RPC TOF-PET (An Unlikely Approach)

1. RPC TOF-PET(An Unlikely Approach) Currently supported by RadForLife (QREN)

2. 02/23 The RPC–PET Team Researchers and engineers Alberto Blanco12, Antero Abrunhosa7, Custódio Loureiro2, Filomena Clemêncio2, Francisco Caramelo3, Grzegorz Korcyl11, Isabel Prata6, Jan Michel8, Jorge Landeck2, M. Kajetanowicz13, Marek Palka11, Michael Traxler4, Miguel Couceiro2,10,12, Nuno Chichorro3,7, Orlando Oliveira12, Paulo Crespo2,12, Paulo Fonte10,12, Paulo Martins12, Rui Alves12, Rui F. Marques2,12 Technicians Américo Pereira12, Carlos Silva12, João Silva12, Joaquim Oliveira12, Nuno Carolino12, Ricardo Caeiro12 Past collaborations Adriano Rodrigues3,7, C.M.B.A. Correia1,2, C. Gil9, Carlos Silvestre10, Durval Costa5, J.J. Pedroso de Lima12, L. Fazendeiro12, Luís Mendes3, M.F. Ferreira Marques9,10, M. P. Macedo1,10, Miguel Oliveira12 1 CEI, Centro de Electrónica e Instrumentação da Universidade de Coimbra, Coimbra, Portugal 2 FCTUC, Departamento de Física da Faculdade de Ciências e Tecnologia da Universidade de Coimbra, Coimbra, Portugal 3 FMUC, Faculdade de Medicina da Universidade de Coimbra, Coimbra, Portugal 4 GSI, Helmholtz Centre for Heavy Ion Research, Darmstadt, Germany 5 HPP, Hospitais Privados de Portugal, Porto, Portugal 6 IBILI, Instituto Biomédico de Investigação da Luz e Imagem da FMUC, Coimbra, Portugal 7 ICNAS, Instituto de Ciências Nucleares Aplicadas à Saúde da Universidade de Coimbra, Coimbra, Portugal 8 IKF, Institut für Kernphysik, Goethe-Universität, Frankfurt, Germany 9 ICEMS, Instituto de Ciência e Engenharia de Materiais e Superfícies de Coimbra, Coimbra, Portugal 10 ISEC, Instituto Superior de Engenharia de Coimbra, Coimbra, Portugal 11 JU, Jagiellonian University of Cracow, Cracow, Poland 12 LIP, Laboratório de Instrumentação e Física Experimental de Partículas, Coimbra, Portugal 13 NE, Nowoczesna Elektronika, Cracow, Poland

3. SIEMENS 03/23 Toward a human wide axial field of view PET scanner with RPC detectors Current PETscanners Full-body, wide axial field of view PET scanner concept CT CT [D.B.Crosetto, 2000] Low geometric efficiency High geometric efficiency High detection efficiency Good energy resolution (~ 12% @ 511 keV) Low time resolution (~ 600 ps) High cost (cristal + PMTs + electronics) Low detection efficiency (< 0.4% @ 511 keV) No energy resolution (but energy sensitivity) Reasonable time resolution (300 ps) Low cost (glass + electronics)

4. 04/23 Toward a human wide axial field of view PET scanner with RPC detectors Glass layers separated by N gaps impinged by perpendicular photons (simulation in GEANT4) [A. Blanco, et al., 2009] Detection efficiency depends also on the photon incidence angle,and detector design (materials and number of active gaps between electrodes) Increasing the detection efficiency (~ 20% for 20 detectors, each with 10 gaps) Increased scatter in the detector

5. 05/23 Toward a human wide axial field of view PET scanner with RPC detectors Extraction efficiencies for a single 400 m thick glass plate (GEANT4) M. Couceiro (PhD Thesis submitted on July 2013)

6. 06/23 Toward a human wide axial field of view PET scanner with RPC detectors First prototype of detection head with 3030 cm2  8 gaps Time resolution – 300 ps FWHM [A. Blanco et al., 2009] Efficiency as expected from GEANT4

7. 07/23 Toward a human wide axial field of view PET scanner with RPC detectors Detailed Simulations (Software and physics) • Simulation concerning spatial resolution • GEANT4 release 9.1, patch 2 • Standard Energy Physics (SEP) package for electromagnetic processes (photons, electrons and positrons), and without hadron, ion and decay physics • Simulation concerning Scatter Fraction and Noise Equivalent Count Rate • GEANT4 release 9.2, patch 4 • Standard Energy Physics (SEP) package for electromagnetic processes (photons, electrons and positrons), hadron, ion and decay physics, andRayleigh scatter provided by Low Energy Physics based on the Livermore libraries • Positron annihilation physics provided by • GEANT4 assuming perfect collinear photons • GATE assuming photon non-collinearity as a Gaussian blur in the polar angle with 0.58 FWHM, corresponding to values measured in water [S. Jan et al., 2004]

8. 08/23 Toward a human wide axial field of view PET scanner with RPC detectors • The scanner consists in a hollow parallelepiped with 4 detection heads • Each detection head has a stack of 20 RPC detectors in the radial direction • Each detector consists of 2 RPC modules, each with 5 gaps and independent axial electrodes, but sharing a common transaxial electrode

9. 09/23 Toward a human wide axial field of view PET scanner with RPC detectors Fine axial position readout • Each detector has 10 independent readout sections (a total of 800 independent readout sections for the scanner) with a: • 0.2 s non-paralyzable dead time for timing signals (ts) and coarse position readout • ps paralyzable dead time (currently 3.0 s) for fine axial and transaxial position readout 1000 mm Transaxial direction Time and coarse position readout Fine transaxial position readout 2400 mm Axial direction ps,1 ps,2+3 ts (0,2 s) ts (0,2 s) ps,2 1 1 2 2 3 3 ps,3 Fine position (3.44mm pitch in the radial direction and 2 mm pitch in the axial and transaxial directions) 1 Event 2 Event 1 2 Both events rejected or accepted with coarse position (3.44mm pitch in the radial direction, 30mm pitch in the transaxial direction, following a 10mm  Gaussian distribution in the axial direction)

10. 10/23 Toward a human wide axial field of view PET scanner with RPC detectors [P.Crespo et al., 2012]

11. 11/23 Toward a human wide axial field of view PET scanner with RPC detectors Spatial resolution obtained for a 1 m diameter spherical source centered in a 1 mm diameter water sphere Only DOI DOI + 1.0 mm Binning DOI + 2.0 mm Binning [M.Couceiro et al, 2012] Mean = 0.8 mm Mean = 1.4 mm Mean = 2.1 mm

12. 200 mm 45 mm 700 mm 12/23 Toward a human wide axial field of view PET scanner with RPC detectors Scatter fraction axial profiles (NEMA NU2–2001) Polyethylene (Dimensions in scale) Phantom center Line source with 3.2 mm inside diameter filled with 18F diluted in water

13. 13/23 Toward a human wide axial field of view PET scanner with RPC detectors 700 mm long phantom 1800 mm long phantom NECR – Noise Equivalent Count Rate (NEMA NU2–2001) NECR [kcps] NECR gain Activity concentration [kBq/cm3]

14. 14/23 A full scanner for mice Expected quantum efficiency and resolution

15. 15/23 A full scanner for mice Almost finished

16. 16/23 A full scanner for mice Readout meant for accuracy Provided by the HADES DAQ group GSI, IKF (Germany) and JU (Poland). DAQ 192 charge amplifiers optimized for large Cin 192 channels 12 bit streaming ADC Digital Pulse Processing by software Few channels of 100ps TDC also used Not so much hardware  low cost

17. 17/23 A full scanner for mice Typical charge spectra with gammas RMS pedestal/strip Pedestals (sum of 7 strips with larger signal) “TOFtracker” (RPC2012) 36 µm resolution tracking cosmic rays Mean Q ~320 ADC units RMS pedestal ~7 ADC units RMS pedestal/strip ~2 ADC units SNR ~ 45

18. 18/23 A full scanner for mice Resolution tests in simplified geometry Two detectors with XY localization Detector a Step Motor Acceptance ±56º Detector b Needle source, 0.2 mm  int. Planar (disk) source

19. 19/23 A full scanner for mice Resolution tests (needle source) Full area, all angles (up to 56º), all gaps (DOI) MLEM reconstruction Joint reconstruction of the source in 2 positions separated by 1mm. ~130k LORs in 3.5M 25m voxels. Color maps: planar profiles including peak density point. Isosufaces: 50% rel. activity Reconstructed activity profile across the black line shown in the upper left panel. Resolution ~0.4mm FWHM + background (Note: source is 0.2mm diam.)

20. 20/23 A full scanner for mice Resolution tests (planar source) 22Na planar source edge-on all angles, all gaps 1mm “mathematical” separation MLEM reconstruction Profiles across image (0.5 mm FWHM) Isosufaces: 50% relative activity

21. X’ 21/23 A full scanner for mice Resolution in final geometry (2 heads only, needle source) PRELIMINARY Calibration not done in full.

22. 22/23 Conclusions • RPC–PET is a Falloff of HEP into Nuclear Medicine [Blanco et al. NIMA 2003] • Disadvantages in comparison to crystal based detectors • Much smaller detection efficiency • No energy resolution, although energy sensitivity • Advantages • Inexpensive • Suitable for large area detectors, covering a large solid angle, increasing system sensitivity [Couceiro et al. NIMA 2007, Crespo et al. MIC 2009] • Increased position accuracy, allowing full 3D detection, minimizing gross parallax errors • Excellent timing resolution of 300 ps FWHM for 511 keV photon pair, allowing TOF-PET • Simulation results indicate that RPC detectors may be successfully used in human full–body TOF–PET, outperforming current commercial PET scanners in what concerns sensitivity, spatial resolution and NECR • Experimental results for a full mice scanner have shown a high spatial resolution, that outperforms current ones

23. 23/23 Acknowledgments The team greatly acknowledge the Laboratory for Advanced Computing of the University of Coimbra for the generous computation time provided in the milipeia cluster. The team also acknowledge to Dr. Miguel Oliveira, formerly in LIPCA and responsible for Coimbra Grid facilities.