REPLY:

In his letter, Dr. Corbus points out the essential role of outcome studies to assess the efficacy of new diagnostic procedures in patients with pulmonary embolism. Imaging techniques are continuously evolving, leading to different levels of technologic and clinical local expertise. This probably explains in part the broad variations in sensitivity (70%–100%) that have been reported for helical CT when a direct comparison was performed against other imaging modalities. Therefore, as claimed by Dr. Corbus, outcome studies relying on a 3-mo follow-up combined with validated diagnostic criteria to achieve a final diagnosis of pulmonary embolism must be encouraged. Musset et al. (1) have recently used this approach to assess the performance of single-array helical CT and have concluded that helical CT should not be used in isolation to exclude the diagnosis of pulmonary embolism.

Dr. Corbus also underlines the potential incremental value of lung SPECT, coupled with a quantification of regional ventilation and perfusion (2), thus focusing on the functional role of pulmonary nuclear imaging. One has to remember the paramount role of nuclear imaging techniques in the knowledge of lung physiology and pathophysiology. With this respect, ventilation imaging by means of radioactive gases is invaluable, and it is regrettable that ^81mKr is no longer produced in some countries.

For these reasons, like Dr. Corbus, we truly hope that quantified lung SPECT will soon be extensively used and evaluated by outcome studies (1). Lung SPECT would also certainly benefit from a cost-effectiveness analysis of diagnostic strategies including this modality (3).