SPIROMETRICALLY CONTROLLED QUANTITATIVE CT FOR ASSESSING DIFFUSE PARENCHYMAL LUNG-DISEASE

Objective: Assessment of lung attenuation by CT reflects changes in th e air-to-tissue ratio of the lung. We have analyzed the interdependenc e of intrathoracic gas volume, lung morphology, and functional disorde r by high resolution CT (HRCT) to assess quantitative disease threshol d in obstructive and restrictive diffuse lung disease. Materials and M ethods: Pulmonary HRCT was performed on 24 healthy volunteers, 11 pati ents with chronic obstructive pulmonary disease (COPD), and 16 patient s with idiopathic lung fibrosis (IPF). HRCT measurement was standardiz ed by taking three scans at the carina +/-5 cm and by defining inspira tion levels by percent vital capacity (VC) via spirometrically gating to the scanner. Results: The mean lung density at 50% VC (DL(50)) for healthy subjects was -819 +/- 3.8 (mean +/- SEM) HU. In contrast, COPD DL(50) was lower, averaging -861 +/- 6.4 HU, and the IPF DL(50) was c onsiderably higher (-731 +/- 17.7 HU), both significantly different (p < 0.001) compared with the control group. The accuracy of quantitativ e HRCT at different inspiration levels was evaluated by scanning the b asal layer at 20, 50, and 80% VC. The control values were - 747 +/- 5. 6, - 816 +/- 3.6, and - 855 +/- 3.0 HU, respectively, which were signi ficantly higher (p < 0.001) than those seen in COPD patients at 20 and 50% VC. Again, the IPF patients exhibited increased lung density (p < 0.001) at all inspiratory levels. Discrimination power was best among all cohorts at 20 and 50% VC. Position-dependent artifacts on lung de nsity were quantified by the anteroposterior density gradient (APG). I rrespective of the underlying disease, APG at 50 and 80% VC was simila r, but was up to twofold higher at 20% VC, indicating that quantitativ e estimates near RV may misrepresent mean lung density. Conclusion: Ou r data indicate that quantitative HRCT measurements should be performe d not near full inspiration or expiration, but at an intermediate degr ee of lung inflation, e.g., 50% VC, for reasons of accuracy, intra- an d intersubjective comparability, and feasibility. We conclude quantita tive HRCT to be a sensitive tool for the evaluation of diffuse parench ymal lung disease.