7307952
Optimal variable-density k-space sampling in MRI
Magnetic resonance imaging (MRI) is often times limited by scan time. To reduce scan time, there have been various efforts to reduce the number of sampling points. In most cases, this is done by utilizing a priori knowledge of the signal of interest. In this paper, we propose an algorithm that will guide the determination of an optimal sampling pattern based on prior knowledge of the signal. Applications of this method include optimal variable-density k-space trajectory design or reduced phase encoding in 3DFT and spectroscopy. Preliminary results are shown as a proof of concept.
18428164
Fast spiral Fourier transform for iterative MR image reconstruction
We present a fast and accurate discrete spiral Fourier transform and its inverse. The inverse solves the problem of reconstructing an image from MRI data acquired along a spiral k-space trajectory. First, we define the spiral FT and its adjoint. These discrete operators allow us to efficiently compute the inverse using fast-converging conjugate gradient methods. Next, we developed a fast approximate spiral FT using the pseudo-polar FFT, to enhance the computational performances and numerical accuracy of the algorithm. Preliminary results demonstrate that the proposed algorithm is more accurate than existing iterative methods that use similar interpolation and grid size.
393666
DAS: Intelligent Scheduling Systems for Shipbuilding
Daewoo Shipbuilding Company, one of the largest shipbuilders in the world, has experienced great deal of trouble with the planning and scheduling of its production process. To solve the problems, from 1991 to 1993, Korea Advanced Institute of Science and Technology (KAIST) and Daewoo jointly conducted the Daewoo Shipbuilding Scheduling (das) Project. To integrate the scheduling expert systems for shipbuilding, we used a hierarchical scheduling architecture. To automate the dynamic spatial layout of objects in various areas of the shipyard, we developed spatial scheduling expert systems. For reliable estimation of person-hour requirements, we implemented the neural network-based person-hour estimator. In addition, we developed the paneled-block assembly shop scheduler and the long-range production planner. For this large-scale project, we devised a phased development strategy consisting of three phases: (1) vision revelation, (2) data-dependent realization, and (3) prospective enhancement. The DAS systems were successfully launched in January 1994 and are actively being used as indispensable systems in the shipyard, resulting in significant improvement in productivity and visible and positive effects in many areas.
17895301
Optimal choice of data restructuring points
Maintaining access efficiency to a data base as updates and/or usage patterns change often requires restructuring the data base. While analytical methods are available for determining the optimal point to restructure, they assume the mean access cost is a smooth function of time or the number of accesses and can be measured exactly at any point in time. The access cost in practice often varies, at least in the short run, In a random manner. This implies a nonzero probability of deciding the optimal reorganization point has been reached when in fact it has not. Determination of the optimal reorganization point must take into account the random behavior of the access cost and the probability (and cost) of deciding too early or too late to perform the reorganization. A technique for choosing the optimal reorganization point subject to random variation in the access cost is developed and some examples are presented.
27969393
Least modification principle for case-based reasoning: a software project planning experience
A software project plan is composed of stages of activities and detailed tasks to be performed, and precedence restrictions among them. A project network is very complex and its construction requires a vast amount of field knowledge and experience. To assist the construction of a software project network, we adopt the case-based reasoning approach. However, the software project network may be designed differently depending upon the adopted development methodology and the style of the manager, so full automation of adjusting a past case is almost impossible. Thus, reducing the modification effort to a minimum is very important for enhancing the project planner's performance. In this research, we develop the framework of the Least Modification Principle (LMP) for Case-based Reasoning to solve this kind of problem. LMP is applicable when a reliable estimation of modification effort is possible. To apply the LMP for project network planning, we have selected 17 factors and the values for each factor to specify software projects. The modification effort is estimated based on the syntactic structure of modification rules. The performance of LMP is demonstrated with each of 31 test cases based on the other 30 past cases. We found that the LMP approach can significantly outperform the Ordinary Factor Matching approach.
223678
Automatic classification of digestive organs in wireless capsule endoscopy videos
Wireless Capsule Endoscopy (WCE) allows a physician to examine the entire small intestine without any surgical operation. With the miniaturization of wireless and camera technologies the ability comes to view the entire gestational track with little effort. Although WCE is a technical break-through that allows us to access the entire intestine without surgery, it is reported that a medical clinician spends one or two hours to assess a WCE video, It limits the number of examinations possible, and incur considerable amount of costs. To reduce the assessment time, it is critical to develop a technique to automatically discriminate digestive organs such as esophagus, stomach, small intestinal (i.e., duodenum, jejunum, and ileum) and colon. In this paper, we propose a novel technique to segment a WCE video into these anatomic parts based on color change pattern analysis. The basic idea is that the each digestive organ has different patterns of intestinal contractions that are quantified as the features. We present the experimental results that demonstrate the effectiveness of the proposed method.
6516775
Distributions of regular branched surface coverings
In a study of surface branched coverings, one can ask naturally: In how many different ways can a given surface be a branched covering of another given surface? This problem was studied by many authors in Quart. J. Math. Oxford Ser. 2 46 (1995) 485, Math. Scand. 84 (1999) 23, Discrete Math. 156 (1996) 141, Discrete Math. 183 (1998) 193, Discrete Math. (in press), European J. Combin. 22 (2001) 1125, Sibirsk. Mat. Zh. 25 (1984) 606 etc. In this paper, as a complete answer to the question for regular coverings, we determine the distribution of the regular branched coverings of any nonorientable surface S when the covering transformation group and a set of branch points are freely assigned.