A comparison of methods for enhancing the detection of areas of decreased attenuation on CT caused by airways disease

Purpose: The purpose of this work was to investigate thin section CT image enhancement of subtle areas of decreased attenuation of the lung parenchyma in suspected airways disease. Method: Forty-seven consecutive patients with chronic sputum production underwent pulmonary function tests and high resolution CT (HRCT). Single section inspiratory (INSP), expiratory (EXP), and minimum intensity projection (MINIP) images through the lower lobes were acquired. A histogram stretch was applied to the INSP and MINIP images, generating two further image formats. The five image types were compared for the extent of decreased attenuation, observer confidence, and correlations with pulmonary function tests. Results: Interobserver variation was lowest with MINIP images (mean weighted kappa: MINIP 0.70, INSP sections 0.65, other image formats less than or equal to 0.48). Observers were most confident with EXP and MINIP images. EXP sections identified more disease than MINIP images (p < 0.001). Correlations with pulmonary function tests were similar for each image format. Conclusion: The HRCT changes of small airways disease are enhanced with image postprocessing. MINIP images are associated with increased observer confidence and agreement as compared with HRCT alone.