RECOMMENDATIONS FOR IMAGE PREFETCH OR FILM DIGITIZATION STRATEGY BASED ON AN ANALYSIS OF AN HISTORIC RADIOLOGY IMAGE DATABASE

Picture archiving and communications systems (PACS) utilize short-and long-term storage to provide both rapid retrieval and large storage ca pacity. Owing to the practical limitations imposed on the size of the much faster short-term storage, it is important to use an effective al gorithm in the retrieval of comparison images from long to short-term storage. A strategy must be used to maximize the likelihood that the r elevant historic images have been previously retrieved into short-term memory. Data were collected with a database consisting of 754 consecu tive examinations and 7,723 associated historic studies. The most freq uent number of previous examinations was zero (11% of patients). In 45 % of cases, no previous matching examinations had been performed. Two basic strategies of image retrieval were evaluated. The first algorith m retrieved the last n studies in chronological order. The second stra tegy tested was retrieval based on a defined interval of time. This st rategy was found to be less efficient. By using the former strategy, a 91% success rate (defined as successful retrieval of the previous mat ching exam) was achieved with retrieval of only 30% of the prior exams . The second approach required retrieval of 70% of the prior exams to achieve a 90% success rate for the previous matching exam. However, th e data from this latter strategy suggest that examinations are often o rdered in clusters. Thus, there was found to be a 72% likelihood that a previous matching exam, if present, would available on a PACS after only 1 week of operation, and an 80% chance after only 1 month of oper ation. The data therefore suggest that digitization of film in a new P ACS environment might not be necessary owing to the relatively short p eriod of time required to populate the database with historical studie s. Copyright (C) 1998 by W.B. Saunders Company.