X-ray Exposures (x-ray + exposure)

Distribution by Scientific Domains

Selected Abstracts

Accelerated growth of intestinal tumours after radiation exposure in Mlh1-knockout mice: evaluation of the late effect of radiation on a mouse model of HNPCC

Yutaka Tokairin
Summary Mlh1 -knockout mice have been developed as a useful model of hereditary non-polyposis colorectal cancer (HNPCC). In this study, we analyzed the pathology of gastrointestinal tumours (GIT) in these mice in detail and examined the possible effects of ionizing radiation on the induction of intestinal tumours to evaluate the late response to radiotherapy in HNPCC. Mlh1,/, mice spontaneously developed GIT and thymic lymphomas by 48 weeks. GIT included not only well differentiated adenocarcinomas but also poorly differentiated and mucinous adenocarcinomas, suggesting that this mouse is a good model for HNPCC. In contrast to colon cancers from HNPCC patients, however, carcinomas of Mlh1,/, mice expressed p53 and showed a lack of transforming growth factor (TGF) -,RII mutation, which resulted in the expression of TGF-,RII protein. Irradiation of 10-week-old Mlh1,/, mice accelerated GIT development but had little effect at 2 weeks. Mlh1+/, and Mlh1+/+ mice were not susceptible to spontaneous or radiation-induced thymic lymphomas and GIT until 72 weeks after birth. The development and pathology of GIT in Mlh1,/, mice suggest that this mouse is a good model for HNPCC, although tumour-related responsible genes might be different from HNPCC. As X-ray exposure promoted carcinogenesis of GIT in adult Mlh1,/, mice, an increased risk of secondary cancers after radiotherapy for HNPCC patients should be taken into consideration. [source]

The Beamline X28C of the Center for Synchrotron Biosciences: a National Resource for Biomolecular Structure and Dynamics Experiments Using Synchrotron Footprinting

Sayan Gupta
Structural mapping of proteins and nucleic acids with high resolution in solution is of critical importance for understanding their biological function. A wide range of footprinting technologies have been developed over the last ten years to address this need. Beamline X28C, a white-beam X-ray source at the National Synchrotron Light Source of Brookhaven National Laboratory, functions as a platform for synchrotron footprinting research and further technology development in this growing field. An expanding set of user groups utilize this national resource funded by the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health. The facility is operated by the Center for Synchrotron Biosciences and the Center for Proteomics of Case Western Reserve University. The facility includes instrumentation suitable for conducting both steady-state and millisecond time-resolved footprinting experiments based on the production of hydroxyl radicals by X-rays. Footprinting studies of nucleic acids are routinely conducted with X-ray exposures of tens of milliseconds, which include studies of nucleic acid folding and their interactions with proteins. This technology can also be used to study protein structure and dynamics in solution as well as protein,protein interactions in large macromolecular complexes. This article provides an overview of the X28C beamline technology and defines protocols for its adoption at other synchrotron facilities. Lastly, several examples of published results provide illustrations of the kinds of experiments likely to be successful using these approaches. [source]

The weak outnumbering the mighty: normal galaxies in deep Chandra surveys

A. E. Hornschemeier
Abstract Chandra is detecting a significant population of normal and starburst galaxies in extremely deep X-ray exposures. For example, approximately 15% of the sources arising in the 2 Ms Chandra Deep Field-North survey are fairly normal galaxies, where "normal" means "Milky Way-type" X-ray emission rather than simply exhibiting an "optically normal" spectrum. Many of these galaxies are being detected at large look-back times (z , 0.1,0.5), allowing the study of the evolution of X-ray binary populations over significant cosmological timescales. We are also detecting individual off-nuclear ultraluminous X-ray sources (e.g., X-ray binaries), providing the first direct constraints on the prevalence of lower-mass black holes at significantly earlier times. The X-ray emission from such "normal" galaxies may also be a useful star-formation rate indicator, based on radio/X-ray cross-identifications. We describe the contribution of normal galaxies to the populations which make up the X-ray background and present their directly measured X-ray number counts. We find that normal and starburst galaxies should dominate the 0.5,2 keV number counts at X-ray fluxes fainter than , 7 × 10,18 erg cm,2 s,1 (thus they will outnumber the "mighty" AGN). Finally, we look to the future, suggesting that it is important that the population of X-ray faint normal and starburst galaxies be well constrained in order to design the next generation of X-ray observatories. [source]

Catheter Ablation of Common-Type Atrial Flutter Guided by Three-Dimensional Right Atrial Geometry Reconstruction and Catheter Tracking Using Cutaneous Patches:

A Randomized Prospective Study
Introduction: EnSite® NavXÔ (NavX) is a novel mapping and navigation system that allows visualization of conventional catheters for diagnostic and ablative purposes and uses them to create a three-dimensional (3D) geometry of the heart. NavX is particularly suitable for ablation procedures utilizing an anatomic approach, as in the setting of common-type atrial flutter (AFL). The aim of this study was to compare NavX-guided and conventional ablation procedures for AFL. Methods and Results: Forty consecutive patients (32 male, 59 ± 12 years) with documented AFL were randomized to undergo fluoroscopy-guided (group I, 20 patients) or NavX-guided (group II, 20 patients) ablation, including 3D isthmus reconstruction. The same catheter setup was used in both groups. The endpoint of bidirectional isthmus block was obtained in all patients. Compared to conventional approaches, NavX-guided procedures significantly reduced fluoroscopy time (5.1 ± 1.4 min vs 20 ± 11 min, P < 0.01) and total x-ray exposure (5.1 ± 3.1 Gycm2 vs 24.9 ± 1.6 Gycm2, P < 0.01). Isthmus geometry reconstruction could be performed in all patients of group II. In 4 patients (20%) of group II, anatomic isthmus variations were detected by NavX. No significant differences in radiofrequency current applications and procedural times were found between the two groups. Conclusion: NavX technology allows geometry reconstruction of the cavotricuspid isthmus. NavX-guided ablation of AFL reduces total x-ray exposure compared to the fluoroscopy-guided approach but does not prolong procedure time. [source]