IJCS | Volume 32, Nº2, May/June 2019

305 Counting recommendation: 8 Posterior: 250,000 counts; Other projections: use same time as the posterior view. The following is a suggested protocol for image acquisition using SPECT/CT: LEHR (Low Energy High Resolution) collimator; 64x64 matrix; 64 views (with a dual-head camera, 32 views per head); 20 sec acquisition; Zoom 1.0 180 degrees (dual-head) or 360 degrees (single-head camera). For CT image acquisition: If the equipment allows it, the algorithm for dose reduction in CT (for example, CareDose, Auto mA); 130 kV; 5 mm slice thickness; Pitch 1.8; 0.8 s rotation time; Number of images = 61 Perfusion: Low energy high resolution collimator (LEHR), with an energy window of 20% centered at 140 keV. Planar imagingmust be obtained in anterior, posterior, left and right anterior and posterior oblique views, in addition to lateral views. Counting recommendation: 8 500,000 to 750,000 counts per image. In the case of perfusion SPECT with low-dose CT, perform tomographic imaging (see the acquisition protocol recommended above). Acquisitions for other indications Shunt investigation: the inhalation phase isn't performed. Following the administration of technetium Tc 99m injection, awhole-body scan should be performed in the anterior and posterior views; a static head imaging may be performed to better assess the brain. Perform differential analysis of lung function prior to surgical procedure: the ventilation phase should not be performed; only lung perfusion imaging should be performed, as described above. Assess lung transplantation: perfusion images and pulmonary ventilation. Interpretation 4,5 Acute PE Diagnosis: The interpretation of ventilation/perfusion lung scans, both planar and SPECT/CT, is based on comparison. Thus, when there are ventilation-perfusion defects, a V/Q matched defect is characterized. When there is a defect in perfusion, but not in ventilation, it can be said that there was a mismatch defect. Thus, when there is a defect in ventilation, and there is not the same area in perfusion, we say that there was a reverse mismatch. In the past, the PIOPED criteria were widely used. These are old criteria based on planar images. In addition, their classification as high, intermediate, and low probability does not meet clinical needs. It is also important to take into consideration the pretest clinical probability calculated using themodifiedWells score (see below) and assess the laboratory tests. The observer’s experience will also be an important factor. Thus, we believe that the report must be as accurate as possible, providing a “yes or no” response for the presence of acute PE. Below are the criteria used by the EANM, which are similar to the ones we use in our clinical practice. The SNMMI has recently published an important document on appropriate use criteria for lung scintigraphy. The diagram below corresponds to the proposed investigation of pulmonary embolism in patients with low to moderate risk of PE (Wells Criteria: < 6). The presence of normal chest x-ray combined with increased D-Dimer values is associated with an accurate indication for ventilation/perfusion lung scintigraphy. In these patients the D-Dimer values are crucial to continue the investigation using imaging methods. Thus, according to the SNMMI document, in patients with higher likelihood for PE (Wells Criteria: > 6), there is no clinical impact associated with the use of the D-Dimer assay for the diagnosis of PE (Figure 2). In these patients, imaging methods must be requested regardless of the D-Dimer values. In the same way, patients with normal chest x-ray are candidates for lung scintigraphy as diagnosis method of choice to CT pulmonary angiography. Lung scintigraphy will Rigolon et al. Guideline for lung scintigraphy Int J Cardiovasc Sci. 2019;32(3)302-309 Guideline