manage images are used. In content-based image retrieval, the images are retrieved on the basis of features such as color, texture, shape, and so on, which were derived from the images themselves. So far, a variety of medical image retrieval systems have been developed using either method (text-based or contentbased) or combining two methods; a rough classification of medical image retrieval methods is displayed in Figure 1 . Therefore, we described two technological approaches for medical image retrieval -past development and present status, and future perspectives. Text-based image retrieval system can be traced back to 1970s. Text-based image retrieval system is prevalent in the search on the internet web browsers. Although text-based methods are fast and reliable when images are well annotated, they cannot search in unannotated image databases. Moreover, text-based image retrieval has the following additional drawbacks, it requires time-consuming annotation procedures and the annotation is subjective [2] . Text-based query commonly results in irrelevant images (Figure 2) . Thus, to support effective image searching, retrieval methods based on the image content were developed. With the widespread dissemination of picture archiving and communication systems (PACSs) in hospitals, the amount of imaging data is rapidly increasing. Effective image retrieval systems are required to manage these complex and large image databases. The authors reviewed the past development and the present state of medical image retrieval systems including textbased and content-based systems. In order to provide a more effective image retrieval service, the intelligent content-based retrieval systems combined with semantic systems are required. Medical Image Retrieval: Past and Present Kyung
REF reviewed both text-based and content-based medical image retrieval systems, drawing a conclusion that the image retrieval service will be more effective if CBIR and semantic systems are combined.
Medical Image Retrieval: Past and Present
Healthcare Informatics Research
Healthcare Informatics Research
Computer Science Medicine