RATIONAL USE OF NON-INVASIVE IMAGING IN PULMONARY EMBOLISM: SCINTIGRAPHY, CT, SPECT/CT

Introduction: Pulmonary embolism is still a challenging disease with a high mortality if untreated. Lung scintigraphy was used for non-invasive imaging for many years, the technical improvements in multidetector computed tomography (MDCT) have produced a significant rise in its use during several last years. Recently, hybrid imaging combined both methods (SPECT/CT) was introduced.
Methods: Lung scintigraphy is based on imaging the distribution of small albumin particles transiently trapped in the lung capillaries after their intravenous injection. Scintigraphy is very sensitive for the detection of any changes of lung capillary perfusion. MDCT pulmonary angiography (PA) is based on imaging the thoracic anatomy as well as the intraluminal filling of pulmonary vessels with contrast media during the flow of blood through the lungs after intravenous injection of contrast agent. SPECT/CT combines the properties of both.
Results: Clinical parameters of pulmonary scintigraphy and MDCT PA are similar. Sensitivity, specificity and accuracy are above 90%, negative predictive value get near 100%, risk of subsequent embolism if the results are negative is below 1%, interobserver variability is around 90%. The patient radiation absorbed dose from MDCT PA is much higher comparing to scintigraphy and MDCT PA also uses potentially risk contrast media. On the other hand, MDCT PA is able to provide alternative diagnoses and it is round-the-clock available.
Conclusion: Both pulmonary scintigraphy and MDCT PA have some strenghts and weaknesses so the selection of particular method should be used according to specific clinical scenarios. Both methods should be used together with clinical probability scoring. SPECT/CT without contrast enhancement seems to be the method of choice in the work-up of suspected pulmonary embolism.