Evaluation of middle cerebral artery stents using multidetector row CT angiography in vivo study: comparison of the three different kernels

Application of High-Resolution Flat Detector Computed Tomography in Stent Implantation for Intracranial Atherosclerotic Stenosis

Objective

To evaluate the utility of high-resolution flat-detector computed tomography (HR-FDCT) compared with conventional flat-detector computed tomography (FDCT) for stent placement in symptomatic intracranial atherosclerotic stenosis (ICAS).

Methods

We retrospectively reviewed the clinical data of 116 patients with symptomatic ICAS who underwent stent implantation. Images were acquired using conventional FDCT [voxel size = 0.43 mm (isotropic)] and HR-FDCT [voxel size = 0.15 mm (isotropic)]. Immediately after stent deployment, dual-volume three-dimensional (3D) fusion images were obtained from 3D digital subtraction angiography (DSA) and HR-FDCT. The image quality for stent visualization was graded from 0 to 2 (0: not able to assess; 1: limited, but able to assess; 2: clear visualization), and the stent-expansion status (“full,” “under-expanded” or “poor apposition”) was recorded.

Results

A total of 116 patients with symptomatic ICAS were treated successfully using 116 stents (58 Neuroform^TM EZ, 42 Enterprise^TM, and 16 Apollo^TM). The mean pre-stent stenosis was 80.5 ± 6.4%, which improved to 20.8 ± 6.9% after stenting. Compared with FDCT, HR-FDCT improved visualization of the fine structures of the stent to improve the image quality that significantly (mean score: 1.63 ± 0.60 vs. 0.41 ± 0.59, P < 0.001). In 19 patients, stent under-expansion (n = 11) or poor apposition (n = 8) was identified by HR-FDCT but not by conventional FDCT. After balloon dilatation, stent malapposition was shown to have improved on HR-FDCT. None of the 19 patients with stent malapposition experienced short-term complications during hospitalization or had in-stent stenosis at 6-month follow-up.

Conclusion

High-resolution flat-detector computed tomography (HR-FDCT) improves visualization of the fine structures of intracranial stents deployed for symptomatic ICAS compared with that visualized using conventional FDCT. High-resolution flat-detector computed tomography improves assessment of stent deployment and could reduce the risk of complications.

Effects of kernel and window setting combinations on assessments of small and complicated vasculature in computed tomography angiographic images of dogs with and without tumors

OBJECTIVE

To evaluate the effect of kernel and window settings on the assessment of small and complicated vasculature in CT angiographic (CTA) images of kidneys, jejunum with mesentery, and tumors in dogs.

ANIMALS

20 healthy dogs and 20 dogs with tumors.

PROCEDURES

Images from CTA performed previously in dogs were reconstructed with 3 different combinations of kernel and window settings (soft kernel with soft tissue window, soft kernel with bone window, and sharp kernel with bone window), and reconstructed images of the left kidney and the jejunum with the mesentery in healthy dogs and tumors in affected dogs were evaluated by reviewers blinded to the settings.

RESULTS

For images of kidney and jejunum with mesentery, reviewers' scores for the conspicuity of vascularity in the arterial phase and the differentiation of the organs from the adjacent structures were significantly higher when viewed in bone window (vs soft tissue window) regardless of kernel setting. For images of head and gastrointestinal tumors, reviewers' scores for differentiation of intratumoral vasculature were higher when viewed in sharp kernel with bone window versus other setting combinations. However, the conspicuity of gastrointestinal, hepatic, or splenic tumoral vessels from the adjacent structures had higher reviewer scores for images in soft kernel with soft tissue window, compared with other setting combinations.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that reconstruction of CTA images with sharp kernel combined with bone window settings might have clinical utility in evaluating and planning treatments for dogs with various tumors; however, additional research is warranted to further identify effects of various kernel and window setting combinations on assessments of small and complicated vasculature in larger and more diverse populations of dogs with and without tumors.

Flat detector CT and its applications in the endovascular treatment of wide-necked intracranial aneurysms-A literature review

Flat detector CT (FDCT) provides cross sectional imaging within an angiographic suite and is increasingly gaining popularity in various areas of interventional radiology, as an alternative imaging modality. Its relatively high spatial resolution improves visualization of intraluminal devices such as intracranial stents or flow-diverters. Device deployment and positioning, in relation to the parent vessel and surrounding structures, are easily assessible with FDCT. Furthermore, with contrast agent administration, it expands the diagnostic capabilities of this new imaging tool. However, beam-hardening artifacts is a major limitation in some cases. The examination can be performed both during the endovascular procedure and for pre- and post-treatment imaging. Intravenous contrast agent injection reduces the risk of complications, making it possible to perform this examination in the outpatient settings. The aim of this paper is to present an overview of published studies reporting experience with FDCT in the field of endovascular neurosurgery and in particular, FDCT's contribution in treatment of wide-necked intracranial aneurysms. The authors have focused specifically on stent-assisted coiling and flow-diverter implantation, since obtaining proper parent vessel wall apposition of these devices is essential for short- and long-term procedural outcomes.

Coronary Stent Artifact Reduction with an Edge-Enhancing Reconstruction Kernel - A Prospective Cross-Sectional Study with 256-Slice CT

Purpose

Metallic artifacts can result in an artificial thickening of the coronary stent wall which can significantly impair computed tomography (CT) imaging in patients with coronary stents. The objective of this study is to assess in vivo visualization of coronary stent wall and lumen with an edge-enhancing CT reconstruction kernel, as compared to a standard kernel.

Methods

This is a prospective cross-sectional study involving the assessment of 71 coronary stents (24 patients), with blinded observers. After 256-slice CT angiography, image reconstruction was done with medium-smooth and edge-enhancing kernels. Stent wall thickness was measured with both orthogonal and circumference methods, averaging thickness from diameter and circumference measurements, respectively. Image quality was assessed quantitatively using objective parameters (noise, signal to noise (SNR) and contrast to noise (CNR) ratios), as well as visually using a 5-point Likert scale.

Results

Stent wall thickness was decreased with the edge-enhancing kernel in comparison to the standard kernel, either with the orthogonal (0.97 ± 0.02 versus 1.09 ± 0.03 mm, respectively; p<0.001) or the circumference method (1.13 ± 0.02 versus 1.21 ± 0.02 mm, respectively; p = 0.001). The edge-enhancing kernel generated less overestimation from nominal thickness compared to the standard kernel, both with the orthogonal (0.89 ± 0.19 versus 1.00 ± 0.26 mm, respectively; p<0.001) and the circumference (1.06 ± 0.26 versus 1.13 ± 0.31 mm, respectively; p = 0.005) methods. The edge-enhancing kernel was associated with lower SNR and CNR, as well as higher background noise (all p < 0.001), in comparison to the medium-smooth kernel. Stent visual scores were higher with the edge-enhancing kernel (p<0.001).

Conclusion

In vivo 256-slice CT assessment of coronary stents shows that the edge-enhancing CT reconstruction kernel generates thinner stent walls, less overestimation from nominal thickness, and better image quality scores than the standard kernel.

Influence of different reconstruction parameters in the visualization of intracranial stents using C-arm flat panel CT angiography: experience in an animal model

BACKGROUND

C-arm flat panel computed tomography angiography (CA-CTA) is a relatively new imaging modality. Consequently, knowledge about postprocessing parameters and their influence on image quality is still limited, especially for the visualization of implanted microstents.

PURPOSE

To optimize reconstruction parameters by evaluating the influence of these different parameters for CA-CTA visualization of microstents in an animal model.

MATERIAL AND METHODS

Eleven microstents were implanted within the left common carotid artery of 11 New Zealand white rabbits. Both CA-CTA, using intra-venous delivery of contrast material, and conventional digital subtraction angiography (DSA) was performed. CA-CTA datasets were reconstructed using three different image characteristics (normal, sharp, smooth). Two experienced neuroradiologists evaluated the image quality and performed measurements of inner and outer stent diameters as well as measurements of the lumen area.

RESULTS

Stent deployment was performed successfully in all animals. Inter-observer correlation coefficient for all measurements was high (r = 0.87-0.92). Lumen area and inner stent diameter were significantly smaller in image characteristic "smooth" (P < 0.01) than in "sharp" and "normal". Outer stent diameter was larger in "smooth" than in "sharp" and "normal" (P < 0.01). Stent strut size was significantly wider using image characteristic "smooth". "Sharp" and "normal" compared best to DSA, with "sharp" providing the closest match to DSA measurements, with the trade-off of significantly more noise than in the "normal" reconstructions.

CONCLUSION

The use of different image characteristics in the postprocessing of CA-CTA datasets has an influence on the visualization of implanted stents. Image characteristic "sharp" and "normal" compared best to DSA.

Intra-arterial DynaCT angiography: an alternative tool to assess the patency of intracranial stent lumen

OBJECTIVE

The aim of this retrospective study was to assess the clinical utility of intra-arterial DynaCT angiographic imaging for the evaluation of intracranial stent patency.

METHODS

Between July 2011 and May 2014, 35 patients with symptomatic intracranial atherosclerotic stenosis (ICAS) were treated with percutaneous transluminal angioplasty and stents. All were evaluated with intra-arterial DynaCT angiographic imaging during the operations and follow-up. All images were further processed with three different kernels (sharp, normal, or smooth).

RESULTS

Thirty-six stents were implanted into the parent arteries. DynaCT provided "good" quality images (median score of 2 or 3 on a 5-point scale) with minimal artifact interference as rated by observers blind to treatment history and other imaging results. The median subjective visibility score was highest (3) using the sharp kernel.

CONCLUSIONS

DynaCT with sharp kernel image processing achieved good visualization of luminal patency following intracranial stents.