Digital image archiving: challenges and choices

In the last five years, imaging exam volume has grown rapidly. In addition to increased image acquisition, there is more patient information per study. RIS-PACS integration and information-rich DICOM headers now provide us with more patient information relative to each study. The volume of archived digital images is increasing and will continue to rise at a steeper incline than film-based storage of the past. Many filmless facilities have been caught off guard by this increase, which has been stimulated by many factors. The most significant factor is investment in new digital and DICOM-compliant modalities. A huge volume driver is the increase in images per study from multi-slice technology. Storage requirements also are affected by disaster recovery initiatives and state retention mandates. This burgeoning rate of imaging data volume presents many challenges: cost of ownership, data accessibility, storage media obsolescence, database considerations, physical limitations, reliability and redundancy. There are two basic approaches to archiving--single tier and multi-tier. Each has benefits. With a single-tier approach, all the data is stored on a single media that can be accessed very quickly. A redundant copy of the data is then stored onto another less expensive media. This is usually a removable media. In this approach, the on-line storage is increased incrementally as volume grows. In a multi-tier approach, storage levels are set up based on access speed and cost. In other words, all images are stored at the deepest archiving level, which is also the least expensive. Images are stored on or moved back to the intermediate and on-line levels if they will need to be accessed more quickly. It can be difficult to decide what the best approach is for your organization. The options include RAIDs (redundant array of independent disks), direct attached RAID storage (DAS), network storage using RAIDs (NAS and SAN), removable media such as different types of tape, compact disks (CDs and DVDs) and magneto-optical disks (MODs). As you evaluate the various options for storage, it is important to consider both performance and cost. For most imaging enterprises, a single-tier archiving approach is the best solution. With the cost of hard drives declining, NAS is a very feasible solution today. It is highly reliable, offers immediate access to all exams, and easily scales as imaging volume grows. Best of all, media obsolescence challenges need not be of concern. For back-up storage, removable media can be implemented, with a smaller investment needed as it will only be used for a redundant copy of the data. There is no need to keep it online and available. If further system redundancy is desired, multiple servers should be considered. The multi-tier approach still has its merits for smaller enterprises, but with a detailed long-term cost of ownership analysis, NAS will probably still come out on top as the solution of choice for many imaging facilities.