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CT Post-Processing Techniques that May be Applied in Evaluating Chest Pathology

Post-processing technique Technical considerations Clinical applications
Multiplanar and curved multiplanar reconstructions (MPR and CMPR) 2D techniques that provide alternate viewing perspectives, usually with conventional window settings. Images are obtained by a reordering of the voxels into 1 voxel-thick tomographic sections, excluding those voxels outside the imaging plane Evaluation of the large airways and pulmonary emboli, particularly for interpretative difficulties on axial sections either due to partial volume averaging or the inability to differentiate periarterial from endoluminal abnormalities
Maximum intensity projection (MIP) A ray is cast through the CT data and only data that are above an assigned value are displayed, thus reducing all data in the line of the ray to a single plane. Sliding slabs of 5–10 mm are commonly used Main use is in vascular imaging and in the evaluation of micronodular disease (more accurate identification of nodules versus vessels, and more precise characterization of nodule distribution)
Mininum intensity projection (MinIP) Similar to MIP, but only data below an assigned value are displayed and thus it is best suited for showing areas of low density May improve conspicuity of subtle density differences of lung parenchyma and therefore highlight regions of emphysema or air trapping
Shaded surface display (SSD) This technique reformats data around a threshold that defines the interface of tissues. SSD does not reveal any internal detail Evaluation of airway abnormalities
Volume rendering Volume rendering is a unique form of 3D visualization. In this process a ray is projected through the dataset and a weighted representation of all the Hounsfield units encountered is displayed depending on their representation within the tissues. Voxels that are only partially filled with a density of interest are also included. The resultant images contain depth information whilst maintaining 3D spatial relationships Used in angiographic examinations and also to evaluate large airway abnormalities
‘Virtual bronchoscopy’ Surface rendering and volume rendering are used to produce endoscopic simulations of the airway Virtual endoscopic or perspective volume rendering images are not widely applied as they seldom give information that cannot be obtained by MPR. However, virtual CT bronchoscopy used in association with 3D techniques providing extraluminal information can provide additional information such as safe routes for tracheobronchial biopsy. Monitoring the position of airway stents is another potential application of this technique

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