High-speed teleradiology system transmits quality images
John Haystead
Contributing Editor
High-speed, high-capacity image transmission and distribution are important requirements for vision and imaging systems used in diagnostic medicine. In many applications, high-resolution digital medical images are needed almost immediately by physicians, surgeons, and radiologists for covering acute patient services. To meet these needs, Devices & Services Co. (D&S Dallas, TX) provides the radiology community with its modular Images-on-Call direct-capture digitizing and image-distribution equipment and software.
Using proprietary wavelet compression techniques, this teleradiology system can rapidly acquire and deliver 1024 x 1024-pixel (and larger) radiological, computed-tomography (CT), magnetic-resonance (MR), or nuclear medicine images to technicians and physicians located both inside and outside a hospital facility. The fully automatic system requires no exposure parameter adjustments such as contrast or brightness at the transmission site. Described as a "mini-PACS" (Picture Archiving and Communication System), the scalable Images-on-Call system can be configured as a single film scanner with local viewing terminals or as a facility-wide or interfacility distribution network with multiple scanners, direct-capture video digitization, automated image archiving, and remote-access wide-area-network (WAN) capabilities via conventional telephone lines.
From its central Radiology Receive Concentrating Center, Radiology Associates (Fort Worth, TX) uses the Images-on-Call system to provide 24-hour radiology services to seven regional hospitals and some small outpatient imaging centers. Prior to the installation of the Images-on-Call centralized system in July 1995, all the participating healthcare facilities had to contact individual on-call radiologists at their homes for after-hours radiology services and reports. In most cases, the radiologists would then have to travel to the hospital to analyze patient images. For some cases, the radiologists would receive and view patient images on standard PCs with single-view screens at their homes.
With the installation of the Images-on-Call system, the 47-radiologist group practice is providing immediate response to all connected sites from one central location during evening hours. As described by principal radiologist, Dr. Richard Jensen, the new system has provided significant economies of scale as well as improved operational efficiencies and response times. "Instead of four radiologists being kept up at night with phone calls, we`re able to assign just one radiologist to the center to handle all of the patient requirements. Turnaround time is now typically minutes as opposed to the lengthy time required for an on-call physician or radiologist to travel to the hospital," he adds.
Image capture
Typically, each remote hospital has its own in-house teleradiology system, which consists of at least one film-digitizing station, a file server, and many viewing terminals. Common terminal locations include the emergency room, intensive-care unit, and surgical departments. In addition, a direct-capture video digitizing station shows the images received from video-based modalities such as the CT, MR, and nuclear-medicine departments. All image-transmission hardware is provided by D&S. In the latter case, D&S supplies its Images-on-Call software modules. User-interface and operating-system software is Windows 3.1/95/98/NT-compatible at the system transmission and receiver ends.
Most hospital systems are linked via a Digital Imaging and Communications in Medicine (DICOM) network gateway. Developed by the American College of Radiology and the National Electrical Manufacturers Association, the DICOM standard allows a variety of medical-imaging equipment to be interconnected on a standard network. It also includes a dictionary of the data elements needed for proper image display and a hardware specification for physically connecting the devices. In addition, users can assess how much meaningful information can be exchanged between two DICOM-compliant imaging devices.
Image distribution
In the generic Images-on-Call architecture, multiple digitizing stations, film scanners, and DICOM sources are linked to a central frame-store server running the Images-on-Call teleradiology software (see Fig. 1). Depending on the size of the application, the server can be either a single high-end personal-computer (PC) or a large PC network.
The Images-on-Call software running on the frame-store server is composed of several modules, all managed by a system coordinator or Supervisor Module. This Supervisor Module manages the data transfers to and from the client modules using interprocess communication techniques and coordinates all the system tasks.
Video digitizer modules communicate with frame grabbers located within either the frame-store computer or the digitizing station over a high-speed Centronix (Montville, NJ) bidirectional parallel bus, manage image acquisition, report errors, and direct user-interface tasks. D&S builds its own autosensing, variable-frequency-video, frame-grabber devices and boards. These devices automatically detect video signals, determine their characteristics, and pipe them to the frame-store computer. The company recently completed a new PCI-bus version of its design. The film-scanner module communicates with laser- or charge-coupled-device film digitizers, manages image acquisition, reports errors, and directs user-interface tasks through high-speed SCSI or parallel data buses.
Users can interact with the Images-on-Call system either through a hand-held controller to enter patient information data or via a primary-modality (device such as a CT or MR scanner) console. The DG-1 DICOM gateway module functions as a Storage Service Class Provider input destination for digital image data pushed from modality consoles.
For example, using a pop-up menu, a technologist at a CT terminal can send study data to preprogrammed recipient destinations with all routing information, whether by WAN, asynchronous transfer modem, or ISDN connection, embedded within the recipient`s address. Hand-held controllers are linked with the digitizers via a medium-speed, two-line serial terminal to store the time and date of use, parameters about the current device and site, and information about user-defined acquisition protocols. A copy of these data is also saved on the frame-store disk drive.
Image compression
A key element of the Images-on-Call system is its controlled-quality wavelet-compression technology. A compression module manages the image and binary-file compression and decompression tasks on a first-in, first-out basis and can operate in either lossless or lossy mode, depending on user preference. Whereas lossy compression techniques can produce artifacts, significant data loss, or both at high compression ratios, the compression ratio at which this task occurs depends on the compression scheme used and the type and size of the image.
"For example," says Patrick Barr, D&S director of research and development, Images-on-Call Teleradiology, "a 2048 x 2508-pixel, 8-bit chest film image can be wavelet-compressed to 30:1 or more with little apparent loss of image quality. However, the same size film image with 12 or 15 CT images can only be wavelet-compressed to about 8:1 or so. There are less dramatic differences among the various types of small-matrix, gray-scale medical images."
The Images-on-Call compression technology allows each application and image type to be tuned for minimal image artifacts, data loss, and user preference. Algorithms are written in a combination of C, C++, and in-line assembly codes to the floating-point unit. According to Barr, targeting the in-line assembly code to the floating-point unit in the host processor provides a significant speed boost.
Image data can be delivered from the system in several ways. Asynchronization modules are used to manage asynchronous (dial-up modem) data transfers. Though individual modules can handle only one analog or digital modem, the system can accept multiple modules. These modules also manage dial-up customer support, dial-up image-transfer requests, and unattended image-reception tasks.
The network mover module can push images over local- or wide-area networks to viewing stations and terminals or to a mass-storage device for later retrieval by a teleradiology server. The DG-2 DICOM submodule gateway delivers digital image data to DICOM-modality consoles or workstations. Source images can be received from a remote facility via the Images-on-Call teleradiology network or locally through a video digitizer connected to a non-DICOM modality. Large teleradiology systems accept the installation of multiple data-mover modules.
According to Barr, although the Images-on-Call system can provide long-term image archiving, its principal uses are for short- to medium-term storage. Noting that, in parallel with the growth of image-study sizes, image-file storage requirements are rapidly increasing, Barr says this is really the purview of full-blown PACS systems that have virtually unlimited on-line or short-term off-line storage capabilities. "Our focus is on teleradiology and concentrates on shipping mission-critical images quickly and efficiently for real-time decision making. For example, the DICOM gateways provide a pathway to the teleradiology system that PACS systems can communicate through," says Barr.
Active teleradiology
The Radiology Associates` central radiology receive center is linked to its multiple user facilities by a combination of standard telephone and ISDN lines. Twelve different communication links provide a range of data-carrying capacities. For example, to service large patient-trauma centers, the DICOM interfaces on the ISDN lines can generate new images at a rate of about one every 10 s, whereas transmissions from other peripheral hospitals over standard telephone lines using 3Com/US Robotics (Santa Clara, CA) modems need longer times.
After acceptance by the central radiology receive center, the images are decompressed and stored on one of three local communications servers. The Images-on-Call system is expandable from a single PC supporting up to four ISDN terminal adapters or modems to networked systems supporting 20 or more telephone lines and multiple workstations.
Then, the decompressed images are moved over to a 133-MHz Pentium PC display server that allows image-viewing from one or more ACR-compliant ViewStations. The separation of tasks allows for simultaneous image reception/decompression and viewing. The Radiology Associates ViewStations are standard PC machines that drive four side-by-side, vertically oriented Image Systems (Minnetonka, MN) 1200 x 1600-pixel portrait monitors. Depending on the format selected, the same image can be displayed on all four monitors simultaneously. In addition, four, six, or 12 different Windowed-images can also be displayed simultaneously.
The on-duty radiologist is notified of an incoming transmission by a flashing icon that identifies the transmission site. As described by Dr. Jensen, because several hospitals or sites can be transmitting simultaneously, "we essentially have 12 programs running in parallel in separate windows, one on top of the other." To manage multiple, simultaneous transmissions, an alert system provides information about each transmission site.
The radiologist then interprets the images and sends a written report back to the sender by facsimile. In addition, the radiologist also reads the report out loud into an automated dictation system that generates a written report, which is delivered by facsimile to the emergency room or other sites within 20 to 30 minutes. At large trauma centers, the report is consecutively transmitted to the emergency room, trauma unit, and radiology departments
According to Dr. Jensen, the radiologist`s image-interpretation time varies depending on the case, type, and complexity of the incoming scan. For example, the total interpretation time from transmission to completion for a negative CT scan is on the order of five to six minutes. Jensen points out that although a standard CT scan of a patient`s head is generally made up of 13(15 CT slices and takes about three minutes to download completely over the ISDN/DICOM network, the radiologist can begin interpreting the images as soon as they are displayed.
Image quality
According to Jensen, the Images-on-Call digitally transmitted imagery is comparable in quality to conventional film and offers other advantages to diagnosticians. "Unlike earlier image-transmission systems that didn`t transmit actual raw image data, now 75% of the images sent from the major centers come with DICOM interfaces that allow the examination of the images in all sorts of display formats."
For example, Jensen notes that a standard chest film given to a radiologist in a hospital does not provide useful information for specifically examining bones. To provide bone information, additional film must be prepared in a different "bone-window" format. On the other hand, "with the DICOM interfaces, we can just click on this configuration and examine bone images immediately."
Strong demand
Radiology Associates is upgrading its receive center, where imaging demands, according to Jensen, have already become unwieldy for just one radiologist. "Although the amount of time required to transmit and process images and studies has been reduced," says Jensen, "the number of images being sent is concurrently increasing. Whereas, the average number we did per week four years ago was about 133 studies, now the center is performing 408 studies on average per week and as many as 88 studies in one night."
To keep pace, the center is adding another complete Images-on-Call ViewStation system for use by a second radiologist. The new workstation will be powered by a Pentium III 450-MHz PC. The company is also upgrading the center`s existing communication file servers with a high-end Hewlett-Packard Co. (Palo Alto, CA) communication server and hub.
Says Barr, "Transmission speed is always a concern with both the number of cases and the number of images per case climbing faster than technology and bandwidth seem to support." He says one area of continuing attention is support for higher-speed WAN networks. "We need to not only support these systems, but also to do it in a transparent way."
Barr also emphasizes that the goal of teleradiology is to push data to the user as opposed to pulling data, as is done in conventional Internet activities. "When the radiologist accesses the system, the images have already been acquired and are waiting to be read," says Barr.
With the Images-on-Call direct-capture digitizing and image-distribution system, each remote hospital typically is configured with an in-house teleradiology system, which consists of at least one film-digitizing station, a file server, and many viewing terminals. Common terminal locations include the emergency room, intensive-care unit, and surgical departments. In addition, a direct-capture video digitizing station shows the images received from different modalities such as computed tomography and magnetic resonance.
FIGURE 1. The Images-on-Call architecture uses multiple digitizing stations, film scanners, and DICOM sources linked to a central frame-store that can be either a PC or a PC network. Software running on the server is composed of several modules including a Supervisor Module that manages the data transfers to and from the client modules using Dynamic Data Exchange techniques.
FIGURE 2. After they are received by the central radiology receive center, images are decompressed and stored on one of three local communications servers. Decompressed images are moved over to PC display-server that allows image-viewing from one or more ACR-compliant View- Stations. These viewers can display a number of different Windowed-images to be displayed simultaneously.
Company Information
Centronix Corp.
Montville, NJ 07045
(973) 402-7420
Fax: (973) 263-1493
Web: www.centronix.com
Devices & Services Co.
Dallas, TX 75229
(214) 902-8337
Fax: (214) 902-8303
Web: www.imagesoncall.com
Hewlett-Packard Co.
Palo Alto. CA 94303
(800) 752-0900
Fax: (650) 857-5518
Image Systems Corp.
Minnetonka, MN 55343
(612) 935-1171
Fax: (612) 935-1386
Web: www.imagesystemscorp.com
Radiology Associates
Fort Worth, TX 76104
(817) 321-030
Fax: (817) 321-0444
Web: www.ratc.com
3Com Corp.
Santa Clara, CA 95052
(408) 326-5000
Fax: (408) 326-5001
Web: www.3Com.com
