Intracranial aneurysm segmentation in 3D CT angiography: method and quantitative validation with and without prior noise filtering.

Intracranial aneurysm volume and shape are important factors for predicting rupture risk, for pre-surgical planning and for follow-up studies. To obtain these parameters, manual segmentation can be employed; however, this is a tedious procedure, which is prone to inter- and intra-observer variability. Therefore there is a need for an automated method, which is accurate, reproducible and reliable. This study aims to develop and validate an automated method for segmenting intracranial aneurysms in Computed Tomography Angiography (CTA) data. Also, it is investigated whether prior smoothing improves segmentation robustness and accuracy. The proposed segmentation method is implemented in the level set framework, more specifically Geodesic Active Surfaces, in which a surface is evolved to capture the aneurysmal wall via an energy minimization approach. The energy term is composed of three different image features, namely; intensity, gradient magnitude and intensity variance. The method requires minimal user interaction, i.e. a single seed point inside the aneurysm needs to be placed, based on which image intensity statistics of the aneurysm are derived and used in defining the energy term. The method has been evaluated on 15 aneurysms in 11 CTA data sets by comparing the results to manual segmentations performed by two expert radiologists. Evaluation measures were Similarity Index, Average Surface Distance and Volume Difference. The results show that the automated aneurysm segmentation method is reproducible, and performs in the range of inter-observer variability in terms of accuracy. Smoothing by nonlinear diffusion with appropriate parameter settings prior to segmentation, slightly improves segmentation accuracy.

Diffusion-weighted imaging to compare different cerebral protection devices in carotid artery stenting.

AIMS: Carotid artery stenting (CAS) is commonly performed with cerebral protection devices. New hyperintense lesions on diffusion-weighted MR imaging (DWI) were used to compare different cerebral protection devices. METHODS AND RESULTS: Patients (n=33) with high-grade symptomatic carotid stenosis were treated with CAS. Two different methods of cerebral embolic protection were used. In 23 patients, a filter device was placed in the distal internal carotid artery. In 10 patients a protection system based on the reversed-flow principle was used. DWI was performed before and after CAS. The number and volume of new hyperintense lesions in the ipsilateral hemisphere were assessed.No stroke or death was recorded. Twenty-three new hyperintense lesions in the ipsilateral cerebral hemisphere were recorded on the post-treatment DWI-series after stent placement in 12 of the 33 procedures (36%). In 8 of the 23 procedures (35%) performed with a filter device and in 4 of the 10 procedures (40%) performed with the reversed-flow device new hyperintense lesions were revealed (13 and 10, respectively). No significant differences were found in the number of lesions and lesion load. The volume per lesion was significantly smaller in the patient group treated with reversed-flow device in comparison to the patient group treated with a filter device (median 0,048 mm3 and 0,013 mm3, respectively; p=0.03). CONCLUSION: This non-randomised study revealed no difference in new subclinical ischaemic lesions in the ipsilateral hemisphere between procedures performed with filter devices and procedures performed with embolic protection using the reversed-flow principle.