A Probabilistic Exclusion Principle for Tracking Multiple Objects

Tracking multiple targets is a challenging problem, especially when the targets are identical, in the sense that the same model is used to describe each target. In this case, simply instantiating several independent 1-body trackers is not an adequate solution, because the independent trackers tend to coalesce onto the best-fitting target. This paper presents an observation density for tracking which solves this problem by exhibiting a probabilistic exclusion principle. Exclusion arises naturally from a systematic derivation of the observation density, without relying on heuristics. Another important contribution of the paper is the presentation of partitioned sampling, a new sampling method for multiple object tracking. Partitioned sampling avoids the high computational load associated with fully coupled trackers, while retaining the desirable properties of coupling.     

Combination of intrathecal sufentanil 10 mug plus bupivacaine 2.5 mg for labor analgesia: is half the dose enough?

The genetic diversity of 88 Streptococcus suis serotype 2 isolates which were recovered from various countries was examined by randomly amplified polymorphic DNA (RAPD) analysis with three primers. This bacterial collection included 80 isolates of porcine origin and 8 of human origin. This investigation allowed the identification of 23 RAPD types containing 1 to 30 isolates originating from one to six countries. Common RAPD patterns were found between human and pig isolates. The isolates were also tested for the production of virulent factors such as hemolysin, muramidase-released protein (MRP), and extracellular factor (EF). All isolates exhibiting the virulent phenotype hemolysin+ MRP+ EF+ clearly clustered on the basis of fingerprinting by RAPD analysis. In a similar way, most of isolates with the hemolysin- MRP- EF- phenotype were assigned to one RAPD cluster. Therefore, RAPD clusters are more related to the phenotype defined with hemolysin, MRP, and EF than to the geographic origin of the isolates. These data indicate that RAPD analysis used in conjunction with phenotypic methods provides a reliable method for the assessment of the clonal relationship between S. suis isolates responsible for infections in pigs or humans, especially for those exhibiting the classic "virulent" phenotype hemolysin+ MRP+ EF+.     

Automated measurement of peak widths for the determination of peak capacity in complex chromatograms

In a large number of cases, the etiology of community-acquired pneumonia (CAP) is not established. Some cases are probably caused by Streptococcus pneumoniae. Transthoracic needle aspiration (TNA) culture has a limited sensitivity which might be improved by antigen detection or gene amplification techniques. We evaluated the capacity of a PCR assay and a latex agglutination test to detect S. pneumoniae in samples obtained by TNA from 95 patients with moderate-to-severe CAP. Latex agglutination and PCR had sensitivities of 52.2 and 91.3%, specificities of 88.7 and 83.3%, positive predictive values of 62.3 and 65.6%, and negative predictive values of 83.3 and 96.5%, respectively, when culture techniques were used as the "gold standard." When we considered expanded criteria for the diagnosis of pneumococcal pneumonia as a standard for our calculations, latex agglutination and PCR had sensitivities of 53.6 and 89.7%, specificities of 93.0 and 90.0%, positive predictive values of 78.9 and 81.3%, and negative predictive values of 80.3 and 94.7%, respectively. The additional diagnosis provided by the PCR assay compared to latex agglutination was 12.2% (95% confidence interval of the difference from 0.4 to 20. 1%). PCR was more sensitive than TNA culture, particularly in patients who had received prior antibiotic therapy (83.3 versus 33. 3%). Although PCR is a very sensitive and specific technique, it has not proved to be cost-effective in clinical practice. Conversely, latex agglutination is a fast and simple method whose results might have significant implications for initial antibiotic therapy.     

Excitotoxic neurodegeneration induced by deprivation of oxygen and glucose in isolated retina

PURPOSE: Ischemic neurodegeneration contributes to many retinal diseases. An isolated retina model has been used to examine the neuronal cell death induced by deprivation of oxygen and glucose (simulated ischemia) as a model for ischemic disease. METHODS: Neurodegeneration in the isolated chick embryo retina was induced by simulated ischemia and assessed using biochemical (lactate dehydrogenase release) and morphologic (light microscopy) techniques. RESULTS: Simulated ischemia led to lactate dehydrogenase release gradually in a period of 6 to 24 hours. Light microscopic observations demonstrated morphologic cell degeneration well before lactate dehydrogenase release occurred. N-Methyl-D-aspartate (NMDA) and non-NMDA receptor blockers individually provided partial protection, and the combination was fully protective. No protection was provided if the antagonists were added after simulated ischemia. When NMDA receptors were blocked by MK-801, cyclothiazide, an inhibitor of desensitization at non-NMDA receptors, enhanced lactate dehydrogenase released after 1 or 2 hours of simulated ischemia. Low concentrations of glucose effectively prevented lactate dehydrogenase release, despite anoxic conditions. CONCLUSIONS: The isolated retina provided a convenient system to characterize quantitatively ischemic cell death. Retinal ischemic neurodegeneration is an excitotoxic process that involves overactivation of NMDA and non-NMDA glutamate receptors. Blockade of both of these receptor subtypes was necessary for complete neuroprotection. Receptor desensitization played a protective role. If even low concentrations of glucose were delivered to an ischemic retina in vitro, substantial neuroprotection could be achieved. This may have implications for the management of acute retinal ischemic episodes.     

Appearances deceive in investigations of cancer clusters

Many a doctor from time to time encounters people concerned about environmental causes of disease, whom he or she cannot answer properly because of lack of knowledge concerning the effects of chemical or physical exposure of the human body (nuclear plants, environmental pollution, electromagnetic radiation). Usually post hoc cluster investigation is very unrewarding especially when there is no clearcut hypothesis or evidence of a causal relation, and when the relative risk is well below 8. From an epidemiological point of view it is surprising that an unexpectedly low frequency of a certain disease in a particular region does not attract this kind of attention. Concerned people will most probably benefit more from risk communication by environmental epidemiologists than from cluster investigation or extensive case-control studies ('fishing expeditions') in case little is known of the etiology.     

Verification of the omni wedge technique

The optimal field shape achieved using a multileaf collimator (MLC) often requires collimator rotation to minimize the adverse effects of the scalloped dose distribution the leaf steps produce. However, treatment machines are designed to deliver wedged fields parallel or perpendicular to the direction of the leaves. An analysis of cases from our clinic showed that for 25% of the wedged fields used to treat brain and lung tumors, the wedge direction and optimal MLC orientation differed by 20 degrees or more. The recently published omni wedge technique provides the capability of producing a wedged field with orientation independent of the orientation of the collimator. This paper presents a comparison of the three-dimensional (3D) dose distributions of the omni wedged field with distributions of wedged fields produced using both the universal and dynamic wedge techniques. All measurements were performed using film dosimetry techniques. The omni wedge generated fields closely matched the conventional wedged fields. Throughout 95% of the irradiated volume (excluding the penubra), the dose distribution of the omni wedged field ranged from +5.5 to -3.5 +/- 1.5% of that of the conventionally wedged fields. Calculation of the omni wedged field is as accurate as conventional wedged field calculation when using a 3D treatment planning systems. For two-dimensional treatment planning systems, where one must assume that the omni wedged field is identical to a conventional field, the calculated field and the delivered field differs by a small amount.