ABC | Volume 114, Nº2, February 2020

Update Update of the Brazilian Guideline on Nuclear Cardiology – 2020 Arq Bras Cardiol. 2020; 114(2):325-429 Figure 52 – Cardiac scintigraphy with MIBG- 123 I. Colored late imaging of the anterior thorax with the regions of interest (ROI) drawn in the mediastinal (M) and cardiac (C) areas, to calculate the heart to mediastinum ratio (HMR) of MIBG- 123 I uptake. This index is the measure of the ratio between the statistical count of the rate of average radiation per pixel in the ROI, drawn in the heart and mediastinum. M = uptake in the mediastinal area C = uptake in the cardiac area Normal HMR values vary from 1.9 to 2.8 with an approximate average of 2.2 ± 0.3 in late images, with results ≥ 1.6 considered predictive of lower risks. 331 HMR reflects the density of receptors and, probably, depicts the integrity of presynaptic nerve endings and of the uptake 1 receptor. This elevated index indicates a predominant localization of the radiotracer in the myocardium, which is expected in normal hearts, to the extent that the finding of reduced HMR indicates lower myocardial uptake of MIBG- 123 I, translating as reduced density of cardiac adrenergic receptors. Late HMR combines information on neuronal function of uptake and the release of storage vesicles in cardiac nerve endings. Figures 53 and 54 show images of patients with normal and altered HMR, respectively. Myocardial washout rate (WR) of MIBG- 123 I is also an important measure of cardiac sympathetic innervation. WR is calculated as the difference in myocardial uptake between the early and late phases and is determined by the percentage of reduction in uptake between these steps, reflecting the amount of catecholamines released in the cardiac synaptic cleft. Cardiac sympathetic hyperactivity is associated with reduced retention of MIBG- 123 I in late images (reduced late HMR) and increased WR. Normal WR control values are 10% ± 9%. 332 Higher values are predictive of worse prognosis, 333 although there are several methods for determining this ratio in the literature. Intra- and inter-observer variability of these measurements is less than 5%. 328 13.3. Clinical Applications of Cardiac Scintigraphy with MIBG- 123 I Imaging studies of cardiac adrenergic activity may be useful in several clinical scenarios (Table 30), including: HF, ventricular arrhythmias (associated with HR and primary arrhythmias), ischemic heart disease, DM, patients undergoing cardiotoxic chemotherapy, pre- and post-cardiac transplant, in early images (15 minutes after injection) and late imaging (4 hours after injection) and the myocardial washout rate (WR) of MIBG- 123 I. 322-324,327-330 Figure 53 – Cardiac scintigraphy with MIBG- 123 I showing normal radiopharmaceutical uptake in the cardiac area (arrow), which denotes preserved cardiac sympathetic activity. Black and white images of the anterior thorax, acquired approximately 15 minutes (early) and 4 hours (late) following intravenous injection of the radiopharmaceutical MIBG- 123 I. Early Late 399