TO THE EDITOR:
In his invited commentary in the May 2002 issue of The Journal of Nuclear Medicine, Dr. Meignan made a powerful argument for expanding the use of lung SPECT (1). The opportunities for quantification of alterations in region lung perfusion and ventilation in the diagnosis and understanding of pulmonary embolism are attractive and exciting—and dependent on tomographic imaging. As Dr. Meignan laments, it is unrealistic to hope for a PIOPED-type study of lung SPECT (although even PIOPED II might be criticized for bias against a competing modality using outmoded technology). However, much can be learned by careful clinical correlation as a means of evaluating diagnostic procedures. Outcome studies in patients on whom a diagnostic test central to their disease has been performed are essential to assess the accuracy and risk of new procedures and may be the only methodology available in many circumstances.
My group is persuaded that lung SPECT offers an ideal screening procedure for suspected pulmonary embolism: easily performed in any clinical setting with a rotating scintillation camera, available in most areas and at all times, accurate, and highly cost effective. We hope that others will heed Dr. Meignan’s message and encourage the use of lung SPECT as the technique of the future.
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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).