Spiral CT angiography: reformating techniques

Clinical applications of spiral CT angiography are mainly based on transver se CT scans which can be completed by several categories of additional refo rmations in order to provide the most accurate evaluation of the vessel(s)- of-interest. Two-dimensional reformations are the second most frequent cate gory of reconstructions generated from a spiral data set, enabling the crea tion of planar (frontal, sagittal or oblique) or curved views of a gieven v essel. Three-dimensional displays can also be generated from most post-proc essing consoles, namely surface shaded displays (SSD), maximum intensity pr ojections (MIP) and images using the volume rendered technique (VRT). Shade d surface displays are based on a binary selection of voxels using a single or double thresholding whereas MIP images result from the selection of the voxels of highest attenuation value. Volume rendered images are generated by means of a probabilistic classification of voxels consisting of a system atic estimation of the amount of the tissue-of-interest in each voxel. In a ddition, a variable degree of opacity (or transparency) can be chosen for t he vascular structures and/or the surrounding anatomical structures, thus a voiding interpretive difficulties due to superimposition. A fourth category of reconstruction, STS-MIP (i.e., sliding-thin-slab MIP) can be applied to the evaluation of peripheral intraparenchymal vasculatures.