Future wireless communication systems have to be realised in a simple and energy efficient manner while guaranteeing sufficient performance. Furthermore, the available frequency resources have to be used flexibly and efficiently. In this context two different approaches have been considered in recent years: On one hand OFDM-based overlay systems in which a primary user dynamically allocates unused frequencies to one or more secondary users [57] and on the other hand unlicensed, easy-to-realise and low-cost ultra-wideband (UWB) systems. This underlying technology operates with an extremely low transmission power over a wide frequency range and does not interfere with existing licensed systems [15].
The accuracy of the Monte Carlo algorithm for fast electron dose calculation, VMC, is demonstrated by comparing calculations with measurements performed by a working group of the National Cancer Institute (NCI) of the USA. For both energies investigated, 9 and 20 MeV, the measurements in water are taken to determine the energy spectra of the Varian Clinac 1800 accelerator. For the majority of the experiments a good agreement is found between measurements and VMC calculations. However, in some cases deviations have been observed, which could be explained by the incompletely known geometry on the one hand and by inconsistent data on the other hand. As a reference, dose distributions calculated by the MDAH pencil-beam algorithm are also presented. It is shown that, especially near low- or high-density inhomogeneities, large dose overestimations and underestimations are calculated by using a pencil-beam approach, whereas VMC is able to reproduce the correct doses for these cases also.
The spatial dimension of man-environment interactions in old age is analyzed within urban, suburban, and rural residential environments of the German Rhine-Main-Agglomeration. By comparing the three levels of organization, utilization, and interpretation, housing conditions as well as geographical distribution and redistribution (migrations) our outside-home-activities and environmental perception show a fundamental influence on the everyday lives of the 750 elderly who were interviewed. The majority of the target population and, especially, the rural elderly is characterized by traditional patterns of spatial organization and distribution, mobility, regional attachment, and a concern about preserving the stability of their current residential environment from changes. The suburban and urban seniors, however, exhibit a greater amount of locational flexibility and utility-oriented behavior patterns. These spatial variations are induced by specific regional values and intensity of local and regional identification. They might be interpreted as different stages in the process of modernization within postindustrial societies. Reflecting, however, the paradigms of planning for the elderly, these different patterns are not systematically considered to the necessary and sufficient extent. Instead of promoting regional or local networks that are favored by senior citizens, agencies usually prefer comprehensive approaches on a macrolevel. First steps to improve this situation and to combine life- and system-world demands have been taken by the federal government, which implemented a neighborhood-related research program on housing for the elderly. As a result of this, further research on environmental aspects on aging should pay more methodological attention to the hitherto neglected regional and local level, and also for the transfer of its findings into planning policy.
Due to the small size and complexity of its constituents, the triangular fibrocartilage complex (TFCC) has been a challenging structure for magnetic resonance (MR) imaging. Higher-field MR units, at 3T and 7T, with increased spatial resolution and the development of novel MR sequences, are promising tools for an improved visualization of the ulnocarpal complex. Anatomically, the TFCC consists of the TFC proper, the ulnomeniscal homolog, the ulnar collateral ligament, the ulnotriquetral and ulnolunate ligament, and radioulnar ligaments at the volar (palmar) and the dorsal side, as well as the sheath of the extensor carpi ulnaris tendon and the capsule of the distal radioulnar joint. This article describes the normal anatomy of the TFCC and its appearance on high-field MRI. Anatomical variants, such as the positive ulnar variance, and changes during pronation and supination are addressed.
Background: Obstetric imaging, subserving fetal evaluation, may yield incidental maternal findings. Based on prenatal magnetic resonance (MR) imaging, this study aims to investigate incidental intervertebral disc degeneration and displacement in young, pregnant women. Methods: This retrospective study included the sagittal 1.5 Tesla, T2-weighted lumbar spine images of 943 pregnant Central Europeans (age range, 18-47 years), who initially had undergone MR imaging because of sonographically suspected fetal abnormalities. Qualitatively, 4715 lumbar intervertebral discs were evaluated for degeneration using a modified Pfirrmann MR classification (nondegenerated, low-grade, moderate, and high-grade degeneration), as well as for displacement. In addition to descriptive statistics, an ordinal regression analysis was performed to analyze the relationship between degeneration and the women's age, and body weight. Results: With regard to the highest degree of degeneration in each woman, 578 (61.3%) showed low-grade, 211 (22.4%) moderate, and 154 (16.3%) high-grade degeneration, and no woman had entirely nondegenerated discs. For the span from 18 to 47 years of age, moderate and high-grade degeneration increased from 6.7% to 36.7% and from 13.3% to 22.4%, respectively. Of 943 women, 57 (6%) had disc displacements, of which 97% were in conjunction with high-grade degeneration. There was a statistically significant relationship (p < 0.001) between degeneration and age, and between degeneration and body weight. Conclusions: In young pregnant women, lumbar intervertebral disc degeneration is a ubiquitous, incidental finding, increasing from the late second decade of life onward, which may be part of physiological aging, as opposed to a small percentage of incidental disc displacements.
In Brief Study Design. Prospective in vivo study of meniscoids in the cervical zygapophysial joints. Objective. To generate reference data for in vivo magnetic resonance (MR) imaging properties of meniscoids in the cervical zygapophysial joints. Summary of Background Data. Meniscoids, also called synovial folds, are tiny anatomic structures within the zygapophysial joints. It has been suggested that pathologic conditions of meniscoids may be a potential source of cervical pain. Prior studies were limited to in vitro observations. To identify pathologic conditions of the meniscoids, it is necessary to obtain reference data of basic in vivo MR imaging properties of meniscoids in a healthy population. Methods. Fifty-six healthy volunteers (33 women, 23 men; mean age 42.0 ± 17.1 years) were investigated in a 3.0 Tesla MR scanner using high resolution isotropic 3-dimensional sequences. Presence, size, location, and signal intensity of the meniscoids were assessed, and their dependence on sex, age, body mass index, and degenerative changes were analyzed by t test and correlation analysis. Results. There was no significant difference in presence (20.3 ± 4.8 vs. 19.7 ± 4.8) and size (3.8 ± 0.7 mm vs. 4.1 ± 0.5 mm) of meniscoids between women and men. Presence of meniscoids decreased with increasing age (r = −0.38, P = 0.004). Size of meniscoids did not significantly depend on age (r = 0.02, P = 0.91). Meniscoid entrapment (location) was a rare condition (0.4%). Tissue composition (signal intensities) of the meniscoids was 61.6% mainly fatty, 15.8% mainly fibrous, and 22.6% mixed. Conclusion. Basic data about in vivo MR imaging properties of cervical meniscoids in a healthy population have been successfully generated. Subsequent studies may use these data as reference for the identification of meniscoid pathologies. Meniscoids are anatomic structures within the zygapophysial joints that are suggested to be potential sources of pain. This study generated reference data for in vivo magnetic resonance imaging properties of meniscoids in a healthy population, including presence, size, location, and signal intensities. These data might serve as reference for the identification of meniscoid pathologies.
