title: Contributions of subdiaphragmatic activity, attenuation, and diaphragmatic motion to inferior wall artifact in attenuation-corrected Tc-99m myocardial perfusion SPECT.
abstract: BACKGROUND
  Subdiaphragmatic activity and diaphragmatic motion both contribute to inferior wall artifacts in technetium 99m myocardial perfusion single photon emission computed tomography (SPECT).
  
  
  RESULTS
  We used an anthropomorphic phantom with ventricular wall activity, liver/spleen inserts containing variable Tc-99m activity, and variable vertical (diaphragmatic) motion amplitude. SPECT and transmission scans were obtained on a GE Optima NX camera. Data were processed by use of filtered backprojection or attenuation correction (AC). Resulting myocardial activity maps were analyzed with standardized inferior-anterior and anterior-lateral wall ratios. At a subdiaphragmatic-myocardial activity ratio of 0.5:1, inferior wall attenuation predominates, producing a cold artifact. AC corrects inferior wall activity to the level of the anterior wall irrespective of diaphragmatic motion. At a subdiaphragmatic-myocardial activity ratio of 1:1, inferior wall counts vary widely depending on the proximity of subdiaphragmatic activity to the ventricle. With increasing diaphragmatic amplitude, the overlap of subdiaphragmatic activity and inferior wall worsens, leading to a complex mixture of cold and hot artifacts, not corrected by AC.
  
  
  CONCLUSIONS
  Concentration and proximity of subdiaphragmatic Tc-99m activity relative to myocardium comprise a major factor in the nature and severity of inferior wall artifacts. If the subdiaphragmatic Tc-99m concentration is equivalent to that in the myocardium, complex, potentially uninterpretable hot and cold inferior wall artifacts are produced.
authors.affiliation: Department of Radiology, Peter MacCallum Cancer Institute, Parkville, East Melbourne, Victoria 3052, Australia. agpitman@unimelb.edu.au
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Pitman
authors.forename: Victor
authors.initials: V
authors.lastname: Kalff
authors.forename: Bruce
authors.initials: B
authors.lastname: Van Every
authors.forename: Borghild
authors.initials: B
authors.lastname: Risa
authors.forename: Leighton R
authors.initials: LR
authors.lastname: Barnden
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Kelly
mesh_terms: D016477:Artifacts; D003964:Diaphragm / Q000503:physiopathology*; D006321:Heart / Q000000981:diagnostic imaging*; D006352:Heart Ventricles / Q000000981:diagnostic imaging*; D007089:Image Enhancement / Q000379:methods; D009068:Movement; D019047:Phantoms, Imaging; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D015656:Respiratory Mechanics; D012680:Sensitivity and Specificity; D017556:Technetium Compounds; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation / Q000379:methods*; D018487:Ventricular Dysfunction, Left / Q000000981:diagnostic imaging*
chemical_list: D019275:Radiopharmaceuticals; D017556:Technetium Compounds