Regional measurements of pulmonary edema by using magnetic resonance imaging

Abstract

A three-dimensional magnetic resonance imaging (MRI) method to measure pulmonary edema and lung microvascular barrier permeability was developed and compared with conventional methods in nine mongrel dogs. MRIs were obtained covering the entire lungs. Injury was induced by injection of oleic acid (0.021–0.048 ml/kg) into a jugular catheter. Imaging followed for 0.75–2 h. Extravascular lung water and permeability-related parameters were measured from multiple-indicator dilution curves. Edema was measured as magnetic resonance signal-to-noise ratio (SNR). Postinjury wet-to-dry lung weight ratio was 5.30 ± 0.38 ( n = 9). Extravascular lung water increased from 2.03 ± 1.11 to 3.00 ± 1.45 ml/g ( n = 9, P < 0.01). Indicator dilution studies yielded parameters characterizing capillary exchange of urea and butanediol: the product of the square root of equivalent diffusivity of escape from the capillary and capillary surface area ( D 1/2 S) and the capillary permeability-surface area product ( PS). The ratio of D 1/2 Sfor urea to D 1/2 Sfor butanediol increased from 0.583 ± 0.027 to 0.852 ± 0.154 ( n = 9, P < 0.05). Whole lung SNR at baseline, before injury, correlated with D 1/2 Sand PS ratios (both P < 0.02). By using rate of SNR change, the mismatch of transcapillary filtration flow and lymph clearance was estimated to be 0.2–1.8 ml/min. The filtration coefficient was estimated from these values. Results indicate that pulmonary edema formation during oleic acid injury can be imaged regionally and quantified globally, and the results suggest possible regional quantification by using three-dimensional MRI.