Computed tomographic measurement of lung density changes in lung water with hemodialysis

In 10 hemodialysis patients, with an ultrafiltration volume ranging from 1 to 4.5 liters per session, the lung density was measured by computed tomography (CT) and the lung volumes by total body plethysmography. From the CT numbers (difference in X-ray attenuation between lung and water, measured in Hounsfield units, HU), and by using a special computer program, quantitative estimates of the densities of normally inflated (pixels between -1,000 and -500 HU), poorly inflated (pixels between -500 and -100 HU) and noninflated lung tissue (pixels between -100 and +100 HU) were obtained. The sizes of the normally and poorly inflated areas were also measured. The results showed that, after dialysis, the normally inflated area was decreased in density and increased in size, and conversely, the size of the poorly inflated area was diminished but without change in density. This finding implied introduction of more gas into the lung. The above observation was reflected by the results of pulmonary function measurements, in that the total lung capacity and functional residual capacity were significantly increased after dialysis. In conclusion, changes in lung fluid (both intra- and extravascular) with hemodialysis can be measured quantitatively by the changes in lung density as estimated by the CT densitometry technique.