Digital X-ray Prototype workstations linked via interNET (DXPNET) Program

This program aims to investigate the technical feasibility and design issues in developing, maintaining and operating an archive of digitized radiographs. It is a collaborative program for which the Communications Engineering Branch on behalf of NLM serves as Technical Manager. The other participants are the National Center for Health Statistics (NCHS) and the National Institute of Arthritis, and Musculoskeletal and Skin Diseases (NIAMS). The impetus for the program arises from the National Health and Nutrition Examination Surveys (NHANES) which NCHS periodically conducts to produce statistics on the health status of the U.S. population. One element of the collected data consists of radiographs, about 17,000 from a survey already completed and an expected additional 10,000 from a current survey. The radiographs are of cervical and lumbar spine, and hands and knees.

The problems that DXPNET addresses are: preservation of the radiographic collection, extracting information from this collection, and providing remotely located users with access to it.

Specific program objectives are to: 1) develop an Electronic Xray Archive (EXA) for digitized NHANES xrays implemented via an optical disk jukebox controlled by a UNIX workstation interfaced to the Internet; 2) develop image retrieval and display workstations, also called Standardized Readings Workstations (SRW), suitable for radiologists to remotely access the images from the archive, retrieve, display and manipulate them for reading; 3) evaluate technical aspects of the design including compression technique, response time, and use patterns.

At the inception of this program, the Communications Engineering Branch developed and tested an affordable prototype PC-based workstation that enables technicians from NCHS to perform quality control on the digital images produced by scanning the xrays, an activity done under contract by Radix Corporation in Los Angeles, CA. Hardware components such as a 386 computer, a 1280 x 1024 pixel monitor, a WORM drive, and an imaging board were integrated and a complete image retrieval and display software system was developed. This workstation is used at NCHS for quality checking the images received from the scanning contractor on 5 1/4 inch WORM-type optical disks.

While the PC-based system remains operational at NCHS for the purpose of being able to access data from the part of the NHANES collection which has been written to WORM, in FY 1993, the QC process at NCHS was augmented by the acquisition of a Sun SPARCclassic workstation and eraseable single-platter optical drive. The Branch provided direct hardware and software system integration support to create a new Sun-based QC workstation. The new workstation which runs Imview, an inhouse-developed software package, has the advantage of enabling a technician to view the images much faster than with the PC-based system; in addition, images may be read directly from the erasable optical platters on which they are now being written by the scanning contractor.

The next steps under way are: to augment the EXA based on a recently acquired 144-disk robotic optical disk jukebox witha RAID system, to augment a pair of Unix-based SRWs that will allow NCHS radiologists to create standardized readings by viewing the xray images on a high resolution (2048 x 2560 pixel) monitor, to deploy one of the two SRWs at NCHS to allow image retrieval from the archive located at NLM, and to develop a workstationfor broader public access to the archive.

We organized a Digitized Radiographic Images: Challenges and Opportunities workshop in 1993 in collaboration with NIAMS and NCHS, and held at the NLM. The workshop convened a wide range of experts in radiology, epidemiology, image compression, user interface and image presentation issues, and statistics. Design issues related to user interface, image presentation and compression were addressed at the workshop.

The software engineering component of this project is both the most challenging and the most potentially useful. The key to success will be the identification and satisfaction of user needs. The software will make the image database accessible. It will allow the retrieval of classes of images based upon user supplied search terms. The NHANES database contains all of the information on each participant; the xray images constitute just one element of a unit record. One long term goal is to have the entire NHANES database searchable on-line so that all possible search criteria are available. Local retrieval of images and other health statistics could be achieved through remote searching of the database. If the NHANES database is not available on-line then an alternative search mechanism will be devised based on a subset of the database.

Image Compression Studies. Since image compression is needed to maximize storage capacity and minimize transmission time, key to making such projects as DXPNET practical, compression studies have been undertaken inhouse and with a collaboratory of external investigators. The participants in this collaboratory are researchers at Stanford University, Monash University (Australia), the Canada-France-Hawaii Telescope Consortium, NASA Ames Research Center, IBM Almaden Research Center, and NIH. While inhouse studies are focussing on the use of the international JPEG standard employing the Discrete Cosine Transform (a lossy technique), our external collaborators are experimenting with both lossy and lossless techniques using DXPNET images downloaded over Internet. These methods include pyramidal/wavelet technique, vector quantization, context-based DPCM, and bitplane partitioning.

Experiments with lossless techniques conducted on a sample of the DXPNET images have yielded a compression ratio averaging 2. The compression times on a Sun 690MP are 20 seconds for cervical images and 35 seconds for lumbar images. Lossy JPEG compression applied to a sample of the images showed no perceptible difference for compression ratios up to 40, after which point unacceptable artifacts appeared. Compression and decompression times averaged 25 seconds. This work has been reported in the literature: Berman LE, Long R, Pillemer SR: Effects of Quantization Table Manipulation on JPEG Compression of Cervical Radiographs. Digest of Technical Papers, Society for Information Display International Symposium, J. Morreale, ed., Society for Information Display, Playa del Rey, CA. 1993, 43: 937-41.

JPEG Evaluation Tool (JET). The degree of compression attained in lossy JPEG compression technique largely depends on the specific quantization table used. JET was developed by Branch researchers to study the effects of this selection on the radiographs in the DXPNET collection. It is a tool that enables a researcher to modify individual elements of the quantization table or use a predetermined table. It offers a graphical user interface to perform this manipulation, and also computes quality-related factors such as root mean square error, normalized mean square error, compression ratio and image entropy. (The description and use of this tool were presented at the 1993 International Symposium of the Society for Information Display, and appears in the proceedings: Berman LE, Nouri B, Roy G, Neve L: Interactive Selection of JPEG Quantization Tables for Digital Xray Image Compression.) Experiments under way with researchers at the NASA Ames Research Center appear especially promising in this area: their tools allowing the manipulation of the JPEG quantization table incorporate aspects of the human visual system, properties of the cosine basis functions, and the physics of the monitor.

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URL: http://archive.nlm.nih.gov/proj/dxpnet/dxpnet.php
Last updated February 20, 2002

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