Research Of Content-based Hepatic CT Image Retrieval System Using Grid Computing And Digital Watermarking Technology

With the development of hospital digitalization and popularity of PACS, medical data expand rapidly. CBIR (Content Based Image Retrieval) was focused for a few years in order to resolve the retrieval issues of medical images. However, CBIR is not applied widely in hospital, for it is still not perfect enough for clinical application.A content-based hepatic CT image retrieval system using grid computing and watermarking technology, CBHIRuGW, is proposed for the retrieval of hepatic CT images, which aims to improve the performance of retrieval precision, data management, retrieval efficiency and patient's data protection. This system increases the utilization of medical image information in diagnostics, teaching and research. CBHIRuGW is composed of storage and retrieval subsystem, each is composed of three groups separately: image features extracting/CBIR group, digital watermarking encoding/decoding group, data/computing grid group. Within CBIR group, a query image classification based image retrieval method is proposed to improve the retrieval precision; within watermarking group, system data security and retrieval efficiency are advanced with using lossless digital watermarking technology; within grid group, The performance of data management and retrieval efficiency are upgraded with usinggrid computing technology. The details of these groups are discussed as follows: Firstly, a query image classification based image retrieval method is proposed. When retrieving images based on sample, images in the database are classified. Those belonging to the same class as the query sample are grouped as the simplified database and image retrieval is limited within the simplified database. At first, the support vector machine, SVM, was used for classification and the precision of retrival with SVM was better than that without the SVM. Then three level threshold classification method, 3-L was proposed for the hepatic CT images and experiments showed that the precision of retrival with 3-L was better than that with SVM.Secondly, Information security and retrieval efficiency were dissussed to protect the patient's private information, promote the retrieval efficiency of an image's revelant information and simplify the data management. Using digital watermarking, all kinds of related information (such as hash value, morphological characteristics, location of the regional focus, texture information and patient's information) is embedded in the image as watermarking, which has many advantages: Firstly, the special coding and password protection of watermarking enable image integrity verification and multi-levels read permissions, which ensures the security of medical data and expands the application of medical images. Secondly, since all relevant information is embedded within medical image, the operation of retrieving relevant information is not required during the retrieval processing, thus the time for manual operation and additional system costs is saved; morover, the network load is reduced and thus the network transmission time is reduced. As a result of these factors, the retrieval efficiency is improved. Finally, because all relevant information is no longer stored as a separate file but embedded into the medical image, the management of the relevant information is simplified. In order to improve the watermark performance and reduce distortion under low and high load conditions, the block sorting based and differences expansion threshold controlled embedding method are proposed.Thirdly, retrieval efficiency and data management were discussed in the paper. The grid computing technology was applied to CBHIRuGW to improve the performance of data management and retrieval efficiency. The platform was simulated by integrating the idle computers in the laboratory. With the platform, the performance of the system's data management and computing is improved. In data management, the system can perform seamless storage and backup management for the PACS system with help of the functional module of data grid. In calculating abilities, use of virtual grid computing platforms, the system can process the last step of the image retrieval - the rigid registration of images in parallel, thus greatly enhancing the efficiency of the system crawl.