Development of RPC based PET B. Pavlov University of Sofia

7.V.2010ECFA 2010, B. Pavlov2 Outline  Positron Emission Tomography (PET)‏  Resistive Plate Chambers (RPC)‏  Why RPC for PET ?  RPC design and optimizations  Detector read-out  Conclusions

7.V.2010ECFA 2010, B. Pavlov3  G. Muehllehner, J.S. Karp, Phys. Med. Biol. 51 (2006) R117–R137  T.K Lewellen, Phys. Med. Biol. 53 (2008) R287–R317  G. Muehllehner, J.S. Karp, Phys. Med. Biol. 51 (2006) R117–R137  T.K Lewellen, Phys. Med. Biol. 53 (2008) R287–R317 Positron-Emission Tomography (PET) ‏

7.V.2010ECFA 2010, B. Pavlov4 Usually cyclotrons are used to generate commonly used PET isotopes IsotopeHalf life 11 C20.3 min 15 O2.03 min 18 F109.8 min 9 B98.0 min 13 N~10 min PET tracers FDG (fluorodeoxyglucose), as a glucose analogue, is taken up by high-glucose-using cells such as brain, kidney, and cancer cells. Commonly used tracers: water ammonia glucose and glucose analogues oxygen

7.V.2010ECFA 2010, B. Pavlov5 Commercial PET

7.V.2010ECFA 2010, B. Pavlov6  B.J. Pichler, H.F. Wehrl, M.S. Judenhofer, J. Nucl. Med. 49/2 (2008) 5–23  N.E. Bolus et al., J. Nucl. Med. Technol. 37/2 (2009)  B.J. Pichler, H.F. Wehrl, M.S. Judenhofer, J. Nucl. Med. 49/2 (2008) 5–23  N.E. Bolus et al., J. Nucl. Med. Technol. 37/2 (2009) PET – physical limitations & problems

7.V.2010ECFA 2010, B. Pavlov7  R. Santonico and R. Cardarelli, Nucl. Instr. Meth. A187, (1981) ‏ Resistive-Plate Chambers (RPC) ‏

7.V.2010ECFA 2010, B. Pavlov8 converter resistive plates detecting strips  A. Blanco et al., Nucl. Instr. Meth. A508, (2003) ‏  P. Fonte, A. Smirnitski, M.C.S. Williams, NIM A 443, (2000) ‏ RPC-PET electron avalanche electron photons

7.V.2010ECFA 2010, B. Pavlov9 High price Higher sensitivity for scattered photons Parallax error Time resolution > 200 ps Spatial resolution ~ 2-3 mm PMT, APD,... FOV cm Much cheaper Sensitivity decreases with E Practically no parallax Time resolution ~ 30 ps Spatial resolution ~ 300 μm No need of PM Large area → large FOV ~ 1 m Not affected by magnetic fields Main problem: increase efficiency for 511 KeV photons Scintillator-based vs RPC-PET

7.V.2010ECFA 2010, B. Pavlov10  A. Blanco et al., Nucl. Instr. Meth. A533, (2004) ‏  A. Blanco et al., Nucl. Instr. Meth. A508, (2003) ‏  C. Lippmann, H. Vincke, W. Riegler, NIM A602, (2009) ‏  S. An et al., ‏ Nucl. Instr. Meth. A594, (2008) ‏  A. Blanco et al., Nucl. Instr. Meth. A508, (2003) ‏  C. Lippmann, H. Vincke, W. Riegler, NIM A602, (2009) ‏  S. An et al., ‏ Nucl. Instr. Meth. A594, (2008) ‏  M. Couceiro et al., Nucl. Instr. Meth. A580, (2007) ‏  A. Blanco et al., Nucl. Instr. Meth. A602, (2009)  M. Couceiro et al., Nucl. Instr. Meth. A580, (2007) ‏  A. Blanco et al., Nucl. Instr. Meth. A602, (2009) spatial resolution of 0.6 mm FWHM without optimization time resolution ~ tens of ps 1.5–2 times lower sensitivity to 300 KeV photons vs 511 KeV ones RPC-PET: state of art

7.V.2010ECFA 2010, B. Pavlov11 RPC PET R&D Two main goals: To increase the efficiency for 511 keV photons To suppress Compton scattered photons Photon spectrum simulation GEANT simulation of different RPC designs GEANT simulation of multigap RPC  N. Ilieva et al., API Conf. Proc. 1203, , (2010)‏

7.V.2010ECFA 2010, B. Pavlov12 gamma (filter)‏ gas resistive plate (insulator)‏ detecting strips converter Gas – converter design Maximal electron yield 0.30% for tungsten, 0.38 % for lead

7.V.2010ECFA 2010, B. Pavlov13 Gas – converter design e yield and ejected electrons for 5 conv. (% from the initial photon number) ‏ BUT higher sensitivity for scattered in the body photons ! e yield for 5 conv. (% from the initial photon number) ‏

7.V.2010ECFA 2010, B. Pavlov14 Gas – insulator - converter design Maximal electron yield for 511 KeV photons (0.315 ± 0.005) % (~ 0.17% lower than in Gas - Conv. design) ‏ converter

7.V.2010ECFA 2010, B. Pavlov15 Gas – insulator - converter design e - yield vs width for 5 different energies => converter width 40 μm e - yield vs photon energy for 40 μm converter

7.V.2010ECFA 2010, B. Pavlov16 Gas – insulator - converter design e - yield vs insulator width for 5 different energies => insulator width 100 ÷ 200 μm

7.V.2010ECFA 2010, B. Pavlov17 Multi-gap GIC design 100 gaps provide sufficient amplification lower-energy photons suppression strips gas gap glass PCB mylar Bi or Pb oxide max yield 511 KeV ~ 43%

7.V.2010ECFA 2010, B. Pavlov18 Multi-gap GIC design Max yield for 511 KeV: (23.8 ± 0.4)% converter Bi, 50 μm glass 50 μm Highest sensitivity for 511 KeV 511 / 307 ~ 2:1

7.V.2010ECFA 2010, B. Pavlov19 86% from the registered photons have energies > 383 KeV Thus Compton suppression is achieved !!! Multi-gap GIC design „Body“ spectrumConvolution of spectrum and response RPC response

7.V.2010ECFA 2010, B. Pavlov20 RPC readout electronics Dedicated electronics based on NINO ASIC and HPTDC is under development. For the moment ALICE TOF FEAs (based on NINO) and HADES TRBs (based on HPTDC) are used.

7.V.2010ECFA 2010, B. Pavlov21 Conclusions  Model investigations towards the design of an RPC-based PET detector are carried out.  RPC design optimized for PET is obtained.  Prototype production technology is developed.  Dedicated electronics is under development.  First prototypes are ready for investigations.

7.V.2010ECFA 2010, B. Pavlov22 Thank you !

7.V.2010ECFA 2010, B. Pavlov23 Back up slides

7.V.2010ECFA 2010, B. Pavlov24 RPC-PET: design & optimization  Simulation of RPC detectors  Detector „basic unit“: two glass plates, 2 mm gas gap 300 μm  Gas composition: 85% C 2 H 2 F 4 + 5% i-C 4 H % SF 6  Electric field: 100 kV/cm  Simulation of RPC detectors  Detector „basic unit“: two glass plates, 2 mm gas gap 300 μm  Gas composition: 85% C 2 H 2 F 4 + 5% i-C 4 H % SF 6  Electric field: 100 kV/cm

7.V.2010ECFA 2010, B. Pavlov25 RPC-PET: design & optimization  Geant 4 ( ‏ Compton scattering, photo-effect multiple scattering, ionization, Bremsstrahlung  Detector „basic unit“: two glass plates, 2 mm gas gap 300 μm  Gas composition: 85% C 2 H 2 F 4 + 5% i-C 4 H % SF 6  Electric field: 100 kV/cm  Geant 4 ( ‏ Compton scattering, photo-effect multiple scattering, ionization, Bremsstrahlung  Detector „basic unit“: two glass plates, 2 mm gas gap 300 μm  Gas composition: 85% C 2 H 2 F 4 + 5% i-C 4 H % SF 6  Electric field: 100 kV/cm

7.V.2010ECFA 2010, B. Pavlov26 38% absorbed // 82% / initial, 51%: E < 511 KeV 18% / initial, 11%: PET image O 61.4 % C 22.9 % H 10.0 % N 2.6 % Ca 1.4 % P 1.1 % K 0.2 % S 0.2 % Na 0.1 % Cl 0.1 % 40 x 40 x 150 cm g/cm 3 Photon propagation in the human body Compton scattering Photo-effect

7.V.2010ECFA 2010, B. Pavlov27 Electron yield in the gas photons: at least one interaction within the converter has lead to the ejection of an electron into the gas gap photon interaction in the converter & electron propagation to the gas k photon interaction coefficient N γ number of photons at x s electron interaction coefficient Thin converter; a – max e yield; saturation 95% yield thickness Photon-beam attenuation / coeff. c Decrease after the max value

7.V.2010ECFA 2010, B. Pavlov28