Spiral CT Angiography with Digital Subtraction of Extra- and Intracranial Vessels

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Abstract
A new imaging modality is presented in which a digital subtraction algorithm is applied to spiral CT angiography of extra- and intracranial vessels. Spiral CT angiography was carried out in 26 patients. When this was done for stereotactic purpose before radiosurgery, a Leksell stereotactic frame was used; in the other cases an atraumatic fixation system was applied. Spiral CT data were acquired twice--before and after contrast agent administration. Then, computerized subtraction of the density values of plain CT from the topographically corresponding enhanced CT was performed. Maximum intensity projection was used to visualize the vessels. This method provided significant effacement of nonvascular structures and a considerably improved visualization of extracranial as well as intracranial vessels could be achieved. In some conditions, e.g., to exclude a suspected thrombotic occlusion of the basilar artery, conventional angiography could even be omitted. Adequate visualization of extra- and intracranial vessels is possible with spiral CT angiography and digital subtraction. An important scope of this modality could be its contribution to radiosurgical planning and the follow-up after radiotherapy. In some conditions, CT subtraction angiography may possibly supersede conventional subtraction angiography.

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