Pulmonary Perfusion Scintigraphy

Pulmonary perfusion scintigraphy is a diagnostic procedure in nuclear medicine that is essentially used to evaluate pulmonary embolism. Pulmonary scintigraphy can be used to detect pulmonary embolism very sensitively (probability of detecting pulmonary embolism if it is present) by visualizing a perfusion disturbance in the pulmonary vessels. An advantage of pulmonary perfusion scintigraphy is that it is a noninvasive diagnostic method that can reliably detect a perfusion disturbance from a vessel diameter of two centimeters.

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 thus becoming necrotic (dying). 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). Pulmonary perfusion scintigraphy can provide diagnostic visualization of the location of the perfusion defect.
  • Lung resection – before surgical removal of a lung lobe or parts of the lung, lung perfusion scintigraphy allows quantification of lung perfusion.
  • 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), lung perfusion is to be determined by scintigraphy.
  • Follow-up after lung transplantation (LUTX).

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)
  • Severe pulmonary hypertension – the presence of severe pulmonary hypertension is an absolute contraindication to the performance of scintigraphy.

Before the examination

  • X-ray of the thorax – a recent X-ray of the thorax must be available before performing lung perfusion scintigraphy.
  • Application of radiopharmaceutical (radioactive substance or a carrier to which a radioactive substance is coupled) – intravenous application of a radiopharmaceutical is necessary to check lung perfusion. For this purpose, the patient must take several deep breaths in and out before the injection can be performed on the supine patient. The necessary dose varies depending on the age of the patient.

The procedure

Pulmonary perfusion testing is of particular importance in the presence of suspected pulmonary artery embolism. Due to the danger to life in acute pulmonary artery embolism, pulmonary perfusion scintigraphy is an excellent diagnostic procedure because the detection of pulmonary artery embolism is reliable. The basic principle of pulmonary perfusion scintigraphy is based on the imaging of Tc-99m-labeled albumin particles, which is a radiopharmaceutical. The albumin particle represents a denatured substance (denaturation – loss of biological function due to a structural change in albumin), and each individual particle is between 15 and 40 µm in size. Due to this size, the Tc-99m-labeled albumin particles become trapped in the first capillary bed of the lung, allowing imaging of perfusion. However, as a consequence of the small amount of material, the microemboli thus produced do not lead to any impairment of blood flow. Pulmonary perfusion scintigraphy can be combined with pulmonary ventilation scintigraphy, so that a combination can improve the detection of acute pulmonary embolism. Acute pulmonary embolism presents on pulmonary perfusion scintigraphy as sharply circumscribed and additional lung segmental perfusion failure.In addition, there is a so-called “mismatch” between lung perfusion and lung ventilation in this area. Lung sections that are well ventilated but poorly perfused are indicative of acute pulmonary embolism. In contrast, an area with a perfusion and ventilation failure, i.e. a so-called “match”, speaks against an acute pulmonary embolism. To ensure meaningful scintigraphy, it is necessary to display perfusion images from different views. However, pulmonary perfusion scintigraphy does not represent unequivocal evidence of pulmonary embolism in the case of a positive finding, because so-called “match symptomatology” can also be caused by other diseases of the lung, such as sarcoidosis.

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.