Endovascular deep brain stimulation: Investigating the relationship between vascular structures and deep brain stimulation targets

BackgroundEndovascular delivery of current using ‘stentrodes’ – electrode bearing stents – constitutes a potential alternative to conventional deep brain stimulation (DBS). The precise neuroanatomical relationships between DBS targets and the vascular system, however, are poorly characterized to date.ObjectiveTo establish the relationships between cerebrovascular system and DBS targets and investigate the feasibility of endovascular stimulation as an alternative to DBS.MethodsNeuroanatomical targets as employed during deep brain stimulation (anterior limb of the internal capsule, dentatorubrothalamic tract, fornix, globus pallidus pars interna, medial forebrain bundle, nucleus accumbens, pedunculopontine nucleus, subcallosal cingulate cortex, subthalamic nucleus, and ventral intermediate nucleus) were superimposed onto probabilistic vascular atlases obtained from 42 healthy individuals. Euclidian distances between targets and associated vessels were measured. To determine the electrical currents necessary to encapsulate the predefined neurosurgical targets and identify potentially side-effect inducing substrates, a preliminary volume of tissue activated (VTA) analysis was performed.ResultsSix out of ten DBS targets were deemed suitable for endovascular stimulation: medial forebrain bundle (vascular site: P1 segment of posterior cerebral artery), nucleus accumbens (vascular site: A1 segment of anterior cerebral artery), dentatorubrothalamic tract (vascular site: s2 segment of superior cerebellar artery), fornix (vascular site: internal cerebral vein), pedunculopontine nucleus (vascular site: lateral mesencephalic vein), and subcallosal cingulate cortex (vascular site: A2 segment of anterior cerebral artery). While VTAs effectively encapsulated mfb and NA at current thresholds of 3.5 V and 4.5 V respectively, incremental amplitude increases were required to effectively cover fornix, PPN and SCC target (mean voltage: 8.2 ± 4.8 V, range: 3.0–17.0 V). The side-effect profile associated with endovascular stimulation seems to be comparable to conventional lead implantation. Tailoring of targets towards vascular sites, however, may allow to reduce adverse effects, while maintaining the efficacy of neural entrainment within the target tissue.ConclusionsWhile several challenges remain at present, endovascular stimulation of select DBS targets seems feasible offering novel and exciting opportunities in the neuromodulation armamentarium.     

Dynamics of lipid adsorption at the electrified water∣1,2-dichloroethane interface

A recently introduced setup to measure the dynamic interfacial tension of expanding drops was used to compare the adsorption behaviour of a series of lipids at the electrified water∣dichloroethane interface. Phospholipids with saturated carbon chains of different length (DMPC, DPPC, DSPC, DAPC, DBPC), an unsaturated phospholipid (DOPC) and an ethanolamine (DSPE) were compared. It was found that the adsorption decreases with increasing chain length. Also, the increase of the flow rate reduces the degree of adsorption effectively. On the timescale of the experiments, the DSPE, DAPC and DBPC adsorption showed no potential dependence, whereas the adsorption of DOPC was stronger than that of the saturated lipids. Adsorption was modelled using the Langmuir adsorption isotherm; the potential dependence of adsorption is discussed.     

不同光凝接触镜填充液对中央角膜厚度的影响

目的　比较在行氩激光全视网膜光凝治疗中使用不同接触镜填充液对中央角膜厚度的影响 ,以寻找最适用于该治疗的填充液。方法　对 4 6例 (5 2眼 )患者进行氩激光全视网膜光凝治疗 ,每次分别随机使用 0 2 5 %氯霉素、1%羧甲基纤维素及医用透明质酸钠组作为安放全眼底激光角膜接触镜填充液 ,在治疗前及治疗后均用角膜测厚仪测量患者中央角膜厚度。结果　治疗后使用 0 2 5 %氯霉素组中央角膜平均增厚 (31 4± 10 2 ) μm ,1%羧甲基纤维素组中央角膜平均增厚 (10 6± 4 3) μm ,医用透明质酸钠组中央角膜平均增厚 (8 0± 3 5 ) μm。方差分析显示 :氯霉素组与另两组差异有极显著性意义 (P <0 0 1) ,羧甲基纤维素组与透明质酸钠组差异无显著性意义 (P >0 0 5 )。结论　 1%羧甲基纤维素及医用透明质酸钠作为安放全眼底激光角膜接触镜的填充液对角膜水肿程度的影响明显小于0 2 5 %氯霉素 ,是可供选用的优良填充液     

Man-Machine Interfaces in Computer Assisted Surgery

The clinical potential of computer assisted surgery (W) has been more and more widely acknowledged since CAS systems have been introduced into the operating room (OR) theater.

Especially the improvements in safety and accuracy are remarkable and strengthen the ties between surgeons and engineers. Tumor stereotaxis was introduced to neurological surgery in the early 1980s, and currently systems with and without robotic navigation are in use for specific medical indications. Recently, solutions for computer assisted orthopedic surgery were developed and applied to various anatomical regions. However, with the establishment of CAS in vivo, a new complex of problems, which was not present in the laboratory setup, was introduced: the man-machine interface.

Currently, the complexity of available CAS systems requires the presence of at least one system engineer (often called the “operator”) in the OR. As a consequence, there is no possibility for direct communication between the surgeon and the machine or software.

Most of the program steps involved in CAS and choices to be made intraoperatively have to be transferred to the software by means of communication of the surgeon with the operator. Particularly, the establishment of a relation between the virtual object (i.e., a medical image) and the surgical object (i.e., the patient), often denoted as “matching” or “skeletal registration” requires intensive interaction of the surgeon with the computer. A literature survey revealed that no CAS system in clinical use exists without a system engineer or a comparable person, and our clinical experience indicated that the matching process is a weak point in most systems. Because it appears to be contradictory to cost-reduction efforts in health care to have a highly paid specialist in the OR, this research evaluates strategies to facilitate the man-machine interface with the final goal of establishing a direct control of the system by the surgeon or the medical personnel traditionally present at surgery. Options to be investigated include 1) a CAS control panel (virtual keyboard) as an integrated component of the existing navigation system and 2) introduction of a commercial voice-recognition system. The implementation of these strategies into the existing CAS setup at the Department of Orthopaedic Surgery at the Inselspital (University of Bern) and clinical experience gained are reported     

外语多媒体软件界面设计的认知策略模式

外语学习软件界面的设计除了应注意实现软件功能的技术因素、表现媒体的物理性状以及信息内容的学科把握 ,还应对软件界面的内容组织方略、交互通达方式、语用认知功能等方面提出要求。界面设计的出发点 ,应该是学生、学习任务及其相应的学习活动。应该根据需求分析、学习者分析、任务和内容分析来确定目标和步骤。外语教学应以语言能力、交际能力、学习策略能力为目标 ,界面设计应以此为据选择表现媒体、结构层次、交互方式和技术手段。     

Contact finite element stress analysis of porous ingrowth acetabular cup implantation, ingrowth, and loosening

Two-dimensional linear and contact finite element analyses were conducted of total hip arthroplasty using metal-backed, porous ingrowth acetabular components. The stress transmission characteristics from the component to the surrounding bone were given special attention. Resultant loads of 20 and 40 degrees medial of vertical were studied, and the influence of adding a metal flange to the rim of the cup was evaluated. The results indicated that when a conventional metal-backed component (without a flange) is initially implanted and subjected to normal loading, these components may experience distraction between the component and the surrounding bone at inferior sites. Compressive stresses in the superior dome cancellous bone, however, will be substantial. If complete porous ingrowth is achieved, the superior dome compressive stresses will be reduced and substantial shear stresses created. In addition, high local bone stresses were found at the component rim. If bone ingrowth is achieved only in specific locations, stress transmission will be dictated by those locations and may differ markedly from the case of complete bone ingrowth. In the event that no porous ingrowth is achieved and a fibrous layer forms around the component, the interface stresses will be similar to those calculated for the natural hip. The addition of a flange to the rim of the cup will reduce the magnitude of the radial stresses transmitted to the cancellous bone superiorly and medially by directly transferring some of the load to the lateral wall of the pelvis. The flange will also help to relieve the high local stresses that are found at the component rim.     

数字化三维重建技术在股前外侧皮瓣血供及其可视化中的应用

目的探讨数字化三维重建技术在股前外侧皮瓣血供与可视化中的应用。方法①健康志愿者6人经肘正中静脉注射造影剂，使用64排多层螺旋CT进行盆腔及双下肢扫描，观察旋股外侧动脉分布及彼此间的吻合情况，将大腿二维灰度．DICOM格式图像以三维体数据的形式输入计算机，应用Amira3．1软件对股前外侧皮瓣结构进行三维重建并立体显示。②明胶一氧化铅混悬液的灌注新鲜成人标本2具，16排多层螺旋CT进行全身连续扫描，观测旋股外侧动脉分布及彼此间的吻合情况，同法应用Amira3.1软件对股前外侧皮瓣结构进行三维重建并立体显示。结果重建的数字化模型可准确反映股前外侧皮瓣血供的解剖学结构。结论采用数字化三维重建技术可以提供正常股前外侧皮瓣的三维动态解剖，为其他皮瓣的数字化重建提供了参考。     

Asymmetric and Axisymmetric Constant Curvature Liquid-Gas Interfaces in Pulmonary Airways

Airway closure and gas trapping can occur during lung deflation and inflation when fluid menisci form across the lumina of respiratory passageways. Previous analyses of the behavior of liquid in airways have assumed that the airway is completely wetted or that the contact angle of the liquid-gas interface with the airway wall is 0, and thus that the airway fluid forms an axisymmetric surface. However, some investigators have suggested that liquid in the airways is discontinuous and that contact angles can be as high as 67. In this study we consider the characteristics of constant curvature surfaces that could form a stable liquid-gas interface in a cylindrical airway. Our analysis suggests that, for small liquid volumes, asymmetric droplets are more likely to form than axisymmetric toroids. In addition, if the fluid contact angle is greater than 13, asymmetric droplets can sustain larger liquid volumes than axisymmetric toroids before collapsing to form menisci. These results suggest that (1) fluid formations other than axisymmetric toroids could occur in the airways; and (2) the analysis of the behavior of fluids and the development of liquid menisci within the lungs should include the potential role of asymmetric droplets.