Pulmonary edema: a CT study of regional changes in lung density following oleic acid injury.

Transmission computed tomography (CT) was used to study the global and regional density changes in the dog lung associated with oleic acid induced lung injury. The same level of the lower thorax was scanned (5 s/scan) during suspended ventilation at functional residual capacity prior to and after oleic acid infusion (0.05 ml/kg) into the right atrium. The first signs of edema were usually seen within 15 to 30 min after oleic acid infusion and consisted of patchy areas of increased density primarily in the peripheral and dependent zones. Mean CT density (Hounsfield units + 1,000) of lung cross sections from five dogs was 198 +/- 9 (SEM) during base line; density significantly (p less than 0.05) increased to 243 +/- 14 30 min after infusion and reached an apparent plateau of 294 +/- 31 75 min after oleic acid infusion. Thermal-dye dilution measurements indicated that extravascular lung water increased by 3.8 ml/kg from base line to 75 min after oleic acid infusion.

Two methods for isolating the lung area of a CT scan for density information.

Extracting density information from irregularly shaped tissue areas of CT scans requires automated methods when many scans are involved. We describe two computer methods that automatically isolate the lung area of a CT scan. Each starts from a single, operator specified point in the lung. The first method follows the steep density gradient boundary between lung and adjacent tissues; this tracking method is useful for estimating the overall density and total area of lung in a scan because all pixels within the lung area are available for statistical sampling. The second method finds all contiguous pixels of lung that are within the CT number range of air to water and are not a part of strong density gradient edges; this method is useful for estimating density and area of the lung parenchyma. Structures within the lung area that are surrounded by strong density gradient edges, such as large blood vessels, airways and nodules, are excluded from the lung sample while lung areas with diffuse borders, such as an area of mild or moderate edema, are retained. Both methods were tested on scans from an animal model of pulmonary edema and were found to be effective in isolating normal and diseased lungs. These methods are also suitable for isolating other organ areas of CT scans that are bounded by density gradient edges.

Radiographic quantitation of reversible blood-brain barrier disruption in vivo.

Cranial computed tomography (CT) was used to quantitate disruption of the blood-brain barrier (BBB) in dogs in vivo following intracarotid infusion of hypertonic mannitol. The degree of opening varied with the same dose and infusion rate. The ratio of contrast enhancement in brain vs. venous blood was elevated in 4 of 5 mannitol-treated animals, with the greatest enhancement occurring in the ipsilateral basal ganglia and cortical gray matter. The statistical significance and reproducibility of the derived CT numbers used for brain and venous blood calculations, as well as the linear relationship between iodine concentration and CT enhancement, was affirmed by obtaining multiple consecutive scans.