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Application of a Flexible PET Scanner Combined with 3 T MRI Using Non-local Means Reconstruction: Qualitative and Quantitative Comparison with Whole-Body PET/CT

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Flexible positron emission tomography (fxPET) employing a non-local means reconstruction algorithm was designed to fit existing magnetic resonance imaging (MRI) systems. We aimed to compare the qualitative and quantitative performance of fxPET among fxPET with MR-based attenuation correction (MRAC), fxPET with CT-based attenuation correction (CTAC) using CT as a part of WB PET/CT, and whole-body (WB) PET/CT.


Sixteen patients with suspected head and neck cancer underwent 2-deoxy-2-[18F]fluoro-d-glucose WB PET/CT scans, followed by fxPET and 3 T MRI scans. Phantom data were compared among the three datasets. For registration accuracy, we measured the distance between the center of the tumor determined by fxPET and that in MRI. We compared image quality, detection rates, and quantitative values including maximal standardized uptake value (SUVmax), metabolic tumor volume (MTV), total lesion glycolysis (TLG), and tumor-to-muscle ratio (TMR) among the three datasets.


The phantom data in fxPET, except the percent contrast recoveries of 17-mm and 22-mm hot spheres, were inferior to those in WB PET/CT. The mean registration accuracy was 4.4 mm between fxPET using MRAC and MRI. The image quality was comparable between two fxPET datasets, but significantly inferior to WB PET/CT (p < 0.0001). In contrast, detection rates were comparable among the three datasets. SUVmax was significantly higher, and MTV and TLG were significantly lower in the two fxPET datasets compared with the WB PET/CT dataset (p < 0.005). There were no significant differences in SUVmax, MTV, and TLG between the two fxPET datasets or in TMR among the three datasets. All quantitative values had significantly positive correlations.


Compared with WB PET/CT, the phantom data and image quality were inferior in fxPET. However, the results of the detection rates and quantitative values suggested the clinical feasibility of fxPET.

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We thank Tetsuya Kobayashi, Junichi Ohi, Keishi Kitamura, and all other staff members of Shimadzu corporation for providing the prototype flexible PET scanner. We also thank Tsuneo Saga, Ayako Kato, Hirofumi Kawakami, Taisuke Nagao, Masaaki Kajisako, and Shigeto Kawase for their technical support. We are grateful for the enrollment of patients by Shunsuke Yuge, Eitaro Kidera, Tomoaki Otani, Kousuke Kitaguchi, and Morimasa Kitamura. We thank Richard Lipkin, PhD, and Benjamin Knight MSc., from Edanz Group (, for editing a draft of this manuscript.

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Authors and Affiliations



Masao Watanabe, Yasutaka Fushimi, Takayoshi Ishimori, Aya Nakajima, Michio Yoshimura, Masahiro Kikuchi, Kazuko Ohno, and Yuji Nakamoto contributed to the study conception and design. Masao Watanabe, Kanae Kawai-Miyake, Takayoshi Ishimori, Aya Nakajima, Michio Yoshimura, Masahiro Kikuchi, Kazuko Ohno, and Yuji Nakamoto acquired data. Masao Watanabe, Kanae Kawai-Miyake, Takayoshi Ishimori, Kazuko Ohno, and Yuji Nakamoto analyzed and interpreted data. Drafting of the manuscript was performed by Masao Watanabe. Masao Watanabe, Yuji Nakamoto, and all the other authors revised the manuscript critically for important intellectual content. All authors approved the final version to be published and agreed to be accountable for all aspects of the work.

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Correspondence to Yuji Nakamoto.

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Ethical Approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This article does not contain any studies with animals performed by any of the authors.

Informed Consent

Informed consent was obtained from all individual participants included in the study.

Conflict of Interest

Yuji Nakamoto obtained financial support from Shimadzu Corporation, Kyoto, Japan. This prototype scanner was developed by this company and was provided to us for free for use in this study. The other authors declare that they have no conflict of interest.

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Masao Watanabe is the first author

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Watanabe, M., Kawai-Miyake, K., Fushimi, Y. et al. Application of a Flexible PET Scanner Combined with 3 T MRI Using Non-local Means Reconstruction: Qualitative and Quantitative Comparison with Whole-Body PET/CT. Mol Imaging Biol 24, 167–176 (2022).

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