Basic Study
Copyright ©The Author(s) 2023. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Radiol. Nov 28, 2023; 15(11): 315-323
Published online Nov 28, 2023. doi: 10.4329/wjr.v15.i11.315
Imaging assessment of photosensitizer emission induced by radionuclide-derived Cherenkov radiation using charge-coupled device optical imaging and long-pass filters
Winn Aung, Atsushi B Tsuji, Kazuaki Rikiyama, Fumihiko Nishikido, Satoshi Obara, Tatsuya Higashi
Winn Aung, Atsushi B Tsuji, Kazuaki Rikiyama, Satoshi Obara, Tatsuya Higashi, Department of Molecular Imaging and Theranostics, Institute for Quantum Medical Science, National Institutes for Quantum Science and Technology, Chiba 263-8555, Japan
Fumihiko Nishikido, Department of Advanced Nuclear Medicine Sciences, Institute for Quantum Medical Science, National Institutes for Quantum Science and Technology, Chiba 263-8555, Japan
Author contributions: Aung W conceptualized and designed the study; Aung W, Rikiyama K and Nishikido F conducted the experiments and analyzed the data; Obara S performed the subtraction image processing; Aung W and Tsuji AB wrote the manuscript; Tsuji AB and Higashi T coordinated the research and contributed to manuscript preparation; all authors contributed to manuscript revision; All authors read and approved the final manuscript.
Supported by Grant-in-Aid for Scientific Research (C) from the Japan Society for the Promotion of Science, No. 21K07740.
Institutional review board statement: This study was reviewed and approved by the Institutional Review Board of National Institutes for Quantum Science and Technology, No. 07-1064-28. No animals or animal-derived samples or patients or patient-derived samples were included in this study.
Conflict-of-interest statement: The authors declare no potential conflicts of interest for this article.
Data sharing statement: All relevant data were presented in the manuscript. Further information is available from the corresponding author at winn.aung@qst.go.jp.
ARRIVE guidelines statement: The authors have read the ARRIVE guidelines, and the manuscript was prepared and revised according to the ARRIVE guidelines.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: https://creativecommons.org/Licenses/by-nc/4.0/
Corresponding author: Winn Aung, MBBS, PhD, Senior Researcher, Department of Molecular Imaging and Theranostics, Institute for Quantum Medical Science, National Institutes for Quantum Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan. winn.aung@qst.go.jp
Received: October 3, 2023
Peer-review started: October 3, 2023
First decision: October 17, 2023
Revised: October 26, 2023
Accepted: November 17, 2023
Article in press: November 17, 2023
Published online: November 28, 2023
Processing time: 51 Days and 15.9 Hours
ARTICLE HIGHLIGHTS
Research background

Cherenkov radiation (CR) is the emission of photons when a charged particle moves faster than the speed of light in a medium. Various radionuclides produce Cherenkov optical emission, which can potentially activate photosensitizers (PSs) in phototherapy.

Research motivation

Several researchers are investigating CR-induced photodynamic therapy using radioisotopes and Cherenkov energy transfer to PSs using optical imaging. However, the effective management of the process, particularly the cost-effective confirmation that a PS is excited by CR and identifying appropriate PSs, remains a challenge.

Research objectives

The purpose of this study is to propose a cost-effective method to determine whether the PS is excited by radionuclide-derived CR and to distinguish the fluorescence emission from PS excitation.

Research methods

Tetrakis (4-carboxyphenyl) porphyrin (TCPP) and Copper-64 (64CuCl2) were utilized as a model PS and a CR-producing radionuclide, respectively. The photo-physical properties (absorbance and fluorescence spectra) of TCPP were measured using a microplate reader and fluorescence spectrometer. Imaging and data acquisition were performed with a charge-coupled device optical imaging system and appropriate long-pass filters of different wavelengths. To visually evaluate the TCPP fluorescence, differential image analysis was conducted using ImageJ software (National Institutes of Health).

Research results

Optical imaging coupled with high-transmittance long-pass filters and subtraction image processing separated the emission spectra of the radionuclide-derived CR and TCPP. The emission spectra of TCPP were obtained by calculation and subtraction based on the serial signal intensity (total flux) difference between 64CuCl2 + TCPP and 64CuCl2. In addition, the differential fluorescence images of TCPP were acquired by subtracting the 64CuCl2 image from the 64CuCl2 + TCPP image.

Research conclusions

This simple and cost-effective method could confirm the PS fluorescence emission generated by radionuclide-derived CR. Moreover, the method can contribute to accelerating the development of Cherenkov energy transfer imaging and the discovery of new effective PSs.

Research perspectives

Several laboratories with conventional optical imaging devices would be able to acquire suitable long-pass filters at low cost and easily apply this method to compare different PSs to identify the optimal PS. A potential limitation of this study, namely the use of limited experiments with only one PS and one radionuclide, could be addressed by conducting much more detailed examinations as the next step.