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✓ The quality of a computerized tomography (CT) scan is significantly reduced by metal artifact caused by a pedicle screw system. The purpose of this study was to develop a method of facilitating the evaluation of pedicle screw position on CT scans obtained after screw insertion. The authors developed an algorithm to process spiral CT scans in a personal computer. This uses a digital image enhancement technique, the curve change-based intensity transformation algorithm. This method can generate a clear image of the screw outlines while reducing metal artifact. The resulting images are displayed in arbitrary planes as well as in axial, coronal, and sagittal planes, to support better the evaluation of pedicle screw position. The algorithm was tested using CT scans obtained in 37 patients in whom 186 pedicle screws had been placed. There were five types of screw systems, all of which were made of titanium alloys. In all cases algorithm-based determination of screw position became more convenient and more accurate than when using the conventional bone window setting. In addition, it provided better soft-tissue visualization than the bone window. The software, by displaying clear outlines of screws and decreasing metal artifact, as well as by reconstructing the images in arbitrary planes, was more helpful in identifying the position of pedicle screws than the conventional bone window setting.

Software Distributed Shared Memory (SDSM) systems usually have the large coherence granularity that is imposed by the underlying virtual memory page size. To alleviate the coherence overheads such as the network traffic to preserve the coherence, or page misses caused by false sharing, relaxed memory models are widely accepted for the SDSM systems. In the relaxed memory models, when a shared page is modified, invalidation requests to other copies are deferred until a synchronization point and, in addition, the requests are transferred only to the processor acquiring the synchronization variable. On a barrier, however, the invalidation requests must be transferred to all the processors that participate in the barrier. As a result, it tends to induce heavy network traffic, and also may lead to useless page misses by false sharing.In this paper, we propose a method to alleviate the coherence overheads of barrier synchronization in shared-memory parallel programs. It performs static analysis to examine data dependency between processors across global barriers, and then inserts special primitives into the program in order to exploit the dependency information at run time. The static analysis finds out code regions where a processor modifies data that will be used only by some of the other processors. At run time, the coherence messages for the data are transferred only to the processors with the help of the inserted primitives. In particular, if the modified data will not be used by any other processors, the primitives enforce that the coherence messages are delivered only to master processor when the parallel execution of the program is finished.We evaluated the performance of this method in a 16-node software DSM system supporting AURC protocol. Program-driven simulation was performed with five benchmark programs: Jacobi, Red-black SOR, Expl, LU, and Water-nsquared. For the applications, the experimental results show that our method can reduce the coherence messages by up to about 98%, and also can improve the execution time by up to about 26%.

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