Convenience implantation therapy

Central venous catheters vary in composition, lumen size, number of injection ports, and other special features that affect ease or convenience of care and maintenance. They may be placed for shorter long-term access. Frequently, short-term central venous access is obtained in critically ill neonates via a catheter placed in the umbilical vein. ° Other sites for central venous access in infants and older children are similar to those in adults. When therapy is expected to last longer than 4 weeks, the catheter usually is tunneled subcutaneously before entering the central vessel, secured initially with retaining sutures, and anchored in place with a felt cuff that promotes the growth of subcutaneous flbrotic tissue around the catheter. The injection port may remain external or be concealed entirely beneath the skin. Implanted central venous catheters have a larger port or reservoir that is surgically placed beneath the skin surface and anchored in the muscle of the chest wall. 

When Cf is used as a neutron source, the data listed in Table 11.2 are useful. Practical applications of Cf make use of the spontaneous-fission neutrons generated by this isotope. Neutrons from Cf sources have been useful in such areas as neutron activation analysis, neutron radiography (complements x-ray radiography), and medical therapy. These neutron sources are most useful where access to nuclear reactors is not possible, not convenient, and/or where a lower neutron flux is adequate. For example, portable neutron activation analysis systems have been designed for use in deep-sea exploration for minerals. Various sizes and forms of Cf sources have been designed for medical applications, both for external irradiation and internal implantation. How extensive the practical application of Cf may become will be determined by the success of experiments using this nuclide. 

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