title: Comparison of technetium-99m sestamibi and thallium-201 retention characteristics in canine myocardium.
abstract: OBJECTIVE
  The aim of this study was to compare the myocardial retention of technetium-99m (Tc-99m) sestamibi and thallium-201 over a wide range of blood flow at different time points after tracer injection.
  
  
  BACKGROUND
  Technetium-99m sestamibi has been proposed as a new perfusion tracer with better physical characteristics than those of thallium-201 for scintigraphic imaging. However, no studies have simultaneously compared the ability of both tracers to assess myocardial blood flow during pharmacologic vasodilation.
  
  
  METHODS
  The myocardial retention of Tc-99m sestamibi and thallium-201 were compared over a wide range of blood flow induced by regional coronary occlusion and dipyridamole infusion in an open chest dog model. Myocardial retention of both tracers was determined by in vitro tissue counting at 2, 5, and 20 min after tracer injection and was correlated with microsphere-determined blood flow.
  
  
  RESULTS
  Thallium-201 demonstrated greater absolute tissue retention than did Tc-99m sestamibi. At 2 min after tracer injection, there was an almost linear relation between the retention of both tracers and myocardial blood flow over a wide flow range. However, this relation was not maintained over time. At 20 min after injection, the retention of both tracers underestimated myocardial blood flow at higher flow rates. At 2, 5 and 20 min after injection, increments of relative tracer retention between the different levels of flow were always greater for thallium-201 than for Tc-99m sestamibi.
  
  
  CONCLUSIONS
  Thallium-201 displays more suitable physiologic characteristics as a flow tracer and may allow better differentiation of myocardial regions with different levels of coronary flow reserve. For both tracers, early cardiac imaging may minimize underestimation of blood flow at higher flow rates.
authors.affiliation: Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor 48109-0028.
authors.forename: P G
authors.initials: PG
authors.lastname: Melon
authors.forename: R S
authors.initials: RS
authors.lastname: Beanlands
authors.forename: T R
authors.initials: TR
authors.lastname: DeGrado
authors.forename: N
authors.initials: N
authors.lastname: Nguyen
authors.forename: N A
authors.initials: NA
authors.lastname: Petry
authors.forename: M
authors.initials: M
authors.lastname: Schwaiger
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity / Q000187:drug effects; D003326:Coronary Circulation / Q000187:drug effects; D004176:Dipyridamole / Q000494:pharmacology; D004285:Dogs; D004353:Drug Evaluation, Preclinical; D006321:Heart / Q000000981:diagnostic imaging* / Q000187:drug effects; D008863:Microspheres; D009206:Myocardium / Q000378:metabolism; D011877:Radionuclide Imaging; D012044:Regression Analysis; D017256:Technetium Tc 99m Sestamibi / Q000493:pharmacokinetics; D013794:Thallium Radioisotopes / Q000493:pharmacokinetics; D013997:Time Factors
chemical_list: D013794:Thallium Radioisotopes; D004176:Dipyridamole; D017256:Technetium Tc 99m Sestamibi