PULMONARY-EMPHYSEMA - QUANTITATIVE CT DURING EXPIRATION

PURPOSE: To determine whether measurement of the relative area of lung with attenuation coefficients lower than a certain threshold on thin- section computed tomographic (CT) scans obtained during expiration is a valuable method of quantifying the extent of pulmonary emphysema. MA TERIALS AND METHODS: Eighty-nine patients underwent CT (with 1-mm coll imation) preoperatively during inspiration and expiration. Relative ar eas of lung with attenuation coefficients lower than various threshold s were calculated. These relative areas were compared with areas found macroscopically to have emphysema (59 patients [51 men, eight women; aged 40-77 years]) and with two microscopic indices (35 patients [29 m en, six women; aged 42-77 years]) assessed on the resected specimens. RESULTS: The valid expiratory CT thresholds were found to be -820 and -910 HU for microscopic and macroscopic emphysema, respectively. Howev er, results of stepwise multiple regression analyses showed that the i nspiratory threshold of -950 HU was superior for both macroscopically and microscopically quantified emphysema. The correlation coefficients in expiratory CT were higher for the pulmonary volumes but similar fo r the diffusing capacity. CONCLUSION: Expiratory quantitative CT is no t as accurate as inspiratory CT for quantifying pulmonary emphysema an d probably reflects air trapping more than reduction in the alveolar w all surface.