Defining the Border of the Subthalamic Nucleus for Deep Brain Stimulation: A Proposed Model Using the Symmetrical Sigmoid Curve Function.

BACKGROUND: The subthalamic nucleus (STN) is an important target during deep brain stimulation (DBS). Accurate lead placement is integral to achieving satisfactory clinical outcomes; however, the STN remains a structure whose visualization is highly variable with borders often difficult to define. We aimed to develop an objective method of evaluating the visibility of the STN on preoperative magnetic resonance imaging (MRI) to standardize future comparative assessments between imaging protocols and patient-specific parameters. METHODS: An imaging study of 64 prospectively collected patients undergoing bilateral DBS of the STN for various movement disorders was performed with institutional approval. MRI scans were acquired using a uniform protocol involving general anesthesia, cranial fixation in a Leksell stereotactic frame, and long acquisition times using a 3T MRI scanner. The images were analyzed using the iPlan Stereotaxy, version 2.6, workstation. High-resolution T2-weighted axial sections were evaluated, and the voxel values in the region of the presumed posterior border of the STN (as defined by the operating neurosurgeon) were obtained. A 4-parameter logistic symmetrical sigmoid curve was used to map the voxel values as they progressed from within to outside the region of the STN border. The inflection point and Hill coefficient of this symmetrical curve was calculated to provide objective information on the location and clarity of the STN border, respectively. These findings were compared with the surgeon's judgment of the STN border. To demonstrate the use of the sigmoid curve, the patients' head volumes were also calculated and evaluated to assess whether larger head volumes adversely affected STN visibility. RESULTS: The symmetrical sigmoid curve model provided objective information on the visibility of the STN on T2-weighted MRI scans and could be generated in 86% of the patients. The other 14% of patients had MRI scans that generated linear graphs, indicating the poorest scoring for STN image quality. No correlation between head volume and STN visibility was identified. CONCLUSIONS: Our proposed statistical model allows for standardized examination of the visibility of the STN border for DBS and has potential for both clinical and academic applications.

Synthesis and characterisation of the vibrational and electrical properties of antiferromagnetic 6L-Ba2CoTeO6 ceramics.

Optimal processing conditions for fabrication of dense single-phase 6L-Ba2CoTeO6 ceramics via the solid-state reaction method were determined. These ceramics possess a room-temperature crystal structure described by the centrosymmetric P3[combining macron]m1 space group. Polarized Raman spectroscopy enabled the observation of all the 25 predicted Raman modes and assignment of their symmetries. On cooling, BCTO ceramics exhibit two antiferromagnetic transitions at 3 K and 12.5 K, in broad agreement with a recent single-crystal study [P. Chanlert, N. Kurita, H. Tanaka, D. Goto, A. Matsuo and K. Kindo, Phys. Rev. B: Condens. Matter Mater. Phys., 2016, 93, 094420]. Low temperature Fourier-transform infrared reflectivity analyses suggest the antiferromagnetic phase transitions to be driven by small distortions of the CoO6 octahedra, lowering locally their C3v symmetry. This causes splitting of the associated vibrational modes, but without a long-range structural change. AC impedance spectroscopy revealed BCTO ceramics to be leaky insulators with an activation energy for conduction of ∼0.15-0.25 eV, which suggests electron hopping between mixed oxidation states of Co.

Crystal structures of K2[XSi5O12] (X = Fe2+, Co, Zn) and Rb2[XSi5O12] (X = Mn) leucites: comparison of monoclinic P21/c and Ia{\overline 3}d polymorph structures and inverse relationship between tetrahedral cation (T = Si and X)-O bond distances and intertetrahedral T-O-T angles.

The leucite tectosilicate mineral analogues K2X2+Si5O12 (X = Fe2+, Co, Zn) and Rb2X2+Si5O12 (X = Mn) have been synthesized at elevated temperatures both dry at atmospheric pressure and at controlled water vapour pressure; for X = Co and Zn both dry and hydrothermally synthesized samples are available. Rietveld refinement of X-ray data for hydrothermal K2X2+Si5O12 (X = Fe2+, Co, Zn) samples shows that they crystallize in the monoclinic space group P21/c and have tetrahedral cations (Si and X) ordered onto distinct framework sites [cf. hydrothermal K2MgSi5O12; Bell et al. (1994a), Acta Cryst. B50, 560-566]. Dry-synthesized K2X2+Si5O12 (X = Co, Zn) and Rb2X2+Si5O12 (X = Mn) samples crystallize in the cubic space group Ia{\overline 3}d and with Si and X cations disordered in the tetrahedral framework sites as typified by dry K2MgSi5O12. Both structure types have tetrahedrally coordinated SiO4 and XO4 sharing corners to form a partially substituted silicate framework. Extraframework K+ and Rb+ cations occupy large channels in the framework. Structural data for the ordered samples show that mean tetrahedral Si-O and X-O bond lengths cover the ranges 1.60 Š(Si-O) to 2.24 Š(Fe2+-O) and show an inverse relationship with the intertetrahedral angles (T-O-T) which range from 144.7° (Si-O-Si) to 124.6° (Si-O-Fe2+). For the compositions with both disordered and ordered tetrahedral cation structures (K2MgSi5O12, K2CoSi5O12, K2ZnSi5O12, Rb2MnSi5O12 and Cs2CuSi5O12 leucites) the disordered polymorphs always have larger unit-cell volumes, larger intertetrahedral T-O-T angles and smaller mean T-O distances than their isochemical ordered polymorphs. The ordered samples clearly have more flexible frameworks than the disordered structures which allow the former to undergo a greater degree of tetrahedral collapse around the interframework cavity cations. Multivariant linear regression has been used to develop equations to predict intertetrahedral T-O-T angle variation depending on the independent variables Si-O and X-O bond lengths, cavity cation ideal radius, intratetrahedral (O-T-O) angle variance, and X cation electronegativity.

The paramedian supracerebellar transtentorial approach to the posterior fusiform gyrus.

BACKGROUND: The posterior fusiform gyrus lies in a surgically challenging region. Several approaches have been described to access this anatomical area. The paramedian supracerebellar transtentorial (SCTT) approach benefits from minimal disruption of normal neurovascular tissue. The aim of this study was to demonstrate its application to access the posterior fusiform gyrus. METHODS: Three brains and six cadaveric heads were examined. A stepwise dissection of the SCTT approach to the posterior fusiform gyrus was performed. Local cortical anatomy was studied. The operability score was applied for comparative analysis on surgical anatomy. RESULTS: The major posterior landmark used to identify the fusiform gyrus with respect to the medial occipitotemporal gyrus was the collateral sulcus, which commonly bifurcated at its caudal extent. Compared with other surgical approaches addressed to access the region, SCTT demonstrated the best operability in terms of maneuverability arc. Favorable tentorial anatomy is the only limiting factor. CONCLUSIONS: The supracerebellar transtentorial approach is able to provide access to the posterior fusiform gyrus via a minimally disruptive, anatomic, microsurgical corridor.

Rietveld refinement of the crystal structures of Rb2 XSi5O12 (X = Ni, Mn).

The synthetic leucite silicate framework mineral analogues Rb2 XSi5O12 {X = Ni [dirubidium nickel(II) penta-silicate] and Mn [dirubidium manganese(II) penta-silicate]} have been prepared by high-temperature solid-state synthesis. The results of Rietveld refinements, using X-ray powder diffraction data collected using Cu Kα X-rays, show that the title compounds crystallize in the space group Pbca and adopt the cation-ordered structure of Cs2CdSi5O12 and other leucites. The structures consist of tetra-hedral SiO4 and XO4 units sharing corners to form a partially substituted silicate framework. Extraframework Rb(+) cations sit in channels in the framework. All atoms occupy the 8c general position for this space group. In these refined structures, silicon and X atoms are ordered onto separate tetra-hedrally coordinated sites (T-sites). However, the Ni displacement parameter and the Ni-O bond lengths suggest that for the X = Ni sample, there may actually be some T-site cation disorder.

Intracranial injectable tumor model: technical advancements.

Background and Objectives Few simulation models are available that provide neurosurgical trainees with the challenge of distorted skull base anatomy despite increasing importance in the acquisition of safe microsurgical and endoscopic techniques. We have previously reported a unique training model for skull base neurosurgery where a polymer is injected into a cadaveric head where it solidifies to mimic a skull base tumor for resection. This model, however, required injection of the polymer under direct surgical vision via a complicated alternative approach to that being studied, prohibiting its uptake in many neurosurgical laboratories. Conclusion We report our updated skull base tumor model that is contrast-enhanced and may be easily and reliably injected under fluoroscopic guidance. We have identified a map of burr holes and injection corridors available to place tumor at various intracranial sites. Additionally, the updated tumor model allows for the creation of mass effect, and we detail the variation of polymer preparation to mimic different tumor properties. These advancements will increase the practicality of the tumor model and ideally influence neurosurgical standards of training.

Lateral extent and ventral laminar attachments of the lumbar ligamentum flavum: cadaveric study.

BACKGROUND CONTEXT: Cadaveric descriptions of the deep layer of the lumbar ligamentum flavum (LF), extending between contiguous borders of adjacent laminae and into the lateral spinal canal region are limited. PURPOSE: To provide detailed descriptions of the lumbar LF. STUDY DESIGN: Cadaveric dissection. METHODS: The deep ligamentum flava of 14 formalin-fixed human cadaver lumbar spines (140 levels) were examined to assess their laminar attachments and lateral extents in relation to the intervertebral foramen. RESULTS: The variable attachment of the deep layer of the LF with respect to the cephalad and caudad laminae was identified and described. At each successive caudal level of the lumbar spine, the deep layer appeared to become a more prominent feature of the posterior vertebral column, lining more of the laminae to which it is attached and encroaching further into the posteroinferior region of the intervertebral foramen at its lateral margins. CONCLUSIONS: We describe our observations of the deep LF in the human lumbar spine. These observations have clinical relevance for the interpretation of radiologic imaging and the performance of adequate decompression in the setting of spinal stenosis.

Sr-fresnoite determined from synchrotron X-ray powder diffraction data.

The fresnoite-type compound Sr2TiO(Si2O7), distrontium oxidotitanium disilicate, has been prepared by high-temperature solid-state synthesis. The results of a Rietveld refinement study, based on high-resolution synchrotron X-ray powder diffraction data, show that the title compound crystallizes in the space group P4bm and adopts the structure of other fresnoite-type mineral samples with general formula A2 TiO(Si2O7) (A = alkaline earth metal cation). The structure consists of titanosilicate layers composed of corner-sharing SiO4 tetra-hedra (forming Si2O7 disilicate units) and TiO5 square-based pyramids. These layers extend parallel to the ab plane and are stacked along the c axis. Layers of distorted SrO6 octa-hedra lie between the titanosilicate layers. The Sr(2+) ion, the SiO4 tetra-hedron and the bridging O atom of the disilicate unit are located on mirror planes whereas the TiO5 square-based pyramid is located on a fourfold rotation axis.

Biphasic calcium phosphate contained within a polyetheretherketone cage with and without plating for anterior cervical discectomy and fusion.

OBJECTIVE: To evaluate the properties of a combination bone graft consisting of biphasic calcium phosphate ceramic, polyetheretherketone (PEEK) cage in one- and two-level surgery. METHODS: Over a 12-month time period, a prospective single surgeon series of 75 patients were included in the study and 58 patients selected based on adequate data points. From these 58 patients, 32 were supplemented with anterior plate fixation and 26 patients without plating. Duration of clinical follow-up was a mean of 12.4 months (range, 6-26 months) in the Plated Group and 10.5 months (range, 6-21 months) in the Non-Plated Group. RESULTS: A 100% fusion rate with nil graft related complications was achieved in the Plated group compared with 96.2% fusion and 11.5% subsidence rates reported in the Non-Plated group. Patients in both groups experienced statistically significant improvement in pain and functional outcomes compared to their pre-operative status; however, there was no significant difference in outcome between the Plated and Non-Plated Groups. CONCLUSIONS: Biphasic calcium phosphate ceramic contained within a PEEK cage is an effective implant for use in anterior cervical surgery with high fusion rates and good clinical outcome.

Reconstruction versus no reconstruction of iliac crest defects following harvest for spinal fusion: a systematic review: A review.

OBJECT: Autologous bone from the iliac crest is commonly used for spinal fusion. However, its use is associated with significant donor site morbidity, especially pain. Reconstructive procedures of the iatrogenic defect have been investigated as a technique to alleviate these symptoms. The goal of this study was to assess the effects of reconstruction versus no reconstruction following iliac crest harvest in adults undergoing spine surgery. METHODS: The authors searched the Cochrane Central Register of Controlled Trials (The Cochrane Library 2011, Issue 4); MEDLINE (1948-Oct 2011); EMBASE (1947-Oct 2011); and the reference lists of articles. Randomized controlled trials (RCTs) or nonrandomized controlled trials (NRCTs) were included in the study. Two independent reviewers selected the studies, extracted data using a standardized collection form, and assessed for risk of bias. RESULTS: Three RCTs (96 patients) and 2 NRCTs (82 patients) were included. These had a moderate to high risk of bias. The results suggest that iliac crest reconstruction may be useful in reducing postoperative pain, minimizing functional disability, and improving cosmesis. No pattern of other clinical, radiological, or resource outcomes was identified. CONCLUSIONS: Although the available evidence is suboptimal, this systematic review supports the notion that iliac crest reconstruction following harvest for spinal fusion may reduce postoperative pain, minimize functional disability, and improve cosmesis.

Bone graft substitutes in anterior cervical discectomy and fusion.

Anterior cervical discectomy with fusion is a common surgical procedure for patients suffering pain and/or neurological deficits and unresponsive to conservative management. For decades, autologous bone grafted from the iliac crest has been used as a substrate for cervical arthrodesis. However patient dissatisfaction with donor site morbidity has led to the search for alternative techniques. We present a literature review examining the progress of available grafting options as assessed in human clinical trials, considering allograft-based, synthetic, factor- and cell-based technologies.

Rietveld refinement of Sr(5)(AsO(4))(3)Cl from high-resolution synchrotron data.

The apatite-type compound, penta-strontium tris-[arsenate(V)] chloride, Sr(5)(AsO(4))(3)Cl, has been synthesized by ion exchange at high temperature from a synthetic sample of mimetite [Pb(5)(AsO(4))(3)Cl] with SrCO(3) as a by-product. The results of the Rietveld refinement, based on high resolution synchrotron X-ray powder diffraction data, show that the title compound crystallizes in the same structure as other halogenoapatites with general formula A(5)(YO(4))(3)X (A = divalent cation, Y = penta-valent cation, and X = F, Cl or Br) in the space group P6(3)/m. The structure consists of isolated tetra-hedral AsO(4) (3-) anions (the As atom and two O atoms have m symmetry), separated by two crystallographically independent Sr(2+) cations that are located on mirror planes and threefold rotation axes, respectively. One Sr atom is coordinated by nine O atoms and the other by six. The chloride anions (site symmetry ) are at the 2a sites and are located in the channels of the structure.

Polymorphism in cyclohexanol.

The crystal structures and phase behaviour of phase II and the metastable phases III' and III of cyclohexanol, C(6)H(11)OH, have been determined using high-resolution neutron powder, synchrotron X-ray powder and single-crystal X-ray diffraction techniques. Cyclohexanol-II is formed by a transition from the plastic phase I cubic structure at 265 K and crystallizes in a tetragonal structure, space group P42(1)c (Z' = 1), in which the molecules are arranged in a hydrogen-bonded tetrameric ring motif. The structures of phases III' and III are monoclinic, space groups P2(1)/c (Z' = 3) and Pc (Z' = 2), respectively, and are characterized by the formation of hydrogen-bonded molecular chains with a threefold-helical and wave-like nature, respectively. Phase III crystallizes at 195 K from a sample of phase I that is supercooled to ca 100 K. Alternatively, phase III may be grown via phase III', the latter transforming from supercooled phase I at ca 200 K. Phase III' is particularly unstable and is metastable with respect to both I and II. Its growth is realised only under very restricted conditions, thus making its characterization especially challenging. The cyclohexanol molecules adopt a chair conformation in all three phases with the hydroxyl groups in an equatorial orientation. No evidence was found indicating hydroxyl groups adopting an axial orientation, contrary to the majority of spectroscopic literature on solid-state cyclohexanol; however, the H atom of the equatorial OH groups is found to adopt both in-plane and out-of-plane orientations.

High-performance X-ray detectors for the new powder diffraction beamline I11 at Diamond.

The design and performance characterization of a new light-weight and compact X-ray scintillation detector is presented. The detectors are intended for use on the new I11 powder diffraction beamline at the third-generation Diamond synchrotron facility where X-ray beams of high photon brightness are generated by insertion devices. The performance characteristics of these detection units were measured first using a radioactive source (efficiency of detection and background count rate) and then synchrotron X-rays (peak stability, light yield linearity and response consistency). Here, the results obtained from these tests are reported, and the suitability of the design for the Diamond powder beamline is demonstrated by presenting diffraction data obtained from a silicon powder standard using a prototype multicrystal analyser stage.

Rietveld refinement of Ba(5)(AsO(4))(3)Cl from high-resolution synchrotron data.

The apatite-type compound Ba(5)(AsO(4))(3)Cl, penta-barium tris-[arsenate(V)] chloride, has been synthesized by ion exchange at high temperature from a synthetic sample of mimetite (Pb(5)(AsO(4))(3)Cl) with BaCO(3) as a by-product. The results of the Rietveld refinement, based on high resolution synchrotron X-ray powder diffraction data, show that the title compound crystallizes in the same structure as other halogenoapatites with general formula A(5)(YO(4))(3)X (A = divalent cation, Y = penta-valent cation, X = Cl, Br) in space group P6(3)/m. The structure consists of isolated tetra-hedral AsO(4) (3-) anions (m symmetry), separated by two crystallographically independent Ba(2+) cations that are located on mirror planes and threefold rotation axes, respectively. The Cl(-) anions are at the 2b sites ( symmetry) and are located in the channels of the structure.