title: The relationship between administered radiopharmaceutical activity in myocardial perfusion scintigraphy and imaging outcome.
abstract: BACKGROUND
  Lower radiopharmaceutical activities are used for myocardial perfusion scintigraphy (MPS) in the UK than in other countries. There is no evidence to suggest that higher activities improve imaging or clinical outcome.
  
  
  METHODS
  We undertook a multicentre study of the relationship between radiopharmaceutical activity and imaging outcome. Fifty-one patients with clinical referrals for MPS followed a 2-day protocol with an injection of 1,000 MBq (99m)Tc-tetrofosmin for each of the stress and rest images. ECG-gated acquisition was performed in three rotations occupying 25, 35 and 40% of a standard acquisition, and rotations were summed to simulate administered activities of 250, 400, 750 and 1,000 MBq. Each set of images was reported by an experienced physician who was blinded to all clinical information and to the simulated activity. Scores were assigned for image quality, low count, attenuation and reconstruction artefact, segmental tracer uptake, segmental and global defect classification, and confidence in the global classification. The images were reported twice to assess intra-observer variability.
  
  
  RESULTS
  Positive relationships were found between administered activity and overall image quality, observer confidence and intra-observer agreement of uptake score, and a negative relationship was found with low-count artefact. For the majority of comparisons, there was no additional improvement with increasing activity from 750 to 1,000 MBq. Intra-observer agreement was found to be better in female patients and in those below average body mass index.
  
  
  CONCLUSIONS
  We conclude that higher administered radiopharmaceutical activities lead to better quality images and improved surrogate parameters for clinical outcome, but that activities above 750 MBq may be unnecessary in average patients.
authors.affiliation: Royal Brompton & Harefield NHS Trust, London, UK.
authors.forename: C N
authors.initials: CN
authors.lastname: Robinson
authors.forename: A
authors.initials: A
authors.lastname: van Aswegen
authors.forename: S A
authors.initials: SA
authors.lastname: Julious
authors.forename: T O
authors.initials: TO
authors.lastname: Nunan
authors.forename: W H
authors.initials: WH
authors.lastname: Thomson
authors.forename: W B
authors.initials: WB
authors.lastname: Tindale
authors.forename: D A
authors.initials: DA
authors.lastname: Tout
authors.forename: S R
authors.initials: SR
authors.lastname: Underwood
mesh_terms: D000368:Aged; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008297:Male; D009943:Organophosphorus Compounds / Q000008:administration & dosage*; D015609:Organotechnetium Compounds / Q000008:administration & dosage*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000008:administration & dosage; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013223:Statistics as Topic
chemical_list: D009943:Organophosphorus Compounds; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; C078700:technetium tc-99m tetrofosmin