Steriography

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For reasons related to how the human brain processes visual information, it is possible to create a 3D image from two images taken a few degrees and fused by crossing ones eyes or using prism glasses. With modern cone beam CT imaging, we find that we use steriography somewhat less, but the ease of acquisition- two planar runs taken six degrees apart- and the decreased radiation compared with a cone beam image still add value in some cases. Prime examples include spinal angiography and any lesion with arteriovenous shunting where two entire stereograms, both at higher frame rate, can be used to explore the physiology of a lesion in every phase in three dimensions.   The 4D acquisition helps with some of the information that steriography can provide, but not all. First, 4D is an "area under the curve" acquisition much like roadmapping meaning that the machine will display any contrast that it sees during the run. This means that you are continually adding to the arterial or venous tree, but never taking away. Want to see a nidus without the arterial pedicles, not possible with 4D. Want to see venous outflow without the overlying nidus, again not possible. With a short bolus and steriography at a high frame-rate however, the components of the in-flow, fistula and outflow of any arteriovenous disease involving shunting can be separated to some extent into its component parts. There are advantages of a 4D acquisition- namely a 3D data. set that can be post processed and manipulated.