By D. Myxir. Jacksonville University.
In childhood and adolescence generic diovan 40 mg on-line, in addition to assessing for hydrocephalus, the lower spine should be imaged to rule out a tethered spinal cord. If a tethered cord is found, consideration of ﬁrst untethering the spinal cord should be given. Patients can have improvement of their Chiari symptoms with cord untethering. Chiari Malformation with Syrinx Obstruction to CSF ﬂow at the foramen magnum is the cause of syrinx development in the setting of a Chiari malformation. For symptomatic patients, posterior fossa decompression is the optimal surgical treatment. In the majority of patients, re- establishing CSF ﬂow at the foramen magnum results in spontaneous collapse of the syrinx. The majority of syrinxes will collapse within a few weeks of posterior fossa decompression, though it can take longer. If the syrinx does not collapse, then surgical drainage of the syrinx is indicated. Syrinx Without Chiari Malformation This group of patients is included here because if a syrinx is diagnosed then a Chiari malformation should be looked for with a brain MRI. If tonsillar ectopia is not iden- tiﬁed then surgical treatment should be aimed at the syrinx itself. Primary surgical treatment involves shunting the syrinx either into the subarachnoid or pleural space. One study described a group of patients with syringomyelia and no tonsillar ectopia who were treated successfully with posterior fossa decompression. He identiﬁed abnormalities in the posterior fossa anatomy on MRI scans and found intradural abnormalities at the foramen magnum at the time of surgery. Cine-ﬂow MRI scan- ning might be helpful in this group of patients to try and identify an alteration in CSF ﬂow at the foramen magnum. A measurable obstruction to CSF ﬂow would support a posterior fossa decompression as the ﬁrst surgical treatment.
Microwave Plasma CVD reactors use very similar conditions to hot ﬁl- ament reactors buy 160 mg diovan with visa, and despite being signiﬁcantly more expensive, are now among the most widely used techniques for diamond growth. MAY systems, microwave power is coupled into the chamber in order to create a discharge or plasma. This leads to heating and fragmentation of the gas molecules, resulting in diamond deposition onto a substrate which is immersed in the plasma. Nowadays, microwave powers of up to 60 kW can be utilised in such systems giving growth rates well in excess of 0. As well as high powers and hence higher growth rates, other advantages of microwave systems over other types of reactors are that they can use a wide variety of gas mixtures, including mixtures with high oxygen content, or ones composed of chlorine- or ﬂuorine-containing gases. The fact that no ﬁlament is involved makes microwave systems inherently cleaner than hot ﬁlament systems, and so they have become the system of choice for making diamond for electronic applications. A number of other deposition methods have been used for growing diamond, with varying degrees of success. These include oxyacetylene welding torches, arc jets and plasma torches, laser ablation and liquid phase crystallisation, but none of these yet realistically compete with the hot ﬁlament or microwave systems for reliability and reproducibility. At ﬁrst sight, this may seem like a daunting array of physical and chemical reactions which need to be grasped if diamond CVD is to be understood. But over the past 10 years there have been a large number of studies of the gas phase chemistry, and we are now beginning to obtain a clearer picture of the important principles involved. The ﬁrst clue was that diamond growth appeared to be independent of the chemical nature of the gas phase precursors – it was only the total number of carbons, hydrogens and oxygens in the reactant molecules that mat- tered. This meant that the gas phase chemistry is so rapid that it simply and effectively breaks down the constituent gases to smaller, reactive components. It is now believed that the most critical component in the gas phase mixture is atomic hydrogen, and indeed, this reactive atom drives the whole chemical system. In a hot ﬁlament system, the thermal energy Diamond thin films 81 Figure 5. Schematic representation of the physical and chemical processes occurring during diamond growth. The process gases ﬁrst mix in the chamber before diffusing toward the substrate surface.