Pseudostenosis phenomenon at volume-rendered three-dimensional digital angiography of intracranial arteries: frequency, location, and effect on image evaluation.

Purpose: To assess the frequency, location, and effect on image interpretation of a pseudostenosis phenomenon at volume-rendered three-dimensional (3D) digital angiography for evaluation of intracranial arteries and to determine the physical characteristics of the phenomenon by using a phantom.

Materials And Methods: Results of a total of 68 volume-rendered 3D digital angiographic examinations in 56 patients with intracranial aneurysms were retrospectively evaluated in comparison with results of digital subtraction angiography regarding the appearance of a pseudostenosis phenomenon. The phenomenon was analyzed by two radiologists in consensus with regard to frequency, location, percentage stenosis, and angle between the axis of the vessel with pseudostenosis and the axis of rotational angiography. The phenomenon's effect on aneurysm evaluation was also analyzed. For assessing the physical properties of the phenomenon, a phantom study was performed with different lengths of tubing and different angles to the axis of rotational angiography.

Results: The pseudostenosis was observed at 23 (34%) of 68 3D digital angiographic examinations and in 53 (5%) of 1161 segments. The percentage stenosis ranged from 3% to 85% (mean, 18% +/- 16.2 [standard deviation]). The arterial segments with pseudostenosis included 15 (25%) of 61 C6 segments, 10 (16%) of 61 M1 segments, and six (10%) of 60 A1 segments. Angles between the two axes ranged from 86 degrees to 93 degrees (mean angle, 90 degrees +/- 1.6). Pseudostenosis affected delineation of the shape and size of two middle cerebral artery aneurysms. At phantom analysis, the phenomenon was most obvious at an angle of 90 degrees and with the longest phantom.

Conclusion: The pseudostenosis phenomenon on volume-rendered 3D digital angiograms was relatively frequently observed in some segments of the intracranial arteries and affected the delineation of middle cerebral artery aneurysms. This phenomenon was associated with the angle to the axis of rotational angiography and the length of the vessel.