Imaging
Bone-free 3D Computed Tomography Angiography Using an Image-processing Application – Imaging Efficacy for Aneurysms Near the Skull Base and Clipped Cerebral Aneurysms
Noriaki Tomura,1 Makoto Koga,2 Takahiro Otani,3 Toshiaki Nishii4 and Satoshi Takahashi5
1. Associate Professor of Radiology, and Chief of Neuroradiology; 2. Research Associate in Radiology; 3. Assistant Professor of Radiology; 4. Research Associate in Radiology; 5. Lecturer in Radiology, Akita University School of Medicine
Abstract
Bone-free 3D computed tomography angiography (CTA) can be carried out to image cerebral aneurysms near the skull base when the elimination of bones is surgically required. The maximum intensity projection (MIP) images were initially obtained using the application. Further post-processing was performed to obtain the MIP and volume-rendering (VR) images. This technique did not increase radiation exposure to patients, and remnant bones in the initial MIP images automatically acquired by the application for bone elimination could be easily removed through post-processing. Although parts of vessels were sometimes removed from the image along with the bones, these could be quickly and easily recovered through post-processing. Thus, bone-free 3D CTA and conventional 3D CTA are complementary tools for imaging cerebral aneurysms near the skull base prior to surgery. This application could also eliminate clips in cases of clipped cerebral aneurysms, and it could improve the accuracy of detecting remnant necks after clipping surgery.
Keywords Computed tomography angiography (CTA), cerebral aneurysm, skull base, bone-free CTA, clipping surgery
Disclosure: The authors have no conflicts of interest to declare. Received: 18 June 2009 Accepted: 23 March 2010 Citation: European Neurological Review, 2010;5(1):103–6 Correspondence: Noriaki Tomura, Hospi-net Center, 6-1, Hiroomote Kawasaki, Akita City, Akita, 010-0041, Japan. E:
tomura@cna.ne.jp
3D computed tomography angiography (3D CTA) is used to image cerebral aneurysms, steno-occlusive lesion of cerebral vessels and brain tumours. 3D CTA has become the accepted alternative to conventional intra-arterial digital subtraction angiography (IADSA) for imaging and detection of aneurysms1–5
and planning treatment.
Multidetector (MD) CT allows a more precise evaluation of aneurysms with a shorter scanning time6
and better spatial resolution. Bony
structures often disturb 3D CTA images near the skull base, and thus as a vessel-extraction technique, on the basis of the CT image registration, the subtraction of CT images of bony structures from CTA images has been developed;7–14
however, there are some limitations to
this technique. For instance, subtle misregistration between the two CT images causes bone fractions in the subtracted images. More importantly, the two CT scans required for the technique expose the patient to two doses of radiation.
We also evaluated the efficacy of this technique in eliminating clip images in patients with clipped cerebral aneurysms.
In an effort to address these concerns, a new image-processing application to eliminate bony structures and clipped cerebral aneurysms has been developed. This application has already been used for 3D CTA in patients with cerebral aneurysms near the skull base, and the efficacy of 3D CTA using this application for bone elimination has been evaluated.15
Aneurysms
The cerebral aneurysms evaluated before surgery were determined to be located at the junction of the internal carotid artery (ICA) and the posterior communicating artery (IC–PC aneurysm), at the
© TOUCH BRIEFINGS 2010 Computed Tomography Scanning
At our hospital, CT was performed with 64 (GE Healthcare, LightSpeed VCT, Milwaukee, WI) or 32 detector rows (GE Healthcare, LightSpeed Pro 32), 120kV, Z-axis automatic tube current modulation (AutomA) (≤600mA), a 0.625mm-section thickness, a field of view (FOV) of 25cm and a scanning time of 0.4 seconds per rotation. The scan range per rotation was 20mm (LightSpeed Pro 32) or 40mm (LightSpeed VCT). Non- ionic contrast medium (350 or 370mgI/ml) was injected using a power injector via a 20-gauge needle in the antecubital vein using a test- injection technique16
or an automatic trigger system. As a test injection, 10ml of contrast medium was injected at a rate of 4ml/second. A reference slice was used to monitor a region of interest in the cervical portion of the ICA to detect the arrival of contrast medium after injection. The proper delay was determined and the right or left common carotid artery was used as the reference point for the automatic trigger system. Acquisition of images started following the appropriate delay after injection of contrast medium. A total of 50ml
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paraclinoid part of the ICA (paraclinoid aneurysm), at the junction of the ICA and the anterior choroid artery (Acho aneurysm), at the cavernous segment of the ICA (cavernous aneurysm), at the junction of the ICA and the ophthalmic artery (IC-oph aneurysm), at the terminal portion of the ICA (IC terminal aneurysm) and at the basilar tip (basilar tip aneurysm). The cerebral clipped aneurysms evaluated were IC–PC aneurysms, paraclinoid aneurysms, aneurysms at the anterior communication arteries (AcomAs), aneurysms at the middle cerebral arteries (MCAs), basilar tip aneurysms and aneurysms at the vertebral artery (VA). All of these were clipped using titanium clips.
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