DOI: 10.1148/rg.251045058
RadioGraphics 2005;25:273-283
© RSNA, 2005
Informatics in Radiology (infoRAD)
Mobile Wireless DICOM Server System and PDA with High-Resolution Display: Feasibility of Group Work for Radiologists1
Norio Nakata, MD,
Susumu Kandatsu, MD,
Naoki Suzuki, MD, PhD and
Kunihiko Fukuda, MD
1 From the Department of Radiology, Jikei University Daisan Hospital, 4-11-1 Izumi-honcho, Komae City, Tokyo 201-8601, Japan (N.N.); the Department of Radiology, National Institute of Radiological Sciences, Chiba, Japan (S.K.); the Institute for High Dimensional Medical Imaging, Research Center for Medical Science, Jikei University School of Medicine, Tokyo, Japan (N.S.); and the Department of Radiology, Jikei University Hospital, Tokyo, Japan (K.F.). Recipient of a Certificate of Merit award for an infoRAD exhibit at the 2003 RSNA Scientific Assembly. Received March 30, 2004; revision requested May 13 and received June 15; accepted June 17. All authors have no financial relationships to disclose. Address correspondence to N.N. (e-mail: nakata@jikei.ac.jp).
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Abstract
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A novel mobile system has been developed for use by radiologists in managing Digital Imaging and Communications in Medicine (DICOM) image data. The system consists of a mobile DICOM server (MDS) and personal digital assistants (PDAs), including a Linux PDA with a video graphics array (VGA) display (307,200 pixels, 3.7 inches). The MDS weighs 410 g, has a 60-GB hard disk drive and a built-in wireless local area network (LAN) access point, and supports a DICOM server (Central Test Node). The Linux-based MDS can be accessed with personal computers (PCs) and PDAs by means of a wireless or wired LAN, and client-server communications can be established at any time. DICOM images can be displayed by using any PDA or PC by means of a Web browser. Simultaneous access to the MDS is possible for multiple authenticated users. With most PDAs, image compression is necessary for complete display of DICOM images; however, the VGA screen can display a 512 x 512-pixel DICOM image almost in its entirety. This wireless system allows efficient management of heavy loads of lossless DICOM image data and will be useful for collaborative work by radiologists in education, conferences, and research.
© RSNA, 2005
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Introduction
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In consultation, conferences, education, and research, radiologists often require not only several key images from an image data set but whole image sets associated with examination of a particular patient or all sequential images from one series from their own teaching files. The significant increases in quantity of images produced on examination of each patient due to the progress in multidetector computed tomography (CT) and high-speed magnetic resonance (MR) imaging have resulted in increases in the total quantity of such teaching files. Therefore, there is a need for an efficient way for radiologists to create and make best use of their teaching files, including large quantities of Digital Imaging and Communications in Medicine (DICOM) images.
There have been a number of reports concerning the creation of electronic teaching files for use in medicine (1–9). Advances in computer technology have reduced the size of servers and facilitated medical image browsing by using wireless local area networks (LANs) (10) and personal digital assistants (PDAs) with high-quality displays (11). Open-source software projects are characterized by a collaborative, consensus-based development process, an open and pragmatic software license, and a desire to create high-quality software. Independent projects are best built by using freestanding components that leverage the power of freely available open-source tools. The Central Test Node (CTN) DICOM toolkit is one of the numerous open-source tools specifically designed to interface with medical resources (12).
Therefore, we have installed open-source picture archiving and communication system (PACS) software along with other necessary open-source software onto a Linux-based pocket-size mobile DICOM server (MDS) to allow management of DICOM images through PDA or laptop personal computer (PC) clients via a wireless LAN. The performance of the DICOM connection of the MDS was tested and compared with that of a conventional DICOM server. In this article, we discuss the image quality of PDA displays and the feasibility of using the MDS for collaborative work by radiologists. Specific topics discussed are the system configuration, the client PDAs, the pocket-size MDS, PDAs with high-resolution display, work flow and usability of the pocket-size MDS, performance evaluation of the DICOM connection, security considerations, the road map for wireless LAN security, and advantages and disadvantages of the MDS.
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System Configuration
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The basic system configuration is shown in Figure 1. The MDS, which includes a dynamic host configuration protocol (DHCP) server and an Ethernet bridge, not only acts as an Institute of Electrical and Electronics Engineers (IEEE) 802.11b wireless access point but also has wired LAN connectivity via an attached exclusive Fast Ethernet cradle. By using this cradle, the MDS was connected with other DICOM archives, a DICOM viewer, and imaging modalities, such as CT and MR imaging, via the wired LAN. Mobile PC and PDA clients were connected to the MDS over a wireless LAN (IEEE 802.11b) with a maximum of 250 clients connected simultaneously.
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Figure 1. Basic design of the system. The MDS includes a Web server, a file transfer protocol (FTP) server, and a dynamic host configuration protocol (DHCP) server and has a built-in Institute of Electrical and Electronics Engineers (IEEE) 802.11b wireless access point. PDA and laptop PC clients connect via a wireless LAN. By using the wired Fast Ethernet LAN cradle, the MDS can connect to other workstations and imaging modalities, such as CT or MR imaging, within the hospital. Mac = Macintosh, nfs = network file server, smb = server message block, Win = Windows.
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Client PDAs
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Three types of PDA clients were used: a Linux PDA, the Pocket PC (Microsoft, Redmond, Wash), and the Palm OS (PalmSource, Sunnyvale, Calif).
The Linux-based Zaurus C-760 (Sharp, Osaka, Japan) is powered by a 400-MHz PXA255 Xscale processor (Intel, Santa Clara, Calif) with 64 MB of synchronous dynamic random-access memory (SDRAM) and 128 MB of flash read-only memory (ROM). It has a 3.7-inch, 640 x 480-pixel touch screen using a thin-film transistor (TFT) liquid crystal display (LCD) and is capable of displaying 16-bit color (65,536 colors) (Fig 2).
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Figure 2a. Linux PDA with a video graphics array (VGA) display. The display is a 3.7-inch, 16-bit color TFT LCD. (a) The screen shows a 512 x 512-pixel DICOM CT image of the lung. (b) The screen shows 128 x 128-pixel thumbnail MR images.
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Figure 2b. Linux PDA with a video graphics array (VGA) display. The display is a 3.7-inch, 16-bit color TFT LCD. (a) The screen shows a 512 x 512-pixel DICOM CT image of the lung. (b) The screen shows 128 x 128-pixel thumbnail MR images.
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The Pocket PC 2002–based iPAQ H3950 (Hewlett-Packard, Palo Alto, Calif) is powered by a 400-MHz PXA250 Xscale processor with 64 MB of SDRAM and 32 MB of flash ROM. It has a 3.8-inch, 240 x 320-pixel touch screen that uses TFT LCD and is capable of displaying 16-bit color (Fig 3).
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Figure 3. (3) Pocket PC with a quarter VGA (QVGA) display. The display is a 3.8-inch TFT LCD. The screen shows a DICOM CT image of the lung, the horizontal size of which is adjusted automatically with lossy compression.
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The Palm OS version 5.2–based Clie PEG-UX50 (Sony, Tokyo, Japan) is powered by a 123-MHz CXD2230GA processor (Sony) with 104 MB of memory (16 MB available for storage of files and programs, 16 MB available for system backup, and an additional 29 MB available for media storage). It has a 3.2-inch, 480 x 320-pixel touch screen that uses TFT LCD and is capable of displaying 16-bit color (Fig 4).
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Figure 4. Palm OS PDA. The display is a 3.2-inch TFT LCD with 480 x 320 pixels. The screen shows a DICOM CT image of the lung, the vertical size of which is adjusted automatically with lossy compression.
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Pocket-size MDS
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The pocket-size server was an FSV-PGX1 (Sony) with a 230-MHz Cyrix MediaGX (VIA Technologies, Taipei, Taiwan) central processing unit (CPU), 64 MB of RAM, and a built-in 2.4-GHz IEEE 802.11b interface. We upgraded the hard drive from the original 20 GB to 60 GB for installation of the open-source DICOM server software. The total weight of the server, measuring 83 x 155 x 31 mm, was 410 g (Fig 5).
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Figure 5a. Photographs of the MDS. (a) The MDS with its cradle. The cradle functions as a power supply and provides Fast Ethernet connectivity. (b) The MDS can be easily carried by radiologists.
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Figure 5b. Photographs of the MDS. (a) The MDS with its cradle. The cradle functions as a power supply and provides Fast Ethernet connectivity. (b) The MDS can be easily carried by radiologists.
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As the original server, running Linux 2.4.20, was not sufficient for installation of the DICOM server software, additional open-source software installation was required for the MDS. We compiled and installed Apache 1.3.27, PostgreSQL 7.2.3, PHP 4.2.2, and the Central Test Node (CTN) software (Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, Mo) for the DICOM server. We coded the server-side scripts for the DICOM viewer and query/retrieve of DICOM images and installed those PHP scripts into the MDS (Fig 6). All software installed on the MDS was free open-source software available under the GNU General Public License (GPL). The total hardware cost of the MDS was about $800.
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Figure 6. Work flow of the MDS. The MDS acts as a portable PACS and server-side DICOM viewer. The DICOM viewer scripts were written in hypertext markup language (HTML) and PHP. HTTP = hypertext transfer protocol.
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PDAs with High-Resolution Display
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The PACS archives contained DICOM images in various resolutions from 256 x 256 pixels to 2,140 x 1,760 pixels. In our hospital, the most common resolution of CT and MR images is 512 x 512 pixels. The standard display resolutions of common PDAs are 320 x 240 pixels for the Pocket PC and 480 x 320 pixels for Palm OS version 5. Therefore, noncompressed DICOM images exceed these common PDA display sizes (Fig 7). Thus, it is necessary to use compressed images to display the whole of the image on these PDAs.
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Figure 7. Conventional PDA display sizes and a DICOM image. Conventional PDA display sizes, such as 320 x 240 pixels (quarter VGA [QVGA]) or 480 x 320 pixels, are too small to allow display of typical 512 x 512-pixel DICOM CT images.
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In 2003, a Linux PDA with a 3.7-inch, 16-bit color video graphics array (VGA) (640 x 480 pixels) TFT display came on the market in Japan (Fig 2). This VGA monitor can display almost the complete 512 x 512-pixel DICOM images (Fig 8). Therefore, we compared this PDA with its state-of-the-art display with common PDA clients for use as a DICOM image viewer. Some companies have recently developed Pocket PCs with VGA screens, and such PDAs with high-resolution VGA displays are expected to come into wide use from 2004.
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Work Flow and Usability of the Pocket-size MDS
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The system uses two basic network modes: a closed personal network environment and a network connected to an existing LAN. The MDS was used as a short-term DICOM archive for teaching files for use in education and research. To store the DICOM images in the MDS, users connected to the MDS through an existing wired LAN. Each user could also access the MDS via a wireless LAN and use a server-side query/retrieve Web menu and DICOM viewer (Fig 9) through a client PC or PDA. After archiving of the target DICOM images, users could carry their own MDS. Examples of use after archiving of DICOM images are as follows:
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Figure 9a. Image-viewing windows of a Web-based DICOM viewer on a Microsoft Windows PC. (a) Screen shows a thumbnail image menu. The images are 128 x 128 pixels. (b) Screen shows a full-size DICOM image. The image is a noncompressed 512 x 512-pixel CT image.
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Figure 9b. Image-viewing windows of a Web-based DICOM viewer on a Microsoft Windows PC. (a) Screen shows a thumbnail image menu. The images are 128 x 128 pixels. (b) Screen shows a full-size DICOM image. The image is a noncompressed 512 x 512-pixel CT image.
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1. Collaboration for research: DICOM data files for research are usually too large to attach to e-mail, and making copies is often too time-consuming. Using the present system, if coauthors wish to refer to the DICOM data for their research, they can share the image data directly using the MDS without the need for copying or burning CDs (compact disks) of the required DICOM images.
2. Conferences using the MDS: At small conferences using DICOM images of cases under discussion, all members can share and independently read a series of DICOM images by accessing the MDS via a wireless LAN instead of using an LCD projector.
3. The MDS is small and light and so can be carried easily. The MDS is lighter than a conventional laptop PC.
4. Ubiquitous access: Users can access the DICOM data stored in the MDS from any location, whether from home or a hotel without a network environment. The client viewers were laptop PCs (Linux, Macintosh [Apple Computer, Cupertino, Calif], or Windows) or PDAs (Linux PDA, Palm OS, or Pocket PC) with server-side control of the MDS.
5. Short-term personal DICOM archive: Radiologists outside their hospital usually cannot gain access to the DICOM data inside their hospital’s secured long-term large-scale PACS.
6. Server message block (SMB) server: Of course, the MDS also has conventional server functions, including the ability to act as an SMB (Samba) server. Radiologists could share their Microsoft Word, PowerPoint, or Excel files, as well as archiving DICOM images.
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Performance Evaluation of the DICOM Connection
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An intranet system was constructed in our institute for the performance evaluation tests (Fig 10). We performed two tests consisting of sending images of different sizes to evaluate the DICOM connection. Test 1 was designed to measure the transfer time of DICOM image data sets and calculate the transmission rates from other DICOM archives using Linux and CTN to the MDS using the wired LAN. Four groups of image data sets with different data sizes were sent (Table 1). In comparison with the MDS experiments, we performed the same experiments using a Silicon Graphics Onyx 3400, on which was installed CTN software, as a reference conventional PACS. Each test was run six times, and the transfer times were measured.
The second test was performed to evaluate the performance of DICOM query/retrieval and display of a series of thumbnail images of our original DICOM Web-based viewer written in the PHP language. Four groups of image data sets with different data sizes were sent (Table 2). The PHP scripts for this Web page were installed on both the MDS and the Silicon Graphics Onyx 3400. Response time, which was defined as the time taken to move the whole test data set and finish displaying all thumbnail images on the screen, was measured from the start of the DICOM query/retrieve signal to the completion of depiction of all series of thumbnail images, all of which were 128 x 128-pixel Joint Photographic Experts Group (JPEG) images, on the client display. Both a Windows XP PC with a wired LAN and a Linux PDA (Zaurus C-760) with a wireless LAN (IEEE 802.11b) were used as clients. For comparison with the MDS, the same tests were also performed by using the Silicon Graphics Onyx 3400. All tests were performed with no other network loading except the connection of the test user.
The results of the two tests are summarized in Tables 3 and 4. In the first test, the transmission rates of the MDS were significantly lower than those of our conventional PACS server (P < .05). However, the average transmission rate of 819.9 kbits/sec from other DICOM archives to the MDS was estimated to be practical for radiologists in our institute.
In the second test, the average response time of the conventional PACS via the wired LAN was significantly shorter than that of the MDS over the wireless connection to the PDA (P < .05). In contrast, the response time of the conventional PACS over the wireless LAN (IEEE 802.11b) with the PDA client was not always significantly faster than that of the MDS. When the MDS was used, the response time with the Windows PC client was significantly shorter (P < .05), but the difference in the response time between the Windows PC and PDA client was small.
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Security Considerations
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Security considerations of the MDS network were as follows:
1. Pass code authentication at start-up of the MDS: When the MDS is started, a six-digit code is requested.
2. Basic Web server (Apache) authentication is installed in the MDS. Hypertext transfer protocol (HTTP) basic authentication is one of the authentication mechanisms outlined in the HTTP specification and requires the client to send a user name and password in clear text as part of the HTTP request. This pair is typically present in all HTTP requests for content in subdirectories of the original request.
3. Three grades of radiofrequency (RF) power control of the signal strength: The RF power of the wireless LAN can be set from several to approximately 50 meters. To secure the wireless LAN, a low RF power can be selected.
4. Wired equivalent privacy (WEP), extended service set identifier (ESS-ID), and media access control (MAC) address authentication of the wireless LAN: Wireless LAN security protocols are provided with secure sockets layer (SSL) encryption, MAC validation, and ESS-ID. As an added layer of security, we enabled WEP encryption features on our wireless access point. However, WEP has been shown to have significant vulnerabilities that allow cryptographic attack on both confidentiality and access control functions (13).
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Road Map for Wireless LAN Security
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Currently, wireless LAN security is a work in progress (14,15). The wireless LAN security road map is shown in Table 5. The IEEE has developed a standard set of specifications for wireless networking generally referred to as the 802.11 wireless standards, which include 802.11a, 802.11b, and 802.11g.
802.11 networks have three basic methods for securing access to an access point: extended service set identifier (ESS-ID), media access control (MAC) address filtering, and the wired equivalent privacy (WEP) encryption mechanism. However, these encryption and authentication methods are flawed, leading to serious security issues (16). The 802.1x standard has been designed to enhance the security of wireless LANs that conform to the IEEE 802.11 standard. This standard defines the extensible authentication protocol (EAP), which uses a central authentication server to authenticate each user on the network. There are a number of variants of EAP, including EAP with transport layer security (EAP-TLS), lightweight EAP (LEAP), and protected EAP (PEAP) (17). Dynamic WEP improves on static WEP by giving each user a unique unicast key and all users the same broadcast key.
Wi-Fi protected access (WPA) is an interim standard developed by the Wi-Fi Alliance that will most likely be included in the eventual IEEE 802.11i standard. WPA uses its temporal key integrity protocol (TKIP) to provide improved data encryption as compared to WEP. In addition to authentication and encryption, WPA also includes vastly improved payload protection. The cyclic redundancy check 32 (CRC32) used in WEP is inherently insecure; it is possible to alter the payload and update the message CRC32 without knowing the WEP key. WPA uses a far more secure message integrity check (MIC), which cannot be circumvented in this way and prevents the execution of replay attacks (18).
IEEE 802.11i, also called WPA version 2 (WPA 2), is a draft IEEE standard for 802.11 wireless network security that is expected to be ratified in 2004 (19). 802.11i defines several new standards and also relies heavily on many existing standards. It defines new encryption key protocols, including the TKIP and the advanced encryption standard (AES), the latter of which is the U.S. government’s next-generation cryptography algorithm.
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Advantages of the MDS
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A large variety of applications are available for laptop PCs running Windows, but they cannot be carried in the pocket. In contrast, PDAs are very small but are less powerful than a laptop PC. The MDS is a supplemental storage device that allows radiologists to carry important DICOM images in their pocket along with a database for personal use and group work for both research and education. The MDS is a novel solution for teaching file management when using large quantities of multidetector CT or high-speed MR images. Conventional DICOM servers are expensive and unwieldy for personal use. In contrast, the MDS is a small and inexpensive personal PACS. In a ubiquitous network environment, radiologists can use PDA or PC clients to access the MDS via any standard Web browser. Thus, the MDS has the advantage of increasing the accessibility of DICOM images over conventional PACS. Moreover, when the MDS is used with the CTN, radiologists can also easily browse DICOM images using the conventional PC-based freeware DICOM viewer software.
Outside of the hospital, radiologists can also communicate using handheld devices compatible with the Wireless Application Protocol (WAP), which is a global standard for developing applications over wireless communication networks (20). However, the maximal data transfer speed of WAP 2.0–compatible third-generation mobile phones, which is 384 kbits/sec in Japan (21), is too slow to download large quantities of CT or MR image data as compared with that of IEEE 802.11b, the standard wireless LAN protocol for PDAs, which is 11 Mbits/sec.
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Disadvantages of the MDS
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We used a pocket-size PC case for the MDS and therefore the hardware specification was limited. The central processing unit (CPU) of the MDS, with performance equivalent to that of a 200-MHz Intel Pentium MMX processor, was sufficient for use in a DICOM server. However, our results suggested that the performance of this CPU was not satisfactory for server-side control of the DICOM viewer. Although PDAs showed good remote access for DICOM query/retrieve management, the performance of the server-side DICOM viewer when using the MDS and the wireless PDA was much poorer than that when using a conventional workstation and wired LAN. The maximum image matrices of new MR and multidetector CT units are 1,024 x 1,024. Therefore, noncompressed DICOM images from those MR and CT units exceed the VGA display size of the PDA.
In the present study, we used very small hardware for the MDS. However, all of the software required for the MDS could be easily installed on a conventional laptop PC or tablet PC. We are currently planning to upgrade the MDS hardware.
Pocket-size PCs, with Intel-compatible CPUs running at speeds over 1 MHz, a weight of 550 g, a 5-inch 800 x 600-pixel touch screen using a TFT LCD, and a 20-GB hard disk drive, have just come on the market as of June 2004 (22). We consider that a pocket-size PC with a display and better specifications than the MDS will be developed within the next few years. The maximum speed of IEEE 802.11b is slower than those of Fast Ethernet and gigabit Ethernet. If there are overwhelming traffic loads with many users on the wireless network, it will slow down the throughput. In the near future, other standards, such as IEEE 802.11g, which has a maximum speed of 54 Mbits/sec, may replace IEEE 802.11b.
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Conclusions
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Our system using a small mobile server is useful for efficient management of heavy loads of lossless image data in both wired and wireless network environments. Using this server and mobile devices, radiologists can gain access to small PACS in either small groups or on an individual level at low cost.
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TAKE-HOME POINTS
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The MDS is helpful for efficient management of heavy loads of lossless image data in a wireless network environment.
Using the MDS with open-source software and mobile wireless devices, radiologists can access small PACS in small groups or on a personal level with low cost.
Radiologists have to pay attention to security issues when using a wireless LAN.
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Footnotes
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Abbreviations: CTN = Central Test Node,
DICOM = Digital Imaging and Communications in Medicine,
IEEE = Institute of Electrical and Electronics Engineers,
LAN = local area network,
LCD = liquid crystal display,
MDS = mobile DICOM server,
PACS = picture archiving and communication system,
PC = personal computer,
PDA = personal digital assistant,
TFT = thin-film transistor,
VGA = video graphics array,
WEP = wired equivalent privacy.
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Abstract
Introduction
