Distinct Signal Patterns Research Articles

Prevalence of Radioactive Signals from Surveillance of an Emergency Department

Since the 11 September 2001 terrorist attacks in the United States, concerns have been raised regarding the threat of a radiological terrorist weapon. Although the probability of the employment of a nuclear device is remote, the potential of a radiological dispersal device (RDD) or "dirty bomb" is of concern. While it is unlikely that such a device would produce massive numbers of casualties, it is far more likely that it would result in public panic and perhaps even disable the local healthcare system. The utility of surveillance with radiation detectors in the healthcare setting has not been fully evaluated. The objective of this study was to characterize the prevalence of radioactive sources entering an urban emergency department (ED). A retrospective review of data obtained from a radiation detector positioned to detect radioactive people entering an ED of an urban academic hospital that serves 45,000 patients/year was performed. Graphical outputs of radioactivity were recorded in Microsoft Excel (Microsoft, Redmond, WA, US) spreadsheets in microREM/hour. Data were collected continuously from 22 December 2003 to 22 January 2004. An event was defined as any elevation in radiation levels >95% confidence interval from the mean level of background radiation over 72 hours (h). A total of 215 events were observed over a 28-day period, with a mean value of 7.7 events/day, and a maximum of 15 events/day. During the 28-day period, the baseline mean level of background radiation was 2-4 microREM/h. Readings ranged from 2,148.28-17,292.25 microREM/h with a maximum sustained detector exposure of 684.37 microREM. Distinct signal patterns were seen at both detectors including tonic, phasic, dual, and short duration spikes. The number of radioactive signals detected from persons entering the ED was much higher than expected. While the vast majority of these signals pose no health threat, they may make routine screening for a radiological terrorist event difficult. Further study is needed to determine this correlation.

Stable carbon isotopes in freshwater mussel shells: Environmental record or marker for metabolic activity?

Mussel shells have been used in a number of paleoecological and environmental studies. The interpretation of stable carbon isotopic composition of shell material is still controversial. The carbon for shell carbonate precipitation can either be derived from ambient dissolved inorganic carbon (DIC), with shells recording environmental signals, or from metabolic CO 2, with the potential to disguise environmental signals. To gain insight into this question, we investigated four nearly 100-yr long-term records of aragonite shells from an extant freshwater bivalve species, the endangered freshwater pearl mussel ( Margaritifera margaritifera L.). Single growth increments of the outer prismatic and the inner nacreous zones were successfully and easily separated with a simple heat treatment for chronological analyses of δ 13C in single layers of each zone. Autocorrelation and semivariance statistical methods reveal that mussels show distinct individual signal patterns, which extend up to 25 yr. Signal patterns are reliably reproduced with replicate samples from defined layers within one shell and show similar patterns with a slight offset for inner nacreous and outer prismatic layers for individual animals. Mussels exposed to the same environmental conditions exhibit distinct and contradictory signature patterns, which do not match between individuals. This observation can only be explained by strong metabolic influences on shell precipitation. Environmental changes in pH, temperature, electric conductivity and atmospheric carbon signature had no or little (<5%) influence, whereas body tissue protein and body tissue δ 13C signatures negatively correlated with the youngest produced shell δ 13C signatures, indicating that respiration causes a preferential loss of light isotopes from body mass and an inverse enrichment in shell aragonite. Hence, the shells of the freshwater pearl mussel yield a long-term record of metabolic activity, whereas the use of δ 13C in these shells as recorder for environmental signals is questionable. This may also be true for shells from other species, for which metabolic carbon incorporation has been acknowledged.

In vitro and in situ magnetic resonance imaging signal features of atherosclerotic plaque-associated lipids.

The goal of this study was to evaluate magnetic resonance imaging (MRI) signal features of the different types of lipids found in human atherosclerotic plaques. A 1.5-T SIGNA scanner was used to acquire T1-, T2-, and proton density-weighted data at four different temperatures for individual lipids and lipid mixtures designed to replicate the proportions of lipids found in plaques. Individual lipids and lipid mixtures were scanned both in a test tube and after implantation in the media of normal porcine aortas. Each of the three broad classes of lipids (triglycerides, unesterified and esterified cholesterol, and phospholipids) had different and distinct MR signal patterns, which allowed discrimination of these classes of lipids in vitro. Further, lipid implantation studies demonstrated that these distinct MR signal patterns could be used to readily distinguish each lipid type from surrounding porcine aortic media. MR signals from lipid mixtures demonstrated marked regional heterogeneity, similar to the heterogeneous lipid distribution characteristic of human atherosclerotic plaques. In summary, MR signals from lipid mixtures that mimic plaque lipid proportions can be detected at body temperature, especially in those mixtures with an increased percentage of cholesteryl esters. These studies raise the possibility that with further advances in technology, MRI may become a useful tool for determining the lipid content and composition of human atherosclerotic plaques in vivo.