title: Attenuation correction in cardiac SPECT without a transmission measurement.
abstract: The accuracy of SPECT cardiac perfusion imaging is impaired by artifacts induced by nonuniform gamma-ray attenuation. This study proposes a method to estimate attenuation in the chest of patients without the additional hardware and expense of transmission imaging.
  
  
  METHODS
  After the standard 201Tl or 99mTc-sestamibi delayed images were obtained, 99mTc macroaggregated albumin (MAA) was injected and dual-energy SPECT acquisition was performed with windows centered at 140 keV and 94 keV. Lung contours were obtained by thresholding the on-peak (140 keV) reconstructions. Outer body contours were defined from images produced by reconstruction of the lower energy scatter window obtained simultaneously at the time of the lung (MAA) imaging. Following assignment of standard attenuation values to the lung and nonlung (soft tissue) regions attenuation correction was achieved by means of a modified iterative Chang algorithm. The results were quantitatively evaluated by imaging of a cardiac phantom filled with uniform activity placed in a chest phantom. Sensitivity to the choice of lung and soft tissue attenuation values, the choice of the threshold used for lung segmentation, and errors in registration of the attenuation map were assessed.
  
  
  RESULTS
  Application of this technique in a chest phantom and in patients imaged with both 201Tl and 99mTc-sestamibi resulted in improvement in artifactually decreased inferior wall activity without adversely affecting the other walls. The results were relatively insensitive to choice of values for lung and soft-tissue attenuation, lung thresholding, and small (< or = 1.3 cm) registration errors.
  
  
  CONCLUSIONS
  This simple method corrects for nonuniform attenuation in males; studies are underway to adapt the method to determine breast contour in females and to determine the value of the method in clinical practice.
authors.affiliation: Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: J W
authors.initials: JW
authors.lastname: Wallis
authors.forename: T R
authors.initials: TR
authors.lastname: Miller
authors.forename: P
authors.initials: P
authors.lastname: Koppel
mesh_terms: D016477:Artifacts; D003327:Coronary Disease / Q000000981:diagnostic imaging*; D006321:Heart / Q000000981:diagnostic imaging*; D006801:Humans; D008171:Lung Diseases / Q000000981:diagnostic imaging; D008297:Male; D008961:Models, Structural; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013668:Technetium Tc 99m Aggregated Albumin; D017256:Technetium Tc 99m Sestamibi; D013794:Thallium Radioisotopes; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods
chemical_list: D013668:Technetium Tc 99m Aggregated Albumin; D013794:Thallium Radioisotopes; D017256:Technetium Tc 99m Sestamibi