Piergiorgio Cerello (INFN - Torino) on behalf of the 4D-MPET* project *4 Dimensions Magnetic compatible module for Positron Emission Tomography INFN Perugia, Pisa, Torino; Polytechnic of Bari; University of Pisa; University of Torino 1
Outline the INFN-4DMPET Project Block Detector Layout Readout Architecture Detailed Detector Simulation Cluster Analysis Results & Conclusions 2
the 4DMPET Project goal The design of a 4D PET detector module compatible with operations inside a MRI system 3
the 4DMPET Project goal Why PET/MRI? Nowadays PET and MRI scans are taken at different times with distinct machines: Movements of the patient on the couch Image fusion techniques need coregistration MRI PET Philips Ingenuity TF PET/MR Combo PET and MRI image fusion 4
the 4DMPET Project goal Why PET/MRI? Hybrid PET/MRI systems provide functional and morphological information at the same time: No image fusion Space and costs saving Better soft tissue contrast Lower radiation doses Hybrid PET/MRI scanner 5
Block Detector Layout An innovative detector concept Silicon Photomultipliers (SiPM) coupled to both sides of a single LYSO scintillator crystal: MRI compatible x and y coordinates measured with high precision [1] Depth of Interaction (DOI): decreases the uncertainty of the z coordinate [2] Time of Flight (TOF): reduces image background noise [3] D = object size t = time resolution Integrated readout electronics is required for time and energy measurement on each pixel 6
Block Detector Layout An innovative detector concept A. LYSO scintillator slab Size: 48 48 10 mm³ T decay ~ 40 ns B. Top / bottom SiPM layers: 16 x 16 square pixels 3 mm pixel pitch 50 µm microcell size C. Independent identical readout boards A B C 7
Block Detector Layout An innovative detector concept A. LYSO scintillator slab Size: 48 48 10 mm³ T decay ~ 40 ns B. Top / bottom SiPM layers: 16 x 16 square pixels 3 mm pixel pitch 50 µm microcell size Pixel size 1.5 mm 3 mm RMS (mm) 1.14 1.13 FWHM (mm) 0.32 0.48 FWTM (mm) 1.61 1.44 C. Independent identical readout boards 8 F. Pennazio et al., Simulations of the 4DMPET SiPM Based PET Piergiorgio Module, 2011 Cerello IEEE Nuc. (cerello@to.infn.it) Sci. Symp./Med. Imag. Conf.
Front-end mixed-mode ASIC Double threshold technique for very high resolution TOF (target: σ T ~ 100 ps) Low threshold on single ph-e for an efficient measurement of the interaction time High threshold to discriminate events from noise (SiPM dark count ~ 2 MHz/mm 2 @ T = 27 C ) F. Pennazio et al., Simulations of the 4DMPET SiPM Based PET Module, 2011 IEEE Nuc. Sci. Symp./Med. Imag. Conf. 9
Front-end mixed-mode ASIC Energy evaluation based on Time Over Threshold (TOT) technique 256 channels, 2 conversion levels: SiPM outputs to digital pulses: front-end, AMS 0.35µm SiGe-BiCMOS digital pulses to TOF+TOT: Time to Digital Converter, UMC 65nm Signal TOT 10
Simulation Validation An innovative detector concept Simulation results are validated by comparing them to data taken to study the coupled SiPM/crystal performance, in different test configuration 1 - White crystal Energy Measurements @ INFN - Pisa Na22 spectrum 3 x 3 mm 2 SiPM by FBK-IRST LYSO 3 x 3 x 10 mm 3 painted white coupled to the pixel with optical grease Data acquisition with a Lecroy oscilloscope @ 2 Gsample/s Piemonte C et al. Recent developments on silicon photomultipliers produced at FBK-irst 2007 IEEE NSS MIC Conf. Record CD-ROM (N41-2) G. De Luca et al., Signal shape of a PET detector based on LSO:Ce,Ca crystals and SiPM 11
Simulation Validation An innovative detector concept 2 - Black crystal Measurements @IFIC,Valencia Na22 source with coincidence module Matrix 64 pixels 1.5mm x 1.5mm 2 pixels LYSO 12mm x 12mm x 5mm painted black coupled to the matrix 6 Cluster finding algorithm Energy Cluster Size xy resolution G Llosa et al. Characterization of a PET detector head based on continuous LYSO crystals and monolithic, 64- pixel silicon photomultiplier matrices. Phys. Med. Biol. 55 (2010) 7299 7315 12
Simulation Layout Working conditions Signal Rate ~ 1.1 khz/mm² (9.9 khz/pixel) with E > 100 kev Dark Count Rate ~ 0.55 MHz/mm² (5 MHz/pixel) corresponding to T ~ 15-20 C Signal to Trigger Ratio (red) Efficiency (blue) as a function of the threshold (# of pixels firing in Δt = 5 ns) 13
Trigger & (ASIC) Cluster Finding Time interval: 781 µs Number of events in the crystal: 2253 (Rate ~ 2.5 MHz/crystal surface) Number of events in the crystal (E > 100 kev): 1984 Trigger condition (Cluster Seed) N >= 3 adjacent pixel signals in Δt < 5 ns Triggers: 11267 (Rate ~ 14.4 MHz/crystal surface) S/T = 0.18 Cluster finding: 10836 clusters RegionGrowing with N_neighbours = 8 on Cluster Seed in -0.1 ns < t_neighbour < 60 ns Cluster pairing (top, bottom surfaces): 1474 clusters Δt_median < 10 ns & ΔR < 3 mm 14
Simulation Results Cluster pairing (top, bottom surfaces): 1474 clusters Δt_median < 10 ns & ΔR < 3 mm RMS: xy: 0.8 mm, t: 2.9 ns, x: 1.04 mm, y: 1.02 mm 15
Simulation Results Energy Resolution at photopeak: 10.9 % Selection 100 < E < 600 kev 1292 events ε = (65 ±3) % 16
Simulation Results XY Resolution with edge correction RMS: 1.24 mm (1.13 in the simulation without background) FWHM: 0.6 mm (0.48 in the simulation without background) 17
Simulation Results Depth Of Interaction Size Asymmetry: (top - bottom)/(top + bottom) RMS: 1.4 mm FWHM: 1.0 mm 18
Simulation Results Time Resolution Cluster time is affected by single pixel dark counts A cluster is defined by N times that sample the crystal decay profile take as cluster time the second / third minimum pixel time! T₂ RMS: 230 ps, FWHM: 100 ps 19
Conclusions An innovative MRI compatible PET detection module is being developed, featuring: LYSO coupled to 3 mm pitch SiPM on both faces Large detection area (48 mm x 48 mm) 8 bits energy information based on TOT High resolution 4D measurements Resolution Energy (kev) xy (mm) DoI (mm) t (ps) σ 10.9% RMS 1.24 1.4 230 FWHM 20% 0.6 1.0 100 20
First measurements by the end of 2012 Thank you! 21
Conclusions Hybrid PET/ MRI INFN 4DM PET Philips Gemini TF PET/CT Yes No Yes Siemens Biograph mmr MR/PET Scintillator crystal Crystal size (mm) LYSO LYSO LSO 48 x 48 x 10 4 x 4 x 22 N.A. Detectors SiPM PMT APD #channel ASIC 256 N.A. 9 TOF Yes Yes N.A. 22
Additional features (ongoing ) LD ASIC to minimize the number of communication devices to one optical input and one optical output Active temperature control: to reduce the SiPM dark count to avoid degradations in the electronics performance Shielding to relax MRI compatibility requirements Two operation modes: clinical (TOF [coarse + fine], TOT) pre-clinical (coarse timestamp only, TOT) 23
References [1] C. Piemonte et al., "Characterization of the First Prototypes of Silicon Photomultiplier Fabricated at ITC-irst", IEEE Trans. on Nucl. Science, Vol. 54, N. 1 February 2007, pp. 236-244. MIC Conf. Record CD-ROM (N41-2),2007. [2] S. E. Derenzo, W. W. Moses, R. H. Huesman and T. F. Budinger, Critical instrumentation issues for 2 mm resolution, high sensitivity brain PET, in Quantification of Brain Function, K. Uemura, N.A. Lassen, T. Jones, et al., Amsterdam: Elsevier Science Publishers, 1993 pp. 25-37. [3] W. Moses, "Recent Advances and Future Advances in Time-of- Flight PET", Nucl Instrum Methods Phys Res A. 2007 October 1; 580(2): 919 924. [4] F. Pennazio et al., Simulations of the 4DMPET SiPM Based PET Module, IEEE Nuclear Science Symposium / Medical Imaging Conference,M6-5, 2316-2320, Valencia, Spain, 2011. 24