In Medical Imaging Physics, the authors cover the spectrum from radiation physics to computed tomography to radiobiology, while including some basic statistics and image analysis, in a style that would be comfortable for resident physicians in radiology, radiological technologists, and students beginning a career in medical physics and radiation biology. The math requirements are minimal, but sufficient for the material presented. In this book, the authors bring together a number of areas that one would normally find only in several separate books. The authors introduce the reader to ͑and explain at the appropriate level of complex-ity͒ basics of radiation ͑its production, its interactions, and its detection͒, types of imaging ͑nuclear medicine, radiography, CT, MR, ultrasound͒, image quality ͑resolution, noise, visual perception͒, and radiobiology. The chapters on radiation provide a good presentation of radioactive decay and interactions with matter, with various levels of depth being provided by the text and the side-bars. The discussion of x-ray imaging was comparable to that seen in other texts. Image quality was covered with a comprehensiveness that was welcome. The chapters on ultrasound and magnetic resonance are very nice introductions to these technologies, written at a level that nonpractitioners can readily grasp. In addition to the theory, the authors discuss the technology used in the various fields: nuclear detectors and instrumentation, ultrasound transducers and instrumentation, and MRI spectroscopy and instrumentation, as well as new developments in imaging. The radiobiology chapters could be especially useful since these issues are now in the public consciousness and would help address questions that can arise during in-services.
Most of the operational information retrieval (IR) systems in existence today useBoolean logic during search. Such systems are usually called Boolean IR systems. These systems, as any other IR systems, are not perfect and the problem of their development (and hence providing better quality service for real users) is one of the most important problems in Information Science. From this viewpoint, the article analyzes existing criticisms of operational systems and points out some of their positive features. At the same time, certain negative effects which hinder the development of existing systems are considered. Finally, the article provides several conclusions about using Boolean logic in developing multiversion IR systems.
On the basis of several pragmatic assumptions we developed an algorithm for the automatic construction of query formulations in Boolean form. The suggested algorithm also substantially simplifies the end-user interaction. The user expresses his search request by a set of documents pertinent to his need. The quality of the search depends only on the algorithm and on how completely and precisely the information need of a user is represented in his search request. The algorithm might also be useful for correcting query formulations on the basis of the user's feedback during his interaction with the system.
Shortest path algorithms for graphs have been widely studied and are of great practical utility. For the case of a general graph, Dijkstra's algorithm is known to be optimal. However, in many practical instances, there is a ''level'' structure which may be imposed on the underlying graph. Utilizing these levels, this paper demonstrates that the time complexity of shortest path generation may be greatly reduced.A new graph structure, the level graph, together with a simple uninformed heuristic, LGS, for searching that structure is introduced, which allows for rapid generation of approximate shortest paths. LGS is studied both analytically and via simulation. It is shown that the length of the path produced by LGS converges rapidly to that of the actual shortest path as the distance between the points increases. 0 1992 John Wiley & Sons, Inc.
Most of the operational information retrieval (IR) systems in existence today use Boolean logic during search. Such systems are usually called Boolean IR systems. These systems, as any other IR systems, are not perfect and the problem of their development (and hence providing better quality service for real users) is one of the most important problems in Information Science. From this viewpoint, the article analyzes existing criticisms of operational systems and points out some of their positive features. At the same time, certain negative effects which hinder the development of existing systems are considered. Finally, the article provides several conclusions about using Boolean logic in developing multiversion IR systems.
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