[High resolution and spirometric synchronization computerized tomography in chronic obstructive bronchopneumopathy]

To assess the feasibility of spirometrically gated HRCT in patients with chronic obstructive pulmonary disease and to correlate the density measures with the results of pulmonary function tests.

Pulmonary function tests and spirometrically gated HRCT were performed, on the same day, in 20 patients with chronic obstructive pulmonary disease. Spirometrically gated HRCT scans at 90 and 10% of the patient's vital capacity were acquired, at three anatomical levels (carena, carena plus 5 cm, carena minus 5 cm). In each section, lung parenchyma was isolated from the other thoracic structures and from the main bronchi and a densitometric evaluation was applied to the regions of interest. A histogram showing the distribution of the pixel frequencies versus lung densities, the mean CT number and the pixel index at -910 HU (for scans acquired at 10% of the patient's vital capacity) and at -950 HU (for scans obtained at 90% of the patient's vital capacity) were obtained. Average acquisition time for the spirometrically gated HRCt was 15-20 minutes, average data processing time was 20 minutes.

The mean CT number and the pixel index at -910 HU obtained at 10% of the patient's vital capacity correlated with the Tiffeneau index (r = 0.85; R = 0.78 respectively). The pixel index at -910 HU correlated also with the ratio of residual volume to total lung capacity (r = 0.65). The mean CT number and the pixel index obtained at 90% of the vital capacity correlated with the lung diffusion of carbon monoxide (r = 0.64 and r = 0.79 respectively).

In our study, we found good correlation between the densitometric values obtained with spirometrically gated HRCT and the respiratory function tests routinely employed to assess the presence and the gravity of obstructive pulmonary disease. A good reproducibility of the data is guaranteed by the spirometical gating which enables standardization of the lung acquisition volume, and by the semiautomatic contour tracing program combined with an automated densitometric evaluation. The main disadvantages of the technique are the relatively long acquisition and evaluation times. Spirometrically gated HRCT densitometry is a promising tool for longitudinal studies of diffuse lung disease (pulmonary emphysema and fibrosis).