Correlation between contrast leakage period of procedural rupture and clinical outcomes in endovascular coiling for cerebral aneurysms.

OBJECTIVE: Intraprocedural rupture (IPR) is a fatal complication of endovascular coiling for cerebral aneurysms. We hypothesized that contrast leakage period may be related to poor clinical outcomes. This study aimed to retrospectively evaluate the relationship between clinical outcomes and contrast leakage period. METHODS: Data from patients with cerebral aneurysms treated via endovascular coiling between January 2010 and October 2018 were retrospectively assessed. The enrolled patient's demographic data, the aneurysm related findings, endovascular treatment and IPR related findings, rescue treatment, and clinical outcome were analyzed. RESULTS: In total, 2,859 cerebral aneurysms were treated using endovascular coiling during the study period, with IPR occurring in 18 (0.63 %). IPR occurred during initial frame coiling (n=4), coil packing (n=5), stent deployment (n=7), ballooning (n=1), and microcatheter removal after coiling (n=1). Tear sites included the dome (n=14) and neck (n=4). All IPRs were controlled and treated with coil packing, with or without stenting. Flow arrest of the proximal balloon was not observed. Temporary focal neurological deficits developed in two patients (11.1%). At clinical follow-up, 14 patients were classified as modified Rankin Scale (mRS) 0, three as mRS 2, and one as mRS 4. The mean contrast leakage period of IPR was 11.2 min (range: 1-31 min). Cerebral aneurysms with IPR were divided into late (n=9, mean time: 17.11 min) and early (n=9, mean time: 5.22 min) control groups based on the criteria of 10 min of contrast leakage period. No significant between-group differences regarding clinical outcomes were observed after IPR (p=1). CONCLUSIONS: In our series, all patients with IPR were controlled with further coil packing or stenting without proximal balloon occlusion within 31 min of contrast leakage. There was no difference in clinical outcomes when the long contrast leakage period group and short contrast leakage period group were compared.

Usefulness of Pointwise Encoding Time Reduction with Radial Acquisition-Magnetic Resonance Angiography after Endovascular Treatment for Intracranial Aneurysms.

PURPOSE: Imaging follow-up after endovascular treatment is important; however, time-of-flight magnetic resonance angiography (TOF-MRA) has limitations associated with magnetic susceptibility and radiofrequency shielding caused by the stent and coils. We evaluated the diagnostic performance of pointwise encoding time reduction with radial acquisition (PETRA)-MRA after endovascular treatment for intracranial aneurysms. MATERIAL AND METHODS: A total of 186 patients with 211 aneurysms who underwent both pointwise encoding time reduction with radial acquisition- and time-of-flight magnetic resonance angiography in the same imaging session for follow-up after endovascular treatment. We subjectively graded the overall image quality, visualization of treated sites, and occlusion status. RESULTS: Although the overall image quality scores of pointwise encoding time reduction with radial acquisition-magnetic resonance angiography were significantly lower than those of time-of-flight magnetic resonance angiography for both observers (4.04 ± 0.81 vs. 4.85 ± 0.35 [observer 1], 4.60 ± 0.69 vs. 4.94 ± 0.24 [observer 2]) (both P < .001), the visibility of treated sites using pointwise encoding time reduction with radial acquisition-magnetic resonance angiography was significantly better than that of time-of-flight magnetic resonance angiography overall (4.27 ± 0.97 vs. 3.42 ± 1.01; P < .001), in the distal internal carotid artery (4.46 ± 0.79 vs. 3.40 ± 1.00; P < .001), and in the middle cerebral artery (4.19 ± 0.93 vs. 3.08 ± 0.53, P = 0.007). Pointwise encoding time reduction with radial acquisition-magnetic resonance angiography showed a higher area under the curve than time-of-flight magnetic resonance angiography for the evaluation of treated aneurysm occlusion, except for posterior circulation aneurysms. CONCLUSIONS: Pointwise encoding time reduction with radial acquisition-magnetic resonance angiography showed better visualization of treated sites and better diagnostic performance than time-of-flight magnetic resonance angiography for anterior circulation aneurysms. However, Pointwise encoding time reduction with radial acquisition-magnetic resonance angiography showed limitations in the follow-up evaluation of posterior circulation aneurysms.

Vertebral Artery Dissecting Aneurysm Causing Central Tapia's Syndrome: A Case Report.

The central type of Tapia's syndrome is an extremely rare presentation, characterized by unilateral paralysis of the vagal and hypoglossal nerves, contralateral hemiparesis, or hemihypesthesia. This report describes a case of a middle-aged patient who developed central Tapia's syndrome due to a right vertebral artery dissecting aneurysm (VADA). The patient complained about swallowing difficulty and odynophagia. Right vocal cord paralysis, mild tongue deviation to the right side, left hypesthesia, and decreased temperature sensation with left hemiparesis were observed in neurologic exams. A right VADA and compression of the medulla oblongata due to the VADA were diagnosed on magnetic resonance imaging. Endovascular flow diversion of the right VADA was performed. After 1 year, all neurological symptoms and vocal cord paralysis were nearly resolved, but left hypesthesia remained with decreased nociception. We present and discuss how a VADA caused those symptoms and propose endovascular flow diversion as a treatment option.

Analysis of External and Internal Disorder to Understand Band-Like Transport in n-Type Organic Semiconductors.

Charge transport in organic semiconductors is notoriously extremely sensitive to the presence of disorder, both internal and external (i.e., related to interactions with the dielectric layer), especially for n-type materials. Internal dynamic disorder stems from large thermal fluctuations both in intermolecular transfer integrals and (molecular) site energies in weakly interacting van der Waals solids and sources transient localization of the charge carriers. The molecular vibrations that drive transient localization typically operate at low-frequency (

Usefulness of pointwise encoding time reduction with radial acquisition sequence in subtraction-based magnetic resonance angiography for follow-up of the Neuroform Atlas stent-assisted coil embolization for cerebral aneurysms.

BACKGROUND: Although time-of-flight magnetic resonance angiography (TOF-MRA) is widely used, it has limited usefulness for follow-up after stent-assisted coil embolization. Contrast-enhanced MRA (CE-MRA) and ultrashort echo time MRA have been suggested as alternative methods for visualization after this procedure. PURPOSE: To compare efficacy and usefulness of pointwise encoding time reduction with radial acquisition (PETRA) sequence in subtraction-based MRA (qMRA), TOF-MRA, and CE-MRA during the follow-up after Neuroform Atlas stent-assisted coil embolization for intracranial aneurysms. MATERIAL AND METHODS: This retrospective study included 23 patients with 24 aneurysms who underwent Neuroform Atlas stent-assisted coil embolization for intracranial aneurysms. All patients were evaluated with PETRA qMRA, TOF-MRA, and CE-MRA at the same follow-up session. The flow within stents, occlusion status, and presence of pseudo-stenosis were evaluated; inter-observer and intermodality agreements for the three methods were also graded. RESULTS: The mean score for flow visualization within the stents was significantly higher for PETRA qMRA and CE-MRA than for TOF-MRA (although no significant difference was found between PETRA qMRA and CE-MRA). Good inter-observer agreement was observed for each modality. PETRA qMRA and CE-MRA were more consistent with digital subtraction angiography (DSA) than TOF-MRA for aneurysm occlusion status. The intermodality agreement was better between PETRA qMRA and DSA, and between CE-MRA and DSA, than between DSA and TOF-MRA. Pseudo-stenosis was most frequently observed in TOF-MRA, followed by CE-MRA and PETRA qMRA. CONCLUSION: PETRA qMRA is useful for evaluating the parent artery patency and occlusion status of aneurysms after Neuroform Atlas stent-assisted coil embolization.

Microsurgical treatment for the recurrent cerebral aneurysm initially treated using coil embolization.

OBJECTIVE: Microsurgical treatment could be a good alternative for the treatment of recurrent cerebral aneurysm after coil embolization. The purpose of this study was to present our experience of microsurgical treatment for recurrent cerebral aneurysm previously treated using coil embolization. METHODS: From June 2012 to May 2019, 34 patients consecutively received microsurgical treatment for a recurrent cerebral aneurysm previously treated using coil embolization after it ruptured. RESULTS: Of the 34 patients with aneurysm, 33 had the aneurysm located in the anterior circulation. The most common location was the anterior communicating artery (13 cases). Immediate radiologic outcome at coil embolization was completed (n=6), residual neck (n=26), and residual sac (n=2). The reason for microsurgical treatment included rebleeding (n=12), persistent residual sac (n=1), and recurrence on follow-up study (n=21). Rebleeding occurred within 10 days after coil embolization in 10 cases, and the other 2 were due to regrowth. In the 20 recurred and saccular aneurysms, coil compaction was present in 11 aneurysms and regrowth in 9 aneurysms. Simple neck clipping (n=29) and clipping with coil mass extraction (n=3) was possible in the saccular aneurysms. The blood blister like aneurysm (n=2) were treated using bypass and endovascular internal carotid artery trapping. In the follow-up study group after microsurgical treatment there were no severe complications due to the treatment. Age, cause of retreatment, and modified Rankin Scale before microsurgery were associated with good outcome (p<0.001). CONCLUSIONS: Microsurgical treatment may be a viable and effective option for treating recurrent aneurysms previously treated by endovascular techniques.

Radiological and clinical outcomes of endovascular coiling of proximal A1 aneurysms.

Aneurysms of the proximal anterior cerebral artery (A1) are rare. Of these A1 aneurysms, proximal A1 aneurysms are among the most challenging for endovascular coiling. This study aimed to evaluate the angiographic features and radiological and clinical outcomes of endovascular coiling of proximal A1 aneurysms. We recruited 38 patients with 38 proximal A1 aneurysms treated with endovascular coiling between September 2005 and April 2016. Baseline patient characteristics, aneurysm morphology, endovascular treatment techniques, immediate post-procedural radiological outcome, and follow-up clinical and radiological outcomes were evaluated, as were risk factors for recurrence. Sixteen proximal A1 aneurysms ruptured (42.1%). Six procedural complications (15.8%), including 5 thromboembolisms and 1 coil migration, were noted. There was no procedural morbidity or mortality. Immediate post-procedural radiological outcomes showed complete occlusion in 23, residual necks in 12, and residual sacs in 3 lesions. Follow-up angiographic outcomes were possible for 28 lesions (73.7%). Follow-up angiography showed sac recurrence in 3 (10.7%) and neck recurrence in 3 (10.7%) lesions. Retreatment was performed in 4 lesions (14.3%); all were treated by endovascular coiling. The presence of aneurysmal ruptures was only significant regarding recurrence in univariate logistic regression analysis. In our study, endovascular coiling of proximal A1 aneurysms was associated with a relatively high rate of procedural complications but not with procedural morbidity and mortality. The recurrence and retreatment rates of endovascular coiling of proximal A1 aneurysms were relatively high, and presence of rupture was significant for recurrence.

Advantages and disadvantages of the ENVOY 6F distal access guiding catheter in endovascular coiling for anterior circulation aneurysms.

OBJECTIVE: Selecting an appropriate guiding catheter to provide both sufficient supportability for working devices and sufficient distal navigability is essential for ensuring the success of a procedure. This study aimed to evaluate the advantages and disadvantages of using the ENVOY 6F distal access (DA) guiding catheter in coil embolization of anterior circulation cerebral aneurysms. METHODS: We included 98 patients (72 [73.5%] women, median age: 63 [range: 25-84] years) who underwent endovascular coiling with the ENVOY 6F DA guiding catheter from May to November 2016. We analyzed data on patient demographics and the number of co-axial techniques to position the guiding catheter, initial and final location of the catheter, and complications related to the catheter. RESULTS: The co-axial technique was used to position the ENVOY 6F DA guiding catheter in the internal carotid artery (ICA) in 20 cases (20.41%). The initial position of the ENVOY 6F DA guiding catheter involved the cervical ICA (79.6%), horizontal petrous ICA (17.3%), and vertical petrous ICA (3.1%). Final control angiograms after endovascular coiling showed proximal change in the final, compared to the initial, position of the ENVOY 6F DA guiding catheter in 25 cases (25.51%). Procedure-related complications were observed in nine patients (9.18%), involving vasospasm in all cases; however, there was no symptomatic case. CONCLUSION: The ENVOY 6F DA guiding catheter had relatively sufficient distal navigability without symptomatic procedural complications. However, the change in the catheter position after endovascular coiling denoted insufficient supportability.

Extremely broadband terahertz generation via pulse compression of an Ytterbium laser amplifier.

We present a system for extremely broadband terahertz (THz) generation based on an Ytterbium (Yb) amplified laser emitting 170-fs-long pulses centered at 1030 nm. The pulses are first spectrally broadened in an Ar-filled hollow-core capillary fiber (HCF) and then recompressed down to ∼18 fs with a chirped-mirror pair. Extreme broadband THz pulses of bandwidths up to 60 THz and peak electric field as high as 55 kV/cm are obtained via two-color plasma generation. The combination of high-power Yb laser systems with gas-filled HCF opens the path towards the realization of the next generation high-repetition-rate, extremely broadband, and intense-field THz time-domain spectroscopy systems.

Dual-energy CT angiography-derived virtual non-contrast images for follow-up of patients with surgically clipped aneurysms: a retrospective study.

PURPOSE: To evaluate the diagnostic performance, image quality, artifacts, and radiation doses of virtual non-contrast (VNC) images, relative to true non-contrast (TNC) images, in patients with surgically clipped aneurysms. METHODS: Seventy-six patients who underwent unenhanced computed tomography (CT) and dual-energy (DE)-CT angiography after surgical clipping of 85 intracranial aneurysms were included in the study. Diagnostic performances of VNC and TNC images were compared with respect to sensitivity, specificity, and positive and negative predictive values. The results of quantitative and qualitative analyses were compared between VNC and TNC images. Radiation doses were also compared between VNC and TNC images. RESULTS: Diagnostic performance of VNC images was lower than that of TNC images; however, addition of contrast-enhanced images improved diagnostic performance. Image noise and mean attenuation of VNC images were significantly higher than those of TNC images in the centrum semiovale, cerebellum, and pons. The quality of VNC images was excellent or sufficient (85.5% for observer 1, 85.5% for observer 2), and complete acceptance of VNC images was achieved in 64.5% for observer 1 and in 71.0% for observer 2; however, the addition of contrast-enhanced images increased the level of acceptance (92.0% for observer 1, 90.9% for observer 2). Clip artifacts were significantly lower in VNC images than in TNC images. CT dose index, dose-length product, and effective dose were significantly lower without TNC images. CONCLUSION: VNC images showed lower diagnostic performance and image quality, and higher image noise than TNC images; however, VNC images could reduce clip artifacts and radiation doses.

Molecular gases for pulse compression in hollow core fibers.

We introduce hydrofluorocarbon molecules as an alternative medium to noble gases with low ionization potential like krypton or xenon to compress ultrashort pulses of relatively low energy in a conventional hollow core fiber with subsequent dispersion compensation. Spectral broadening of pulses from two different laser systems exceeded those achieved with argon and krypton. Initially 40 fs, 800 nm, 120 µJ pulses were compressed to few optical cycles duration. With the same approach a compression factor of more than 10 was demonstrated for an ytterbium-based laser (1030 nm, 170 fs, 200 µJ) leading to 15.6 fs.

Recurrence of Small Cerebral Aneurysms (< 4 mm) Treated Endovascularly Using Target® Nano™ Coils.

OBJECTIVE: In our series, endovascular coiling with Target® Nano™ coils (Stryker Neurovascular, Fremont, CA, USA) with diameters of 1 or 1.5 mm exhibited favorable technical feasibility in the treatment of small cerebral aneurysms (< 4 mm). However, little is known about the recurrence of small cerebral aneurysms treated using Target® Nano™ coils. We investigated recurrence following the treatment of small cerebral aneurysms using Target® Nano™ coils. MATERIALS AND METHODS: Between January 2012 and November 2013, 143 patients with 148 small cerebral aneurysms (< 4 mm) were included our study. A total of 135 cerebral aneurysms (91.2%) were unruptured; 45 cerebral aneurysms (30.4%) were treated by endovascular coiling using Target® Nano™ coils. Follow-up radiological images were obtained for 132 cerebral aneurysms (89.2%) over a range of 3 to 58 months (mean, 34.3 months; standard deviation, 14.2). RESULTS: In the group treated with Target® Nano™ coils, radiological outcomes revealed complete occlusion in 33 (73.3%), residual necks in eight (17.8%), and residual sacs in four (8.9%) cases. Follow-up radiological outcomes revealed complete occlusion in 35 (77.8%) and residual necks in four (8.9%) cases that exhibited stable coil masses. In the group that was not treated with Target® Nano™ coils, radiological outcomes revealed complete occlusion in 69 (67%), residual necks in 18 (17.5%), and residual sacs in 16 (15.5%) cases. Follow-up radiological outcomes revealed complete occlusion in 87 (84.5%) and residual necks (5.8%) in six cases that exhibited stable coil masses. No significant differences were observed in the radiological outcomes or follow-up radiological outcomes between the two groups. No recurrences or retreatments occurred in our series. CONCLUSION: Endovascular treatment using Target® Nano™ coils may be a robust treatment option for small cerebral aneurysms (< 4 mm).

Causes of early rebleeding after coil embolization of ruptured cerebral aneurysms.

OBJECTIVE: Early rebleeding after coil embolization of a ruptured cerebral aneurysm is rare but may cause severe disability or death. We present a case series of early rebleeding after coil embolization of ruptured cerebral aneurysms and investigate the incidence, clinical outcome and possible mechanism through retrospective analysis of angiographic and surgical findings. PATIENTS AND METHODS: This study included 347 consecutive patients who had undergone successful coil embolization of 347 ruptured cerebral saccular aneurysms. Clinical and angiographic data and findings from emergent surgery were analyzed retrospectively. RESULTS: Early rebleeding occurred in eight aneurysms (2.3%) and was especially frequent among anterior communicating artery lesions (6 out of 122, 4.9%). The other two events involved posterior communication artery lesions. The maximum diameter of the aneurysms that developed early rebleeding was 4.89 ± 0.65 mm, ranging from 3.9 to 5.7 mm. In seven out of eight patients, the immediate radiologically determined occlusion status was a residual neck, and the remaining patient had a residual sac. The coil packing density was between 21% and 34%. Six cases of rebleeding were detected within 48 h, 1 case was detected on the 5th day, and 1 case was detected on the 10th day. Coil compaction was not detected by follow-up angiography after early rebleeding. We performed surgical clipping as a rescue procedure in 5 cases and additional coil embolization in 1 case. During follow-up angiography and rescue clipping, inflow of blood to the aneurysm was detected in 6 cases. Three patients died, and the other 3 patients were severely disabled. The mechanisms of early rebleeding were divided into two types. First, blood may flow into the rupture site through a gap between the coil mesh and the aneurysm neck. Second, blood may enter the rupture site through the coil mesh due to insufficient thrombus formation. CONCLUSIONS: The early rebleeding rate after coil embolization of ruptured cerebral aneurysms in our study was 2.3%. The ruptured aneurysms were small in size (<6 mm), and rupture frequently occurred in the anterior communicating artery. In most cases, inflow of blood to the aneurysm was detected by follow-up angiography or during rescue surgery.

Direct compression of 170-fs 50-cycle pulses down to 1.5 cycles with 70% transmission.

We present a straightforward route for extreme pulse compression, which relies on moderately driving self-phase modulation (SPM) over an extended propagation distance. This avoids that other detrimental nonlinear mechanisms take over and deteriorate the SPM process. The long propagation is obtained by means of a hollow-core fiber (HCF), up to 6 m in length. This concept is potentially scalable to TW pulse peak powers at kW average power level. As a proof of concept, we demonstrate 33-fold pulse compression of a 1 mJ, 6 kHz, 170 fs Yb laser down to 5.1 fs (1.5 cycles at 1030 nm), by employing a single HCF and subsequent chirped mirrors with an overall transmission of 70%.

Generation of high-field terahertz pulses in an HMQ-TMS organic crystal pumped by an ytterbium laser at 1030 nm.

We present the generation of high-peak-electric-field terahertz pulses via collinear optical rectification in a 2-(4-hydroxy-3-methoxystyryl)-1-methilquinolinium-2,4,6-trimethylbenzenesulfonate (HMQ-TMS) organic crystal. The crystal is pumped by an amplified ytterbium laser system, emitting 170-fs-long pulses centered at 1030 nm. A terahertz peak electric field greater than 200 kV/cm is obtained for 420 µJ of optical pump energy, with an energy conversion efficiency of 0.26% - about two orders of magnitude higher than in common inorganic crystals collinearly pumped by amplified femtosecond lasers. An open-aperture Z-scan measurement performed on an n-doped InGaAs thin film using such terahertz source shows a nonlinear increase in the terahertz transmission of about 2.2 times. Our findings demonstrate the potential of this terahertz generation scheme, based on ytterbium laser technology, as a simple and efficient alternative to the existing intense table-top terahertz sources. In particular, we show that it can be readily used to explore nonlinear effects at terahertz frequencies.

Superficial Temporal Artery-Sparing Mini-Pterional Approach for Cerebral Aneurysm Surgery.

OBJECTIVE: The purposes of this study were to introduce a superficial temporal artery (STA)-sparing mini-pterional approach for the treatment of cerebral aneurysms and review the surgical results of this approach. METHODS: Between June 2010 and December 2015, we performed the STA-sparing mini-pterional approach for 117 patients with 141 unruptured intracranial aneurysms. We analyzed demographic, radiologic, and clinical variables including age, sex, craniotomy size, aneurysm location, height of STA bifurcation, and postoperative complications. RESULTS: The mean age of patients was 58.4 years. The height of STA bifurcation from the superior border of the zygomatic arch was 20.5 mm±10.0 (standard deviation [SD]). The craniotomy size was 1051.6 mm2±206.5 (SD). Aneurysm neck clipping was possible in all cases. Intradural anterior clinoidectomy was performed in four cases. Contralateral approaches to aneurysms were adopted for four cases. Surgery-related complications occurred in two cases. Permanent morbidity occurred in one case. CONCLUSION: Our STA-sparing mini-pterional approach for surgical treatment of cerebral aneurysms is easy to learn and has the advantages of small incision, STA sparing, and a relatively wide surgical field. It may be a good alternative to the conventional pterional approach for treating cerebral aneurysms.

Recurrent Carotid Cavernous Fistula Originating from a Giant Cerebral Aneurysm after Placement of a Covered Stent.

We report the case of a recurrent carotid cavernous fistula (CCF) originating from a giant cerebral aneurysm (GCA) after placement of a covered stent. A 47-year-old woman presented with sudden onset of severe headache, and left-sided exophthalmos and ptosis. Cerebral angiography revealed a CCF caused by rupture of a GCA in the cavernous segment of the left internal carotid artery. Two covered stents were placed at the neck of the aneurysm. The neurological symptoms improved at first, but were aggravated in the 6 months following the treatment. Contrast agent endoleak was seen in the distal area of the stent. Even though additional treatments were attempted via an endovascular approach, the CCF could not be cured. However, after trapping the aneurysm using coils and performing superficial temporal artery-middle cerebral artery bypass, the neurological symptoms improved. In cases of recurrent CCF originating from a GCA after placement of a covered stent, it is possible to treat the CCF by endovascular trapping and surgical bypass.

Treatment of a Giant Serpentine Aneurysm in the Anterior Cerebral Artery.

A giant serpentine aneurysm (GSA) in the anterior cerebral artery (ACA) poses a technical challenge in treatment given its large size, unique neck, and dependent distal vessels. Here we report the case of a GSA in the ACA successfully treated with a combined surgical and endovascular approach. A 54-year-old woman presented with dull headache. On brain computed tomography (CT), a large mass (7 cm × 5 cm × 5 cm) was identified in the left frontal lobe. Cerebral angiography revealed a GSA in the left ACA. Bypass surgery of the distal ACA was performed, followed byocclusion of the entry channel via an endovascular approach. Follow-up CT performed 5 days after treatment revealed disappearance of the vascular channel and peripheral rim enhancement. Follow-up imaging studies performed 7 months after treatment revealed gradual reduction of the mass effect and patency of bypass flow. No complications were noted over a period of 1 year after surgery.

High-Resolution Magnetic Resonance Imaging of Intracranial Vertebral Artery Dissecting Aneurysm for Planning of Endovascular Treatment.

The equipment and techniques associated with magnetic resonance imaging (MRI) have rapidly evolved. The development of 3.0 Tesla MRI has enabled high-resolution imaging of the intracranial vessel wall. High-resolution MRI (HRMRI) can yield excellent visualization of both the arterial wall and lumen, thus facilitating the detection of the primary and secondary features of intracranial arterial dissection. In the present report, we describe the manner in which HRMRI affected our endovascular treatment planning strategy in 2 cases with unruptured intracranial vertebral artery dissection aneurysm. HRMRI provides further information about the vessel wall and the lumen of the unruptured intracranial vertebral artery dissecting aneurysm, which was treated by an endovascular approach in the 2 current cases.

A Vanadium Dioxide Metamaterial Disengaged from Insulator-to-Metal Transition.

We report that vanadium dioxide films patterned with λ/100000 nanogaps exhibit an anomalous transition behavior at millimeter wavelengths. Most of the hybrid structure's switching actions occur well below the insulator to metal transition temperature, starting from 25 °C, so that the hysteresis curves completely separate themselves from their bare film counterparts. It is found that thermally excited intrinsic carriers are responsible for this behavior by introducing enough loss in the context of the radically modified electromagnetic environment in the vicinity of the nanogaps. This phenomenon newly extends the versatility of insulator to metal transition devices to encompass their semiconductor properties.