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Positron emission tomography detects metabolic viability in myocardium with persistent 24-hour single-photon emission
R C Brunken1, F V Mody, R A Hawkins
1Department of Radiological Sciences, UCLA School of Medicine 90024-1721.
Insights
Delayed imaging with 201Tl SPECT can underestimate myocardial viability in coronary artery disease (CAD) patients. Positron emission tomography (PET) reveals metabolic activity in most fixed 24-hour 201Tl defects, but severe defects show less viability.
Area of Science:
- Nuclear cardiology
- Cardiovascular imaging
- Myocardial viability assessment
Background:
- Four-hour 201Tl SPECT imaging may underestimate myocardial viability in coronary artery disease (CAD).
- Delayed imaging could potentially improve the assessment of myocardial tissue viability.
- This study assessed myocardial metabolic activity using PET in CAD patients with impaired ejection fraction and 24-hour 201Tl SPECT defects.
Purpose of the Study:
- To compare the assessment of myocardial viability using 24-hour 201Tl SPECT and PET.
- To determine the extent of metabolic activity in fixed and reversible 201Tl SPECT defects.
- To evaluate the relationship between the severity of 201Tl defects and metabolic activity.
Main Methods:
- 26 CAD patients with impaired ejection fraction underwent 24-hour 201Tl SPECT and PET imaging.
- Myocardial viability was assessed by comparing perfusion (201Tl SPECT) and metabolism (PET).
- SPECT defects were categorized as fixed, partially reversible, or completely reversible based on visual scoring.
Main Results:
- PET identified metabolic activity in 51% of fixed 201Tl defects and 53% of partially reversible defects.
- The proportion of fixed defects with metabolic activity decreased as the severity of the 201Tl defect increased.
- Completely reversible defects showed varying results, with 50% normal, 42% showing ischemia, and 8% infarction on PET.
Conclusions:
- PET can identify glucose metabolic activity in most fixed 24-hour 201Tl defects in CAD patients.
- Very severe 24-hour 201Tl defects are less likely to demonstrate metabolic activity on PET.
- PET provides a more comprehensive assessment of myocardial viability compared to delayed 201Tl SPECT.
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.
Methods And 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.
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