IJCS | Volume 32, Nº2, May/June 2019

306 Figure 1 - Adapted from Waxman, et al. Appropriate Use Criteria for Ventilation–Perfusion Imaging in Pulmonary Embolism. be the imaging modality of choice for investigation of suspected PE in patients with allergy to iodine, renal failure and inadequate venous access, even with abnormal chest x-ray. Negative Acute PE: Positive Acute PE: Normal perfusion pattern conforming to the anatomic boundaries of the lungs; Matched or reversed mismatch V/P defects of any size, shape, or number in the absence of mismatch; Mismatch that does not have a lobar, segmental or subsegmental pattern, such as a stripe sign (perfusion defect with a normal perfusion stripe sign interposed between the defect and the adjacent pleural surfaces). V/P mismatch of at least one segment or two subsegments that conforms to the pulmonary vascular anatomy (peripheral wedge- shaped defects – pleural based defects, and that conforms to the pulmonary vascular anatomy). Inconclusive study: There are some causes for false-positive results. The main cause is an old or chronic PE. At the end of a hospital stay inwhich the patient was diagnosedwith PE, it is recommended to perform a Ventilation/Perfusion Scintigraphy for this study to serve as reference for future suspicion of a PE. That is because, in some patients, the defect observed in the perfusion imagemay not normalize and remain as a mismatch defect. Nevertheless, in the vast majority of cases inwhich acute PE does occur, or the scintigraphy normalizes after treatment, or an infarction occurs in the region of the PE, the defect is regarded as a matched ventilation-perfusion defect. Other reasons for false positive results are: certain rare cases of pulmonary and mediastinal tumors, vasculitis and arteriovenous malformations; however, these possibilities, in general, do not represent a diagnostic problem when the overall patient’s data is considered. Presence of multiple abnormalities identified in the images that do not correspond to any specific disease. Rigolon et al. Guideline for lung scintigraphy Int J Cardiovasc Sci. 2019;32(3)302-309 Guideline