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Resolution studies on a small animal RPC-PET prototype

Resolution studies on a small animal RPC-PET prototype. A. Blanco 1 , N. Carolino 1 , C.M.B.A. Correia 2 , L. Fazendeiro 1 , Nuno C. Ferreira 3 , M.F. Ferreira Marques 4,5 , R. Ferreira Marques 1,6 , P. Fonte 1,5 , C. Gil 4 , M. P. Macedo 2,5.

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Resolution studies on a small animal RPC-PET prototype

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  1. Resolution studies on a small animal RPC-PET prototype A. Blanco1, N. Carolino1, C.M.B.A. Correia2, L. Fazendeiro1, Nuno C. Ferreira3, M.F. Ferreira Marques4,5, R. Ferreira Marques1,6, P. Fonte1,5, C. Gil4, M. P. Macedo2,5 1 LIP, Laboratório de Instrumentação e Física Experimental de Partículas, 3004-516 Coimbra, Portugal. 2 CEI, Centro de Electrónica e Instrumentação, Univ. Coimbra, 3004-516 Coimbra, Portugal. 3 IBILI, Instituto Biomédico de Investigação de Luz e Imagem, Faculty of Medicine, 3000, Coimbra Portugal. 4 ICEMS, Departamento de Física, Universidade de Coimbra, 3004-516 Coimbra, Portugal. 5 ISEC, Instituto Superior de Engenharia de Coimbra, 3031-199 Coimbra, Portugal 6 Departamento de Física, Universidade de Coimbra, 3004-516 Coimbra, Portugal.

  2. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra • Summary • Small Animal PET overview. The basic idea of construction with RPCs. • The first prototype. • Experimental intrinsic and image spatial resolution. • Different contributions. Effect of positron range distribution. • Simulated performance • Conclusions Resolution studies on a small animal RPC-PET prototype

  3. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea HIDAC Micro PET-Focus YAP-PET Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra The small animal PET • Scintillator based technology (BGO, LSO, YAP, …), MWPC. • Ring diameter / axial length  150 mm / 50 mm => ~ low geometry acceptance • Spatial resolution  1 - 2 mm FWHM • Timing resolution ~ 2-3 ns • Central Point absolute sensitivity •  5 - 70 cps/KBq • Applications: Development of new drugs, human disease studies, validation of Gene therapies, ...

  4. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra The basic idea for a small animal PET with RPCs • High geometry acceptance > 90%. • Fully 3D measurement of the interaction point of the photon => No parallax error. • Sub-millimetre spatial resolution. • High timing resolution ~ 0.3 ns FWHM* • Moderate Efficiency. • Compatible with Magnetic Resonance Imaging. Use the plates as a g conversor * Nucl. Instr. And Meth A, 443 (2003) 88-93

  5. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra RPCs Charge-sensitive electronics allowing interstrip position interpolation 32 strips 16 plates 16 stacked RPCs. ....... ....... Aimed at verifying the concept and show the viability of a sub-millimetre spatial resolution. Depth of interaction Z 2D measurement of the photon interaction point. 3D measurement possible NIMA 508 (2003) 70–74 X Transaxial

  6. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea • Copper (on a PCB) and glass electrodes. • 32 1-mm wide X pickup strips. • 0.3 mm Gap. • Not optimized for high efficiency. Glass electrode (anode) Copper electrode (cathode) X Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra RPCs Transaxial coordinate Depth of interaction Active area 32 x 10 mm2 0.3 mm spacers

  7. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Scanner

  8. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea 22Na source 0.22 Ø x 0.5 mm Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Intrinsic spatial resolution: How to measure . LORs Red lines correspond to real data acquired with the 22Na source LOR = Line of Response. Connects the interaction points of the photons. D = Distance between each LOR and the center of the system

  9. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea • Annihilation photon non-collinearity. • N(x) = exp(-x2/2σ2), where FWHM = 2.35σ = 0.0022dswith ds the system diameter (mm). • Positron range. • P(x) = C1exp(-k1x) + (1-C1)exp(-k2x) • Source size. • S(x)=sqrt(size2 - x2), where size is the source radio (mm). • Detector response. • D(x) = exp(-x2/2σdet2) • Scatter background. • SC(x) = exp(-k3x) • R(x) = C2(N(X) P(X) D(X) S(X))+(1-C2)SC(X) • Annihilation photon non-collinearity. • N(x) = exp(-x2/2σ2), where FWHM = 2.35σ = 0.0022dswith ds the system diameter (mm). • Positron range. • P(x) = C1exp(-k1x) + (1-C1)exp(-k2x) • Source size. • S(x)=sqrt(size2 - x2), where size is the source radio (mm). • Detector response. • D(x) = exp(-x2/2σdet2) • Annihilation photon non-collinearity. • N(x) = exp(-x2/2σ2), where FWHM = 2.35σ = 0.0022dswith ds the system diameter (mm). • Positron range. • P(x) = C1exp(-k1x) + (1-C1)exp(-k2x) • Source size. • S(x)=sqrt(size2 - x2), where size is the source radio (mm). • Annihilation photon non-collinearity. • N(x) = exp(-x2/2σ2), where FWHM = 2.35σ = 0.0022dswith ds the system diameter (mm). • Positron range. • P(x) = C1exp(-k1x) + (1-C1)exp(-k2x) • Source size. • S(x)=sqrt(size2 - x2), where size is the source radio (mm). • Detector response. • D(x) = exp(-x2/2σdet2) • Scatter background. • SC(x) = exp(-k3x) • Annihilation photon non-collinearity. • N(x) = exp(-x2/2σ2), where FWHM = 2.35σ = 0.0022dswith ds the system diameter (mm). • Annihilation photon non-collinearity. • N(x) = exp(-x2/2σ2), where FWHM = 2.35σ = 0.0022dswith ds the system diameter (mm). • Positron range. • P(x) = C1exp(-k1x) + (1-C1)exp(-k2x) Phys. Med. Biol. 44 (1999) 781-799. 520 m FWHM 1550 m FWTM K2 = 3.75 mm-1 J. Nucl. Med. 34 101 1993. IEEE TNS, vol 33, No 1, (1986), 565-569 FWHMdet = 220 µm C2 = 0.04, K3 = 0.32 mm-1 Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Intrinsic spatial resolution • Annihilation photon non-collinearity. • N(x) = exp(-x2/2σ2), where FWHM = 2.35σ = 0.0022dswith ds the system diameter (mm). • Positron range. • P(x) = C1exp(-k1x) + (1-C1)exp(-k2x) • Source size. • S(x)=sqrt(size2 - x2), where size is the source radio (mm). • Detector response. • D(x) = exp(-x2/2σdet2) • Scatter background. • SC(x) = exp(-k3x) Point spread function

  10. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Intrinsic spatial resolution. Using a magnetic field Using an intense static homogeneous magnetic field => Improve spatial resolution ?? - Positron range is reduced(only two dimensions perpendicular to B) big effect with high energy radioisotopes. - Annihilation photon non-collinearity is reducedby mixing orthopositronium and parapositronium states,small effect. - Wirrwar et al. IEEE TNS Vol 44 No 2, April 1997. • Bibliography: • Hammer et al. Phy. Med. Biol. 40 (1995) 691-697. • Hammer et al. IEEE TNS vol 42 No 4, August 1995. • - Raylman et al. IEEE TNS vol 43 No 4, August 1996. Remember: This technology can operate in a magnetic field

  11. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Intrinsic spatial resolution. Geant4 simulations with B • Comparing G4 with a measurement using 68Ga Geant4 * Positron Range  Adjusted Gaussian Response 0 T (1.0 mm FWHM, 5.7 mm FWTM) 5 T (1.1 mm FWHM, 2.8 mm FWTM) Geant4 => Geant4 compares reasonably well with this measurement.

  12. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Intrinsic spatial resolution. Geant4 simulations with B Geant4 simulation for 22Na • The effect for 22Na is very small even at 10 T. • The idea is still valid for high energy radioisotopes (13N, 68Ga, 82Sr).

  13. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Intrinsic spatial resolution: Limits Spatial resolution calculated as: R = C2*(N  P  D  S) + (1-C2)*SC Diameter system 60 mm RPC-PET 18F => 520m Physical limit 18F => 350 m positron range + non-collinearity

  14. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Image spatial resolution. Positron range contribution The positron distributioncontributes in different ways to the sinogram and to the final image. 1D-histogram of the 3D-distribution contribution to: Sinogram PSF (intrinsic resolution) 2D-histogram profile of the 3D-distribution contribution to: Image PSF (image resolution)

  15. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Proceeding IEEE MIC (2004) M2-177 Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Image spatial resolution. Maximum likelihood-expectation maximization with resolution modeling (ML-EM) ~ 305 m FWHM Filtered Back Projection FBP ~ 465 m FWHM 0.46 0.31 0.47 0.48 0.45 0.30 0.32 0.29 Homogeneous spatial resolution over the entire detector

  16. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Simulated count rate performance Evaluation of the count rate performance Prompts, Randoms, and NECR Mouse size phantom: 25 Ø x 70 mm (34 cm3) Annihilations and photons on the detector surface from the simulation. • Characteristic of the simulated system: • 90% Solid angle coverage => defining a FOV of 60 Ø x 100 mm axial. • Narrow coincidence window 1 ns. (Timing resolution 300 ps FWHM*) • Dead time ~ 100 ns. • 10% - 15% detection efficiency. * Nucl. Instr. And Meth A, 443 (2003) 88-93

  17. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Simulated count rate performance: Prompts 1000 Kcps True + Scatter 500 Kcps Typical injected doses for mouse studies (3.7 MBq – 37 MBq)

  18. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Simulated count rate performance: Randoms The high timing resolution keeps the random events at a low values Typical injected doses for mouse studies (3.7 MBq – 37 MBq)

  19. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Simulated count rate performance: NEC 318 Kcps 240 Kcps Typical injected doses for mouse studies (3.7 MBq – 37 MBq)

  20. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Performance Comparison between different small animal PET parameters and the expected parameters of the RPC-PET. • Yuan-Chuan Tai et al., “MicroPET II: design, development and initial performance of an improved MicroPET scanner for small-animal imaging”, Phys. Med. Biol. 48 (2003) 1519-1537. • Yongfeng Yang, et al., “Optimization and performance evaluation of the microPET II scanner for in vivo small-animal imaging”, Phys. Med. Biol. 49 (2004) 2527-2545. • A. del Guerra, G. Di Domenico, M. Scandola, G. Zavattini, “YAP-PET: first results of a small animal Positron Emission Tomograph based on YAP:Ce finger crystals”, IEEE Trans. Nucl. Sci., vol 45, No. 6 December 1998, 3105-3108. • G. Di Domenico et al., “Characterization of the Ferrera animal PET scanner”, Nucl. Instr. And Meth. A, 477 (2002) 505-508. • A.P. Jeavons, R.A. Chandler, C.A.R. Dettmar, “A 3D HIDAC-PET Camera with Sub-millimetre Resolution for Imaging Small Animals”, IEEE Trans. Nucl. Sci., vol. 46, No. 3, June 1999, 468-473. • Richard Laforest et al. “Performance Evaluation of the microPET – Focus F120”, presented at IEEE NSS/MIC Rome 2005.

  21. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Conclusions • Results concerning the spatial resolution of an RPC-PET prototype have been presented. • An intrinsic spatial resolution of 520 mm FWHM with a intrinsic detector resolution of 220 mm FWHM have been measured. The resolution is largely dominated by intrinsic physical limits. • We studied by simulation the possibility to reduce the physical contributions using magnetic fields. Only for high energy radioisotopes. • Measured image spatial resolution of 305 mm FWHM using a ML-EM algorithm, homogeneous over the entire detector. • Asimulated peak NECR of 318 Kcps have been obtained for a optimized system dedicated to small animal PET. • This technology seems to be very appropriate for small animal PET studies, providing a very high spatial resolution and high sensitivity at a low cost.

  22. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Groups of sums of 4 charges => Save electronic Q1 Q2 Q3 Q4 Interstrip position interpolation Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra

  23. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra

  24. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra

  25. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Image spatial resolution: Construction Small range of angles available Data are transported to the rest of sinograma through the known sinogram curve

  26. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Simulated count rate performance: NEC 318 Kcps 240 Kcps NECR - The number of true coincidences that would create an image of similar quality in the absence of noise (scattered and random coincidences). Typical injected doses for mouse studies (3.7 MBq – 37 MBq)

  27. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Efficiency Vs nº stacked RPCs 0.25 All interactions 30 60 100 0.2 140 0.15 Detecting Efficiency 0.1 Counter-scattered 0.05 0 50 150 250 350 450 550 Energy (KeV) Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Simulated count rate performance Mouse size phantom: 25 Ø x 70 mm (34 cm3) Geant 4 Annihilations and photons on the detector surface from the simulation. • Characteristic of the simulated system: • 90% Solid angle coverage => defining a FOV of 60 Ø x 100 mm axial. • Narrow coincidence window 1 ns. (Timing resolution 300 ps FWHM) • Dead time ~ 100 ns. • 10% - 15% detection efficiency.

  28. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra Simulated count rate performance Evaluation of the count rate performance Randoms, Prompts, Scatter and NECR Mouse size phantom: 25 Ø x 70 mm (34 cm3) NECR – Noise equivalent Count Rate The number of true coincidences that would create an image of similar quality in the absence of noise (scattered and random coincidences). Where T = True events, S = Scatter events, R = Random events Annihilations and photons on the detector surface from SIMSET. • Characteristic of the simulated system: • 90% Solid angle coverage => defining a FOV of 60 Ø x 100 mm axial. • Narrow coincidence window 1 ns. (Timing resolution 300 ps FWHM) • Dead time ~ 100 ns. • 10% - 15% detection efficiency.

  29. RPC2005 VIII Workshop on Resistive Plate Chambers. October 10-15, 2005. Seoul, Korea Resolution studies on a small animal RPC-PET prototypeAlberto Blanco. LIP-Coimbra RC passive network RC passive network X-strips (deposited on glass) Single-gap timing RPCs with bidimensional position-sensitive readout for very accurate TOF systems NIMA 508 (2003) 70–74 TESTED X right X left out left 10 strips for each coordinate at 4 mm pitch Y-strips (on PCB) out right

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