The bony structure in the skull base imposes many difficulties for diagnostic CT angiography. Vendors and software manufacturers have devised various methods to overcome this limitation. Research presented at the European Congress of Radiology in Vienna in March found two prototype bone removal programs to be fast and reliable.

The first technique, an automatic bone removal method, uses high-resolution thin-cut CT images with contrast injection and a multithreshold-based, multistep region growth technique. Dr. Joel D. Neuman and colleagues from the U.S., Europe, and Asia evaluated 40 clinical cases of cerebral vascular CTA covering the circle of Willis and skull base on four-slice scanners.

The technique effectively removed the whole skull and most of the bones in a single mouse click, enabling neuroradiologists to successfully detect aneurysms and their feeding vessels, and the presence of vascular thrombosis, said Neuman, section chief of noninvasive vascular imaging at Easton Hospital in Easton, PA.

The second method, a bone-masking technique, uses coregistration of contrast images with low-dose noncontrast images, requiring no fiduciary markers. Bones are then subtracted. In 30 cases, the technique showed superior ability to remove bones in the area of the skull base, including the clivus, and to detect aneurysms and arterial occlusions, Neuman said. Additionally, carotid arteries very close to the bones were well displayed.

The automatic bone removal technique runs about one minute per case, while the second technique runs approximately 2.5 minutes.