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 und erwent pulmonary function tests and high resolution CT (HRCT). Single secti on inspiratory (INSP), expiratory (EXP), and minimum intensity projection ( MINIP) images through the lower lobes were acquired. A histogram stretch wa s applied to the INSP and MINIP images, generating two further image format s. The five image types were compared for the extent of decreased attenuati on, observer confidence, and correlations with pulmonary function tests. Results: Interobserver variation was lowest with MINIP images (mean weighte d kappa: MINIP 0.70, INSP sections 0.65, other image formats less than or e qual to 0.48). Observers were most confident with EXP and MINIP images. EXP sections identified more disease than MINIP images (p < 0.001). Correlatio ns with pulmonary function tests were similar for each image format. Conclusion: The HRCT changes of small airways disease are enhanced with ima ge postprocessing. MINIP images are associated with increased observer conf idence and agreement as compared with HRCT alone.