CT attenuation of paired HRCT scans obtained at full inspiratory/expiratory position: comparison with pulmonary function tests

Abstract.

The purpose of this prospective study was to measure lung attenuation at paired HRCT obtained at full inspiratory/expiratory position, to correlate with pulmonary function tests (PFTs) and to characterize different types of ventilatory impairment. One hundred fifty-five patients with and without pulmonary disease underwent paired HRCT obtained at full inspiratory/expiratory position. Three scan pairs were evaluated by densito- and planimetry using dedicated software. The PFTs were available for correlation in all patients (mean interval 5 days). Mean lung density (MLD) at full inspiration was –813 HU, and MLD at full expiration was –736 HU; both, as well as the expiratory attenuation increase, demonstrated significant correlations with static and dynamic lung volumes: up to r=0.68, p<0.05 for residual volume. The MLD and emphysema indices correlated markedly better for scans obtained at full expiration than at full inspiration, e.g. correlation with the residual volume: r=0.68 compared with r=0.55. Even better correlations were obtained for the lung area (229 cm² at inspiration, 190 cm² at expiration), up to r=0.74 for the lung area in expiration and the intrathoracic gas volume. Inspiratory MLD and the expiratory attenuation increase were able to differentiate obstructive and restrictive ventilatory impairment from normal subjects, the best results were obtained from scans obtained at full expiratory position (p<0.05). In conclusion, scans obtained at full expiratory position reveal more functional information than scans obtained at full inspiratory position. Quantitative analysis of CT obtained at full expiratory position provides good estimations of static and dynamic lung volumes as well as significant differences between normal subjects and patients with ventilatory impairment.