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Impact of random and scattered coincidences from outside of field of view on positron emission tomography/computed tomography imaging with different reconstruction protocols

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Abstract

Image quality in positron emission tomography (PET) is affected by random and scattered coincidences and reconstruction protocols. In this study, we investigated the effects of scattered and random coincidences from outside the field of view (FOV) on PET image quality for different reconstruction protocols. Imaging was performed on the Discovery 690 PET/CT scanner, using experimental configurations including the NEMA phantom (a body phantom, with six spheres of different sizes) with a signal background ratio of 4:1. The NEMA phantom (phantom I) was scanned separately in a one-bed position. To simulate the effect of random and scatter coincidences from outside the FOV, six cylindrical phantoms with various diameters were added to the NEMA phantom (phantom II). The 18 emission datasets with mean intervals of 15 min were acquired (3 min/scan). The emission data were reconstructed using different techniques. The image quality parameters were evaluated by both phantoms. Variations in the signal-to-noise ratio (SNR) in a 28-mm (10-mm) sphere of phantom II were 37.9% (86.5%) for ordered-subset expectation maximization (OSEM-only), 36.8% (81.5%) for point spread function (PSF), 32.7% (80.7%) for time of flight (TOF), and 31.5% (77.8%) for OSEM + PSF + TOF, respectively, indicating that OSEM + PSF + TOF reconstruction had the lowest noise levels and lowest coefficient of variation (COV) values. Random and scatter coincidences from outside the FOV induced lower SNR, lower contrast, and higher COV values, indicating image deterioration and significantly impacting smaller sphere sizes. Amongst reconstruction protocols, OSEM + PSF + TOF and OSEM + PSF showed higher contrast values for sphere sizes of 22, 28, and 37 mm and higher contrast recovery coefficient values for smaller sphere sizes of 10 and 13 mm.

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Authors and Affiliations

  1. Department of Medical Physics, Iran University of Medical Sciences, Tehran, Iran

    Mahak Osouli Alamdari

  2. Chronic Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran

    Pardis Ghafarian & Mehrdad Bakhshayesh-Karam

  3. PET/CT and Cyclotron Center, Masih Daneshvari Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran

    Pardis Ghafarian

  4. Departments of Radiology and Physics, University of British Columbia, Vancouver, BC, Canada

    Arman Rahmim

  5. Research Center for Molecular and Cellular Imaging, Advanced Medical Technologies and Equipment Institute, Tehran University of Medical Sciences, Tehran, Iran

    Mohammad Reza Ay

  6. Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, Tehran, Iran

    Mohammad Reza Ay

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  1. Mahak Osouli Alamdari
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  2. Pardis Ghafarian
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Contributions

All authors contributed to the study conception and design. PG, MRA, and AR were involved in technical contribution of the study. Clinical contribution was performed by MBK. Material preparation, data collection and analysis were performed by MOA. The first draft of the manuscript was written by MOA and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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Correspondence to Pardis Ghafarian.

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The authors declare that they have no competing interests.

Additional information

This work was supported by the Tehran University of Medical Sciences under Grant No. 36291 and PET/CT and Cyclotron Center of Masih Daneshvari Hospital at Shahid Beheshti University of Medical Sciences.

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Alamdari, M.O., Ghafarian, P., Rahmim, A. et al. Impact of random and scattered coincidences from outside of field of view on positron emission tomography/computed tomography imaging with different reconstruction protocols. NUCL SCI TECH 34, 184 (2023). https://doi.org/10.1007/s41365-023-01321-0

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