A new way of assessing ultrasound, a non-invasive technique using sound waves to produce pictures inside of the body, may be effective in diagnosing idiopathic pulmonary fibrosis (IPF), a study reported.
This approach was able to quantify lung scarring, a hallmark of IPF, in a study in rats, as well as to detect the presence of fluid in the lungs (edema).
The study, “In-Vivo Assessment of Pulmonary Fibrosis and Pulmonary Edema in Rodents Using Ultrasound Multiple Scattering,” was published in the journal IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control.
IPF changes the structure of lung tissues, such as with thickening of the alveoli — the small air sacs responsible for gas exchange. Techniques currently used to assess scarring (fibrosis) and the amount of lung fluid, however, can be invasive, expensive, or highly complex, hampering the diagnosis of both conditions.
“Assessing the extent of fibrosis in the lung currently requires computerized tomography (CT) scans, and sophisticated pulmonary function tests … Both aspects of the assessment present challenges,” Marie Muller, PhD, the study’s corresponding author and a researcher at North Carolina State University, said in a press release.
“CT scans use radiation, so you want to limit their use. They are also expensive, and require a trained radiologist. For all of these reasons, they are not suitable for frequent monitoring,” Muller added.
One of the pulmonary function tests available is called diffusing capacity of the lung for carbon monoxide (DLCO), which measures the amount of gas exchange in the lung.
But DLCO also “requires specialized equipment that you won’t find outside of hospitals and some large pulmonary clinics,” and as a specialized technology “testing can be expensive,” said Tom Egan, MD, also a study author and a professor of surgery at University of North Carolina.
Researchers at these universities tested an ultrasound approach to quantify the amount of fibrosis and to detect edema in the lungs of rat models. Animals were injected with bleomycin, a compound that induces pulmonary fibrosis, and followed for three weeks.
Animals were assessed using probes to direct several ultrasound waves at lung tissue, which then bounce back to a transducer — a device that converts energy from one form to another. Data is collected and fed into a computational model to determine the density of alveoli in the lung.
“In this study, we verify the hypothesis that changes in the micro-architecture of the lung parenchyma can be characterized by exploiting multiple scattering of ultrasound waves by the alveolar structure,” the researchers wrote. “We hypothesize that in a fibrotic lung, the thickening of the alveolar wall reduces the amount of air (compared to a healthy lung), thereby minimizing the scattering events.”
The transport mean free path (L*) and Backscatter Frequency Shift (BFS), two parameters used in physics, were applied to evaluate the behavior of ultrasound waves.
Results showed significant differences in the L* values between control (healthy) and fibrotic rats, and in BFS values between fibrotic rats and those with edema, suggesting that the behavior of ultrasound waves can be used to diagnose IPF and to distinguish the disease from pulmonary edema.
“Ultrasound is a good solution because it does not pose a cancer risk [no radiation is used], it’s portable, it’s relatively inexpensive, and our technique effectively gives users a quantitative assessment of the fibrosis,” Muller said.
“The quantitative element of this work is particularly important, given that previous approaches to assessing lung health with ultrasound could really only provide qualitative assessments. They could say that lung health was bad or good, but couldn’t give you measurable gradients between the two,” Muller added.
This quantitative feature would also allow the technique to be used with minimal training, and to compare data across time, the researchers emphasized.
Furthermore, “if this new ultrasound technology can reduce our reliance on DLCO tests, that would likely reduce costs for patients,” Egan said.
A grant from the National Institutes of Health (NIH) is allowing these researchers to investigate if their ultrasound technique could quantify pulmonary edema in heart failure patients. The team is also applying for funding to pursue work in people with pulmonary fibrosis.
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