1. INFN PISA ACTIVITIES IN WP2 M. G. Bisogni university and INFN pisa functional imaging and instrumentation group ENVISION WP2 MEETING TUESDAY FEB 2,

2. WP2.1 Crystal Based TOF-PET  To investigate the possibility to develop a fast TOF- PET scanner demonstrator that will achieve a position resolution of the order of few centimeters using crystal detectors.  The scanner mast have a timing resolution in the 100 ps range.  The INFN tasks in WP2.1  Development of a demonstrator of an in-beam TOF positron camera  Tomographic reconstruction and prediction of measured activity distributions from treatment planning

3. Two read-out approaches  Fast, position sensitive Photo Multipliers Tubes  Advantages: both coordinates and Depth Of Interaction can be determined with a small number of channels  Drawbacks: sensitive to magnetic fields  Silicon Photo Multipliers (SiPM, also called MPPC)  Advantages: fast, compact, low bias voltage, insensitive to magnetic fields  Drawbacks: never been used in large systems so far

4. The SiPM solution 4 p + substrate π epilayer p high-electric field multiplication region n + cathode h +V GM oxide 4 µm e-e- hole SiPM: Multicell Avalanche Photodiode working in limited Geiger mode - 2D array of microcells: structures in a common bulk. - Vbias > Vbreakdown: high field in multiplication region - Microcells work in Geiger mode: the signal is independent of the particle energy - The SiPM output is the sum of the signals produced in all microcells fired. SOLID STATE PHOTODETECTOR  High gain(~ 10 6 ) low bias voltage (~ 50V) Linear response with the photon flux (for Nfot <<Ncell) PDE dark noise(1-2 MHz/mm 2 @ 1 fotone)

5. SiPM… PtPt …a matrix of avalanche photodiodes operating in Geiger mode. - The photon is absorbed and generates an electron/hole pair - The electron/hole diffuses or drifts to the high-electric field multiplication region - The drifted charge undergoes impact ionization and causes an avalanche breakdown. - Resistor in series to quench the avalanche (limited Geiger mode). As produced at FBK-irst,Trento, Italy 

6. DASIPM INFN project 6  Collaboration with FBK- irst (Trento, Italy), that has been developing SiPMs since 2005:  First detectors - Single SiPMs (2006)  First matrices 2x2 (2007)  First matrices 4x4 (2008)  First matrices 8x8 (2009)  Breakdown voltage VB ~ 30V, very good uniformity.  Gain: ~10 6  Linear for a few volts over V BD.  Related to the recharge of the diode capacitance C D from V BD to V BIAS during the avalanche quenching. G=(VBIAS-VB) x C D /q  Dark rate :  1-3 MHz at 1-2 photoelectron (p.e.) level, ~kHz at 3-4 p.e (room temperature).  Not a concern for PET applications.

7. Intrinsic timing 7  Intrinsic timing measured at s.p.e level: 60 ps (  ) for blue light at 4V overvoltage.  SiPM illuminated with a pulsed laser with 60 fs pulse width and 12.34 ns period, with less than 100 fs jitter.  Two wavelengths used: = 400  7 nm and  = 800  15 nm.  Time difference between contiguous pulses is determined.  The timing decreases with the number of photoelectrons as  1/√(Npe)  20 ps at 15 photoelectrons. λ = 800 nm λ = 400 nm — contribution from noise and method (not subtracted) [eye guide] [G. Collazuol et al., VCI 2007, NIM A 2007, A581, 461-464] λ = 400 nm at 4 V overvoltage [fit as 1/√(N pe )]

8. SiPM: risoluzione temporale intrinseca λ = 800 nm λ = 400 nm — contribution from noise and method (not subtracted) Risoluzione temporale intrinseca al di sotto dei 100 ps a livello di singolo fotoelettrone. Misurata illuminando il SiPM con laser Ti:sa  Larghezza impulso 60 fs  Frequenza ~80 MHz  Time jitter < 100fs G. Collazuol et al. Single photon timing resolution and detection efficiency of the IRST silicon photo-multipliers

9. Tests of SIPM in a MR system (MRI) in collaboration with the Wolfson Brain Imaging Center, Cambridge, UK 9  S.p.e and 22 Na energy spectra acquired with gradients off (black line) and on (red line).  No real difference is appreciated in the data.  Differences in photopeak position is due to temperature changes in the magnet apparent change in gain due to changes in breakdown voltage gradients off gradients on gradients off gradients on [ R.C.Hawkes,et al. 2007 IEEE NSS-MIC, Honolulu, USA, October 28-November 3, 2007: M18-118. ]

10. coincidence timing 10  Coincidence measurement with two LSO:Ce crystals (1x1x10 mm 3 ) coupled to two SiPMs Post and Schiff. Phys. Rev. 80 (1950), 1113 Measurements in agreement with what we expect!! Where:` = average number of photons: ~ 100 photons at the photopeak Q = Trigger level: ~1 photoelectron.  = Decay time of the scintillator For two scintillators in coincidence expected : => √2 σ ~ 630 ps. Measured => ~ 600 ps sigma. [G.Llosa,et al., IEEE Trans. Nucl. Sci. 2008, 55(3), 877-881.

11. SiPM: time resolution with scintillators G. Llosa et al. NSS MIC 2008

12. New Ca co-doped LSO:Ce crystals  LSO:Ce shows limitations as  Afterglow that limits the high counting rate applications  Non-linearity especially under 100 keV  The newly developed LSO:Ce crystals co-doped with calcium divalent cations showed higher light output and faster light pulses  The most recent studies also showed that co-doping of LSO:Ce with Ca substantially reduces afterglow intensity. C. L. Melcher and J. S. Schweitzer, “Cerium-doped lutetium oxyorthosilicate: A fast, efficient new scintillator,” IEEE Trans. Nucl. Sci., vol. 39, no. 4, pp. 502–505, Aug. 1992. C. L. Melcher et al, “Effects of Ca Co-Doping on the Scintillation Properties of LSO:Ce,” IEEE Trans. Nucl. Sci., vol. 55, no. 3, pp. 1178–1182, Jun.2008. C. L. Melcher et al. “Effects of calcium co-doping on charge traps in LSO:Ce,” in Proc. IEEE Nuclear Science Symp. Conf. Rec., Oct. 26–Nov. 3 2007, vol. 4, pp. 2476–2479, 2007.

13. Timing performances of LSO:Ce, Ca with SiPMs 2 Hamamatsu MPPC 100-C in time coincidence 3x3x10 mm^3 LSO:Ca wrapped in teflon Bias voltage = 71V Threshold = 9,8 mV Cnc window = 15 ns Results  sigma=152 ps  sigma/√2 = 107 ps  FWHM=357 ps  FWHM/ √(2)= 253ps preliminary

14. SiPM Matrices 14  The small dimensions of SiPMs are not adequate to cover large field of views. To overstep this limitation, FBK-irst, in the framework of the INFN project DASIPM2, started the development of matrices of SiPMs on the same silicon substrate with the goal to preserve the spatial resolution capabilities of the SiPM but on a larger sensitive area.

15. Different geometries 15  Matrices 16 elements (4x4) 1mm  1x1mm 2 2x2mm 2 3x3mm 2 (3600 cells) 4x4mm 2 (6400 cells) Different geometry,size,microcell size and GF. 4 mm 40x40  m 2 => GF 44% 50x50  m 2 => GF 50% 100x100  m 2 => GF 76% circular 1.3cm

16. Matrices for INFN-DaSiPM2 project (2009) 16 1.3cm 8x8 matrix 1.5mm element pitch 625 (50  m x 50  m)  cells read-out both on one or two sides

17. Position Reconstruction 17 G. Llosa, IEEE NSS-MIC 2009

18.  Large detector gain wide dynamic range required ! Example: 300 hit micro-cells, gain=10 6, Q TOT =48pC voltage swing on a 5pF integration capacitance Q TOT /C = 9.6V !!  Avalanche breakdown very fast signal, accurate timing feasible wideband electronics  Front-end electronic noise: negligible contribution Current-mode approach Front-end electronics for SiPM C. Marzocca, IEEE-NSS-MIC 2009

19. Main features of the chip  Three operating modes: write configuration, read configuration and acquisition  Two acquisition modes: “sparse read-out” and “serial read-out”  Standard cell read-out logic  All the channels share the same Vrif (8-bit DAC) and I_th (4-bit DAC)  8 bit successive approximation ADC from a library  Fast-OR circuit operating in current mode, to increase the speed of operation Layout of the prototype (3.2 x 2.2 mm 2, CMOS 0.35  m)

20. Fast-OR output: jitter measurements Worst case dispersion  ( μ S + 3  S ) - ( μ D - 3  D )  652 ps Slowest case: one excited channel, sligthly above threshold Average delay μ S = 1.77ns Standard deviation  S = 50 ps Fastest case: two excited channels, well above threshold Average delay μ D = 1.42ns Standard deviation  D = 50.5 ps

21. 1.2 cm A conceptual design for the TOF-PET module 4.8 cm 1 cm Sipm matrix 8x8 pixels Pitch 1.5 mm Single SiPM 4x4 mm^2

22. To do…  Further measurements with:  SiPM from differnt providers  LYSO Ca co-doped crystals with different Ca concentration  Systematics  Integration of components  Dead-area minimization, feed-through solution  Exploring different solutions for the assembly of detectors and electronics  Temperature monitoring and control  Compatibility with magnetic field

23. I fasci adronici terapeutici producono nel tessuto biologico emettitori β + a breve emivita per frammentazione del proiettile e/o del target La distribuzione di attività è spazialmente correlata con la distribuzione di dose Trovando la distribuzione di annichilazione dei β + è possibile estrarre informazioni sulla dose in modo non invasivo Il principio del PET monitoring in beam p n 16 O 15 O  Gamma ray imaging SiPM-PET SiliPET Adroterapia PBR in-beam PET  Imaging RX Mammografia microCT 16 O 12 C 15 O 11 C n n Low Z beam High Z beam

24. * Vecchio, S. et al, IEEE Conference record 2007, cdrom: m13-61. * F. Attanasi et al., Nuclear Instruments and Methods in Physics Research A 591 (2008), 296–299 Longitudinal dose profiles Longitudinal activity profiles The feasibility of range monitoring 50% fall off reconstructed activity distribution is reproduced with an accuracy of about ± 200 μ m  Gamma ray imaging SiPM-PET SiliPET Adroterapia PBR in-beam PET  Imaging RX Mammografia microCT