Medical researchers and engineers from North Carolina State University have found a new approach that uses ultrasound to measure fluid levels in the lungs. The noninvasive approach can track progress in treating pulmonary edema, which is common in patients with congestive heart failure.

"Historically, it has been difficult to use ultrasound to collect quantitative information on the lung, because ultrasound waves don't travel through air—and the lung is full of air," said Marie Muller, an assistant professor of mechanical engineering at North Carolina State University in Raleigh and co-author of a paper on the topic, in a statement.

In order to improve techniques that show how much fluid is in the lungs, Muller and colleagues conducted two sets of experiments using rats and rat lung tissue to test their noninvasive approach. The first set of experiments consisted of injecting rat lung tissue with saline solution to mimic fluid-filled tissue. This allowed researchers to quantify the amount of fluid in the lung to within one milliliter. In the second set of experiments, researchers calculated the mean difference between how far an ultrasound wave travelled between two air pockets.

The study published in Ultrasound in Medicine and Biology showed the mean difference for the fluid-filled lungs was 1,040 micrometers, while the mean distance in healthy lungs was 332 micrometers.

"This is important, because one could potentially track this mean distance value as a way of determining how well pulmonary edema treatment is working," Muller says.

In an effort to further their study, researchers will be developing two trials, one in humans and the other in a veterinary clinic.