1 Alberto Del Guerra – DASIPM2 Collaboration
1st Workshop on “Photon Detection”
(13-14 JUNE ,2007 PERUGIA)Risultati sperimentali ed applicazioni
dei SIPM a pixel ed a matrice dell’FBK-irst da parte della
collaborazione DASIPM
Alberto Del GuerraDepartment of Physics and INFN, Sezione di Pisa,
Pisa, I-56127 Italy
Spokesman of the DaSiPM2 collaboration:
University and INFN Bari, Bologna, Perugia, Pisa, Trento and FBK-irst (Trento), Italy
2 Alberto Del Guerra – DASIPM2 Collaboration
SUMMARY● SiPM features
● Gain● Noise● PDE● Dynamic Range● Time Resolution● Dependence upon temperature● Radiation Damage
● SiPM performance w/Scintillators (i.e., LSO/LYSO)● Energy resolution● Timing resolution● Magnetic field MRI● ASIC
● PET Application (FP7 project: COMPANION)
3 Alberto Del Guerra – DASIPM2 Collaboration
Example: SiPM technology at IRST (TN, Italy)
C.Piemonte NIM A 568 (2006) 224
≈≈
n+
p
epi
p+
Shallow-Junction GM-APD
13
14
15
16
17
18
19
20
0 0.2 0.4 0.6 0.8 1 1.2 1.4
depth (um)
Do
pin
g c
on
c. (1
0^) [
1/cm
^3]
0E+00
1E+05
2E+05
3E+05
4E+05
5E+05
6E+05
7E+05
E fi
eld
(V/c
m)
Doping
Field
n+ p
• n+-on-p layer structure• Anti-reflective coating (ARC) optimized for λ~420nm• Very thin (100nm) n+ layer (“low” doping min. recombination)
• Thin high-field region (max. doping of p layer also fixes low VBD )• Trenches for optical insulation of cell (low cross-talk)• Fill factor 20% - 30% (to be optimized)• RQ with doped polysilicon
Optimization for the blue light (420nm)1mm
1m
m
SiPM geometry: 1x1mm2
• 25x25 cells• cell size: 40x40 mm2
Substrate500 µm
fullydepletedregion4 µm
4 Alberto Del Guerra – DASIPM2 Collaboration
Dynamic range
SiPM output = sum of binary SPAD output !
The output signal is proportional to the number of fired cells as long as the number of photons in a pulse (Nphoton) times the photodetection efficiency PDE is significant smaller than the number of cells Ntotal.
)1( total
photon
N
PDEN
totalfiredcells eNNA
Saturation
Best working conditions: Nphoto-electrons < NSiPM cells
eg: 20% deviation from linearity if 50% of cells respond
5 Alberto Del Guerra – DASIPM2 Collaboration
Time resolution - Experimental Method
• SiPM exposed to pulsed femto-second laser in low light intensity conditions (single photon) • SiPM signal is sampled at high rate and the time of the pulses measured by waveform analysis
• Time resolution measured by studying the distribution of time differences between successive pulses (on the same SiPM device)(G.Collazuol et al. VCI 07)
6 Alberto Del Guerra – DASIPM2 Collaboration
Experimental Setup (CNR Pisa)
Pump LaserMillenia V (Spectra-physics)solid state CW visible laser
Mode-lockedTi:sapphire LaserTsunami (Spectra-physics)femtosecond pulsed laser
wavelength: tuned at 800±15 nmpulse width: ~ 60 fspulse period: ~ 80MHzpulse timing jitter < 100 fs
pump laser Ti:sappirelaser
SHG
Crystal for Second Harmonic Generation (SHG) conversion 800 nm 400 nmefficiency at % level
Filtersblue + neutralfor rejecting IR lightand tune intensity
Dark boxSiPM +
amplifier
Low noise LVsuppliers
LeCroy SDA 6020
Analog bandwidth: 6GHzSampling rate: 20GS/sVertical resolution: 8 bits
(Aknowledments: E.Marcon, LeCroy)
External trigger fromTi:sappire laser signal
ElectronicsI V conversion via RL (500Ω)Two stage voltage amplification (= x50)based on high-bandwidth low-noise RF amplifier: gali-5 (MiniCircuit) Zin= 50Ω
(Aknowledments: F.Morsani and L.Zaccarelli, INFN-Pisa)
RLCC
CC CC
Cb
-Vb
GND
Vout
Rs
gali5 gali5
hn
SiPM
Data taking conditions:• different Vbias
• both at 800 nm and 400 nm• with different light intensities (counting rates in the range 10-20 Mhz ie 15-30 KHz per single cell)
7 Alberto Del Guerra – DASIPM2 Collaboration
Data at λ=800nm fit gives reasonable χ2 with an additional exponential term exp(-Δt/t)
•Δt ~ 0.2-0.8ns in rough agreement with diffusion tail lifetime: Δt ~ L2 / p2 D if L is taken to be the diffusion length• Contribution from the tails ~ 10-30% of the resolution function area
1 p.e.
2 p.e.
∆t
Laser period
Overvoltage=4V
λ=400nm
Overvoltage=4V
λ=800nm
FIT: gauss+const
FIT: gauss+const+exponential
Mod (∆t,Tlaser) [ns]
Mod (∆t,Tlaser) [ns]
Distributions of the difference in time between successive peaks (modulo the measured laser period Tlaser=12.367ns)
Single photon timing resolution
8 Alberto Del Guerra – DASIPM2 Collaboration
IRST – single photon timing
• λ = 800 nm• λ = 400 nm— contribution from noise and method (not subtracted)
eye guide
n+ pp
depletion region
p+
hν
e–h+
e–h+
high-field region
depletion regiondepletion region
neutralregion
9 Alberto Del Guerra – DASIPM2 Collaboration
CPTA – single photon timing
• l = 800 nm
• l = 400 nm
a) Green-Red sensitive SSPM 050701GR_TO18
b) Blue sensitiveSSPM 050901B_TO18
eye guideTwo different structures:a) thick n+/p b) p+/n deep junction
10 Alberto Del Guerra – DASIPM2 Collaboration
Comparison with Hamamatsu devices
• l = 800 nm
• l = 400 nm
eye guide
HPK-2HPK-3
1600 cells (25x25)
400 cells (50x50)
11 Alberto Del Guerra – DASIPM2 Collaboration
Over-voltage = 3V
Over-voltage = 5V
No p
inh
ole
Ø=
20
0m
m
Ø=
25
mm
Ø=
10
mm
No relevant spread Uniformity of rise-time among different cells
Dependence of single photon timingon the light spot size and positionBy using pinhole in front of the SiPM
IRST – timing studies
Poisson statistics: σt ∝ 1/√Npe
•contribution from noise subtracted
— fit to c/√Npe
λ=400nmOvervoltage = 4V
N of simultaneous photo-electrons
Dependence of SiPM timing on the number of simultaneous photons
12 Alberto Del Guerra – DASIPM2 Collaboration
Thermal-electrical characterization 1/4● Ileak vs Bias vs Temperature
M. Petasecca et al., Perugia (2007)
13 Alberto Del Guerra – DASIPM2 Collaboration
Thermal-electrical characterization 2/4● Vbreakdown vs Temperature
(**) K.G.McKay,Avalanche Breakdown in Silicon,Physical Review,Vol.94 Number 4, May 1954
M. Petasecca et al., Perugia (2007)
14 Alberto Del Guerra – DASIPM2 Collaboration
Thermal-electrical characterization 3/4● Gain vs Bias vs Temperature
The residual Gain dependence is due to the variation of Pt with temperature.
…but the Breakdown voltage is dependent with the temperature so…
M. Petasecca et al., Perugia(2007)
15 Alberto Del Guerra – DASIPM2 Collaboration
FBK-SiPM APD
∆Vbk /Vbk(@300K) % ~0.2 0.1
∆Vbk [mV] ~ 60 30 60-200 **
∆G/G(@300K) % ~ 3 1.5 3.4*
* Spanoudaki et al., IEEE NSS-MIC 2005
** J.P.R. David and G.J.Rees, RAD Hard Workshop 2003
Variation of Vbk and Gain with 1 °C ∆T
VARIATION with TEMPERATURE
16 Alberto Del Guerra – DASIPM2 Collaboration
Radiation damage
Expected effects:1) Increase of dark count rate due to introduction of generation centers
2) Increase of after-pulse rate due to introduction of trapping centers loss of single cell resolution
Dark rate increase DDC~ Pt/qe• α ΦeqVoleff
where α ~ 3 x 10-17 A/cm is a typical value ofthe radiation damage parameter for low E hadrons and Voleff ~ AreaSiPM x GF x Wepi
The effect is the same as in normal junction diodes: • independent of the substrate type• dependent on particle type and energy• proportional to fluence
The few existing preliminary measurements are in agreement with expectations for the radiation damage parameter a within a factor of 2 (Musienko and Danilov, VCI07)
C.PiemonteFNAL 25/10/2006
17 Alberto Del Guerra – DASIPM2 Collaboration
Radiation damage
Dark count rate increase
M.Danilov - VCI07
CALICE collaboration
MEPhI/Pulsar SiPM
~ Positron 28 MeV (8*10**10 cm**2)
Photonique/CPTA deviceY.Musienko – Vienna VCI 2007
18 Alberto Del Guerra – DASIPM2 Collaboration
Summary of SiPM featuresMost important features of a SiPM are:• sensitivity to extremely low photon fluxes providing proportional information with excellent resolution and high photon detection efficiency• extremely fast response with low fluctuation (sub-ns risetime and <100ps jitter)
More features:• low bias voltage (<100V)• low power consumption (<50µW/mm2)• long term stability• insensitive to magnetic fields (up to 15T) and EM pickup• robust and compact• low cost (in the future! now ~140$/mm2) + low peripheral costs
Technology parameters: may be tuned to match the specific application● silicon quality (dark rate, after-pulse)● doping concentration (operating voltage and its range)● layer structure and thickness (PDE wavelength range, optical cross-talk)● optical cell insulation (optical cross-talk)● effective area of the cells (gain, fill factor, dynamic range, recovery time)● quenching resistor (recovery time, dynamic range)
19 Alberto Del Guerra – DASIPM2 Collaboration
Great variety of possible applications
● Calorimetry in magnetic fields● Fiber tracking (spectrometers, beam monitoring)● Particle ID (TOF, RICH, fast timing with cherenkov, Transition Radiation)● Astroparticle (Imaging Air Cherenkov Telescopes)● Space applications (calorimetry, traking, TOF)● Medical imaging (PET) + timing + magnetic and RF fields (MRI)● Thin scintillators read-out● Time resolved X-Ray correlation spectroscopy● Fast timing applications
20 Alberto Del Guerra – DASIPM2 Collaboration
Medical imaging (PET)
Aims: PET detectors with• high spatial resolution (sub-millimeter)• high sensitivity (low dose or high signal/background ratio)• high time resolution (TOFPET background rejection)• DOI capability (no or less parallax)• no sensitivity to magnetic fields, EM pickup and RF (simultaneous NMR scan)
Key issues:• Granularity: matrices of SiPM
• High PDE for short wavelengths (420nm): • for coupling to high light yield crystals (scintillators)• max E resolution high efficiency to reject background Compton scattering
• Optical coupling with scintillator • Dynamic range and recovery time: multi cell signal saturation and fluctuation • Gain stability with V and T: individual control of O(10000) channels
Many photons applicationBlue sensitive SiPM
21 Alberto Del Guerra – DASIPM2 Collaboration
Matrices of SiPM - IRST
G.LLosa et al. IEEE NSS 2006 CD record M06-88
The first matrices of 2x2 blue sensitive SiPMs have been developed at IRST
SEM photograph of a section of a 3D detector
To avoid the anode wire bonding on the active surfaceaim to use the 3D technology at IRST to have a conducting contact to bring the anode to the backside.
22 Alberto Del Guerra – DASIPM2 Collaboration
A 22Na spectrum was obtained with a 1 mm x 1 mm x 10 mm LSO crystal coupled to a SiPM (GF~30.9%) Two devices were operated in time coincidence. A typical energy resolution of 21% FWHM was obtained.
World best resolution w/ LSO (3x3x20) and PT XP2020 10%(FWHM) [intrinsic 8.9% at 511 keV] [Balcerzyk et al., IEEE TNS 47(2000)1319]
SiPMs
22Na Source
Scintillatorcrystals
R ~ 17.6 % FWHM
Best spectrum
Typical spectrumR ~ 21.0 % FWHM
9/18/06 24
Scintillator readout with SiPM matrices
- LSO crystal (1x1 mm2) coupled to one pixel - time coincidence with a PMT
R ~ 29%
M6 @ 35.7
9/18/06 25
Scintillator readout with SiPM matrices
R ~ 30%
- LSO crystal (1x1 mm2) put in the centre - time coincidence with a PMT - gain calibration with a LED
M6 @ 35.7
9/18/06 27
Timing: cosa ci aspettiamo dalla teoria?
*Post, Schiff Phys. Rev. 80 p.1113 (1950)
Dove…<N> = numero medio di fotoniQ = CFV * <N> = tempo di decadimento dello scintillatore
Se… = 40 ns per LSO<N> ~ 100 per il fotopicco
~ 400 ps
Triggerando sul primo fotone Q=1 Triggerando al 20% Q=20
~ 1.78 ns
*
9/18/06 29
External trigger from gradient amplifier
Pulse generator
SiPMLED
55 µs
Shielded electronics
Magnet 1T
LED trigger
SiPM signal is acquired while the gradient is increasing
scope
SiPM signal integrated and histogrammed
SiPM in ststic magnetic field + gradient
9/18/06 30
single SiPM in magnetic resonance: Z gradient on
Black: reference spectrum acquired inside the magnet with
the gradient off
Red: spectrum acquired with the gradient on
SiPM dark signal
Pickup coil signal
9/18/06 31
single SiPM in magnetic resonance: Z gradient on
Black: reference spectrum acquired inside the magnet with
the gradient off
R~30.4%
LSO (1x1 mm^2) - 22Na - no coincidence
R~29.6%
Red: spectrum acquired with the gradient on
Spectra can be superimposed if acquired in a short time
9/18/06 32
SiPM electrical model
Rq: quenching resistor (hundreds of k)
Cd: photodiode capacitance (few tens of fF) Cq: parasitic capacitance in parallel to Rq (smaller than Cd)
Cg : parasitic capacitance due to the routing of the bias voltage to the N microcells, realized with a metal grid (few tens of pF)
IAV: current source modelling the total charge delivered by a microcell during the avalanche
A parameter extraction procedure has been developed, based on both static and dynamic measurements, to perform realistic simulations.
9/18/06 33
Validation of the parameter extraction procedure
Two different amplifiers have been used to read-out the detector
a) Transimpedance amplifier
BW=80MHz, Gain=2.7k
b) Voltage amplifier
BW=360MHz, Gain=140
The fitting between simulations and measurements is quite good
9/18/06 34
Front-end electronics: main specifications
Self-triggered electronics
Dynamic range: about 50% of SiPM micro-cell occupancy ( SiPM gain 106 , no of micro-cells = 625 total charge 48pC )
The required jitter for the self-trigger signal (few hundreds of picoseconds) calls for large bandwidth (about 250MHz)
Power consumption: about 2mW per channel
Threshold for the self-trigger signal: adjustable, from few micro-cells to the full dynamic range
Important feature: fine adjustment of the SiPM bias voltage
9/18/06 35
Front-end architecture
Current buffer
Baseline holder
To current discriminatorCf
Vdd
Vbl-
+
SiPM
VBIAS
M : 1
Rf
Shaper
Peak detector
Vdd
-
+
-
+
The front-end is based on an input current buffer, which allows to achieve large bandwidth and dynamic range.
An output branch of the current buffer, suitably scaled, is sent to an integrator, which extracts the charge information.
Another output branch goes to a current discriminator, which provides the self-trigger signal.
9/18/06 36
The current buffer
Vg1
Vg2
Vref
Iout
M0
M1
M2
M3 M4
M5
SiPM
Vcc
A prototype of the input current buffer has been designed, based on a current feedback scheme
Vref can be used to vary the bias voltage of the detector, which is DC coupled to the front-end
The technology used is a standard 0.35m CMOS
Simulated input impedance 20
Simulated bandwidth (including the SiPM model connected at the input) 250MHz
Noise negligible
Dynamic range equivalent to about 300 micro-cells
9/18/06 37
Current buffer: first measurements
A test board which performs current-to-voltage conversion and amplification has been realized
An infrared pulsed laser has been used as optical source (about 260 micro-cells hit)
The bias voltage of the detector has been varied from 32.5V to 36V
The measurements show the good linearity performance of the current buffer.
Output waveform of the test board as a function of the SiPM bias voltage
Peak of the output waveform as a function of the SiPM bias voltage
39 Alberto Del Guerra – DASIPM2 Collaboration
Proposal COMPANION for FP7
● Development of a combined PET/MRI scanner for small animals.
● [Submitted 19 April. Results end June. (Start 1 Jan 2008?)] - 8 groups from 4 countries:
Institution Main tasks
1 UP University of Pisa Pisa, Italy Simulation+ PET construction + testing
2 FBK IRST Trento, Italy Photodetectors development
3 PB Politechnic Institute of Bari
Bari, Italy ASIC development
4 WBIC Wolfson Brain Imaging Center
Cambridge,UK Gradient development + preclinical application in neurology
5 CC Cancer Institute of Cambridge
Cambridge,UK Preclinical application in oncology
6 UV University of Valencia Valencia, Spain Simulation+ image reconstruction + attenuation correction
7 UM Technical University of Madrid
Madrid, Spain Readout system + image reconstruction
8 TEI Technological Educational
Institute of Athens
Athens, Greece Simulation +Image fusion and motion correction
COMPANION - COmbined MRI-PET for small ANimal-Imaging in Oncology and Neurology CONFIDENTIAL
40 Alberto Del Guerra – DASIPM2 Collaboration
Design● PET/MRI imposes hard restrictions:
● Space limitation inside the MR scanner.● Sensitivity to magnetic fields.
● Attempts with light guides and APDs.
20 cm
~12 cm
8 cm
Split gradient
≤ 2.5 cm
PET ring
• Split gradient coil with the PET tomograph placed inside (20 cm outer radius to fit inside standard magnets from 7 to 11T).
• PET inner diameter: ~12 cm to accommodate inside RF coils and rat/mouse bed. • Maximum axial length: 8 cm. Maximum transaxial thickness: 2.5 cm.
41 Alberto Del Guerra – DASIPM2 Collaboration
● The PET tomograph consists of a ring composed of 16 detector heads. ● The heads are: LSO slab 7.2 cm long x 2.4 cm wide x 1 cm thick;● Read out by SiPM matrices. Total thickness ~1.8 cm.
7.2 cm
≤ 2.5 cm
2.4 cm
12.4 cm
12.4 cm
2.4 cm
≤ 2.5 cm
PET design
42 Alberto Del Guerra – DASIPM2 Collaboration
● LSO continuous scintillator slab 7.2 cm x 2.4 cm x 1 cm thick with matrix readout.
● Simulations predict better performance than detector heads with pixellated crystals. Better spatial resolution, possible DOI (even with one layer).
● Readout by SiPM matrices and dedicated ASIC
SiPM matrix LSO crystal slab:72 mm x 24 mm10 mm thick
10 mm
72 mm
24 mm
Scintillator
43 Alberto Del Guerra – DASIPM2 Collaboration
● Matrices: Aim- backplane readout● Phase 1: Matrices with lateral readout (1 mm x 1 mm SiPM
elements in 1.5 mm x 1.5 mm pitch).● Phase 2: Matrices with backplane readout (1.5 mm x 1.5 mm in
1.5 mm x 1.5 mm pitch -Almost no dead area).● Improved PDE (PET efficiency).● Same layout, number of channels● Development in parallel. Not delaying the PET scanner
construction.● Technology already developed at IRST.● Final decision according to performance, yield...
Matrices
44 Alberto Del Guerra – DASIPM2 Collaboration
LATERAL READOUT.
coolingpipes TOP VIEW
SIDE VIEW
scintillator support
SiPM matrix ASICs
72 mm
24 mm
~1.8 mm
… … …
… … …
support
fan-out
holes to reach the sensor
BACKPLANE READOUT.
Possible layout
45 Alberto Del Guerra – DASIPM2 Collaboration
Simulation results● Expected performance (GEANT4):
● FOV axial 7 cm, transaxial FOV ~6 cm. ● spatial resolution at the CFOV , below 1mm3.● efficiency around 11% for an energy threshold of 250 keV.
Better than Siemens INVEON
46 Alberto Del Guerra – DASIPM2 Collaboration
Conclusions
SiPM might really replace PMT in many applications, due to their• sensitivity to extremely low photon fluxes• extremely fast response
IRST developed devices with excellent sensitivity to blue:• devices working as expected • very good reproducibility of the performances • very good yield • very good understanding of the device• flexible geometry (linear and 2-D matrices under development)
Photo-detection efficiency (IRST devices):• Quantum efficiency: > 95% in the blue region (optimized for 420nm)• Triggering probability: growing linearly with overvoltage • Geometrical fill factor: 15-30% to be optimized 44-76% soon available
Single photon timing resolution (IRST devices):• σt at the level of 50ps for typical working overvoltage (4V)
• σt at the level of 20ps for ~15 photoelectrons
Applications of SIPM in various fields are under development (e.g. PET)
47 Alberto Del Guerra – DASIPM2 Collaboration
Publications by the Collaboration (2006-2007)
1. F. Corsi, et al.. “Modelling a Silicon Photo Multiplier (SiPM) as a signal source for optimum front-end design”, NIM A, 2007, 572, 416-418.
2. V.Bindi, et al., “Preliminary Study of Silicon Photomultipliers for Space Missions”, NIM A 2007, 572, 662-667.
3. N.Dinu, et al., “Development of the first Prototypes of Silicon Photomultipliers (SiPM) at ITC-irst”, NIM A, 2007, 572, 422-426.
4. C.Piemonte, et al., “Characterization of the first prototypes of Silicon Photomultipliers fabricated at ITC-irst”, IEEE Trans Nucl Sci. 2007, 54(1), 236-244.
5. C.Piemonte, et al.,“ New results on the characterization of ITC-irst Silicon Photomultipliers”, Conference Records of the 2006 IEEE Nuclear Science Symposium and Medical Imaging Conference, San Diego, USA, October 29-November 4, 2006, cd_ROM, N42-4.
6. G.Llosa, et al.“Novel Silicon Photomultipliers for PET application” Conference Records of the 2006 IEEE Nuclear Science Symposium and Medical Imaging Conference, San Diego, USA, October 29-November 4, 2006, cd_ROM, M06-88, and submitted to IEEE Trans. Nucl. Sci.(2006).
7. F.Corsi, et al., “Electrical characterization of Silicon Photo-Multiplier Detectors for Optimal Front-End Design” Conference Records of the 2006 IEEE Nuclear Science Symposium and Medical Imaging Conference, San Diego, USA, October 29-November 4, 2006, cd_ROM, N30-222.
8. G. Collazuol, et al., “Single timing resolution and detection efficiency of the ITC-irst Silicon Photomultipliers”, presented at the XI VCI, Vienna 19-24 February 2007, accepted for publication in NIM A (2007)
9. G.Llosa, et al.,”Silicon Photomultipliers for very high resolution small animal PET and PET/MRI”, to be presented at the Second International Conference of the European Society for Molecular Imaging, Napoli, Italy, June 14-15, 2007 (Abstract)
10. G.Llosa et al. “ Novel Solid State detector and their application to very-high resolution PET and Hybrid Systems.” to be presented at the ENC 2007, Brussels, 16-19 September 2007, and submitted to Radiation Protection Dosimetry
11. A. Del Guerra “Silicon photomultiplier(SIPM): the Ideal Photodetector for the Next Generation of TOF, DOI, MRI compatible, High Resolution, High Sensitivity PET”, to be presented at the “Joint Molecular Imaging Conference” , Sept 8-11, 2007, Rhode Island, NY(USA)
● + 1 submission to X EFOMP (sept 2007)
1. + 4 submissions to IEEE NSS MIC 2007 (nov 2007)
48 Alberto Del Guerra – DASIPM2 Collaboration
International grants and collaborations (Pisa based)
Established● Marie Curie Individual Fellowship (2007-2008)● Italy-UK [Pisa-Cambridge (2007)]● Italy-Spain [Pisa-Valencia (2007-2008)]● Pisa University- UCI (US)Requested● NIH (US) (2nd revision) {P.I. w/ Univ. of
Washington} ● FP7
● COMPANION {P.I. w/ other seven partners}● PEM-MRI {partner}
49 Alberto Del Guerra – DASIPM2 Collaboration
Acknowledgments
Deepest thanks go to the members of the DASIPM2 collaboration:
● Claudio Piemonte & collaborators (FBK-irst and Trento)
● Francesco Corsi & collaborators (Bari)● Giovanni Ambrosi & collaborators (Perugia)● Giuseppe Levi & collaborators (Bologna)● Pisa TEAM (Gabriela Llosa, Sara Marcatili, Gianmaria Collazuol, S. Moehrs, N.Belcari, Maria G. Bisogni)