An innovative detector concept for hybrid 4D-PET/MRI Imaging

Transcription

1 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

2 Outline the INFN-4DMPET Project Block Detector Layout Readout Architecture Detailed Detector Simulation Cluster Analysis Results & Conclusions 2

3 the 4DMPET Project goal The design of a 4D PET detector module compatible with operations inside a MRI system 3

4 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

5 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

6 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

7 Block Detector Layout An innovative detector concept A. LYSO scintillator slab Size: 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

8 Block Detector Layout An innovative detector concept A. LYSO scintillator slab Size: 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) FWHM (mm) FWTM (mm) 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.

9 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 T = 27 C ) F. Pennazio et al., Simulations of the 4DMPET SiPM Based PET Module, 2011 IEEE Nuc. Sci. Symp./Med. Imag. Conf. 9

10 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

11 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 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 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

12 Simulation Validation An innovative detector concept 2 - Black crystal 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)

13 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 ~ C Signal to Trigger Ratio (red) Efficiency (blue) as a function of the threshold (# of pixels firing in Δt = 5 ns) 13

14 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: (Rate ~ 14.4 MHz/crystal surface) S/T = 0.18 Cluster finding: 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

15 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

16 Simulation Results Energy Resolution at photopeak: 10.9 % Selection 100 < E < 600 kev 1292 events ε = (65 ±3) % 16

17 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

18 Simulation Results Depth Of Interaction Size Asymmetry: (top - bottom)/(top + bottom) RMS: 1.4 mm FWHM: 1.0 mm 18

19 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

20 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 FWHM 20%

21 First measurements by the end of 2012 Thank you! 21

22 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

23 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

24 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 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 [3] W. Moses, "Recent Advances and Future Advances in Time-of- Flight PET", Nucl Instrum Methods Phys Res A October 1; 580(2): [4] F. Pennazio et al., Simulations of the 4DMPET SiPM Based PET Module, IEEE Nuclear Science Symposium / Medical Imaging Conference,M6-5, , Valencia, Spain,