A new technique called parametric response mapping used to analyze lung CT scans can help physicians distinguish between early-stage damage to the airway and emphysema, according to a study published online in Nature Medicine. The PRM technique was originally developed to show a response of brain tumors to treatment.
“Essentially, with the PRM technique, we’ve been able to tell sub-types of COPD apart, distinguishing functional small airway disease or fSAD from emphysema and normal lung function,” Brian Ross, PhD, said in a release. Ross is a professor of radiology and biological chemistry at the University of Michigan Medical School, and the paper’s senior author.
Researchers assessed 194 patients selected from the much larger COPDGene study. The patients had at least a 10-pack-year history of smoking. All CT data were obtained and analysis was performed as part of the COPDGene project.
The researchers used the computer techniques to overlay the CT scan image, taken during a full inhalation, with an image that was taken during full exhalation. Using the images, the researchers created a three-dimensional map of the lungs. The density of healthy lung tissue will change more between the two images than that of diseased lung tissue.
PRM assigns colors to each small 3-D area, called a voxel, according to the difference in signal changes between the two scans. Green means healthy, yellow means a reduced ability to push air out of the small sacs, and red means severely reduced ability, researchers said.
Spirometry is still considered the best test for diagnosing COPD, but researchers said it is limited in its ability to distinguish between different types of lung damage COPD patients experience.
By repeating the imaging over time, it would be possible to track COPD progression, said lead author Craig Gabán, assistant professor of radiology. More studies need to be done to see if this would be an effective approach.
From left to right, PRM images of the lungs of a healthy person, two people with mild to moderate COPD, and a person with severe emphysema. Green is healthy tissue, yellow is small airway damage, and red is more severe damage. Images courtesy the Center for Molecular Imaging, University of Michigan.