MULTINUCLEAR NMR IMAGING OF REGIONAL LUNG WATER

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Pulmonary edema is one of the most common complications of left ventricular failure. It is typically suggested by symptoms like dyspnea and diagnosed by auscultation of the chest or radiography. It is frequently relatively far advanced before it can be reliably detected. Radiographically, it is difficult to distinguish from inflammatory or other pulmonary infiltrates and in many patients the discrimination of pulmonary edema from infection can be difficult and pivotal for the choice of therapy. The nuclear magnetic resonance T1 and T2 relaxation times are sensitive to the total free tissue water and should be independent of the spin density per unit volume. If so, they can be used for measuring lung water. Edema fluid is an ultrafiltrate of plasma with a sodium ion concentration similar to plasma. Therefore, increased extracellular water should be measurable as an increase in sodium signal intensity. By using a paramagnetic agent that is confined to the vascular compartment and measuring the blood T1 and the total T1, it will be possible to compute the T1 of the extravascular compartment in physiologic situations where diffusion between compartments is "fast." Edema tends to be patchy, frequently occupying the dependent portions of the lungs preferentially. An advantage of an imaging method for measurement is that it can account for the nonhomogeneous distribution of edema. Regional measurements made from images will be compared directly to gravimetric measurements to determine the accuracy of the method. This will be studied in a 1.4 Tesla animal imaging system using animal models for atelectasis permeability edema and hemodynamic edema.