Rastislav Pjontek

Metal artifact reduction for flat panel detector intravenous CT angiography in patients with intracranial metallic implants after endovascular and surgical treatment

Background Flat panel detector CT angiography with intravenous contrast agent injection (IV CTA) allows high-resolution imaging of cerebrovascular structures. Artifacts caused by metallic implants like platinum coils or clips lead to degradation of image quality and are a significant problem. Objective To evaluate the influence of a prototype metal artifact reduction (MAR) algorithm on image quality in patients with intracranial metallic implants. Methods Flat panel detector CT after intravenous application of 80 mL contrast agent was performed with an angiography system (Artis zee; Siemens, Forchheim, Germany) using a 20 s rotation protocol (200° rotation angle, 20 s acquisition time, 496 projections). The data before and after MAR of 26 patients with a total of 34 implants (coils, clips, stents) were independently evaluated by two blinded neuroradiologists. Results MAR improved the assessability of the brain parenchyma and small vessels (diameter <1 mm) in the neighborhood of metallic implants and at a distance of 6 cm (p<0.001 each, Wilcoxon test). Furthermore, MAR significantly improved the assessability of parent vessel patency and potential aneurysm remnants (p<0.005 each, McNemar test). MAR, however, did not improve assessability of stented vessels. Conclusions When an intravenous contrast protocol is used, MAR significantly ameliorates the assessability of brain parenchyma, vessels, and treated aneurysms in patients with intracranial coils or clips.

Retrieval of Migrated Coils with Stent Retrievers: An Animal Study

BACKGROUND AND PURPOSE: Coil migration is a potentially serious complication of endovascular aneurysm treatment. The aim of the study was to systematically investigate the effectiveness of coil retrieval with a stent retriever in an animal model. MATERIALS AND METHODS: A total of 148 coils of various types and sizes were placed into arteries of varying diameters in a porcine in vivo model. Coil retrieval was performed by placing a Trevo ProVue stent retriever over the coil and trying to trap a part of the platinum coil within the stent mesh by advancing the microcatheter over the stent or simply by retrieving the stent without trying to trap the coil by advancing the microcatheter. RESULTS: Coil retrieval was successful in 101 of 102 cases (99%), in which trapping of the coil within the stent retriever by advancing the microcathter was applied. When we only pulled back the stent without trapping the coil, retrieval was successful in only 5 of 46 cases (11%). Coil type, coil structure (2D versus 3D), actual coil shape in the affected vessel, investigator experience, aspiration, coil localization, and vessel diameter had no significant influence on retrieval outcome. There was no case of vessel perforation. CONCLUSIONS: Retrieval of migrated platinum coils with a stent retriever is an effective treatment option for migrated coils when the correct technique is applied.

Genetic Imbalance in Patients with Cervical Artery Dissection

Background: Genetic and environmental risk factors are assumed to contribute to the susceptibility to cervical artery dissection (CeAD). To explore the role of genetic imbalance in the etiology of CeAD, copy number variants (CNVs) were identified in high-density microarrays samples from the multicenter CADISP (Cervical Artery Dissection and Ischemic Stroke Patients) study and from control subjects from the CADISP study and the German PopGen biobank. Microarray data from 833 CeAD patients and 2040 control subjects (565 subjects with ischemic stroke due to causes different from CeAD and 1475 disease-free individuals) were analyzed. Rare genic CNVs were equally frequent in CeAD-patients (16.4%; n=137) and in control subjects (17.0%; n=346) but differed with respect to their genetic content. Compared to control subjects, CNVs from CeAD patients were enriched for genes associated with muscle organ development and cell differentiation, which suggests a possible association with arterial development. CNVs affecting cardiovascular system development were more common in CeAD patients than in control subjects (p=0.003; odds ratio (OR) =2.5; 95% confidence interval (95% CI) =1.4-4.5) and more common in patients with a familial history of CeAD than in those with sporadic CeAD (p=0.036; OR=11.2; 95% CI=1.2-107). Conclusion: The findings suggest that rare genetic imbalance affecting cardiovascular system development may contribute to the risk of CeAD. Validation of these findings in independent study populations is warranted.

Molecular Ultrasound Imaging of αvβ3-Integrin Expression in Carotid Arteries of Pigs After Vessel Injury.

ObjectivesInterventions such as balloon angioplasty can cause vascular injury leading to platelet activation, thrombus formation, and inflammatory response. This induces vascular smooth muscle cell activation and subsequent re-endothelialization with expression of &agr;v&bgr;3-integrin by endothelial cells and vascular smooth muscle cell. Thus, poly-N-butylcyanoacrylate microbubbles (MBs) targeted to &agr;v&bgr;3-integrin were evaluated for monitoring vascular healing after vessel injury in pigs using molecular ultrasound imaging. Materials and MethodsApproval for animal experiments was obtained. The binding specificity of &agr;v&bgr;3-integrin–targeted MB to human umbilical vein endothelial cells was tested with fluorescence microscopy. In vivo imaging was performed using a clinical ultrasound system and an 8-MHz probe. Six mini pigs were examined after vessel injury in the left carotid artery. The right carotid served as control. Uncoated MB, cDRG-coated MB, and &agr;v&bgr;3-integrin–specific cRGD-coated MB were injected sequentially. Bound MBs were assessed 8 minutes after injection using ultrasound replenishment analysis. Measurements were performed 2 hours, 1 and 5 weeks, and 3 and 6 months after injury. In vivo data were validated by immunohistochemistry. ResultsSignificantly stronger binding of cRGD-MB than MB and cDRG-MB to human umbilical vein endothelial cells was found (P < 0.01). As vessel injury leads to upregulation of &agr;v&bgr;3-integrin, cRGD-MBs bound significantly stronger (P < 0.05) in injured carotid arteries than at the counter side 1 week after vessel injury and significant differences could also be observed after 5 weeks. After 3 months, &agr;v&bgr;3-integrin expression decreased to baseline and binding of cRGD-MB was comparable in both vessels. Values remained at baseline also after 6 months. ConclusionsUltrasound imaging with RGD-MB is promising for monitoring vascular healing after vessel injury. This may open new perspectives to assess vascular damage after radiological interventions.

Feasibility, Safety, and Efficacy of Flow-Diverting Stent-Assisted Microsphere Embolization of Fusiform and Sidewall Aneurysms.

BACKGROUND Treatment of wide-necked internal carotid artery aneurysms is frequently associated with incomplete occlusion and high recurrence rates. Furthermore, platinum coils cause strong beam-hardening artifacts, hampering subsequent image analyses. OBJECTIVE To assess the feasibility, safety, and efficacy of flow-diverting, stent-assisted microsphere embolization of fusiform and sidewall aneurysms in vitro and in vivo. METHODS Using a recirculating pulsatile in vitro flow model, 5 different aneurysm geometries (inner/outer curve, narrow/wide neck, and fusiform) were treated (each n = 1) by flow-diverting stent (FDS) implantation and subsequent embolization through a jailed microcatheter using calibrated microspheres (500-900 μm) larger than the pores of the FDS mesh. Treatment effects were analyzed angiographically and by micro computed tomography. The fluid of the in vitro model was filtered to ensure that no microspheres evaded the aneurysm. The experiment was repeated once in vivo. RESULTS In vitro, all 5 aneurysms were safely and completely occluded by FDS-assisted microsphere embolization. Virtually complete aneurysm occlusion was confirmed by angiography and micro computed tomography. No microspheres escaped into the circulation. The experiment was successfully repeated in 1 pig with a sidewall aneurysm generated by vessel occlusion. An embolic protection system placed distally of the FDS in vitro and in vivo (each n = 1) contained no microspheres after the embolization. Thus, no microspheres were lost in the circulation, and the use of an embolic protection system seems feasible to provide additional safety. CONCLUSION FDS-assisted microsphere embolization of fusiform and sidewall aneurysms is feasible and yields virtually complete aneurysm occlusion while avoiding coil-associated beam-hardening artifacts.

High-Pitch Low-Dose Whole-Body Computed Tomography for the Assessment of Ventriculoperitoneal Shunts in a Pediatric Patient Model: An Experimental Ex Vivo Study in Rabbits.

ObjectiveThe aim of this study was to assess the diagnostic value of whole-body low-dose (LD) computed tomography (CT) for the detection of ventriculoperitoneal (VP) shunt complications in pediatric patients compared with radiographic shunt series (SS) in an ex vivo rabbit animal model. MethodsIn the first step, 2 optimized LD-CT imaging protocols, with high pitch (pitch, 3.2), low tube voltages (70 kVp and 80 kVp), and using both filtered back projection and iterative reconstruction, were assessed on a 16-cm solid polymethylmethacrylate phantom regarding signal-to-noise ratio and radiation dose. Taking both radiation dose and signal-to-noise ratio into account, the LD-CT protocol (80 kVp; 4 mA; pitch, 3.2) was identified as most appropriate and therefore applied in this study.After identification of appropriate LD-CT protocol, 12 VP shunts were implanted in 6 rabbit cadavers (mean weight, 5.1 kg). Twenty-four mechanical complications (extracranial and extraperitoneal malpositioning, breakages, and disconnections) were induced in half of the VP shunts. Low-dose CT and conventional SS were acquired in standard fashion. Dose-area products (DAPs) for SS and LD-CT were collected; effective radiation doses for both SS and LD-CT were estimated using CT-Expo (v. 2.3.1.) and age-specific effective dose (ED) estimates. Qualitative scoring of diagnostic confidence on a 5-point Likert scale (1, very low diagnostic confidence; 5, excellent diagnostic confidence) and blinded readings of both SS and LD-CTs were performed. ResultsAmong the 24 VP shunt complications, LD-CT yielded excellent sensitivity and specificity for the detection of VP shunt complications (sensitivity, 0.98; specificity, 1; 95% confidence interval, 0.92-1) with excellent interobserver agreement (&kgr; = 0.90). Shunt series yielded good sensitivity and specificity (sensitivity, 0.75; specificity, 1; 95% confidence interval, 0.58–0.92) with moderate interobserver agreement (&kgr; = 0.56). No false-positive findings were registered. Compared with SS, LD-CT yielded significantly lower ED and DAPs (ED, 0.039 vs 0.062 mSv; DAP, 20.5 vs 26.3; P < 0.05). ConclusionsIn this experimental ex vivo pediatric patient model, LD-CT yields excellent sensitivity for the detection of VP shunt complications at higher diagnostic confidence and lower radiation exposure compared with SS.

Implant-specific follow-up imaging of treated intracranial aneurysms: TOF-MRA vs. metal artifact reduced intravenous flat panel computed tomography angiography (FPCTA)

AIM To compare the diagnostic quality of time-of-flight magnetic resonance angiography (TOF-MRA) and metal-artefact-reduction (MAR) flat-panel-detector computed tomography angiography (FPCTA) and to determine the imaging technique best suited for evaluation endovascular and surgically treated aneurysms. METHODS The image quality of TOF-MRA and MAR-FPCTA of 44 intracranial implants (coiling: n=20; clipping: n=15; coiling + stenting: n=9) in a patient cohort of 25 was evaluated by two independent readers. Images obtained using MAR-FPCTA (20 second scan time, 496 projections, intravenous contrast medium administration; Artis Zee, Siemens Healthcare, Forchheim) were compared with TOF-MRA-images (1.5 or 3 T). Nominal data were analysed using McNemars chi-square test and ordinal variables using the Wilcoxon rank test. RESULTS Compared to TOF-MRA, MAR-FPCTA was significantly better suited to detect aneurysm remnants and to evaluate parent vessels after clipping (p<0.01). For coil packages >160 mm3, TOF-MRA provided significantly better assessment than MAR-FPCTA (p<0.01). For small coil packages (<160 mm3), no significant difference between TOF-MRA and MAR-FPCTA (p=0.232) was observed. For different clip sizes (cut-off 492 mm3) likewise no significant differences were found. The interobserver comparison showed high interrater agreement. CONCLUSION MAR-FPCTA is significantly better suited for follow-up examinations of clipped aneurysms, whereas for larger coil packages TOF-MRA is preferable. Smaller coil packages can be analysed using MAR-FPCTA or TOF-MRA.

Imaging of ventriculoperitoneal shunt complications : comparison of whole body low-dose computed tomography and radiographic shunt series

Objective To determine diagnostic value and radiation exposure of low-dose computed tomography (LD-CT) compared to radiographic shunt series (SS) for the detection of ventriculoperitoneal (VP) shunt complications. Methods Fourteen VP shunts were implanted in 7 swine cadavers. Mechanical complications were induced in 50% of VP shunts. Low-dose CT (80 kVp, 10 mAs, Pitch = 1.5) and SS were acquired. Dose area product (DAP) and effective doses for SS and LD-CT were collected. Scoring of diagnostic confidence and blinded readings of SS and CT data were performed. Results The sensitivity of LD-CT was high (0.97; 95% confidence interval, 0.91–1.00) with excellent interobserver agreement (&kgr; = 0.88). Similarly, the sensitivity of SS was high (0.82; 95% confidence interval, 0.68–0.95) with good interobserver agreement (&kgr; = 0.68). In contrast, LD-CT was associated with significantly higher diagnostic confidence (4.64 ± 0.41 vs 2.71 ± 0.73; P < 0.01) and significantly lower radiation exposure (effective dose: 0.26 mSv vs 1.06 mSv; DAP: 265.4 &mgr;Gym2 vs 724.8 &mgr;Gym2; P < 0.001). Conclusions For the assessment of suspected VP shunt complications, LD-CT provides excellent sensitivity and higher diagnostic confidence with lower radiation exposure compared with SS.

Development of a Polymer-Based Biodegradable Neurovascular Stent Prototype: A Preliminary In Vitro and In Vivo Study

Biodegradable stents are not established in neurovascular interventions. In this study, mechanical, radiological, and histological characteristics of a stent prototype developed for neurovascular use are presented. The elasticity and brittleness of PLA 96/4, PLDL 70/30, PCL, and PLGA 85/15 and 10/90 polymers in in vitro experiments are first analyzed. After excluding the inapt polymers, degradability and mechanical characteristics of 78 PLGA 85/15 and PLGA 10/90 stent prototypes are analyzed. After excluding PLGA 10/90 stents because of rapid loss of mass PLGA 85/15 stents in porcine in vivo experiments are analyzed. Angiographic occlusion rates 7 d, 1 month, 3 months, and 6 months after stent implantation are assessed. Histological outcome measures are the presence of signs of inflammation, endothelialization, and the homogeneity of degradation after six months. One case of stent occlusion occurs within the first 7 d. There is a prominent foreign-body reaction with considerable mononuclear and minor granulocytic inflammation combined with incomplete fragmental degradation of the struts. It is possible to produce a stent prototype with dimensions that fit the typical size of carotid arteries. Major improvements concerning thrombogenicity, degradation, and inflammatory response are required to produce biodegradable stents that are suitable for neurovascular interventions.