SPECT/CT imaging of lung perfusion in the diagnosis of pulmonary embolism: Comparison with planar ventilation-perfusion lung scintigraphy

The aim of this study is to assess a new tool for the diagnosis of acute pulmonary embolism (PE): single-photon emission computed tomography lung perfusion imaging associated with unenhanced computed tomography (SPECT/CT) compared to planar ventilation-perfusion (V.Q.) lung scintigraphy. Methods One hundred and three patients with suspected acute PE underwent V.Q. scintigraphy (two scans were not interpretable) followed by perfusion SPECT/CT. The two types of images were analysed separately: (1) according to the modified P.I.O.P.E.D. scintigraphic criteria for V.Q. lung scan and (2) with regard to SPECT/CT mismatches suggestive acute PE (segmental perfusion defects detected on SPECT images not matched with CT abnormalities). Results On average, the number of segmental perfusion defects per patient was higher with SPECT/CT than with planar scintigraphy (4.3 ±3.6 versus 2.8 ±2.6; p < 0.001). A mismatch was found with SPECT-CT in 0% (0/18) of normal scintigraphy, and 8% (3/39) for low, 32% (8/25) for intermediate and 74% (14/19) for high probabilities of PE at scintigraphy. The presence of a SPECT/CT mismatch was also associated with higher pretest probability of acute PE (p = 0.001), even for the 25 patients in the intermediate-probability subgroup (p = 0.02). Finally, a SPECT/CT match was found in 29 patients that was not suggestive of acute PE due to the presence, in areas with perfusion defects on SPECT images, of the following CT abnormalities: hypo density and/or emphysema (71%), condensation or atelectasis (38%), pleural disease (7%), extra-pulmonary structure (14%) and/or bronchial obstruction (7%). Conclusion In patients with suspected acute PE, the results obtained with pulmonary SPECT/CT images are consistent with those obtained with V.Q. scintigraphy and the pretest probability of PE. Further studies comparing SPECT/CT imaging with angiographic techniques are now required to evaluate more specifically the diagnostic value of this new tool. (authors)