Ultra-Low-Dose CT Can Effectively Detect Emphysema and Fibrosis

Parenchymal abnormalities observed with ultra-low-dose computed tomography (uLDCT) using prone images are strongly associated with physiologically significant abnormalities in lung function, according to study findings published in BMJ Open Respiratory Research.

Although uLDCT uses a level of radiation similar to that of a chest x-ray (CXR), it is not known how well uLDCT can detect important parenchymal lung abnormalities that may not be seen on a chest x-ray. The Western Australia Asbestos Review Program (ARP) began using uLDCT chest scans to monitor those exposed to asbestos after 2012. Investigators therefore conducted a cross-sectional study was to compare the lung parenchymal findings from uLDCT scans in ARP participants with physiological measures of respiratory function to determine how accurately chest CT at ultra-low doses can show parenchymal pathology.

All ARP participants had at least 3 months of cumulative asbestos exposure history and/or pleural plaques on imaging. Participants were eligible for the current analysis if they had an annual review between January 1, 2018, and December 31, 2018, and a uLDCT screening scan and lung function assessment, which were usually conducted within 1 to 2 days of each other.

A total of 1344 participants (median age, 72.0 [interquartile range, 65.0-78.0] years; 84.9% male) with paired uLDCT and lung function assessments were identified. A majority (68.1%) had mixed occupational asbestos fiber exposure, and 65.2% reported ever-smoking with a median tobacco exposure of 19.5 (IQR, 8.4-39.0) pack-years. The participants had an overall mean (SD) forced expiratory volume in 1 second (FEV₁) of 91.3% (18.8) predicted, forced vital capacity (FVC) of 96.7% (17.1), FEV₁/FVC ratio of 0.71 (0.09), and actual diffusion of carbon monoxide (DLCO) of 23.3 (7.3) mL/min/mm Hg.

Of the cohort, 721 (53.6%) patients had no CT parenchymal abnormality, 158 (11.8%) had emphysema, 465 (34.6%) had linear fibrosis, and 94 (7.0%) had fibrosis and emphysema.

The mean dose length product was 8.9 (SD 1.9) mGy/cm or 0.12 (SD 0.03) mSv. The median (IQR) emphysema score was 4.0 (2.0-8.0) and the median linear fibrosis score was 4.0 (2.0-6.0). Overall, 220 indeterminate nodules were recorded (137 ground glass) and 4 confirmed cases of lung cancer were noted, with no cases of mesothelioma.

Statistically significant between-group differences were found for all physiologic parameters compared with the control group (ie, participants with no abnormality). A strong and significant correlation was observed for total emphysema score and obstructive FEV₁/FVC ratio (r=0.512, P <.0005). Analysis also showed a moderate inverse correlation with percent predicted FEV₁ (r=0.24, P <.0005) and a weak correlation with percent predicted FVC (r=0.19, P =.02).

The linear fibrosis score was moderately well associated with percent predicted FEV₁ (r=0.21, P <.0005) and percent predicted FVC (r=0.21, P <.0005) and weakly associated with FEV₁/ FVC ratio (r=0.095, P =.001). A moderate association was found between emphysema score and lower DLCO (r=0.337) and linear fibrosis score and lower DLCO (r=0.362), both P <.0005.

In multivariate analysis, increasing age, emphysema, and fibrosis scores predicted reduced DLCO (P <.0005, adjusted R²=0.30).

In discussing study limitations, the investigators noted that gold standard approaches to early lung cancer detection, such as using 2 readers and formal consensus methods, were not used by ARP. Another limitation is the study’s lack of comparison of uLDCT images with imaging generated by SDCT (a gold standard for radiologic diagnosis) or chest x-ray.

“These data add to the expanding literature demonstrating the utility of uLDCT, now for the reliable diagnosis of low contrast lung pathology,” stated the researchers. “We contend that a transition away from the ‘routine CXR’ towards uLDCT may be indicated.”