title: Iodine-131 imaging using 284 keV photons with a small animal CZT-SPECT system dedicated to low-medium-energy photon detection.
abstract: OBJECTIVE
  Iodine-131 is widely used for radionuclide therapy because of its β-particle and for diagnostic imaging employing its principal gamma ray. Since that principal gamma ray has the relatively high energy of 364 keV, small animal single-photon emission computed tomography (SPECT) imaging systems may be required to possess the ability to image such higher energy photons. The aim of this study was to investigate the possibility of imaging I-131 using its 284 keV photons instead of its 364 keV photons in a small animal SPECT imaging system dedicated to the detection of low-medium-energy photons (below 300 keV).
  
  
  METHODS
  The imaging system used was a commercially available preclinical SPECT instrument with CZT detectors that was equipped with multi-pinhole collimators and was accompanied by a CT imager. An energy window for I-131 imaging was set to a photopeak of 284 keV with a low abundance compared with 364 keV photons. Small line sources and two mice, one of each of two types, that were injected with NaI-131 were scanned.
  
  
  RESULTS
  Although higher counts occurred at the peripheral region of the reconstructed images due to the collimator penetration by the 364 keV photons, the shape of the small line sources could be well visualized. The measured spatial resolution was relatively poor (~1.9 mm for full width at half maximum and ~3.9 mm for full width at tenth maximum). However, a good linear correlation between SPECT values and the level of I-131 radioactivity was observed. Furthermore, the uptake of NaI-131 to the thyroid gland for the two mice was clearly identified in the 3D-SPECT image fused with the X-ray CT image.
  
  
  CONCLUSIONS
  We conclude that the use of an energy window set on the photopeak of 284 keV and the multi-pinhole collimator may permit I-131 imaging for a preclinical CZT-SPECT system that does not have the ability to acquire images using the 364 keV photons.
authors.affiliation: Institute of Resource Development and Analysis, Kumamoto University, 2-2-1 Honjo, Chuo-ku, Kumamoto, 860-0811, Japan. akojima@kumamoto-u.ac.jp.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Kojima
authors.affiliation: Institute of Resource Development and Analysis, Kumamoto University, 2-2-1 Honjo, Chuo-ku, Kumamoto, 860-0811, Japan.
authors.forename: Kumiko
authors.initials: K
authors.lastname: Gotoh
authors.affiliation: Department of Radioisotope Science, Graduate School of Medical Sciences, Kumamoto University, 2-2-1 Honjo, Chuo-ku, Kumamoto, 860-0811, Japan.
authors.forename: Masako
authors.initials: M
authors.lastname: Shimamoto
authors.affiliation: Department of Pathology and Experimental Medicine, Kumamoto University, 1-1-1 Honjo, Chuo-ku, Kumamoto, 860-8556, Japan.
authors.forename: Koki
authors.initials: K
authors.lastname: Hasegawa
authors.affiliation: Center for AIDS Research, Kumamoto University, 2-2-1 Honjo, Chuo-ku, Kumamoto, 860-0811, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Okada
mesh_terms: D000818:Animals; D002104:Cadmium; D005720:Gamma Rays; D007457:Iodine Radioisotopes; D051379:Mice; D009010:Monte Carlo Method; D017785:Photons; D013691:Tellurium; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation / Q000379:methods*; D015032:Zinc
chemical_list: C474490:CdZnTe; D007457:Iodine Radioisotopes; D002104:Cadmium; D015032:Zinc; D013691:Tellurium
keywords: 284 keV photons; A small animal CZT-SPECT system; Iodine-131 imaging