title: Phantom evaluation of simultaneous thallium-201/technetium-99m aquisition in single-photon emission tomography.
abstract: This study investigated downscatter effects in cardiac single-photon emission tomographic studies with simultaneous thallium-201/technetium-99m acquisition, and evaluated a previously proposed subtraction technique for downscatter compensation. Ten studies were carried out with different defect sizes and locations and varying activity distributions using four energy windows: 70+/-10% keV, 140+/-10% keV, 100+/-10% KeV, and 103+/-16% keV. The subtraction technique used the 100- or 103-keV data to remove scattered 99mTc counts from the 70-keV data. The size and contrast of infarcts in the dual-isotope 70-keV image were artificially decreased compared to those in the 140-keV image, caused by scattered 99mTc counts that were comparable to the primary 201Tl counts in the 70-keV window. The subtraction technique produced larger defects and more heterogeneous activity in the myocardial wall in dual-isotope 70-keV images compared to the corresponding 201Tl-only images. These artifacts were caused by the markedly different spatial distributions of scattered 99mTc counts in the 100-keV (or 103-keV) window as compared with the 70-keV window. It is concluded that scattered 99mTc photons may cause overestimation of ischemia and myocardial viability in simultaneous dual-isotope patient studies. The proposed subtraction technique was inaccurate and produced image artifacts. Adequate downscatter compensation methods must be developed before applying simultaneous 201Tl/99mTc acquisition in clinical practice.
authors.affiliation: Department of Diagnostic Radiology, University of Maryland Medical Center, Baltimore, Maryland 21201-1595, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Cao
authors.forename: C C
authors.initials: CC
authors.lastname: Chen
authors.forename: C
authors.initials: C
authors.lastname: Maunoury
authors.forename: L E
authors.initials: LE
authors.lastname: Holder
authors.forename: T C
authors.initials: TC
authors.lastname: Abraham
authors.forename: A
authors.initials: A
authors.lastname: Tehan
mesh_terms: D016477:Artifacts; D006321:Heart / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D009203:Myocardial Infarction / Q000000981:diagnostic imaging; D017202:Myocardial Ischemia / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D013382:Subtraction Technique; D013667:Technetium; D013794:Thallium Radioisotopes; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation / Q000379:methods*
chemical_list: D013794:Thallium Radioisotopes; D013667:Technetium