Comparison of ventilation-perfusion single-photon emission computed tomography (V/Q SPECT) versus dual-energy CT perfusion and angiography (DECT) after 6 months of pulmonary embolism (PE) treatment

• Incomplete resolution of pulmonary emboli occurs frequently.
• Residual V/Q-SPECT defects correspond in the majority of cases with defects seen on DECT.
• Some (11.1%) defects on V/Q-SPECT are not present on comparable DECT images.

BackgroundThe natural evolution of treated symptomatic pulmonary embolism shows often incomplete resolution of pulmonary thrombi. The prevalence of perfusion defects depend on the image modality used. This study directly compares V/Q SPECT with DECT.MethodsA single-center prospective observational cohort study of patients with intermediate risk PE, reassessed at the end of treatment with V/Q SPECT. Abnormal V/Q SPECT images were compared with DECT.ResultsWe compared DECT en V/Q SPECT in 28 consecutive patients with persistent V/Q mismatch on V/Q SPECT, 13 men and 15 woman, mean age 60 (+17), range 23–82 year. One patient was excluded from the final analysis due to inferior quality DECT. In 18/27 (66.7%) the results were concordant between CTPA (persistent embolus visible), DECT (segmentary defects on iodine map) and V/Q SPECT (segmentary ventilation–perfusion mismatch). In 3/18 (11.1% of the total group) the partialy matched V/Q SPECT defect could be explained on DECT lung images by lung infarction. In 6/27 (22.1%) only hypoperfusion was seen on DECT iodine map. In 3/27 (11.1%) results were discordant between V/Q SPECT and DECT images.ConclusionSix months after diagnosis of first or recurrent PE, residual pulmonary perfusion-defects encountered on V/Q-SPECT corresponds in the majority of patients with chronic thromboembolic disease seen on DECT. In 22.1% of patients V/Q SPECT mismatch only corresponds with hypoperfusion on iodine map DECT scan. Some (11.1%) of the chronic thromboembolic lesions seen on V/Q SPECT can not be explained by DECT results.