A Big Byte: PACS Widen Image Storage Boundaries

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By nature, digital medical images are large. A single CT scan can easily consume 100MB of disk space. And even larger still are the estimates that the healthcare industry will store 68 petabytes (one petabyte equals a million gigabytes) this year alone, according to The Enterprise Storage Group, a storage industry market research firm in Milford, Mass. That number will grow to 238 petabytes by 2006, for a compounded annual growth rate of 52 percent.

These image sets are quite literally becoming a big issue at hospitals, and due to changes in patient lifecycle management and the Health Insurance Portability and Accountability Act (HIPAA), the data have to be kept forever. In light of the mind-boggling numbers above, the questions become where do you put all this data, and how do you manage it?

When IT managers are planning the storage portion of a picture archiving and communications system (PACS) implementation, they need to think about the entire life-cycle of a medical image. Image storage has become the primary concern and key component of PACS, in large part because up to 60 percent of all hospital storage is used by and originates with the system, says Jon Mello, director of the global healthcare unit at EMC Corp. in Hopkinton, Mass.

"The first stage of a PACS image lifecycle includes image capture and its active use during a patient visit. The image gets stored in a short-term cache for 30 to 90 days, where it can be accessed quickly. The second stage is long-term storage. Partly in order to support HIPAA, all that expensive short-term cache needs to be moved to long-term storage. This is fixed content that keeps it authentic," says Mello.

A several terabyte image cache stored on disk can serve up a patient's x-rays or other medical images immediately. It's the most expensive part of PACS storage, because it's made up of high-throughput, fast access spinning disks with Fibre Channel or other high-speed data transfer rates. These images are in use while a patient is being treated, and a clinician needs to look at treatment progress over short time periods.

"Hospitals need a storage management infrastructure to migrate data based on accessibility," says John Galasso, a healthcare marketing specialist at Storage Technology Corp. (StorageTek), based in Louisville, Colo. "When a cardiologist is doing angioplasty, those images need to be on the fastest and most expensive media available for immediate access."

The next stage, says Galasso, is when there's a need for immediate - but not instantaneous - access to an image. If a patient is getting chemotherapy every week, a clinician may need to view images over time. Archival storage, while still online, is for images that are only viewed once per year or less. A mammogram, for example, that only needs to be viewed every year to monitor a spot. Rather than Fibre Channel or other high-throughput technology, the best solution for this is this is an Advanced Technology Attachment (ATA) device.

Finally, a hospital should have a tape library for disaster recovery and to comply with HIPAA, discrete media that can be removed and put in a vault, says Galasso.

Two years ago, North Bronx Healthcare Network, one of six regional networks established by the New York City Health and Hospitals Corp., brought an Agfa IMPAX PACS live in the Jacobi Medical Center and North Central Bronx Hospital (total of 870 beds; total cost $6 million).

"Our goal was to tightly integrate the PACS with our Misys Healthcare Systems RIS and clinical information system (CIS)," says CIO Dan Morreale. "The PACS is designed so that as physician's reports are finalized and read by radiologists, they're loaded immediately on the RIS, so the image is tied to the report. A variety of users in the hospitals, ranging from primary-care physicians, specialists in oncology and cardiology can click on a patient's radiology image to view the report," explains Morreale.

Upon installation, Morreale attached 5 GB of storage, which he thought would be enough for the next five years. But as utilization increased, that capacity soon proved inadequate. The organization upgraded to 128 terabytes of content addressed storage (CAS) for archived images, and another 30 terabytes for its storage area network (SAN), both from EMC.

"We had storage devices scattered throughout the organization. Our immediate need was SAN-based, and we didn't want to do the archiving on optical because it's slower. It takes one or two minutes for an optical image to come up. Using one management tool from EMC, we can grow as our needs change - whether it's SAN, network-attached storage (NAS), or CAS for the archive," says Morreale.

Because PACS images are organized in short-term storage for fast retrieval, long-term archival storage for occasional viewing, and remote storage where they will be kept forever, the technology has changed the way radiologists and physicians think about diagnostics and treatment, says Robert Cecil, network director in the divisions of radiology and cardiology at Cleveland Clinic in Cleveland, Ohio.

Before the organization implemented a PACS with a StorageTek image archive, physicians compared freshly acquired images with prior case images about four times per day. The prior case images were electronically available, but offline on optical disk, which made for a cumbersome image retrieval process, says Cecil.

"Before, the physician could click on the image to request it, but a human would have to walk over and look through 5,000 optical disks, load the requested image, and send it back. It could take a half hour or it could take two hours. With the StorageTek image archive, the number of prior case image reviews is up to 200 per day. We can do better medicine," says Cecil.

Similarly, when cardiology images were stored on cine film, in canisters housed in large rooms, physicians looked at prior cases in only 2 to 5 percent of total cases. Within 90 days of implementing the archival storage, the number increased to 90 percent, says Cecil.

The Cleveland Clinic uses disk-based RAID buffering and storage for the first few days to a month of active patient imaging. The data are concurrently written to a StorageTek 9840-9940 Powderhorn tape storage system The system uses the ASM Hierarchical Storage Management system to allow retrievals of any exam's imaging data in as little as 30 seconds. Approximately 3 terabytes of front-end RAID storage facilitates tape management, and 200 terabytes of managed data are on tape.

"We plan to continue to evolve the tape system to enable us to keep imaging data forever," says Cecil. "Advances in tape density and performance make tape uniquely scalable and allow cost effective physical migration of data to newer faster and denser media as technology evolves."