ABC | Volume 114, Nº2, February 2020

Update Update of the Brazilian Guideline on Nuclear Cardiology – 2020 Arq Bras Cardiol. 2020; 114(2):325-429 10.6. Positron Emission Tomography 282,283 This non-invasive exam is the reference for detecting myocardial viability, as it simultaneously offers information on myocardial perfusion and metabolism. In normal fasting and aerobic metabolism conditions, while resting, long-chain free fatty acids (FFA) represent around 65% to 70% of energy supply to the cardiac muscle, with a lower participation of glucose (15% to 20%), 21 whereas, in post-prandial conditions, glucose becomes the preferred substrate. In the presence of ischemia, the oxidative metabolism of FFA is diminished and glucose also becomes the preferredmyocardial substrate. In this manner, even if the energy produced by anaerobic glycolysis is not enough to maintain myocardial contractility, it is vital for the preservation of cellular membrane integrity, which is characteristic of dysfunctional, yet viablemyocardium. Some positron emitters, such as fluorine-18, labeling a glucose analogue or fluorodeoxyglucose (FDG), may be used to evaluate viable (or hibernating) myocardium, which is defined as metabolically active tissue, in the presence of a coinciding perfusion defect. FDG- 18 F penetrates the cells of the myocardium by the same transport mechanism as glucose and, following phosphorylation to FDG-6-P, remains in the intracellular medium in proportion to the rate of glycolysis, reflecting the Figure 50 – Imaging protocols with the use of thallium-201 ( 201 Tl) for characterizing viability of the myocardium. A represents the classic sequence for defining ischemia (Day 1), with the injection of a dose of approximately 3 to 4 mCi during stress, without subsequent reinjection, adding new image acquisition 24 hours later (Day 2); B, C, and D emphasize the need for reinjection of 201 Tl with an approximate dose of 1 mCi and sequencing as demonstrated in the proposed protocol. Day 1 Day 2 Injection of Tl-201 Stress Stress 15 min Stress image Review Interval of 2.5 - 4 hours Resting image Review 24 hours Redistribution image Review Time Optional, depending on medical interpretation of images Injection of Tl-201 Stress Injection of Tl-201 Stress Day 1 Day 2 Stress 15 min Stress image Review Interval of 2.5 - 4 hours Resting image Review 15 min Reinjection of Tl-201 Reinjection image Reinjection of Tl-201 Review Time Time Optional, depending on medical interpretation of images Optional, depending on medical interpretation of images Image at 24 hours Review Day 1 Day 2 Reinjection of Tl-201 Stress 15 min Stress image Review Interval of 2.5 - 4 hours Resting image Review Time Optional, depending on medical interpretation of images Stress 15 min Stress image Review Interval of 2.5 - 4 hours Resting image Review 15 min Reinjection image Review Image at 24 hours Injection of Tl-201- Stress 392