Relative lung areas with attenuation coefficients lower than -960 or -970 HU and 1st percentile are valid indexes to quantify pulmonary emphysema on multi-detector row CT scans.

At CT quantification of pulmonary emphysema, the tube current-time product can be reduced to 20 mAs, but both tube current-time product and section thickness should be kept constant in follow-up examinations.

Quantitative computed tomography assessment of lung structure and function in pulmonary emphysema. A. Madani, C. Keyzer, P.A. Gevenois. #ERS Journals Ltd 2001. ABSTRACT: Accurate diagnosis and quantification of pulmonary emphysema during life is important to understand the natural history of the disease, to assess the extent of the disease, and to evaluate and follow-up therapeutic interventions.Since pulmonary emphysema is defined through pathological criteria, new methods of diagnosis and quantification should be validated by comparisons against histological references.Recent studies have addressed the capability of computed tomography (CT) to quantify pulmonary emphysema accurately. The studies reviewed in this article have been based on CT scans obtained after deep inspiration or expiration, on subjective visual grading and on objective measurements of attenuation values. Especially dedicated software was used for this purpose, which provided numerical data, on both two-and three-dimensional approaches, and compared CT data with pulmonary function tests.More recently, fractal and textural analyses were applied to computed tomography scans to assess the presence, the extent, and the types of emphysema. Quantitative computed tomography has already been used in patient selection for surgical treatment of pulmonary emphysema and in pharmacotherapeutical trials. Computed tomography (CT) is an imaging method providing transverse anatomical images in which the value of each picture element (i.e. pixel) corresponds to the x-ray attenuation of a defined volume of tissue (i.e. voxel). The X-ray attenuation values for each set of projections (i.e. slice) are registered by the computer and organized in a matrix form. The number of calculated pixels determines the image matrix size, influences the image resolution, and should thus be as high as possible. In clinical practice, the matrix size is actually 5126512 pixels. The X-ray attenuation, also called tissue density, is numerically expressed in Hounsfield units (HU). The scale of attenuation values ranges from -1,000 HU, corresponding to the attenuation value of air, to 3,000 HU, with 0 HU corresponding to the attenuation value of water. The thousands of pixels included in one scan make CT the most precise morphological method able to assess the pulmonary structure in vivo [1].In pulmonary emphysema, the major advantage of CT is that in addition to providing data concerning overall lung destruction, it also identifies the specific locations in the lung where the alveolar surface has been destroyed. The ability to estimate the extent and severity of pulmonary emphysema during life is important for several reasons. 1) Accurate detection of lung destruction when it appears and careful mapping of its progression are required to understand the natural history of emphysema.2) The treatment of advanced disease by lung volume reduction surgery (LVRS) requires knowledge of the location of the lesions and objective methods of assessing the surgical