Abstract
Picture archiving and communications systems (PACS) utilize short- and long-term storage to provide both rapid retrieval and large storage capacity. Owing to the practical limitations imposed on the size of the much faster short-term storage, it is important to use an effective algorithm in the retrieval of comparison images from long to short-term storage. A strategy must be used to maximize the likelihood that the relevant historic images have been previously retrieved into short-term memory. Data were collected with a database consisting of 754 consecutive examinations and 7,723 associated historic studies. The most frequent 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 algorithm retrieved the lastn studies in chronological order. The second strategy tested was retrieval based on a defined interval of time. This strategy was found to be less efficient. By using the former strategy, a 91% success rate (defined as successful retrieval of the previous matching 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, the data from this latter strategy suggest that examinations are often ordered 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 operation. The data therefore suggest that digitization of film in a new PACS environment might not be necessary owing to the relatively short period of time required to populate the database with historical studies.
Key Words: digital, computer, radiology, imaging, algorithm, workstation, efficiency, archival, storage, database, digitization
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