Lung Scintigraphy: Current Methods and Interpretation Criteria in Clinical Practice
Introduction. In current clinical practice lung scintigraphy is mainly used to exclude pulmonary embolism (PE). Recently new scintigraphic methods (single photon emission computed tomography - SPECT), as well as simplified criteria for scan interpretation have been developed.
Methods. We retrospectively collected data from the emergency department (ED) on 98 outpatients who underwent planar ventilation/perfusion (V/Q) scintigraphy and 49 outpatients from the ED who underwent V/Q SPECT. V/Q planar images were interpreted according to PIOPED and 0.5 segment mismatch criteria, and perfusion scans according to PISA-PED criteria. SPECT images were interpreted according to the criteria suggested in EANM guidelines. Final diagnosis of PE was based on the clinical decision of the attending physician and evaluation of a 12 months follow-up period.
Results. Using PIOPED and 0.5 segment mismatch criteria, planar V/Q scans were diagnostic in 84% and 93% of cases, respectively. Among the diagnostic scan readings, specificities of PE negative scans were 98% for PIOPED and 99% for 0.5 segment mismatch criteria. V/Q SPECT showed a sensitivity of 100% and a specificity of 98%, without non-diagnostic scans. In patients with low pretest probability, perfusion scans without ventilation gave definitive readings in 80% of cases, with a specificity of 91%.
Conclusions. In outpatients from the ED, lung scintigraphy yielded diagnostically definitive results and was reliable in ruling out PE. V/Q SPECT showed excellent specificity and sensitivity without non-diagnostic results. Using 0.5 segment mismatch criteria, there were considerably less non-diagnostic readings in comparison to PIOPED. In all patients and in the group of patients with low pretest probability, diagnostic accuracy of perfusion scintigraphy according to PISA-PED criteria was inferior to that of combined V/Q scintigraphy.