A study on image diagnosis of lung impairment caused by aspiration

Purpose of the present study is to evaluate lung impairment in an acute aspiration model by using new CT method and to assess the application of the method for clinical cases. Subjects in experimental model were anesthetized and mechanically ventilated beagle dogs (n=5), and subjects in clinical cases were patients with aspiration in acute phase (n=5). For the preparation of the acute aspiration model, 2% Gastrografin (diatrizoate megulumine) aqueous solution was instilled cumulatively (0.1-3.0 ml/kg) into the right main bronchus through the endobronchial tube. Two methods of CT scan, Spirometric gating CT (SGCT) and Dynamic CT, were performed before and after instillation. SGCT can adjust the pulmonary volume at each scan by built-in spirometer. Three-dimensional reconstruction of the whole lung image was obtained with scan data by SGCT. Dynamic CT method was utilized for assessment of the ventilation dynamics. Continuous scan of the lung at the carina level was performed during ventilation and time-series image data were obtained at a rate of 5 frames/sec. The CT densitometry of the Dynamic CT images were carried out and time-attenuation curves with ventilation were analyzed. In experimental model, the whole lung images by SGCT after instillation showed invasion of Gastrografin into right lower lobe and the compensatory overinflation in the other lobes. The time-attenuation curves by Dynamic CT showed that both the mean and amplitude of the attenuation increased in the right lower lobe where the Gastrografin instilled. But the amplitude decreased when the mean value showed no apparent change at the first period of instillation. In acute phase of the aspiration, the amplitude will be the sensitive index of the ventilation impairment. In clinical case subjects were scanned during spontaneous breathing by Dynamic CT. Both the mean and amplitude of the attenuation of the time-increased when the aspiration occurred. After four days passed, the mean value increased remarkably in severe patients, however, the amplitude of attenuation showed no significant change. The results reflect change in compliance of the severely impaired lung. The ventilation imbalance caused by aspiration was visualized by SGCT. Analysis of Dynamic CT images make possible evaluation of the lung function and it may contribute diagnosis of the lung impairment caused by aspiration. (author)