title: Positron emission tomography detects metabolic viability in myocardium with persistent 24-hour single-photon emission computed tomography 201Tl defects.
abstract: BACKGROUND
  Four-hour 201Tl redistribution images underestimate myocardial viability in patients with coronary artery disease (CAD). Because 4-hour defects often redistribute late, delayed imaging may enhance assessment of tissue viability. Myocardial metabolic activity was therefore assessed with positron emission tomography (PET) in 26 CAD patients with impaired ventricular function (ejection fraction, 32.1 +/- 13.9%) and 24-hour single-photon emission computed tomography (SPECT) 201Tl defects.
  
  
  RESULTS
  On circumferential profile analysis, PET ischemia was defined by preserved glucose metabolism in hypoperfused myocardium, and PET infarction was defined by concordant reductions in perfusion and metabolism. On 19 stress-redistribution and seven rest-redistribution SPECT studies, four observers visually scored 201Tl activity in eight segments on a scale from 0 (normal) to 3 (complete defect). Using an improvement in visual score > or = 0.75 to define redistribution, there were 100 fixed, 17 partially reversible, and 12 completely reversible defects. PET identified tissue metabolic activity in 51 (51%) segments with fixed defects (21 PET ischemia, 30 PET normal) and nine (53%) segments with partially reversible defects (five PET ischemia, four PET normal). When grouped by 24-hour score, the proportion of fixed defects with metabolic activity varied from 84% (scores < or = 1.4) to 15% (scores > 2.6). For partially reversible defects, only 53% with scores < 2.0 and one of two with scores > or = 2.0 were considered metabolically viable on PET. Of 12 completely reversible defects, six (50%) were normal, five (42%) had PET ischemia, and one (8%) had PET infarction. The proportion of fixed defects with metabolic activity did not depend on whether a rest or stress study was performed or on the change in visual score used to define 201Tl redistribution (0.25, 0.50, 0.75, and 1.00).
  
  
  CONCLUSIONS
  In CAD patients, PET identifies glucose metabolic activity in the majority of fixed 24-hour 201Tl defects. However, very severe (near-complete) 24-hour 201Tl defects are less likely to exhibit metabolic activity on PET imaging than are defects with less-pronounced reductions in segmental 201Tl activity.
authors.affiliation: Department of Radiological Sciences, UCLA School of Medicine 90024-1721.
authors.forename: R C
authors.initials: RC
authors.lastname: Brunken
authors.forename: F V
authors.initials: FV
authors.lastname: Mody
authors.forename: R A
authors.initials: RA
authors.lastname: Hawkins
authors.forename: C
authors.initials: C
authors.lastname: Nienaber
authors.forename: M E
authors.initials: ME
authors.lastname: Phelps
authors.forename: H R
authors.initials: HR
authors.lastname: Schelbert
mesh_terms: D017023:Coronary Angiography; D003327:Coronary Disease / Q000000981:diagnostic imaging* / Q000378:metabolism; D003847:Deoxyglucose / Q000031:analogs & derivatives; D005260:Female; D005462:Fluorine Radioisotopes; D019788:Fluorodeoxyglucose F18; D006321:Heart / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D009206:Myocardium / Q000378:metabolism*; D013794:Thallium Radioisotopes; D013997:Time Factors; D014055:Tomography, Emission-Computed; D015899:Tomography, Emission-Computed, Single-Photon; D016277:Ventricular Function, Left / Q000502:physiology
chemical_list: D005462:Fluorine Radioisotopes; D013794:Thallium Radioisotopes; D019788:Fluorodeoxyglucose F18; D003847:Deoxyglucose