SAFIR: a fast PET insert for pre-clinical MRI with high temporal resolutionBecker Robert1, Jean-Pierre Cachemiche2, Casella Chiara1, Dissertori Günther1, Fischer Jannis1, Howard Alexander1, Jeitler Astrik3,1, Lustermann Werner1, Christian Morel, Josep Oliver4, Röser Ulf1, Wang Qiulin5,1, Weber Bruno6

1ETH Zurich, Institute of Particle Physics - Zurich, Switzerland 2Aix Marseille Université, CNRS/IN2P3, CPPM UMR - Marseille, France 3HTWG Konstanz, Computer Sciences - Konstanz, Germany 4CSIC, Instituto de Física Corpuscular - Valencia, Spain 5Tsinghua University, Institute of Medical Physics - Beijing, China 6University of Zurich, Institute of Pharmacology and Toxicology - Zurich, Switzerland

SAFIR - Small Animal Fast Insert for mRi - http://safir.ethz.ch

Coincidence time resolution

Introduction Construction

Simulations

Objective Development of a high rate PET insert for pre-clinical 7T MRI system (Bruker 70/30) with unprecedented temporal resolution

Motivation Quantitative dynamic PET imaging truly simultaneous with MRI using (among others) short lived isotopes 15O

Highlights - Temporal resolution of ~5s- Very fast data acquisition – large number of counts 10 kHz / mm2 of detector area

Requirements - High injected activity: up to 500 MBq – compensate partially the low number of counts for short time intervals- Small coincidence time window (CTW): < 1ns – limiting random coincidences- Excellent coincidence time resolution (CTR): ~300ps FWHM- High sensitivity: ~6%- Good spatial resolution ~1.5 mm FWHM

Crystal CTR SIPAT LYSO:Ce 190 psSIPAT LYSO:Ce:Ca(0.5) 139 ps

Crystals 1.5x1.5x12 mm3

Setup 22Na + 2 LYSO crystals in coincidences

Sensors Digital SiPM (PDPC,Philips)Interface Air coupling (no grease)Wrapping None

ToFPET: 411 ps FWHM

0 100 200 300 400 5000

5

10

15

20 TruesRandomsNECRNECR 10% scatter

activity in MBq

Mcp

s

2) CTR using ToFPET and STiC ASICs, single crystals

STiC: 388 ps FWHM

1) CTR LYSO standard vs Ca co-doped (fig. 1)

Coincidence setup, crystals are ‘air-coupled’ to Hamamastu MPPCs Improved results expected using optical glue and crystal wrapping

3) CTR using ToFPET and MPPC + crystal matrices

1) Geant4 detector modelGeometry 200 mm length

120 mm diameter

Crystals 2x2x12 mm3

NECR T2 / (T + f*R+ S) (fig. 2)Point source 5M decays / activity pointdE 20% FWHMdT (crystal) 180 ps sigmaCTR 600 ps FWHMEnergy window (350-650) keV

Fig. 2: NECR simulated data, f=1

Laboratory tests with 22Na, ~2MBq CTR = 482 ps FWHM

Setup:2 matrices of 4x4 crystals - ESR foilCrystal size: 2.1x2.1x12mm3 Hamamatsu MPPC array 4x4, TSVPixel size 50x50 µm2, LC no trenchesSensor size 2x2 mm2, pitch 2.2 mm

System tests at Univ. of Zurich Hospital with FDG (see fig. 8) measured CTR activity dependent• CTR 672 ps FWHM at 0 MBq• CTR 890 ps FWHM at 400 MBq

Fig. 1: Newly installed Bruker 70/30 MR scanner at the Animal Imaging Center of ETH and University of Zurich at ETH-Hönggerberg campus.

PET insert development: 3 stepsPhase 1 (~1y)close to completion

Components evaluation, i.e. crystals, crystal matrices, photo-sensors, front-end readout ASICsSystem design optimization using MC simulations (GEANT4) and Image Reconstruction (STIR)

Phase 2 (~1y) - Construction of first ring system SRS1- performance evaluation in real life application- Development of dedicated 4-D reconstruction software

Phase 3 (~1y) - Construction of optimized full scanner based on SRS1 results

Detector conceptCrystals LYSO, 8x8 arrayscrystal orientation Radialcoupling to photo sensors one-to-oneSensors 8x8 SiPM arrays, TSVSensor gain stability Active controlCooling Active (Air, Freon)

1.0 mm1.2 mm

4.0 mm

3.2 mm2.4 mm

1.6 mm

3) Derenzo phantom (fig. 3)Activity 500 MBqDuration 1sBackground ZEROReconstruction OSMAPOSL (STIR)

Fig. 3: Reconstructed Derenzo phantomSpheres down to 1.6 mm can be reconstructed

Fig. 2: Artistic of the detector tube, half equipped, with components of realisitic dimensions. Serivces, are not drawn.

Fig. 3: Agile LYSO 8x8 (left),Hamamatsu MPPC 4x4 (right)

Readout electronicsAmplification and Digitization on the detector

ASIC developed for ToF applicationsSTiC or ToFPET (64ch, CTR ~350 ps, low power, LVDS signal outputs (160/320) bit/s

Transmission Optical links (5-10) Gbit/sDAQ uTCA based

2) Spatial resolution- Following NEMA- FORE re-binning- 2DFBP

Radial: ~1.5 mmTangential: ~1.5mmAxial: ~(1-3) mm depending on ring difference

Fig. 8: CRT vs activity

Fig. 1: LYSO – LYSO:Ca, CTR comparison

Fig. 2: CTR resolution, TOFPET ASIC Fig. 2: CTR resolution, STIC ASIC

Fig. 3: MC simulation: spatial resolution