Coronary Artery Stents in Multislice Computed Tomography

Improving Visualization of In-stent Lumen Using Prototype Photon-counting Detector Computed Tomography with High-resolution Plaque Kernel

The study aimed to compare the performance of photon-counting detector computed tomography (PCD CT) with high-resolution (HR)-plaque kernel with that of the energy-integrating detector CT (EID CT) in terms of the visualization of the lumen size and the in-stent stenotic portion at different coronary vessel angles. The lumen sizes in PCD CT and EID CT images were 2.13 and 1.80 mm at 0°, 2.20 and 1.77 mm at 45°, and 2.27 mm and 1.67 mm at 90°, respectively. The lumen sizes in PCD CT with HR-plaque kernel were wider than those in EID CT. The mean degree of the in-stent stenotic portion at 50% was 69.7% for PCD CT and 90.4% for EID CT. PCD CT images with HR-plaque kernel enable improved visualization of lumen size and accurate measurements of the in-stent stenotic portion compared to conventional EID CT images regardless of the stent direction.

Medical Imaging Compatibility of Magnesium- and Iron-Based Bioresorbable Flow Diverters

BACKGROUND AND PURPOSE

Bioresorbable flow diverters are under development to mitigate complications associated with conventional flow-diverter technology. One proposed advantage is the ability to reduce metal-induced artifacts in follow-up medical imaging. In the current work, the medical imaging compatibility of magnesium- and iron-based bioresorbable flow diverters is assessed relative to an FDA-approved control in phantom models.

MATERIALS AND METHODS

Bioresorbable flow diverters, primarily composed of braided magnesium or antiferromagnetic iron alloy wires, were compared with an FDA-approved control flow diverter. The devices were assessed for MR imaging safety in terms of magnetically induced force and radiofrequency heating using 1.5T, 3T, and 7T field strength clinical scanners. The devices were deployed in phantom models, and metal-induced image artifacts were assessed in the 3 MR imaging scanners and a clinical CT scanner following clinical scan protocols; device visibility was assessed under fluoroscopy.

RESULTS

The magnesium-based bioresorbable flow diverter, iron-based bioresorbable flow diverter, and the control device all demonstrated MR imaging safety in terms of magnetically induced force and radiofrequency heating at all 3 field strengths. The bioresorbable flow diverters did not elicit excessive MR imaging artifacts at any field strength relative to the control. Furthermore, the bioresorbable flow diverters appeared to reduce blooming artifacts in CT relative to the control. The iron-based bioresorbable flow diverter and control device were visible under standard fluoroscopy.

CONCLUSIONS

We have demonstrated the baseline medical imaging compatibility of magnesium and antiferromagnetic iron alloy bioresorbable flow diverters. Future work will evaluate the medical imaging characteristics of the bioresorbable flow diverters in large-animal models.

Spectral Photon-Counting Computed Tomography: A Review on Technical Principles and Clinical Applications

Photon-counting computed tomography (CT) is a technology that has attracted increasing interest in recent years since, thanks to new-generation detectors, it holds the promise to radically change the clinical use of CT imaging. Photon-counting detectors overcome the major limitations of conventional CT detectors by providing very high spatial resolution without electronic noise, providing a higher contrast-to-noise ratio, and optimizing spectral images. Additionally, photon-counting CT can lead to reduced radiation exposure, reconstruction of higher spatial resolution images, reduction of image artifacts, optimization of the use of contrast agents, and create new opportunities for quantitative imaging. The aim of this review is to briefly explain the technical principles of photon-counting CT and, more extensively, the potential clinical applications of this technology.

Fourth update on CT angiography of coronary stents: in vitro evaluation of 24 novel stent types

Background Non-invasive evaluation of coronary stent patency by coronary computed tomography angiography (cCTA) remains challenging. Multiple studies showed that CT technology but also individual stent design strongly influence the assessability of coronary stents by cCTA. Purpose To expand the available data on cCTA characteristics of coronary stents by 24 novel types to help interpreting examinations of patients after stent placement and selecting which stents are suitable for assessment by cCTA. Material and Methods Twenty-four novel coronary stents (17 cobalt-chromium, six stainless-steel, one platinum-chromium) were examined in a coronary phantom. Standard cCTA parameters with stent-specific algorithms were used. Image quality was quantified for each stent using established parameters (in-stent attenuation alteration and visible lumen diameter). Results Most stents (n = 14) showed lumen visibilities of 45-55%. No severe restriction of lumen visibility (>60%) was found. The majority of stents (n = 13) caused only small intraluminal attenuation deviations and no severe alterations (>20%) were found. When grouped by manufacturing material, no significant differences were found between cobalt-chromium and stainless-steel with identical mean visible diameters (1.52 ± 0.17 mm vs. 1.52 ± 0.13 mm) and comparable attenuation alterations (35.04 ± 16.56 HU vs. 21.25 ± 14.60 HU). The only platinum-chromium stent showed a smaller visible diameter (1.23 mm) and higher attenuation alteration (41.70 HU), but was also deemed to be assessable by cCTA. Conclusion All 24 novel evaluated stents are eligible for non-invasive evaluation by cCTA without significant differences between cobalt-chromium and stainless-steel stents. This updated catalogue of CT appearances of current coronary stents may serve as reference when taking care of patients with stents in need of coronary imaging.

Ultra-High-Resolution Computed Tomography Angiography for Assessment of Coronary Artery Stenosis

BACKGROUND

Limitations of coronary computed tomography (CTA) include false-positive stenosis at calcified lesions and assessment of in-stent patency. A prototype of ultra-high resolution computed tomography (U-HRCT: 1,792 channels and 0.25-mm slice thickness×128 rows) with improved spatial resolution was developed. We assessed the diagnostic accuracy of coronary artery stenosis using U-HRCT.Methods and Results:Seventy-nine consecutive patients who underwent CTA using U-HRCT were prospectively included. Coronary artery stenosis was graded from 0 (no plaque) to 5 (occlusion). Stenosis grading at 102 calcified lesions was compared between U-HRCT and conventional-resolution CT (CRCT: 896 channels and 0.5-mm slice thickness×320 rows). Median stenosis grading at calcified plaque was significantly improved on U-HRCT compared with CRCT (1; IQR, 1-2 vs. 2; IQR, 1-3, P<0.0001). Assessability of in-stent lumen was evaluated on U-HRCT in 79 stents. Stent strut thickness and luminal diameter were quantitatively compared between U-HRCT and CRCT. Of 79 stents, 83.5% were assessable on U-HRCT; 80% of stents with diameter 2.5 mm were regarded as assessable. On U-HRCT, stent struts were significantly thinner (median, 0.78 mm; IQR, 0.7-0.83 mm vs. 0.83 mm; IQR, 0.75-0.92 mm, P=0.0036), and in-stent lumens were significantly larger (median, 2.08 mm; IQR, 1.55-2.51 mm vs. 1.74 mm; IQR, 1.31-2.06 mm, P<0.0001) than on CRCT.

CONCLUSIONS

U-HRCT with improved spatial resolution visualized calcified lesions with fewer artifacts. The in-stent lumen of stents with diameter ≥2.5 mm was assessable on U-HRCT.

Diagnostic performance of two corrected transluminal attenuation gradient metrics in coronary CT angiography for the evaluation of significant in-stent restenosis by dual-source CT: a validation study with invasive coronary angiography

AIM

To determine the diagnostic potential of transluminal attenuation gradients (TAG) with exclusion of stented coronary segments (TAG-ExS) and TAG-corrected contrast opacification (CCO) excluding stented coronary segments (TAG-CCO-ExS) for the assessment of in-stent restenosis (ISR).

MATERIALS AND METHODS

TAG-ExS and TAG-CCO-ExS were calculated in 93 coronary arteries with 190 stents. The diagnostic performances and the incremental values of the two metrics to coronary computed tomography angiography (CCTA) were analysed and compared.

RESULTS

For all stents and stents >3 mm in diameter, TAG-ExS and TAG-CCO-ExS were significantly lower in ≥50% than that in <50% of ISR (both p<0.05). For stent diameters ≤3 mm, significantly lower TAG-CCO-ExS (p=0.000), but not TAG-ExS (p=0.059), was found in ≥50% than in <50% of ISR. Addition of TAG-ExS or TAG-CCO-ExS to CCTA, did not improve the diagnostic accuracy of CCTA significantly (all p>0.05). Only TAG-CCO-ExS had a significant impact on CCTA for the reclassifications of ISR (p=0.046) in stent diameters ≤3 mm.

CONCLUSIONS

TAG-ExS and TAG-CCO-ExS did not provide incremental diagnostic value over CCTA in assessing ISR. TAG-CCO-ExS slightly enhanced the reclassifications of ISR for stents ≤3 mm in diameter.

CT Angiography of Stented Carotid Arteries: Comparison with Doppler Ultrasonography

Purpose:

To determine whether computed tomographic angiography (CTA) is a feasible modality for assessing stented carotid arteries and whether in-stent restenosis based on CTA concurs with ultrasonography (US).

Methods:

A retrospective review was conducted of 37 follow-up CTA and US images from 27 patients (23 men; median age 70 years, range 56–77) who received 34 nitinol carotid stents. CTA and US images were compared with respect to assessability and percent stenosis. Both visual estimation (≥50% or not) and the NASCET method were used to determine percent stenosis in CTA images. For US, a determination of ≥50% stenosis was based on peak systolic velocity (≥200 cm/s) and an internal carotid artery to common carotid artery ratio ≥2.5. Percent stenosis values by CTA were also compared to values (n=7, 21%) determined by catheter angiography.

Results:

CTA and US images were “totally assessable” in 27 (73%) and 15 (41%), “totally non-assessable” in 0 (0%) and 3 (8%), and “partially assessable” in 10 (27%) and 19 (51%), respectively. Assessability of CTA images was equal to or better than that of US images in 33 (89%). The percent stenoses by CTA and US were comparable in 20 cases. CTA found ≥50% stenosis using the NASCET method in 4 of 20 stents; none of these showed ≥50% stenosis by visual estimation of CTA or by spectral Doppler US. Compared with catheter angiography, CTA overestimated percent stenosis from 34% to 66% (mean 53%). US confirmed 2 angiographically proven restenoses, but CTA identified only 1.

Conclusion:

CTA provides better image quality for stented carotid arteries than US, but it might be inferior to US in determining restenosis in assessable cases. Therefore, CTA is likely to be an alternative to US in cases of non-assessability. A large-scale study including more restenosis cases is warranted to reveal which modality is more reliable for diagnosis of restenosis.

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.

Progress in interventional cardiology: challenges for the future

Cardiovascular disease is the leading cause of death in the western and developing countries. Percutaneous transluminal coronary interventions have become the most prevalent treatment option for coronary artery disease; however, due to serious complications, such as stent thrombosis and in-stent restenosis (ISR), the efficacy and safety of the procedure remain important issues to address. Strategies to overcome these aspects are under extensive investigation. In this review, we summarise relevant milestones during the time to overcome these limitations of coronary stents, such as the development of polymer-free drug-eluting stents (DES) to avoid pro-inflammatory response due to the polymer coating or the developement of stents with cell-directing drugs to, simultaneously, improve re-endothelialisation and inhibit ISR amongst other techniques most recently developed, which have not fully entered the clinical stage. Also the novel concept of fully biodegradable DES featured by the lack of a permanent foreign body promises to be a beneficial and applicable tool to restore a natural vessel with maintained vasomotion and to enable optional subsequent surgical revascularisation.

Promoting endothelial recovery and reducing neointimal hyperplasia using sequential-like release of acetylsalicylic acid and paclitaxel-loaded biodegradable stents

INTRODUCTION

This work reports on the development of a biodegradable dual-drug-eluting stent with sequential-like and sustainable drug-release of anti-platelet acetylsalicylic acid and anti-smooth muscle cell (SMC) proliferative paclitaxel.

METHODS

To fabricate the biodegradable stents, poly-L-lactide strips are first cut from a solvent-casted film. They are rolled onto the surface of a metal pin to form spiral stents. The stents are then consecutively covered by acetylsalicylic acid and paclitaxel-loaded polylactide-polyglycolide nanofibers via electrospinning.

RESULTS

Biodegradable stents exhibit mechanical properties that are superior to those of metallic stents. Biodegradable stents sequentially release high concentrations of acetylsalicylic acid and paclitaxel for more than 30 and 60 days, respectively. In vitro, the eluted drugs promote endothelial cell numbers on days 3 and 7, and reduce the proliferation of SMCs in weeks 2, 4, and 8. The stents markedly inhibit the adhesion of platelets on days 3, 7, and 14 relative to a non-drug-eluting stent. In vivo, the implanted stent is intact, and no stent thrombosis is observed in the stent-implanted vessels without the administration of daily oral acetylsalicylic acid. Promotion of endothelial recovery and inhibition of neointimal hyperplasia are also observed on the stented vessels.

CONCLUSION

The work demonstrates the efficiency and safety of the biodegradable dual-drug-eluting stents with sequential and sustainable drug release to diseased arteries.

Development and characterization of a coronary polylactic acid stent prototype generated by selective laser melting

In-stent restenosis is still an important issue and stent thrombosis is an unresolved risk after coronary intervention. Biodegradable stents would provide initial scaffolding of the stenosed segment and disappear subsequently. The additive manufacturing technology Selective Laser Melting (SLM) enables rapid, parallel, and raw material saving generation of complex 3- dimensional structures with extensive geometric freedom and is currently in use in orthopedic or dental applications. Here, SLM process parameters were adapted for poly-L-lactid acid (PLLA) and PLLA-co-poly-ε-caprolactone (PCL) powders to generate degradable coronary stent prototypes. Biocompatibility of both polymers was evidenced by assessment of cell morphology and of metabolic and adhesive activity at direct and indirect contact with human coronary artery smooth muscle cells, umbilical vein endothelial cells, and endothelial progenitor cells. γ-sterilization was demonstrated to guarantee safety of SLM-processed parts. From PLLA and PCL, stent prototypes were successfully generated and post-processing by spray- and dip-coating proved to thoroughly smoothen stent surfaces. In conclusion, for the first time, biodegradable polymers and the SLM technique were combined for the manufacturing of customized biodegradable coronary artery stent prototypes. SLM is advocated for the development of biodegradable coronary PLLA and PCL stents, potentially optimized for future bifurcation applications.

Coronary artery stent evaluation by combining iterative reconstruction and high-resolution kernel at coronary CT angiography

PURPOSE

To evaluate stent lumen visualization by combining high-resolution cardiac kernel and the iterative reconstruction (iDose) on an anthropomorphic moving heart phantom and in patients at coronary computed tomography (CT) angiography.

MATERIALS AND METHODS

We used the moving heart phantom and a 64 detector-row CT, retrospectively gated helical scanning, and image reconstruction. The heart rate was set at nonpulsating condition of 0 beats/min, 50 beats/min, and 80 beats/min. The 120-kV images were reconstructed in synchronization with electrocardiogram data using filtered back projection (FBP) or iDose algorithm and standard kernel/filter (CB) or high-resolution kernel/filter (CD). We measured image noise, the kurtosis, and stent lumen diameter in the phantom study. We also assessed the visual inspections by two radiologists.

RESULTS

With cardiac motion at 50 and 80 beats/min, the difference of kurtosis improved with CD relative to CB (P < .05). iDose algorithm with level 7 provided lowest noise, with no statistically significance in difference of the kurtosis relative to level 4 (P > .05). Without cardiac motion at 0 beats/min, the stent lumen diameter measurements with CD kernel were better relative to CB kernel (P < .05). In addition, no significant difference was found in stent lumen diameter between iDose level 4 and level 7 (P > .05).

CONCLUSION

The use of iDose and a sharp kernel allowed improved stent visualization at a lower radiation dose.

CT Imaging of Coronary Stents: Past, Present, and Future

Coronary stenting became a mainstay in coronary revascularization therapy. Despite tremendous advances in therapy, in-stent restenosis (ISR) remains a key problem after coronary stenting. Coronary CT angiography evolved as a valuable tool in the diagnostic workup of patients after coronary revascularization therapy. It has a negative predictive value in the range of 98% for ruling out significant ISR. As CT imaging of coronary stents depends on patient and stent characteristics, patient selection is crucial for success. Ideal candidates have stents with a diameter of 3 mm and more. Nevertheless, even with most recent CT scanners, about 8% of stents are not accessible mostly due to blooming or motion artifacts. While the diagnosis of ISR is currently based on the visual assessment of the stent lumen, functional information on the hemodynamic significance of in-stent stenosis became available with the most recent generation of dual source CT scanners. This paper provides a comprehensive overview on previous developments, current techniques, and clinical evidence for cardiac CT in patients with coronary artery stents.

Diagnostic accuracy of 64-slice computed tomography coronary angiography for the detection of in-stent restenosis: a meta-analysis

BACKGROUND

We sought to evaluate the diagnostic accuracy of 64-slice multi-detector row computed tomography (MDCT) compared with invasive coronary angiography for in-stent restenosis (ISR) detection.

METHODS

MEDLINE, Cochrane library, and BioMed Central database searches were performed until April 2009 for original articles. Inclusion criteria were (1) 64-MDCT was used as a diagnostic test for ISR, with >50% diameter stenosis selected as the cut-off criterion for significant ISR, using invasive coronary angiography and quantitative coronary angiography as the standard of reference; (2) absolute numbers of true positive, false positive, true negative, and false negative results could be derived. Standard meta-analytic methods were applied.

RESULTS

Nine studies with a total of 598 patients with 978 stents included were considered eligible. On average, 9% of stents were unassessable (range 0-42%). Accuracy tests with 95% confidence intervals (CIs) comparing 64-MDCT vs invasive coronary angiography showed that pooled sensitivity, specificity, positive and negative likelihood ratio (random effect model) values were: 86% (95% CI 80-91%), 93% (95% CI 91-95%), 12.32 (95% CI 7.26-20.92), 0.18 (95% CI 0.12-0.28) for binary ISR detection. The symmetric area under the curve value was 0.94, indicating good agreement between 64-MDCT and invasive coronary angiography.

CONCLUSIONS

64-MDCT has a good diagnostic accuracy for ISR detection with a particularly high negative predictive value. However, still a relatively large proportion of stents remains uninterpretable. Accordingly, only in selected patients, 64-MDCT may serve as a potential alternative noninvasive method to rule out ISR.

Evaluation of coronary artery in-stent restenosis by 64-section computed tomography: factors affecting assessment and accurate diagnosis

PURPOSE

To determine factors affecting the ability of 64-multislice computed tomography (MSCT) to detect, assess, and accurately diagnose significant coronary arterial in-stent restenosis (ISR).

MATERIALS AND METHODS

The institutional review board approved this study and waived informed consent. Sixty patients underwent CT coronary angiography using 64-MSCT, after implantation of coronary artery stents (n=91). We assessed diagnostic accuracy for ISR with CT in comparison with conventional coronary angiography as the gold standard, visually and with measurement of in-stent coronary lumen density. Possible factors that influenced the diagnostic performance of CT were evaluated, which included image quality (IQ), stent characteristics, and location.

RESULTS

Sixty-nine stents (75.8%) were assessable. Low IQ, location in the left circumflex coronary artery, and narrow stent diameter were associated with poor assessment (P<0.05). In stents that could be assessed, sensitivity, specificity, positive predictive value, and negative predictive value of 64-MSCT were 90.0%, 73.5%, 58.1%, and 94.7%, respectively, for significant ISR. The diagnostic accuracy in assessable stents showed a significant increase with better IQ, thinner strut thickness, and nondrug eluting stent. False-positive diagnoses of ISR by CT were explained by coronary lumen density measurements.

CONCLUSIONS

Evaluation of stents by 64-MSCT is not recommended in stents with diameters of < or = 2.75 mm or stents located at the left circumflex coronary artery. The diagnostic accuracy of 64-MSCT is affected by IQ and strut thickness in assessable stents. Significant ISR can be excluded with high reliability in selected patients.

Assessment of in-stent restenosis using 64-MDCT: analysis of the CORE-64 Multicenter International Trial

OBJECTIVE

Evaluations of stents by MDCT from studies performed at single centers have yielded variable results with a high proportion of unassessable stents. The purpose of this study was to evaluate the accuracy of 64-MDCT angiography (MDCTA) in identifying in-stent restenosis in a multicenter trial.

MATERIALS AND METHODS

The Coronary Evaluation Using Multidetector Spiral Computed Tomography Angiography Using 64 Detectors (CORE-64) Multicenter Trial and Registry evaluated the accuracy of 64-MDCTA in assessing 405 patients referred for coronary angiography. A total of 75 stents in 52 patients were assessed: 48 of 75 stents (64%) in 36 of 52 patients (69%) could be evaluated. The prevalence of in-stent restenosis by quantitative coronary angiography (QCA) in this subgroup was 23% (17/75). Eighty percent of the stents were <or=3.0 mm in diameter.

RESULTS

The overall sensitivity, specificity, positive predictive value, and negative predictive value to detect 50% in-stent stenosis visually using MDCT compared with QCA was 33.3%, 91.7%, 57.1%, and 80.5%, respectively, with an overall accuracy of 77.1% for the 48 assessable stents. The ability to evaluate stents on MDCTA varied by stent type: Thick-strut stents such as Bx Velocity were assessable in 50% of the cases; Cypher, 62.5% of the cases; and thinner-strut stents such as Taxus, 75% of the cases. We performed quantitative assessment of in-stent contrast attenuation in Hounsfield units and correlated that value with the quantitative percentage of stenosis by QCA. The correlation coefficient between the average attenuation decrease and >or=50% stenosis by QCA was 0.25 (p=0.073). Quantitative assessment failed to improve the accuracy of MDCT over qualitative assessment.

CONCLUSION

The results of our study showed that 64-MDCT has poor ability to detect in-stent restenosis in small-diameter stents. Evaluability and negative predictive value were better in large-diameter stents. Thus, 64-MDCT may be appropriate for stent assessment in only selected patients.

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.

The evolution of cardiovascular stent materials and surfaces in response to clinical drivers: a review

This review examines cardiovascular stent materials from the perspective of a range of clinical drivers and the materials that have been developed in response to these drivers. The review is generally chronological and outlines how stent materials have evolved from initial basic stainless steel devices all the way through to the novel biodegradable devices currently being explored. Where appropriate, pre-clinical or clinical data that influenced decisions and selections along the way is referenced. Opinions are given as to the merit and direction of various ongoing and future developments.

Coronary artery stent evaluation using a vascular model at 64-detector row CT: comparison between prospective and retrospective ECG-gated axial scans

Objective

We wanted to evaluate the performance of prospective electrocardiogram (ECG)-gated axial scans for assessing coronary stents as compared with retrospective ECG-gated helical scans.

Materials and Methods

As for a vascular model of the coronary artery, a tube of approximately 2.5-mm inner diameter was adopted and as for stents, three (Bx-Velocity, Express2, and Micro Driver) different kinds of stents were inserted into the tube. Both patent and stenotic models of coronary artery were made by instillating different attenuation (396 vs. 79 Hounsfield unit [HU]) of contrast medium within the tube in tube model. The models were scanned with two types of scan methods with a simulated ECG of 60 beats per minute and using display field of views (FOVs) of 9 and 18 cm. We evaluated the in-stent stenosis visually, and we measured the attenuation values and the diameter of the patent stent lumen.

Results

The visualization of the stent lumen of the vascular models was improved with using the prospective ECG-gated axial scans and a 9-cm FOV. The inner diameters of the vascular models were underestimated with mean measurement errors of -1.10 to -1.36 mm. The measurement errors were smaller with using the prospective ECG-gated axial scans (Bx-Velocity and Express2, p < 0.0001; Micro Driver, p = 0.0004) and a 9-cm FOV (all stents: p < 0.0001), as compared with the other conditions, respectively. The luminal attenuation value was overestimated in each condition. For the luminal attenuation measurement, the use of prospective ECG-gated axial scans provided less measurement error compared with the retrospective ECG-gated helical scans (all stents: p < 0.0001), and the use of a 9-cm FOV tended to decrease the measurement error.

Conclusion

The visualization of coronary stents is improved by the use of prospective ECG-gated axial scans and using a small FOV with reduced blooming artifacts and increased spatial resolution.

Evaluation of peripheral artery stent with 64-slice multi-detector row CT angiography: prospective comparison with digital subtraction angiography

PURPOSE

To assess the accuracy of 64-slice multi-detector row computed tomography (MDCT) angiography in the evaluation of peripheral artery in-stent or peristent restenosis, with conventional digital subtraction angiography (DSA) as the reference standard.

MATERIALS AND METHODS

Forty-one patients (30 men, 11 women; mean age, 69.8+/-9.2 years) with symptomatic peripheral arterial occlusive disease after peripheral artery stenting (81 stented lesions) underwent both conventional DSA and 64-slice MDCT angiography. Each stent was classified as evaluable or unevaluable, and every stent was divided into three segments (proximal stent, stent body, and distal stent), resulting in 243 segments. For evaluation, stenosis was graded as follows: 1, none or slight stenosis (<25%); 2, mild stenosis (25-49%); 3, moderate stenosis (50-74%); 4, severe stenosis or total occlusion (> or =75%). Two readers evaluated all CT angiograms with regard to narrowing of in-stent or peristent restenosis by consensus. Results were compared with findings of the DSA.

RESULTS

Of 81 stents, 62 (76.5%) were determined to be assessable. The metal artifact of the gold marker and motion artifact increased uninterpretability of the images of stents. Overall, 24 of 28 in-stent restenosis and 38 of 53 persistent restenosis were correctly detected by MDCT (85.7% and 71.7% sensitivity). In evaluable stents, 21 of 22 in-stent restenoses and 27 of 28 persistent restenosis were correctly detected (95.4% and 96.4% sensitivity). Additionally, as the grade of stenosis increases, the mean level of CT values in the stent lumina decreases linearly accordingly.

CONCLUSION

64-Slice MDCT has a high accuracy for the detection of significant in-stent or peristent restenosis of assessable stents in patients with peripheral artery stent implantation and therefore can be considered as a valuable noninvasive technique for stent surveillance.

Double coronary artery stent fracture with coronary artery microaneurysms

Even though drug-eluting stent (DES) implantation is an effective treatment for coronary artery stenosis, there are growing concerns related to the real usefulness of DESs due to their increased incidence of thrombosis, stent fracture, and late stent malapposition in comparison to bare metal stents. We have previously reported a case of stent fractures and multiple microaneurysms in both the left anterior descending and left circumflex coronary arteries. In the present case, we demonstrate the ability of dual-source spiral computed tomography to evaluate the various complications of DESs.

In vitro imaging of coronary artery stents: Are there differences between 16- and 64-slice CT scanners?

PURPOSE

To compare the performance of 64-slice with 16-slice CT scanners for the in vitro evaluation of coronary artery stents.

METHODS AND MATERIALS

Twelve different coronary artery stents were placed in the drillings of a combined heart and chest phantom, which was scanned with a 16- and 64-slice CT scanner. Coronal reformations were evaluated for artificial lumen narrowing, intraluminal attenuation values, and false widening of the outer stent diameter as an indicator of artifacts outside the stent.

RESULTS

Mean artificial lumen narrowing was not significantly different between the 16- and 64-slice CT scanner (44% versus 39%; p=0.408). The differences between the Hounsfield Units (HU) measurements inside and outside the stents were significantly lower (p=0.001) with 64- compared to 16-slice CT. The standard deviation of the HU measurements inside the stents was significantly (p=0.002) lower with 64- than with 16-slice CT. Artifacts outside the stents were not significantly different between the scanners (p=0.866).

CONCLUSION

Visualization of the in-stent lumen is improved with 64-slice CT when compared with 16-slice CT as quantified by significantly lesser intraluminal image noise and less artificial rise in intraluminal HU measurement, which is the most important parameter for the evaluation of stent patency in vivo.

Usefulness of multislice computed tomography to assess patency of coronary artery stents versus conventional coronary angiography

BACKGROUND

The aim of the present study was to assess the in-stent restenosis and occlusion of coronary artery stents by multislice computed tomography (MSCT) compared with conventional coronary angiography in patients with atypical chest pain and not practicable/non-conclusive stress test.

METHODS

Between December 2004 and March 2006, 81 patients were scheduled and of these 72 (65 men, mean age 61 years) with 90 stents underwent MSCT angiography using a 16-slice scanner, Toshiba Aquilion 16, 8-12 months after stent placement.

RESULTS

Of the 90 stents, 71 (79%) could be assessed and 19 (21%) were excluded because the image quality at the stent level was incompatible with diagnostic assessment. This results in sensitivity, specificity, and positive and negative predictive values for all assessable stents in the identification of occlusion and/or in-stent restenosis of 82, 96, 87, and 94%, respectively. When the 19 uninterpretable stents were included in the analysis, the diagnostic accuracy of MSCT in detecting in-stent restenosis and occlusion resulted in a sensitivity of 82%, specificity of 71%, positive predictive value of 40%, and negative predictive value of 94%.

CONCLUSION

The results of the study suggest that MSCT angiography is a useful method for evaluating patency/occlusion of large (>or=3 mm) coronary stents in symptomatic patients with atypical chest pain and concomitant not practicable/non-conclusive exercise or stress imaging test.

Coronary stent assessment on multidetector computed tomography: Source and predictors of image distortion

BACKGROUND

Metallic stent struts cause imaging artifacts on multidetector computed tomography (MDCT) which interfere with the assessment of in-stent coronary restenosis. We examined the degree of image distortion of implanted coronary stents on MDCT, comparing different stent types, sizes and orientation.

METHODS

We quantified stent dimensions and image distortion of 151 non-opacified coronary stents in 89 patients (81% men, age 65+/-10 years) who underwent MDCT with a 40 slice MDCT scanner. Stent dimension by MDCT was compared with measurements obtained from quantitative coronary angiographic (QCA) in the immediate post-implantation angiogram and with manufacturers' data.

RESULTS

Stent image quality was good for 107 stents (71%), moderate for 38 (25%) and poor in 6 (4%), 2 (<1%) of which were not assessable. Blooming artifact resulted in a mean MDCT luminal (inner) diameter 30+/-14% smaller than QCA diameter (2.0+/-0.5 vs 2.9+/-0.3 mm, p<0.001) and a mean outer diameter exceeding QCA by 31+/-14% (3.8+/-0.5 vs 2.9+/-0.3 mm, p<0.001). MDCT luminal stent diameter was unrelated to strut thickness or the vessel stented but appeared to be smaller for vertically orientated stents (p=0.017), cobalt alloy (vs stainless steel) (p=0.011) and also for different stent types (p=0.006).

CONCLUSION

The luminal dimension of implanted coronary stents, as visualized with 40 slice MDCT, was one third smaller than on invasive angiography. This decrease in visualized stent luminal diameter forms the basis for the difficulty in accurate assessment of in-stent restenosis by MDCT.

Assessment of vertebral artery stents using 16-slice multi-detector row CT angiography in vivo evaluation: comparison of a medium-smooth kernel and a sharp kernel

OBJECTIVES

To assess the lumen visibility of extracranial vertebral artery stents examined with 16-slice multi-detector row computed tomography (MDCT) angiography in vivo using a medium-smooth kernel (B30s) and a sharp kernel (B60s), and to compare these with digital subtraction angiography (DSA) after stent placement.

METHODS

Twenty stents from 20 patients (14 men, 6 women; mean age, 62.7+/-10.1 years) who underwent CT angiography (CTA) with 16-slice MDCT were retrospectively analyzed. In CT angiograms using a B30s and a B60s, the lumen diameters and CT attenuations of the stented vessels were measured three times by three observers, and artificial luminal narrowing (ALN) was calculated. To assess measurement reliability on CT angiograms, the intraclass correlation coefficient (ICC) was used. DSA served as the reference standard for the in-stent luminal measurements on CT angiography. The median interval between CT angiography and DSA was 1 day (range 1-10).

RESULTS

For interobserver reliability, intraclass correlation coefficients for the lumen diameters on CT angiograms with a B30s and a B60s were 0.90 and 0.96, respectively. The lumen diameters on CT angiograms using a B30s were consistently smaller than that on CT angiograms using a B60s (p<0.01). The mean ALN was 37+/-7% on CT angiograms using a B30s and 25+/-9% on CT angiograms using a B60s. The mean CT attenuation in in-stent lumen was 347+/-55HU on CT angiograms using a B30s and 295+/-46HU on CT angiograms using a B60s. The ALN and CT attenuation within the stented vessels between CT angiograms using a B30s and a B60s was significant (p<0.01).

CONCLUSIONS

16-slice MDCT using a sharp kernel allows good visualization of the stented vessels and is useful in the assessment of vertebral artery stent patency after stent placement.

Usefulness of 64-slice multidetector computed tomography for detecting drug eluting in-stent restenosis

The aim of this study was to evaluate the accuracy of a new-generation spiral multidetector computed tomographic scanner (the Brilliance 64) in the diagnosis of coronary in-stent restenosis (ISR). Forty-one patients with 87 coronary stents (70 drug-eluting stents) implanted were examined. Patients underwent multidetector computed tomography (MDCT) 6.7 +/- 6.9 days before scheduled invasive coronary angiography, using intravenous contrast enhancement. Images were reconstructed in multiple formats using retrospective electrocardiographic gating. Stents were viewed in their long and short axes and were visually classified for the presence or absence of binary ISR (diameter reduction >50%), including the 5-mm borders proximal and distal to the stent. ISR was found by invasive coronary angiography in 13 of the stented segments (15%) and in 8 patients (19%). Of these, 11 cases of ISR were correctly detected by MDCT; additionally, 1 severely calcified stented segment was considered as occluded by MDCT (sensitivity 84%, 95% confidence interval [CI] 54% to 98%). Seventy-three of 74 stented segments without ISR were correctly classified by MDCT (specificity 97%, 95% CI 93% to 100%), whereas 2 stented segments were classified as false-negative ISR. The positive predictive value was 92% (95% CI 84% to 97%), the negative predictive value was 97% (95% CI 90% to 99%), and predictive accuracy was 96% (95% CI 90% to 99%). After the exclusion of the calcified stented segment, the sensitivity, specificity, positive predictive value, negative predictive value, and predictive accuracy were 84% (95% CI 74% to 91%), 100% (95% CI 96% to 100%), 100% (95% CI 96% to 100%), 97% (CI 90% to 99%), and 98% (95% CI 92% to 99%), respectively. In conclusion, even with improved scanner technology, the sensitivity for the detection of ISR was moderate (84%). Thus, further studies are needed to determine whether MDCT will be a clinically useful and cost-effective tool for the evaluation of ISR in the clinical arena.

Contrast-enhanced 64-Section Coronary Multidetector CT Angiography versus Conventional Coronary Angiography for Stent Assessment

PURPOSE

To prospectively evaluate the accuracy of 64-section computed tomography (CT) for diagnosis of stent restenosis, by using conventional coronary angiography as the reference standard.

MATERIALS AND METHODS

The ethics committee granted permission for the study; patients gave written consent. Contrast material-enhanced coronary CT angiography was performed in 53 patients (45 men, eight women; mean age, 54 years +/- 9 [standard deviation]) suspected of having stent restenosis. Coronary CT angiographic findings were compared with conventional coronary angiographic findings. Two physicians analyzed coronary CT angiographic data sets with multiplanar reformatted images and three-dimensional reformations by using a volume-rendering technique and looked for stent detectability, low-attenuation in-stent filling defects, and grades of restenosis. Conventional coronary angiographic results were interpreted by one of several observers in consensus for stent restenosis; they were blinded to coronary CT angiographic data. Statistical software and general estimating equations were used for data analysis.

RESULTS

One hundred ten stents were identified in 53 patients. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of coronary CT angiography in detection of in-stent restenosis were 96.9%, 88.0%, 77.5%, 98.5%, and 91%, respectively. Coronary CT angiography depicted in-stent low-attenuation filling defects with an accuracy of 91% and negative predictive value of 98.5% (95% confidence interval: 90.9, 99.9). Coronary CT angiography depicted the status of 97 of 107 stents. There was no significant difference between in-stent lumen visibility and stent diameter (P = .104). Coronary CT angiography helped diagnose 15 of 18 stent restenoses with less than 50% narrowing, five of five stent restenoses with 50%-74% narrowing, and nine of nine (100%) stent restenoses with 75% or greater narrowing or total occlusion of the stent lumen.

CONCLUSION

Coronary CT angiography can depict in-stent low-attenuation filling defects, which appear to be a reliable sign of stent restenosis, and 64-section CT depicts such defects with a high degree of accuracy.