Ventilation scintigraphy (synonym: pulmonary ventilation scintigraphy) is a diagnostic nuclear medicine procedure used to evaluate pulmonary embolism. Ventilation scintigraphy is combined with pulmonary perfusion scintigraphy for the diagnosis of suspected pulmonary embolism in order to differentiate between acute pulmonary embolism and a secondary pulmonary perfusion disorder. A secondary pulmonary perfusion defect is a flow obstruction on pulmonary perfusion scintigraphy, usually caused by pneumonia (lung inflammation) or emphysema (permanent overinflation of the alveoli). Ventilation scintigraphy is a noninvasive procedure, so the risk of complications is considered low.
Indications (areas of application)
- Pulmonary artery embolism – pulmonary vessels can be completely or incompletely occluded by a thrombus (blood clot), preventing adequate supply to the tissue behind the vessel occlusion and causing death. The thrombus usually migrates from the deep veins of the legs or the iliac veins into the bronchial vasculature via the pulmonary artery. Depending on the severity of the pulmonary artery embolism, symptoms may include markedly decreased blood pressure, acute dyspnea (shortness of breath), and tachypnea (accelerated breathing). The combination of pulmonary perfusion scintigraphy and ventilation scintigraphy, in addition to localization of the perfusion disturbance, can also allow differentiation between pulmonary artery embolism and stenosis (narrowing) or occlusion of a vessel due to a secondary pulmonary perfusion disturbance.
- Lung resection – before surgical removal of a lung lobe or parts of the lung, the diagnostic method should be a combination of pulmonary perfusion scintigraphy and ventilation scintigraphy to check the lung areas.
- Condition after Norwood surgery – this surgical procedure is a surgical therapeutic measure for a present hypoplastic left heart syndrome. After successful surgery for this syndrome, which describes a maldevelopment of the heart and aorta (main artery), ventilation scintigraphy in conjunction with pulmonary perfusion scintigraphy is an important diagnostic control method.
Contraindications
Relative contraindications
- Lactation phase (breastfeeding phase) – breastfeeding must be interrupted for 48 hours to prevent risk to the child.
- Repeat examination – no repeat scintigraphy should be performed within three months due to radiation exposure.
Absolute contraindications
- Gravidity (pregnancy)
- Ventilated patients – ventilatory scintigraphy should not be performed in ventilated patients because the risk of contamination is not commensurate with the diagnostic benefit.
- Status asthmaticus – this is a particularly severe manifestation of bronchial asthma characterized by prolonged attack symptomatology.
Before the examination
- Breathing technique – for the performance of ventilation scintigraphy, the extent to which the patient under examination has mastered a correct breathing technique for scintigraphy is of important significance for the validity of the procedure. Therefore, the patient should perform a breathing exercise under guidance, practicing a calm, deep and slow inspiration (inspiration phase).
- Uptake of the radiopharmaceutical (radioactive substance or a carrier to which a radioactive substance is coupled) – for example, in ventilation scintigraphy, the patient receives the 185 MBq Xe-133, which is a radiopharmaceutical. To receive the radiopharmaceutical, the patient is connected to a closed ventilation system via a tube. After a three-minute ventilation period, a sufficient concentration of the radiopharmaceutical is achieved. According to the guidelines of the German Society of Nuclear Medicine, the dose of the pharmaceutical in children should be reduced to prevent unnecessary exposure to radiation.
The procedure
Ventilation scintigraphy allows precise observation of ventilation conditions in the bronchial system.Ventilation of the lung represents a crucial factor in the diagnosis of acute pulmonary artery embolism because pulmonary artery embolism presents as a sharply limited and additionally lung segment-related circulatory failure. However, ventilation of the nonperfused lung area should be considered physiologic in this case, because pulmonary artery embolism can initially affect only blood flow and not ventilation. Therefore, the combination of ventilation scintigraphy with pulmonary perfusion scintigraphy is ideal, because the use of both methods can reveal a so-called “mismatch” between pulmonary perfusion and pulmonary ventilation, which clearly speaks for an acute pulmonary artery embolism. In contrast, an area with a perfusion and ventilation failure, i.e. a so-called “match”, speaks against an acute pulmonary embolism. In addition to xenon, krypton can also be used as a radioactive pharmacon. To produce reproducible results, ventilation images from eight views should be obtained in scintigraphy. To avoid erroneous images, patient movements should be omitted, otherwise the results may be distorted. Of particular importance is the radioactivity that is deposited on the patient’s chest by contamination. Contamination is based on the principle that the xenon administered is heavier than air and therefore sinks to the bottom. This can lead to errors in the evaluation of the scintigraphy.
After the examination
- In general, no special measures are necessary after the examination. Only breastfeeding patients should refrain from breastfeeding for 48 hours and discard breast milk during this time.
Possible complications
- Intravenous application of radiopharmaceutical may result in local vascular and nerve lesions (injuries).
- Radiation exposure from the radionuclide used is rather low. Nevertheless, the theoretical risk of radiation-induced late malignancy (leukemia or carcinoma) is increased, so that a risk-benefit assessment should be performed.