Outline Introduction to Positron Emission Tomography (PET) Why use - PowerPoint PPT Presentation

Application of Multi Pixel Photon Counters (MPPC) to PET Kirchhoff-Institut für Physik • Nicola D‘Ascenzo DESY Hamburg • Alexander Tadday Kirchhoff-Institut für Physik - Universität Heidelberg Light 07 workshop 23-28.09.07 Ringberg Castle, Tegernsee 1

Outline • Introduction to Positron Emission Tomography (PET) • Why use Multi Pixel Photon Counters (MPPC)? • Background reduction • Setup • Results 2

Introduction to PET Inorganic Scintillator (Common BGO, LSO PMT‘s) 11 C, 13 N, 15 O, 18 F 3

Why use MPPC‘s • Scintillation light from LSO is blue • MPPC has high sensitivity in the blue range Peak emission of LSO (420nm) Source: Hamamatsu

Why use MPPC‘s • Spatial Resolution • Small size ➥ possibility to study single crystal readout with size from 1 × 1-3 × 3mm 2 • Fusion of PET and MRI (small PET detector contained in MRI) • Not sensitive to magnetic fields • High gain, low operation voltage 5

Reduction of Background 6

Energy Resolution True coincidence Scattered coincidence Annihilation point Gamma ray Line of response Why is energy resolution crucial Only photo-peak for PET? is allowed Cut scattered events but keep true events ➥ need good energy resolution 7

Timing Resolution True coincidence Random coincidence Annihilation point Gamma ray Line of response Keep coincidence window as small as possible to reduce Random coincidences ➥ need good timing resolution 8

Time of Flight PET • Accuracy of position measurement is: ( for ∆ t = 500ps ) ∆ x = c 2 ∆ t = 7 . 5 cm • ➥ No gain in spatial resolution but noise variance decreases f = D ∆ x = 2 D D: Size of emission source c ∆ t Submitted to IEEE Transactions on Nuclear Science LBNL-51788 !"#$%#&'"#() 1'2%3"435)'67& *%&%+&",- *%&%+&",- ."/0)% ."/0)% *%&%+&", *%&%+&",- ."/0)% ."/0)% Advantages of Improved timing accuracy in PET Cameras using LSO Scintillator, W.W. Moses LBNL-51788 9

Setup Scintillating crystal Source Na 22 & Gate ≈ 160ns QDC LeCroy Model 1182 250pC FSR Computer 10

Used Scintillators Peak Crystal Size Decay time emission LSO 1 × 1 × 15mm 3 (Lutetium 420nm 40ns 3 × 3 × 15mm 3 Orthosilicate), Hilger Crystals LFS similar to (Lutetium Fine 3 × 3 × 15mm 3 blue LSO Silicate), Lebedev Institute 11

Readout with MPPC‘s from Hamamatsu Active area Operating Dark rate Dark rate Pixels Gain 10 5 voltage 0.5 pixels 1.5 pixels 220k - 400 1 × 1mm 2 76V 9k - 10kHz 7.4 - 7.5 250kHz 3.2 - 3.3 320k - 3600 3 × 3mm 2 70V 7.4 - 7.5 MHz 330kHz 12

Results: Energy Resolution 13

1 × 1 × 15mm 3 LSO with 1 × 1mm 2 MPPC � 1 � 2 � 2 � σ ( E ) � 2 + ( ∆ intr ( E )) 2 + � σ noise √ ≈ E E N blue sensitive ~ 8% for LSO negligible MPPC Energy resolution of 14% (fwhm) was measured Resolution ∆ E ≈ 14% Coupling between E crystal and MPPC is main systematic error ≈ 10% Improvement possible! 14

3 × 3 × 15mm 3 LSO & LFS with 3 × 3mm 2 MPPC‘s LSO Crystal LFS Crystal Resolution Resolution (fwhm) (fwhm) ∆ E ∆ E ≈ 10% ≈ 11% E E LSO and LFS are equal within systematics ~ 3% Typical value with “traditional“ Photomultiplier tube (511kev) : 10% 15

Timing Measurement 16

Setup Oscilloscope: Tektronix Model 7204, Bandwidth No Preamplifiers needed! 4GHz, 20GS/s Direct evaluation with ⇒ Time oscilloscope resolution 50ps Oscilloscope 17

Timing Measurement 2. MPPC Signals N cut 1. Define coincidence threshold N pe 1. 2. Define timing threshold N cut N pe S 1 > N pe ∧ S 2 > N pe ∆ t = t 1 ( N cut ) − t 2 ( N cut ) Energy-Spectrum LSO 3x3mm^2 h1 h1 Entries Entries 4096 4096 Mean Mean 1694 1694 Events N pe RMS RMS 814.6 814.6 1600 Integral 3.441e+05 Integral 3.441e+05 1400 1200 1000 800 600 400 200 18 0 0 500 1000 1500 2000 2500 3000 3500 4000 QDC-Channels

Timing Measurement “Background event“ “Photoelectric event“ - Background A Background is superimposed and ruins the timing ➥ Need to go to high coincidence threshold 19

Results Timing Events Events ! ! 2 2 / ndf / ndf ∆ t = (650 ± 20) ps ! ! 2 2 / ndf = 40 / 48 / ndf = 40 / 48 36.2 / 42 36.2 / 42 400 80 p0 p0 268 268 ± ± 25.1 25.1 p0 p0 71.2 71.2 ± ± 2.6 2.6 ~ 10pe p1 p1 (fwhm) 5.36 5.36 ± ± 0.01 0.01 p1 p1 5.36 5.36 0.01 0.01 ± ± 350 70 p2 p2 0.309 0.309 ± ± 0.021 0.021 p2 p2 0.276 0.276 ± ± 0.009 0.009 p3 p3 136 136 ± ± 27.2 27.2 p3 p3 1.15 1.15 0.73 0.73 ± ± 300 60 p4 p4 5.37 5.37 ± ± 0.02 0.02 p4 p4 4.9 4.9 ± ± 10.3 10.3 p5 p5 0.607 0.607 ± ± 0.029 0.029 p5 p5 3.98 3.98 37.71 37.71 ± ± 250 50 ∆ t = (1 . 4 ± 0 . 07) ns Increasing coincidence ~ 50pe (fwhm) 200 40 150 threshold 30 100 20 50 10 0 0 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 Time [ns] Time [ns] Background worsens timing Events 35 2 2 / ndf = 28.8 / 11 / ndf = 28.8 / 11 ! ! from 700ps to 1.4ns ∆ t = (578 ± 35) ps p0 p0 22.3 22.3 2.0 2.0 ± ± 30 p1 p1 5.39 5.39 ± ± 0.02 0.02 (fwhm) p2 p2 0.246 0.246 ± ± 0.015 0.015 25 p3 p3 500 500 ± ± 212.1 212.1 p4 p4 5.36 5.36 ± ± 1.41 1.41 20 p5 p5 -0.002 -0.002 ± ± 0.000 0.000 ~ 70pe 15 10 5 0 0 1 2 3 4 5 6 7 8 9 20 Time [ns]

Conclusion & Outlook • MPPC‘s show very promising properties for the application of Geiger Mode Avalanche Photodiodes in PET • Energy Resolution: 10% (fwhm) • Timing Resolution: 580ps (fwhm) • More studies needed • Which Crystal LSO, LFS • spatial resolution of matrix • Build a prototype and verify the concept 21

End of Presentation Thank you for your attention! 22