from the thesis works of ignazio vilardi anna palasciano francesca ciocia
DESCRIPTION
Spatial & Energy resolutions (exp.& MC) for the Axial HPD-PET concept with YAP and LYSO crystals. from the thesis works of Ignazio Vilardi Anna Palasciano Francesca Ciocia. New 3D axial HPD-PET concept. p. PMTs. Arrays of long ( Lc ~ 10-15 cm ) crystal bars - PowerPoint PPT PresentationTRANSCRIPT
Spatial & Energy resolutions (exp.& MC)
for the Axial HPD-PET concept with YAP and LYSO crystals
from the thesis works of
Ignazio Vilardi
Anna Palasciano
Francesca Ciocia
The 3D PET cameras
Standard radial concept
Many rings of crystal–photodetector blocks
radially displacedLc =1.5-3cm
New 3D axial HPD-PET concept
Arrays of long (Lc~10-15 cm) crystal bars read out at both sides by segmented HPDs
Concept made possible by CERN development of rectangular segmented 5‘’ HPDs with integrated self-triggering electronics
p
PMTs
axis
axis
A HPD-PET CAMERA MODULE• Array of 208 scintill.s (LSO, LYSO, YAP, LaBr3, n=1.8-1.9)
• 16x13 crystals (3.2[Rx]x3.2[Ry]x150[Lc] mm3)
tx=51mm, ty=42mm tX,Y>3·a (LSO) 2⊥)~ 90%
• with spacing: 4x4 mm2 Rx = 64 mm, Ry = 52 mm
"Proximity focused“ HPDs
• sapphire window (n~1.8):
(better light transmission)
(crystal-window refractive indices matching)
• optical transport image 1 : 1
• segmented (4x4 mm2) silicon detector pads
(each crystal readout by its pad, no cross-talk)
• each pad with integrated lecture electronics (2 VATA-Gp5)
Gain HPD : ~ 3.103 (Uop= 12 kV ) or 5.103 (Uop = 20 kV)
Rx
Ry Lc
LYSO crystals
sapphire window
ring electrodes
silicon sensor
readout chips
Bi-alkali photocathode
“Reference Radial PET”: The High Resolution Research Tomograph (HRRT) (CTI, MPI, Karolinska …)
AFOV25 cm
31 cm
• 8 panels with 9 13 blocks
• 2 64 crystals per block
• 120000 crystals 2.12.1x7.5mm3
• 936 (20x20 mm2) PMTs
PM
T2
PM
T1
LSO
LSO = 7 ns
88 matrix (2x2 cm2) 4PMTs
z (FWHM) ~ 5 mm V= (FWHM) ~ 20 mm3
Lc =15mm ~ 1 a 2( )~ 53% ⊥
E/E (511 keV) ~ 17%Heavy electronics (PSD)
7.5
7.5
K. Wienhard et al., IEEE Trans. Nucl. Sci. 49 (2002) 104–10
Lc
•ANGER LOGIC: a block seen by 4 PMTs CM of signals in 4 PMTs interac. point (x,y) of
•DOI (z) from PHOSWICH tecnique Pulse Shape Discrimin. (PSD)
x
y
z
Criteria to be taken into account: light yield, absorption length, photofraction, self absorption, decay time, availability, machinability, price.
YAP:Ce LSO:Ce LuAP:Ce LaBr3:Ce
Density ρ (g/cm3) 5.55 7.4 8.34 5.3
Effective atomic charge Z 32 66 65 46.9
Scintillation light output (photons / MeV) 18000 23000 ~10000 ~61000
wavelength max of max. emission (nm) 370 420 370 356
Refractive index n at max 1.94 1.82 1.95 ~1.88
Bulk light abs. length bulk (cm) at max
~20 ~40
Principal decay time (ns) 27 40 18 30±5
Mean γ atten. length a at 511keV (mm) 22.4 11.5 10.5 ~20
Photo fraction at 511 keV (%) 4,5 32.5 30.5 15
Energy resolution (FWHM) at 663 keV 4.5 8 2.9
Inorganic Scintillation crystals
BGO
7.13
75
~9000
480
~2.15
300
~11.6
41.5
LSO (LYSO) is the most interesting crystal scintillator : fast (40 ns), short att. length (~12mm) at 511keV, high photofraction (32%), not hygroscopic, but high intrinsic energy resolution (~ 5% FWHM)
• x,y from fired scintillator σ(x,y) = 3.2 mm/√12= 0.92 mm x,y (FWHM) = 2.2 mm
• z (DOI) from the ratio of the photoelectrons detected at the two crystal ends σ(z) linked to the scint. choice
Reduced # of photodet., scint., electr. (12 module PET: only 24 HPDs)
No limit to module radial (x,y) dimension
higher efficiency
Double scatt. events in one module(Compton-photoel.) reconstruction higher efficiency
HPD2
HPD1
x
y
z
208 4 x 4 mm2 Si ‘pads’ centred on crystal matrix
1) ADVANTAGES OF THE AXIAL HPD-PET CONCEPT
High Granularity exact
reconstruction of the interaction point (no parallax error)
(Rx)
(Ry)
COMPTON + PHOTOELECTRIC events-
~ 25% Compton events (50 keV [energy cut] < E < 170 keV) followed by
a photoelectric one in the same module can unambiguously be reconstructed
possibility to reconstruct the int. point of part of ’s that suffers a double (Compton + photoelectric) event in the same module
2) ADVANTAGES OF THE AXIAL HPD-PET CONCEPT
detection efficiency increases but spatial (DOI) resolution worsens
HPD2
HPD1
σz, σE/E, σt : (only statistical)
Lc, eff, No: KEY PARAMETERS OF THE HPD-PET CONCEPT
Z
, exp exp2
, ln
2
12/1
2
1
eff
C
effo
eff
zCeff
zLz
N
ENFL
N
Nz
, )(
exp2
, exp2
02
01
eff
C
eff
zLNN
zNN
.21 NNzN pe
, ,Rint pe
Tpe
E
N
c
N
ENF
E
• Lc: crystal length
• eff: attenuation length of scint. photons
1/eff = 1/(bulk* cos) + c’/(cabs)
• No: light yield ≡ p.e.’s (511keV ) in a Lc~0 crystal
(nph/keV, sci.ph.transport, q.e. & wind. of photodet.)
cabs
a) crystal axial length (Lc) worsens all resolutions limit of Lc: 10 ~ 15 cm
c) contrasting effects of eff on σz & σE/E, σt
optimize eff value by wrapping or coating the crystal lateral surface
b) light yield (No) improves all resolutions
PROOF of the HPD-PET CONCEPT with YAP and LYSO crystals and PMTs
BaF2 (used with a 22Na source)
Pb collimator Pb + source
YAP (Preciosa Co) LYSO (Photonic Materials) (3.2 x 3.2 x 50-150 mm3) • PMT H3164-10 (=8mm, nw=1.47,bialkali)• B8850Quantacon(=5cm,nw=1.47,bialkali)
linear translator M-511(Phys.Instrum.)
polished 3x3x100 mm3 YAP-LYSO comparison
z=1 cm z = 5 cm z =9 cm
YAP+H3164-10QL+QR (5cm)= 1692 ch
LYSO+H3164-10QL+QR (5cm)= 2295 ch
22Na source
photoelectric peak (511 keV) Compton
ΔE/E(FWHM) ~ 10%
LYSO produces more light (pe’s) than YAP LYSO has a higher photofraction, lower energy resolution than YAP
~ 14%
eff in polished(n2=1) 3x3x100 mm3 YAP-LYSO
LYSO= 42.6±0.9 cm
YAP= 20.8±0.4 cm
QL
LYSO more transparent (higher eff than YAP)
too high -eff values (poor z) both for LYSO and YAP
exp(-z/eff), ≈ n1/n2, n1/nW
1/z2 ≈ n1/nW
No/2
Crystal wrappings or metal-coatings change light attenuation length of a YAP (3.2 x 3.2 x 100 mm3)
best solution
polished
No/2
at z=0: N0(teflon) > N0(polished) (diffusing wrapping)
eff (polished) / eff(teflon) = 1.9
possibility to tune eff value with metal coatings
metal coating (n2) reduces No
QL
NO = 510±18 pe
NO = 753±34 pe
E/E, z, tdc (z=5cm) in coated 10cm YAP & LYSO (511 keV) vs
eff
NO = 724±34 pe
/
0
22
zz e
N
ENF
int/
0
ReN
ENF
E zStat
E
/
''
mzte
ca
YAP LYSOa) statisticalb) phenomen.
very low eff in a Lc=5 cm YAP with raw (smeared) lateral surfaces
no exp behaviour of Q1 (fermi function) no coincident Q1-Q2 signals in a Lc = 10 cm YAP very low eff , but dependent with z
good z but z-dependent, bad E/E
crystal length worsens z, does not influence much E/E
worse z and E/E values at lower E
very low eff (raw lat.surf) values Lc limited, z-dep. of z
z , E/E in coated-smeared YAP & LYSO vs z, eff, Lc, E
Geant4 simulations for YAP long crystals + PMTs
I incident unpol. opt. photons
A absorption
R reflectionT transmission
D Lambertian diffusion
SR diffuse reflect. (smear)ST diffuse transmiss.
long and thin cylindrical crystal (n1, Nph/keV)lat.surface: polished, smeared (), wrapped (nwrap), coated
(nwrap,ik,t) polished bases coupled to PMTs (nwin, t,q.e.)
Polar diagram of reflected-refracted scintillation photons
nwrap nwin
nwrap
does not change eff
decreases Noworsens E/E, z, t
(nwin=1.47) (nwrap=1.0)
nwin decreases eff
increases Noimproves E/E, z, t
*refr.ind.match
*
absorption diffusion smearing
absorp. & diffus. •similar effects•decrease eff
(diff. increases No)•improve z
•worsen E/E, t
smearing •to be avoided (N1 no more exp.)
Geant4 reproduction of exp. results
YAP + H3164-10 PMTs
Geant4 predictions for engraved crystals
mechanical or laser ablation mechanical or laser ablation engravingsengravings (effects similar to absorp.)•decrease eff
•improve spatial resol.•worsen energy-time resol. &• high reproducibility to the N0 and eff values of the many HPD-PET crystals
Full ring scannerA possible final configuration for a HPD-PET
R = 170 mm12 modules
=34 cm
Lc = 15 cm
2496 crystals 3.2x3.2x150mm3
24 5” rect. HPDs
det.Vol. 3834cm3
det.depth 41mm
~ 0.165
TOT(LSO) (%) ~ 8.5 (ph) + 7.5 (Co-rec)
TOT(LaBr3)(%) ~ 1.9 (ph) + 4.9 (Co-rec)
xy
z
HRRT vs. HPD-PET
8 panels 9x13 blocks
=31 cm
AFOV = 25 cm
120000 crystals 2.1x2.1x7.5mm3
936 PMTs 2x2cm2
det.Vol. 3962cm3
det.depth 15mm
~ 0.344
TOT (LSO)(%) (exp) ~ 6.9
AFOV25 cm
31 cm
HPD-PET(Lc=10cm) vs HRRT
crystal nw No(pe)
eff
(cm)z FWHM
(mm)
E/E FWHM
(%)
HPD-PET
exP
YAP polish 1.47 950 21 19.3 10.8
YAP teflon 1.47 1120 10.5 12.7 11.2
LYSO polish 1.47 1200 42 34.5 14.6
LYSO teflon 1.47 750 20 22.1 16.4
MC
YAP polish 1.8 1500 16 8.9 8.9
YAP teflon 1.8 1640 9 7.7 9.4
HRRT
exP
LSO 5 17