PSMR2015, 17-20 May 2015, Isola d’Elba, Italy4th Conference on PET/MR and SPECT/MR
An innovative high rate preclinical PET/MR detector towards dynamic multimodal imaging.
Becker Robert, Cachemiche Jean-Pierre, Casella Chiara, Commichau Volker, Di Calafiori Diogo, Dissertori Günther, Fischer Jannis, Howard Alexander, Jeitler Astrik, Lustermann Werner, Morel Christian, Josep Oliver, Röser Ulf, Wang Qiulin, Weber Bruno
SAFIR - Small Animal Fast Insert for MRI
1. Introduction2. Construction and readout electronics3. NECR4. Spatial resolution5. High rate tests6. Summary / Outlook
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Objective: construction of a high rate PET insert for a Bruker BioSpin 70/30 USR MRI scanner (7T static field) with unprecedented temporal resolution (~5s), capable of truly simultaneous PET/MR acquisition.
Users:• Institute for Biomedical Engineering (IBE), ETH/University of Zurich, Prof. M. Rudin• Institute of Pharmacology and Toxicology (IPT), University of Zurich, Prof. B. Weber
Infrastructure:Bruker BioSpin 70/30 USR MRI scanner (7T static field) Installed at the Animal Imaging Center at Hoenggerberg(http://www.lifescience-zurichevents.ch/index.php?id=55&L=1)
Motivation:Quantitative dynamic PET imaging truly simultaneous with MRI using (among others) short lived isotopes 15O Study coronal blood flow and its underlying mechanism
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PET insert performance• High sensitivity ~5%• Good spatial resolution of <2mm FWHM• Excellent coincidence resolving time (CRT) ~300ps FWHM.
front-end electronics and DAQ• Operation at up to ~500 MBq source activity (10 times more than usual) data rates
~40kHz / ch• (almost) ZERO dead time, low pile-up• Large number of channels: ~16000
PET insert constraints• MR compatible: (i) no magnetic materials (ii) immune to high power RF switching fields
(300MHz) (iii) immune to static 7T field• Mechanical dimensions: Fitting inside the gradient coils (200 mm inner diameter) of the
MR system, leaving space for the receiving coils and the animal
image reconstruction• Quantitative, resolve temporal evolution of tracer concentration with precision of (5 – 10) s
> Such a PET detector is not existing > Several PET insert developments are ongoing, typically aiming at high spatial resolution, none at high temporal resolution
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Geometry:• Modules with 8x8 crystals:
one-to-one coupling of crystals to photo-sensors
8x8 crystal matrix:• 2.1 x 2.1 x 12mm3
• LYSO or LSO all sides polished
• 5 sides, 3M ESR foil + optical glue
8x8 SiPM matrix (TSV):• 2.0 x 2.0 mm2 sensors• 2.2 mm pitch• Hamamatsu
Kapton cable
FE card with readout ASCI
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Geometry:• Xtal dimensions: 2.1 x 2.1 mm2;
12 mm long• Modules with 8x8 crystals• Arranged into a ring of 24 modules• modules, ~130 mm inner diameter
Based on the reference design, a single ring system will be constructedStructure:• Mechanics will be planned for the
final system• Includes cooling interface to readout
electronics boards
Objective• Construction within ~1 year• Selection of components close
to completion
Design will be further optimized towards a full detector
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Geometry:• Build blocks of 5 modules• Integrate cooling for electronics
Kapton cable
FE cards with readout ASIC
Kapton cable
support
Five 8x8 crystal matrices
cooling/support
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Electronics compartment
Electronics compartmentSensor compartment
Dimensions:• Outer diameter ~200 mm, Inner diameter ~130 mm• Overall length ~1000 mm • Sensor compartment ~200 mm, electronic compartments ~400 mm
Modularity:• 10 rings with 24 modules of 8x8 crystals each 240 modules 240 SiPM arrays 15360 crystals 15360 SiPMs 15360 readout channels
• Total power consumption: (0.5-1.0) kW active liquid cooling• Operation temperature: ambient or lower (-20 degC)?
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Front-End ASIC 64 channel:• Pre-amplifier• Leading edge discriminator timing measurement with ~50 ps resolution• Time over threshold discriminator energy measurement with ~20 % FWHM• Two candidates TOFPET or STiC3 (both under investigation)• Power consumption (10 – 30) mW per channel• Data word (one hit): 48 bit• Digital data output: 1(2) LVDS links with 160 Mbit/sec 8/10 bit encoding
Data transmission: optical interfaces• 30 LVDS inputs 4.8 Gbit/sec• 1 optical output 5(10) Gbit/sec
DAQ• microTCA crate with optical receiver boards (AMC40)• Low jitter clock distribution (< 40 ps)• ASIC’s configuration
Auxiliary• Bias supply system and temperature monitoring including feedback• Power conversion system• Temperature and humidity monitoring
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NECR Noise Equivalent Count RateNECR = T2 / (T + f*R+ S): T true coincidences (trues)R random coincidences (randoms)S scatter coincidences (scatters)f=1, in the future singles based random estimation – almost error free
Data from GEANT4 simulation with additional:- Gaussian energy smearing: 20% FWHM- Gaussian time smearing (according to CRT)- Energy cut: (350-650) keV- Multiple window coincidence sorting
02468
101214
0 500 1000 1500 2000 2500
NEC
R in
Mcp
s
CTW in ps
NECR maximum for given CTW:- Depends on CRT- Slightly depends on activity use NECR optimum for 500 MBq Example: CRT 600 ps FWHM
NECR for different CRT’s, optimum CTW
CRT in ps 300 400 500 (3400)
CTW in ps 284 344 404 3400
0
5
10
15
20
25
0 200 400 600 800 1000
NEC
R in
Mcp
s
activity in MBq
300 ps
400 ps
500 ps
3.4 ns
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Crystal CRT FWHM
SIPAT LYSO:Ce 446 ps
SIPAT LSO:Ce:Ca(0.5) 327 ps
Crystals 1.5x1.5x12 mm3
Setup 22Na + 2 LYSO crystals in coincidence
Sensors Digital SiPM (PDPC, Philips)
Interface Air coupling (no grease)
Wrapping None
Digital SIPM (Philips) LSO:Ce:CaLYSO:Ce
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ToFPET: 411 ps FWHM
Coincidence setup, LYSO:Ce crystals, ‘air-coupled’ to Hamamatsu MPPCs22Na source ~2.5 MBq activity Improved results expected using optical glue and crystal wrapping
STiC: 388 ps FWHM
Work to achieve similar results using LYSO matrices instead of single crystals is ongoing
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Spatial resolution- Following NEMA- STIR: FORE, 2DFBP- Crystals 1.5x1.5x12 mm3
> Slightly smaller crystals than in the reference design
Radial: ~1.5 mm FWHMTang.: ~1.5 mm FWHMAxial: ~(1-3) mm FWHM depending on ring difference
0
0.5
1
1.5
2
2.5
3
0 5 10 15 20 25 30
reso
lutio
n FW
HM
in m
m
radial distance from center in mm
radial tangential axial ring diff 5 axial ring diff 9
NEMA National Electrical Manufacturers AssociationSTIR Software for Tomographic Image ReconstructionFORE Fourier Rebinning 2D FBP two-dimensional filtered back-projection
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1.0 mm1.2 mm
4.0
mm
3.2 mm2.4 mm1.
6 m
m
Line profiles
Derenzo phantom simulation: GEANT4Simulation 1s, 500 MBq in the spheres
Background Rat phantom, ZERO activityCrystals 2.0x2.0x12 mm3, pitch 2.2 mm (uniform)
Geometry 91 rings (uniform), 180 xtals / ring
Reconstruction OSMAPOSL (STIR)
1.6 mm
2.4 mm
4.0 mm3.2 mm
Voxel size: 0.55x0.55x1.1 mm3
Spheres- Concentration:1.42 MBq / µl
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1.0 mm1.2 mm
4.0
mm
3.2 mm2.4 mm1.
6 m
m
Line profiles
Derenzo phantom simulation: GEANT4Simulation 1s, 500 MBq in the spheres
Background Rat phantom, 1.74 kBq / µl Crystals 2.0x2.0x12 mm3, pitch 2.2 mm (uniform)
Geometry 91 rings (uniform), 180 xtals / ring
Reconstruction OSMAPOSL (STIR)
1.6 mm
2.4 mm
4.0 mm3.2 mm
Spheres- Concentration:100 kBq / µl
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2) CRT setup: • LYSO:Ce crystals matrices with ESR foil
(Hilger), crystal size: 3.1x3.1x12 mm3
0.0
200.0
400.0
600.0
800.0
0.00 20.00 40.00 60.00 80.00
CRT
FWH
M in
ps
rate per channel in kHz
18F UniZ Hospital 22Na lab
0.00
20.00
40.00
60.00
80.00
0 100 200 300 400
rate
per
cha
nnel
in k
Hz
activity in MBq
TOFPET: System tests at Univ. of Zurich Hospital with FDG1) Setup: • Detector heads: MPPC array plus LYSO matrices• Hamamatsu MPPC array 4x4, TSV, pixel size
50x50 µm2, sensor size 3x3 mm2, pitch 3.2 mm• 1 head on one side on one ASIC, 1 head opposite• TOFPET single channel rate was limited to 90 kHz
in our DAQ configuration
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Converging on a single ring configuration:• LSO/LYSO crystals: 2.1x2.1x12mm3
• Hamamatsu 8x8 MPPC array, 2x2 mm2 sensors, 50x50 µm2 pixel, TSV• 24 detector heads• Readout ASIC – ToFPET or STiC
First ring system available mid of 2016:• Tests in the Bruker 70/30 MR system• Data acquisition and processing software• Reconstruction software including first 4D algorithm
In parallel to first ring system• Continue detector head performance optimization
• Geometry: spatial resolution• Sensor and crystal: timing resolution
• Optimize readout electronics system• Optimize reconstruction software
Full system 2017++• Test of the complete ring system and analysis of results
This work was supported by the ETH Zurich Foundation through ETH Research Grant ETH-30 14-2, and by an SSSTC Exchange Grant EG 02-03201.
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