The object of this study was to elucidate what is actually measured in electrogastrography. Comparison of gastric signals simultaneously recorded from serosal and cutaneous electrodes in the conscious dog led to the following findings: 1. In the absence of phasic contractile activity and electrical response activity (ERA), the cutaneous recordings contained a frequency corresponding to the fundamental frequency of the electrical control activity (ECA) of the stomach (about 0.08 Hz). 2. Tachygastrias gave rise to cutaneous signals containing the tachygastric frequency (about 0.25 Hz). 3. The amplitude of the electrogastrogram increased when ERA occurred. It is concluded that both ECA and ERA are reflected in the electrogastrogram. A model is proposed that describes the electrogastrogram as the result of field potentials generated by depolarization and repolarization dipoles.

SUMMARY Using cutaneous electrodes an electrogastrographic study was made of gastric myoelectrical activity in both the fasting and postprandial states in 48 patients with unexplained nausea and vomiting and in 52 control subjects. A gastric emptying study, using a radio-labelled solid phase meal, was carried out in 30 of these 48 patients. A follow up study was done after one year. In 48% of the patients abnormal myoelectrical activity was found which was characterised by: (1) instability of the gastric pacemaker frequency; (2) tachygastrias in both the fasting and postprandial states; (3) the absence of the normal amplitude increase in the postprandial electrogastrogram. This last characteristic was correlated with a delayed gastric emptying of solids. The present study shows that with electrogastrography in a heterogeneous group of patients with unexplained nausea and vomiting a subgroup can be discerned with abnormal myoelectrical activity. Our findings suggests that this abnormal myoelectrical activity is related to these symptoms.

An extensive series of dual-energy X-ray absorptiometry (DXA) scans and dual polyenergetic X-ray simulation studies of 150 different phantom arrays were carried out to evaluate quantitatively the extent of systematic inaccuracies inherent in DXA in vivo bone mineral density (BMD). These measurements are particularly relevant to lumbar vertebral and proximal femoral sites. The phantoms were specially fabricated near perfect absorptiometric representations of bone material, red marrow (

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In the last decade, the fractal dimension has become a popular parameter to characterize image textures. Also in radiographs, various procedures have been used to estimate the fractal dimension. However, certain characteristics of the radiographic process, e.g., noise and blurring, interfere with the straightforward application of these estimation methods. In this study, the influence of quantum noise and image blur on several estimation methods was quantified by simulating the effect of quantum noise and the effect of modulation transfer functions, corresponding with different screen-film combinations, on computer generated fractal images. The results are extrapolated to explain the effect of film-grain noise on fractal dimension estimation. The effect of noise is that, irrespective of the noise source, the fractal dimension is overestimated, especially for lower fractal dimensions. On the other hand, blurring results in an underestimation of the dimensions. The effect of blurring is dependent on the estimation method used; the dimension estimates by the power spectrum method are lowered with a constant value, whereas the underestimation by the methods working in the spatial domain is dependent on the given dimension. The influence of the MTF and noise on fractal dimension estimation seriously limits the comparability of fractal dimensions estimated from radiographs which differ in noise content or MTF. Only when the power spectrum method is used, it is possible to correct for the influence of different MTFs of screen-film combinations. It is concluded that only when using the same object-focus distance, the same exposure conditions, the same digitizer at the same resolution, can fractal dimensions as estimated in radiographs be reliably compared.