Small vessel stents for intracranial angioplasty: in vitro evaluation of in-stent stenoses using CT angiography

Multiple predictors of in-stent restenosis after stent implantation in symptomatic intracranial atherosclerotic stenosis

OBJECTIVE

This study aimed to identify predictors of intracranial in-stent restenosis (ISR) after stent placement in symptomatic intracranial atherosclerotic stenosis (ICAS).

METHODS

The authors retrospectively collected data from consecutive patients who suffered from symptomatic ICAS and underwent successful stent placement in Beijing Tiantan hospital. Eligible patients were classified into "ISR," "indeterminate ISR," or "no-ISR" groups by follow-up digital subtraction angiography or CT angiography. A multivariate logistic regression model was used to explore the predictors of intracranial ISR after adjustments for age and sex. In addition, ISR and no-ISR patients were divided into two groups based on the strongest predictor, and the incidence of ISR, recurrent stroke, and symptomatic ISR was compared between the two groups.

RESULTS

A total of 511 eligible patients were included in the study: 80 ISR, 232 indeterminate ISR, and 199 no-ISR patients. Elevated high-sensitivity C-reactive protein (hs-CRP; odds ratio [OR] 4.747, 95% confidence interval [CI] 2.253-10.01, p < 0.001), Mori type B and C (Mori type B vs Mori type A, OR 3.119, 95% CI 1.093-8.896, p = 0.033; Mori type C vs Mori type A, OR 4.780, 95% CI 1.244-18.37, p = 0.023), coronary artery disease (CAD; OR 2.721, 95% CI 1.192-6.212, p = 0.017), neutrophil/lymphocyte ratio (NLR; OR 1.474 95% CI 1.064-2.042, p = 0.020), residual stenosis (OR 1.050, 95% CI 1.022-1.080, p = 0.001) and concurrent intracranial tandem stenosis (OR 2.276, 95% CI 1.039-4.986, p = 0.040) synergistically contributed to the occurrence of intracranial ISR. Elevated hs-CRP (hs-CRP ≥ 3 mg/L) was the strongest predictor for ISR, and the incidence of ISR in the elevated hs-CRP group and normal hs-CRP group (hs-CRP < 3 mg/L) was 57.14% versus 21.52%, respectively, with recurrent stroke 44.64% versus 16.59%, and symptomatic ISR 41.07% versus 8.52%.

CONCLUSIONS

Elevated hs-CRP level, NLR, residual stenosis, Mori type B and C, CAD, and concurrent intracranial tandem stenosis are the main predictors of intracranial ISR, and elevated hs-CRP is crucially associated with recurrent stroke in patients with symptomatic ICAS after intracranial stent implantation.

New technique: the use of the THRIVE sequence in the follow-up of patients who received endovascular intracranial aneurysm treatment

PURPOSE

To determine the diagnostic accuracy of 3D time of flight MR angiography (TOF-MRA), contrast enhanced MR angiography (CE-MRA), and T1-weighted high-resolution isotropic volume examination (THRIVE) at 3 T for the evaluation of intracranial aneurysm occlusion after endovascular treatment and to evaluate the usability of the THRIVE sequence in endovascular treatment follow-up.

METHODS

In 3 T MR follow-up examinations of 66 aneurysms in 50 patients treated endovascularly, 3D TOF-MRA (index test), THRIVE (index test), and CE-MRA (reference standard) examinations were performed in a retrospective consecutive case series. Source images were classified as class 1, class 2, and class 3 according to the Raymond criteria using MIP (maximum intensity projection) techniques. The compatibility between sequences was evaluated with the Kappa test. The sensitivity and specificity were also calculated.

RESULTS

In the evaluation of THRIVE and CE-MRA sequences, compatibility was determined in 61 cases in total, with an overall fit of 61/66 (92.42%). A statistically significant correlation was found between THRIVE and CE-MRA (p < 0.001, κ = 0.800). In the evaluation of TOF and CE-MRA sequences, compatibility was determined in 54 cases in total, and the overall fit was 54/66 (81.8%). A statistically significant agreement was found between TOF and CE-MRA (p < 0.001, κ = 0.502). Assuming that CE-MRA is a reference standard, the sensitivity and specificity of the TOF sequence were 44.4% and 97.9%, respectively, and the sensitivity and specificity of the THRIVE sequence were 77.8% and 97.9%, respectively.

CONCLUSION

The THRIVE sequence can be used as a noncontrast method for monitoring endovascularly treated intracranial aneurysms.

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.

Clinical Utility of Angiographic CT with a Flat-detector Angiographic System during Endovascular Procedure

OBJECTIVE

We evaluated the feasibility of angiographic computed tomography (ACT) for visualizing stent material in patients who underwent intracranial or extracranial stent placement to treat atherosclerotic lesions or stent assisted coil embolization.

MATERIALS AND METHODS

We performed intrarterial and intravenous ACT on biplane angiography system equipped with flat panel detectors (Axiom Arits dBA; Siemens Medical Solutions, Forchheim, Germany). Vistipaque 320 was injected for contrast medium, total 150 mL at flow rate of 5 mL/s through artery and 77 mL at flow rate of 3.5 mL/s through vein.

RESULTS

ACT is a new imaging modality that provides a clear visualization of stent strut.

CONCLUSION

Therefore this new application has potential to become the noninvasive option for follow-up after endovascular surgery using stents.

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.

Spectral Imaging for Intracranial Stents and Stent Lumen

Introduction

Application of computed tomography for monitoring intracranial stents is limited because of stent-related artifacts. Our purpose was to evaluate the effect of gemstone spectral imaging on the intracranial stent and stent lumen.

Materials and Methods

In vitro, we scanned Enterprise stent phantom and a stent–cheese complex using the gemstone spectral imaging protocol. Follow-up gemstone spectral images of 15 consecutive patients with placement of Enterprise from January 2013 to September 2014 were also retrospectively reviewed. We used 70-keV, 140-keV, iodine (water), iodine (calcium), and iodine (hydroxyapatite) images to evaluate their effect on the intracranial stent and stent lumen. Two regions of interest were individually placed in stent lumen and adjacent brain tissue. Contrast-to-noise ratio was measured to determine image quality. The maximal diameter of stent markers was also measured to evaluate stent-related artifact. Two radiologists independently graded the visibility of the lumen at the maker location by using a 4-point scale. The mean of grading score, contrast/noise ratio and maximal diameter of stent markers were compared among all modes. All results were analyzed by SPSS version 20.

Results

In vitro, iodine (water) images decreased metallic artifact of stent makers to the greatest degree. The most areas of cheese were observed on iodine (water) images. In vivo, iodine (water) images had the smallest average diameter of stent markers (0.33 ± 0.17mm; P < .05) and showed the highest mean grading score (2.94 ± 0.94; P < .05) and contrast/noise ratio of in-stent lumen (160.03 ±37.79; P < .05) among all the modes.

Conclusion

Iodine (water) images can help reduce stent-related artifacts of Enterprise and enhance contrast of in-stent lumen. Spectral imaging may be considered a noninvasive modality for following-up patients with in-stent stenosis.

Flat-detector computed tomography evaluation in an experimental animal aneurysm model after endovascular treatment: A pilot study

We compared flat-detector computed tomography angiography (FD-CTA) to multislice computed tomography (MS-CTA) and digital subtracted angiography (DSA) for the visualization of experimental aneurysms treated with stents, coils or a combination of both.In 20 rabbits, aneurysms were created using the rabbit elastase aneurysm model. Seven aneurysms were treated with coils, seven with coils and stents, and six with self-expandable stents alone. Imaging was performed by DSA, MS-CTA and FD-CTA immediately after treatment. Multiplanar reconstruction (MPR) was performed and two experienced reviewers compared aneurysm/coil package size, aneurysm occlusion, stent diameters and artifacts for each modality.In aneurysms treated with stents alone, the visualization of the aneurysms was identical in all three imaging modalities. Residual aneurysm perfusion was present in two cases and visible in DSA and FD-CTA but not in MS-CTA. The diameter of coil-packages was overestimated in MS-CT by 56% and only by 16% in FD-CTA compared to DSA (p < 0.05). The diameter of stents was identical for DSA and FD-CTA and was significantly overestimated in MS-CTA (p < 0.05). Beam/metal hardening artifacts impaired image quality more severely in MS-CTA compared to FD-CTA.MS-CTA is impaired by blooming and beam/metal hardening artifacts in the visualization of implanted devices. There was no significant difference between measurements made with noninvasive FD-CTA compared to gold standard of DSA after stenting and after coiling/stent-assisted coiling of aneurysms. FD-CTA may be considered as a non-invasive alternative to the gold standard 2D DSA in selected patients that require follow up imaging after stenting.

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.

The effectiveness of 3T time-of-flight magnetic resonance angiography for follow-up evaluations after the stent-assisted coil embolization of cerebral aneurysms

BACKGROUND

Artifacts introduced by stents limit the value of magnetic resonance (MR) imaging as a follow-up modality after the stent-assisted coil embolization of cerebral aneurysms.

PURPOSE

To investigate the usefulness of 3 Tesla (3T) time-of-flight (TOF) MR angiography (MRA) for the follow-up evaluation.

MATERIAL AND METHODS

Twenty-two aneurysms of 20 patients treated with stent-assisted coil embolization were followed up with 3T TOF MRA and digital subtraction angiography (DSA) with three-dimensional rotational angiography (3DRA). The status of coiled aneurysms was compared with 3T TOF MRA and DSA with 3DRA in terms of complete occlusion, residual neck, and residual aneurysm. TOF MRA at 3T was performed 1 day before DSA with 3DRA, with a mean follow-up period of 20.1 ± 10.8 months.

RESULTS

Twenty (90.9%) of 22 cases were concordant between the two modalities. The degree of agreement and correlation between them were high (κ=0.771, P<0.001; r=0.832 and P<0.001). When evaluating the status of residual neck, the sensitivity was 80% (4/5 cases); specificity was not available because there were no cases of complete occlusion. For the status of residual aneurysm, the sensitivity and specificity were 94.1% (16/17 cases) and 100% (all 5 cases), respectively.

CONCLUSION

TOF MRA at 3T with source images could be useful as a non-invasive follow-up modality after the stent-assisted coil embolization of cerebral aneurysms. Further study with a larger patient sample is needed to confirm the effectiveness of 3T TOF MRA.

Quantitative analysis of high-resolution, contrast-enhanced, cone-beam CT for the detection of intracranial in-stent hyperplasia

BACKGROUND

Intracranial in-stent hyperplasia is a stroke-associated complication that requires routine surveillance.

OBJECTIVE

To compare the results of in vivo experiments to determine the accuracy and precision of in-stent hyperplasia measurements obtained with modified C-arm contrast-enhanced, cone-beam CT (CE-CBCT) imaging with those obtained by 'gold standard' histomorphometry. Additionally, to carry out clinical analyses comparing this CE-CBCT protocol with digital subtraction angiography (DSA).

METHODS

A non-binned CE-CBCT protocol (VasoCT) was used that acquires x-ray images with a small field-of-view and applies a full-scale reconstruction algorithm providing high-resolution three-dimensional (3D) imaging with 100 µm isotropic voxels. In an vivo porcine model, VasoCT cross-sectional area measurements were compared with gold standard vessel histology. VasoCT and DSA were used to calculate in-stent stenosis in 23 imaging studies.

RESULTS

Porcine VasoCT cross-sectional stent, lumen, and in-stent hyperplasia areas strongly correlated with histological measurements (r(2)=0.97, 0.93, 0.90; slope=1.14, 1.07, and 0.76, respectively; p<0.0001). Clinical VasoCT percentage stenosis correlated well with DSA percentage stenosis (r(2)=0.84; slope=0.76), and the two techniques were free of consistent bias (Bland-Altman, bias=3.29%; 95% CI -14.75% to 21.33%). An illustrative clinical case demonstrated the advantages of VasoCT, including 3D capability and non-invasive IV contrast administration, for detection of in-stent hyperplasia.

CONCLUSIONS

C-arm VasoCT is a high-resolution 3D capable imaging technique that has been validated in an animal model for measurement of in-stent tissue growth. Successful clinical implementation of the protocol was performed in a small case series.

Intravenous flat-detector computed tomography angiography for high-grade carotid stenosis

AIM

The significant feature of intravenous flat-detector computed tomography (IV FDCT) angiography is its role in neurointerventional setting without patient transfer. However, few studies have addressed the accuracy of IV FDCT in estimating carotid stenosis and length. This study examined the reliability of IV FDCT in the diagnosis of high-grade carotid stenosis and stenosis length with digital subtraction angiography (DSA) as the reference.

METHODS

Intravenous flat-detector CT and DSA were conducted simultaneously for 33 patients with 42 stenosed carotid arteries who were suspected of having symptomatic high-grade stenosis by carotid duplex ultrasound, magnetic resonance angiography, or CT angiography. The degree of stenosis and length discrepancy between 2 tests were recorded by 2 readers.

RESULTS

The intraobserver and interobserver agreements were excellent for measuring high-grade carotid stenosis (κ = 0.87 and 0.82). Intravenous flat-detector CT had a sensitivity of 96.3%, specificity of 93.3%, and negative predictive value of 93.3% for detecting high-grade stenosis (≥70%) compared with DSA. Bland-Altman plots demonstrated excellent correlation of the degree of stenosis IV FDCT with DSA. Length discrepancy (IV FDCT - DSA, in millimeters) did not differ significantly according to degree of stenosis (Spearman rank test; r = 0.18, P = 0.26).

CONCLUSIONS

Intravenous flat-detector CT can be a feasible and time-saving test for evaluating high-grade carotid stenosis and stenosis length.

Feasibility of intravenous flat panel detector CT angiography for intracranial arterial stenosis

BACKGROUND AND PURPOSE

I.v. FDCT angiography is an emerging technology for the detection of intracranial vascular disease. This study was conducted to determine the feasibility of i.v. FDCT in estimating major atherosclerotic intracranial arterial stenosis with DSA as the reference.

MATERIALS AND METHODS

DSA and i.v. FDCT were performed simultaneously in patients with transient ischemic attack or acute cerebral infarction. The degree and length of stenosis were measured. The stenotic vessels were categorized into 4 groups by the grade of stenosis: normal (<30%), mild (30%-49%), moderate (50%-69%), or severe (>70%). The vessels of the normal group were excluded from analysis to reduce spectrum bias. Measurement of vessels was recorded by using an electric ruler by a qualified endovascular neurosurgeon and a neuroradiologist.

RESULTS

Eight hundred forty-two vessel segments in 69 patients were calculated. Mild (n = 56), moderate (n = 47) and severe stenosis (n = 46) groups were analyzed. I.v. FDCT had a sensitivity of 97.6%, specificity of 96.9%, and negative predictive value of 96.9% for detecting ≥50% stenosis and respective values of 91.9%, 98.2%, and 97.4% for depicting ≥70% stenosis. The difference of stenotic length between the 2 tests was not significant as an increase in the severity of stenosis (Spearman rank correlation test; r = -0.12, P = .13).

CONCLUSIONS

I.v. FDCT can be a feasible alternative as a noninvasive method for evaluating stenosis of the major intracranial arteries.

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

BACKGROUND

There are very few reports assessing middle cerebral artery (MCA) stents using multidetector computed tomography (MDCT).

PURPOSE

To assess MCA stents using multidetector CT angiography (CTA) in vivo evaluation: the differences in the CTA results according to the three different kernels.

MATERIAL AND METHODS

We retrospectively evaluated 27 MCA stents from 26 patients who underwent CTA with 16- and 64-slice MDCT after percutaneous transluminal angioplasty and stenting (PTAS). By CTA, using medium-smooth kernel (B30), medium-sharp kernel (B50), and sharp kernel (B60), the lumen diameter, artificial luminal narrowing (ALN), and subjective visibility score of the stented vessels were evaluated. The subjective visibility score ranged from 1 (poor quality) to 5 (excellent) using a five-point scale.

RESULTS

There were excellent inter-observer agreements for the lumen diameter measurements (P < 0.001). The mean diameter of the stented vessels was 2.10 ± 0.31 mm on digital subtraction angiography (DSA), 0.93 ± 0.20 mm on CTA using B30, 1.18 ± 0.27 mm on CTA using B50, and 1.29 ± 0.29 mm on CTA using B60. The mean ALN was 55.7 ± 6.0% on CTA using B30, 43.8 ± 7.5% on CTA using B50, and 38.7 ± 8.3% on CTA using B60. CTA with higher kernels had a smaller ALN than images with smaller kernels. The median subjective visibility score on the CTA using B50 was 3, which was higher than for the other kernels. The differences in the lumen diameter, ALN, and the subjective visibility score of the stented vessels on CTA using the three different kernels was statistically significant (P < 0.001).

CONCLUSION

The sharp kernel was better to assess the lumen diameter and ALN, but was inferior to the medium-sharp kernel for in-stent evaluation due to high image-to-noise. CTA with medium-sharp kernel showed good lumen visibility and acceptable ALN for MCA stents. This could therefore be a non-invasive, readily applicable clinical method for assessing MCA stent patency after stent placement.

Angiographic CT after intravenous contrast agent application: A noninvasive follow-up tool after intracranial angioplasty and stenting

BACKGROUND AND PURPOSE

ICAS is one of the therapeutic options in symptomatic cerebral artery stenosis. iaDSA is the current criterion standard examination after ICAS for the detection of ISR. In this study, we evaluated ivACT as a potential noninvasive follow-up alternative.

MATERIALS AND METHODS

In 17 cases, ivACT and iaDSA were performed after ICAS. Both procedures were carried out on a flat-panel-detector-equipped angiography system. Postprocessing of ivACT acquisitions was performed on a dedicated workstation producing multiplanar reformations of the stent region and other intracranial arteries. Restenotic lesions were compared with iaDSA measurements. All studies were independently evaluated by 2 experienced neuroradiologists blinded to patients data.

RESULTS

In 5 cases, ISR was diagnosed on iaDSA images. All restenotic lesions were reliably detected (sensitivity, 100%; 95%CI, 48%-100%) and could be correctly quantified on ivACT images in comparison with iaDSA. The neuroradiologists correctly excluded ISR in 11 of 12 lesions after viewing the ivACT examinations (specificity, 92%; 95%CI, 62%-100%). Measurements of ISR on ivACT were highly correlated to iaDSA (Pearson r = 0.94, P < .01).

CONCLUSIONS

IvACT is a promising noninvasive follow-up examination after ICAS. With its high spatial resolution, it can reliably detect or exclude ISR. Contrary to iaDSA, there is no need for a recovery period after ivACT and the risk of neurologic complications is practically lowered to zero.

Assessment of the Intracranial Stents Patency and Re-Stenosis by 16-Slice CT Angiography with Optimized Sharp Kernel : Preliminary Study

OBJECTIVE

Our retrospective study aimed to determine whether 16-slice computerized tomography (CT) angiography optimized sharp kernel is suitable for the evaluation of visibility, luminal patency and re-stenosis of intracranial stents in comparison with conventional angiography.

METHODS

Fifteen patients with symptomatic intracranial stenotic lesions underwent balloon expandable stent deployment of these lesions (10 middle cerebral arteries, 2 intracranial vertebral arteries, and 3 intracranial internal carotid arteries). CT angiography follow-up ranged from 6 to 15 months (mean follow-up, 8 months) after implantation of intracranial stents and conventional angiography was confirmed within 2 days. Curved multiplanar reformations with maximal intensity projection (MIP) with optimal window settings for assessment of lumen of intracranial stents were evaluated for visible lumen diameter, stent patency (contrast distal to the stent as an indirect sign), and re-stenosis by two experienced radiologists who blinded to the reports from the conventional angiography.

RESULTS

All of stents deployed into symptomatic stenotic lesions. All stents were classified as patent and no re-stenosis, which was correlated with results of conventional angiography. Parts of the stent lumen could be visualized in all cases. On average, 57% of the stent lumen diameter was visible using optimized sharp kernel. Significant improvement of lumen visualization (22%, p<0.01) was observed using the optimized sharp kernel compared with the standard sharp kernel. Inter-observer agreements on the measurement of lumen diameter and density were judged as good, respectively (p<0.05).

CONCLUSION

Sixteen-slice CT using the optimized sharp kernel may provide a useful information for evaluation of lumen diameter patency, and re-stenosis of intracranial stents.

Flat panel detector angiographic CT for stent-assisted coil embolization of broad-based cerebral aneurysms

BACKGROUND AND PURPOSE

The purpose of this work was to evaluate angiographic CT (ACT) in the combined application of a self-expanding neurovascular stent and detachable platinum coils in the management of broad-based and fusiform intracranial aneurysms.

MATERIALS AND METHODS

Eleven patients harboring wide-necked intracranial aneurysms were treated with a flexible self-expanding neurovascular stent and subsequent aneurysm embolization with platinum microcoils. ACT was performed after the interventional procedure to analyze stent position and the relationship of coils to the stent. Postprocessing included multiplanar reconstructions (MPRs) and maximum intensity projections (MIPs). ACT volume datasets were postprocessed for soft tissue visualization.

RESULTS

Accurate stent placement with subsequent coil occlusion of the aneurysms was feasible in all of the patients. Similar to nonsubtracted digital subtraction angiography (DSA) images, radiopaque platinum stent markers showed excellent visibility in ACT as well. The stent struts themselves, hardly visible in nonsubtracted DSA, were visible in MPRs and MIPs of ACT in all of the patients. In aneurysms larger than 10 mm in diameter, accurate stent assessment at the level of the coils was limited due to beam hardening artifacts. Postprocedural ACT in all of the patients did not reveal any evidence of procedure-related intracranial hemorrhage.

CONCLUSION

ACT provides cross-sectional, 3D visualization of endovascular stents otherwise hardly visible with plain fluoroscopy. ACT enables us to accurately determine stent position, which may be helpful in complex stent-assisted aneurysm coiling procedures. However, in aneurysms larger than 10 mm in diameter, beam hardening artifacts caused by the endoaneurysmal coil package impair visibility of the stent. Further data are necessary to evaluate the usefulness of ACT in stent-assisted aneurysm coiling.

CT angiographic appearance of in-stent restenosis of intracranial arteries treated with the Wingspan stent

Four patients underwent angioplasty and stenting of medically refractory symptomatic intracranial atherosclerosis with the new Wingspan stent system. In all 4 patients, CT angiography (CTA) showed an abnormality within the stented segment that was suggestive of nonocclusive in-stent thrombus. However, subsequent conventional angiography findings were typical for in-stent restenosis. The CTA imaging features of in-stent restenosis are important to recognize, and the misinterpretation of in-stent restenosis as in-stent thrombus may result in inappropriate management.

Intracranial aneurysm stenting: follow-up with MR angiography

Intracranial stenting is increasingly being used to treat intracranial aneurysms and stenoses. We wanted to assess the utility of magnetic resonance angiography (MRA) in the follow-up of patients treated with various types of intracranial stents and to assess the utility of performing gadolinium-enhanced MRA. A total of 19 patients having undergone intracranial stenting for aneurysms were imaged by MRI at 1.5T. A total of 20 stents were placed in 19 patients. In addition to conventional T2- and diffusion-weighted MRI, 3D time-of-flight MRA was performed before and after contrast administration. In the case of metallic INX stents (N = 7), there was a signal drop at the level of the vessel. which did not allow to evaluating the parent vessel, whereas this was visible in Nitinol stents (N = 8). Additionally a stent with a wire had a small artifact (N = 3). Contrast administration also improved vessel lumen visualization. In the case of Nitinol stents, MRA can be used to reliably demonstrate the vessel lumen after intracranial stenting. The use of postcontrast 3D time-of-flight imaging helps improve the intraluminal definition.

64- Versus 16-slice CT angiography for coronary artery stent assessment: in vitro experience

OBJECTIVES

We sought to assess the visualization of different coronary artery stents and the delineation of in-stent stenoses using 64- and 16-slice multidector computed tomography (MDCT).

MATERIALS AND METHODS

A total of 15 different coronary stents with a simulated in-stent stenosis were placed in a vascular phantom and scanned with a 16-slice and a 64-slice MDCT at orientations of 0 degree, 45 degrees, and 90 degrees relative to the scanner's z-axis. Visible lumen diameter and attenuation in the stented and the unstented segment of the phantom were measured. Three readers assessed stenosis delineation and visualization of the residual lumen using a 5-point scale.

RESULTS

Artificial lumen narrowing (ALN) was significantly reduced with 64-slice CT compared with 16-slice CT. At an angle of 0 degree, 45 degrees, and 90 degrees relative to the scanner's z-axis, the ALN for 16-slice CT was 42.2%, 39.8%, and 44.0% using a slice-thickness of 1.0 mm and 40.9%, 40.4%, and 41.6% using a slice thickness of 0.75 mm, respectively. With 64-slice CT, the ALN was 39.1%, 37.3%, and 36.0% at the respective angles. The differences between attenuation values in the stented and unstented segment of the tube were significantly lower for 64-slice CT. Mean visibility scores were significantly higher for 64-slice CT.

CONCLUSION

Use of the 64-slice CT results in superior visualization of the stent lumen and in-stent stenosis compared with 16-slice CT, especially when the stent is orientated parallel to the x-ray beam.

Carotid Artery Stent Implantation: Evaluation with Multi–Detector Row CT Angiography and Virtual Angioscopy—Initial Experience

Approval for this HIPAA-compliant study was obtained from the institutional review board; informed consent was not required for retrospective review of patient studies that had been performed for clinical evaluation. The purpose of this study was to retrospectively compare the accuracy of intrastent luminal diameter, as measured on transverse computed tomographic (CT) angiograms and virtual angioscopic views, with the manufacturer's specifications for phantom diameter and with digital subtraction angiographic (DSA) measurements of stent diameter obtained in patients. Intrastent diameter was measured by using standard and stent-optimized reconstruction kernels with three window settings. Endoluminal virtual angioscopic views of the stent-containing vessels were also generated. Measurements at CT angiography were compared with known specifications for the phantom and with DSA measurements in patients. Erroneous measurements of intrastent diameter occurred when a standard kernel and nonoptimized window settings were used. A set of parameters that minimized error relative to measurements obtained at DSA was also identified. Virtual angioscopy helped demonstrate morphologic aspects of stenosis that were otherwise difficult to appreciate.

Angioplasty and stenting of intracranial stenosis

PURPOSE OF REVIEW

The review summarizes recent advances in angioplasty and stenting of intracranial atherosclerotic stenosis.

RECENT FINDINGS

Several single-center studies show that, with the technological advancements in device technology, intracranial stenting is feasible even in the distal internal carotid artery or middle cerebral artery. However, the clinical outcomes vary between moderate and high risk rates for morbidity and mortality. To date, the only prospective multi-center study that has been conducted is the SSYLVIA (Stenting of Symptomatic Atherosclerotic Lesions in the Vertebral or Intracranial Arteries) study, which demonstrated stroke rates of 6.6% and 13.1% at 30 days and 1 year, respectively. A unique feature of this trial is the assessment of restenosis rates and their potential association with clinical symptoms and risks. A promising new concept for stent-assisted procedures in the intracranial vasculature is the use of self-expanding stents. The high flexibility of these stents makes them suitable for treatment of lesions of the distal internal carotid artery and middle cerebral artery that are either inaccessible or difficult to reach with a balloon-mounted stent. Additionally, these self-expanding stents may result in fewer traumas to the parent vessel and in reduced rates of iatrogenic complications and restenosis.

SUMMARY

Intracranial angioplasty with or without stenting is a promising treatment option. Patient selection, careful periprocedural medical management, and a highly skilled neuroendovascular surgeon are all required to perform the procedure with an acceptable risk. If stenting is to be shown to be a safe therapeutic alternative, prospective trials comparing stenting with optimal medical treatment need to be performed.

Peripheral artery stent visualization and in-stent stenosis analysis in 16-row computed tomography: an in-vitro evaluation

The accuracy of 16-row multidetector CT in the visualization of different peripheral artery stents and in the appraisal of in-stent stenosis was assessed. Nine different stent types (nitinol and stainless steel) with three diameters (6, 8 and 10 mm) were used; altogether 27 stents were analyzed in a barrel-shaped vascular model. Low-grade (<40%) and high-grade (>60%) in-stent stenoses were simulated by polyurethane sticks (70 HU) of differing diameters (2-6 mm). Imaging was performed with 16x0.75-mm detector collimation, 130 mAs, 120 kV, 12-mm table feed/rotation, 1.0-mm slice thickness and 0.5-mm increment. The stent diameter, strut thickness, in-stent attenuation values, degree and degree of in-stent stenosis were evaluated. Nitinol stents showed significantly (P<10-6) less stent lumen narrowing, artificial strut thickening and overestimation of the degree of in-stent stenoses than stainless steel stents. In-stent attenuation values and artificial strut thickening were significantly (P<10-6) lower in 10- and 8-mm stents than in 6-mm stents. Stent lumen narrowing was significantly less in 10-mm stents than in 8-mm (P<10-4) or 6-mm (P<10-6) stents. In-stent stenoses were significantly overestimated, irrespective of the stent diameter. In 6-mm stents overestimation was significantly higher than in 8-mm (P<0.01) or 10-mm stents (P<10-6). Under in-vitro conditions 16-row MDCT allowed an accurate identification of in-stent stenosis, but significantly overestimated the effective degree of the stenosis.