ABC | Volume 114, Nº2, February 2020

Update Update of the Brazilian Guideline on Nuclear Cardiology – 2020 Arq Bras Cardiol. 2020; 114(2):325-429 5.2. Myocardial Perfusion Scintigraphy with Tomography Imaging (SPECT) Technological evolution of computerized systems has made it possible to divide the myocardium of the left ventricle (LV) into tomographic slices measuring only a few millimeters. In conventional gamma cameras (with iodide sodium crystals) the size of a pixel (the smallest component of a digital image) is 6.4 mm, and in CZT (cadmium zinc telluride semiconductors) technology it is 4 mm, representing related cross sections and, consequently, the method’s spatial resolution. 29-31 The resulting images facilitate the separation of nearby regions, improving contrast resolution and allowing for better detection of differences in concentrations of radioactivity in the myocardium. The SPECT technique also allows for detection of ischemic regions, even those that are small in size, i.e., approximately 2% of LV mass, in tissue with relatively normal tracer concentration. Protocols: The preferred means of obtaining perfusion images of the myocardium and LV function with tracers labeled with technetium-99m ( 99m Tc) is known as the “1-day protocol” (Figure 3A), made up of 2 stages, (resting-stress or stress-resting). During the first step, the injected dose of MIBI- 99m Tc, measured in millicuries (mCi) or megabecquerels (mBq), is three times lower than the dose administered during the second phase, thus avoiding the residual activity effect or “shining through” phenomenon. Another option is the “2- day protocol” (Figure 3B), where in each phase is performed on a separate day. In this case, similar doses and acquisition parameters are used. It is important to emphasize that, in situations where stress images are taken before resting ones, even if the perfusion images are normal, it is nevertheless important to obtain resting images, except in specific cases, given that analysis of LV function in both situations may provide relevant information, including the possibility of detecting patients with homogenous tracer distribution due to balanced severe coronary diseases. Furthermore, the detection of transient LV dilatation may also be useful in this case, and this requires that both phases be performed. However, in asymptomatic patients who have intermediate/low risks and no clinical evidence of CAD, who have undergone the stress phase as the initial MPS stage and whose perfusion images are normal, it is possible to dispense with the resting phase, in what is known as the “stress only protocol.” In this situation, recent studies have provided evidence that the test’s prognostic value is maintained and that diagnostic ability is similar to the costs of high sensitivity. Furthermore, the patient receives a lower dose of radioactive activity, and total exam time is reduced. 32,33 5.3. Myocardial Perfusion Scintigraphy with Tomographic Images Synchronized with Electrocardiogram (Gated- SPECT) 34-41 Cardiac images should be acquired synchronized with patient ECG, allowing for additional analysis of ventricular Figure 3 – Perfusion image acquisition and myocardial function with the radiopharmaceuticals sestamibi (MIBI) or tetrofosmin labeled with technetium-99m or 99m Tc: “one-day” protocol (A) and “two-day” protocol (B). The legends “ 99m Tc Injection/Resting” and “ 99m Tc Injection/Stress” represent administration of the radiopharmaceutical MIBI- 99m Tc during both stages, with dosage measured in millicuries (mCi), established in accordance with equipment and acquisition model used, as well as patient weight. In Protocol A, the stress dose is 3 times higher than the resting dose; in Protocol B, the resting and stress doses are similar, considering an interval of 24 hours between image acquisition. 99m Tc Injection/Resting 99m Tc Injection/Stress 30 to 60 minutes Resting Image Stress 15 to 45 minutes Stress Image Review 30 to 60 minutes Resting Image Stress 15 to 45 minutes Stress Image Review 99m Tc Injection/ Resting 99m Tc Injection/ Stress Time Time Day 1 Day 2 337