Hyperpolarized lung MRI portrays the perils of smoking

A relatively new MR technique that vastly improves imaging resolution is able to find the minute lung pathology associated with smoking habits—even before respiratory symptoms become a drag, according to a study published ahead of print Oct. 13 in Radiology.

The most common assessment for smoking-associated abnormalities is the pulmonary function test, which is most often used to evaluate patients for chronic obstructive pulmonary disease (COPD). Researchers, including Hooman Hamedani from the Perelman School of Medicine and University of Pennsylvania in Philadelphia, evaluated hyperpolarized MR imaging as a tool for the detection, disease staging and monitoring of lung and respiratory problems linked to smoking.

“Autopsy studies have shown that the entire suite of clinical respiratory tests may fail to detect any observable changes even if up to 30 percent of lung tissue is impaired,” wrote the authors. “In addition, [pulmonary function tests] are at times unable to help differentiate between healthy individuals and patients with early stage disease.”

The findings of this prospective human study using hyperpolarized MRI exceeded the authors’ expectations, and conventional testing methods by not only revealing abnormalities in the lungs indicating such diseases as COPD, emphysema and bronchitis, but by differentiating subpopulations of disease.

“We anticipated that the use of this technology to measure alveolar oxygen tension would help detect small smoking-induced functional alterations with greater accuracy than current clinical techniques,” wrote Hamedani et al. “This hypothesis was confirmed. Most important, we found that the ability of alveolar oxygen tension heterogeneity [via alveolar partial pressure of oxygen] to enable differentiation among nonsmokers, asymptomatic smokers, and symptomatic smokers exceeds that of the established clinical tests.”

The standard deviation of alveolar partial pressure of oxygen was the only parameter that differentiated these patient populations and, additionally, could demonstrate abnormalities in lung function prior to symptoms.

“Moreover, because it also revealed statistically significant differences between symptomatic and asymptomatic smokers, this study demonstrates that [measuring the standard deviation alveolar partial pressure of oxygen] can help detect more serious functional abnormalities as well. Although the observation of altered function does not unequivocally prove that these alterations are related to the subsequent development of disease, the results agree with the findings of many other imaging studies, which have demonstrated greater heterogeneity in ventilation, perfusion, and ventilation-perfusion mismatch in smokers and patients with COPD.”

A statistical analysis showed that hyperpolarized MR lung imaging was able surpass all current clinical respiratory evaluations by a significant margin of 30 percent under the operating curve with the addition of alveolar partial pressure of oxygen.

“It is possible that the masking of locally altered [alveolar partial pressure of oxygen] is related to the well-known tendency of the lung to compensate for local disease or injury and to maintain adequate global function even when a significant fraction of the organ is compromised. Although crucial for continued systemic health, this compensatory mechanism likely contributes to the insensitivity of other global metrics, including the pulmonary function tests, to early disease.”