Although innovations in storage technology are not as glamorous as the introduction of a new diagnostic imaging modality, digital archives form the backbone of healthcare information and image systems. It’s a truism in the PACS world that whatever storage a facility has in place today will need to be increased by an order of magnitude to meet the coming needs of a healthcare enterprise.
“According to a study by the University of California Berkeley School of Information Management and Systems, in order to meet escalating requirements there will be a need to improve today’s storage offering by 10 times,” said John Colang. “The study shows that by 2010, a 100-fold increase will likely be necessary.”
Colang, a radiologic technologist and a project manager in Intel’s Digital Health Division, recently presented his thoughts on the emerging technology of holographic storage for PACS at the 2007 American Healthcare Radiology Administrators conference in Orlando, Fla.
He noted that as result of the shift from plain-film radiography to more advanced imaging modalities, PACS administrators are demanding greater storage capacities and faster retrieval times. The result of the widespread adoption of digital imaging procedures has been the creation of a large volume of image files, which has put an acute strain on storage and archival systems.
“Holography holds great promise as a technology that can overcome two approaching physical barriers to data storage through a powerful combination of high storage-transfer densities and fast data-transfer rates,” he said.
Welcome to the holodeck
According to Colang, the fundamentals of holographic storage consist of a few key technologies that work together to exploit light sensitive media in three dimensions.
“Holographic storage differs from other recording technologies in two fundamental ways,” he said. “First, holography enables massively parallel recording and reading of data rather than the serial approach of traditional methods. Second, and more importantly, holography exploits the entire thickness of a recording medium rather than just the surface.”
Holographic recording is accomplished via a laser beam being split into two beams: a signal beam and a reference beam. The intersection of the two beams creates an interference pattern of bright and dark regions. The interference pattern is captured by a photosensitive medium and the hologram is the image of that interference pattern. To read this image, a laser beam shines on the hologram, recreating the data pattern.
“The process for recording data onto the signal beam is accomplished by a device called a spatial light modulator (SLM),” he said. “The SLM translates the electronic data of 0’s and 1’s into an optical checkerboard pattern of light and dark pixels. The data are then arranged in an array or page of around a million bits. By varying the reference beam angle, wavelength, or media position, many different holograms can be recorded in the same volume of material.”
To read the data, Colang said that the reference beam deflects off the hologram, thus reconstructing the stored information. The hologram is then projected onto a detector that reads the data in parallel.
Holographic technology allows for the simultaneous retrieval of an entire array of data, rather than the bit-by-bit method employed by current archive systems. Colang, citing an example from Physics World, said that if 1,000 holograms, each containing 1 million pixels, could be retrieved every second then the output data rate would reach 1 gigabit per second.
“The rapid development of holography for displaying 3D images led to the realization that holograms could potentially store data at a volumetric density of one bit per cubic wavelength,” he said. “Given a typical laser wavelength of around 500 nanometers, this density corresponds to 1 terabit per cubic centimeter or more.”
Colang said that the flexibility of the technology allows for the development of a wide variety of holographic storage products that range from handheld devices for consumers to enterprise storage products.
“Imagine 2 gigabytes (GB) of data on a postage stamp, 20 GB on a credit card, or 200 GB on a disk,” he said.
If you’re looking to replace your current archive with holographic storage, you may want to hang onto your current system for a little bit longer. The remaining barrier to full-scale commercialization of the technology lies in the media used to capture the data.
“This is perhaps the most problematic and challenging component of holographic technology,” Colang noted.
The substrate material, commonly lithium niobate crystals, is expensive and has to be grown individually. In addition, there have been reported problems with displaced electrons generating local electric fields that distort the crystal lattice. In effect, Colang observed, this creates a pattern of minute optical flaws in the material.
“The material used must be easy to manufacture and must be able to withstand a potentially destructive readout process,” he said. “This new-generation media must also have precise optical qualities and must exhibit thermal and environmental stability.”
According to Colang, there are a clutch of start-up firms as well as established players in the data-storage market that are working toward solving this issue.
The technology is still too immature to determine what the actual cost per GB of storage will be, Colang noted. However, some analysts have projected a price point considerably lower than current storage media.
“Comparative data suggest that the cost for the new holographic media will probably be somewhere in the neighborhood of $.06 to $.20 per GB compared with data tape, which costs $.25 to $1 per GB and video tape, which costs between $1 and $3 per GB,” he said.
In addition to more storage for less money, a vastly reduced physical footprint, and transfer rates an order of magnitude faster than current technology, holograms also may have a longer archive life than spinning disks, data or video tape.
“The average archive life of holographic media is predicted to be approximately 50 years by the companies positioning their prototypes in the market,” Colang said. “If this prediction is substantiated by solid research in the months ahead this would compare nicely with other optical type drives, but is vastly better than data tape, video tape, or hard disk drives.”
Although holographic storage is not yet ready for deployment in the mission-critical environment of the healthcare enterprise, administrators for diagnostic image and information systems will want to keep a close eye on holography developments.
“A new technology is emerging that may prove to enable a more efficient image lifecycle,” Colang said.