Is the quantitative analysis of lung computed tomography accurate in ALI/ARDS patients?

The CT scan allows an accurate morphologic analysis of an 'ARDS' lung. In addition, with the spiral CT it is also possible to perform a quantitative analysis using dedicated software. The quantitative analysis is based on the strict correlation between the X-ray attenuation in a given volume of tissue and the physical density of that volume. The CT is determined by the percentage of radiation that is absorbed by that volume.

However, due to the necessity of a manually drawing of the lung (i.e. to include the lung and to exclude big vessels, trachea, pleural effusion, etc.), it would be possible to increase the inaccuracy of the analysis.

The aim of this study was to evaluate the accuracy of analysis between trained physicians (four medical doctor) and two radiologists. We enrolled 12 intubated sedated paralyzed patients ALI/ARDS patients (mean age 63.5 ± 16.9 years, BMI 24.1 ± 4.7 m², tidal volume 532 ± 195 ml, PEEP 11.2 ± 1.9 cmH₂O, PaO₂/FiO₂ 205 ± 57). The CT scan was done for clinical purpose, in static conditions, at end expiration 5 or 15 cmH₂O PEEP and at end inspiration 45 cmH₂O airway pressure. The exposures were taken at 120 KV and 250 mA. The lung volume, weight and the distribution of lung weight between the different parts was measured using the 'Maluna' software (University of Mannheim, Germany).

The results show that the quantitative analysis, although requiring a physician to manually draw the region of interest of the lung, presents a high degree of accuracy.

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