LaBr 3 :Ce, the latest crystal for nuclear medicine

Transcription

1 10th Topical Seminar on Innovative Particle and Radiation Detectors 1-5 October 2006 Siena, Italy LaBr 3 :Ce, the latest crystal for nuclear medicine Roberto Pani On behalf of SCINTIRAD Collaboration INFN and University La Sapienza Rome Italy

2 In 2004, INFN promoted the development of a scintillation camera based on LaBr 3 :Ce continuous crystal shape. LaBr3:Ce crystals are now available with continuous shape covering up to cm 2 with a thickness of 1 cm or more. (the high hygroscopicity and fragility of material have introduced serious concerns in pixellated manufacturing). AIM of the work Verify if LaBr 3 :Ce meets the requirements for SPECT imaging and it has the potential to replace NaI:Tl as the material of choice for SPECT.

3 Emission Tomography Relation To Anatomic Imaging Person alive Person dead MRI scan Anatomical information source patient detector Predominately gamma ray imaging PET scan functional information An MRI/CT scan shows you that you have a brain A PET/SPET scan shows that you use it Courtesy of Klaus Mueller Computer Science Department Stony Brook University

4 Summary scintillator specs Density (g/cm 3 ) Attenuation length at 511 kev (mm) Photoel. effect (%) Light yield (ph/mev) Decay time (ns) E/E (662 kev) % Emiss. max nm NaI:Tl , Bi 4 Ge 3 O 12 (BGO) , Lu 2 SiO 5 :Ce (LSO) , > Lu 2(1-x) Y 2x SiO 5 :Ce (X = 0.1) (LYSO) , > LuAlO 3 :Ce (LuAP) , LaCl 3 :Ce , (65%) LaBr 3 :Ce , (97%) LuI 3 :Ce , (72%) courtesy Carel W.E.Van Eijk

5 Radiation absorption 140 kev Crystals ρ density (g cm -3 ) τ (cm -1 ) µ (cm -1 ) τ / µ HVL (cm) Thick. 80% eff. (cm) LaBr 3 :Ce LaCl 3 :Ce NaI:Tl CsI:Tl

6 BrilLianCe TM 380: LaBr 3 :Ce 3 x 3 Light yield BrilLanCe 380 3x ,000 photons/mev (NaI:Tl 40,000 ph/mev) Decay time 16 ns (NaI:Tl 230 ns) kev FWHM 3.00% channel 345 cm 3 volume

7 BrilLianCe TM 380 : Absorption efficiency (LaBr 3 :Ce) 140 kev 80 kev 511 kev Courtesy of Saint Gobain Crystals

8 Energy Resolution Energy resolution FWHM 100% 10% 1% LaBr:Ce 4mm thick / PMT LaBr:Ce 0.5 inch Ø thick 0.5 /PMT / A LaBr:Ce 0.5 inch Ø thick 0.5 /APD / B NaI(Tl) Dorenbos TNS 2004 Theoretical=2.35/sqrt(Nphe) 10 Energy (kev) A PMT Hamamatsu R6231 B Si-APD Hamamatsu S Active Area 10 x 10 mm 2

9 LaBr 3 :Ce γ imager Hamamatsu H8500 Flat Panel PMT Photodetector assembly for 10x10 cm 2 LaBr 3 :Ce crystal Detector n 1: LaBr 3 :Ce continuous crystal 10 mm thick + 3 mm window coupled to Flat Panel PSPMT External size 52 x 52 mm mm 2 active area 1.5 mm glass window Metal channel dynodes 8 8 matrix 6.0 mm anodes Detector n 2: LaBr 3 :Ce continuous crystal 5 mm thick integral assembled with Flat Panel PSPMT Extremely compact (15 mm of thickness) Ideal for closely packing in array (1.5 mm edge dead zone) Charge spread less than 1mm

10 Flat Panel Electronic Readout Southampton Read64 Control Logic Multi-anode 64 channels photocatode PSPMT H8500 Flat Panel Last Dynode Anode 1 Anode 2 Anode 16 Anode 48 Anode 64 RAL HX2 Integrating Amplifier (16 ch) RAL HX2 Integrating Amplifier (16 ch) RAL HX2 Integrating Amplifier (16 ch) RAL HX2 Integrating Amplifier (16 ch) Multiplexer NI DAQ 6110E DAQ Board (A/D) Event Trigger PC Comparator

11 Position Arithmetic for continuous scintillator in single photon counting Scintillation light flash on photocathode X & Y Position Centroid Algorithm Position: Energy: X = Σ i i n i Σ i n i Ε = Σ i n i Charge distribution sampling by anode array Anode array (Hamamatsu H8500) k i n = i n i k k k n i

12 one γ-ray interaction Position determination by light sharing σ im σ lightpsf n phe Image PSF 1mm FWHM Many γ-ray interactions counts (a.u.) Scintillation light PSF 15 mm FWHM 0 Co 57 pulse height analisys ER Pulse height (a.u.) 1 n phe measured position (mm) Spatial Resolution Position linearity l = dx dx mechanical position (mm) SR σ = imm l

13 Charge distribution treatment for position linearity correction Original charge distribution from single γ interaction LaBr 3 :Ce 10 mm thick Squared charge Threshold level

14 Position linearity correction Co 57 Spot scanning 1.5 mm step Measured Position (m Measured Position (mm) raw data charge threshold = 1 y=x Corrected Raw The correct position linearity relation enables to carry out the true intrinsic spatial resolution Mechanical Position (mm) Counts Raw data Image Pixel LaBr 3 :Ce integral assembly Counts (a.u Threshold & squared charge image pixel

15 LaBr 3 :Ce Position Linearity Enhancement Continuous Crystals 10 mm thick + 3 mm window 3 inch PSPMT Hamamatsu R2486 Sanchez F. et al., Design and tests of a portable mini gamma camera, Med.Phys., Vol.31, June 2004

16 LaBr 3 :Ce Energy and Spatial Resolution Enhancement Continuous Crystals 3 inch PSPMT Hamamatsu R2486 Sanchez F. et al., Medical Physics, Vol.31, June 2004

17 Intrinsic Spatial Resolution vs Energy 10.0 LaBr 3 (Ce) 10 mm Anger Camera 10 mm Intrinsic SR (mm) 1.0 LaBr 3 (Ce) 5 mm LaBr 3 (Ce) 1.5 mm 1 broken line E keV Energy (kev)

18 Intrinsic Spatial Resolution vs energy 5mm Overall SR = 1.51 mm 80 kev LaBr 3 :Ce integral assembly 5 mm thick 5mm Overall SR = 1.24 mm 302 kev ISR min =0.83mm ISR avg =1.14mm ISR min =0.48mm ISR avg =0.73mm mm collimated Ba 133 source counts 400 counts image pixels image pixels

19 Spatial resolution vs crystal thickness Co 57 1 mm collimated source - Detector 1.5 mm step LaBr 3 :Ce 5 mm thick - integral assembly LaBr 3 :Ce 10 mm thick - 3 mm window Intrinsic SR = 1.00 mm mean value Intrinsic SR = 2.05 mm mean value mm best value mm best value Counts 1100 Counts Image Pixel Image Pixel

20 LaBr:Ce can solve limitations offered by segmented detectors Mario transmission Pb mask Co57 flood field irradiation E.J.Hoffman NIM A(1997) R. Pani University La Sapienza Rome Italy (S. Majewsky, Jlab, Va, USA) CsI(Tl) 4x4 array 1.2 mm pixel CsI(Tl) 4x4 array 1.2 mm pixel LaBr 3 :Ce 5 mm thickness Spatial Resolution = 0.90 mm Efficiency: 80% LaBr 3 :Ce 1.5 mm thickness Spatial Resolution = 0.65 mm Efficiency: 35% CZT crystal Medipix II INFN Napoli ( P. Russo) 50 µm pixel 800 µm pixel 400 µm pixel

21 PET based on pixellated LaBr 3 :Ce goes commercial Time resolution Time of Flight information x D Increasing Obesity Background from Scattering! x = uncertainty in position along LOR = c. t/2 TOF Sensitivity gain ~ D/ x t = 300 ps x = 4.5 cm > 5 x better Signal to Noise ratio courtesy Carel W.E.Van Eijk

22 Positron Emission Tomography Full Module - LaBr 3 :Ce crystals 1620 (60x27) 4mm x 4mm x 30mm 10 PMTs - 50 mm diam - Raw Signals 30mm courtesy Philips Research Laboratories

23 Conclusion Continuous LaBr 3 :Ce crystal shows superior spatial and energy resolution performances than scintillators of previous generation. This work confirms the expected high potential of the LaBr 3 :Ce gamma camera for single photon imaging. Pixellated LaBr 3 :Ce crystal can improve PET performances for large ring scanners