Radiation dose reduction at a price: the effectiveness of a male gonadal shield during helical CT scans

BACKGROUND: It is estimated that 60 million computed tomography (CT) scans were performed during 2006, with approximately 11% of those performed on children age 0–15 years. Various types of gonadal shielding have been evaluated for reducing exposure to the gonads. The purpose of this study was to quantify the radiation dose reduction to the gonads and its effect on image quality when a wrap-around male pediatric gonad shield was used during CT scanning. This information is obtained to assist the attending radiologist in the decision to utilize such male gonadal shields in pediatric imaging practice. METHODS: The dose reduction to the gonads was measured for both direct radiation and for indirect scattered radiation from the abdomen. A 6 cm(3 )ion chamber (Model 10X5-6, Radcal Corporation, Monrovia, CA) was placed on a Humanoid real bone pelvic phantom at a position of the male gonads. When exposure measurements with shielding were made, a 1 mm lead wrap-around gonadal shield was placed around the ion chamber sensitive volume. RESULTS: The use of the shields reduced scatter dose to the gonads by a factor of about 2 with no appreciable loss of image quality. The shields reduced the direct beam dose by a factor of about 35 at the expense of extremely poor CT image quality due to severe streak artifacts. CONCLUSION: Images in the direct exposure case are not useful due to these severe artifacts and the difficulties in positioning these shields on patients in the scatter exposure case may not be warranted by the small absolute reduction in scatter dose unless it is expected that the patient will be subjected to numerous future CT scans

Two new species of Odontostilbe historically hidden under O. microcephala (Characiformes: Cheirodontinae)

Specimens historically identified as Odontostilbe microcephala from the upper rio Paraná and Andean piedmont tributaries of the río Paraguay are reviewed and split in three species. We found that the distribution of O. microcephala is restricted to the Andean slope of the río Paraguay basin. The species is distinguished from congeners with subterminal mouth by the elongate body, usually 10-12 gill rakers on upper branch and smaller horizontal orbital diameter (24.6-32.8 % HL, mean 28.7%). Specimens from upper rio Paraná constitute two new species, diagnosed from other Cheirodontinae by the presence of mesopterygoid teeth, grouped on median portion and forming a continuous row. The new species are distinguished from each other by having premaxillary teeth with five cusps vs. nine cusps and by the number of lamellae in left and right sides of central median raphe of olfactory rosette with 20-21 vs. 11-12.Espécimes historicamente identificados com Odontostilbe microcephala do rio Paraná e tributários do río Paraguay, foram revisados e separados em três espécies. A distribuição de O. microcephala é restrita ao sopé andino da bacia do río Paraguay. A espécie é distinta das congêneres com boca subterminal pela forma alongada, geralmente 10-12 rastros branquiais no ramo superior e menor diâmetro horizontal da órbita (24,6-32,8 % CC, média 28,7%). Espécimes do alto rio Paraná constituem duas espécies novas diagnosticadas de outros Cheirodontinae pela presença de dentes no mesopterigoide, agrupados em sua porção média e formando uma fileira continua. As novas espécies distinguem-se por ter dentes premaxilares com cinco cúspides vs. nove cúspides e pelo número de lamelas nos lados esquerdo e direito da rafe central da roseta olfativa com 20-21 vs. 11-12

Short spatial and temporal scale patterns of fish assemblages in a subtropical rainforest mountain stream

The fish fauna of a subtropical mountain stream in Argentina was surveyed for the first time. The abundance and occurrence of species were explored considering variation in hydrology, seasonality and the abiotic environment. We collected 221 individuals of 23 species from 10 families and four orders. Small sized species and small individuals dominated the fish fauna. The small characid Astyanax saguazu was the most conspicuous species. Hydrology, seasonal changes in water temperature and variation in water conductivity affected the abundance and distribution of fish. Hypobrycon maromba is recorded in Argentina for the first time.Fil: Rosso, Juan Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Mabragaña, Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Avigliano, Esteban. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias. Centro de Estudios Transdisciplinarios del Agua; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Schenone, Nahuel Francisco. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias. Centro de Estudios Transdisciplinarios del Agua; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Diaz de Astarloa, Juan Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Phylogeography of Cnesterodon decemmaculatus (Cyprinodontiformes: poeciilidae) in Southern Pampas, Argentina: ancient versus recent patterns in freshwater fishes

The Southern Pampean Area includes the southernmost limit of the Brazilian subregion and represents an interesting model to study how evolution of the landscape has affected the distribution of freshwater fishes in time and space. The hydrogeographic pattern of the region results from a combination of factors including climatic and sea level changes occurred since the Miocene and extending into the Quaternary. The hydrologic basins of this region are isolated, and have a similar ichthyological composition among them. Here we use a phylogeographic approach to infer how paleoclimatic changes affected the distribution of genetic variation in the populations of freshwater fishes. We analyzed the control region of mtDNA of Cnesterodon decemmaculatus and compared it with published data for the species Jenynsia multidentata and Corydoras paleatus in the same area. Cnesterodon decemmaculatus showed two main haplotypes with scarce divergence and wide geographical distribution within the area. The low divergence found between the Cnesterodon decemmaculatus haplotypes and the results obtained in the demographic analyses could suggest that the presence of this species in the area have a recent demographic history. These results are in contrast with the pattern reported for Jenynsia multidentata and Corydoras paleatus, where data suggest an ancient history in the area. The incongruence in the observed phylogeographical patterns could be due to the different ecological requirements of each species, and to the various responses of them to the environmental conditions resulting from geologic and paleoclimatic changes occurred in the region during the Late Quaternary.Fil: Bruno, María Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Biología. Laboratorio de Genética; ArgentinaFil: Mapelli, Fernando Javier. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Biología. Laboratorio de Ecofisiología; ArgentinaFil: Casciotta, Jorge Rafael. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento Científico Zoología Vertebrados; ArgentinaFil: Almirón, Adriana Edith. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento Científico Zoología Vertebrados; ArgentinaFil: Lizarralde, Marta Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentin