Quantitative Computed Tomography of Diffuse Lung Disease

Quantitative computed tomography (QCT) techniques to determine the severity of diffuse lung disease have been progressively developed, validated, and refined over the past 25 years, and the maturity of this field is reflected in the quality of the papers included in this symposium on quantitative CT. The purpose of the symposium is to acquaint the readers of JTI with the current state of the art of QCT. I believe that the papers in this edition will become standard references for those seeking to implement QCT on a clinical or research basis. In order for QCT to enter the clinical mainstream, it is important to use standardized technique. Dr Newell and co-authors describe how to optimize technique for specific questions, including consideration of radiation dose.1 In implementing routine QCT, it is critical to understand the range of normal findings on QCT,2 and to learn how to adjust for or incorporate sources of variation. Drs Smith and Barr thoughtfully describe the methodology for assessing normal populations, and delineate the multi-step process that will be required for developing reference equations for QCT parameters.3 Dr Coxson comprehensively discusses the known sources of technical variation in QCT,4 and shows that, with proper study design, valuable information regarding extent of diffuse lung disease is available. QCT has been most widely used and best validated for emphysema.5 However, as indicated in the article by Lynch and Al Qaisi,6 comprehensive quantitative evaluation of COPD also requires quantitative evaluation of the bronchi and of expiratory gas trapping.7 Such comprehensive evaluation, integrated with visual characterization, is already providing major insights into the genetics of COPD,8 and in the future will likely provide assessment of treatment efficacy in clinical trials as well as guiding optimal treatment of individual patients. QCT is also increasingly used in evaluation of lung fibrosis. While basic histogram-based measures have been shown to correlate with physiology and mortality,9 there is increasing recognition that a texture-based method is very helpful for determining the extent of fibrotic abnormality.10 In this issue, Dr Bartholmai and co-authors provide a paper summarizing their elegant approach to quantification of fibrotic lung disease.11 The glyph-based method provides at a glance an attractive visual summary of the volumetric proportions of fibrotic abnormality, emphysema, and other parenchymal abnormalities, and will be particularly useful in depicting the longitudinal course of individual subjects. I would like to thank Dr Phillip Boiselle for providing the impetus for this symposium, all of the authors for taking the time to provide and edit these outstanding contributions, and Emily Senerth of Wolters Kluwer Health for excellent editorial assistance. David A. Lynch, MB, MD Division of Radiology, National Jewish Health, 1400 Jackson Street, Denver, CO 80206