SmartPET Ge Planar Detector System

SmartPET Ge Planar Detector System
H.C. Boston, A.J. Boston, R.J. Cooper, A.N. Grint,
A.R. Mather, P.J. Nolan, D.P. Scraggs, G. Turk
SORMA : May 2006 : Helen Boston
Overview
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•
•
•
•
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Overview of the SmartPET project
The requirements of the system
The detectors
The design of the SmartPET system
Analogue results
Initial characterisation the detector
SmartPET Project
•
•
SORMA : May 2006 : Helen Boston
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•
Investigate use of Ge for purpose of Positron
Emisson Tomography
Dual head small animal demonstrator
Require a detector system with good energy
and time resolution, and some way of getting
good spatial resolution
Full characterisation required to understand
detector
SORMA : May 2006 : Helen Boston
SmartPET Detectors
• Each detector houses an electrically segmented
orthogonal strip Germanium detector (DSSGeD)
• The active crystal volume is 60 x 60 x 20 mm
• Strip pitch is 5mm giving a spatial resolution of 5 x 5
x 20mm
• 24 readouts per detector
• Electrical segmentation so
no loss in efficiency
• Each detector has a 72
hour LN dewar attached
• Energy resolution of detectors
on all strips for 122keV <
1.6keV
SORMA : May 2006 : Helen Boston
SmartPET Detectors
In Lab
SmartPET: Design
60 mm
5 mm
50 mm
60 mm
91 cm
Initial measurements
• Analogue system
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•
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HV – ORTEC 659 NIM unit
± 12V supplied by NIM bin
671 ORTEC spectroscopic amplifier unit
ORTEC software for data collection
SORMA : May 2006 : Helen Boston
• Measurements
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•
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Check to see signal present for each strip
Measure DC offset and sensitivity
Resolution measurements using a variety of sources
Possible problems investigated further
Scope
Spec
Amp
Maestro
241Am
Data
300000
¾AC
∼0.3microns
∼Strip gap 300microns
¾DC
∼50microns
∼Strip gap 180microns
10000
Number of Counts
250000
17.8
8000
DC06
26.3
20.8
6000
200000
4000
150000
2000
0
100000
10
20
30
50000
0
0
250000
200000
26.3
4000
0
10
20
30
50000
0
0
60
•AC06
•FWHM = 1.45 keV
•DC06
•FWHM = 1.12 keV
8000
100000
40
20.8
12000
150000
20
Energy (keV)
16000
Number of Counts
SORMA : May 2006 : Helen Boston
17.8
AC06
20
40
Energy (keV)
60
152Eu
Number of counts (log)
SORMA : May 2006 : Helen Boston
10000
1000
100
10
Spectrum
Energy
(keV)
FWHM
122
1.78
244
1.84
344
1.88
779
2.12
964
2.34
1111
2.40
1408
2.90
1
0
1000
2000
3000
4000
5000
6000
Channel Number
Efficiency at 511keV ~ 1 in every 1000 events fully collected
i.e. 0.1% absolute efficiency
Detector Characterisation
What is characterisation?
• Provides a full description of the detector
response
• Full characterisation of germanium crystals
– Detailed source scans
SORMA : May 2006 : Helen Boston
T90
90%
T30
∆E
30%
10%
241Am
AC
DC
• XY position information
• Energy deposited on one
AC and DC strip (mγ=1)
AC01
DC12
DC01
AC12
AC face scan
• 60keV gate, 6keV wide
• 120 sec per position
241Am
AC
Subtracted scan
• Position gated = 10.4M
• M1 gated = 9.3M
• Subtracted = 1.1M
• 10.74% data lost in
charge sharing
• Mγ=2 not expected at
60keV
241Am
DC
Subtracted scan
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•
•
•
Position = 9.6M
M1 gated = 9.2M
Subtracted = 0.4M
4.6% data lost in
charge sharing
241Am
AC
DC
AC01
AC face scan
AC12
DC12
T30
DC01
T90
AC
DC
Side
DC
ScanAC
DC12
1
AC
2
0
C
A
1
DC01
57Co
DC AC
• HT coupling capacitors
• Maximum intensity close
to centre depth
AC coupled side
DC coupled side
Side scan
• AC electrodes visible
• 120 sec per position
AC01
AC12
57Co
DC12
DC face scan
50
40
30
40
50
60
70
80
90 100
110
100
90
80
70
60
50
40
30
20
10
70
60
50
50
40
40
R ise tim e (ns)
T30
Y (m m )
DC01
AC12
Y (m m )
AC01
R ise tim e (ns)
AC coupled side
30
30
40
20
50
60
70
80
90 100
10
X (mm)
X (mm)
40
30
40
50
60
70
80
X (mm)
90 100
140
120
50
100
40
30
40
80
60
50
60
70
80
X (mm)
90 100
40
20
R ise tim e (ns)
160
Y (m m )
50
200
180
160
140
120
100
80
60
40
20
R ise tim e (ns)
T90
Y (m m )
DC coupled side
57Co
X=77 Risetimes
200
100
AC
DC
90
AC
DC
190
180
170
Risetime (ns)
70
Risetime (ns)
SORMA : May 2006 : Helen Boston
80
60
50
160
150
140
40
130
30
120
20
110
10
100
0
2
4
6
8
10
12
14
16
18
20
0
2
4
6
8
10
12
Depth (mm)
Depth (mm)
T30
T90
14
16
18
20
Conclusion
• Full characterisation of the first detector
completed
SORMA : May 2006 : Helen Boston
– All channels have signal present
– Analogue measurements have been conducted
– A full surface and side scan of the data has
been completed
• PSA to be presented by Ren Cooper
• Future :
– PET images and Compton Camera
– Redo areas of the detector with a smaller
collimator to investigate strip gaps