Storage 101

Healthcare facilities beware. Data storage systems can be one of the greatest expenses for many picture archiving and communications system implementations. Cost is contingent upon the number of choices required to design and implement a PACS archive, which are many since all archives need two levels of storage: short-term and long-term. Providers needn't overbuy or under buy and must always keep in mind the declining cost of storage and the potential increase in patient data and images.

Different levels of storage exist within the framework of a PACS archive. The first level is a temporary directory that receives the files directly from the imaging modality. The amount of time the study resides there depends on the storage architecture of the organization. The application "talks" with the modalities and is responsible for reformatting the data and sending it to a more permanent form of storage, where it is then housed for a length of one to two years.

This rung on the PACS storage ladder is referred to as short term or online storage. There, electronic PACS images are typically stored for 12 to 18 months on fast-access, spinning disc media, such as RAID (redundant array of inexpensive disks) with a retrieval rate of two to five seconds. Another copy of the study is automatically written to a long-term storage device (near line storage) for both state retention mandates and disaster recovery. This allows the short-term archive to "purge" itself of unneeded data after reaching a capacity of 80 percent.

Providers agree that two years' worth of digital images in short-term storage is sufficient. "If you have 12 to18 months [of] short-term, then you are going to have 95 percent of all the images you want on the storage," says Richard Howe, PhD, vice president of information technology (IT) consulting for VHA Inc., a healthcare cooperative. Depending on the size of the facility, the number of modalities connected to the PACS, the retention time needed for the data and patient demographics, short-term storage capacities consist of multiple terabytes, with the option of scalability for increases in image volume.

As a vehicle to actually access the storage, PACS archives typically deploy the use of some form of networked storage, such as SAN (storage attached network) or NAS (network attached storage). SAN is a dedicated network for connecting storage devices to computers, while NAS is not directly attached to the servers and the storage is accessed using network standard protocols. The benefit of networked storage is that its capacity can be increased without interruptions to systems and workflow. The two differ in cost; SANs are about two and a half times more expensive than NAS because they require dedicated networks and gigabyte switches that are fairly expensive.

"You can acquire one terabyte of NAS storage for less than $15,000, which continues to drop," says Thomas Hough, principal of True North Consulting & Associates Inc. "You can acquire one terabyte of SAN storage for under $20,000 with additional terabytes costing less than $10,000. NAS tends to work well with large diagnostic imaging exam data sets. NAS will store the data and allow it to be retrieved very quickly. The only bottle neck in that process is the size of the network pipe going in to the NAS. It can be a little slower than a SAN in terms of delivering images."


When providers utilize networked storage, whether its SAN or NAS, they are enhancing the performance level of their archive. Orlando Regional Healthcare System (ORHS) is a not-for-profit healthcare network in Florida. Totaling 1,572 beds, ORHS consists of seven hospital facilities, M.D. Anderson Cancer Center Orlando and several ancillary organizations. GE Healthcare's Centricity PACS is in the process of deployment at ORHS and they just acquired new enterprise storage systems from IBM Inc. for radiology. "The infrastructure is in place, now it is just a matter of installing both the short-term and long-term storage throughout the organization," says John Berghuis, IS director of technology at ORHS.

Taking a centralized management approach to PACS, all of short-term storage will be deployed on IBM's TotalStorage Enterprise Storage Server (ESS) Shark 800 SAN. They are rolling out 22 TB for just PACS short-term and electronic images will be stored there for two years. Using an OC-48 fiber Sonnet Ring, all of the facilities will be connected via gigabit Ethernet. "We have implemented a new critical, clinical network for PACS alone completely separate from the normal network," says Berghuis. "For example, e-mail will not ride the same network as PACS resides." Accessing images from the short-term archive will take clinicians two to three seconds anywhere throughout the corporation.

Berghuis notes that short-term storage and long-term storage will overlap. As soon as an image is written to short-term storage, it will be immediately queued up and written to long-term storage [IBM's Fast T 900 SAN]. Therefore, two copies of the image will exist for disaster recovery purposes.

ORHS went with a SAN instead of a NAS due to bandwidth and a more streamlined protocol for communication. "NAS has an Ethernet interface and a SAN has a fiber channel interface," says Berghuis. "Fiber channel has twice the bandwidth of Ethernet and the protocol used to communicate over fiber channel is a lot more efficient than Ethernet."


According to VHA's Howe, many healthcare organizations are buying bigger network storage units to store electronic images and other information. Enterprise storage systems allow hospitals to fraction off some room for PACS in addition to other applications, such as hospital information or electronic medical record information and imaging modalities such as those used in cardiology, pathology and the vascular lab.

"It provides virtual storage for each of those subsystems," says Howe. "The advantages are that it's enterprise-based and the organization has one main location for backup. Keep in mind that providers must ask whether or not the applications can be integrated with a common SAN or NAS unit."

At Commonwealth Health Corp. (CHC), a three-hospital healthcare system in Kentucky that consists of a main medical center in Bowling Green (330 beds), as well as two remote locations in Scottsville (157 beds) and Franklin (25 beds), it is a requirement for any vendor that comes in with a database structure to be SAN-compliant.

Installing Fujifilm Medical Systems' Synapse web-based PACS last year, electronic images are acquired and sent from the remote centers over a WAN (wide area network), as well as acquired at the main medical center, and sent to a central PACS imaging server and SAN.

Using a 15 TB SAN (EMC Inc.'s Clariion), 6TB have been designated for PACS. "The imaging server is part of the SAN," explains Matt Ebaugh, senior vice president and CIO at Commonwealth. "The SAN is segmented so that 3TB of storage is built into the imaging server within the SAN fabric. Additional applications that utilize the SAN include the organization's HIS and CIS, document imaging solution for medical record and patient financial services, and file sharing."

The storage is considered short-term as of now because they have not gone to compression to the reference level yet. A lossless diagnostic image is stored for 30 days, after which it changes to a lossy clinical image. "We are not ready to go to that reference study which can exceed 150:1 compression," notes Ebaugh. "That's one of the big things that organizations have to wrestle with and you really need to trust your radiologists and your clinicians. Because as an IT professional we cannot really tell a clinician or physician that this is good enough, he or she has to tell us to insure the best outcome for the patient is maintained."


Christus Health is a multi-state health system headquartered in Dallas that comprises more than 40 hospitals and long-term care facilities in more than 70 communities in Texas, Arkansas, Louisiana, Oklahoma, Missouri, Utah and Mexico. The healthcare organization decided to house online storage on a NAS. Performing a detailed needs analysis for each hospital, the organization purchased enough online storage for one year. One of the economical advantages of online storage is the ability to increase overall capacity as the number of digital modalities connected to the PACS increases, thus taking advantages of declining storage costs.

Christus is just beginning to deploy PACS throughout the enterprise. For the regions that are digital, the hospitals have rolled out McKesson Corp.'s Medical Imaging PACS (except for two facilities in southeast Texas that use Agfa Healthcare's IMPAX PACS) and EMC's NetWin 200 servers for short-term storage.

James Jones, solutions architect at Christus, says the healthcare system decided upon a three-tier approach to storage for two reasons: speed and price. "The tier one storage is on the image servers," details Jones. "The images stay on these servers for approximately 48 hours and have a local level-one storage of 300 gigabytes. This gives us the fastest retrieval times for the most current images the radiologists access. Tier two storage is on the NAS. Images stay on this storage for approximately one year. Access is relatively fast and the storage is relatively cheap. Once it reaches capacity of 80 percent, we clear that off and the data are archived in long-term storage in our enterprise data center."

Jones says that NAS was much less expensive than a SAN as well as easier to install and configure. "NAS uses TCP/IP over Ethernet, which means we can use our existing network infrastructure," he says. "We saved a huge amount of money not having to run fiber-optic cables, purchase and install fiber-optic cables or switches, purchase and install HBAs to connect the disks to the SAN fabric and training more personnel to manage regional SANs. With eight regional data centers, the cost of added personnel alone is an enormous expense."


In some cases, a healthcare organization may decide to begin archiving and retrieving digital images before installing a PACS. That is what Washington Hospital Center did, a 907-bed facility affiliated with the MedStar Health System.

Before the hospital deployed PACS, electronic images went directly from the imaging modalities to InSiteOne Inc.'s RAID archive (InDex OnLine). InSiteOne is an outside archive vendor that offers an application service provider (ASP) model to PACS. The ASP model allowed Washington to spend less money on storage upfront and more money on building a PACS in the department, says Denis Dionne, assistant vice president for imaging at MedStar.

Dionne refers to the archive-first approach as a 'poor mans PACS.' "Any modality that was DICOM out, we began pushing it to the archive, which included CT, MRI and computed radiography from the emergency care area," says Dionne. "An InSiteOne server, loaded up with RAID, sits in the radiology center computer room. Initially, the hospital made an agreement with InSiteOne to have six months of RAID onsite. Now we have an agreement that gives us one year of onsite RAID."

Today, the hospital has installed a PACS (Philips Medical Systems' Radiology PACS) that has some local RAID storage that can store images up to three months old for absolute, immediate retrieval. The studies that are three- to 12-months old are housed in InSiteOne's onsite RAID architecture. When an exam is committed to short-term storage, it stays local but is also sent over dedicated T1 transmission lines to a long-term archive [DVD jukeboxes] at the company's main facility in Wallingford, Conn. "So automatically there is a duplicate copy in Connecticut and they also burn a redundant copy in the Phoenix, Ariz., facility," says Dionne. "If physicians are looking at anything over 15 months old, then they are literally going offsite to Connecticut for retrieval."

While using an ASP-model allowed capital dollars to be spent on PACS in the department, having the archive first helped ease the transition to softcopy viewing. "When the hospital went live with PACS in June 2003, we had two and a half years of historicals already in the database," says Dionne. "We don't worry about redundancy or HIPAA compliance either. We know the archive is monitored around the clock."


For multi-center healthcare organizations, image management is an enterprise-wide endeavor. Health Alliance is an integrated healthcare delivery system with a total of 7,600 beds that covers the greater Cincinnati area. It consists of six hospital facilities including teaching and acute-care hospitals as well as a physician care group. The radiology departments at The Christ Hospital and The Jewish Hospital implemented Cerner Corp.'s ProVision PACS, and two more facilities plan to come up live in the next six months.

Today, both Christ and Jewish hospitals each have a PACS server with two and three months worth of RAID for current studies. The rest go to DVD jukeboxes. For installation in January, IT budgeted for a SAN enterprise unit to handle the images for all the hospitals.

Each hospital will keep two year's worth of images on a local RAID 5 or SAN unit (depending on the size) and they will all be connected to an enterprise SAN unit that will act as the long-term strategy. The enterprise SAN will consist of 150 TB, which was sized based on a five-year projection of PACS images, according to Greg Herr, director of imaging technology for clinical engineering.

"The benefits are that we can have an enterprise storage area that all the PACS can access, query and pull images out of," says Herr. "The SAN itself is spinning disc so we won't have access time of a jukebox or DVD. IT felt more comfortable with SAN technology for enterprise storage reliability and diversity."


While the archive component of a PACS differs greatly among healthcare organizations, all are configured to provide clinicians with secure, reliable and instant access to images throughout the enterprise. For the short-term, providers want to get as much online availability of images as possible and increase capacity as needed. Selection of hardware will be contingent upon volume of data that are produced per modality, the number of modalities sending images to PACS, the retention time of data, patient demographics and frequency of access.