kent burr, adrian ivan, don castleberry, jim leblanc detector technology lab, ge research
DESCRIPTION
Design of Scintillator Arrays for Dual-End Depth-of-Interaction Encoding Small-Animal PET Detectors. Kent Burr, Adrian Ivan, Don Castleberry, Jim LeBlanc Detector Technology Lab, GE Research. PET Scanner. Position Sensitive APD. Actual Event Line. Scintillator block. No DOI. - PowerPoint PPT PresentationTRANSCRIPT
Kent Burr, Adrian Ivan, Don Castleberry, Jim LeBlanc Detector Technology Lab, GE Research
Design of Scintillator Arrays for Dual-End Depth-of-Interaction Encoding Small-Animal PET Detectors
Shrink the bore and use long crystals Increase sensitivitybut …Parallax error Lose resolution
No DOI
PET Scanner
3D Position Information Breaks Inverse Relationship between Sensitivity and Resolution
Position Sensitive
APDScintillator
block
DOI resolution = 5 mm
Actual Event Line
Recon Line
Challenges in Small-Animal PET
*animated
Position Sensitive APD* introduction
high resistivity layer on back of APD
DA
BC
4 corner contacts on back
deep-diffused silicon APD
optical photons incident on front surface
*PSAPDs manufactured by Radiation Monitoring Devices, Inc., Watertown, MA, USA.
x = (A+B)-(C+D)(A+B+C+D)
y = (A+D)-(B+C)(A+B+C+D)
0 200 400 600 800 1000 1200 1400 16001
10
100
1000
10000
Gain
Bias Voltage (V)
T = 20°C
0 500 1000 1500 2000 2500 3000
-15
-10
-5
0
GainGain
Tem
pera
ture
Coeffi
cien
t (
%/
°C)
normal operating range
Bottom PSAPD pulse heightTop
PS
APD
pu
lse h
eig
ht
511 keV
DOI = 0mm (center of crystals)
Top PSAPD
Scintillator
arrayBottom PSAPD
z
scintillator slab
PMT
22Na source
Depth-of-Interaction Illustration
*animated
Top PSAPD
Scintillator
arrayBottom PSAPD
z
scintillator slab
PMT
22Na source
Bottom PSAPD pulse height
Top
PS
APD
pu
lse h
eig
ht
Top PSAPD
Scintillator
arrayBottom PSAPD
z
scintillator slab
PMT
22Na source
Bottom PSAPD pulse height
Top
PS
APD
pu
lse h
eig
ht
Top PSAPD
Scintillator
arrayBottom PSAPD
z
scintillator slab
PMT
22Na source
Bottom PSAPD pulse height
Top
PS
APD
pu
lse h
eig
ht
Top PSAPD
Scintillator
arrayBottom PSAPD
z
scintillator slab
PMT
22Na source
Bottom PSAPD pulse height
Top
PS
APD
pu
lse h
eig
ht
Top PSAPD
Scintillator
arrayBottom PSAPD
z
scintillator slab
PMT
22Na source
Bottom PSAPD pulse height
Top
PS
APD
pu
lse h
eig
ht
Top PSAPD
Scintillator
arrayBottom PSAPD
z
scintillator slab
PMT
22Na source
Bottom PSAPD pulse height
Top
PS
APD
pu
lse h
eig
ht
Top PSAPD
Scintillator
arrayBottom PSAPD
z
scintillator slab
PMT
22Na source
Bottom PSAPD pulse height
Top
PS
APD
pu
lse h
eig
ht
Depth-of-Interaction Illustration
*animated
Scintillator Array Designscintillator array attributescintillator material
array size, crystal dimensions
reflector material
crystal side surface roughness
selection
mixed lutetium silicate, MLS
8x8 array,1.65mm x 1.65mm x 22mm
• Teflon tape• VM2000 (3M Corp.)• P (polished, 7nm rms)• M5 (lapped with 5m grit, 16nm rms)• M10 (lapped with 10m grit, 700nm rms)• M20 (lapped with 20m grit, 1000nm rms)
reason
high light output,high density & Z,fast decayPSAPD size, resolution, sensitivity, crystal cutting capabilitiesexperimental
experimental
VM2000Teflon
reflector material
reflector material
VM2000• laser cut film• much faster assembly• improved reproducibility• reduced dead-space• somewhat reduced light collection efficiency(~75% of Teflon)
Teflon• best light collection• time-consuming to assemble• well-known problems with reproducibility, shrinkage, wicking, etc.
1mm
Scintillator Array Experiments
Black
P
P
P
P
P
P
M5
M5
M5
M5
M5
M5
M10M10
M10
M10
M10
M10
M20
M20
M20
M20
M20
M20
• 4 different surfaces (P, M5, M10, M20)
• 2 reflector materials (Teflon, VM2000)
• 5x5 array of crystals (parallel data acquisition under identical conditions)
• 1.9mm x 1.9mm x 20mm MLS crystals• 14mm x14mm PSAPD• arrangement chosen so that:
• each row and column have at least one of each crystal type• central 3x3 of array has at least two crystals of each type• “black” crystal used for unambiguous identification of crystals• each corner crystal has different surface• each 2x2 in corner has one crystal of each type, except for corner that has “black” crystal
Scintillator Array Experiments: Results
Polished M5 M10 M200
2
4
6
8
10
DO
I R
eso
luti
on
(m
m)
Surface Treatment
VM2000, 12.4°CTeflon, 19.6°CTeflon, 9.8°C
0
5
10
15
20
Polished M5 M10 M20En
erg
y R
eso
luti
on
(%
)
Surface Treatment
VM2000, 12.4°CTeflon, 19.6°CTeflon, 9.8°C
1
2
3
4
5
6
0Tim
ing
Reso
luti
on
(n
s)
Polished M5 M10 M20Surface Treatment
Teflon, 12.1°C
Roughening the surface improves DOI …
… without degrading energy resolution and timing resolution.
Detector Evolution
*animated
Detector SpecificationsPSAPD• 14 mm x 14 mm active area• operated at 10°C and -1630V• gain ~950• leakage current ~1µA
Scintillator array• 8x8 MLS• 1.65 mm x 1.65 mm x 22.00 mm• 1.75 mm pitch• 3M VM2000 reflective film• rough side surfaces, polished ends• coupled to PSAPD using Cargille Meltmount
Electronics• corner contacts: low noise JFET input wide bandwidth transimpedance amplifier with a 100 kohm transimpedance gain• trigger and energy signal from analog sum of corner contacts
Flood Histogram – 22Na
Energy Window: 250-650 keV
0
100
200
300
400
500
600
DOI Resolution
Energy Window: 250-650 keVIntegrated counts from all crystals.
Nor
mal
ized
Cou
nts
-10 -5 0 5 100
0.2
0.4
0.6
0.8
1
Depth (mm)
Width of Electronically Collimated Beam
-3 -2 -1 0 1 2 30
5
10
15
Distance (mm)
Cou
nt
Rate
(H
z)
FWHM = 2.3 mm
measurements(left scale)
Error Function fit(left scale)Implied Beam Profile
(arbitrary vertical scale)
scintillator slab
PMT
PMT
22Na source
z
DOI Resolution (deconvolved)
Energy Window: 250-650 keVIntegrated counts from all crystals.
Nor
mal
ized
Cou
nts
-10 -5 0 5 100
0.2
0.4
0.6
0.8
1
Depth (mm)
DOI Resolution Map*
DO
I Reso
lutio
n (FW
HM
, mm
)*
2.6
2.7
2.8
2.9
3
3.1
3.2
3.3
Crystal Column Number
Cry
stal R
ow
Nu
mb
er
1 2 3 4 5 6 7 8
1
2
3
4
5
6
7
8
*without deconvolution of beam width
Energy Resolution Map
15
15.5
16
16.5
17
17.5
18
18.5
19
19.5
Crystal Column Number
Cry
stal R
ow
Nu
mb
er
1 2 3 4 5 6 7 8
1
2
3
4
5
6
7
8
En
erg
y R
eso
lutio
n (FW
HM
, %)
Timing Resolution Distribution
2.5 3 3.5 4 4.5 5 5.50
5
10
15
Timing Resolution (FWHM, ns)
Nu
mb
er
of
Cry
stals
Radiation Damage? (preliminary measurements)Small-animal PET is not a “high radiation” environment.
*depending on scanner utilization assumptions
small-animal scanner
14mm x 14mm PSAPDs
~10 cm bore
22 mm long MLS crystals
Exposed PSAPD to 2 - 10 years* equivalent accumulated 511 keV flux
test setup
22Na source
8mm x 8mm PSAPD
4x4 array of 22 mm long MLS crystals
short distance
(bias to operating voltage for entire exposure, 10°C)
0 20 40 60 80 100 120 140 1600
20
40
60
800
50
100
150
200
pre-
radi
atio
n
0 20 40 60 80 100 120 140 1600
20
40
60
800
50
100
150
200
250
300
post
-rad
iatio
n
No Negative Impact on Performance Observed
ConclusionDemonstrated High-Res DOI PET detector with:
• 8x8 array of 1.65 mm x 1.65 mm x 22.00 mm crystals, with surface treatments chosen to optimize DOI resolution
• Minimal dead-space within array • Compact front-end electronics • No radiation damage effects observed• Tileable design• Excellent performance
• DOI resolution of <3 mm FWHM• Energy resolution of ~16% FWHM• Timing resolution of ~4 ns FWHM
(vs. plastic)
References• DOI in PET
L. R. MacDonald and M. Dahlbom, "Parallax Correction in PET Using Depth of Interaction Information," IEEE Trans. Nucl. Sci., vol. 45, no. 4, pp. 2232 – 2237, Aug. 1998.
Y. Shao, R. M. Manjeshwar, F. P. Jansen, P. N. Kumar, A. F. Chatziioannou, “Simulation Studies for a High Resolution and High Sensitivity Small Animal PET with DOI Detection Capability,” presented at IEEE Medical Imaging Conference, M6-11, Portland, OR, Oct. 2003.
• dual-end readoutW. W. Moses, S. E. Derenzo, "Design Studies for a PET Detector Module Using a PIN Photodiode to Measure Depth of Interaction," IEEE Trans. Nucl. Sci., vol. 41, pp. 1441 – 1445, Aug. 1994.
Y. Shao, K. Meadors, R. W. Silverman, R. Farrell, L. Cirignano, R. Grazioso, K. S. Shah, S. R. Cherry, "Dual APD Array Readout of LSO Crystals: Optimization of Crystal Surface Treatment," IEEE Trans. Nucl. Sci., vol. 49, no. 3, pp. 649 – 654, June 2002.
• PSAPDsK. S. Shah, R. Farrell, R. Grazioso, E. S. Harmon, E. Karplus, "Position-Sensitive Avalanche Photodiodes for Gamma-Ray Imaging," IEEE Trans. Nucl. Sci., vol. 49, no. 4, pp. 1687 – 1692, Aug. 2002.
• MLSC. M. Pepin, P. Berard, R. Lecomte, "Comparison of LSO, LGSO and MLS Scintillators," in Proc. IEEE Nuclear Science Symposium, vol. 1, San Diego, CA, Nov. 2001, pp. 124 – 128.
• VM2000R. S. Miyaoka, S. G. Kohlmyer, T. K. Lewellen, "Performance Characteristics of Micro Crystal Element (MiCE) Detectors," IEEE Trans. Nucl. Sci., vol. 48, no. 4, pp. 1403 – 1407, Aug. 2001.
Acknowledgment• K. Shah and R. Farrell (RMD).• T. Lewellen, R. Miyaoka, and M. Janes (U. Wash).