CT and MRI of Pulmonary Emphysema: Assessment of Lung Structure and Function
Computed tomography (CT) is a radiological modality that provides transverse anatomical images. In these images, the value of each picture element (pixel) corresponds to the X-ray attenuation of a defined volume of tissue (voxel). The X-ray attenuation values for each set of projections (slice) are registered by a computer and organized in the form of a matrix. The number of calculated pixels not only determines the image matrix size, but also impacts on the image resolution, and should therefore be as high as possible. In clinical practice, the matrix size is 512×512 pixels. The X-ray attenuation, that is sometimes termed “tissue density”, is numerically expressed in Hounsfield units (HU). The scale of attenuation values ranges from -1000 HU, corresponding to the attenuation value of air, to 3000 HU, with 0 HU corresponding to the attenuation value of water. The thousands of pixels and respective attenuation values included in one scan make CT the most precise modality for the in vivo assessment of pulmonary parenchyma (Hoffman and McLennan 1997).
KeywordsQuantitative Compute Tomography Total Lung Capacity Pulmonary Emphysema Lung Volume Reduction Surgery Compute Tomography Section
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