Oblique views in lung perfusion scanning: clinical utility and limitations.

Over 300 perfusion lung scans were reviewed to assess the clinical utility of routinely performed anterior and posterior oblique projections. The characteristics of normal anterior and posterior oblique views were analyzed and compared with lateral projections. The four oblique images contributed materially toward characterization of perfusion defects in 63% of all abnormal studies; the contribution of posterior obliques was 48%, anterior obliques, 15%. For scans displaying at least one focal defect, oblique views were of benefit in over 70% of cases, with posterior obliques accounting for 55%. Oblique views contributed little when perfusion abnormalities involved both lung fields diffusely. The posterior oblique projection was of more value than the anterior oblique because of its ability to clarify lower-lobe abnormalities significantly. A scanning artifact in the posterior oblique views, due to attenuation of the near lung activity by scapula and shoulder-girdle musculature, was seen in 90% of normal studies.