IJCS | Volume 32, Nº2, May/June 2019

304 at least three times the counting rate of the ventilation activity to ensure that the image shows pulmonary perfusion, because both agents are labeled with  99m Tc. 4,5 Perfusion: 40–150 MBq (3–4 mCi); depending on the number of particles administered, this value could be higher), and should be in the range of 200,000–700,000 particles. The particles administered should be within a size range of 15 to 100 micrometers. In Brazil, currently available preparations have at least 90% of MAA particles between 10-100 micrometers in size. 9 In certain clinical conditions, the number of particles must be reduced, such as pulmonary hypertension and presence of right to left shunting. In the case of right-to- left shunt investigation, the number of particles should be decreased to 100,000 - 150,000. Pregnant women: as mentioned before, it is preferable to perform only the perfusion analysis with 99m Tc macroaggregated dose reduction (0.5 to 1 mCi). 4,5 Pediatric dosage Ventilation: Minimum activity should be no less than 10 MBq (0.27 mCi) to allow for sufficient count statistics to achieve good quality images. Since approximately 10% is retained within the lungs, it is suggested to administer as much as 15 times the activity of the DTPA needed (4 mCi). 3 Solid 99m Tc-labeled carbon particles in argon carrier gas - the activity administered should be calculated according to the distributor manual. Perfusion: 1.11 MBq/kg (0.03 mCi/kg), with a minimumof 14.8MBq/kg (0.4mCi) if no 99m Tc ventilation study is performed or 2.59 MBq/kg (0.07 mCi/kg) if a 99m Tc ventilation study is performed. The number of particles depends on the age and weight, according with the table below: In case of pulmonary hypertension and cardiac shunt investigation, these values should be reduced, depending on the age and the weight of the patient. Precautions to be taken during tracer injection Since the particles tend to decant, the syringe should be gently rotated prior to use. Blood should not be drawn back into the syringe to prevent MAA aggregation, because it can cause damage to the images. It is important that a single dose be administered over 30 seconds. The patient is oriented to inhale and breathe deeply during the tracer administration, facilitating its uniformdistribution. Imaging acquisition Nowadays, there are 3 possibilities to acquire the images: planar imaging, SPECT imaging and SPECT/ CT imaging. Several studies have demonstrated that SPECT imaging yields a higher sensitivity compared to planar imaging. Major segmental defects and more periferal defects are detected by planar imaging. However, especially mesial defects and subsegmental defects are more easily detected by SPECT imaging. SPECT imaging can detect around 50% more defects compared to inhalation imaging. Despite this, the recent Apropriate Use Criteria published by the Society of NuclearMedicine and Molecular Imaging (SNMMI) recommends that both types of imaging (planar or SPECT) are valid in the clinical practice. 10,11 We recommend that SPECT imaging be performed whenever possible. SPECT/CT combines increased sensitivity of SPECT imaging with high specificity of CT imaging. Several studies have shown that SPECT/CT provides increased sensitivity, specificity and accuracy compared to planar imaging. The improved specificity of SPECT/CT may reduce the number of false-positive results by 50%. Some studies have even demonstrated that SPECT/CT can increase specificity of scintigraphy to almost 100%, and make the study more accurate than CTA. 12-16 However, to our knowledge, there are no studies which assess the clinical impact on patient evolution when SPECT/CT is also used. Thus, the authors suggest that SPECT/CT imaging be performedwhenever possible due to its higher accuracy, even though other studies are needed to confirm the impact on the clinical management of patients. Ventilation: 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. Parameter Newborn 1 year 5 years 10 years 15 years Weight (kg) 3.5 12.1 20.3 33.5 55.0 Dosage (mCi) 0.2 0.5 1.0 1.5 2.5 Particles 10-50 50-150 200-300 200-300 200-700 Rigolon et al. Guideline for lung scintigraphy Int J Cardiovasc Sci. 2019;32(3)302-309 Guideline