title: Ultrahigh-resolution Cerenkov-light imaging system for positron radionuclides: potential applications and limitations.
abstract: OBJECTIVE
  Cerenkov-light imaging provides inherently high resolution because the light is emitted near the positron radionuclide. However, the magnitude for the high spatial resolution of Cerenkov-light imaging is unclear. Its potential molecular imaging applications also remain unclear. We developed an ultrahigh-resolution Cerenkov-light imaging system, measured its spatial resolution, and explored its applications to molecular imaging research.
  
  
  METHODS
  Our Cerenkov-light imaging system consists of a high-sensitivity charged-coupled device camera (Hamamatsu Photonics ORCA2-ER) and a bright lens (Xenon 0.95/25). An extension ring was inserted between them to magnify the subject. A ~100-μm-diameter (22)Na point source was made and imaged by the system. For applications of Cerenkov-light imaging, we conducted (18)F-FDG administered in vivo, ex vivo whole brain, and sliced brain imaging of rats.
  
  
  RESULTS
  We obtained spatial resolution of ~220 μm for a (22)Na point source with our developed imaging system. The (18)F-FDG rat head images showed high light intensity in the eyes for the Cerenkov-light images, although there was no accumulation in these parts in the PET images. The sliced rat brain showed much higher spatial resolution for the Cerenkov-light images compared with CdWO4 scintillator-based autoradiography, although some contrast decrease was observed for them.
  
  
  CONCLUSIONS
  Even though the Cerenkov-light images showed ultrahigh resolution of ~220 μm, their distribution and contrast were sometimes different from the actual positron accumulation in the subjects. Care must be taken when evaluating positron distribution from Cerenkov-light images. However, the ultrahigh resolution of Cerenkov-light imaging will be useful for transparent subjects including phantom studies.
authors.affiliation: Department of Radiological and Medical Laboratory Sciences, Nagoya University Graduate School of Medicine, 1-1-20 Daiko-Minami, Higashi-ku, Nagoya, 461-8673, Japan, s-yama@met.nagoya-u.ac.jp.
authors.forename: Seiichi
authors.initials: S
authors.lastname: Yamamoto
authors.forename: Tadashi
authors.initials: T
authors.lastname: Watabe
authors.forename: Hayato
authors.initials: H
authors.lastname: Ikeda
authors.forename: Yasukazu
authors.initials: Y
authors.lastname: Kanai
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Watabe
authors.forename: Yoshimune
authors.initials: Y
authors.lastname: Ogata
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Kato
authors.forename: Jun
authors.initials: J
authors.lastname: Hatazawa
mesh_terms: D000818:Animals; D001345:Autoradiography; D001921:Brain / Q000000981:diagnostic imaging; D019788:Fluorodeoxyglucose F18; D057054:Molecular Imaging / Q000295:instrumentation / Q000379:methods*; D019047:Phantoms, Imaging; D011868:Radioisotopes; D011877:Radionuclide Imaging / Q000295:instrumentation / Q000379:methods*; D019275:Radiopharmaceuticals; D011923:Rats, Nude; D012878:Skin Neoplasms / Q000000981:diagnostic imaging; D012979:Sodium Radioisotopes
chemical_list: D011868:Radioisotopes; D019275:Radiopharmaceuticals; D012979:Sodium Radioisotopes; D019788:Fluorodeoxyglucose F18
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