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Smith RL, Bartley L, O'Callaghan C, Haberska L, Marshall C. NEMA NU 2-2018 evaluation and image quality optimization of a new generation digital 32-cm axial field-of-view Omni Legend PET-CT using a genetic evolutionary algorithm. Biomed Phys Eng Express 2024; 10:025032. [PMID: 38346328 DOI: 10.1088/2057-1976/ad286c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2023] [Accepted: 02/12/2024] [Indexed: 02/21/2024]
Abstract
A performance evaluation was conducted on the new General Electric (GE) digital Omni Legend PET-CT system with 32 cm extended field of view. The first commercially available clinical digital bismuth germanate system. The system does not use time of flight (ToF). Testing was performed in accordance with the NEMA NU2-2018 standard. A comparison was made between two other commercial GE scanners with extended fields of view; the Discovery MI - 6 ring (ToF enabled) and the Discovery IQ (non-ToF). A genetic evolutionary algorithm was developed to optimize image reconstruction parameters from image quality assessments. The Omni demonstrated average spatial resolutions at 1 cm radial offset as 3.9 mm FWHM. The total system sensitivity at the center was 44.36 cps/kBq. The peak NECR was measured as 501 kcps at 17.8 kBq ml-1with a 35.48% scatter fraction. The maximum count-rate error below NECR peak was 5.5%. Using standard iterative reconstructions, sphere contrast recovery coefficients were from 52.7 ± 3.2% (10 mm) to 92.5 ± 2.4% (37 mm). The PET-CT co-registration accuracy was 2.4 mm. In place of ToF, the Omni employs software corrections through a pre-trained neural network (PDL) (trained on non-ToF to ToF) that takes Bayesian penalized likelihood reconstruction (Q.Clear) images as input. The optimum parameters for image reconstruction, determined using the genetic algorithm were a Q.Clear parameter,β, of 350 and a 'medium' PDL setting. Using standard iterative reconstructions, the Omni initially showed increased background variability compared to the Discovery MI. With optimized PDL reconstruction parameters selected using the genetic algorithm the performance of the Omni surpassed that of the Discovery MI on all NEMA tests. The genetic algorithm's demonstrated ability to enhance image quality in PET-CT imaging underscores the importance of algorithm driven optimization and underscores the requirement to validate its use in the clinical setting.
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Affiliation(s)
- Rhodri Lyn Smith
- The Wales Research and Diagnostic Positron Emission Tomography Imaging Centre, Cardiff University, School of Medicine, Cardiff, CF14 4XN, Wales, United Kingdom
| | - Lee Bartley
- Radiology, Cardiff and Vale University Health Board, University Hospital of Wales, Cardiff, CF14 4XW, Wales, United Kingdom
| | - Christopher O'Callaghan
- Radiology, Cardiff and Vale University Health Board, University Hospital of Wales, Cardiff, CF14 4XW, Wales, United Kingdom
| | - Luiza Haberska
- The Wales Research and Diagnostic Positron Emission Tomography Imaging Centre, Cardiff University, School of Medicine, Cardiff, CF14 4XN, Wales, United Kingdom
| | - Chris Marshall
- The Wales Research and Diagnostic Positron Emission Tomography Imaging Centre, Cardiff University, School of Medicine, Cardiff, CF14 4XN, Wales, United Kingdom
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Mohr P, Efthimiou N, Pagano F, Kratochwil N, Pizzichemi M, Tsoumpas C, Auffray E, Ziemons K. Image Reconstruction Analysis for Positron Emission Tomography With Heterostructured Scintillators. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2023; 7:41-51. [PMID: 37397180 PMCID: PMC10312993 DOI: 10.1109/trpms.2022.3208615] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/15/2023]
Abstract
The concept of structure engineering has been proposed for exploring the next generation of radiation detectors with improved performance. A TOF-PET geometry with heterostructured scintillators with a pixel size of 3.0 × 3.1 × 15 mm3 was simulated using Monte Carlo. The heterostructures consisted of alternating layers of BGO as a dense material with high stopping power and plastic (EJ232) as a fast light emitter. The detector time resolution was calculated as a function of the deposited and shared energy in both materials on an event-by-event basis. While sensitivity was reduced to 32% for 100-μm thick plastic layers and 52% for 50 μm, the coincidence time resolution (CTR) distribution improved to 204 ± 49 and 220 ± 41 ps, respectively, compared to 276 ps that we considered for bulk BGO. The complex distribution of timing resolutions was accounted for in the reconstruction. We divided the events into three groups based on their CTR and modeled them with different Gaussian TOF kernels. On an NEMA IQ phantom, the heterostructures had better contrast recovery in early iterations. On the other hand, BGO achieved a better contrast-to-noise ratio (CNR) after the 15th iteration due to the higher sensitivity. The developed simulation and reconstruction methods constitute new tools for evaluating different detector designs with complex time responses.
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Affiliation(s)
- Philipp Mohr
- Factuly of Chemistry and Biotechnology, FH Aachen University of Applied Sciences, 52428 Jülich, Germany, and also with the Experimental Physics Department, European Organization for Nuclear Research (CERN), 1201 Geneva, Switzerland. He is now with the Department of Nuclear Medicine and Molecular Imaging, University of Groningen, University Medical Center Groningen, 9713 GZ Groningen, The Netherlands
| | - Nikos Efthimiou
- Department Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104 USA
| | - Fiammetta Pagano
- Physics Department, University of Milano-Bicocca, 20126 Milan, Italy, and also with the Experimental Physics Department, European Organization for Nuclear Research (CERN), 1201 Geneva, Switzerland
| | - Nicolaus Kratochwil
- Experimental Physics Department, European Organization for Nuclear Research (CERN), 1211 Geneva, Switzerland
| | - Marco Pizzichemi
- Physics Department, University of Milano-Bicocca, 20126 Milan, Italy, and also with the Experimental Physics Department, European Organization for Nuclear Research (CERN), 1201 Geneva, Switzerland
| | - Charalampos Tsoumpas
- Department of Nuclear Medicine and Molecular Imaging, University of Groningen, University Medical Center Groningen, 9713 GZ Groningen, The Netherlands, and also with the Biomedical Imaging Science Department, Leeds Institute of Cardiovascular and Metabolic Medicine, University of Leeds, LS2 9JT Leeds, U.K
| | - Etiennette Auffray
- Experimental Physics Department, European Organization for Nuclear Research (CERN), 1211 Geneva, Switzerland
| | - Karl Ziemons
- Faculty of Biomedical Engineering and Technomathematics, FH Aachen University of Applied Sciences, 52428 Jülich, Germany
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Schaart DR, Schramm G, Nuyts J, Surti S. Time of Flight in Perspective: Instrumental and Computational Aspects of Time Resolution in Positron Emission Tomography. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2021; 5:598-618. [PMID: 34553105 PMCID: PMC8454900 DOI: 10.1109/trpms.2021.3084539] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The first time-of-flight positron emission tomography (TOF-PET) scanners were developed as early as in the 1980s. However, the poor light output and low detection efficiency of TOF-capable detectors available at the time limited any gain in image quality achieved with these TOF-PET scanners over the traditional non-TOF PET scanners. The discovery of LSO and other Lu-based scintillators revived interest in TOF-PET and led to the development of a second generation of scanners with high sensitivity and spatial resolution in the mid-2000s. The introduction of the silicon photomultiplier (SiPM) has recently yielded a third generation of TOF-PET systems with unprecedented imaging performance. Parallel to these instrumentation developments, much progress has been made in the development of image reconstruction algorithms that better utilize the additional information provided by TOF. Overall, the benefits range from a reduction in image variance (SNR increase), through allowing joint estimation of activity and attenuation, to better reconstructing data from limited angle systems. In this work, we review these developments, focusing on three broad areas: 1) timing theory and factors affecting the time resolution of a TOF-PET system; 2) utilization of TOF information for improved image reconstruction; and 3) quantification of the benefits of TOF compared to non-TOF PET. Finally, we offer a brief outlook on the TOF-PET developments anticipated in the short and longer term. Throughout this work, we aim to maintain a clinically driven perspective, treating TOF as one of multiple (and sometimes competitive) factors that can aid in the optimization of PET imaging performance.
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Affiliation(s)
- Dennis R Schaart
- Section Medical Physics & Technology, Radiation Science and Technology Department, Delft University of Technology, 2629 JB Delft, The Netherlands
| | - Georg Schramm
- Department of Imaging and Pathology, Division of Nuclear Medicine, KU/UZ Leuven, 3000 Leuven, Belgium
| | - Johan Nuyts
- Department of Imaging and Pathology, Division of Nuclear Medicine, KU/UZ Leuven, 3000 Leuven, Belgium
| | - Suleman Surti
- Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104 USA
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