Open wet ashing of some types of biological materials for the determination of mercury and other toxic elements.

An open wet decomposition procedure for trace element analysis of biological material has been worked out. It is based on the utilization of nitric acid, hydrochloric acid and hydrogen peroxide and is well suited for the determination of As, Bi, Cd, Cr, Hg, Pb, Sb, Se and Tl. For these elements the recoveries were examined by the radiotracer technique, with lichens, pine needles, grass and human hair as representative biological samples. In addition to the conventional labelling technique, use was also made of in situ labelling. In all cases, recoveries between 93 and 100% were achieved, which are adequate for quantitative trace element analysis.

On the stability of shared near neighbor clustering.

This correspondence concentrates on the detection of stable clustering results when using the nonparmetric clustering technique of Jarvis and Patrick. This technique incorporates the concept of similarity based on sharing of near neighbors. Essentially, in this clustering scheme, two parameters are involved: neighborhood depth and similarity threshold. Combining a penalty for chaining with the detection of so-called hierarchical stable solutions in the field of all possible solutions, due to the setting of the two parameters, is experimentally shown to provide a powerful method for discriminating between reliable and unreliable results.

Data compression of x-ray cardio-angiographic image series.

Medical x-ray images are increasingly stored and transmitted in a digital format. To reduce the required storage space and transmission bandwidth, data compression can be applied. In this paper we describe a new method for data compression of cardio-angiographic x-ray image series. The method is based on so-called overlapped-transform coding. A comparison with the well-known block-based transform-coding methods JPEG and MPEG is presented. We found that overlapped-transform coding does not introduce any blocking artefacts, in contrast to block-based transform coding, which introduces clearly visible blocking artefacts at compression ratios above 8. Clinical evaluations of the new method have pointed out that the image quality obtained at a compression ratio of 12 is adequate for diagnostic applications.