1. Introduction to the ClearPEM projects
Joao Varela
LIP, Lisbon
On behalf of the ClearPEM Collaboration
Jornadas LIP
Universidade do Minho, 7-9 January 2010

2. The ClearPEM Projects
High performance PET scanner for breast cancer detection. Scanner is in clinical tests.
Other applications to brain imaging and PET animal are being pursued
Projects developed by the ClearPEM consortium, in the framework of Crystal Clear at CERN
IP licensed to PETsys, SA

3. The ClearPEM scanner Good spatial resolution ( ~1.5 mm in whole FoV)
Fine crystal segmentation (2x2 mm)
DoI measurement with good resolution (FWHM ~2 mm)
Dual APD readout of individual crystal pixels
High Sensitivity ( ~ 40 cps/kBq in center FoV)
Long LYSO crystals (20 mm)
Two detector plates with large active area
Reduced Random Background (~30%)
Large flux of single photons (up to 10 MHz)
Coincidence time resolution of ~4 ns FWHM

4. The ClearPEM scanner

5. The ClearPEM detector Two detector plates:
6144 LYSO 2x2x20 mm3 crystals
12288 APD pixel channels
Dual readout of crystal pixels for DoI measurement
160x180 mm2 active area
Water cooling
75% of detector channels presently installed

6. ASIC Performance Pulse Shape Noise Amplifier rise time: 20ns
Variation of baseline and pulse shape 1-2%
Noise
Pedestal RMS = 2.2 ADC Counts = 5keV
ENC = 1300 e- r.m.s.
Inter-channel dispersion ~ 8%
Response to test pulse
Noise measurement

7. Data Acquisition Performance
Trigger Performance
Events in coincidence up to 1.5MHz
(This involves computation of energy and time, Compton grouping and transmission to the trigger processor)
Acquisition rate up to 0.8MHz
(This involves readout of the event dataframe after issuing a trigger)
Disk storage rate ~ 400MB/s
High performance useful for fast calibration runs
Needed for other PET applications

8. Ancillary Systems Cooling Bias Voltages
Water cooling of detector plates at 18 oC
Stability of temperature ± 0.1 oC
Bias Voltages
Regulation of APD bias voltages on the detector heads (64 regulation channels)
Long-term stability of HV ~ 28 mV rms
r.m.s. ~28 mV
40 hours

9. Energy Resolution Energy measurements: 137Cs
Na-22 spectra summed for all crystals
Energy measurements:
Average energy resolution at 511 keV for the full scanner is 16.0%
Dispersion of energy resolution of individual crystals is 8.8%
Good energy linearity (~ up to few percent)
137Cs
Resolution ~12.5%
Photopeak measurements

10. Time Resolution Time measurement:
Typical pulse sampling
Time measurement:
Photon time is extracted from the pulse samples fitted by the function:
Coincidence time resolution of the whole scanner is 5.2 ns FWHM
137Cs
50 MHz sampling
Resolution ~12.5%
Time difference in coincidence events
All scanner
coincidences

11. Energy in bottom vs top APDs
DoI Resolution
Asymmetry distributions
for different impact points in the crystal
Depth of interaction measurement
DoI is measured from light asymmetry in crystal dual readout
From direct measurement (collimated photons):
DoI resolution ~ 2 mm FWHM
for light asymmetry ±40%
Lu-176 background in crystals is used for DoI calibration in whole scanner
Average light asymmetry is ±59%
Energy in bottom vs top APDs

12. Energy Dependence on DoI
Photopeak position as a function of DoI
Energy is independent of DoI:
E[keV]=Kabs.(Etop+Krel.Ebottom)
Z[mm]=CDOI.((Etopkrel.Ebottom)/(Etop+krel.Ebottom))
Photopeak position is independent of DoI (up to few percent)
Energy resolution does not depend on DoI
137Cs
Resolution ~12.5%
Energy resolution as a function of DoI

13. Scanner Calibration Energy: Depth of interaction (Lu-176 background):
Distribution of energy calibrations
Energy:
Dispersion of channel gains 15.3%
Depth of interaction (Lu-176 background):
Dispersion of DoI calibration constants 7.8%
Time calibration:
Two pulse shape parameters per channel
Dispersion of time calibration constants 2%
~4600 crystals
Distribution of pulse peak time
~4600 crystals

14. ClearPEM Sensitivity 14 Sensitivity measurement: Na-22 source
A(22Na) = 2.73 µCi ± 0.3% (101kBq)
Sensitivity at center of FoV for 10 cm Detector Head opening is 1.0%
( keV, 20 ns)
Correction factors:
Incomplete (75%) detector: 1.3
In-detector Comptons: ~2
Corrected sensitivity: ~2.6%
Monte Carlo estimation: 3.1%
Count rate scan
Sensitivity (100 mm ): 1.0% 14

15. ClearPEM Spatial Resolution
With DoI
Point source imaging
Na-22 point source in a grid with 5mm pitch
Energy window keV
Sinograms of 16 source positions are added
Reconstruction with 3D-OSEM / STIR
Spatial resolution
Transaxial mm FWHM
(corrected for source size ~1mm)
DoI effect
Images without using DoI information show considerable blurring
5 mm
1 mm
Without DoI

16. ClearPEM Image Uniformity
Images of uniform Ge-68 source
Reconstruction with 4 orientations of the detector plates
Absorption, scatter and corrections are not applied
Image artifacts due to detector effects are corrected
Good image uniformity
Cylinder filled with positron emitter Ge-68
EW= keV
TW=4 ns
6 iterations 3D-OSEM

17. Clinical Tests Program
Scanner Installation
Hospital IPO, Porto
Phase 1 (present)
Patients indicated for PET/CT (other disease)
Negative breast exams
Tuning the image reconstruction with real cases
11 exams done
Phase 2
Patients with positive indication from x-rays mammography
Assessment of PEM sensitivity / specificity
Comparison to mammography and MRI
ClearPEM scanner at IPO Porto

18. Initial clinical exams
Example of typical exam:
dose 8 mCi
150 mm detector plate opening
4 angular orientations
coincidence window ±4 ns
energy window keV
fraction of randoms in FoV is 35%
Reconstruction:
3D-OSEM
randoms, attenuation and scatter corrections not applied
simple normalization correction
on-going work to reduce statistical noise

19. ClearPEM and Ultrasound
Dualmodal PET – US
CERIMED , Hospital Marseille, other partners
Ultra-sound probe with elastography capabilities
Cross-reference system and PET-US image fusion
Construction of second ClearPEM machine is well advanced
ClearPEM-Sonic

20. PET Animal
Pre-clinical studies with small and medium size animals
PET/MR insert
Texas Institute of Preclinical Studies
Application to brain imaging /EPFL
35 cm
60 cm
4.5 cm
Cooling
plates
Detector
modules
Version with DoI

21. High performance PET Improvements to Electronics/DAQ
Optical S-link (under test)
ASICv4 (in design)
Intelligent Front End Board (in project)
PET Ring Trigger (hw ready)
PET Time-of-Flight (FWHM ~200 ps)
SiPM and TOF ASIC
(collaboration with Torino and CERN)
SPAD single-photon detectors integrated with TDCs
(collaboration with TUDelft and CERN)

22. The ClearPEM Collaboration
E. Albuquerque1, F. G. Almeida2,13, P. Almeida3, E. Auffray10, J. Barbosa2, A. L. Bastos9, V. Bexiga1, R. Bugalho4, C. Cardoso4, S. Carmona8, J.F. Carneiro2, B. Carriço4, C. S. Ferreira4, N. C. Ferreira5, M. Ferreira4, M. Frade4, F. Gonçalves1, C. Guerreiro5, P. Lecoq10, C. Leong1, P. Lousã6, P. Machado1, M. V. Martins3, N. Matela3, R. Moura4, J. Neves4, P. Neves6, N. Oliveira3, C. Ortigão4, F. Piedade6, J. F. Pinheiro4, P. Relvas6, A. Rivetti , P. Rodrigues4, I. Rolo4, A. I. Santos8, J. Santos2, M. M. Silva1, S. Tavernier11, I. C. Teixeira1,9, J. P. Teixeira1,9, J. C. Silva4,10, R. Silva4, A. Trindade4, J. Varela4, 12
1 INESC-ID, 2 INEGI, 3 IBEB/FCUL, 4 LIP, 5 IBILI/FMUC, 6 INOV, 8 HGO, 9 IPO, 10CERN, 11VUB
Funded by