Pulmonary quantitative CT imaging in focal and diffuse disease: current research and clinical applications

The frenetic development of imaging technology - both hardware and software - provides exceptional potential for investigation of the lung. In the last two decades, computed tomography (CT) was exploited for detailed characterization of pulmonary structures and description of respiratory disease. The introduction of volumetric acquisition allowed increasingly sophisticated analysis of CT data by means of computerized algorithm, namely quantitative computed tomography (QCT). Hundreds of thousands of CTs have been analyzed for characterization of focal and diffuse disease of the lung. Several QCT metrics were developed and tested against clinical, functional, and prognostic descriptors. Computer aided detection (CAD) of nodules, textural analysis of focal lesions, densitometric analysis and airway segmentation in obstructive pulmonary disease, and textural analysis in interstitial lung disease are the major chapters of this discipline. The validation of QCT metrics for specific clinical and investigational needs prompted the translation of such metrics from research field to patient care. The present review summarizes the state of the art of QCT in both focal and diffuse lung disease, including a dedicated discussion about application of QCT metrics as parameters for clinical care and outcomes in clinical trials.