Critical reviews in bioengineering最新文献

A rational goal of clinical pharmacology is to described and predict the relationship between drug dose and drug effect. The processes involved in the dose-effect relationship can be described in two main categories - pharmacokinetics, which is concerned with factors affecting the dose-active site concentration process, and pharmacodynamics, which describes the active site concentration-effect process. The development of models of the dose-effect relationship will be described starting with dose-effect models which do not distinguish between pharmacokinetics and pharmacodynamics, progressing to models based upon pharmacokinetic predictions of the active site concentration, and finally describing models which combine both pharmacokinetic and pharmacodynamic models to predict both active site concentrations and the drug effect.

Biomedical image processing is a very broad field; it covers biomedical signal gathering, image forming, picture processing, and image display to medical diagnosis based on features extracted from images. This article reviews this topic in both its fundamentals and applications. In its fundamentals, some basic image processing techniques including outlining, deblurring, noise cleaning, filtering, search, classical analysis and texture analysis have been reviewed together with examples. The state-of-the-art image processing systems have been introduced and discussed in two categories: general purpose image processing systems and image analyzers. In order for these systems to be effective for biomedical applications, special biomedical image processing languages have to be developed. The combination of both hardware and software leads to clinical imaging devices. Two different types of clinical imaging devices have been discussed. There are radiological imagings which include radiography, thermography, ultrasound, nuclear medicine and CT. Among these, thermography is the most noninvasive but is limited in application due to the low energy of its source. X-ray CT is excellent for static anatomical images and is moving toward the measurement of dynamic function, whereas nuclear imaging is moving toward organ metabolism and ultrasound is toward tissue physical characteristics. Heart imaging is one of the most interesting and challenging research topics in biomedical image processing; current methods including the invasive-technique cineangiography, and noninvasive ultrasound, nuclear medicine, transmission, and emission CT methodologies have been reviewed. Two current federally funded research projects in heart imaging, the dynamic spatial reconstructor and the dynamic cardiac three-dimensional densitometer, should bring some fruitful results in the near future. Miscrosopic imaging technique is very different from the radiological imaging technique in the sense that interaction between the operator and the imaging device is very essential. The white blood cell analyzer has been developed to the point that it becomes a daily clinical imaging device. An interactive chromosome karyotyper is being clinical evaluated and its preliminary indication is very encouraging. Tremendous efforts have been devoted to automation of cancer cytology; it is hoped that some prototypes will be available for clinical trials very soon. Automation of histology is still in its infancy; much work still needs to be done in this area. The 1970s have been very fruitful in utilizing the imaging technique in biomedical application; the computerized tomographic scanner and the white blood cell analyzer being the most successful imaging devices...

Three separate topics are covered in this review. The first deals with the technique of signal averaging. The concept of ensemble averaging is explored, and alternatives to this traditional tool are considered such as crosscorrelation averaging, latency corrected averaging, median averaging, etc. Different measures of variability of single evoked potentials are finally discussed. The second topic deals with modeling of the evoked potentials. The direct and inverse problems of source localization are discussed. Recent results of the application of these techniques to single evoked potentials are given. The third topic deals with the use of principal components for signal representation and comparison. Geometric consideration and varimax rotation of coefficients are discussed and examples given.

Of all the features of the electrocardiogram, the T wave shows the earliest and most dramatic correlation with abnormalities of electrical behavior in the heart. Yet, it has remained difficult to make quantitative connections between the T wave and electrical activity in the heart at the cellular level. It is the purpose of this paper to review attempts at deriving T waves from a knowledge of the membrane electrical activity in the heart and the geometry and conductive properties of the heart and its surrounding medium. We first summarize the problem of calculating T-wave potentials on the body surface, based on physical laws. Next, we review the empirical conclusions that have been reached through observations of the T wave, including its connection with repolarization of the cell membrane, the distributed nature of the current source during the T wave, and the gradient in action potential duration responsible for the positive polarity of the normal T wave. Six quantitative models have been proposed for the T wave; we compare these models and comment on their accuracy and underlying assumptions. Finally, we discuss ideas that have been suggested for the membrane mechanism of repolarization and the T wave.

Most cells and tissues have electrical properties relevant to their natural function. Most cells and tissues have rather complex structure, consisting of folding and invaginating membranes and specialized connections and organelles. The localization of electrical properties is particularly important, since each of the complex structures must be expected to have a specific role in the electrical function of the tissue. The structural analysis of electrical properties consists then in the measurements of the electrical properties of the individual components of the tissue or cell. The structural analysis proceeds by a qualitative analysis of the topology of the preparation, followed by quantitative measurements of the morphometric parameters, the surface, and volume of the relevant structures. A theoretical analysis is performed to determine the electrical properties expected from such a structure. Measurements of natural and induced electrical properties are then made. Comparison of the observed electrical properties with those predicted allows determination of the properties of individual components of the tissue. In this manner the role of individual membrane systems in the function of both skeletal muscle and the lens of the eye has been determined.

Since Berger's original observations of alpha intensity reductions accompanying mental activity, studies have attempted to elucidate spontaneous (background) EEG correlates of complex mental functions in normal adults. These efforts have failed to develop a model that successfully relates EEG patterns to aspects of cognition. Representative studies are criticized, and guidelines of minimal criteria for conducting research in this area are presented.