Assessment of pulmonary air trapping and obstruction in expiration:: an experimental MFI study

Purpose: The aim of this experimental study was to evaluate the potential of a simple expiration technique by means of magnetic resonance imaging (MRI) in an animal model to detect pulmonary air-trapping areas after artificial bronchial obstruction. Material and Methods: Sixteen pigs were evaluated by means of a modified T1-weighted FLASH with fat saturation in respiratory arrest (TR=4.6 ms, TE= 1.8 ms, alpha= 10 degrees, S.D.=3-5 mm). A measurement of the signal intensity (SI) in the peripheral lung tissue was made in both inspiration and expiration before and after inhalation of 2 ml of 0.5% acetylcholine to simulate a bronchial obstruction. A final measurement of the lung SI was also made after bronchospasmolytic induction through salbutamol beta(2)-mimetic bronchodilator). Results: In expiration, a mean SI increase in peripheral lung tissue of about 183% was seen in comparison to inspiration (mean SI increase of 11-32). After inhalation of 0.5% acetylcholine, the expirational signal increase in peripheral lung tissue was only 114% of the original SL The expirational signal homogeneity decreased after inhalation of acetylcholine. After inhalation of salbutamol, the lung tissue signal elevation in expiration was 193%. Conclusion: We interpret the low expiratory signal elevation after acetylcholine inhalation as a result of an air-trapped bronchial constriction in certain areas. The simple expiratory technique in an animal model showed that it is suitable to demonstrate obstructive air trapping using MRI. (c) 2005 Elsevier Inc. All rights reserved.