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PACS Storage Technology Update : Holographic Storage

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MAY/JUNE 2006 RADIOLOGY MANAGEMENT 38 PACS Storage Technology Update: Holographic Storage s the trend in diagnostic imaging moves away from traditional film to digital imaging, the traditional hard copy film storage center is being replaced by electronic recording and storage media. A properly implemented PACS can significantly increase efficiency within a radiology department. Increasing the efficiency in throughput of the medical image through the stages of image capture, interpre- tation, result-reporting and subsequent retrieval is a major benefit to a fully digital medical imaging department. A new technology is emerging that may prove to enable a more effi- cient image lifecycle. PACS users are demanding more stor- age and faster retrieval times. Holographic storage and retrieval systems hold promise as future technology leaders in this market segment. More data can be stored because holographic images record data in three dimensions instead of just on the surface of the media. This technology could someday replace magnetic, single layer storage with optical, three dimensional (3D) holographic storage. Literature Review Strategy A review of the literature was performed using the Acade- mic Search Premier database via the EBSCOhost® search engine. Key words “holographic storage” were entered into the EBSCO database search field for default fields and the search yielded several pages of results. Selected articles had been peer-reviewed and published between 1999-2005, limiting the search to the most recent literature. A second- ary search was also performed at Google Scholar using the same key words and limiting the search for articles pub- lished between 2001-2005. The filter for “peer reviewed” documents was removed because many of the documents returned were extremely technical in content. This search returned over 300 relevant articles. Materials were selected for high level content readability. As more radiology departments move from conven- tional film and paper media toward digital systems, By John E. Colang and James N. Johnston A This paper focuses on the emerging technology of holographic stor- age and its effect on picture archiving and communication systems (PACS). A review of the emerging technology is presented, which includes a high level description of holographic drives and the asso- ciated substrate media, the laser and optical technology, and the spatial light modulator. The potential advantages and disadvantages of holographic drive and storage technology are evaluated. PACS administrators face myr- iad complex and expensive storage solutions and selecting an appro- priate system is time-consuming and costly. Storage technology may become obsolete quickly because of the exponential nature of the advances in digital storage media. Holo- graphic storage may turn out to be a low cost, high speed, high volume storage solution of the future; however, data is inconclusive at this early stage of the technology lifecycle. Despite the current lack of quantitative data to support the hypoth- esis that holographic technology will have a significant effect on PACS and standards of practice, it seems likely from the current information that holographic technology will generate significant effi- ciencies. This paper assumes the reader has a fundamental under- standing of PACS technology. The credit earned from the Quick Credit test accompanying this article may be applied to the AHRA certified radiology administrator (CRA) communication and information management domain. E X E C U T I V E S U M M A R Y
Transcript
Page 1: PACS Storage Technology Update : Holographic Storage

M AY / J U N E 2 0 0 6 R A D I O L O G Y M A N A G E M E N T3 8

PACS StorageTechnology Update :

Hologra p h i c Storage

s the trend in diagnostic imaging moves away fromtraditional film to digital imaging, the traditional hard

copy film storage center is being replaced by electronicrecording and storage media.A properly implemented PACScan significantly increase efficiency within a radiologydepartment. Increasing the efficiency in throughput of themedical image through the stages of image capture, interpre-tation, result-reporting and subsequent retrieval is a majorbenefit to a fully digital medical imaging department. A newtechnology is emerging that may prove to enable a more effi-cient image lifecycle. PACS users are demanding more stor-age and faster retrieval times. Holographic storage andretrieval systems hold promise as future technology leadersin this market segment. More data can be stored becauseholographic images record data in three dimensions insteadof just on the surface of the media. This technology couldsomeday replace magnetic, single layer storage with optical,three dimensional (3D) holographic storage.

Literature Review Strategy

A review of the literature was performed using the Acade-mic Search Premier database via the EBSCOhost® searchengine. Key words “holographic storage” were entered intothe EBSCO database search field for default fields and thesearch yielded several pages of results. Selected articles hadbeen peer-reviewed and published between 1999-2005,limiting the search to the most recent literature. A second-ary search was also performed at Google Scholar using thesame key words and limiting the search for articles pub-lished between 2001-2005. The filter for “peer reviewed”documents was removed because many of the documentsreturned were extremely technical in content. This searchreturned over 300 relevant articles. Materials were selectedfor high level content readability.

As more radiology departments move from conven-tional film and paper media toward digital systems,

By John E. Colang a n d James N. Johnston

A

• This paper focuses on the emerging technology of holographic stor-age and its effect on picture archiving and communication systems(PACS). A review of the emerg ing technology is presented, whichincludes a high level description of holographic drives and the asso-ciated substrate media, the laser and optical technology, and thespatial light modulator.

• The potential advantages and disadvantages of holographic driveand storage technology are evaluated. PACS administrators face myr-iad complex and expensive storage solutions and selecting an appro-priate system is time-consuming and costly.

• Storage technology may become obsolete quickly because of theexponential nature of the advances in digita l storage media. Holo-graphic storage may turn out to b e a l ow cost, high speed, highvolume storage solution of the future; however, data is inconclusiveat this early stage of the technology lifecycle.

• Despite the current lack of quantitative data to support the hypoth-esis that holographic technology will have a significant effect onPACS and standards of practice, it seems likely f rom the currentinformation that holographic technology will generate significant effi-ciencies. This paper assumes the reader has a fundamental under-standing of PACS technology.

The credit earned from the Quick Credit testaccompanying this article may be applied to theAHRA certified radiology administrator (CRA)

communication and information management domain.

E X E C U T I V E

S U M M A R Y

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and as diagnostic imaging procedures produce largerimage files, the strain on storage and archival systemsbecomes acute. Physicians are also becoming morereliant on sophisticated imaging modalities such as CTscans, MRI scans, nuclear medicine scans, and ultra-sound scans. These modalities produce image files thatrange from 10 Megabytes (MB) to 90 MB in size perprocedure. As a result of this shift from plain-filmradiography to more advanced imaging modalities,PACS administrators are demanding greater storagecapacities and faster retrieval times.

PACS administrators, and healthcare in general, arenot the only consumers of data storage technologyclamoring for more storage capacity. According to“How Much Information,” a study by the University ofCalifornia Berkeley School of InformationManagement and Systems, in order to meet escalatingrequirements there will be a need to improve today’sstorage offerings by 10 times. The study shows by 2010,a 100-fold increase will likely be necessary.

This need for increased data storage is even moreacute in PACS technologies where there are require-ments to store large volumes of data. Nagy and Farmer1

classify storage as online, near line, or offline. “Onlinestorage refers to data that is stored on magnetic harddrives with access times in milliseconds and transfertimes in the range of 10s and 100s of megabytes(MB)/second. Online storage is immediately available toyour PACS application. Near line storage typically refersto a tape or jukebox in which robotic arms can retrievethe tapes automatically and insert them into a drive toread or write data. Generally, a near line system canaccess data within 60 seconds and is able to transfer dataat a few MB/sec. Offline storage is removable tape oroptical media that is stored on a shelf in a catalog and isretrieved manually.”1

Nagy and Farmer concluded that the relationshipbetween online and near line storage is a direct trade-offbetween cost and performance. PACS administratorswould have to make choices regarding how long to keepmedical images online commensurate with online stor-age capacity, budget, and amount of data. Estimates varydepending on the source, but most hospitals requireapproximately 10 terabytes (TB) of storage annually forevery 225,000 radiologic procedures performed. Nagy

and Farmer point out that, relative to other healthcareapplications, PACS requires disproportionate amountsof data storage—100 to 1000 times as much. PACSadministrators must be able to scale capacity commen-surate with this requirement. The peak loading on aPACS storage system for a large hospital with multiplesimultaneous requests is approximately 30 to 50MB/second. Early technology was expensive andplagued with mechanical failures. Storing data on diskis less expensive than using jukebox technology.Typically, PACS administrators use dedicated storagesystems for the PACS archive database. According toInternational Data Corp., in fiscal year 2003, Fortune500 companies spent $7 billion on approximately 1200TB (1 TB = 1000 gigabytes) of data stored on magnetictape.2 The primary purpose of the PACS database is tomove large radiologic images through the network asquickly as possible so users of the system can work withthe data and images. Capacity, speed, reliability, and costper TB are all performance factors that are critical to thesuccess of a PACS archive database. Technological gainsin the areas of storage media, disk types, and networksare exponential in nature. Therefore, the risk of select-ing a storage or retrieval technology that may quicklybecome cost prohibitive or obsolete always exists.

Current Storage Requirements

Various types of conventional magnetic storage are avail-able, each with its own set of advantages and disadvan-tages. From a PACS administrator’s point of view, therenever seems to be enough storage. From high resolutionCT scans that are as large as 30 MB per scan to multiplediagnostic imaging studies done on long term chronicpatients, the need for more capacity continues to grow.Eventually, scientists hope to advance the holographicmemory technology so that one single disk the size of aCD-rom could potentially hold 1 TB of data (equivalent toimages from thousands of exams). Companies that marketthis technology are announcing prototypes that can hold200 times the amount of data that standard disks currentlyhold. Ultimately, the amount of data a system can storeand the speed at which the archive performs retrievals arekey to its success. Storage needs vary depending on the fre-quency and type of studies an imaging department per-

According to a study by t h e University of California Berkeley

School of Information Management and Systems, in ord e r to

meet escalating requirements there w i l l b e a n e e d to improve

today ’ s storage offerings by 10 t i m e s . T h e study shows by

2010 , a 100-fold increase will l ikely be necessary.

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forms and data exists to help PACSadministrators extrapolate thecapacity that will be needed. Table 1describes uncompressed storagerequirements by modality perstudy.3,4 Modalities such as cardiaccatheterization, angioplasty, andperipheral vascular angiography,followed by echo cardiography andmulti-slice CT, produce the mostnumber of images and consequent-ly exert an increased demand onstorage. Some estimates call for 3.1TB of storage capacity for every100,000 exams (see Table 2).3 Table2 summarizes typical uncom-pressed storage requirements per100,000 studies per year excludingmulti-slice CT, 3T MR, and mammography. CT, MR, CR,DR, and angiography exert the greatest demand for storagewith estimates ranging from 20-35 MB (average) per study.Holographic storage technology could potentially providethe ability to assure PACS administrators of future storagecapacity.

Holographic Drive Technology

Holographic media is an emerging technology which couldreplace conventional magnetic and optical drive and stor-age systems connected to PACS in the near future. Manytechnologists and materials scientists have pondered the

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PAC S Storage Technology Update: Holographic Storage

Table 1. Typical Uncompressed Storage Requirements by Modality per Study

Per Study BasisImage Size N o . o f I m a g e s MB of Storage

Modality X Y Z Ave Range Ave Range

CR 2000 2500 2 3 2–5 30 20 to 50

DR 3000 3000 2 3 2–5 54 36 to 90

CT 512 512 2 60 40–300 32 21 to 157

Multi-slice CT+ 512 512 2 500 200–1000 262 105 to 524

MR 256 256 2 200 80–1000 26 11 to 131

Mammography*** 3000 3000 2 6 4–8 108 72 to 144

Ultrasound* 640 480 2* 30 20–60 18 12 to 37

Echo Cardio** 640 480 1 1125 750–1500 346 230 to 461

Nuclear Medicine 256 256 2 10 4–30 1.3 0.5 to 3.8

Film Digitizer 2000 2500 2 3 2–5 30 20 to 50

Digital Fluoro 1024 1024 1 20 10–50 20 10 to 50

Radiology Angio 1024 1024 1 15 10–30 15 10 to 30

Cardiac Catheterization+ 1024 1024 1 150 120–240 450 360 to 720

Angioplasty+ 1024 1024 1 150 120–240 450 360 to 720

Peripheral Vascular Angio++ 1024 1024 1 150 120–180 450 360 to 540

*Monochrome 8 bits, color 24 bits, average 16 b i t s o r 2 bytes**15 frames per sec, 5 sec loops, 10 to 20 loops per study, average 15 loops, monochrome—1 byte deep***Image size will vay with digital mammography vendor+Multi-slice CT study may exceed 1GB when thin (1mm or less) are acquired for virtual presentation++The typical acquisition matrix for some vendors is 512 x 512 rather than 1024 x 10243

(Table courtesy of Smith E, University of Rochester, 2004.)

Table 2. Typical Uncompressed Storage Requirements per100,000 Studies per Year Excluding Multi-Slice CT, 3 T M R

and Mammography

% o f Ave. MB GB per year perModality Studies per study 100,000 studiesAngiography 3 20 60

CR & DR 64 35 2240

CT 20 32 640

MR 5 21 105

NM 3 1.3 3.9

US 5 18 90

Total TB per 100,000 studies 3.1 TB

(Table courtesy of Smith E, University of Rochester, 2004.)

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future of digital storage technologies. Dahr5 suggests thatholography holds great promise as a technology that canovercome two approaching physical barriers to data storagethrough a powerful combination of high storage transferdensities and fast data transfer rates.

What Is Holographic Storage?

The fundamentals of holographic storage consist of a fewkey technologies that work together to exploit light sensi-

tive media in three dimensions. Holographic storage,according to Dahr, differs from other recording technolo-gies in two fundamental ways. First, holography enablesmassively parallel recording and reading of data rather thanthe serial approach of traditional methods. Second, andmore importantly, holography exploits the entire thicknessof a recording medium rather than just the surface. Figure1 outlines the basic lifecycle of a hologram from the record-ing phase, where two laser beams intersect to create aninterference “checkerboard” of bright and dark regions that

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Figure 1. Simplification of how a hologram is created. (Courtesy of InPhaseTechnologies, Longmont, Colorado)

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is subsequently recorded by a photosensitive medium. Thehologram is the actual image of that interference patternthat is now stored within the medium. This hologram isactivated or read by shining one beam of light on the holo-gram, thereby reconstructing it.

One technology developer sums up the differences bysaying, “Instead of laying down the data on the surfacelayer of the medium like in conventional digital record-ings, holography uses lasers and light to record data inthree dimensions. Unlike other technologies that recordone datum at a time, holography allows a million bits ofdata to be written and read in parallel with a single flashof light. This enables transfer rates significantly higherthan current optical storage devices.”6

Physics World describes the process: “Since an entirepage of data can be retrieved by a photo detector at thesame time, rather than bit-by-bit, the holographicscheme promises fast read-out rates as well as highstorage densities. If a thousand holograms, each con-taining a million pixels, could be retrieved everysecond, for example, then the output data rate wouldreach 1 gigabit per second.”7

Figure 2 demonstrates how data is recorded usinglight from a single beam that is split into two beams.The spatial light modulator encodes data onto the sig-nal beam.

How Are Data Recorded?

Unlike conventional digital recording where the informa-tion is stored on the surface of the recording media (theCD or the DVD), the hologram recording technology uses3D layers by bouncing light from a single laser beam. Tech-nologists describe the data recording technology:

The beam is split into two beams, the signalbeam (which carries the data) and the referencebeam. The hologram is formed where thesetwo beams intersect in the recording medium.The process for encoding data onto the signalbeam is accomplished by a device called a spa-tial light modulator (SLM). The SLM translatesthe electronic data of 0’s and 1’s into an optical“checkerboard”pattern of light and dark pixels.The data is arranged in an array or page ofaround a million bits. The exact number of bitsis determined by the pixel count of the SLM.Atthe point of intersection of the reference beamand the data carrying signal beam, the holo-gram is recorded in the light sensitive storagemedium. A chemical reaction occurs in themedium when the bright elements of the signalbeam intersect the reference beam, causing thehologram stored. By varying the referencebeam angle, wavelength, or media positionmany different holograms can be recorded inthe same volume of material.6

It is the variation of the reference beam angle, wave-length, or media position that significantly increasesthe storage capacities of this new technology sincemany holograms can exploit the same physical space inthree dimensions.

How Are Data Read?

In order to read the data, the reference beam deflects off thehologram, thus reconstructing the stored information. Thishologram is then projected onto a detector that reads thedata in parallel. This parallel read-out, according to industryspecialists, is the innovation that allows the fast transfer rate.Figure 3 illustrates how data are read by using the referencebeam to deflect off of the hologram. It creates several parallelreads, thus allowing ultra fast recovery and presentation ofdata. Note the 3D nature of the rendered holograms.

The Spatial Light Modulator

According to Physics World, to use volume holography as astorage technology, digital data must be imprinted onto theobject beam for recording and then retrieved from thereconstructed object beam during readout. The SLM is thedevice used to insert data into the system and it is a planararray consisting of thousands of pixels.

Physics World sums it up nicely by describing eachpixel as an “independent microscopic shutter that caneither block or pass light using liquid-crystal or micro-mirror technology.”7 The authors of the Physics Worldarticle point out that this is dependent upon the powerof the laser and the sensitivities of the materials used for

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PAC S Storage Technology Update: Holographic Storage

Figure 2 . Demonstration of how data isrecorded using light from a single beamthat is split into t wo beams. (Courtesyof InPhase Technologies, Longmont,Colorado)

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the substrate. The data are read using an array of detec-tor pixels, such as a CCD camera or a semiconductorsensor. The object beam often passes through a set oflenses that image the SLM pixel pattern onto the outputpixel array. Figure 4 offers a graphical representation ofthis mechanism. To maximize the storage density, thehologram is usually recorded where the object beam istightly focused. When the hologram isreconstructed by the reference beam, aweak copy of the original object beam con-tinues along the imaging path to thecamera, where the optical output can bedetected and converted to digital data.7

Technology Barriers

A review of the literature indicates that govern-ment and private enterprise seem to be on trackto solve many of the technical issues that onceprevented widespread use of holographic drivetechnology. The most challenging technicalissue has been selection of a suitable storagemedia. Materials science problems and relatedtechnologies have proven to be the most signifi-cant barriers. The problem in the past was pri-marily with the materials used in the actualholographic disk.Many advances have occurredsince Hellemans’analysis in 1999,which said:

… turning holographic storage into theequivalent of a super-disk drive, able tospeedily write as well as retrieve vastamounts of data, will take optical mate-rials with an elusive combination of

properties. They will have to record hologramsquickly, preserve them faithfully, and erase olddata to make room for new. For now, materialsthat can preserve holograms for long periodsare often slow to record them or can’t be erased;materials that record data quickly often lose theoptical traces over time.8

Materials Science Is the Key

To understand how this technology works, a good under-standing of materials science is important since the mediaused to capture the data is perhaps the most problematicand challenging component of holographic technology.Scientists have been trying for years to overcome the tech-nical barriers related to the media and materials. Helle-mans’ article explains how the actual materials and theirlimitations created opportunities for advancement.

Materials problems may be slowing develop-ments now, but, ironically, it was a materialsproblem that kicked off the field of holo-graphic storage in the first place. More than 3decades ago, researchers found that brightlight changes the optical properties of lithiumniobate, a material they were studying as apossible optical switch because its refractiveindex changes in response to an electric field.8

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Two Basics of a Holographic Data-Storage System

Data are i mprinted onto the object beam by shining the lightthrough a pixelated device called a spatial light modulator. T h e refer-ence beam overlaps with the object beam on the storage material,where the interference pattern is s tore d a s a change in absorption,refractive index or thickness of the medium. A pair of lenses imagethe data through the storage material onto a p i xelated detector array,such a s t h e charge coupled device (CCD).

Figure 4 . Basics of a holographic data-storage system. The spatial light modulato r i s a key part of the holographic image technology. (Courtesy ofPhysics World)

Figure 3 . Illustration showing how dataare read by us ing the reference beam todeflect off the hologram. (Courtesy ofInPhase Technologies, Longmont, Colorado)

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Materials Science Challenges

There are some technical shortcomings associated with theuse of lithium niobate. Niobate crystals, according to Helle-mans, are expensive and have to be grown individually. Thestorage media must have a high dynamic range, high photo-sensitivity, dimensional stability and optical clarity. Many ofthe outstanding challenges reported in the literature have todo with the materials science engineering aspect of this tech-nology. One of the most perplexing problems with imple-mentation of holographic data storage using photorefractivematerials is the ultimate erasure of the data due to volatilereadout.9 Electrons are excited to higher energy levels inareas where the light is intense, enabling them to migratethrough the material. The displaced electrons generate localelectric fields that distort the crystal lattice, in effect creatinga pattern of minute optical flaws in the material.8

The material used must be easy to manufacture andmust be able to withstand this potentially destructivereadout process. The new generation media must alsohave precise optical qualities and must exhibit thermaland environmental stability.

Many innovative companies have alreadyannounced product advances and releases in this area.Some companies have plans to release products thatthey claim have overcome the limitations mentionedseveral years ago by Hellemans.

Other Technical Obstacles

Lasers were a limiting factor in the development of holo-graphic drive and storage technology because they were cost-ly and unreliable. These limitations have been eliminated bythe advances made in laser technology.Another limiting fac-tor in this technology was the detector mechanism. The firstgeneration detectors were expensive and performed poorly.Because of the popularity of digital cameras, active pixel sen-sor arrays are now readily available at lower cost and higherquality. Other technical problems, such as high operatingtemperatures, slow performance of the spatial light modula-tors, and commercial availability of the micro-mirrors andferroelectric modulators, have been resolved or are in theprocess of refinement in the prototypes. 6

Some scientists report that they are confident theyhave overcome these technical obstacles reported byother scientists and technologists in the field.

We believe the substantial advances in record-ing media, recording methods, and the demon-strated densities described here coupled withthe recent commercial availability of systemcomponents remove many of the obstacles thatpreviously prevented the practical considera-tion of holographic data storage and greatlyenhance the prospects for holography tobecome a next-generation storage technology.6

Cost of Storage and OtherVariables

PACS administrators are demanding more storage at alower cost, more reliable hardware, and a smaller footprint.Most hospitals have limited physical infrastructure andhave run out of room to place additional media storagedevices. As the demand for more storage increases, holo-graphic drives may solve the problem of storing largeamounts of medical images in small spaces. This technolo-gy is still too immature to determine what the actual costper gigabyte (GB) of storage will be. Some analysts predictthat the cost could range up to $20 per GB of storage. Nextto cost, speed and footprint are the two biggest concerns.Straub explains in his 2004 article that changing the inputangle of one of the beams permits a new hologram to bestored in the same volume of material. This adjustmentcould offer terabit storage capacities in small spaces. Thesuperimposition of many holograms within the same vol-ume of storage media will exponentially increase futurestorage capacity thresholds.1

Cost Comparison

The cost of storage is evaluated on a case by case basisdepending upon the type of media selected and the esti-mated capacity. Comparative data suggests that the cost forthe new holographic media will probably be somewhere inthe neighborhood of $.06-$.20 per GB compared to datatape which costs between $.25 and $1, and video tapewhich costs between $1 and $3 per GB. The most expensivestorage media is hard disk drives which start at around $3per GB and go up from there. The average archive life ofholographic media is predicted to be approximately 50years by the companies positioning their prototypes in themarket. If this prediction is substantiated by solid researchin the months ahead, this would compare nicely with otheroptical type drives, but is vastly better than data tape, videotape, or hard disk drives.6

Other Physical Comparisons

Table 3 compares various parameters from magnetic, opti-cal, and tape drives. Holographic drives are not included inthis comparison. Note that there are pros and cons associ-ated with each type of currently deployed media. PACSadministrators must evaluate which technology is best suit-ed for present needs.

Is the Future Bright forHolographic Technology?

Holography was discovered in the 1940s, but it was notuntil the development of the laser in the 1960s that it wasconsidered a storage potential.

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The rapid development of holography for dis-playing 3-D images led to the realization thatholograms could potentially store data at avolumetric density of one bit per cubic wave-length. Given a typical laser wavelength ofaround 500 nm, this density corresponds to1012 bits (1 terabit) per cubic centimeter ormore. (In comparison, a DVD optical-diskplayer reads data 100 times slower.)

In the mid-1970s, research into holographicdata storage all but died out due to the lack ofsuitable devices that could transfer 2-D pixi-lated images.6

Recent advances in technology have led to increasedconsumer interest in holographic storage as a viablealternative for storing medical images. Although theinitial focus for product development has not beenspecifically pointed at healthcare applications, there ispotential that once the technology is released, it wouldhave tremendous application in the PACS environ-ment. Holographic technology is about to hitmainstream. Quain10 reported at the National

Association of Broadcasters conference in mid-April(2005) that optical storage technology companies haddemonstrated a new prototype optical drive that canstore digital information not just on the surface of anoptical disk, but also within a disk as 3D images. Theprototype stores up to 300 GB on a single disk. Thiswas accomplished by developing a unique photopoly-mer. The initial holographic drives, ready for release tomarket in Q3 of 2006, will be write-once designs forprofessional archiving with models priced at about$10,000 and $15,000. Manufacturers are expected tooffer an inexpensive ROM product for consumers.10

Development of the prototype holographic drivehas been a collaborative effort between governmentand private enterprise, according to Electronic News.11

The industry credits the innovation of key recordingtechniques and holographic media, along with com-mercial availability of critical components, to strongpartnerships with leading storage companies and gov-ernment funding. Advances have been made toincrease data storage capacities up to 1.6 TB on a sin-gle disk. The prototype writes the data with a singleflash of a 407 nm laser beam. Multiple pages of data,referred to as a book, are recorded in one spot on the

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Table 3. Parameters from Magnetic, Optical, and Tape Drives

Parameter Magnetic Disk Optical Disk Magnetic TapeRetrieval Random Typically Serial Serial

Study retrieval time A few seconds Typically 10 seconds Typically a minute oror more more

Use On-line immediate Near-line access Long-term archiveaccess Long-term archive Disaste r recovery

Departmental or Disaste r recoveryenterprise archive

Disaste r recovery

Uncompressed storage Up to 300 plus GB, Currently Up to 500 GBcapacity access time will approximately 30 GB

tend to decreasewith capacity ofdisk

Life expectancy and Excellent, but can Excellent if properly Finite and varies by typereliability of media be corrupted handled of tape

Human intervention Minimal to none Some and varies by Some and varies by typerequired type of optical disk of tape and jukebox

jukebox

Relative cost Must be evaluated on a case by case basis

(Table courtesy of Smith E, University of Rochester, 2004.)

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disk, providing approximately 12 MB of data in a sin-gle book location. Electronic News explains the actualtechnology that makes this type of innovation possible:

The prototype drive includes all drive subsys-tems such as the auto load/unload mechanics,servo system, holographic read/write head,data channel and electronics. The media car-tridge is loaded and unloaded automaticallyusing a mechanism designed by private enter-prise. The servo system regulates both radialand rotational movement of the media andthe angle of the reference beam. The holo-graphic read/write head is the heart of the sys-tem, and in the past availability of high quality,yet affordable optical components was anissue. However, the 407 nm blue lasers recent-ly available in other optical devices provide thewavelength required for high capacity holo-graphic storage. CMOS active pixel sensorarrays used in digital cameras are also avail-able, as are spatial light modulators used indigital TVs and projectors. This technologydepends on its industry partners to continueto optimize these components for use in holo-graphic storage.11

Some of these breakthrough technologies werefunded partially by the NTA for the eventual use ingeospatial image archive applications. This technologyrepresents a true collaboration between private andpublic sectors.

Conclusion

PACS for medical imaging require vastly increased storagetechnologies that are affordable and reliable. Expandedinterest by physicians to image patients using sophisticatedmodalities such as CT and MRI scans have produced ter-abytes of medical imaging data that need to be stored. Acommensurate increase in the need for storage capacityand speed of retrievals for online and near-line storage ofmedical images by PACS administrators has developed.Current storage technologies are expensive to implementand quick to become obsolete. Holographic drive technol-ogy holds hope to change the current paradigms held byPACS administrators by offering a fast and affordable stor-age solution for the future. This technology is still in itsinfancy, but recent technological advances in the media andthe technology within the components offers hope thatholographic drives may prove to be a viable storage solu-tion for the future. Further research is needed to clarifywhether or not holographic storage will become the pre-ferred drive and storage technology for PACS. PACSadministrators should carefully educate themselves regard-

ing possible storage solutions before committing to anenterprise-wide solution that may soon become obsoletedue to emerging technologies. Data is not currently avail-able to explicitly define the cost and reliability of this tech-nology since it has not been deployed commercially at thetime this paper was written. Scientists remain concernedwith the long term stability of the materials and withpotential destructive readout issues. However, indicationsare that by 2010, holographic storage devices may maketheir way into mainstream PACS deployment to provide asolution for fast, reliable, and inexpensive storage.

References1Nagy P, Farmer J. Demystifying data storage: Archiving

options for PACS. Appl Radiol. 2004;May:18-22.2Straub J. The Digital Tsunami: A perspective on data storage.

Information Management Journal. 2004;38:42.3Smith E. What’s in Storage? ADVANCE for Imaging and

Oncology Administrators. 2004;May:27-30.4Konkachbaev A, Elmaghraby A. Interface for digital medical

image databases. 4th International IEEE EMBS SpecialTopic Conference on Information Technology Applicationsin Biomedicine 2003. Piscataway, NJ: IEEE Computer Soci-ety Press; 2003:238-241.

5Dhar L. A new venture in holographic storage. IndustrialPhysicist. 2001;7(3):26.

6InPhase Technologies: What is holographic storage. 2005.7Burr GW, Coufal H, Hoffnagle JA et al. Optical data storage

enters a new dimension. Physics World. 2000;6:37-42.8Hellemans A. Holograms can store terabytes, but where? Sci-

ence. 1999;286:1502.9Liu Y, Kitamura K, Ravi G, Takekawa S, Nakamura M. Growth

and two-color holographic storage properties of Mn-dopedlithium nibate crystals with varying Li/Nb ratio. J ApplPhys. 2004;96(11):5996-6001.

10Quain J. A new dimension in storage. PC Magazine. 2005;24.11Lucent venture unveils holographic drive prototype. Elec-

tronic News. 2005;51(2).

John Colang, RT, i s a g raduate student at MidwesternState University and is a candidate for the Master ofScience in Radiologic Sciences degree in December of2006. He i s a PMI certified Project Manager and isemploye d by Intel Corp. in Albuquerque as a ProjectManager for IT. John is a lso a member of the ARRTand ASRT and may be contacted [email protected].

Dr. James Johnston is an ass istant professor of RadiologicSciences at Midwestern State Univers i ty in Wichita Falls,Texas where h e teaches in the associate’s, bachelor’s,radiologist assistant, and master’s programs. James maybe contacted at [email protected].

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1. Which of the following are major benefits to a fullydigital medical imaging department?a. Increasing efficiency in the stages of image captureb. Increasing efficiency in the result-reportingc. Increasing efficiency in interpretationd. All of the above

2. Holographic storage increases capacity because theimages record data:a. On the surface of the mediab. In three dimensionsc. on magnetic taped. none of the above

3. What are some reasons that the strain on storage andarchival systems has become acute?a. More department have moved from conventional film to

digital systemsb. Diagnostic imaging procedures produce larger image filesc. There is more dependency on sophisticated imaging

modalitiesd. All of the above

4. According to a study at the University of CaliforniaBerkeley, by 2010 departments will need to improvetoday’s storage offerings by:a. 10 timesb. 100 timesc. 1000 timesd. No improvement will be necessary

5. Data storage may be classified as:a. Onlineb. Near linec. Offlined. All of the above

6. When data is stored on magnetic hard drives withaccess times in milliseconds and transfer times in therange of 10s and 100s MB/second is defined as:a. Online storageb. Offline storagec. PACSd. None of the above

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7. A tape or jukebox is generally used in what type ofstorage?a. Online b. Near linec. Offlined. All of the above

8. When removable tape or optical media is stored on ashelf in a catalog and is retrieved manually, this isreferred to as:a. Online storageb. Jukebox storagec. Offline storaged. Near line storage

9. For every 225,000 radiologic procedures performed,it is estimated that most hospital require approximately:a. 10 MB of storage annuallyb. 10 TB of storage annuallyc. 1000 gigabytesd. None of the above

10. The primary purpose of the PACS database is to movelarge Radiologic images through the network asquickly as possible.a. Trueb. False

11. Relative to other healthcare applications, PACSrequires less data storage capacity.a. Trueb. False

12. Eventually, scientists hope to advance the holographicmemory technology so that one single disk the size ofa CD-rom could potentially hold:a. 1 TB of dateb. Images from thousands of examsc. 200 times the amount of data that standard disks

currently holdd. All of the above

13. What type(s) of procedures produce the most num-ber of images and exert the most demand on storage?a. Multi-slice CTb. Cardiac Catheterizationc. Peripheral vascular angiographyd. All of the above

14. Holographic media is an emerging technology whichcould replace conventional magnetic and optical driveand storage systems connected to PACS in the nearfuture.a. Trueb. False

15. Which of the following is true of holography?a. Enables massively parallel recording of datab. Enables massively parallel reading of datac. Exploits the entire thickness of a recording mediumd. All of the above

16. Instead of laying down the data on the surface layer ofthe medium like in conventional digital recordings,holography uses:a. One datum at a timeb. A photo detector to retrieve data bit-by-bitc. Lasers and light to record data in three dimensionsd. None of the above

17. The device that translates the electronic data of 0’sand 1’s into an optical “checkerboard”patterns oflight and dark pixels is called a(an):a. Digital video recorderb. Hologram refractorc. Spatial light modulatord. All of the above

18. At the present time, lasers are a limiting factor in thedevelopment of holographic drive and storage technology because they are costly and unreliable.a. Trueb. False

19. When compared to other types of storage, holograph-ic media will probably cost about:a. $.06-$.20 per GBb. $.25-$1 per GBc. $3 plus per GBd. The same as other types of storage

20. Holography was first discovered in the:a. 1930sb. 1940sc. 1950sd. 1960s

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