title: Influence of downscatter in simultaneously acquired thallium-201/technetium-99m-PYP SPECT.
abstract: Simultaneously acquired dual-isotope imaging is a unique and useful approach in SPECT. Photon spillover, however, is a potential limitation of this technique.
  
  
  METHODS
  To investigate the degree of 99mTc downscatter into the 201Tl window in patients, simultaneously acquired dual-isotope 201Tl/99mTc-pyrophosphate imaging was performed in 17 patients with acute myocardial infarction (MI). Thallium-201 SPECT imaging was performed first, with a 201Tl photopeak window after the 201Tl injection (early 201Tl images), followed by 99mTc injection and SPECT acquisition using dual-isotope windows (dual 201Tl images). Twenty-four hours after the 99mTc injection, a third set of 201Tl images was obtained (24-hr 201Tl images). Thallium defect size (extent score) and defect severity (severity score) were calculated from these three sets of 201Tl images to quantify the MI.
  
  
  RESULTS
  Technetium-99m accumulation of varying intensity was recognized in all patients. Extent scores and severity scores were identical in early 201Tl images and 24-hr 201Tl images. Both scores, however, in the dual 201Tl images were decreased by 36% and 53%, respectively.
  
  
  CONCLUSIONS
  There in a considerable 99mTc downscatter into the 201Tl window, which prevents precise quantification of MI in simultaneously acquired dual-isotope 201Tl/99mTc-pyrophosphate imaging.
authors.affiliation: Division of Cardiology, Matsuyama Red Cross Hospital, Ehime, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Ando
authors.forename: T
authors.initials: T
authors.lastname: Fukuyama
authors.forename: W
authors.initials: W
authors.lastname: Mitsuoka
authors.forename: S
authors.initials: S
authors.lastname: Egashira
authors.forename: Y
authors.initials: Y
authors.lastname: Imamura
authors.forename: H
authors.initials: H
authors.lastname: Masaki
authors.forename: T
authors.initials: T
authors.lastname: Ashihara
mesh_terms: D005260:Female; D006321:Heart / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000000981:diagnostic imaging*; D016698:Technetium Tc 99m Pyrophosphate; D013794:Thallium Radioisotopes; D013997:Time Factors; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
chemical_list: D013794:Thallium Radioisotopes; D016698:Technetium Tc 99m Pyrophosphate