Transcript Multi-layered PET detector Module with Continuous

Continuous Scintillator Slab with
Microchannel Plate PMT for PET
Heejong Kim1, Chien-Min Kao1, Chin-Tu Chen1,
Jean-Francois Genat2, Fukun Tang2, Henry Frisch2,
Woong-Seng Choong3, William Moses3
1. Department of Radiology, University of Chicago, IL
2. Enrico Fermi Institute, University of Chicago, IL
3. Lawrence Berkeley National Laboratory, Berkeley, CA
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Outline
1.
2.
3.
4.
5.
Introduction
Material and Methods
Experimental Tests
Results
Summary
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1. Introduction
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The advantages of using Microchannel Plate(MCP) PMT.
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Monolithic scintillator slab.
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Higher packing fraction.
Convenience in Crystal machining.
Transmission Line readout scheme.
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Position sensitiveness.
Fast time response.
Compact size than conventional PMT.
Readout both ends of the strip.
A PET detector design, using continuous slab LSO with
MCP PMT, has been investigated. The preliminary results
of Geant4 simulation study are presented here. The real
tests to validate the simulation has been conducted with
Photonis Planacon MCP(XP85022) and the results are also
shown.
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MCP & Transmission Line board
Fig.1 - Photonis Planacon MCP(XP85022) with 1024(32x32) anodes(left)
and Transmission line(TL) baord with 32 microstip(right). One microstrip is
connected to one raw of MCP anode(32) and signals are readout at both
ends of a TL.
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2.Material and Methods
A. Detector configuration
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One detector module consists of two layers of LSO
slab and MCP assembly.
LSO slab dimension : 102x102x5mm3.
MCP assembly dimension : 102x102x9.15mm3 It
includes photocathode and TL structure. (MCP with
8’’x8’’ area is under development.)
MCP is coupled to LSO slab at back side.
An alternative configuration was also simulated.
Single layer of 10mm thickness slab. Two MCPs
are coupled the LSO slab at both sides.
Distance between two detector modules : 5cm
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Double layers vs Single layer
Fig. 2 Simulation set-up with tow detector modules. Two layers of
scintillator slab(5mm thick) and MCP assembly( left). Bule colored part
is the scintillator slab and MCP is shown in grey. For comparison,
10mm thick single scintillator slab are coupled with two MCPs at both
sides.(right)
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B.Simulation Setup
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Photon generation and transport was simulated by
Geant4.
Two 511keV photons are generated back to back
at the middle of two detector modules and sent to
the detector centers.
The side edges of the slab was treated black to
avoid the light reflection at the edge.
The surface between LSO slab and MCP glass was
optically coupled with the optical grease.
LSO characteristics( simulation input parameters)
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Light yield : 30,000/MeV
Decay time : 40ns
Resolution : 10.4%( FWHM)
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Q.E & LSO emission spectra
Fig. 3 Quantum efficiency of XP85022 as a function of the wavelenth(left).
Emissin spectra of LSO before(after) XP85022 Q.E applied : Geant4
generated(right).
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Signal Readout Scheme
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Electrical signal was formed based on the measured
XP85022 characteristics combining with the Geant4
simulation outputs: optical photon’s position and
arrival time at photocathode.
For each individual photo electron, the measured
single photo electron response assigned. Convolute
pulses due to all the photo-electron within the area
of TL strip.
TL signal then propagates to both ends of TL.
In the first layer MCP, 24 TL strips run vertically. By
applying Anger logic to measured TL signals, X
coordinate can be obtained.
TLs runs horizontally in the second layer to get Y
coordinate.
In addition, the position can be measured form the
measured time difference at both ends of TL.
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3. Experimental Tests
The test set-up was built using a XP85022 MCP and TL board
to measure the characteristics of the MCP. The measured
single photo-electron response(SER) was fed to the simulation
for electrical signal
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XP85022
Chevron type, 10um pore
Textronix DPO7354
Oscilloscope recorded the
waveform of TL at
10GS/s.
The charge of pulse are
obtained by integrating
TLwaveform.
Fig. 4 MCP/TL assembled for the real test. 4 TL channels were connected
through SMA to the DPO7354 Oscilloscope. A LSO crystal with 1”x1”
area is on top of MCP.
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A. Single Electron Response(SER)
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SER was measured using the pulsed LED as a light source.
The rise time of SER was measured ~560ps.
The SER signal was spread in ~5 TL.
( may due to the gap between MCP out and anode)
Fig. 5 Integrated charge of SER waveforms(left). Averaged waveform of
SER; the maximum TL signal only(right).
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The MCP gain vs HV
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Absolute gain of the XP85022 was calculated
from the integrated charge of SER.
The gain at HV = -2300V : 1.5 x 106
Fig. 6 XP85022 MCP gain as a function of HV.
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B. Responses to 511keV photon
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MCP/TL coupled to 25x25x8.5mm3 LSO crystal.
Hamamatsu R9800PMT with 6.2x6.2x25mm3 LSO for coincidence
Use Na22 for positron source.
Waveform recorded by Tektronix DPO7354 scope
E resolution =
13.8% FWHM
Fig. 7
Test set-up for 511keV gamma coincidence(left) Energy
distribution of R9800PMT(right).
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Energy( real test)
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Energy sum of 3 TLs : only left side of TL.
The peak is not at 511keV.
Light is widely spread and readout channel was only 3.
Peak at ~75keV of 3 TL corresponds 511keV.
Energy sum of 3TL is well matched.
Simulation of Test Setup
Real Test
Fig. 8 Energy sum of 3 TL signal by 511keV photon.
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Coincidence Timing ( real test)
Testselection
Real
Event
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Real Test
requirement for the coincidence timing.
R9800PMT : 400 < E < 600 keV
MCP 3TL Sum :
60 < E < 90keV
Coincidence timing resolution = ~590ps( FWHM)
contribution from R9800PMT side = ~200ps (FWHM)
Simulation of the test setup
Fig. 9 coincidence time distribution.
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4. Results - Energy
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Sum of 5 TL signals
Energy resolution : ~12%
Use the measured XP85022 SER for the TL signal.
Fig 10. Energy distribution.
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Result - Coincidence Timing
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The event time was extracted by Leading Edge(LE) to the
maximum TL signal. ( Threshold : 3mV)
Energy window [400, 600] keV required for coincidence event.
The detection efficiency : ~14%( ~37% for one module).
Coincidence timing resolution : ~360 ps.
Alternative configuration in Fig.2 : ~600ps
Fig. 11 Event time difference of coincident event.
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Results - Position
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The centroid of the most energetic 5 TL signal.
RMS of X reconstructed coordinate = ~2.3mm
Degraded near edge due to light absorbing at the surface.
Y coordinate using the time difference : ~3.2mm (RMS)
Fig. 12 Reconstructed X coordinate(left). The 511keV gamma
injected 20mm off the center. The deviation of reconstructed
position from the injection point: (X_recon - X_gamma)
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5.Summary
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A PET detector design using continuous scintillator
slab and MCP PMT with Transmission Line readout
was studied.
Geant4 was used for optical photon simulation.
Real test setup using XP85022 MCP and TL board
was built to measure SER of MCP.
The measurement from the test set-up was used
to
simulate TL signal with Geant4 output.
The preliminary results from the study show
promising results.
Energy resolution~12% at 511keV was obtained.
The coincidence time resolution ~360ps with
~13% detection efficiency were estimated.
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References
1. J. L. Wiza, NIMA 162 (1979) 587-601
2. F. Bauer et al, IEEE NSS/MIC CR(2006) 2503-2505
3. J. Anderson et al, IEEE NSS/MIC CR(2008) 24782481
4. S. Agostinelli et al, NIMA 506(2003) 250-303
5. http://www.photonis.com
6. J.S. Huber et al, IEEE TNS 48(2001) 684-688
7. J.-F. Genat et al, NIMA 607(2009) 387-393
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