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Conceptual study of a liquid xenon ?-PET for
small animal imaging
Sebastien JAN ISN - Grenoble - France
Why liquid xenon (LXe) medium for detection in
PET ?
Design of LXe ?-PET and DOI measurement
Monte Carlo simulation and results
RD investigations
2
Why liquid xenon medium for detection in PET ?
Good scintillation properties for PET
Some difficulties
Light collection at ? 178 nm is one of
challenging part of this project !
3
Design of a liquid xenon ?-PET
x
z
y
One module 10x10 light guides kapton matrix
with deposition of Al MgF2 on it 2 PS-PMT for
light collection Active volume 2 cm in x,y - 5
cm in z
?-PET
16 modules 32 PS-PMT Axial FOV 5
cm Transaxial FOV 10 cm
4
DOI Measurement
No DOI information with a classical PET
system like BGO Block
No information about Depth Of Interaction !
BGO detector block
PM
PM
y
Parallax error or radial elongation
x
z
DOI measurement with the design of LXe
?-PET
x,y given by the light guide where the energy is
deposited (PM1-PM2)/(PM1PM2) ? z
PM1
PM2
x
z
y
x, y, z for each event !
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Monte Carlo Simulation
GEANT4 - Free At CERN !
Geometry and material definitions - Water phantom
active medium cryostat ? generation - 15O
11C 18F Annihilation ? tracking - ? ? non
colinearity is taken into account Package
LowEM-Processes in GEANT4 ? Rayleigh scatterings,
Compton and photoelectric effects
C Code
UV photons generation of ? hit in LXe module -
40000 photons/MeV UV propagation in the light
guides - reflectivity coefficient 90
Simulation of the PS-PMT response - quantum
efficiency 15
Acquisition in 3D mode - Data Files
ROOT - Free at CERN !
IDL
Analysis - Energy resolution sensitivity
scatter fraction spatial resolution Sinogram
construction
Filtered Back Projection reconstruction method
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Monte Carlo results
Single photon energy deposited spectrum in the
liquid xenon
Energy resolution 15 _at_ 511 keV (FWHM)
7
Spatial Resolution
Set-Up Water phantom - Ø 4 cm
H 4 cm 18F point sources in the central
transaxial plane Same activity for each sources
- 400.106 ? are generated Energy Threshold 250
keV - 650 keV
Transaxial Resolution at the center of FOV (FWHM)
1.57 mm
DOI measurement provides a good uniformity of
this result at different radius value in the FOV
8
Image Reconstruction
4 point sources in the water phantom
(18F) Reconstruction of the central slice - Slice
width 3 mm 2D reconstruction with FBP algorithm
5 mm
y
x
Good separation between point sources
9
Simulation with a more realistic phantom
Water cylinder Ø 4 cm - H 4 cm Five hot
tubes filled with the same 18F concentration Recon
struction of the central slice
Original distribution
Monte Carlo reconstruction
3 mm
4 mm
5 mm
1 mm
2 mm
10
Preliminary comparisons between 18F and 15O
18F
15O
Resolution (FWHM) 1.6 mm
Resolution (FWHM) 2.9 mm
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Sensitivity
3D acquisition Energy threshold 250 keV - 650
keV At the center of FOV
1.2 for real coincidences 1 for true
coincidences
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RD investigations
Light collection PS-PMT Tests UV
detection at ? 180 nm Photo Tube HAMAMATSU
R5900-00-C12 quartz window RbCs photo-cathode 6x
and 6y cross-plated anodes localisation by a
center of gravity calculation
Construction of one module For the LXe
?-PET Deposition of Al MgF2 on a kapton matrix
? 10x10 light guides with 2x2 mm2 for each one
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Results of PS-PMT test at 180 nm and room
temperature
Profiles of center of gravity obtained with
quartz optical fiber travelling mm/mm Excellent
separation !
Resolution at FWHM for one center of gravity
distribution 0.25 mm (fwhm)
Non linearity of the PS-PMT (variation of the
photo-cathode efficiency) Must be corrected
before reconstruction !
PMT must be tested at 165 K
14
Cryogenic system - LXe Station cryostat
LXe Station built by Air Liquid - deliver 2000
December Cryostat built at the
laboratory Tested at 119.8 Kelvin with liquid
krypton (165 K for liquid xenon)
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Conclusions
Simulation GEANT 4 of a LXe ?-PET ? design
performances
GEANT 4 simulation can be extended in a general
PET simulator - User could define materials,
geometry, isotope, phantom with an interactive
panel and the simulator will provide PET data
Testing new PET design and reconstruction
algorithm
Specification for the future developments in
?-PET resolution (fwhm)
1.5 mm - sensitivity 2
LXe ?-PET Resolution (fwhm) 1.5 mm

Sensitivity 1
DOI measurement
Module prototype for LXe ?-PET is being
built ? It will be tested in the second half of
2001