution of 0.25 at
511keV.
 (ii) Detector characteristics: quantum detection
efficiency of 0.98 , light output of 30000
photons/MeV, intrinsic resolution of 0.088 and
transfer efficiency coefficient of 0.28.
 (iii) Energy window: between 250 and 650 keV
 (iv) Time Resolution: coincidence window of 120
ns, dead time window of 120 ns and dead time
offset of 700 ns.
 (v) F-18 FDG source half life of 6586.2 s
 (vi) Slice time of 1 s and acquisition time of 10s.
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9. Results and Discussion
 i) Diagram with
Characteristics of the
Biograph DUO PET/CT
(black line) and estimation
from Gate Simulation (blue)
 ii) Diagram Number of
counts – Energy Mev (2
picks at 0.2 MeV and 0.511
MeV)
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10. Results and Discussion
 iii)Number of Counts –
Energy (MeV) ( pick at 0.25
MeV)
 ii)Diagram Number of counts
– Energy Mev (2 picks at 0.2
MeV and 0.511 MeV) (± 1
deg)
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11. Results and Discussion
 Root Mean Square (RMS) energy
is 99.06 keV
 Mean energy is 407.5 keV
 FWHM of energy and RER are 0.6
and 6% for the peak near 0.511
MeV
 As thickness increases, FWHM,
RER and SNR increase
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12. Results and Discussion
 Energy Resolution Of System
◦ A) 2 cm LSO thickness
◦ B) 3 cm LSO thickness
 The peak of the 3.0 cm thick
crystals is sharper , more wide
and has more counts than the
one of the 2.0 cm thickness.
This attributes to the higher
detection efficiency of the
thicker LSO detectors at 0.511
MeV
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13. Results and Discussion
 As detector thickness
increases, the axial distribution
sensitivity of the number of
counted photons is enhanced
at the centre, viz. the energy
distribution is sharper.
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14. Results and Discussion
 The increase with thickness
of the photon detection
sensitivity of a block of 64
LSO crystals points in
another way that blocks of
thicker crystals detect and
count more photons.
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15. Conclusions
 Non-significant changes were observed for:
◦ positron kinetic energy spectrum
◦ interactions of positrons with matter
◦ positron annihilation distance
◦ number of annihilation processes
◦ gamma ray production
◦ distribution and scattering of gamma-rays
 The detector absorption efficiency is strongly affected by the
scintillator thickness.
 Possible use of 3.0 cm thick LSO crystals will increase
detection efficiency of the system, RER and SNR
 But will delay signal process and increase the construction
cost and may be accompanied by paralax effects .
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16. Thank You !
http://env-hum-comp-res.teipir.gr/
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