Coherent Electron Optics with Ballistically Coupled Quantum Point Contacts.

The realization of integrated quantum circuits requires precise on-chip control of charge carriers. Aiming at the coherent coupling of distant nanostructures at zero magnetic field, here we study the ballistic electron transport through two quantum point contacts (QPCs) in series in a three terminal configuration. We enhance the coupling between the QPCs by electrostatic focusing using a field effect lens. To study the emission and collection properties of QPCs in detail we combine the electrostatic focusing with magnetic deflection. Comparing our measurements with quantum mechanical and classical calculations we discuss generic features of the quantum circuit and demonstrate how the coherent and ballistic dynamics depend on the details of the QPC confinement potentials.

Large Contribution of Fermi Arcs to the Conductivity of Topological Metals.

Surface-state contributions to the dc conductivity of most homogeneous metals exposed to uniform electric fields are usually as small as the system size is large compared to the lattice constant. In this Letter, we show that surface states of topological metals can contribute with the same order of magnitude as the bulk, even in large systems. This effect is intimately related to the intrinsic anomalous Hall effect, in which an applied voltage induces chiral surface-state currents proportional to the system size. Unlike the anomalous Hall effect, the large contribution of surface states to the dc conductivity is also present in time-reversal invariant Weyl semimetals, where the surface states come in counterpropagating time-reversed pairs. While the Hall voltage vanishes in the presence of time-reversal symmetry, the twinned chiral surface currents develop similarly as in the time-reversal-broken case. For this effect to occur, the relaxation length associated with scattering between time-reversed partner states needs to be larger than the separation of contributing surfaces, which results in a characteristic size dependence of the resistivity and a highly inhomogeneous current-density profile across the sample.

Intracranial vessel wall MRI.

There are many different methods of imaging the intracranial arteries; however, the vast majority of currently used techniques are based on luminal imaging. Although this is useful, it does have limitations as many different pathological processes can produce the same appearance. Therefore, directly imaging the site of the pathology - the vessel wall itself - offers the hope of discriminating between different disease processes. In this review, we will discuss the current status of vessel wall magnetic resonance imaging alongside its potential usefulness in differentiating between various disease entities.

Non-Gaussian fluctuations of mesoscopic persistent currents.

The persistent current in an ensemble of normal-metal rings shows Gaussian distributed sample-to-sample fluctuations with non-Gaussian corrections, which are precursors of the transition into the Anderson localized regime. We here report a calculation of the leading non-Gaussian correction to the current autocorrelation function, which is of third-order in the current. Although the third-order correlation function is small, inversely proportional to the dimensionless conductance g of the ring, the mere fact that it is nonzero is remarkable, since it is an odd moment of the current distribution.

Aharonov-Bohm oscillations in disordered topological insulator nanowires.

A direct signature of electron transport at the metallic surface of a topological insulator is the Aharonov-Bohm oscillation observed in a recent study of Bi2Se3 nanowires [Peng, Nature Mater. 9, 225 (2010)] where conductance was found to oscillate as a function of magnetic flux ϕ through the wire, with a period of one flux quantum ϕ0=h/e and maximum conductance at zero flux. This seemingly agrees neither with diffusive theory, which would predict a period of half a flux quantum, nor with ballistic theory, which in the simplest form predicts a period of ϕ0 but a minimum at zero flux due to a nontrivial Berry phase in topological insulators. We show how h/e and h/2e flux oscillations of the conductance depend on doping and disorder strength, provide a possible explanation for the experiments, and discuss further experiments that could verify the theory.

Antiplatelet Management for Stent-Assisted Coiling and Flow Diversion of Ruptured Intracranial Aneurysms: A DELPHI Consensus Statement.

BACKGROUND AND PURPOSE: There is a paucity of data regarding antiplatelet management strategies in the setting of stent-assisted coiling/flow diversion for ruptured intracranial aneurysms. This study aimed to identify current challenges in antiplatelet management during stent-assisted coiling/flow diversion for ruptured intracranial aneurysms and to outline possible antiplatelet management strategies. MATERIALS AND METHODS: The modified DELPHI approach with an on-line questionnaire was sent in several iterations to an international, multidisciplinary panel of 15 neurointerventionalists. The first round consisted of open-ended questions, followed by closed-ended questions in the subsequent rounds. Responses were analyzed in an anonymous fashion and summarized in the final manuscript draft. The statement received endorsement from the World Federation of Interventional and Therapeutic Neuroradiology, the Japanese Society for Neuroendovascular Therapy, and the Chinese Neurosurgical Society. RESULTS: Data were collected from December 9, 2019, to March 13, 2020. Panel members achieved consensus that platelet function testing may not be necessary and that antiplatelet management for stent-assisted coiling and flow diversion of ruptured intracranial aneurysms can follow the same principles. Preprocedural placement of a ventricular drain was thought to be beneficial in cases with a high risk of hydrocephalus. A periprocedural dual, intravenous, antiplatelet regimen with aspirin and a glycoprotein IIb/IIIa inhibitor was preferred as a standard approach. The panel agreed that intravenous medication can be converted to oral aspirin and an oral P2Y12 inhibitor within 24 hours after the procedure. CONCLUSIONS: More and better data on antiplatelet management of patients with ruptured intracranial aneurysms undergoing stent-assisted coiling or flow diversion are urgently needed. Panel members in this DELPHI consensus study preferred a periprocedural dual-antiplatelet regimen with aspirin and a glycoprotein IIb/IIIa inhibitor.

Considerations for Antiplatelet Management of Carotid Stenting in the Setting of Mechanical Thrombectomy: A Delphi Consensus Statement.

BACKGROUND AND PURPOSE: There are only few data and lack of consensus regarding antiplatelet management for carotid stent placement in the setting of endovascular stroke treatment. We aimed to develop a consensus-based algorithm for antiplatelet management in acute ischemic stroke patients undergoing endovascular treatment and simultaneous emergent carotid stent placement. MATERIALS AND METHODS: We performed a literature search and a modified Delphi approach used Web-based questionnaires that were sent in several iterations to an international multidisciplinary panel of 19 neurointerventionalists from 7 countries. The first round included open-ended questions and formed the basis for subsequent rounds, in which closed-ended questions were used. Participants continuously received feedback on the results from previous rounds. Consensus was defined as agreement of ≥70% for binary questions and agreement of ≥50% for questions with >2 answer options. The results of the Delphi process were then summarized in a draft manuscript that was circulated among the panel members for feedback. RESULTS: A total of 5 Delphi rounds were performed. Panel members preferred a single intravenous aspirin bolus or, in jurisdictions in which intravenous aspirin is not available, a glycoprotein IIb/IIIa receptor inhibitor as intraprocedural antiplatelet regimen and a combination therapy of oral aspirin and a P2Y12 inhibitor in the postprocedural period. There was no consensus on the role of platelet function testing in the postprocedural period. CONCLUSIONS: More and better data on antiplatelet management for carotid stent placement in the setting of endovascular treatment are urgently needed. Panel members preferred intravenous aspirin or, alternatively, a glycoprotein IIb/IIIa receptor inhibitor as an intraprocedural antiplatelet agent, followed by a dual oral regimen of aspirin and a P2Y12 inhibitor in the postprocedural period.

Continuous-variable tomography of solitary electrons.

A method for characterising the wave-function of freely-propagating particles would provide a useful tool for developing quantum-information technologies with single electronic excitations. Previous continuous-variable quantum tomography techniques developed to analyse electronic excitations in the energy-time domain have been limited to energies close to the Fermi level. We show that a wide-band tomography of single-particle distributions is possible using energy-time filtering and that the Wigner representation of the mixed-state density matrix can be reconstructed for solitary electrons emitted by an on-demand single-electron source. These are highly localised distributions, isolated from the Fermi sea. While we cannot resolve the pure state Wigner function of our excitations due to classical fluctuations, we can partially resolve the chirp and squeezing of the Wigner function imposed by emission conditions and quantify the quantumness of the source. This tomography scheme, when implemented with sufficient experimental resolution, will enable quantum-limited measurements, providing information on electron coherence and entanglement at the individual particle level.

The unexplained success of stentplasty vasospasm treatment : Insights using Mechanistic Mathematical Modeling.

BACKGROUND: Cerebral vasospasm (CVS) following subarachnoid hemorrhage occurs in up to 70% of patients. Recently, stents have been used to successfully treat CVS. This implies that the force required to expand spastic vessels and resolve vasospasm is lower than previously thought. OBJECTIVE: We develop a mechanistic model of the spastic arterial wall to provide insight into CVS and predict the forces required to treat it. MATERIAL AND METHODS: The arterial wall is modelled as a cylindrical membrane using a constrained mixture theory that accounts for the mechanical roles of elastin, collagen and vascular smooth muscle cells (VSMC). We model the pressure diameter curve prior to CVS and predict how it changes following CVS. We propose a stretch-based damage criterion for VSMC and evaluate if several commercially available stents are able to resolve vasospasm. RESULTS: The model predicts that dilatation of VSMCs beyond a threshold of mechanical failure is sufficient to resolve CVS without damage to the underlying extracellular matrix. Consistent with recent clinical observations, our model predicts that existing stents have the potential to provide sufficient outward force to successfully treat CVS and that success will be dependent on an appropriate match between stent and vessel. CONCLUSION: Mathematical models of CVS can provide insights into biological mechanisms and explore treatment approaches. Improved understanding of the underlying mechanistic processes governing CVS and its mechanical treatment may assist in the development of dedicated stents.

Correction to: The unexplained success of stentplasty vasospasm treatment : Insights using Mechanistic Mathematical Modeling.

Correction to: Clin Neuroradiol 2019 https://doi.org/10.1007/s00062-019-00776-2 The original version of this article unfortunately contained a mistake. The Acknowledgements were missing. The correct information is given ….

The Medina Embolic Device: Karolinska experience.

Background The aim of this study was to report our single centre experience with the Medina Embolic Device (MED). Methods We performed a retrospective analysis of prospectively collected data to identify all patients treated with the MED. A total of 14 aneurysms (non-consecutive), in 13 patients, were treated including one ruptured and one partially thrombosed aneurysm. Fundus diameter was ≥5 mm in all cases. We evaluated the angiographic appearances, the clinical status, complications, and the need for adjunctive devices or repeat treatments. Results Aneurysm location was cavernous internal carotid artery (ICA; n = 1), supraclinoid ICA ( n = 1), terminal ICA ( n = 2), anterior communicating artery (AComA; n = 4), A2-3 ( n = 1), M1-2 junction ( n = 1), posterior communicating artery (PComA; n = 1), superior cerebellar artery (SCA; n = 1), and basilar tip ( n = 2). The average aneurysm fundus size was 8.6 mm (range 7-10 mm) and average neck size 3.75 mm (range 1.9-6.9 mm). Immediate angiographic results were modified Raymond-Roy occlusion classification (mRRC) I n = 2, mRRC II n = 1, mRRC IIIa n = 2, mRRC IIIb n = 2, the remaining 7 aneurysms showed complete opacification. At follow-up angiography (mean 5 months) mRRC I n = 5, mRRC II n = 5, mRRC IIIa n = 3, and persistent filling was seen in 1 aneurysm. Overall, four patients had repeat treatment and one is pending further treatment. Of the aneurysms treated with more than one MED, 75% showed complete occlusion at 6-month follow up whereas only one aneurysm treated with a single device showed complete occlusion. Overall, three patients had temporary complications and there were no deaths. Conclusions The MED is an intra-saccular flow-diverting device with satisfactory angiographic results and an acceptable safety profile. Use of a single MED cannot be recommended and further longer term studies are needed prior to widespread clinical use.

The challenges of extrapulmonary presentations of sarcoidosis: A case report and review of diagnostic strategies.

A patient presenting with overweight, amenorrhea, diabetes insipidus, and oral, nasal, and pharyngeal inflammation was admitted to our hospital. Using a non-invasive approach, we were able to narrow the differential diagnosis down to a systemic lymphoproliferative or granulomatous disease, most likely sarcoidosis. This diagnosis was eventually confirmed by a biopsy of an enlarged tonsil. To our knowledge, tonsil biopsies have not been reported to be of help in the diagnostic strategy for systemic sarcoidosis. In this report, we review the possible diagnostic approaches and point out that the pharyngeal tonsils, if enlarged or inflamed, can be targeted to obtain tissue for histological confirmation.

Cilostazol: an antiplatelet agent for the neurointerventionist?

Antiplatelet agents are essential for the successful management of patients undergoing a variety of neurointerventional procedures. The most commonly used anti-platelet agents are aspirin, clopidogrel and prasugrel. However, there exist an alternative class of anti-platelet agent that may prove useful for neurointerventionists. In particular a drug called cilostazol may have numerous added advantages above and beyond its antiplatelet effect that may be valuable for our patients. In this short review we aim to highlight some of these potential advantages.

TEM/AFM investigation of size and surface properties of nanocrystalline ceria.

A series of ceria nanoparticles were synthesized by using a microemulsion method. The effect of relative concentration of surfactant/water on the size and the surface roughness of ceria nanoparticles was examined using transmission electron microscopy (TEM) and atomic force microscopy (AFM) respectively. The investigation confirmed a relationship between the size and the roughness properties of the nanoceria as a function of the water to surfactant ratio. With increasing dilution of the surfactant, the size distribution became narrow such that average particle size decreased linearly as the ratio increased without affecting lower size threshold of particles (approximately 10 nm). The surface roughness, on the other hand was found to increase with increasing water to surfactant ratio implying diluted surfactant would provide rougher surface of ceria nanoparticles. The information can be used to tailor the adhesion properties of nanoceria by optimizing the size distribution as well as surface roughness as a function of water to surfactant ratio.

Surpass flow diverter in the treatment of intracranial aneurysms: a prospective multicenter study.

BACKGROUND AND PURPOSE: Incomplete occlusion and recanalization of large and wide-neck brain aneurysms treated by endovascular therapy remains a challenge. We present preliminary clinical and angiographic results of an experimentally optimized Surpass flow diverter for treatment of intracranial aneurysms in a prospective, multicenter, nonrandomized, single-arm study. MATERIALS AND METHODS: At 24 centers, 165 patients with 190 intracranial aneurysms of the anterior and posterior circulations were enrolled. The primary efficacy end point was the percentage of intracranial aneurysms with 100% occlusion on 6-month DSA. The primary safety end point was neurologic death and any stroke through a minimum follow-up of 6 months. RESULTS: Successful flow-diverter delivery was achieved in 161 patients with 186 aneurysms (98%); the mean number of devices used per aneurysm was 1.05. Clinical follow-up (median, 6 months) of 150 patients (93.2%), showed that the primary safety end point occurred in 18 subjects. Permanent neurologic morbidity and mortality were 6% and 2.7%, respectively. Morbidity occurred in 4% and 7.4% of patients treated for aneurysms of the anterior and posterior circulation, respectively. Neurologic death during follow-up was observed in 1.6% and 7.4% of patients with treated intracranial aneurysms of the anterior and posterior circulation, respectively. Ischemic stroke at ≤30 days, SAH at ≤7 days, and intraparenchymal hemorrhage at ≤7 days were encountered in 3.7%, 2.5%, and 2.5% of subjects, respectively. No disabling ischemic strokes at >30 days or SAH at >7 days occurred. New or worsening cranial nerve deficit was observed in 2.7%. Follow-up angiography available in 158 (86.8%) intracranial aneurysms showed 100% occlusion in 75%. CONCLUSIONS: Clinical outcomes of the Surpass flow diverter in the treatment of intracranial aneurysms show a safety profile that is comparable with that of stent-assisted coil embolization. Angiographic results showed a high rate of intracranial aneurysm occlusion.

Pituitary magnetic resonance imaging is not required in the postoperative follow-up of acromegalic patients with long-term biochemical cure after transsphenoidal surgery.

After successful transsphenoidal surgery for acromegaly, life-long follow-up is required, because 10-15% of patients develop recurrence of disease. We assessed whether it is safe to perform postoperative follow-up with only biochemical evaluation in acromegalic patients initially cured by transsphenoidal surgery. We studied 32 patients cured after transsphenoidal surgery for acromegaly during a follow-up of 8.7 +/- 6.4 yr (mean +/- sd). Serial measurements of serum GH during glucose tolerance test and magnetic resonance imaging (MRI) scans were performed. Serial MRI scans were reevaluated by three independent neuroradiologists, who were blinded for the clinical and biochemical data, for growth of suspected tumor tissue. Twenty-three patients remained biochemically cured in the long term, whereas nine of the 32 patients developed recurrence of disease, indicated by elevated serum GH concentrations during glucose tolerance test and clinical symptoms/signs. None of the 23 patients with long-term biochemical cure showed growth of tumor tissue according to two neuroradiologists, whereas the third neuroradiologist assessed three of 23 patients as having tumor growth despite continuing biochemical cure. In the nine patients with biochemical recurrence, no tumor growth was found in the series of postoperative MRI scans, according to two of the three independent radiologists, whereas the third radiologist found tumor growth in four patients with recurrent disease. In conclusion, in patients with acromegaly, initially cured by transsphenoidal surgery, it appears safe to check for recurrent disease during long-term follow-up of these patients by biochemical markers only.

Entrance and exit TL-dosimetry in the conservative treatment of breast cancer: a pilot study for the EORTC-Radiotherapy Cooperative Group.

Mailed dosimetry, using thermoluminescent dosimeters, can play an important role in quality assurance procedures in radiotherapy. In 1989, a pilot study was started with the main aim to show the feasibility of this method for the multicentre EORTC trial 22881 on the conservative management of breast carcinoma. Two anthropomorphic breast phantoms and six patients with breast carcinoma were irradiated according the prescriptions of the protocol. TLD measurements of the entrance and exit dose were performed in 6 MV tangential X-ray beams. It proved to be possible to correlate the dose measured in the entrance and exit points of the beams to the calculated dose closely under the surface. A thickness of at least 5 mm bolus material must be applied over the dosimeters and a distance of at least 3 cm from the lateral and medial field borders must be maintained in order to reach a clinically acceptable accuracy in the measurements.

Brain metastases and non-small cell lung cancer. Prognostic factors and correlation with survival after irradiation.

A total of 250 patients with brain metastases from non-small cell lung cancer (NSCLC) were treated with irradiation of their brain metastases. The median overall survival was 3.1 (95% CI: 2.7-3.5) months. 32/250 patients presenting with solitary brain metastasis underwent surgical resection. Their 1-year survival rate of 58% was significantly better than 89/250 patients with a solitary lesion but without surgery (14%, P=0.001). Patients with an absent or controlled primary tumor (101/250, 40.5%) had a 1-year survival rate of 26% as opposed to 11% for patients presenting with an active primary tumor (P=0.051). Patients presenting with metastases to the brain only showed a significant survival advantage over patients with extracranial metastases (1-year survival of 21% vs 6%, P=0.001). Karnofsky performance score, neurofunction status and response to steroids were also identified as prognostic factors. The total dose whole brain irradiation (WBI) was prognostic of significance with a 1-year survival of 35% for 30 Gy and boost, 23.5% for 30 Gy and 4% for the patients irradiated to a dose of 20 Gy WBI (P=0.001). When patients were grouped into the RTOG RPA (Recursive partitioning analysis) classes, patients within class I (73/250) had a 1-year survival of 28.5%, patients in class II (145/250) a survival of 14% at 1 year and patients into class III only a 6% 1-year survival rate. In a multivariate analysis, surgical resection, neurofunction class, metastatic extent and WBI dose remained significant prognostic factors. Although survival remains poor, there needs to be a continued interest in these patients, probably by participating in clinical trials.