AJR 2004; 183:529-533
© American Roentgen Ray Society
A Simple Method for Extracting DICOM Images from a Magnetooptic Disk
Chun-Shan Yam1,
Arkadiusz Sitek,
Vassilios Raptopoulos and
Michael Larson
1 All authors: Department of Radiology, Beth Israel Deaconess Medical Center, 1
Deaconess Rd., WCC, Rm. 306, Boston, MA 02215.
Received October 9, 2003;
accepted after revision December 7, 2003.
Address correspondence to C.-S. Yam
(csyam{at}caregroup.harvard.edu).
Abstract
OBJECTIVE. Our objective was to develop a simple and easy-to-use
method to extract DICOM images from magnetooptic (MO) disks to the computer
desktop for research purposes.
CONCLUSION. The method we developed allows users to extract DICOM
images directly from MO disks to a PC desktop. The hardware component that we
used is commercially available and is plug-and-play. The system is lower in
cost than a clinical workstation. Users do not need to have special computer
skills to use our method. DICOM images can be transferred directly from the MO
disks to computer desktop folders using drag-and-drop. In our implementation,
we store the DICOM files in a shared folder in our hospital network, so users
can access the data from their office or research computers.
Introduction
Magnetooptic (MO) recording is a common industry practice for long-term
data storage and external backup. Most medical scanner manufacturers also use
MO technology as their standard archiving medium for medical images
[1,
2]. One of the major advantages
of the MO disk is that data can be rewritten repeatedly without significant
damage to the disk. Most of the industrial-grade MO disks can be rewritten
millions of times before noticeable failure is observed. The capacity of MO
disks is large, allowing the storage of multiple patient studies in a single
cartridge. For example, a typical MO disk with a storage capacity of 5.2 GB
can store up to 10,000 CT or 40,000 MR images. Because of this unique
advantage, most PACS vendors also use MO disks as their primary long-term
archive. This kind of storage is called a "jukebox" and may
contain hundreds of MO disks of patient data. A typical PACS jukebox can store
several terabytes of data.
The use of MO disks for data storage is already standard practice in
radiology for both clinical and research endeavors. However, this use raises
compatibility and accessibility issues for the research community. First, MO
disks can be read only by the manufacturer's proprietary software and
hardware. Users must have the same type of archiving system (such as a
clinical workstation) to read the data. In most cases, the users would need to
find and get permission to share a compatible clinical workstation or purchase
their own systems. The typical cost of a basic clinical workstation with MO
disks ranges from $50,000 to $100,000. Although a clinical workstation may be
available to read the images, it is difficult to transfer the data to a
stand-alone desktop computer for research purposes. Transfer requires the
installation of a data transfer mechanism such as File Transfer Protocol (FTP)
on the clinical workstation [3,
4]. However, the use of FTP on
a clinical workstation is not recommended and is usually prohibited by the
vendor.
Many researchers in radiology face the problem of downloading data from the
MO disks, but this problem is acute for researchers participating in
multicenter clinical trials. Our goal was to develop a low-cost and
simple-to-use method of extracting the DICOM images from MO disks.
System Installation
The schematic of our MO data extraction system is shown in
Figure 1A. A standard desktop
PC (GX110, Dell) running Windows 2000 Professional operating system
(Microsoft) and an external 5.2-GB MO storage drive (RMO-S551/SD, Sony
Electronics) serve as the primary workstation to extract the MO data. A
connection was established between the PC and the MO drive with a commercially
available peripheral component interconnect (PCI) small computer system
interface (SCSI) card (model 2906, Adaptec). The total cost of this system,
including the PC and MO drive, is usually less than $1,500.
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Fig. 1A. —System schematic and setup. Diagram of overall system for reading
magnetooptic (MO) media to shared files. Drive used is 5.2 GB rewritable drive
(RMO-S551/SD, Sony Electronics) with built-in firmware for displaying MS
DOS-based (Microsoft) file system that is currently being used in most MO
media. SCSI = small computer system interface.
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The system installation is a two-step plug-and-play process. Step 1
installs the PCI interface card; for most of the newer PC systems, installing
a PCI card is simple and does not require any tools. Step 2 connects the
external MO drive to the host PC via the PCI interface card. We used a 6-ft
(180-cm) SCSI cable to connect the drive to the PCI card. Most SCSI devices
have two SCSI connectors to connect ("daisy-chain") multiple
devices to the same PC. For a successful SCSI connection loop, the last SCSI
device in the chain must be terminated. Because the MO drive is the only SCSI
device used in our system, we used the built-in terminator to end the
connection loop. The system setup with the MO drive connected to the host PC
is shown in Figure 1B.
Installation is now complete, and the system is ready for data extraction.
Because the MO drive is a SCSI device, it must be powered on before the host
PC is turned on. This rule is important for using external SCSI devices. Once
the system is turned on, the MO drive will be automatically mounted to the
Windows operating system. For our system setup, the MO drive appears as a
removable drive icon "Drive G:\" on the desktop. We did not need
to install any driver software for the SCSI card or the MO drive because we
are using the Windows 2000 Professional operating system. Windows NT users
will need to install drivers, but the installation process is intuitive and
easy to follow. Several system reboots may be needed. Users do not need
special computer skills to perform the hardware installation.
The ability to read MO disks in our system is mainly due to the
platform-independent industry standards of SCSI and PCI connectivity. Hardware
running on Mac OS, Linux, and Unix operating systems can also use this system
schematic.
Implementation
We have tested our system with some commonly used rewritable MO disks from
Sony (Sony Electronics) and Maxoptix (GE Healthcare) with different storage
capacities: 600 MB and 1.2, 2.3, and 5.2 GB. Figures
2A,
2B and
3A,
3B are screen-capture images
showing the file contents of a GE disk and a Siemens MO disk, respectively. In
both cases, we used 2.3-GB disks. Both the GE and Siemens MO disks are
compliant with the current DICOM 3.0 guidelines
[1]. DICOM specifies protocols
and formats for the exchange of images, time-based waveforms, reports, and
associated information for medical applications. In most DICOM storage media,
a set of DICOM information is described by an index file, DICOMDIR, which
accompanies the files that it references. As seen in Figures
2A and
3A, the DICOMDIR index file
appears in the root directory (or top folder) for both GE and Siemens MO
disks. Individual DICOM files are stored in subfolders with their names in
alphanumeric order. Figures 2B
and 3B are screen-capture
images of some representative DICOM files from the subfolders in GE and
Siemens disks, respectively.
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Fig. 2B. —Screen-capture images of system directories of magnetooptic (MO)
disk from GE Healthcare. Screen-capture image of subdirectory of MO disk shows
DICOM files named in alphanumeric index. Note that files are compressed in
this particular case.
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Fig. 3B. —Screen-capture images of system directories of magnetooptic (MO)
disk from Siemens. Screen-capture image of subdirectory of MO disk shows DICOM
files named in numeric index. Note that files are uncompressed in this
particular case.
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Because the names of the folders and files in the MO disk follow an
internal index and not the actual demographics such as patient name or
scanning date, it is difficult to locate specific DICOM files. To correlate
the folders and files to demographic information, we extracted this
information from the DICOMDIR file. The DICOMDIR file is basically an ASCII
file containing information on how images are stored in the MO media. In fact,
DICOMDIR is a collection of DICOM objects written in sequential order
[1]. Each object contains three
individual entities: tag, length, and data. The tag is a 4-byte segment
indicating the identity of the object, such as patient name and study date.
The length is another 4-byte segment representing the type and size of the
information. The data are the actual information that creates the image.
Following this schematic, we wrote a Visual Basic for Applications (VBA)
macro in MS Word (Microsoft) to decode the patient name, study date, and file
location for each individual image. Table
1 shows some of the decoded DICOM objects of a GE DICOMDIR file
from a HiSpeed helical CT scanner (GE Healthcare). With this table, users can
easily identify their DICOM files and then drag-and-drop to copy the selected
files directly from the MO disk. In our implementation, we store all the DICOM
files in a shared folder in our hospital network, so that users can access
their data from their office computers. The ability to identify desired images
derives from the nature of the DICOM standard rather than the choice of VBA in
MS Word. Any system that can read SCSI MO disks can be programmed to read the
DICOMDIR file and extract the desired study filenames.
Data Analysis
Although it is not in the scope of this article to discuss the selection or
application of image processing software in radiology research, we tested some
of the extracted DICOM images using ezDICOM software, which is an open-source
freeware program for radiology education and research
[5]. To load an image in the
application, drag and drop the DICOM files into the application window or its
desktop icon. In our implementation, we selected the DICOM file from the MO
disk and dragged it to the application icon. The DICOM images are displayed at
the original window and level settings.
Figure 4A is the screen-capture
image of a CT scan loaded in ezDICOM. Basic image manipulation and pixel
analysis can be archived through simple mouse actions. The software has a
builtin color map for functional imaging data analysis. Also, the detailed
DICOM information can be displayed by pressing the F3 key on the keyboard.
Figure 4B is a screen-capture
image of the detailed DICOM information extracted from the CT image shown in
Figure 4A.
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Fig. 4B. —Screen-capture CT loaded in ezDICOM software. Screen-capture image
of detailed DICOM information extracted using ezDICOM software shows detailed
DICOM header information for CT image (A) that lists in ezDICOM
software when F3 key is pressed. List contains all header information for that
image and includes patient name or identification number; study date,
protocol, and time; series description; image position; kVp and mA; slice
thickness; and more.
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Performance
Our system has been in use in our department for more than 1 year. We have
used it to extract DICOM files mainly for research studies. We installed the
system in our media laboratory as a central location and saved all the
extracted data in a secured network folder on our hospital network. Users are
required to have a valid username and password to access this shared folder.
Because all research studies conducted in our institution are compliant with
the Health Insurance Portability and Accountability Act (HIPAA), no
patient-identifying information has been used. However, for studies performed
before the HIPAA standard took effect, patient names may be used to label
scans. In such cases, we suggest researchers use only the patient's initials
to name the extracted files.
Limitation
Although our system has proven to be compatible with DICOM-compliant MO
disks from GE and Siemens, other non-DICOM archiving media such as tapes and
write-once-read-many cartridges, many of which require obsolete hardware, will
not be compatible. In our experience, such old archiving media are also
incompatible even with new hardware supplied by the same manufacturer.
However, with the increasing demand for digital images in radiology, a greater
number of medical scanner manufacturers are becoming DICOM-compliant. More
information on current DICOM development, vendor and imaging conformance, and
software resources is available at the Radiological Society of North America
Internet site [6].
Discussion
We developed a simple method for extracting DICOM images from MO disks
using a commercially available PC and an external MO drive. The system is low
in cost ($1,500) compared with a typical clinical workstation
($50,000-100,000), and the hardware installation is basically plug-and-play.
Users do not need special computer skills to use our method. Images can be
transferred directly from the MO disk to a PC desktop folder or a shared
folder in a network drive. We have tested our system with MO disks from GE and
Siemens. We also showed the use of ezDICOM software for basic image
processing. The success of this solution mainly depends on the industry
standards of SCSI, PCI, and DICOM. Although our system was implemented on a
Windows platform, other systems such as Mac OS, Linux, and Unix can also be
used.
References
- American College of Radiology, National Electrical Manufacturers
Association. ACR-NEMA Digital imaging and communications
standard. Washington, DC: National Electrical Manufacturers
Association, 1985. Publication 300-1985
- Bidgood WD Jr, Horii SC. Introduction to the ACR-NEMA.
RadioGraphics1992; 12:345
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- Gale DR, Gale ME, Schwartz RK, Muse VV, Walker RE. An automated
PACS workstation interface: a timesaving enhancement.
AJR 2000;174:33
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- Maldjian JA, Listerud J. Automated teaching file and slide database
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- ezDICOM Web site. Available at
www.psychology.nottingham.ac.uk/staff/cr1/ezdicom.html.
Accessed May 28, 2004
- Radiological Society of North America Web site. Available at
rsna.org/practice/dicom/dicom.html.
Accessed May 28, 2004
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Abstract
Introduction
