Regional lung functional impairment in acute airway obstruction and pulmonary embolic dog models assessed with gadolinium-based aerosol ventilation and perfusion magnetic resonance imaging

RATIONALE AND OBJECTIVES: Gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA)-based aerosol ventilation and perfusion magnetic resonance (MR) images were used to define regional functional impairment in acute airway obstruction (AO) and pulmonary embolic (PE) dog models. METHODS: The aerosol study was performed in 10 anesthetized normal dogs in a supine position during 20-minute spontaneous inhalation of an aerosol of 100- or 200-mmol-Gd/L Gd-DTPA solute produced by an ultrasonic nebulizer in an open-circuit delivery system, combined with a dynamic perfusion study after a 3-second intravenous bolus injection of a 0.1 mmol/kg dose of Gd-DTPA. These MR studies were also performed in the same 10 dogs approximately 30 minutes after obstructing the segmental (n = 6) or lobar (n = 4) bronchus with a balloon catheter, and in another six dogs after segmental (n = 6) and lobar (n = 4) pulmonary arterial embolization with enbucrilate. Regional lung enhancement was assessed on time-signal intensity (SI)-curves and ventilation- and perfusion-weighted images produced by a subtraction technique. RESULTS: The normal lungs were gradually and gravity-dependently enhanced with time after Gd-DTPA aerosol inhalation regardless of the respiratory SI changes, except for three animals with the fastest breathing rate. The averaged maximal relative lung SI increase against the baseline in the successful animals was significantly greater in the slowly and deeply breathing animals than in the fast and shallow breathing animals, regardless of the difference in Gd-concentration (100 mmol Gd/L: 153.3% +/- 69.7% vs. 54.2% +/- 23%; P < 0.001; and 200 mmol Gd/L: 189.7% +/- 68.0% vs. 75.6% +/- 42.2%; P < 0.0001, respectively). There was an additional enhancement of 382% +/- 101 in the ventral lung and 722% +/- 160 in the dorsal lung on the pulmonary arterial phase perfusion image even in the slowly and deeply breathing animals who inhaled 200-mmol-Gd/L aerosol, and the enhancement effect was significantly greater compared with that with the aerosol (P < 0.0001). The ventilation- and perfusion-weighted images clearly defined the regionally matched perfusion-ventilation deficits in all the AO models, and the regionally mismatched perfusion-ventilation in all the PE models. CONCLUSION: Gd-based aerosol can provide efficient lung enhancement in spontaneously and adequately breathing animals, using a relatively noninvasive aerosol delivery system. The combined use of Gd-based perfusion MR imaging may be acceptable for defining regionally impaired function associated with acute AO and PE.