IJCS | Volume 32, Nº2, May/June 2019

303 Table 1 - Indications for ventilation / perfusion scintigraphy 1. Diagnosis of acute pulmonary thromboembolism; 2. Diagnosis of chronic pulmonary thromboembolism; 3. Assesment of the rate of resolution of PE (compared to previous study); 4. Assessment and quantification of right to left shunt; 5. Differential quantification of pulmonary function before pulmonary resection; 6. Lung transplant evaluation; 7. Assessment of the etiology of pulmonary hypertension; 8. Assessment of chronic parenchymal diseases. perfusion lung scintigraphy as the method of choice for the diagnosis of PE, because it has the advantage of less exposure of the mother to radiation. 2 Exam duration About 1 hour in total (acquisition of ventilation and perfusion images). Preparation The patient must be capable of tolerating the dorsal decubitus position necessary to perform the images and be cooperative enough to carry out the preparation for inhalation, as described hereafter. The patient’s standard chest radiograph, preferably in both posterior–anterior and lateral projections, and recently acquired (within a few-day-period), should be reviewed. The authors indicate a maximum interval of 48 hours. A CT scan can substitute for the chest radiography. In the assessment of PE, the standard chest radiography must be the first exam used to exclude other pathologies. 5 Relevant information to perform the procedure The likelihood of the patient having pulmonary thromboembolism 6 should be assessed (through D-dimer testing or using the modified Wells score [Table 2], for instance), as well as by assessing the patient’s medical history (history of deep venous thrombosis (DVP), previous PE, chest X-rays, use of anticoagulant or thrombolytic). 4,5 The patient should be instructed about the exam and how to adequately perform the aerosol ventilation procedure, if possible practicing before the exam starts. Radiotracers Ventilation: Tc-diethylenetriaminepentaacetic acid (DTPA) labeled with 99m Tc, 99m Tc labeled microcolloid or solid 99m Tc-labeled carbon particles in argon carrier gas. The latter should be preferred, as far as available, because it has amore uniformdistribution in the lungs with lower retention in the airways and bronchi. 7 Perfusion: 99m Tc macro aggregated albumin ( 99m Tc- MAA). Marking and quality control Marking and quality must always be done according to manufacturer guidelines. However, pharmacopoeial criteria must be respected (pH between 5.0 - 6.0 and radiochemical purity ≥ 90%). 4,5 Adult activity Ventilation: The usual dispensed activity of 99m Tc DTPA or sulfur colloid is 900–1300 MBq (25–35 mCi) in the nebulizer, fromwhich only approximately 20–40MBq (0.5–1.0 mCi) will reach the lungs. 8 Solid 99m Tc-labeled carbon particles in argon carrier gas – the activity administered should be calculated according to the distributor manual. Since it is more difficult to achieve higher activity in the lungs with inhalation, it should always be performed first. It is essential that the perfusion activity should be Table 2 - Modified Wells Score Modified wells criteria Points Clinical symptoms of DVT 3 PE is more likely than other diagnoses 3 HR > 100 bpm 1.5 Prior DVT/PE 1.5 Hemoptysis 1 Malignancy 1 Clinical probability: High > 6; Intermediate: 2 - 6; Low < 2. Rigolon et al. Guideline for lung scintigraphy Int J Cardiovasc Sci. 2019;32(3)302-309 Guideline