Sellar and Parasellar Metastatic Tumors

The sellar and parasellar (SPS) region is a complex area rich in vital neurovascular structures and as such may be the location of first manifestation of a systemic malignancy. Metastases to this region are rare; breast cancer is the most common source among those that metastasize to the SPS region. Ophthalmoplegia, headache, retroorbital or facial pain, diabetes insipidus, and visual field defects are the most commonly reported symptoms. Lack of specific clinical and radiological features renders SPS metastases difficult to differentiate from the other frequently encountered lesions in this area, especially when there is no known history of a primary disease. Currently accepted management is multimodality therapy that includes biopsy and/or palliative surgical resection, radiation, and chemotherapy. Although no significant survival benefits have been shown by the surgical series, surgical resection may improve quality of life. Here we review the relevant literature and present six illustrative cases from our own institution

MRI-validation of SEP monitoring for ischemic events during microsurgical clipping of intracranial aneurysms

OBJECTIVE: During surgical clipping of intracranial aneurysms, reduction in SEP amplitude is thought to indicate cortical ischemia and subsequent neurological deficits. Since the sensitivity of SEP is questioned, we investigated SEP with respect to post-operative ischemia. METHODS: In 36 patients with 51 intracranial aneurysms, clinical evaluation and diffusion-weighted MRI (DWI) was performed before and within 24h after surgery. During surgery, time of temporary occlusion was recorded. MRI images were reviewed for signs of ischemia. RESULTS: For 43 clip applications (84%), we observed neither pathologic SEP events nor ischemia in MRI. In two cases where reduction lasted >10 min after clip release, SEP events correlated with ischemia in the MRI. Only one of the ischemic patients was symptomatic and developed a transient hemiparesis. CONCLUSIONS: While pathologic SEP events correlated with visible ischemia in MRI only in two cases with late SEP recovery, ischemia in MRI may have been transient or may not have reached detection threshold in the other cases, in agreement with the absence of permanent neurological deficits. SIGNIFICANCE: In complex aneurysm cases, where prolonged temporary occlusion is expected, SEP should be used to detect ischemia at a reversible stage to improve the safety of aneurysm clipping. Copyright © 2011 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved

Optimization schemes for queueing networks with applications to flexible manufacturing systems.

Product-form queueing networks have been useful for modeling complex systems such as flexible manufacturing systems and computer systems. While the literature is rich with queueing models, little attention has been paid to the use of these models in optimization schemes. This dissertation addresses the optimal design of complex systems in conjunction with closed queueing network theory. The overall plan is as follows: Product-form queueing network models are used to evaluate system "performance measures" for a given setting of system "decision parameters". The performance measures are useful in the computation of system cost functions and/or their sensitivities with respect to decision parameters. Optimization algorithms are applied in order to find the set of decision parameter values which optimize performance measures and/or minimize the cost of the system. Typical performance measures are the throughput (production rate) and average queue lengths at individual nodes of the system. Sensitivities of performance measures with respect to the decision parameters are derived in closed-form. These sensitivities are used to study the concavity (convexity) properties of performance measures. Both the concavity properties and the sensitivities of performance measures are then utilized in the formulation and solution procedures of the optimization models. Decision variables for the design and operation of queueing systems include service rates, routing of jobs, number of servers, and level of work-in-process. Models with a single decision variable type, such as service rates, are considered first. Hybrid models which include several types of decision variables such as service rates and work-in-process levels are then addressed. Constraints include meeting production goals, capital budgeting, and bounds on decision variables. The optimization models are discussed and solved to optimality. Numerical examples are provided and results are analysed

LPCVD TUNGSTEN MULTILAYER METALLIZATION FOR VLSI SYSTEMS.

Advances in microlithography, dry etching, scaling of devices, ion-implantation, process control, and computer aid design brought the integrated circuit technology into the era of VLSI circuits. Those circuits are characterized by high packing density, improved performance, complex circuits, and large chip sizes. Interconnects and their spacing dominate the chip area of VLSI circuits and they degrade the circuit performance through the unacceptable high time delays. Multilayer metallization enables shorter interconnects, ease of design and yet higher packing density for VLSI circuits. It was shown in this dissertation that, tungsten films deposited in a cold-wall LPCVD reactor offer viable solution to the problems of VLSI multilayer interconnects. Experiments showed that LPCVD tungsten films have good uniformity, high purity, low resistivity, low stress-good adherence and are readily patterned into high resolution lines. Moreover, a multilayer interconnect system consisting of three layers of tungsten metallization followed by a fourth layer of aluminum metallization has been designed, fabricated and tested. The interlevel dielectric used to separate the metal layers was CVD phosphorus doped silicon dioxide. Low ohmic contacts were achieved for heavily doped silicon. Also, low resistance tungsten-tungsten intermetallic contacts were obtained. In addition to excellent step coverage, high electromigration resistance of interconnects was realized. Finally, CMOS devices and logic gates were successfully fabricated and tested using tungsten multilayer metallization schemes.Digitization note: pg. 112 missing from paper original; appears to be pagination error rather than missing content