15th European Molecular Imaging Meeting
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SPECT, PET Technologies & Standardization

Session chair: Wissam Beaino (Amsterdam, Netherlands); Julia Mannheim (Tubingen, Germany)
 
Shortcut: PW11
Date: Wednesday, 26 August, 2020, 5:30 p.m. - 7:00 p.m.
Session type: Poster

Contents

Abstract/Video opens by clicking at the talk title.

800

Design of a highly scalable TOF-PET detector: the UTOFPET project

Esther Ciarrocchi1, 2, Maria G. Bisogni1, 2, Niccolò Camarlinghi1, 2, Pietro Carra1, 2, Matteo Morrocchi1, 2, Giancarlo Sportelli1, 2, Valeria Rosso1, 2, Marco D'Inzeo3, Giovanni Franchi3, Lorenzo Perillo3, Andrea Puccini3, Edoardo Charbon4, Claudio Bruschini4, Francesco Gramuglia4, Esteban Venialgo4, Karel Deprez5, Roel Van Holen5, 6, Mariele Stockhoff6, Charlotte Thyssen6, Ewout Vansteenkiste5, Stefaan Vandenberghe6, Nicola Belcari1, 2

1 University of Pisa, Department of Physics, Pisa, Italy
2 INFN, Section of Pisa, Pisa, Italy
3 AGE Scientific srl, Lucca, Italy
4 École polytechnique fédérale de Lausanne (EPFL), AQUA Laboratory, Institute of Microengineering, Neuchâtel, Switzerland
5 Molecubes NV, Gent, Belgium
6 Ghent University, Department of Electronics and Information Systems, Medical Image and Signal Processing (MEDISIP), Gent, Belgium

Introduction

The UTOFPET (Ultra-Time-of-Flight PET) project aims at developing a highly modular and scalable TOF-PET detector module, suitable for various applications, from brain-dedicated to total-body PET. The project wants to achieve beyond-state-of-the-art performance: spatial resolution less than 1 mm, timing resolution below 140 ps FWHM (i.e., a coincidence time resolution, CTR, of 200 ps), maximum sustainable count-rate of 1 Mcps, and enough processing power to perform on-board real-time measurements of event position, energy and time.

Methods

The UTOFPET detector (Fig.1) is based on a continuous LYSO scintillator crystal read out by 256 SiPMs. The preferred SiPM pitch is 3.2 mm, leading to a photodetector size of 51.8×51.8 mm2. Four ASIC boards bias the SiPMs and read their outputs, independently, by means of four 16-channel FlexToT ASICs and an FPGA with 64 TDCs to convert FlexToT outputs to time and charge. A SoC-FPGA collects the ASIC outputs to perform the event clustering and to extract position, energy and time information. The only centralized infrastructure is the one used for clock distribution. Here, we report the energy and time performance of six SiPM types, tested using two HRFLexToT evaluation boards, and the event positioning capability of a lightweight neural network (NN) architecture on simulated data.

Results/Discussion

Figure 2a shows the energy resolution of the six SiPM types as a function of the overvoltage, using a 22Na source and a single SiPM coupled to a 3×3×5 mm3 LYSO crystal.  The CTR for the six SiPM types as a function of the overvoltage is shown in Fig.2b, expressed as the FWHM of the time difference distribution between the triggers of the first digital pulse for the two ASICs. For these measurements, a 68Ge source was used, an energy window of 1 FWHM around the photo-peak was considered, no time-walk correction was applied, and the threshold of the ASIC discriminator was chosen as the lower compatible with the noise level of the SiPMs and electronics. The NN event positioning capability is shown in Fig.2c on a simulated irradiation grid. The chosen network architecture uses 3 hidden layers with a total of about 1.000 parameters. The FWHM of the reconstructed spot and the average reconstruction error are shown in Fig.2d.

Conclusions

Initial measurements confirm the feasibility of sub-200 ps CTR. The proposed event positioning algorithm reached a FWHM of 0.4 mm and an average error in the reconstructed position of 0.12 mm with simulated data. We are studying methods to improve the light collection efficiency and thus the detector time performance by employing retro-reflectors on the back-side of the crystal and photonic crystal interfaces between the crystal and the SiPMs.

Acknowledgment

The research leading to these results has received funding from the the European Union’s Horizon 2020 research and innovation programme under grant agreement No 688735 (Photonics Based Sensing ERA-NET Cofund), Regione Toscana and VLAIO. 

Figure 1. Scheme of the UTOFPET detector.
Figure 2. Summary of results with single detectors and simulations.
a) Energy resolution as a function of overvoltage for 6 SiPM types. b) Coincidence time resolution as a function of overvoltage for 6 SiPM types. c) Event-positioning reconstruction capability of the NN algorithm on simulated data. d) FWHM of the reconstructed spot and average reconstruction error for the NN algorithm for the simulated data.
Keywords: tof-pet, coincidence time resolution, scintillator crystal
801

Performance of nanoScan PET/CT and PET/MRI and comparison of image derived quantifications with ex vivo tissue distribution in tumor bearing mice

Marion Chomet1, Maxime Schreurs1, Ricardo Vos1, Marc Huisman1, Mariska Verlaan1, Esther Kooijman1, Guus A. M. S. van Dongen1, Danielle J. Vugts1, Wissam Beaino1

1 Amsterdam UMC, VU University, Radiology and Nuclear medicine, Radionuclide Center, Amsterdam, Netherlands

Introduction

Ex vivo tissue distribution is the gold standard for the evaluation and quantification of radiotracers accumulation in tumor xenografts. This technique uses high number of animals especially when it is performed at multiple time points. Positron emission tomography (PET) imaging can be used as an alternative technique that allows longitudinal evaluation of tracer distribution in the same animal at different time points. Our aim was to evaluate the performance of a nanoPET/CT and PET/MRI scanners and determine their potential in accurate quantification of tumor uptake.

Methods

NEMA NU 4-2008 phantoms [1] were filled with 20 MBq of 11C, 18F, 89Zr or 68Ga and scanned until decay in a Mediso nanoScan PET/CT and PET/MRI. N87 xenograft nu/nu mice (n=20) were injected IV with [18F]FDG (≥10MBq), kept 50 min under anesthesia and further imaged for 20 min in the PET/CT or PET/MRI camera. At end of scan, animals were sacrificed immediately and organs of interest were collected and measured in a gamma counter to determine %ID/g. Data were reconstructed using TeraTomo reconstruction algorithm with attenuation and scatter correction. Amide analysis software was used for phantom analysis. Analysis on tumor bearing mice was performed using Vivoquant software. Uptake in tumors and other organs was compared with ex vivo tissue distribution.

Results/Discussion

With the PET/CT, the highest recovery coefficient, thus the lowest Partial Volume Effect (PVE) was obtained for 18F with a recovery coefficient of 80% in the 5 mm cylinder ROI (Fig.1). 11C and 89Zr had a lower but comparable recovery with respectively 76% and 77%. Finally, 68Ga had the lowest recovery with 54% in the 5 mm ROI. The comparison of [18F]-FDG uptake (%ID/g) in the tumor obtained from the PET/CT image analysis and the biodistribution showed a correlation of R2=0.61. When the total counts (Bq) in the tumors were compared, the correlation was higher with an R2 of 0.94 (Fig.2). For the PET/MRI a similar correlation between the image quantification of [18F]-FDG uptake in the tumor and the biodistribution data was also observed (R2=0.68 for the %ID/g and 0.92 for the total uptake in Bq). The comparison of [18F]-FDG brain uptake obtained from the tissue distribution and the PET/CT showed a very good correlation with an R2=0.99 (%ID/g) and R2=0.91 (total counts in Bq).

Conclusions

In conclusion, the Mediso nanoScan PET/CT and PET/MRI showed very similar performance with a slightly better recovery and lower PVE for the PET/CT when attenuation and scatter correction was applied.  PET imaging can potentially be used as an alternative for the classic ex vivo tissue distribution to determine the tracer uptake in tumor xenografts. However, in depth analysis needs to be performed and compared with other PET isotopes.

Acknowledgment

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska–Curie grant agreement No 675417

References
[1] Szanda I, Mackewn J, Patay G, Major P, Sunassee K, Mullen GE, Nemeth G, Haemisch Y, Blower PJ, Marsden PK, National Electrical Manufacturers Association NU-4 Performance Evaluation of the PET Component of the NanoPET/CT Preclinical PET/CT Scanner, J. Nucl. Med. 52, 1741–1747 (2011).
Fig.1
Determination of PVE for 11C, 18F, 89Zr and 68Ga  with the PET/CT (A) and the PET/MRI (B).
Fig.2
Correlation between PET/CT assessed tumor uptake and ex vivo tissue distribution.
Keywords: preclinical imaging, PET/CT, PET/MRI, quantification, tissue distribution
803

Performance evaluation of U-SPECT5 E-Class: multi-pinhole imaging with 2 stationary detectors

Jan V. Hoffmann1, 2, Jan P. Janssen1, 2, Takayuki Kanno2, 3, Takahiro Higuchi1, 2, 4

1 University Hospital of Würzburg, Department of Nuclear Medicine, Würzburg, Germany
2 University Hospital of Würzburg, Comprehensive Heart Failure Center, Würzburg, Germany
3 Kanazawa University, Department of Quantum Medical Technology, Kanazawa, Japan
4 Okayama University, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan

Introduction

Small-animal SPECT systems with multipinhole collimation and three large stationary detectors have been shown their superiority when compared to the SPECT scanners with moving detectors (1). Recently an economically attractive version with two large stationary detectors has been introduced. We investigated the performance to analyse the capabilities of this novel SPECT system.

Methods

The recently developed U-SPECT5-CT E-Class scanner (MILabs) with two stationary detectors and multipinhole collimation was used for acquiring data with point source, Jaszczak-like hot rod and uniformity phantoms to analyse sensitivity, spatial resolution, image uniformity and contrast-to-noise ratio. Three dedicated mouse collimators with pinhole sizes of 0.25 mm; 0.6 mm and 1.0 mm for extra ultra-high resolution (XUHR-M), general-purpose (GP-M) and ultra-high sensitivity (UHS-M) were investigated. The number of pinholes counts 75 for all three collimators. Activity concentration applied amounts to 309.7±20.4 MBq/ml and the scan duration was 45 min. We focused on the isotope 99mTc. All raw data was reconstructed by using the new SR-OSEM algorithm with 3 iterations and 128 subsets (2).

Results/Discussion

The peak sensitivity achieved 229 cps/MBq (XUHR-M); 835 cps/MBq (GP-M); 2023 cps/MBq (UHS-M). Spatial resolution was determined visually with hot-rod phantoms as 0.35 mm (XUHR-M); 0.50 mm (GP-M) and 0.70 mm (UHS-M). Image uniformity for maximum resolution amounts to 40.7% (XUHR-M); 29.1% (GP-M) and 24.5% (UHS-M). To achieve the best possible image quality considering contrast and noise, each collimator showed its advantage close to their maximum spatial resolution.

Conclusions

Although the investigated SPECT scanner uses only two large stationary detectors instead of three, the system’s performance records only minor deficits regarding the highest possible image quality. The effects of the lower sensitivity on the noise level might be improved by increasing either scanning time or injection dose, but further validation especially concerning animal models is necessary.

References
[1] Deleye, S, Van Holen, R, 2013, 'Performance evaluation of small-animal multipinhole muSPECT scanners for mouse imaging', Eur J Nucl Med Mol Imaging, 40(5), 744-758.
[2] Vaissier, PE, Beekman, FJ, 2016, 'Similarity-regulation of OS-EM for accelerated SPECT reconstruction.', Phys Med Biol., 61(11), 4300-4315.
Keywords: small-animal SPECT, preclinical SPECT, multipinhole SPECT, U-SPECT5 E-class
804

Capabilities of multi-pinhole SPECT as a tool for preclinical in-vivo rat imaging

Jan P. Janssen1, 2, Jan V. Hoffmann1, 2, Takayuki Kanno2, 3, Takahiro Higuchi1, 2, 4

1 University Hospital of Würzburg, Department of Nuclear Medicine, Würzburg, Germany
2 University Hospital of Würzburg, Comprehensive Heart Failure Center, Würzburg, Germany
3 Kanazawa University, Department of Quantum Medical Technology, Graduate School of Medical Sciences, Kanazawa, Japan
4 Okayama University,, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan

Introduction

Compared to clinical systems preclinical multi-pinhole SPECT provides subhalfmillimetre-high spatial resolution (1) but the limiting factor in in-vivo SPECT-performance is the sensitivity even by using multiple pinholes. We investigated the capabilities of a novel micro-SPECT system by using phantoms and performing in-vivo 99mTc-MIBI-myocardial perfusion imaging in rats by maintaining high image quality.

Methods

Sensitivity, count linearity, spatial resolution, uniformity, noise and contrast were determined for U-SPECT5-CT E-Class scanner with 2 stationary detectors using an ultra-high-resolution rat and mouse multi-pinhole collimator. Point source, hot-rod, and uniform phantoms with a 99mTc-solution were scanned for different activity concentrations and acquisition times. All acquisition data was reconstructed by SR-OSEM (2) 4 iterations 128 subsets and image quality was adapted by gaussian smoothing. Two rats injected with ~100 MBq 99mTc-MIBI were imaged for 6x 10-min-frames (whole-body scan). Visual comparison of phantom and in-vivo scans with different gaussian filters to optimize image quality, was performed. Like this, we determined the dependency of resolution on the activity concentration.

Results/Discussion

Sensitivity was 558 cps/MBq, count rate performance showed <10% data loss for 300 MBq compared to 100 MBq, hot rods as small as 1.2 mm were resolved, uniformity was 16 %. Resolution was 1.2 mm for high count studies, 2.2 mm in the heart for 60 min acquisition time, 2.8 mm, for 30 min scan and 3.5 mm for 10 min, respectively (Figure 1). Uptake was 2.03%. In comparison of 10 min, 30 min and 60 min acquisition time of the heart-scan high image quality was only maintained by gaussian filtering with a minimum of 2.2 mm FWHM for the 60-min-measurement, which was validated by the corresponding phantom measurements.

Conclusions

This method for in-vivo imaging in small-animal SPECT is helpful for study design regarding injection dose, acquisition time, post-filtering and collimator choice. The algorithm SR-OSEM with fixed reconstruction parameters is a big help in simplifying the study planning, although there are still challenges concerning the limited injection dose and acquisition time in in-vivo settings especially concerning dynamic scans.

References
[1] Deleye, S, Van Holen, R, 2013, 'Performance evaluation of small-animal multipinhole muSPECT scanners for mouse imaging', Eur J Nucl Med Mol Imaging, 40(5), 744-758.
[2] Vaissier, PE, Beekman, FJ, 2016, 'Similarity-regulation of OS-EM for accelerated SPECT reconstruction.', Phys Med Biol., 61(11), 4300-4315.
Filter-dependent image quality in phantom and in-vivo heart images.
(A) Hot Rod Phantom with 320.2MBq/ml scanned for 30 minutes representing the maximum performance. Rod Size (mm): 1.8 / 2.0 / 2.2 / 2.5 / 2.8 / 3.1. (B) The Tc99m-MIBI uptake of a rat heart, 108.51 MBq ID, in the vertical long axis for 60-, 30- and 10-minute acquisition time. All scans were reconstructed by SROSEM 4 iterations, 128 subsets and smoothed with a gaussian post filter ranging from 1.2 mm – 4.0 mm FWHM. The red frame indicates good image quality, for the images on the left side noise is too high whereas on the right side contrast is too low.
Keywords: Small-animal imaging, multipinhole SPECT, molecular imaging, myocardial imaging, 99mTc-MIBI